Patent Application
20190384211
The present invention relates to a heater for use with a fixing device mountable in an image forming apparatus heater such as an electrophotographic copying machine or an electrophotographic printer, and relates to a fixing device including the heater.
As the fixing device mounted in the copying machine or the printer of an electrophotographic type, a fixing device of a film heating type has been known. The fixing device of this type includes a rotatable cylindrical film, a plate-like heater for heating the film while contacting an inner peripheral surface of the film, and a pressing roller for forming a nip in cooperation with the heater through the film. A recording material on which an unfixed toner image is carried is heated while being nipped and fed through the nip, whereby the toner image is fixed on the recording material.
In a copying machine or a printer, it has been known that when images are continuously printed on small size recording materials in the same print intervals as those of large size recording materials, non-passing regions, of a nip of the fixing device, where the small size recording materials do not pass excessively increase in temperature. When the non-passing regions of the nip of the fixing device excessively increase in temperature, the film heated by the heater and a holder supporting the heater are damaged.
As a method of suppressing overheating of the non-passing regions of the nip, a device in which a heat generating resistor to be formed on a substrate of a heater is divided into a plurality of heat generating blocks and in which a heat generating distribution of the heater is switched depending on a size of a recording material has been disclosed in Japanese Laid-Open Patent Application (JP-A) 2014-59508. Further, JP-A 2014-59508 also discloses a constitution in which in at least one heat generating block, a plurality of pieces of heat generating resistors are electrically connected in parallel to each other.
In the constitution in which the plurality of pieces of heat generating resistors are electrically connected in parallel to each other, with respect to a longitudinal direction of the heater, a temperature difference generates between a region in which the heat generating resistors exist and a region in which the heat generating resistors do not exist. For this reason, in the case a locating position of a temperature detecting element on the substrate changes due to a variation during manufacturing of the device, there was a possibility that a heat quantity received from the heater by the temperature detecting element changes and thus a detection temperature varies. Further, in recent years, further improvement in image quality has been required, so that it has been desired that accuracy of temperature control of the heater is improved.
A principal object of the present invention is to provide a heater capable of suppressing a variation in detection temperature even when a locating position of a temperature detecting element on a heating member changes due to a variation during manufacturing of a device.
Another object of the present invention is to provide a fixing device including the heater.
According to an aspect of the present invention, there is provided a heater for use with a fixing device for fixing an image formed on a recording material, comprising: an elongated substrate; a first electroconductive member provided on the substrate along a longitudinal direction of the substrate; a second electroconductive member provided on the substrate along the longitudinal direction; a plurality of heat generating resistors provided between the first electroconductive member and the second electroconductive member and electrically connected between the first electroconductive member and the second electroconductive member in parallel to each other; and a temperature detecting element configured to detect a temperature of the heater, wherein the following relationships are satisfied: W≥L and W≥S, where W represents a dimension of the temperature detecting element measured in the longitudinal direction, L represents a dimension, measured in the longitudinal direction, of one of the heat generating resistors at least partially overlapping with the temperature detecting element with respect to the longitudinal direction, and S represents a dimension between adjacent heat generating elements of the heat generating elements.
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
Parts (a), (b) and (c) of
Parts (a) to (d) of
Parts (a), (b) and (c) of
Parts (a), (b) and (c) of
Parts (a), (b) and (c) of
Embodiments of the present invention will be described with reference to the drawings. Although these embodiments are preferred embodiments of the present invention, the present invention is not limited to the following embodiments, but constitutions thereof can be replaced with other various constitutions within a scope of a concept of the present invention.
With reference to
In the image forming apparatus A, an image forming portion 10 for forming images on recording materials includes a photosensitive drum 1 as an image bearing member, a charging member 2, a laser scanner 3, a developing device 4, a transfer member 5 and a cleaner 6 for cleaning an outer peripheral surface of the photosensitive drum 1.
An operation of the image forming portion B is well known, and therefore, will be omitted from detailed description.
Recording materials P accommodated in a cassette 7 in an apparatus main assembly A1 are supplied one by one by rotation of a roller 8, and then the fed recording material P is conveyed, by rotation of a roller pair 9, to a transfer portion formed by the photosensitive drum 1 and the transfer member 5. At the transfer portion, the recording material P on which the toner image is transferred is sent to a fixing device C as a fixing portion, and the toner image is heat-fixed on the recording material P by the fixing device C. The recording material P coming out of the fixing device C is discharged onto a tray 12 by rotation of roller pairs 10 and 11.
Then, the fixing device C will be described with reference to
The fixing device C includes a heat-resistant film 21 as a cylindrical heating member, a ceramic heater 22 as a heating member for heating the film 21 in contact with an inner peripheral surface of the film 21, and a holder 20 as a supporting member for supporting the heater 22. The fixing device C further includes a stay 23 as a reinforcing member and a roller 24 as a pressing member.
The heat-resistant holder 20 inserted in a hollow portion of the film 2 supports the heater 22 by a groove 20a provided along a direction Y perpendicular to a recording material feeding direction X on a flat surface of the holder 20 on the roller 24 side. The holder 20 also has a function as a guiding member for guiding rotation of the film 21.
The film 21 has a film thickness of about 40-100 μm in total thickness in order to improve a quick start property by reducing thermal capacity thereof. As this film 21, a single layer film of PI, PTFE, PFA, FEP or the like which have a heat-resistant property, a parting property, strength, a heat-resistant property and the like can be used. Or, a composite layer film prepared by coating a surface layer of PTFE, PFA, FEP or the like on an outer peripheral surface of a film base layer of a material such as polyimide, polyamideimide, PEEK, PES or PPS can be used.
In this embodiment, a film 21 prepared by providing, on an outer peripheral surface of a polyimide film, a coat layer in which an electroconductive agent is added into a fluorine-containing resin material such as PTFE or PFA is used but is not particular about such a film. As the base layer, metal such as stainless steel may also be used. Further, between the base layer and the surface layer, a rubber layer of a silicone rubber may also be provided.
The heater 22 includes an elongated substrate 22a.
On a flat surface of the substrate 22a on the film non-sliding surface side, electroconductive members 22b1 and 22b2 are provided and extent in the direction Y perpendicular to the recording material feeding direction X, and a plurality of pieces (two pieces in this embodiment) of the electroconductive members are disposed with respect to the recording material feeding direction X. The electroconductive member (first electroconductive member) 22b1 is provided along the direction Y perpendicular to the recording material feeding direction X on an upstream side of the substrate 22a with respect to the recording material feeding direction X, and the electroconductive member (second electroconductive member) 22b2 is provided along the direction Y perpendicular to the recording material feeding direction X on a downstream side of the substrate 22a with respect to the recording material feeding direction X.
A material of each of the electroconductive members 22b1 and 22b2 is Ag or Ag/Pt, and each of the electroconductive members 22b1 and 22b2 is about 1 mm in dimension measured in the direction X and is several tens of μm in thickness with respect to a direction Z. The electroconductive members 22b1 and 22b2 are applied onto the substrate 22a by screen printing. With respect to the direction Y, to one end portion of the electroconductive member 22b1, an electrode 22c1 is electrically connected, and to the other end portion 22b2, an electrode 22c2 is electrically connected.
The heater 22 further includes a plurality of pieces of heat generating resistors for generating heat by energization. The plurality of pieces of heat generating resistors 22d are made of Ag/Pd (silver/palladium) having a PTC (positive temperature coefficient) and is applied in a thickness of about several tens of μm onto the flat surface of the substrate 22a by screen printing.
In this embodiment, between the two pieces of the electroconductive members 22b1 and 22b2 (22bW in dimension therebetween), the plurality of pieces (90 pieces in this embodiment) of the heat generating resistors 22d are connected in parallel to each other. A dimension 22bL is a recording material passing region and is also a region where the heat generating resistors 22d are provided. The heat generating resistors 22d provided in plurality of pieces are disposed obliquely to the direction Y and the direction X. These plurality of pieces of the heat generating resistors 22d overlap with adjacent pieces of the heat generating resistors. As a result, it is possible to suppress non-uniformity of a temperature distribution.
In this embodiment, 22bL=220 mm and 22bW=7 mm are set.
A protective layer 22e covers the electroconductive members 22b1 and 22b2 and the heat generating resistors 22d. As the protective layer 22e, a glass layer or a fluorine-containing resin layer is used.
A thermistor 25 as a temperature detecting element is provided on the flat surface of the substrate 22a on the film sliding surface side, and is prepared by printing a material having a NTC (negative temperature coefficient) on the flat surface of the substrate 22a.
To the thermistor 25, electroconductive patterns 25a are electrically connected. The electroconductive patterns 25a extend from the thermistor 25 toward an end portion of the substrate 22a in the direction Y.
A protective layer 22f covers an entire region of the film sliding surface of the substrate 22a. As the protective layer 22f, a glass layer or a fluorine-containing resin layer is used.
As shown in
The roller 24 includes a core metal 24a made of iron, aluminum or the like, and a roller portion 24b of a silicone rubber provided on an outer peripheral surface of the core metal 24a and is 3 mm in thickness and 20 mm in outer diameter. On an outer peripheral surface of the roller portion 24b, a parting layer 24c in which a fluorine-containing resin material is dispersed from the viewpoints of a conveying property of the film 21 and prevention of contamination with toner is provided.
As shown in
The opposite end portions of the stay 23 are pressed by springs 32 in a direction (recording material thickness direction Z) perpendicular to a generatrix direction of the film 21. By this pressure, the holder 20 presses the heater 22 against an inner surface of the film 21, so that the outer peripheral surface (surface) of the film 21 is press-contacted an outer peripheral surface (surface) of the roller 24. As a result, the roller portion 24b of the roller 24 is depressed and elastically deformed, so that a nip N is formed by the roller surface and the film surface.
When a gear G (
When electric power is supplied from a power (voltage) source AC (
The recording material P carrying unfixed toner images (unfixed images) t thereon is heated while being nipped and fed through the nip N, whereby the toner images are fixed on the recording material P.
(3) Detection Temperature when a Locating Position of Thermistor 25 Changes
Parts (a), (b) and (c) of
With respect to the direction Y, a dimension of the thermistor 25 is W, and a dimension in which the thermistors 25 (P1, P2 and P3) overlap with each other is L. A dimension of a region, between adjacent heat generating resistors 22d, where the thermistor 25 is locatable and where the heat generating resistors 22d do not exist is S. In this embodiment, L=1.8 mm and S=0.6 mm, so that a relationship of L≥S is satisfied. Further, W=2.0 mm is set. Accordingly, relationships of W≥L and W≥S are satisfied.
Here, in the device C of this embodiment, a tolerance of a relative position between the thermistor 25 and the heater 22 with respect to the direction Y is ±0.2 mm.
In part (b) of
In part (c) of
As shown in part (c) of
When the locating position of the thermistor 25 shifts in the direction Y due to a variation during manufacturing of the device C, the temperature distribution within a range of the dimension W of the thermistor 25 changes, so that a heat quantity received from the heater 22 by the thermistor 25 changes. As a result, a resistance value of the thermistor 25 changes, so that a variation in detection temperature occurs. In this embodiment, a difference between a maximum (value) and a minimum (value) of the detection temperature with respect to the positional deviation due to the tolerance is defined as the variation in detection temperature. In the image forming apparatus A in which the device C is mounted, in order to suppress a lowering in image quality such as uneven glossiness, there is a need that the variation in detection temperature of the thermistor 25 is made 2° C. or less.
A result of verification as to the device C of this embodiment by the present inventors is shown in
As shown in
Accordingly, in the case where W≥S (=0.6 mm) is satisfied, the difference between the maximum and the minimum of the detection temperature reaches 2.5° C. at the maximum, so that a lowering in image quality cannot be sufficiently suppressed. In the case where in addition to W≥S, W≥L (=1.8 mm) is also satisfied, it is understood that the difference between the maximum and the minimum of the detection temperature falls within 0.6° C. or less. In this embodiment, W=2.0 mm and therefore the difference between the maximum and the minimum is 0.4° C.
In the device C of this embodiment, when L, S and W satisfies relationships of W≥L and W≥S, a variation of the detection temperature of the thermistor 25 in the case where a contact position of the thermistor 25 and the heater 22 varies can be suppressed to 2° C. or less. For that reason, temperature control of the heater 22 can be carried out with accuracy, so that the image quality can be further improved.
Here, L, S and W are not limited to the above-described numerical values, but when the relationships of W≥L and W≥S are satisfied, a similar effect can be obtained. For example, in the case of L=3.0 mm and S=1.0 mm, when W is set at W=3.0 mm or more, a similar effect can be obtained.
A shape of the thermistor 25 is not limited to a rectangular shape. Parts (a) to (d) of
In this embodiment, the thermistor 25 was disposed on the film sliding surface side of the heater 22, and the electroconductive members 22b1 and 22b2 and the heat generating resistors 22d were disposed on the film non-sliding surface side of the heater 22, but the thermistor 25 may also be disposed on the film non-sliding surface side. In this case, the thermistor 25 is formed, as an upper layer, on the protective layer 22e by printing. Similarly, the electroconductive members 22b1 and 22b2 and the heat generating resistors 22d may also be disposed on the film sliding surface side. In this case, the electroconductive members 22b1 and 22b2 and the heat generating resistors are formed, as an upper layer, on the protective layer 22f by printing.
The heat generating resistors 22d may also be not formed in an inclined manner with respect to the direction Y and the direction X.
Another embodiment of the fixing device C will be described.
In the device C of this embodiment, the dimension L of the heat generating resistor 22d of the heater 22 and the distance S of adjacent heat generating resistors 22d are different from those of Embodiment 1. In this embodiment, L=0.6 mm and S=1.8 mm are set, so that a relationship of L<S is satisfied. The dimension W of the thermistor is 2.0 mm. This satisfies relationships of W≥L and W≥S.
Parts (a), (b) and (c) of
Here, also in the device C of this embodiment, a contact position between the thermistor 25 and the heater 22 has a tolerance of ±0.2 mm with respect to the direction Y.
In part (b) of
In part (c) of
As shown in part (c) of
A result of verification as to the device C of this embodiment by the present inventors is shown in
As shown in
Accordingly, in the case where W≥L (=0.6 mm) is satisfied, the difference between the maximum and the minimum of the detection temperature reaches 4.7° C., so that a lowering in image quality cannot be sufficiently suppressed. In the case where W≥L and W≥S (=1.8 mm) also satisfied, it is understood that the difference between the maximum and the minimum of the detection temperature falls within 0.7° C. or less. In this embodiment, W=2.0 mm and therefore the difference between the maximum and the minimum is 0.3° C.
In the device C of this embodiment, when L, S and W satisfies relationships of W≥L and W≥S, a variation of the detection temperature of the thermistor 25 in the case where a contact position of the thermistor 25 and the heater 22 varies can be suppressed to 2° C. or less. For that reason, temperature control of the heater 22 can be carried out with accuracy, so that the image quality can be further improved.
Another embodiment of the fixing device C will be described.
In the device C of this embodiment, the dimension L of the heat generating resistor 22d of the heater 22 and the distance S of adjacent heat generating resistors 22d are different from those of Embodiment 1. In this embodiment, L=1.2 mm and S=1.2 mm are set, so that a relationship of L=S is satisfied. The dimension W of the thermistor is 1.4 mm. This satisfies relationships of W≥L and W≥S.
Parts (a), (b) and (c) of
Here, also in the device C of this embodiment, a contact position between the thermistor 25 and the heater 22 has a tolerance of ±0.2 mm with respect to the direction Y.
In part (b) of
In part (c) of
As shown in part (c) of
A result of verification as to the device C of this embodiment by the present inventors is shown in
As shown in
Accordingly, when W is not less than L or S (=1.2 mm), it is understood that the difference between the maximum and the minimum of the detection temperature falls within 2° C. or less. In this embodiment, W=1.4 mm and therefore the difference between the maximum and the minimum is 1.5° C.
In the device C of this embodiment, when L, S and W satisfies relationships of W≥L and W≥S, a variation of the detection temperature of the thermistor 25 in the case where a contact position of the thermistor 25 and the heater 22 varies can be suppressed to 2° C. or less. For that reason, temperature control of the heater 22 can be carried out with accuracy, so that the image quality can be further improved.
Another embodiment of the fixing device C will be described.
In the device C of this embodiment, the dimension W is different from that of Embodiment 1. In this embodiment, the dimension W is 2.4 mm. This satisfies relationship of (integral multiple of L+S)−0.4 mm≤W≤(integral multiple of L+S)+0.4 mm (almost integral multiple of L+S).
Parts (a), (b) and (c) of
Here, also in the device C of this embodiment, a contact position between the thermistor 25 and the heater 22 has a tolerance of ±0.2 mm with respect to the direction Y.
In part (b) of
In part (c) of
As shown in part (c) of
A result of verification as to the device C of this embodiment by the present inventors is shown in
As in this embodiment, when the dimension W of the thermistor 25 is not less than (integral multiple of L+S)−0.4 mm and is not more than (integral multiple of L+S)+0.4 mm (almost integral multiple of L+S), an area of the heat generating resistors 22d and an area, where the heat generating resistors 22d do not exist, which are included in the thermistor 25 in the case where the positional deviation of the thermistor 25 is caused can be maintained at substantially certain values. For that reason, heat quantity received from the heater 22 by the thermistor 25 can be maintained at a substantially certain value. Therefore, a change in resistance value of the thermistor can be further suppressed compared with Embodiment 1, so that an error of the detection temperature can be further reduced.
As in sections of 2.0 mm-2.8 mm, 4.4 mm-5.2 mm, and 6.8 mm-7.6 mm in
In the device C of this embodiment, when W is a value which is almost integral multiple of L+S, a variation of the detection temperature of the thermistor 25 in the case where a contact position of the thermistor 25 and the heater 22 varies can be further suppressed compared with Embodiment 1. For that reason, temperature control of the heater 22 can be carried out with accuracy, so that the image quality can be further improved compared with Embodiment 1.
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 such modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Application No. 2018-113485 filed on Jun. 14, 2018, which is hereby incorporated by reference herein in its entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2018-113485 | Jun 2018 | JP | national |
