Patent Grant
9042749
The present application is related to, claims priority from and incorporates by reference Japanese Patent Application No. 2011-213544, filed on Sep. 28, 2011.
This invention relates to a fixing device that fixes a toner image transferred on a medium onto the medium by heat and pressure, and an image forming apparatus that includes such a fixing device, and a fixing device heating unit that uses some components of the fixing device.
Electrographic printers, photocopy machines, facsimile machines and the like are examples of an image forming apparatus that transfers a black-and-white or color toner image formed on a toner image forming part onto a medium, such as a sheet and the like. Such an image forming apparatus includes a fixing device. Conventionally, this type of fixing device includes a movable endless fixing belt, a sheet heating body that heats the fixing belt, a fixing roller that stretches the fixing belt with the sheet heating body, a pressure application roller provided to face the fixing roller via the fixing belt, and a nip part formed at a contact part of the pressure application roller and the fixing belt. The toner image is fixed on the medium by feeding the medium on which the toner image has been transferred to and passing through the nip part and by applying heat from the sheet heating body and pressure by the fixing roller and the pressure application roller at the time of passage (see Japanese Laid-Open Patent Application No. 2007-322888).
However, the above-described conventional technology does not consider a case in which an overtemperature protector is used for protecting the sheet heating body from overtemperature. One of objects of the present invention is to solve such a problem.
Considering the objections, a fixing device of the invention includes an endless belt that supplies heat to a medium, a heat diffusion member that stretches the endless belt, a heating body that heats the heat diffusion member, an overtemperature protector that is positioned to face the heating body; and a pressure application support member that is positioned between the heating body and the overtemperature protector.
With such a structure, the fixing device reduces a chance that the temperature of an overtemperature protector unnecessarily increases, by providing a pressure application support member between a heating body and an overtemperature protector.
In another view of the invention, a fixing device heating unit includes a heat diffusion member that diffuses heat including a two-step indented part, the two-step indented part including a first indented section and a second indented section larger than the first indented section, a heating body that heats the heat diffusion member and that has a first width, the heating body being fitted in the first indented section and including a first side facing the heat diffusion member and a resistance heating body being provided on the first side, a pressure application support member that contacts the heating body and has a second width larger than the first width, the pressure application support member being fitted in the second indented section, and heat transfer from the heating body to the heat diffusion member is faster than from the heating body to the pressure application support member.
Embodiments of a fixing device of an image forming apparatus according to the present invention are explained below with reference to figures.
Here, the toner image forming part 43, the transfer part 44 and the fixing device 45 are positioned so that the toner image forming part 43 and the transfer part 44 are positioned on the upstream side and that the fixing device 45 is positioned on the downstream side in a carrying direction of the sheet 12 fed from the sheet accommodation part 40. In addition, the toner image forming part 43 and the transfer part 44 are provided so as to face each other across a carrying path for the sheet 12. The LED head 42 is positioned above the toner image forming part 43.
In this configuration, when the print controller (not shown) receives a print instruction from a host device or the like, or when an instruction for printing is inputted from an input part of the device, a sheet 12 is fed from the sheet accommodation part 40 and is carried to the toner image forming part 43 by the sheet carrying part 41 at a timing for image formation.
The LED head 42 exposes the toner image forming part 43 in response to the print information to form an image as a latent image. The image formed on the toner image forming part 43 is formed to a toner image by a development device. The toner image is transferred onto the sheet 12 by the transfer part 44.
After that, the sheet 12 is carried to the fixing device 45 by the sheet carrying part 41. After the toner image is fixed onto the sheet 12 by the heat and pressure at the fixing device 45, the sheet 12 is carried by the sheet carrying part 41 and is ejected onto a stacker.
Next, the fixing device 45 shown in
The sheet heating body 1 is a device that heats up the fixing belt 4 and is attached to the pressure application support member 2. The heat diffusion member 3 is a device that diffuses and transfers the heat of the sheet heating body 1 to the fixing belt 4. The elastic member 8 is a device that applies load to the sheet heating body 1, the pressure application support member 2 and the heat diffusion member 3 and applies tension to the fixing belt 4. A coil spring and the like are used as the elastic member 8. The elastic member 8 is positioned between the pressure application support member 2 and the support member 9. The support member 9 is fixed relative to the main body device and supports the pressure application support member 2 and the sheet heating body 1 via the elastic member 8.
The pressure application roller 7 is provided to contact an outer circumferential surface of the fixing belt 4 at a position opposite from the heat diffusion member 3. The pressure application member 5 and the fixing roller 6 are arranged to be adjacent to, and face, each other. The pressure application member 5 and the fixing roller 6 are arranged to press the fixing belt 4 against the pressure application roller 7. Here, the elastic member 10 presses the pressure application member 5 against the pressure application roller 7 and is held by the support member 17 that is relatively fixed to the main body device. The contact part of the fixing belt 4 and the pressure application roller 7 forms a nip part. The sheet 12, on which the toner image by a toner 11 has been transferred, is fed into the nip part.
The temperature detection device 18 that abuts an inner circumferential surface of the fixing belt 4 is provided in the present fixing device 45. However, the temperature detection device 18 may abut the outer circumferential surface of the fixing belt 4. Alternatively, the temperature detection device 18 may be of a non-contact type in which the temperature detection device 18 is provided with a minute gap.
In addition, an attachment member 13 is attached at a center part of the support member 9 via a plurality of elastic members 14. An overtemperature protector 15 is attached on the attachment member 13. The overtemperature protector 15 abuts the lower surface of the pressure application support member 2 by a biasing force of the elastic member 14.
The pressure application support member 2 is made of a metal with excellent heat conductivity and processability, such as aluminum, copper and the like; an alloy having such a metal as a main component; or an iron, iron-type alloys, stainless steel or the like with high heat durability and stiffness, and is formed in a plate form with uniform thickness. The pressure application support member 2 is not used in the conventional fixing device. The overtemperature protector 15 is a thermostat that detects a temperature and cuts off a power source that supplies electric power to the sheet heating body 1 when the detected temperature exceeds a certain temperature. In the present embodiment, the upper limit value of the operational temperature is 270° C.
Here, the indented part is formed such that a relationship L<d is established, where L is a distance between the abutting part 3a and the heat transfer parts 3d in a direction in which the elastic member 8 biases the sheet heating body 1, and d is a thickness of the sheet heating body 1. With such a relationship, the sheet heating body 1 is securely contacted to the abutting part 3a of the heat diffusion member 3 by the biasing force of the elastic member 8 via the pressure application support member 2.
In addition, with L<d, a space is created between the pressure application support part 2 and the heat transfer part 3b to prevent the heat transfer between the pressure application support member 2 and the heat transfer part 3b from being blocked by the space, a surface area of the pressure application support member 2 is formed larger than a surface area of the sheet heating body 1 so as to form projection areas A. The projection areas A are areas by which the pressure application support member 2 project from the sheet heating body 1 on the surface where the pressure application support member 2 and the sheet heating body 1 abut each other. In addition, heat conductive grease 19 is applied in the projection areas A.
Specifically, as shown in
For the heat conductive grease 19, silicon oil is used as base oil, and zinc oxide is added for improving heat conductivity. By doing so, the heat is efficiently conducted between the pressure application support member 2 and the heat diffusion member 3. Therefore, the heat is balanced between the pressure application support member 2 and the heat diffusion member 3, and thus, the heat is transferred such that the temperature of the pressure application support member 2 becomes close to the temperature of the heat diffusion member 3. As a result, the temperature of the pressure application support member 2 is not unnecessarily increased, thereby reducing unnecessary increase in the temperature of the overtemperature protector 15. Moreover, an effect to transfer heat to the heat diffusion member 3 from a back surface C of the sheet heating body 1, which has been transferred to the pressure application support member 2 side, is obtained. Therefore, the heat at the sheet heating body 1 is efficiently transferred to the heat diffusion member 3, and thereby, an effect of reducing the time for the fixing belt 4 to reach to a target temperature is obtained.
A gear (not shown) is provided on an end of the fixing roller 6. As the gear is driven by the rotational force transmitted from the sheet carrying part 41, the fixing roller 6 rotates. The rotational force of the fixing roller 6 is transmitted to the fixing belt 4 and the pressure application roller 7 by the frictional force. As a result, the fixing belt 4 and the pressure application roller 7 respectively follow and rotate in the arrow direction in
Moreover, the fixing roller 6 is biased by an elastic member (not shown), such as a spring and the like, so as to press the pressure application roller 7 via the fixing belt 4. The pressure application member 5 is biased by an elastic member 8, such as a coil spring shown in
If the base 71 is made of nickel, polyimide, stainless steel or the like, a thickness of the base 71 is preferably approximately 30 μm to 150 μm to achieve both strength and flexibility.
For the elastic layer 72, silicon rubber or fluororubber that has high heat resistance is used. If silicon rubber is used, a thickness of the elastic layer 72 is preferably 50 μm to 300 μm to achieve both low hardness and high heat conductivity. If fluororesin is used, the thickness of the elastic layer 72 is preferably 10 μm to 50 μm to achieve both durability against reduction of body due to friction and high heat conductivity.
For the release layer 73, a resin with high heat resistance like the elastic layer 72 and low surface free energy after formation, for example, a representative or fluorine-based resin, such as polytetrafluoroethylene (PTFE), perfluoroalkoxy alkane (PFA), perfluoroethylene-propene copolymer (FEP) and the like, is used. A thickness of the release layer 73 is preferably 10 μm to 50 μm.
In addition, the fixing belt 4 may be provided with the release layer 73 on the thin base 71 as shown in
The fixing belt 4 with such a configuration is stretched as being wound on the heat diffusion member 3, the pressure application member 5 and the fixing roller 6 with the elastic layer 72 or the release layer 73 facing outside.
Operation of the above-described configuration is explained. In
The sheet 12, on which the toner 11, that is, the toner image, has been transferred, is carried through the nip part formed at a press-contact part between the fixing belt 4 and the pressure application roller 7. At that time, as the toner 11 and the sheet 12 are heated by the fixing belt 4, and as the pressure application member 5 and the fixing roller 6 respectively applies pressure onto the pressure application roller 7, the toner image is fixed to the sheet 12.
In addition, the pressure application support member 2 is regulated in the above description by a range of the thickness. Where C2 is a heat capacity of the pressure application support member 2, a range of the heat capacity C2 is preferably configured in a range of 11.75 J/K or greater and 24.2 J/K or less. Moreover, where C1 is a heat capacity of the heat diffusion member 3, the heat capacity C2 is preferably configured at 30% or greater and 62% or less of the heat capacity C1.
As shown in
[Evaluation Conditions]
As understood from
The fixing device 45 of the present embodiment has a configuration in which the pressure application support member 2 is placed between the sheet heating body 1 and the overtemperature protector 15. The overtemperature protector 15 abuts the lower surface of the pressure application support member 2 by the biasing force of the elastic member 14. An evaluation was conducted to obtain usage conditions for the fixing device 45 of the present embodiment including the above-described configuration.
[Evaluation Conditions]
Pressure application support member 2: Aluminum plate with width of 16 mm, length of 326 mm, and thickness of 1 mm (heat capacity C2a=11.7 J/K), 1.5 mm (heat capacity C2b=18 J/K) and 2 mm (heat capacity C2b=24.2 J/K) (three types)
Other evaluation conditions are the same as the case of the reference fixing device.
Similar to the reference fixing device, for the fixing device 45 of the present embodiment, the temperature history for the starting time from the room temperature was measured using the three types of the pressure application support member 2 with different thicknesses.
As shown in
However, as the thickness of the pressure application support member 2 increases, the heat capacity increases. Accordingly, the starting time increases. Nonetheless, in the case where the thickness of the pressure application support member 2 is 2 mm, the starting time was 24.3 seconds, which did not show a significant delay compared with the reference fixing device.
This is assumed that, although the heat capacity increases by the amount of the pressure application support member 2 in the fixing device 45 of the present embodiment, the temperature of the pressure application support member 2 heated by the sheet heating body 1 increases faster than the temperature of the heat diffusion member 3, and a heat transfer occurs from the pressure application support member 2 and the heat diffusion member 3 at that time, resulting in an increase of the heat capacity applied to the fixing belt 4. Therefore, the contact between the pressure application support member 2 and the heat diffusion member 3 contributes to an effect of reducing the starting time. Accordingly, the thickness of the pressure application support member 2 is equal to or less than 2 mm to achieve the same condition as the starting time for the reference fixing device.
Based on the above results, the thickness of the pressure application support member 2 is equal to or greater than 1 mm and equal to or less than 2 mm to use the overtemperature protector 15 and the pressure application support member 2 by abutting each other while securing the starting time with the reference fixing device.
Excellent effects are obtained by satisfying:
T2max≧(C1×T1max)/(C2×α) (1)
where C1 is the heat capacity of the heat diffusion member 3, C2 is the heat capacity of the pressure application support member 2, T1max is the maximum reaching temperature of the fixing belt 4, and T2max is the maximum reaching temperature of the overtemperature protector 15.
Here, the value α is a coefficient. In the present embodiment, with the maximum reaching temperature T1max of the fixing belt 4 being 164° C. (T1max=164° C.), the maximum reaching temperature T2max being 255° C. (T2max=255° C.), and the heat capacity C1 being 39.1 J/K (C1=39.1 J/K) as fixed design values, the heat capacity C2 is adjusted by changing the thickness of the pressure application support member 2 by 0.5 mm. The thickness of the pressure application support member 2, with which T2max exceeded 270° C., is 0.5 mm. Therefore, with the thickness of the pressure application support member 2 being 1.0 mm (heat capacity C2=11.7) as a boarder value, the value a that corresponds to the boarder value is calculated by plugging the above-described design values in the below equation.
T2max≧(C1×T1max)/(C2×α)
α=2.14
By plugging α in Equation (1), Equation (2) is obtained.
T2max≧(C1×T1max)/(C2×2.14) (2)
As shown in the present embodiment, with the configuration in which the sheet heating body 1 is pressed against the heat diffusion member 3 by the pressure application support member 2, and in which the overtemperature protector 15 abuts the opposite side of the pressure application support member 2 from the abutting surface of the pressure application support member 2 abutting the sheet heating body 1, the temperature of the fixing belt 4 reaches a predetermined temperature before the maximum reaching temperature of the overtemperature protector 15 reaches a predetermined value, by setting the components to satisfy Equation (2).
As explained above, according to the present embodiment, a chance that the temperature the overtemperature protector 15 unnecessarily increases is reduced by providing the pressure application support member 2 between the sheet heating body 1 and the overtemperature protector 15. In addition, by configuring the thickness of the pressure application support member 2 in a range equal to or greater than 1 mm and equal to or less than 2 mm, the overtemperature protector 15 is maintained within a range of the operational upper limit temperature while securing predetermined starting time.
In the present embodiment, the sheet heating body 1 and the pressure application support member 16 provided on an inner surface of the heat diffusion member 3 are pressed against the heat diffusion member 3 at certain load applied by the elastic member 8 fixed on the support member 9 and stretches the fixing belt 4 with the heat diffusion member 3.
Other parts are similar to the above-described first embodiment.
The pressure application support member 16, together with the sheet heating body 1, is pressed by a plurality of elastic members 14 using coil springs. Therefore, there is a risk of deformation, such as warping and the like, due to twisting by an external force and/or heat. When the pressure application support member 16 is deformed, the contact state between the sheet heating body 1, the pressure application support member 16 and the heat diffusion member 3 in the longitudinal direction changes. As a result, the temperature of the heat diffusion member 3 becomes uneven in the longitudinal direction, and as such, the surface temperature of the fixing belt 4 that contacts the toner 11 and the sheet 12 and fixes the toner image by the toner 11 onto the sheet 12 as shown in
Therefore, in the present second embodiment, the pressure application support member 16 is configured to have the shape shown in
In addition, in the present embodiment, to secure the starting time and the range of use of the overtemperature protector 15, the heat capacity of the pressure application support member 16 is configured in a range of 12.5 J/K or more and 25 J/K or less.
According to the second embodiment, in addition to the advantages similar to those in the first embodiment, the heat conduction is made uniform in the longitudinal direction because the deformation by the external force and warping due to heat are prevented by forming the pressure application support member 16 in the U shape. Moreover, because of this, the uneven surface temperature of the fixing belt 4 is prevented. Therefore, there is an advantage that the fixing of the toner image without uneven gloss is achieved. In the above-described embodiments, the fixing device is explained that is installed in an electrographic printer as an image forming device. However, the above embodiments are also applicable in the multifunction peripheral (MPF), facsimile machines, photocopy machines and the like.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2011-213544 | Sep 2011 | JP | national |
| Number | Name | Date | Kind |
|---|---|---|---|
| 6075228 | Goto et al. | Jun 2000 | A |
| 8412084 | Ishida et al. | Apr 2013 | B2 |
| Number | Date | Country |
|---|---|---|
| 07-199701 | Aug 1995 | JP |
| 2004-191514 | Jul 2004 | JP |
| 2007-322888 | Dec 2007 | JP |
| Number | Date | Country | |
|---|---|---|---|
| 20130078018 A1 | Mar 2013 | US |
