Patent Application
20160282754
This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2015-060400 filed Mar. 24, 2015.
The present invention relates to a developing device and an image forming apparatus including the developing device.
According to an aspect of the invention, there is provided a developing device including a developing housing that contains developer and has an opening that faces an image carrier capable of carrying an electrostatic latent image; a developer carrier that faces the opening in the developing housing, the developer carrier carrying and transporting the developer while rotating in such a manner that the developer carrier faces the image carrier; a layer-thickness regulating member that is provided for an upstream gap, which is one of gaps formed between the developer carrier and the developing housing and which is located upstream of the opening in a rotational direction in which the developer carrier rotates, the layer-thickness regulating member regulating a layer thickness of the developer on the developer carrier; and a sealing member that is provided for a downstream gap, which is another one of the gaps formed between the developer carrier and the developing housing and which is located downstream of the opening in the rotational direction of the developer carrier, the sealing member being formed of an elongated flexible plate that extends in a rotational axis direction of the developer carrier, being fixed to the developing housing at an upstream side in a width direction, which is a direction along the rotational direction of the developer carrier, and being in contact with the developer on the developer carrier at a downstream side in the width direction, thereby sealing the downstream gap. The sealing member has plural cuts arranged in the rotational axis direction of the developer carrier, the cuts extending from a free end of the sealing member in the width direction by a length that is approximately 60% or more of a dimension of the sealing member from the free end to a fixed end in the width direction, and being at an angle of approximately 30° or less with respect to a reference line that extends in the rotational direction of the developer carrier.
Exemplary embodiments of the present invention will be described in detail based on the following figures, wherein:
Referring to
In the above-described technical structure, the developer may be either one-component developer or two-component developer. There is no particular limitation regarding the shape, material, etc., of the layer-thickness regulating member 6 as long as the layer-thickness regulating member 6 is capable of regulating the layer thickness of the developer on the developer carrier 4 before the developer reaches a developing region in which the image carrier 1 and the developer carrier 4 oppose each other. Also, there is no particular limitation regarding the developer supplying member 7 as long as the developer supplying member 7 is capable of supplying the developer to the developer carrier 4. In
There is no particular limitation regarding the sealing member 8 as long as the sealing member 8 is a flexible plate, and a resin film sheet made of polyester, polycarbonate, or the like may be used. In the case where a film sheet is used, if the cuts 9 are not formed, the sealing member 8 absorbs moisture and swells, in particular, in high-humidity environments, and is deformed into a wavy shape at the free end 8a thereof. When the sealing member 8 is deformed in this manner, a large gap is formed between the sealing member 8 and the developer carrier 4 and there is a risk that the developer will leak through the gap. In this example, the cuts 9 are formed in the sealing member 8 to suppress the deformation of the sealing member 8.
The developing device 2 according to the present exemplary embodiment may be structured as follows.
That is, the cuts 9 may be formed such that the pitch thereof is 30 mm or less or approximately 30 mm or less over a region in which the developer adheres to the developer carrier 4 in the rotational axis direction of the developer carrier 4. When the pitch of the cuts 9 is too large, cut sections 8c formed between the adjacent cuts 9 are easily deformed in a manner similar to that in the case where the cuts 9 are not formed. To suppress such a deformation, the pitch of the cuts 9 may be 30 mm or less or approximately 30 mm or less.
Also, the cuts 9 may be formed such that the pitch thereof is 5 mm or more or approximately 5 mm or more. When the pitch of the cuts 9 is too small, the strength of the cut sections 8c formed between the adjacent cuts 9 is insufficient. In such a case, the sealing member 8 cannot be reliably pressed against the developer carrier 4. To prevent this, the pitch may be 5 mm or more or approximately 5 mm or more.
The developing device 2 may be included in an image forming apparatus. In such a case, the image forming apparatus may include the image carrier 1 capable of carrying an electrostatic latent image and the above-described developing device 2 that develops the electrostatic latent image on the image carrier 1 with the developer.
The present invention will be described in more detail based on an exemplary embodiment of the present invention illustrated in the accompanying drawings.
Referring to
In the present exemplary embodiment, the image forming units 22 (22a to 22d) form black, yellow, magenta, and cyan images, and are arranged in that order from the upstream side in the direction in which the intermediate transfer belt 230 rotates (the order in which the image forming units are arranged is not necessarily limited to this). Each image forming unit 22 includes a photoconductor 31; a charging device (charging roller in this example) 32 that charges the photoconductor 31 in advance; an exposure device 33 (exposure device shared by the image forming units 22 in this example) that forms an electrostatic latent image on the photoconductor 31 charged by the charging device 32; a developing device 34 that develops the electrostatic latent image formed on the photoconductor 31 with toner of the corresponding color (the toner has, for example, a negative polarity in this example); and a cleaning device 35 that removes substances that remain on the photoconductor 31.
The exposure device 33 includes an exposure housing 41 that contains, for example, four semiconductor lasers (not shown), a single polygon mirror 42, imaging lenses (not shown), and mirrors (not shown) corresponding to the respective photoconductors. Light beams emitted from the semiconductor lasers for the respective colors are reflected by the polygon mirror 42, so that optical images are guided to exposure points on the corresponding photoconductors 31 through the imaging lenses and mirrors. The toners of the respective colors are supplied to the developing devices 34 from toner cartridges 36 (36a to 36d).
In the present exemplary embodiment, the transfer module 23 is structured such that the intermediate transfer belt 230 is looped around, for example, a pair of rollers 231 and 232, one of which is a driving roller. First transfer devices (first transfer rollers in this example) 51 are arranged on the back side of the intermediate transfer belt 230 so as to correspond to the photoconductors 31 of the image forming units 22. A voltage having a polarity opposite to the charging polarity of the toner is applied to each of the first transfer devices 51, so that the toner images on the photoconductors 31 are electrostatically transferred onto the intermediate transfer belt 230.
A second transfer device 52 is disposed so as to face a portion of the intermediate transfer belt 230 that corresponds to the roller 232 located downstream of the most downstream image forming unit 22d. The second transfer device 52 transfers the images formed on the intermediate transfer belt 230 by the first transfer process onto a recording medium by a second transfer process (simultaneous transfer process).
In the present exemplary embodiment, the second transfer device 52 includes a second transfer roller 521 that is pressed against a surface of the intermediate transfer belt 230 on which the toner images are formed, and a backup roller (the roller 232 is used as the backup roller in this example) that is arranged on the back side of the intermediate transfer belt 230 and serves as a counter electrode for the second transfer roller 521. The second transfer roller 521, for example, is grounded, and a bias having the same polarity as the charging polarity of the toner is applied to the backup roller (the roller 232). A belt cleaning device 53 is disposed on the intermediate transfer belt 230 at a location upstream of the most upstream image forming unit 22a. The belt cleaning device 53 removes toner that remains on the intermediate transfer belt 230.
The recording-medium feeding device 24 includes a feed roller 61 that feeds the recording media. Transport rollers 62 that transport each recording medium are arranged immediately downstream of the feed roller 61. Positioning rollers 63 are arranged on the recording-medium transport path 25 at a location immediately upstream of the second transfer position. The positioning rollers 63 feed the recording medium to the second transfer position at a predetermined time. A fixing device 66 is arranged on the recording-medium transport path 25 at a location downstream of the second transfer position. As illustrated in
In the present exemplary embodiment, a manual feed device 71 is provided on a side of the apparatus housing 21. A recording medium placed on the manual feed device 71 is fed to the recording-medium transport path 25 by a feed roller 72. A double-sided recording module 73 is also provided on the apparatus housing 21. When a double-sided recording mode for forming images on both sides of the recording medium is selected, the recording-medium output device 67 is operated in the reverse direction and a recording medium on which an image is formed on one side thereof is introduced into the double-sided recording module 73 by guide rollers 74 disposed in front of an entrance of the double-sided recording module 73. Then, the recording medium is transported along a recording-medium returning path 76 by an appropriate number of transport rollers 77, so that the recording medium is transported to the positioning rollers 63 again.
As illustrated in
In this example, tracking rollers (not shown) for position adjustment having a diameter slightly greater than that of the developing roller 121 is provided at both ends of the developing roller 121. The tracking rollers are brought into contact with the surface of the photoconductor 31 so that the gap between the developing roller 121 and the photoconductor 31 is adjusted to a predetermined gap.
As illustrated in
In this example, the attracting/layer-regulating magnetic pole (N3), the developing magnetic pole (S1), and the transporting magnetic poles (N1, S2, N2) are arranged such that the adjacent magnetic poles have opposite polarities. The transporting magnetic poles (N2) and the attracting/layer-regulating magnetic pole (N3), which are adjacent to each other, have the same polarity, and therefore generate a repulsive magnetic field and serve as separating magnetic poles that temporarily remove the developer carried by the developing sleeve 131. A developing voltage (not shown) is applied to the developing sleeve 131 so that a predetermined developing electric field is formed between the photoconductor 31 and the developing sleeve 131.
In this example, the developing housing 120 has a developer containing section 134 that is sectioned into two chambers 134a and 134b by a partition wall 135. One developer containing chamber 134a contains the developing roller 121 and one stirring-and-transporting member 122, and the other developer containing chamber 134b contains the other stirring-and-transporting member 123. The partition wall 135 has communication holes (not shown) at both ends thereof in the longitudinal direction. The pair of stirring-and-transporting members 122 and 123, which are arranged in the respective chambers of the developer containing section 134, rotate so as to circulate the developer between the two chambers of the developer containing section 134 through the communication holes. In this example, each of the stirring-and-transporting members 122 and 123 includes a rotating shaft 136 and a helical blade 137 provided at the periphery of the rotating shaft 136. One stirring-and-transporting member 122 is disposed substantially directly below the developing roller 121, and the developer that is stirred and transported by the stirring-and-transporting member 122 is supplied to the developing roller 121. Therefore, the stirring-and-transporting member 122 serves as a developer supplying member that supplies the developer to the developing roller 121.
In this example, the layer-thickness regulating member 124 is provided for an upstream gap 120a formed between the developing roller 121 and the developing housing 120 at a location upstream of the opening, which corresponds to a region in which the developing roller 121 and the photoconductor 31 oppose each other, in a rotational direction in which the developing roller 121 rotates. The layer-thickness regulating member 124 is formed of a plate-shaped member, and is fixed to an attachment portion 140 provided on the developing housing 120 in advance. The layer-thickness regulating member 124 forms a gap for regulating the layer thickness of the developer between the developing housing 120 and the developing roller 121, thereby regulating the layer thickness of the developer on the developing roller 121.
In this example, a sealing member 80 seals a downstream gap 120b formed between the developing roller 121 and the developing housing 120 at a location downstream of the opening in the rotational direction of the developing roller 121. The sealing member 80 is formed of an elongated flexible plate that extends in a rotational axis direction of the developing roller 121. The sealing member 80 is fixed to the developing housing 120 at an upstream side in a width direction, which is a direction along the rotational direction of the developing roller 121, and is in contact with the developer on the developing roller 121 at a downstream side in the width direction.
Referring to
The sealing member 80 is disposed between the end sealing members 90 at both ends so that the ends of the sealing member 80 are both in contact with the respective end sealing members 90. In the present exemplary embodiment, the sealing member 80 is formed of, for example, an elongated polyester sheet having a thickness of 100 μm. The sealing member 80 have plural cuts 82 that extend from a free end 80a of the sealing member 80 in the width direction by a length that is 60% or more or approximately 60% or more of the dimension of the sealing member 80 from the free end 80a to a fixed end 80b in the width direction. The cuts 82 are arranged in the rotational axis direction of the developing roller 121. The pitch of the cuts 82 in the rotational axis direction of the developing roller 121 is 20 mm. In this example, the cuts 82 are at an angle of approximately 0° with respect to the reference line that extends in the rotational direction of the developing roller 121, which corresponds to the direction of arrow A in
More specifically, in this example, the sealing member 80 has cuts 82 that extend from the free end 80a toward the fixed end 80b in the width direction. The length L of the cuts 82 is 60% of the overall width W, and the pitch P of the cuts 82 is 20 mm.
The operation of the developing device 34 will now be described.
The operation of the developing device 34 performed when the image forming apparatus carries out an image forming process will be described.
In each of the image forming units 22, when an electrostatic latent image is formed on the photoconductor 31, the developing roller 121 and the stirring-and-transporting members 122 and 123 of the developing device 34 are rotated in predetermined directions. The attracting/layer-regulating magnetic pole (N3) causes the developer to adhere to the developing roller 121 after the developer is charged. The layer thickness of the developer is regulated by the layer-thickness regulating member 124, and then the electrostatic latent image on the photoconductor 31 is developed in the developing region Pd.
After the development process, the developer passes through the sealed portion that is sealed by the sealing member 80, and returns to the inside of the developing housing 120 due to the rotation of the developing roller 121. Then, the developer is separated from the developing roller 121 by the repulsive magnetic field generated by the separating magnetic poles N2 and N3. The toner scatters when the developer is separated from the separating magnetic poles N2 and N3. The toner that has scattered floats in the developing housing 120 in the form of a cloud. When the inner pressure increases due to the toner cloud, there is a risk that the toner will leak through an opening in the developing housing 120. The increase in the inner pressure of the developing housing 120 also occurs when, for example, the size of the developing device 34 is reduced or the operational speed of the developing device 34 is increased. Also in this case, there is a risk that the developer (in particular, toner) will leak out of the developing housing 120.
In the present exemplary embodiment, gaps between the developing roller 121 and the developing housing 120 from which the developer may leak include the upstream gap 120a, which is located at an upstream side in the rotational direction of the developing roller 121, and the downstream gap 120b, which is located at a downstream side in the rotational direction of the developing roller 121.
In general, the inner pressure of the developing housing 120 increases as the developing speed increases. When the developer (in particular, toner in this example) scatters and leaks out of the developing housing 120, components may be stained and reduction in image quality (fogging) may be occur. Therefore, gaps in the developing housing 120 need to be dealt with carefully. Among the gaps between the developing housing 120 and the developing roller 121, it is not necessary to consider leakage of the developer from the developing housing 120 through the upstream gap 120a, at which the layer-thickness regulating member 124 is provided. However, it is necessary to take the downstream gap 120b, at which the sealing member 80 is provided, into careful consideration.
The function of the cuts 82 in the sealing member 80 will now be described.
First, the structure of the comparative example illustrated in
In a high-humidity environment (for example, 30° C., 85% RH), a film sheet generally swells. In particular, when the film sheet is long, the film sheet expands by a large amount in the longitudinal direction thereof. When the film sheet is not fixed at any portion thereof, the entire film sheet expands, and deformation of the sheet is not large. However, when the sheet is fixed at one end thereof in the width direction, as in the sealing member 80′, the sheet expands by a large amount toward the free end thereof (in the directions shown by the arrows in
In contrast, as illustrated in
In the present exemplary embodiment, a polyester sheet is used as the sealing member 80. However, the sealing member 80 is not limited to this, and may instead be, for example, a polycarbonate sheet. In addition, the thickness of the sheet is not limited to 100 μm, and may instead be, for example, a thickness in the range of 50 to 125 μm.
Furthermore, although two-component developer is used as the developer in the developing device 34 according to the present exemplary embodiment, one-component developer may instead be used.
The effect of the cuts formed in the sealing member according to the exemplary embodiment is evaluated. The evaluation is performed by using an experimental device illustrated in
The experimental conditions are as follows:
(1) Sealing Member: 100-μm-thick polyester sheet whose length from the free end to the fixed end is 10 mm is used.
(2) Cut Pitch: the cut length from the free end is set to about 8 mm, and the pitch P is changed in the range of 1 to 50 mm.
(3) Cut Angle θ: the cut length from the free end (length in the direction along the rotational direction of the developing roller) is set to about 8 mm, and the angle θ is changed in the range of 5 to 50°.
(4) Cut Length L: the cuts are formed in the direction along the rotational direction of the developing roller, and the length L is changed in the range of 0 to 10 mm.
(1) When the cut pitch P is 30 mm or less, the amount of toner that adheres to the sheet is 1 mg or less. When the cut pitch P is increased to 40 mm and 50 mm, the amount of toner that adheres to the sheet suddenly increases. When the pitch P is too small (5 mm or less), the amount of toner that adheres to the sheet slightly increases.
(2) When the cut angle θ is 30° or less, the amount of toner that adheres to the sheet is substantially 0 mg. When the angle θ is increased, the amount of toner that adheres to the sheet suddenly increases.
(3) When the cut length L is 6 mm or more, the amount of toner that adheres to the sheet is substantially 0 mg. When the length L is reduced, the amount of toner that adheres to the sheet gradually increased.
In this example, the amount of toner that adheres to the sheet is desirably approximately 0 mg. However, it is determined that the sealing member is suitable for practical use when the amount of toner that adheres to the sheet is about 1 mg. Therefore, the range of the cut pitch P is set to 30 mm or less, the range of the cut angle θ to 30° or less, and the range of the cut length L to 6 mm or more (which corresponds to 60% or more).
It is also confirmed that it is more desirable to set the cut pitch P in the range of 10 to 30 mm, the cut angle θ in the range of 30° or less, and the cut length L in the range of 6 mm (which corresponds to 60%) or more. It may seem that the pitch P may be set to 5 mm or less since the amount of toner that adheres to the sheet is 1 mg or less even when the pitch P is 5 mm or less. However, it is determined that the pitch P is desirably 10 mm or more in consideration of the process of forming the cuts and the strength of the cut sections.
Similar evaluations are performed by the inventors by using sealing members made of different materials and having different thicknesses and widths. As a result, it is confirmed that leakage of the developer may be suppressed when the cut pitch P is in the range of 10 to 30 mm, the cut angle θ in the range of 30° or less, and the cut length L in the range of 60% or more.
The cut angle θ may be set such that the cut sections extend in the same direction (inclined in the same direction in the case where the cut sections are inclined). However, when the cut angle is small, the cuts may, of course, be formed in different directions or at different angles.
With regard to the evaluation results, the above-described phenomenon of the sealing member is probably caused by the following factors.
First, the cut pitch P will be discussed.
Referring to
In contrast, as illustrated in
When the pitch P is two large, as illustrated in
The cut angle θ will be discussed with reference to
When the cuts are formed at the angle θ illustrated in
In contrast, when the cut angle θ is too large as in
The cut length L will be discussed with reference to
When the cuts have the length L illustrated in
In contrast, as illustrated in
Thus, the effectiveness of the sealing member according to the example is confirmed.
The foregoing description of the exemplary embodiments of the present invention has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obviously, many modifications and variations will be apparent to practitioners skilled in the art. The embodiments were chosen and described in order to best explain the principles of the invention and its practical applications, thereby enabling others skilled in the art to understand the invention for various embodiments and with the various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the following claims and their equivalents.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2015-060400 | Mar 2015 | JP | national |
