Patent Application
20160231668
This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2015-023295 filed Feb. 9, 2015.
The present invention relates to electric conductive rollers, transfer devices, and image forming apparatuses.
An electric conductive roller according to an aspect of the invention includes a shaft, a cylindrical first elastic body having an electric conductivity and covering the shaft while being in contact with an outer periphery of the shaft, and a second elastic body having an annular shape, disposed at an end portion of the first elastic body, covering the shaft at a distance from the shaft, and having an electric conductivity, the second elastic body having a thickness that gradually increases from a portion between a free end of the second elastic body and a boundary between the second elastic body and the first elastic body to the free end while the second elastic body is retaining an outside diameter greater than or equal to an outside diameter of the first elastic body.
Exemplary embodiments of the present invention will be described in detail based on the following figures, wherein:
The following describes a mode of embodying the invention (referred to as exemplary embodiment, below), followed by description of modification examples obtained by modifying the exemplary embodiment (first to seventh modification examples) and description of examples.
In the following description, directions denoted by arrows X and −X in the drawings indicate an apparatus width direction and directions denoted by arrows Y and −Y in the drawings indicate an apparatus height direction. Directions perpendicular to both the apparatus width direction and the apparatus height direction (directions denoted by arrows Z and −Z) indicate an apparatus depth direction.
Referring now to the drawings, an exemplary embodiment is described below. Firstly, the entire configuration of an image forming apparatus 10 according to an exemplary embodiment is described, followed by description of the configuration of a characteristic portion (transfer device 30) according to the exemplary embodiment, description of the operation of the image forming apparatus 10 according to the exemplary embodiment, and description of effects of the exemplary embodiment.
As illustrated in
The toner image forming unit 20 has a function of forming a toner image G held by a transfer belt TB constituting the transfer device 30 by performing steps of electric charging, exposure to light, and development. The transfer belt TB is described below. Here, the toner image forming unit 20 is an example of a forming unit. The toner image G according to the exemplary embodiment is formed with, for example, a negatively charged toner T.
The toner image forming unit 20 includes single-color units 21Y, 21M, 21C, and 21K that form toner images of different colors, that is, yellow (Y), magenta (M), cyan (C), and black (K). The single-color units 21Y, 21M, 21C, and 21K have the same configuration except for the colors of toner images G that they form. In the following description, the letters of the alphabet (Y, M, C, and K) in the symbols for the single-color units 21Y, 21M, 21C, and 21K are omitted when the single-color units 21Y, 21M, 21C, and 21K and their components do not need to be distinguished from one another. Each single-color unit 21 includes a photoconductor 22, a charging device 24, an exposure device 26, and a developing device 28. The photoconductor 22 is cylindrical. The photoconductor 22 is disposed so that its axis is aligned with the apparatus depth direction. In
The transfer device 30 has a function of rotating while holding toner images G of different colors that have been formed at the single-color units 21 and first-transferred to the transfer device 30 and a function of second-transferring, at a nip N2, the toner images F of the different colors onto a transported medium P, described below. The configuration of the transfer device 30 is described below.
The transporting device 40 has a function of transporting a medium P so that the medium P passes through a nip N2 and a nip N3, described below.
The fixing device 50 has a function of heating and pressing, at the nip N3, toners T constituting toner images G that have been second-transferred to the medium P by the transfer device 30 to fix the toners T onto the medium P. The fixing device 50 includes a heating portion 50A and a pressing portion 50B.
The controller 60 has a function of controlling all the components of the image forming apparatus 10 other than itself.
The description given above is about the entire configuration of the image forming apparatus 10 according to the exemplary embodiment.
Referring now to the drawings, a characteristic portion (transfer device 30) according to the exemplary embodiment is described.
As illustrated in
The transfer belt TB is an endless belt. Each first roller 32 is disposed below the corresponding photoconductor 22 and forms a nip N1 together with the photoconductor 22 by nipping the transfer belt TB therebetween. Each first roller 32 first-transfers a toner image G of the corresponding color formed on the corresponding photoconductor 22 to the transfer belt TB in response to an application of a voltage (first-transfer voltage) from a power source (not illustrated). The driving roller 34 is driven by a driving source (not illustrated) and rotates around its axis to rotate the transfer belt TB in the direction of arrow R. In this configuration, the transfer belt TB, while rotating in the direction of arrow R, receives toner images G of different colors first-transferred from the single-color units 21 and carries the toner images G of different colors on the outer perimeter to the nip N1. Here, the transfer belt TB is an example of a holding belt. The sheet resistance of the transfer belt TB according to the exemplary embodiment is, for example, 1.0×106 Ω/sq or higher and less than 1.0×1010 Ω/sq. Here, “sq” denotes a unit volume of 1 m3.
The second transfer portion 36 has a function of second-transferring toner images G of different colors held by the transfer belt TB to a medium P transported by the transporting device 40. As illustrated in
As illustrated in
The shaft 80 includes a cylindrical body 82, having a diameter of D3, and protrusions 84, protruding from both longitudinal ends of the body 82 and having a diameter of D4 (<D3). As illustrated in
The elastic body 90 has electric conductivity. The elastic body 90 includes a first elastic body 92 and second elastic bodies 94. In this description, having electric conductivity means, for example, that the volume resistivity is below 1.0×109 Ω·m. The elastic body 90 according to the exemplary embodiment has, for example, a volume resistivity of 1.0×104 Ω·m or higher and less than 1.0×108 Ω·m. An example of the elastic body 90 according to the exemplary embodiment is an electrically conductive foam (foam containing urethane foam and electrically conductive member).
As illustrated in
The second elastic bodies 94 are disposed on both longitudinal ends of the first elastic body 92. As illustrated in
As described above, the outside diameter of the first elastic body 92 and the outside diameter of each second elastic body 94 at the boundary BP are D1, and thus D1 and D2 satisfy the inequality D2/D1>1. The outside diameter D2 of each second elastic body 94 at the free end FE is 1.03×D1. Thus, D1 and D2 satisfy the inequality D2/D1≦1.10. Accordingly, in the second roller 70 according to the exemplary embodiment, the outside diameter D1 of the first elastic body 92, the outside diameter D1 of each second elastic body 94 at the boundary BP and the outside diameter D2 of each second elastic body 94 at the free end FE satisfy the inequality 1<D2/D1≦1.10.
The bearings 100 have a function of supporting the second roller 70. As illustrated in
The bearings 100 have a function of preventing electric-current leakages at the protrusions 84 of the shaft 80 and at the second elastic bodies 94 (particularly, at the protrusions 84 and at the free end FE of each second elastic body 94). Thus, as illustrated in
The BUR 110 has a function of causing the second roller 70 and the transfer belt TB to form a nip N2 by coming into contact with the inner periphery of the transfer belt TB. Thus, as illustrated in
As illustrated in
The resistor 114 is, for example, an electrically conductive solid rubber and is solider than the elastic body 90 of the second roller 70. Thus, in the state where the nip N2 is formed (in the state where the BUR 110 is in an operation position, described below), the resistor 114 presses the transfer belt TB and squashes the elastic body 90 together with the transfer belt TB. The resistor 114 according to the exemplary embodiment has, for example, a volume resistivity of greater than or equal to 1.0×103 Ω·m and less than 1.0×104 Ω·m. In other words, the volume resistivity of the resistor 114 is smaller than the volume resistivity of the elastic body 90.
The movable portion (not illustrated) has a function of vertically moving the BUR 110. Specifically, the movable portion includes a pair of bearings (not illustrated), a pair of tension springs (not illustrated), and a pair of cams (not illustrated). The bearings of the pair are fitted to both end portions of the shaft 112. The tension springs of the pair pull the BUR 110 upward in the state where their ends are hooked on the corresponding bearings of the pair. The cams of the pair press the corresponding bearings of the pair in the state of being fixed to both end portions of the shaft (not illustrated). The pair of cams rotate while pressing the pair of bearings as a result of a driving source (not illustrated) rotating the shaft around its axis. In this configuration, the movable portion vertically moves the BUR 110.
Here,
The power source PS has a function of applying a voltage (second transfer voltage) to the BUR 110 and forming an electric field that causes toner images G held on the transfer belt TB to be transferred (second-transferred) to a medium that passes through the nip N2.
During a second transfer, the power source PS applies a voltage having a polarity (negative polarity) the same as the polarity of the toner T to portions of the shaft 112 of the BUR 110 protruding beyond the resistor 114 via leaf springs (not illustrated). As described above, the shaft 80 of the second roller 70 is in contact with the grounded compression spring. When the power source PS applies a negative voltage to the BUR 110 while the BUR 110 is in the operation position, the power source PS forms, at the nip N2, an electric field that causes the toner T held on the transfer belt TB to be transferred (second-transferred) to a medium P. The power source PS according to the exemplary embodiment applies to the shaft 112 of the BUR 110 a voltage within the range of approximately −3 to −2 kV in the standard environment (for example, an environment of a temperature of 23° C. and a humidity of 65%) and a voltage of approximately −9 kV in a low-temperature low-humidity environment (for example, an environment of a temperature of 10° C. and a humidity of 15%).
The following provides supplement on description of the transfer device 30.
As illustrated in
As described above (as illustrated in
The width of a medium P used in the exemplary embodiment is smaller than the width, in the apparatus depth direction, of a portion of the nip N2 formed by the transfer belt TB and the first elastic body 92. Both widthwise end portions of the medium P thus pass through the nip N2 without deviating from the nip N2 formed by the transfer belt TB and the first elastic body 92.
As described above, the outer periphery of the second roller 70 (outer periphery of the elastic body 90) is disposed so as to come into contact with the transfer belt TB at the nip N2. In other words, the transfer belt TB and the second roller 70 (elastic body 90) have such a relation that the second roller 70 touches the transfer belt TB. In other words, the transfer belt TB is an object touched by the second roller 70 (elastic body 90).
The configuration of the image forming apparatus 10 has been described thus far.
Referring now to the drawings, the operation of the image forming apparatus 10 according to the exemplary embodiment is described.
The controller 60 that has received image data from an outside apparatus (not illustrated) operates the toner image forming unit 20. Then, each toner image forming unit 20 forms a toner image G on the corresponding photoconductor 22 as a result of the corresponding charging device 24 charging the photoconductor 22, the corresponding exposure device 26 exposing the photoconductor 22 to light, and the corresponding developing device 28 developing the toner image G.
Subsequently, each first roller 32 receives an application of a first transfer voltage from the power source (not illustrated) and first-transfers the toner image G formed on the corresponding photoconductor 22 to the rotating transfer belt TB at the nip N1. The movable portion (not illustrated) moves the BUR 110, in the stand-by position, to the operation position and the BUR 110 causes the second roller 70 and the transfer belt TB to form the nip N2. Thereafter, at the time when each toner image G that has been first-transferred to the rotating transfer belt TB and held on the transfer belt TB arrives at the nip N2 together with the transfer belt TB, the transporting device 40 transports a medium P to the nip N2. The power source PS applies a second transfer voltage to the shaft 112 of the BUR 110 and forms an electric field that causes the toner images G held on the transfer belt TB to be transferred to the medium P that passes through the nip N2. As a result, the second transfer portion 36 second-transfers the toner images G on the transfer belt TB to the medium P that passes through the nip N2. Subsequently, the transporting device 40 transports the medium P to a nip N3. Then, the fixing device 50 heats the toner images G second-transferred to the medium P using the heating portion 50A and presses the toner images G using the pressing portion 50B to fix the toner images G to the medium P. The medium P to which the toner images G have been fixed is ejected by the transporting device 40 to the outside of the image forming apparatus 10, whereby the operation of the image forming apparatus 10 is finished.
The operation of the image forming apparatus 10 has been described thus far.
Subsequently, effects of the exemplary embodiment are described.
Referring now to the drawings, effects (first and second effects) of the exemplary embodiment are firstly described in comparison with conceivable comparative modes described below. In the description of the comparative modes, components that are the same as those included in the exemplary embodiment are denoted by the same reference symbols.
As illustrated in
When a second transfer is performed using the transfer device 30A according to the comparative mode, an electric-current leakage may occur between the transfer belt TB and the shaft 80 of the second roller 70A. When an electric-current leakage occurs, an electric current flows from the shaft 80 to the transfer belt TB, failing to form an electric field that causes the toner images G on the transfer belt TB to be second-transferred to a medium P. In addition, when an electric-current leakage occurs between the transfer belt TB and the shaft 80, a second transfer error (a failure in transferring a toner image G to a medium P passing through the nip N2 during the electric-current leakage) occurs at the second transfer portion 36A (transfer device 30A). In the image forming apparatus 10A, an image forming failure attributable to the second transfer error occurs. Such electric-current leakages between the transfer belt TB and the shaft 80 particularly increasingly occur for example when a voltage of approximately −9 kV is applied to the BUR 110 in the low-temperature low-humidity environment.
When an electric-current leakage occurs between the transfer belt TB and the shaft 80, an electric current flowing in response to the electric-current leakage presumably flows through a current passage formed between an end portion of the body 82 of the shaft 80 and the transfer belt TB. This current passage is presumed as the shortest route on the surface of each second elastic body 94A (inner periphery and the free end FE) forming the nip N2. As described above, the reason why electric-current leakages between the transfer belt TB and the shaft 80 particularly increasingly occur in the low-temperature low-humidity environment is presumably because a larger quantity of moisture in the atmosphere is more likely to adhere to the surface of the second elastic bodies 94A than in the case of the standard environment. The above-described presumption is believed to be reasonable from the evaluation results of the examples (
As illustrated in
Thus, the second roller 70 according to the exemplary embodiment, when constituting the second transfer portion 36, is less likely to cause electric-current leakages (has a higher leakage voltage) at the second elastic bodies 94 than the second roller 70A according to the comparative mode. Accordingly, the transfer device 30 according to the exemplary embodiment is more likely to minimize transfer errors attributable to the electric-current leakages than the transfer device 30A according to the comparative mode. In addition, the image forming apparatus 10 according to the exemplary embodiment is more likely to minimize image forming failures attributable to the transfer errors than the image forming apparatus 10A according to the comparative mode. Here, a leakage voltage is a voltage applied to one of the shaft 112 of the BUR 110 and the shaft 80 of the second roller 70, while the other one of the shafts 112 and 80 is grounded, and a voltage at which an electric-current leakage occurs between the transfer belt TB and the shaft 80. As described above, in the second transfer portion 36 according to the exemplary embodiment, the shaft 80 is grounded and a voltage is applied to the shaft 112. In the second transfer portion 36 according to the exemplary embodiment, a second transfer voltage applied to the shaft 112 is naturally controlled so that it does not exceed the leakage voltage (so that it is smaller than an absolute value of the leakage voltage).
As illustrated in
Thus, the second roller 70 according to the exemplary embodiment, when constituting the second transfer portion 36, is less likely to cause an electric-current leakage in a gap between the outer periphery of each second elastic body 94 and the transfer belt TB than the second roller 70A according to the comparative mode. Accordingly, the transfer device 30 according to the exemplary embodiment is more likely to minimize transfer errors attributable to electric-current leakages than the transfer device 30A according to the comparative mode. In addition, the image forming apparatus 10 according to the exemplary embodiment is more likely to minimize image forming failures attributable to transfer errors than the image forming apparatus 10A according to the comparative mode.
Subsequently, third to fifth effects of the exemplary embodiment are described.
As described above, the second elastic bodies 94 of the second roller 70 according to the exemplary embodiment gradually thicken from the boundary BP to the free end FE and D1 and D2 satisfy the inequality D2/D1≦1.10.
Here, it is presumed that a second roller (not illustrated) having D1 and D2 that satisfy the inequality 1.10<D2/D1 forms a nip N2 together with the transfer belt TB. Second elastic bodies of this presumed second roller have an outside diameter that changes at a higher rate from the boundary BP to the free end FE than the second elastic bodies 94 according to the exemplary embodiment. Specifically, these second elastic bodies have a higher rate of change of the thickness than the second elastic bodies 94 according to the exemplary embodiment. Thus, these second elastic bodies are less likely to be deformed into a nip N2 over an area from the boundary BP to the free end FE, whereby a gap is more likely to be formed between the outer periphery of each second elastic body and the transfer belt TB. In contrast, the second elastic bodies 94 according to the exemplary embodiment are less likely to form a gap between themselves and the transfer belt TB than the second elastic bodies of the second roller having D1 and D2 that satisfy the inequality 1.10<D2/D1.
Thus, the second roller 70 according to the exemplary embodiment, when constituting the second transfer portion 36, is less likely to cause electric-current leakages in a gap between the outer periphery of each second elastic body 94 and the transfer belt TB than the second roller having D1 and D2 that satisfy the inequality 1.10<D2/D1. Accordingly, the transfer device 30 according to the exemplary embodiment is capable of reducing transfer errors attributable to the electric-current leakages further than the transfer device including the second roller having D1 and D2 that satisfy the inequality 1.10<D2/D1. In addition, the image forming apparatus 10 according to the exemplary embodiment is more likely to minimize image forming failures attributable to the transfer errors than the image forming apparatus including the transfer device.
As described above, the second transfer portion 36 according to the exemplary embodiment includes a movable portion (not illustrated). Also as described above, while an image forming operation is not performed, the second roller 70 according to the exemplary embodiment is in the unloaded state, as illustrated in
Thus, in the second transfer portion 36 according to the exemplary embodiment, the second elastic bodies 94 are less likely to retain permanent deformation than a second transfer portion that does not include a movable portion (or a second transfer portion in which the second roller 70 forms a nip N2 all the time together with the transfer belt TB). Thus, the second transfer portion 36 according to the exemplary embodiment is less likely to cause rotation failures (nonuniform peripheral speed during rotation) in association with the electric-current leakages at the second elastic bodies 94 and the remaining permanent deformation on the second elastic body 94 than a second transfer portion that does not include a movable portion. A second transfer portion that does not include a movable portion and a transfer device and an image forming apparatus that include the second transfer portion are included within the range of the technical scope of the invention.
As described above, the elastic body 90 according to the exemplary embodiment is made of an electrically conductive foam (foam containing urethane foam and an electrically conductive member). Thus, when being rubbed against the transfer belt TB, the second roller 70 according to the exemplary embodiment is less likely to be torn (has a greater tolerance) than, for example, a second roller having a similar shape as the second roller 70 including an elastic body 90 made of nitrile butadiene rubber (NBR or nitrile rubber). A second roller having a similar shape as the second roller 70 and including an elastic body 90 made of nitrile butadiene rubber (NBR or nitrile rubber), a second transfer portion including the second roller, and a transfer device and an image forming apparatus including the second transfer portion are included within the range of the technical scope of the invention.
Referring now to
As illustrated in
The effects of the first modification example are similar to those of the exemplary embodiment.
As illustrated in
The effects of the second modification example are the same as those of the exemplary embodiment.
As illustrated in
The effects of the third modification example are the same as the first, third, and fifth effects of the exemplary embodiment.
As illustrated in
The effects of the fourth modification example are the same as those of the exemplary embodiment.
As illustrated in
The effects of the fifth modification example are the same as those of the exemplary embodiment.
As illustrated in
The effects of the sixth modification example are the same as those of the exemplary embodiment.
As illustrated in
The effects of the seventh modification example are the same as the first, third, and fifth effects of the exemplary embodiment.
The details of specific exemplary embodiments of the invention have been described thus far. The present invention, however, is not limited to the above-described exemplary embodiments. Other exemplary embodiments are conceivable within the range of the technical scope of the invention.
For example, the second roller 70 according to the exemplary embodiment has been described as a roller used for a second transfer. However, as long as the second roller 70 is usable for forming an electric field, the second roller 70 does not have to be an electric conductive roller used for a second transfer. The second roller 70 may be used as, for example, a charging roller that electrically charges the photoconductor 22, a first transfer roller used for first-transferring a toner image G on the photoconductor 22 to the transfer belt TB, or a roller used for other purposes. The second rollers 70B, 70C, 70D, 70E, 70F, 70G, and 70H according to the modification examples obtained by modifying the second roller according to the exemplary embodiment (first to seventh modification examples, or hereinafter referred to as second rollers according to modification examples) are also similarly usable for other purposes.
It has been described that the second roller 70 according to the exemplary embodiment is grounded and a second transfer voltage is applied to the BUR 110. However, a second transfer voltage may be applied to the second roller 70 and the BUR 110 may be grounded, instead.
In the description of the exemplary embodiments, the second roller 70 according to the exemplary embodiment and the second rollers according to the modification examples have been separately described. However, a second roller obtained by combining the configurations of different second rollers is also included within the range of the technical scope of the invention. For example, the shape of the outer periphery of each second elastic body 94E of the second roller 70E according to the fourth modification example may be changed to the shape of the outer periphery of each second elastic body 94 of the second roller 70 according to the exemplary embodiment, each second elastic body 94B of the second roller 70B according to the first modification example, or each second elastic body 94C of the second roller 70C according to the second modification example.
In the description of the exemplary embodiments, the second elastic bodies 94, 94B, 94C, 94D, 94E, 94F, 94G, and 94H have been described using the second roller 70 according to the exemplary embodiment and the second rollers according to the modification examples as examples. However, the shapes of the second elastic bodies 94, 94B, 94C, 94D, 94E, 94F, 94G, and 94H are not limited to these shapes. Each second elastic body may have any shape as long as it covers the corresponding protrusion 84 of the shaft 80 while being spaced apart from the protrusion 84 and it gradually thickens from the boundary BP to the free end FE while the second elastic body is retaining an outside diameter greater than or equal to the outside diameter D1 of the first elastic body 92.
In the description of the second transfer portion 36 according to the exemplary embodiment, the BUR 110 is vertically moved by a movable portion (not illustrated). Instead, the BUR 110 may be disposed in the operation position without the movable portion being provided to the second transfer portion 36 and the second roller 70 may be made vertically movable by another movable portion (not illustrated).
Referring now to the drawings, examples and comparative examples are described.
Hereinbelow, an example and comparative examples (comparative examples 1 and 2) are described. Firstly, second rollers according to the example and the comparative examples were fabricated in the following manner. Then, leakage voltages that occur in the second rollers according to the example and the comparative examples were evaluated. Outstanding properties and evaluation results of the second rollers according to the example and the comparative examples are illustrated in the table in
Each of the second rollers according to the example and the comparative examples (comparative examples 1 and 2) was attached to DocuCentre-V C7775 (manufactured by Fuji Xerox Corporation). Under the low-temperature low-humidity environment (environment of a temperature of 10° C. and a humidity of 15%), a cyan halftone image was printed over the entirety of an image forming area of an A4-size medium P (plain paper copy paper) and the printed image was observed to evaluate the leakage voltage.
The second roller according to the example was shaped like the second roller 70 according to the exemplary embodiment (see
The second roller (not illustrated) according to the comparative example 1 has the same configuration as the second roller according to the example except that the second roller according to the comparative example does not include the second elastic bodies 94.
A second roller according to the comparative example 2 has the same configuration as the second roller according to the example except that the outside diameter of the second elastic bodies 94 is equivalent to the outside diameter of the first elastic body 92 (that is, both thicknesses are 3 mm). The second roller according to the comparative example 2 is shaped like the second roller 70A according to the comparative mode (see
In the table illustrated in
As illustrated in the table in
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 |
|---|---|---|---|
| 2015-023295 | Feb 2015 | JP | national |
