Patent Application
20080038031
The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate exemplary embodiments, features, and aspects of the invention and, together with the description, serve to explain the principles of the invention.
Various exemplary embodiments, features, and aspects of the present invention will now herein be described in detail with reference to the drawings. It is to be noted that the relative arrangement of the components, the numerical expressions, and numerical values set forth in these embodiments are not intended to limit the scope of the present invention unless it is specifically stated otherwise.
Now, an exemplary embodiment of the present invention will be described below.
The image forming unit 102 includes photosensitive drums a through d and an exposure unit 6. A toner image of four colors, namely, yellow, magenta, cyan, and black, is formed on a surface of the photosensitive drums a through d. The exposure unit 6 irradiates the surface of the photosensitive drums a through d with a laser beam according to image information and forms an electrostatic latent image. Each of the photosensitive drums a through d is driven by a motor (not illustrated). A primary charging device (not illustrated), a development unit (not illustrated), and a transfer charging device (not illustrated) are provided as a unit of process cartridges 1a through 1d, and disposed around the photosensitive drums a through d.
An intermediate transfer belt 2 rotates in a direction indicated by an arrow in
A secondary transfer unit 3 serially transfers the full color images formed on the intermediate transfer belt 2 to a sheet P. A sheet conveyance unit 103 is disposed on a downstream of the fixing unit 5. The sheet conveyance unit 103 conveys the sheet P having an image fixed thereon by the fixing unit 5. The sheet conveyance unit 103 includes a curl correction unit 70 and a discharge roller pair 11. The curl correction unit 70 is disposed on the downstream of the fixing unit 5. The discharge roller pair 11 constitutes a discharge unit (not illustrated) that discharges a sheet P, whose curl has been corrected by the curl correction unit 107, onto a discharge tray 7.
Now, processing for forming an image performed by the image forming apparatus 100 having the above-described configuration will be described below.
When a user generates an instruction for starting image forming processing, the exposure unit 6, according to image information sent from a personal computer (not illustrated), irradiates with a laser beam the surface of the photosensitive drums a through d, which is evenly charged to a predetermined polarity and at a predetermined potential, to form an electrostatic latent image. Then, the development unit develops the electrostatic latent image with the toner to visualize the image.
For example, first, the exposure unit 6 irradiates the photosensitive drum a with a laser beam generated based on an image signal of a yellow component of a document via a polygon mirror of the exposure apparatus 6 to form an electrostatic latent image in color yellow on the photosensitive drum a. Then, the development unit develops the electrostatic latent image using a yellow toner to visualize the image as a yellow toner image.
Subsequently, when the yellow toner image reaches a primary transfer portion, in which the photosensitive drum a abuts the intermediate transfer belt 2 while rotating, the yellow toner image formed on the photosensitive drum a is primarily transferred onto the intermediate transfer belt 2 by a primary transfer bias applied to the transfer charging device 2a.
Then, when a portion of the intermediate transfer belt 2 having the yellow toner image transferred thereon is moved as the intermediate transfer belt travels, a magenta toner image similarly formed on the photosensitive drum b is transferred onto the intermediate transfer belt 2 on the yellow toner image. Furthermore, cyan and black toner images are similarly transferred overlapping on the yellow and magenta toner images in the primary transferring portion as the intermediate transfer belt 2 travels. A full-color toner image is thus formed on the intermediate transfer belt 2.
Then, the sheets P, stacked in a paper feed cassette 4 during the toner image forming processing, are fed sheet by sheet by a pickup roller 8 to a registration roller 9 through a sheet conveyance path 45. A timing for conveying the sheet P is adjusted by the registration roller 9. Then, the sheet P is conveyed to the secondary transfer unit 3. The secondary transfer unit 3 collectively transfers onto the sheet P the toner images of four colors formed on the intermediate transfer belt 2 while a secondary transfer bias is applied to a secondary transfer roller 3a (i.e., the transfer unit).
The sheet P having the toner image is guided by a conveyance guide 40, which is disposed between the secondary transfer unit 3 and a fixing roller pair of the fixing unit 5, and is conveyed to the fixing unit 5. In the fixing unit 5, toners of respective color are melted and mixed together by heat and pressure to be fixed on the sheet P as a full-color image.
The sheet P having the fixed image is subjected to curl correction by the curl correction unit 70 disposed on the downstream of the fixing unit 5. Then, the corrected sheet P is discharged on the sheet discharge tray 7 through a discharge path 42 by the discharge roller pair 11.
The sheet conveyance path 45 and a sheet conveyance path between the secondary transfer unit 3 and the fixing roller pair of the fixing unit 5 constitute a main sheet conveyance path for conveying the sheet upward. The secondary transfer unit 3, the fixing roller pair of the fixing unit 5, and the curl correction unit 70 are disposed at midpoints of the main sheet conveyance path, in this order from the bottom.
Further, the image forming apparatus 100 is capable of forming an image on both sides of a sheet. In a duplex printing mode of the image forming apparatus 100, the sheet P is reversed by the discharge roller pair 11 and switched by a switching flapper 46, to be conveyed into a duplex conveyance path 47. A second curl correction unit 12 is disposed in the duplex conveyance path 47. The second curl correction unit 12 can provide a curl to the sheet P in a direction in which the sheet P is bent away from the intermediate transfer belt 2, in the secondary transfer unit 3. Subsequently, the sheet P is fed again to the registration roller 9 via a confluence portion 48 between the sheet conveyance path 45 and the duplex conveyance path 47. A toner image is formed by the image forming processing similar to that performed for a first side of the sheet.
The fixing unit according to the present exemplary embodiment is of a power saving type that implements a standby-less operation. Furthermore, the fixing unit is of a fixing belt heating type and also pressing rotation member drive type (tensionless type). As illustrated in
Furthermore, referring to
An entrance guide 23 (
The pressure roller 22 includes a stainless core metal 22a and an elastic layer 22b formed around the stainless core metal 22a by injection molding. The elastic layer 22b is made of silicone rubber having a thickness of approximately 3 mm and covered with an approximately 40 μm-thick perfluoroalkoxy (PFA) resin tube. The pressure roller 22 is disposed between front and back side boards (not illustrated) of the apparatus frames 24, while both edge portions of the core metal 22a are rotatably held therebetween.
A fixing belt unit 20A (
In the present exemplary embodiment, both of the edge portions of the heater holder 17 are urged in an axial direction of the pressure roller 22 by a pressure mechanism (not illustrated), with a force of 98 N for each edge portion (196 N in total).
Thus, an outer surface of the fixing heater 16 comes into pressure-contact with the elastic layer 22b of the pressure roller 22 via the fixing belt 20, with a predetermined level of pressure which is enough to resist the elasticity of the elastic layer 22b. Thus, the fixing nip portion 27 having a predetermined width necessary for heat-fixing can be formed. The pressure mechanism has a pressure releasing mechanism (not illustrated). The pressure releasing mechanism releases the pressure of the pressure roller 22 at the time of treating with a paper jam so that a jammed sheet P can be easily removed.
The pressure roller 22 is rotated by a drive unit (not illustrated) in a direction indicated by an arrow (
As a result, the fixing belt 20 slides while an inner surface is in close contact with the outer surface of the fixing heater 16, and is rotated around an outer periphery of the heater holder 17 in a direction indicated by an arrow (
Subsequently, the fixing heater 16 is powered on in a state where the fixing belt 20 is rotated as the pressure roller 22 rotates. At this time, the surface temperature of the fixing belt 20 is adjusted to 180° C. After the surface temperature of the fixing belt 20 is thus adjusted, the sheet P carrying an unfixed toner image t is guided along the entrance guide 23 to the fixing nip portion 27 between the fixing belt 20 and the pressure roller 22. In the fixing nip portion 27, the sheet P is pinched and conveyed through the fixing nip portion 27 together with the fixing belt 20. The side of the sheet P carrying the toner image t is in close contact with the outer surface of the fixing belt 20.
When the sheet P is thus pinched and conveyed, the heat generated by the fixing heater 16 is applied to the sheet P via the fixing belt 20. Accordingly, the unfixed toner image t on the sheet P is melted and fixed by heat and pressure. Then, the sheet P passes through the fixing nip portion 27 and is discharged from the fixing belt 20 by curvature separation.
Referring to
The hollow roller 72 is made of a metal such as stainless steel or aluminum which is by far harder than the roller portion 71a of the sponge roller 71, and has an outer diameter of 9 mm and thickness of 0.45 mm. In the present exemplary embodiment, in order to prevent the toner from adhering to the sponge roller 71 and the hollow roller 72, the surfaces of the sponge roller 71 and the hollow roller 72 are coated with thin fluoride resin tube layers 71c and 72c, respectively. The layers 71c and 72c have thickness of about 0.1 mm. The layers 71c and 72c can be made of polytetrafluoroethylene (PTFE) or PFA. Furthermore, the thin fluoride resin tube layers 71c and 72c that coat the surfaces of the sponge roller 71 and the hollow roller 72, have no significant influence on thermal conductivity.
The material used for the first roller is not limited to foam silicone rubber. That is, the elastomer can be made of other rubber materials or resin materials, as long as high heat resistance and large heat capacity can be obtained.
Referring to
In the present exemplary embodiment, the sponge roller 71 and the hollow roller 72 are pressed by pressure springs 79 with a pressure level of 2.5 N at one end (5 N in total). A desired nip can be formed owing to the pressure between the sponge roller 71 (the roller portion 71a) and the hollow roller 72, as illustrated in
Here, a curl correction effect produced by the curl correction unit 70 depends on a pressure force (mechanical energy) between the sponge roller 71 and the hollow roller 72 as well as temperature of the sheet (thermal energy). In general, in terms of mechanical energy, the lower the applied pressure, the lower the curl correction effect becomes. In terms of thermal energy, the farther the sheet P is conveyed away from the fixing unit 5, the lower the temperature of the sheet P becomes, therefore, the lower the curl correction effect becomes.
Moreover, in the case of using the fixing unit 5 according to the present exemplary embodiment, no standby mode is required. Accordingly, the fixing unit 5 and the peripheral components including the curl correction unit 70 have not been warmed up before a print job starts. As a result, when the print job starts from the state in which the fixing unit 5 and the peripheral components including the curl correction unit 70 have not been warmed up, if the curl correction unit 70 is not warmed up before the sheet P reaches the curl correction unit 70, the temperature of the sheet P decreases. Accordingly, the curl correction effect on the sheet P also declines.
In this case, when a plurality of sheets is serially printed, the degrees of curl of a first sheet and a last sheet significantly differ. Accordingly, the sheet P cannot be securely output with an appropriate state of curling.
In order to address this problem, it is necessary to warm up the curl correction unit 70 and maintain the warmed-up state when the fixing heater 16 adjusts the start-up temperature of the fixing unit 5 up to predetermined temperature.
Accordingly, in the present exemplary embodiment, the curl correction unit 70 includes the sponge roller 71 having a sponge-like shaped roller portion 71a and the hollow roller 72. The roller portion 71a has low thermal conductivity. The hollow roller 72 has a surface rigidity which is higher than the sponge roller 71, and is made of a metal of low heat capacity. Since the heat capacity of the hollow roller 72 is low, the temperature of the hollow roller 72 can be quickly raised by absorbing the heat generated by the fixing unit 5.
The sponge roller 71 can also be heated by the thus heated hollow roller 72. Since the roller portion 71a of the sponge roller 71 is made of a sponge material having low thermal conductivity, the heat on the surface of the sponge roller 71 cannot easily escape. Accordingly, the surface temperature of the sponge roller 71, which has been raised by the heat generated by the fixing unit 5 and transmitted via the hollow roller 72, can be easily maintained.
Moreover, the curl correction unit 70 is disposed between the fixing unit 5 and the discharge roller pair 11, above the fixing unit 5. Furthermore, the curl correction unit 70 according to the present exemplary embodiment is disposed at a position where a nip center distance between the curl correction unit 70 and the fixing unit 5 is 30 mm.
The heat is applied from the fixing unit 5 to the hollow roller 72 by both heat radiation and convection.
Accordingly, a guide 41 (
As the curl correction unit 70 is arranged as described above, the curling of sheet can be securely performed even in the case of duplex image forming, since both sides of the sheet pass through the curl correction unit 70 warmed up by the heat that is generated by the fixing unit 5. Moreover, a greater curl correction effect can be obtained since the temperature of the sheet P is high.
Now, the curl correction processing by the curl correction unit 70 will be described below.
When a job starts from a cold state, as described above, toner images are formed on the photosensitive drums a through d. Then, the formed toner images are transferred onto a sheet P via the intermediate transfer belt 2. Then, the transferred toner images are fixed on the sheet P by the fixing unit 5.
Since the curl correction unit 70 is disposed close to the fixing unit 5 and the hollow roller 72 is made of metal with a high thermal conductivity, the heat generated by the fixing unit 5 can be effectively transmitted to rapidly raise the surface temperature of the curl correction unit 70.
Furthermore, when the sheet P having the fixed toner image thereon enters a nip of the curl correction unit 70 as illustrated in
As described above, in the present exemplary embodiment, the roller pair 71 and 72 of the curl correction unit 70 includes the sponge roller 71 and the metal hollow roller 72 having low heat capacity. Accordingly, the curl correction unit 70 can be heated up in a short time and the warmed-up (heated) state can be maintained. Thus, a sheet curl can be effectively and securely corrected.
Moreover, in the present exemplary embodiment, the curl correction unit 70 is disposed at a position close to the fixing unit 5. Accordingly, the sheet P having passed through the fixing unit 5 cannot be cooled down and the heat generated by the fixing unit 5 can be efficiently utilized. Thus, it is not necessary to increase the pressure generated by the curl correction unit 70. Accordingly, power can be saved and a long life of the apparatus can be implemented.
In the above-described exemplary embodiment, the sponge roller 71 is disposed so as to face a non-image forming side of a sheet P and the hollow roller 72 is disposed so as to face an image forming side. However, the rollers 71 and 72 can be disposed such that the direction of correcting the sheet curl is opposite to the above-described direction, depending on tendency of a sheet curl in the image forming apparatus of the present invention.
Moreover, the outer diameters and shapes of the sponge roller 71 and the hollow roller 72, and the distance between the curl correction unit 70 and the fixing unit 5 are not limited to those described above. For example, the outer diameters and shapes of the sponge roller 71 and the hollow roller 72, and the distance between the curl correction unit 70 and the fixing unit 5 can be set depending on design conditions such as a life of the curl correction unit 70, power supplied from the image forming apparatus to the curl correction unit 70, and a surface temperature raising of the curl correction unit 70 according to the amount of heat generated by the fixing unit 5 in the case where a job is started from a cold state.
Furthermore, in the present exemplary embodiment, the fixing unit 5 is used which saves electric power. However, a commonly used heat roller fixing unit, which performs standby heating, can be used. Also in this case, the thermal energy generated by the fixing unit 5 can be efficiently utilized.
Moreover, in the present exemplary embodiment, the curl correction unit 70 is disposed between the fixing unit 5 and the discharge roller pair 11. However, the function of the discharge roller pair 11 for discharging the sheet P to an outside of the image forming apparatus can be provided on the curl correction unit 70. That is, the curl correction unit 70 can discharge the sheet P instead of the discharge roller pair 11.
Furthermore, according to a conventional method, condensation occurs on the surface of the curl correction unit 70 due to moisture (vapor) coming from the sheet P which appears immediately after fixing when warm-up is not sufficiently performed. Since the curl correction unit 70 according to the present exemplary embodiment can raise its surface temperature in a short period of time, such condensation can be prevented.
That is, since the curl correction unit 70 can raise its surface temperature in a short period of time as described above, the vapor coming from the sheet P immediately after fixing can be maintained as vapor in the vicinity of the curl correction unit 70. Accordingly, condensation can be prevented even in the case where a job starts in a cold state. Thus, transfer unevenness (image unevenness) occurring due to wet sheets caused by condensation in the case of duplex image forming can be suppressed.
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 modifications, equivalent structures, and functions.
This application claims priority from Japanese Patent Application No. 2006-219009 filed Aug. 10, 2006, which is hereby incorporated by reference herein in its entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2006-219009 | Aug 2006 | JP | national |
