The present application claims priority to and incorporates by reference the entire contents of Japanese priority document 2008-102030 filed in Japan on Apr. 10, 2008.
1. Field of the Invention
The present invention relates to a developing unit that develops a latent image on a latent-image carrying member with toner, a processing unit, and an image forming apparatus.
2. Description of the Related Art
A conventional developing unit has been disclosed in Japanese Patent Application Laid-open No. 2007-133389. The developing unit includes a cylindrical toner carrying member that is rotatably held on a rotation axis.
Elongated electrodes, which extend in a linear direction of the rotation axis, are arranged on the toner carrying member at a predetermined pitch. An alternating electric field is formed between the mutually adjacent electrodes on a surface of the toner carrying member. Directions of the alternating electric field are changed such that toner hops from the top of one of the electrodes and lands onto an adjacent electrode. As a result of repeatedly hopping between adjacent electrodes, the toner is transported from one place to another place on the toner carrying member, along with rotations of the toner carrying member, and finally reaches a developing area opposite a latent-image carrying member. In the developing area, the toner, which hops from the surface of the toner carrying member and flies up to the vicinity of the latent-image carrying member, is pulled by the electric field due to a latent image and adheres to the latent image. Due to this, the latent image develops into a toner image.
In another known developing unit, the toner is transported to the developing area using a movement due to hopping instead of being transported to the developing area due to a surface movement of a toner carrying member itself. For example, a developing unit disclosed in Japanese Patent Application Laid-open No. 2004-198675 uses a toner carrying member in which three types of electrodes called A-phase electrodes, B-phase electrodes, and C-phase electrodes are repeatedly arranged in a sequence. The toner sequentially hops from the A-phase electrodes onto the B-phase electrodes, from the B-phase electrodes onto the C-phase electrodes, and from the C-phase electrodes onto the A-phase electrodes on the surface of the toner carrying member. Thus, the toner is transported towards the developing area without the toner carrying member actually rotating.
The method of hopping toner enables to realize low potential developing that cannot be realized in an existing monocomponent developing method or a bicomponent developing method. For example, the toner can be caused to selectively adhere to an electrostatic latent image where an electric potential difference between the electrostatic latent image and the surrounding non-image portion is only several tens of volts (V).
Various methods are used for supplying toner on the surface of a toner carrying member. For example, in the developing unit disclosed in Japanese Patent Application Laid-open No. 2007-133389, the toner inside a toner housing unit is transported towards a roller member due to rotatable driving of an agitator. The roller member rotates while touching a blade member. The roller member carries the toner, on the surface of the roller member itself and causes, along with self-rotation, the toner to enter a touching portion of the roller member and the blade member. The toner, which enters the touching portion, is strongly rubbed against the blade member and is friction-charged. Upon passing the touching portion along with the rotations of the roller member, the toner moves up to the vicinity of the surface of the toner carrying member and gets transferred onto the toner carrying member. Thus, the toner is supplied from the roller member to the toner carrying member.
In the developing unit disclosed in Japanese Patent Application Laid-open No. 2004-198675, a bicomponent developer, which contains toner and magnetic carrier, is caused to stick to a surface of a rotating magnet sleeve and transported up to the vicinity of the toner carrying member along with rotations of the magnet sleeve. Next, the electric potential difference between the magnet sleeve and the toner carrying member is used to transfer the toner in the bicomponent developer, which is carried on the magnet sleeve, onto the surface of the toner carrying member. Thus, the developing unit uses the bicomponent developer to supply the toner to the toner carrying member.
In developing units disclosed in Japanese Patent Publication No. H1-31611 and Japanese Patent Publication No. H4-46428, a portion of a circumferential surface of a cylindrical toner carrying member is immersed into the toner inside the toner housing unit. The toner carrying member is rotated in this state and the toner inside the toner housing unit is scooped up by the surface of the toner carrying member.
However, in the conventional technique, excessive stress is imparted on the toner. Specifically, upon carrying out various experiments using a prototype of a developing unit that uses the hopping method, the inventors discovered that hopping of the toner on the surface of the toner carrying member sufficiently friction-charges the toner. Even if the toner is not suitably charged in advance, the toner is sufficiently friction-charged due to repeated collision with the surface of the toner carrying member during the hopping until the toner is transported to the developing area. However, the developing unit disclosed in Japanese Patent Application Laid-open No. 2007-133389 charges the toner before supplying the toner to the toner carrying member. Due to this, the toner is strongly rubbed against the blade member on the rotating roller member. Such rubbing imparts unnecessary stress on the toner.
In the developing unit that is disclosed in Japanese Patent Application Laid-open No. 2004-198675 and that uses the bicomponent developer to supply the toner to the toner carrying member, generally the toner is replenished into the bicomponent developer when required and mixed by stirring. The replenished toner is slidingly rubbed with the magnetic carrier at the time of getting mixed by stirring and is friction-charged. Thus, in a structure that uses the bicomponent developer, before being supplied to the toner carrying member, the toner is inevitably slidably rubbed with the magnetic carrier in the bicomponent developer and is friction-charged. Such slidable rubbing imparts unnecessary stress on the toner.
In the developing units disclosed in Japanese Patent Publication No. H1-31611 and Japanese Patent Publication No. H4-46428, in a touching area of the toner inside the toner housing unit and the toner carrying member having the circumferential surface partially immersed into the toner, the toner is subjected to friction at the surface of the rotating toner carrying member. Such friction imparts unnecessary stress on the toner.
In the developing unit that uses the hopping method, the toner can also be supplied to the toner carrying member by using a method that is widely used in a general monocomponent developing unit. Specifically, a rotatable toner supplying member such as a sponge roller is caused to rotate while touching the toner carrying member and the toner on the toner supplying member is transferred onto the surface of the toner carrying member at a touching portion. However, in the method mentioned earlier, the toner is subjected to friction at the touching portion of the rotating toner supplying member and the toner carrying member. Such friction imparts unnecessary stress on the toner.
It is an object of the present invention to at least partially solve the problems in the conventional technology.
According to an aspect of the present invention, there is provided a developing unit that transports toner for supplying the toner onto a surface of a toner carrying member by a toner supplying unit, while causing the toner to hop on the surface using an electric field, to a developing area that is an area opposite the toner carrying member and a latent-image carrying member, causes the hopped toner to adhere to a latent image on the latent-image carrying member in the developing area, and develops the latent image. The developing unit includes a brush member that includes a base member and a plurality of raisings that are erected on a surface of the base, wherein the brush member traps toner within the raisings and causes a flicker movement in the raisings of the brush so that the toner trapped within the raisings is shaken and flown due to the flicker movement to the surface of the toner carrying member.
According to another aspect of the present invention, there is provided a processing unit that is used in an image forming apparatus that includes a latent-image carrying member that carries a latent image, a charger that charges the latent-image carrying member, a developing unit that develops the latent image on the latent-image carrying member, a transferring unit that transfers a toner image, obtained due to developing, from a surface of the latent-image carrying member to a transfer member, and a cleaning unit that cleans transfer residual toner that is adhering to the surface of the latent-image carrying member after a transferring process. At least one of the latent-image carrying member, the charger, and the cleaning unit is housed, along with the developing unit, in a common housing as a single unit and can be integrally attached to or detached from a main body of the image forming apparatus. The developing unit transports toner for supplying the toner onto a surface of a toner carrying member by a toner supplying unit, while causing the toner to hop on the surface using an electric field, to a developing area that is an area opposite the toner carrying member and the latent-image carrying member, causes the hopped toner to adhere to a latent image on the latent-image carrying member in the developing area, and develops the latent image. The developing unit includes a brush member that includes a base member and a plurality of raisings that are erected on a surface of the base, wherein the brush member traps toner within the raisings and causes a flicker movement in the raisings of the brush so that the toner trapped within the raisings is shaken and flown due to the flicker movement to the surface of the toner carrying member.
According to still another aspect of the present invention, there is provided an image forming apparatus including a latent-image carrying member that carries a latent image and a developing unit. The developing unit transports toner for supplying the toner onto a surface of a toner carrying member by a toner supplying unit, while causing the toner to hop on the surface using an electric field, to a developing area that is an area opposite the toner carrying member and the latent-image carrying member, causes the hopped toner to adhere to a latent image on the latent-image carrying member in the developing area, and develops the latent image. The developing unit includes a brush member that includes a base member and a plurality of raisings that are erected on a surface of the base, wherein the brush member traps toner within the raisings and causes a flicker movement in the raisings of the brush so that the toner trapped within the raisings is shaken and flown due to the flicker movement to the surface of the toner carrying member.
The above and other objects, features, advantages and technical and industrial significance of this invention will be better understood by reading the following detailed description of presently preferred embodiments of the invention, when considered in connection with the accompanying drawings.
Exemplary embodiments according to the present invention are explained next with reference to the accompanying drawings.
An experiment, which is carried out by the inventors of the present invention on a developing unit that uses a hopping method, is explained first.
The toner layer 5 is formed on the substrate 4 by developing a solid image to a thin layer by using a bicomponent developing unit (not shown). Polyester toner having a granule diameter of approximately 6 μm is used to develop the solid image. As shown in
After occurrence of the flare, the AC voltage is stopped and a charge on the toner is measured periodically. It is observed that the charge on the toner increased with time and finally reached a saturation value. Thus, it is ascertained that the toner on the surface of the toner carrying member is friction-charged due to hopping, although the charge is negligible, and that the toner in the flare status can be sufficiently friction-charged until transportation to a developing area.
An image forming apparatus according to an embodiment of the present invention is explained next.
Therefore, as shown in
The shaft members 33 and 34 that do not include flanges are shown in
Formation of the roller 32, which includes the first electrodes 32b and the second electrodes 32c, is explained next while referring to
An A-phase AC voltage is applied to the first electrodes 32b via the shaft member 33 and a B-phase AC voltage is applied to the second electrodes 32c via the shaft member 34. Waveforms of the A-phase AC voltage and the B-phase AC voltage are shown in
Setting a peak-to-peak voltage (hereinafter, “Vpp”) of the A-phase AC voltage and the B-phase AC voltage in a range of 100 V to 1000 V is desirable. If Vpp is less than 100 V, an AC electric field of sufficient strength cannot be formed between the electrodes and suitable hopping of the toner cannot be obtained. Vpp exceeding 1000 V can cause electrical discharge between the electrodes, i.e., between the first electrodes 32b and the second electrodes 32c. The AC electric field cannot be formed between the electrodes and the toner will not hop if electrical discharge occurs between the electrodes.
Setting a frequency f of the A-phase AC voltage and the B-phase AC voltage in a range of 0.1 kilohertz (kHz) to 10 kHz is desirable. If the frequency f is less than 0.1 kHz, a reciprocating speed of the toner will be slower than that is required for developing. If the frequency f exceeds 10 kHz, hopping of the toner cannot follow a direction switching speed of the AC electric field between the electrodes.
A center value of the A-phase AC voltage and the B-phase AC voltage is set to a value between a latent image electric potential and a background electric potential of a photosensitive drum that is explained later.
In the AC voltage of a rectangular waveform shown in
As shown in
The photosensitive drum 10 is a commonly known general organic photosensitive drum that is rotatably driven in a clockwise direction by a driving unit (not shown). A charger (not shown) uniformly charges a surface of the rotating photosensitive drum 10 at a predetermined rotating position. Next, an optical writing unit (not shown) optically scans the surface of the photosensitive drum 10, thus causing the photosensitive drum 10 to carry an electrostatic latent image.
The photosensitive drum 10 treats as a background portion, an organic photosensitive layer having a thickness of 13 μm that is uniformly charged by the charger to −300 V to −500 V. Next, the optical writing unit optically scans the background portion at a resolution of 120 dots per inch (dpi) to form the electrostatic latent image. An electric potential of the electrostatic latent image is approximately 0 V to −5 V.
The developing unit 30 includes inside a casing 38, a toner housing unit, the toner carrying member 31, a toner recollecting electrode 37, an agitator 39, and a toner-supplying brush roller 40. The toner housing unit houses therein the toner (not shown) that is transported towards the toner-supplying brush roller 40 due to rotatable driving of the agitator 39 that is a rotating member. The toner-supplying brush roller 40 supplies the toner onto the surface of the toner carrying member 31.
The toner carrying member 31 is rotated in a counterclockwise direction by a driving unit (not shown). The toner is supplied onto the surface of the rotatably driven toner carrying member 31 at a position opposite the toner-supplying brush roller 40. Along with rotations of the toner carrying member 31, the supplied toner is transported to the developing area while forming the flare on the surface of the toner carrying member 31 due to repeated hopping. Next, the toner, which has formed the flare in the developing area, adheres to the electrostatic latent image on the photosensitive drum 10 and contributes to developing.
A flicker wire 45, which is a touching member, touches the brush of the toner-supplying brush roller 40 at a predetermined rotation angle position.
As shown in
The rotating toner-supplying brush roller 40 traps inside the brush, the toner that is transported from the agitator 39 that is shown in
When the toner-supplying brush roller 40 rotates further, the raisings 40b, which are significantly bent due to touching with the flicker wire 45, are separated from the flicker wire 45. When separating from the flicker wire 45, the significantly bent raisings 40b are rapidly extended straight due to strength of the raisings 40b themselves, thus carrying out a flicker movement. The toner, which is trapped among the raisings 40b, is shaken off from the raisings 40b due to the flicker movement and flies from inside the brush. Flying of the toner causes formation of a toner cloud (a floating toner cluster) between the toner-supplying brush roller 40 and the toner carrying member 31. The toner in the toner cloud is pulled by the AC electric field that is formed between the electrodes on the toner carrying member 31, and the toner is transferred onto the surface of the toner carrying member 31, thus forming the flare.
Thus, the toner supplying unit forms the toner cloud at the position opposite the toner carrying member 31, thus supplying the toner to the surface of the toner carrying member 31. In this structure, the toner is supplied to the surface of the toner carrying member 31 without causing the toner to strongly rub against a blade member, without causing a friction between the toner and the magnetic carrier, without causing a friction between the toner and the rotating toner carrying member, or without causing a friction between the toner carrying member 31 and a rotating toner supplying member. Thus, unnecessary stress, which is imparted on the toner that is supplied to the toner carrying member 31, can be reduced.
The flicker wire 45, which is the touching member, is extremely thin and a touching area of the flicker wire 45 with the brush is small. Due to this, a contact frictional force on the toner can be significantly reduced. The toner supplying unit can be easily assembled in a small space inside the casing 38.
A power source (not shown) applies an electric voltage to the brush of the toner-supplying brush roller 40. The electric potential difference between the brush and the toner carrying member 31 (the average electric potential of the AC voltage that is applied to the electrodes of the toner carrying member 31) results in formation of the electric field that causes the toner to electrostatically move from the brush to the toner carrying member 31. The electric field enables to efficiently transfer the toner in the toner cloud onto the surface of the toner carrying member 31.
For applying the electric voltage to the brush of the toner-supplying brush roller 40, a method to apply the electric voltage via the rotating shaft member 40a or a method to apply the electric voltage via the flicker wire 45 can be used.
Only the DC voltage having the same polarity as the polarity of the toner can be applied as the electric voltage to the brush. Alternatively, a DC/AC superimposed voltage, which includes the AC voltage superimposed on the DC voltage, can also be applied to the brush. When using the DC/AC superimposed voltage, an adhesive force of the raisings 40b and the toner weakens due to an operation of the AC electric field and clouding of the toner due to the flicker movement of the raisings 40b can be fostered.
As shown in
In the image forming apparatus according to the embodiment, a base material resin (a main component of the toner), which is used as the toner, is formed of polyester or styrene acrylic and has a minus polarity (negative polarity) as normal charge polarity. Both the background portion of the photosensitive drum 10 and the electrostatic latent image are of the same polarity as the normal charge polarity of the toner (negative polarity in the embodiment) and the toner is caused to selectively adhere to the electrostatic latent image having the electric potential that is attenuated than the electric potential of the background portion. Such a method is called reverse developing.
As shown in
The toner, which repeatedly collides with the surface protective layer 32d due to hopping, is sufficiently friction-charged until being transported towards the developing area.
A material having a plus polarity (positive polarity) as the normal charge polarity can also be used as the toner. When using the toner of a positive polarity, a material, which promotes friction charging of a positive polarity side of the toner along with friction with the toner, can be used as the protective coating 3.
A charging sequence of the toner indicates a charging sequence of the entire toner that includes an external additive such as silica, titanium oxide etc. added to a toner base material resin (granules). A hierarchy in the charging sequence can be investigated using the following method. In other words, the toner is caused to rub against the surface protective layer 32d for a predetermined time period, and the toner is collected by sucking. Next, the charge amount of the collected toner is measured using an electrometer. Based on a measurement result, if the charge on the toner has increased to the negative polarity, the measurement result indicates that the toner is positioned at a negative side than the surface protective layer 32d in the charging sequence. If the charge on the toner has increased to the positive polarity, the measurement result indicates that the toner is positioned at a positive side in the charging sequence.
An intermediate layer can also be arranged between the surface protective layer 32d and the electrodes. The intermediate layer can be formed of a conductive material such as titanium (Ti), tin (Sn), iron (Fe), copper (Cu), chromium (Cr), nickel (Ni), zinc (Zn), magnesium (Mg), aluminium (Al), titanium oxide (TiO2), tin oxide (SnO2), ferric oxide (Fe2O3), magnetite (Fe3O4), cuprous oxide (CuO), chromium oxide (Cr2O3), nickel oxide (NiO), zinc oxide (ZnO), magnesium oxide (MgO), aluminium oxide (Al2O3) etc.
As shown in
A recollecting unit recollects the toner that has not contributed to developing from the surface of the toner carrying member 31. The recollecting unit includes the toner recollecting electrode 37 shown in
The toner can be mechanically scraped and collected from the surface of the toner carrying member 31 by pressing a recollecting member, such as a blade, against the toner carrying member 31 or by using a flicker member to cause raisings of a rotating fur brush to touch the toner carrying member 31 while carrying out the flicker movement. However, mechanical scraping imparts unnecessary stress on the toner. In the image forming apparatus according to the embodiment, the toner is recollected without causing the recollecting member to rub against the toner that is being subjected to the flare. Thus, the toner can be recollected without imparting unnecessary stress due to rubbing.
A toner image, which is developed on the photosensitive drum 10, is transferred by a transferring unit (not shown) to a recording sheet that is a transfer member.
For Structure 1, the toner degradation level is “5”. However, for Structure 2, the toner degradation level is low, i.e., “3”, that is within a desirable range. Thus, supplying the toner, which is subjected to clouding due to the flicker movement of the toner-supplying brush roller 40 to the toner carrying member 31, enables to significantly reduce degradation of the toner. For Structure 3, the toner degradation level is still low, i.e., “1”, thus indicating further improvement. Unlike Structure 2, because Structure 3 does not cause friction of the toner due to rubbing of the toner-supplying brush roller 40 and the toner carrying member 31, degradation of the toner is further reduced.
The developing unit 30 according to the embodiment and the modifications explained earlier is housed in a common housing along with the photosensitive drum 10 and functions as a single processing unit that is attached to or detached from a main body of the image forming apparatus.
In the embodiment of the image forming apparatus explained earlier, the flare phenomenon is obtained by causing the toner to hop such that the toner reciprocates between two adjacent electrodes, and the toner is transported to the developing area by the surface movement of the toner carrying member. However, the present invention can also be applied to the following image forming apparatus. In other words, similarly as the method disclosed in Japanese Patent Application Laid-open No. 2007-133389, the image forming apparatus causes the toner to repeatedly hop from one electrode towards the other adjacent electrode in a direction from one end side towards the other end side of the toner carrying member, thus transporting the toner towards the developing area. The present invention can also be applied to an image forming apparatus that transports the toner towards the developing area by using both the movement of the toner due to hopping and the surface movement of the toner carrying member.
The developing unit 30 uses as a brush member, the rotatable toner-supplying brush roller 40 that includes the rotating shaft member 40a and the brush that includes the raisings 40b that are erected on the circumferential surface of the rotating shaft member 40a. The developing unit 30 includes the toner supplying unit that includes the flicker wire 45 as the touching member that touches the brush of the rotating toner-supplying brush roller 40 at a predetermined rotation position and causes the raisings 40b of the brush to carry out the flicker movement. Due to the structure mentioned earlier, the raisings 40b, which have moved to the predetermined rotation position, can be subjected to the flicker movement by simply rotatably driving the toner-supplying brush roller 40.
In the developing unit 30 according to the embodiment, the wire-shaped flicker wire 45 is used as the touching member. In the structure mentioned earlier, because the touching area of the flicker wire 45 and the brush is less, the contact frictional force on the toner can be significantly reduced. The toner supplying unit can be easily assembled in a small space inside the casing 38.
In the developing unit 30 according to the first modification, the plate-shaped flicker plate 46 is used as the touching member. Due to this, compared to the flicker wire 45, the flicker plate 46 can cause the raisings 40b to carry out the flicker movement for a longer time without getting damaged. The flicker plate 46 can be imposed more easily than the flicker wire 45.
In the developing unit 30 according to the second modification, both the wire-shaped flicker wire 45 and the plate-shaped flicker plate 46 are used as the touching members. Using the structure mentioned earlier enables to apply the DC voltage having the same polarity as the polarity of the toner to any one of the touching members, among the flicker wire 45 and the flicker plate 46, thus causing the touching member to include a function to charge the toner inside the brush using charge injection, and enables the other touching member to include a function to form the electric field that causes the toner cloud to move from the brush side to the toner carrying member 31 side and to cause the other touching member to weaken the adhesive force between the toner and the raisings 40b using the AC electric field, thus fostering clouding of the toner.
In the developing unit 30 according to the embodiment and the first and the second modifications, the toner-supplying brush roller 40 is arranged at a non-touching position with respect to the toner carrying member 31. Due to this, compared to a structure in which the toner-supplying brush roller 40 touches the toner carrying member 31, the stress on the toner at the time of supply can be reduced.
In the developing unit 30 according to the embodiment and various modifications, a voltage applying unit is included that applies the electric voltage to the brush of the toner-supplying brush roller 40. The structure mentioned earlier enables to form between the brush and the toner carrying member 31, using the electric potential difference between the brush and the toner carrying member 31, the electric field that causes the toner to electrostatically move from the brush to the toner carrying member 31. Thus, the toner in the toner cloud can be efficiently transferred onto the surface of the toner carrying member 31.
In the developing unit 30 according to the embodiment and the first and the second modifications, the recollecting unit is included that recollects from the surface of the toner carrying member 31, the toner that has passed the developing area. Thus, the structure mentioned earlier enables to avoid destabilization of the toner amount on the surface of the toner carrying member 31 that occurs due to return of the toner to a toner supply position.
In the developing unit 30 according to the embodiment and the first and the second modifications, the recollecting unit that is used includes the toner recollecting electrode 37 that is an opposite electrode member positioned opposite the surface of the toner carrying member 31 and a recollection-electric-potential-difference causing unit that causes the electric potential difference for toner recollection between the surface of the toner carrying member 31 and the toner recollecting electrode 37. The structure mentioned earlier enables to recollect the toner without causing a toner recollecting member to touch the toner carrying member 31, thus enabling to avoid imparting of stress on the toner at a touching portion.
In the developing unit 30 according to the third and the fourth modifications, the toner-supplying brush roller 40 is arranged at a touching position with respect to the toner carrying member 31. Due to this, the toner-supplying brush roller 40 can also be used as the recollecting unit and a cost of the developing unit 30 can be reduced.
In the developing unit 30 according to the embodiment and various modifications, the casing 38 includes the opening for exposing a portion of the surface of the toner carrying member 31 towards the photosensitive drum 10. The casing 38 further includes the sealing member 36 that is the fly preventing member for preventing the toner from flying from inside the casing 38 to outside the casing 38 via the gap between the toner carrying member 31 and the opening. The structure mentioned earlier enables to prevent the toner, which is shaken from the toner-supplying brush roller 40 and clouded, from flying outside the casing 38 via the gap.
According to an aspect of the present invention, toner, which is shaken from inside a brush due to a flicker movement of raisings, is caused to float in the vicinity of a surface of a toner carrying member. Thus, the toner is supplied to the surface of the toner carrying member without causing the toner to strongly rub against a blade member, without causing a friction between the toner and a magnetic carrier, without causing a friction between the toner and the rotating toner carrying member, or without causing a friction between the toner carrying member and a rotating toner supplying member. Thus, unnecessary stress, which is imparted on the toner that is supplied to the toner carrying member, can be reduced.
Although the invention has been described with respect to specific embodiments for a complete and clear disclosure, the appended claims are not to be thus limited but are to be construed as embodying all modifications and alternative constructions that may occur to one skilled in the art that fairly fall within the basic teaching herein set forth.
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