The present application claims priority from Japanese Patent Application No. 2021-004688, which was filed on Jan. 15, 2021, the disclosure of which is herein incorporated by reference in its entirety.
The following disclosure relates to a heating unit used for a fixing device of an electrophotographic type image forming apparatus or the like.
In the past, there has been known a fixing device in which a rotating belt is interposed between a ceramic heater and a pressure roller. In the fixing device, the ceramic heater includes a substrate and a resistance heating element, in which a sheet-shaped heat conductive member is disposed so as to be in contact with a back surface located on an opposite side of a nip surface which is in contact with the belt. A through hole is formed in the heat conductive member, and a temperature detecting member is in contact with the back surface of the ceramic heater through the through hole.
Incidentally, in a case where the heater is configured such that the resistance heating element is provided on the substrate, a temperature difference occurs between a portion of the heater near to the resistance heating element and a portion of the heater apart from the resistance heating element. Accordingly, when the temperature detecting member is directly brought into contact with the back surface of the heater as in the related-art technique, it may be difficult to detect an accurate temperature due to unevenness in temperature caused by disposition of the resistance heating element.
In view of the above, an object of the present disclosure is to detect the accurate temperature by the temperature detecting member.
In one aspect of the disclosure, a heating unit includes a heater including a substrate and a resistance heating element provided on the substrate, a temperature sensor configured to detect a temperature of the heater, an endless belt configured to rotate around the heater, a holder supporting the heater, a first heat conductive member located between the heater and the holder, the first heat conductive member including a first heater-side surface facing the heater, a first opposite surface located on an opposite side of the first heater-side surface, and an opening, the first heat conductive member having a heat conductivity higher than that of the substrate, and a second heat conductive member disposed at a position at least corresponding to the opening when viewed in an orthogonal direction orthogonal to the first opposite surface, the second heat conductive member including a second heater-side surface facing the heater and a second opposite surface located on an opposite side of the second heater-side surface. The temperature sensor is in contact with the second opposite surface of the second heat conductive member.
The objects, features, advantages, and technical and industrial significance of the present disclosure will be better understood by reading the following detailed description of the embodiments, when considered in connection with the accompanying drawings, in which:
A heating unit 1 according to an embodiment is used for a fixing device of an image forming apparatus, or a device that transfers foil by heat, and the like. As illustrated in
The belt 3 is an endless belt, which is made of metal or resin. The belt 3 rotates around the heater 10 while being guided by the holder 20. The belt 3 has an outer circumferential surface and an inner circumferential surface. The outer circumferential surface comes into contact with a sheet to be heated. The inner circumferential surface is in contact with the heater 10.
The heater 10 includes a substrate 11, resistance heating elements 12 provided on the substrate 11, and a cover 13. The substrate 11 is formed of a long rectangular plate made of ceramic. The heater 10 is a so-called ceramic heater. The resistance heating elements 12 are formed on one surface of the substrate 11 by printing. As illustrated in
The cover 13 covers the resistance heating elements 12. The cover 13 is made of, for example, glass. The heater 10 includes a nip surface 15 which is in contact with the inner circumferential surface of the belt 3 and a back surface 16 located on an opposite side of the nip surface 15.
The holder 20 is a member supporting the heater 10. The holder 20 includes a support portion 21 and guide portions 22. The support portion 21 has a plate shape corresponding to the shape of the heater 10. The support portion 21 includes a support surface 21A which is a surface facing the side on which the heater 10 is disposed and an inside surface 21B located on an opposite side of the support surface 21A. As illustrated in
The thermistor 50 includes two thermistors which are a first thermistor 50A and a second thermistor 50B. The first thermistor 50A and the second thermistor 50B are the same components. The first thermistor 50A detects a temperature at the center in the longitudinal direction of the heater 10. The first thermistor 50A is used for controlling the temperature of the heater 10 such that the temperature of the heater 10 becomes a target temperature based on the temperature detected by the first thermistor 50A. The second thermistor 50B detects the temperature of the heater 10 at a position nearer to an end of the heater 10 in the longitudinal direction than the position detected by the first thermistor 50A. The second thermistor 50B is used for detecting that the temperature is increased at the position near to the end of the heater 10. The holder opening 25A is disposed at a position corresponding to the first thermistor 50A. The first thermistor 50A and the second thermistor 50B may not be the same component. In this case, it is preferable that the first thermistor 50A is a member with higher accuracy in temperature detection than the second thermistor 50B in a temperature range during printing operation.
The energization interrupting member 60 is a member configured to interrupt energization to the resistance heating elements 12 when the heater 10 is abnormally increased in temperature. The holder opening 26 is disposed at the position corresponding to the energization interrupting member 60.
Returning to
The first heat conductive member 30 is a member configured to uniformize the temperature of the heater 10 in the longitudinal direction by conducting heat in the longitudinal direction of the heater 10. The first heat conductive member 30 is a sheet-like member, and is located between the heater 10 and the support portion 21 of the holder 20. When the sheet as a heating target is interposed between the heating unit 1 and another pressure member, the first heat conductive member 30 is interposed between the heater 10 and the support portion 21. The first heat conductive member 30 includes a first heater-side surface 31 which is in contact with the back surface 16 of the heater 10 and a first opposite surface 32 located on an opposite side of the first heater-side surface 31. The first opposite surface 32 is in contact with the support surface 21A of the support portion 21.
As illustrated in
The second opening 36 is disposed at one end portion of the first heat conductive member 30 in the longitudinal direction, and has a long rectangular shape in the longitudinal direction. The second opening 36 is disposed at a position corresponding to the holder opening 26, namely, the position corresponding to the energization interrupting member 60.
The first opening 35B is disposed at the other end portion of the first heat conductive member 30 in the longitudinal direction, and has a long rectangular shape in the longitudinal direction. The first opening 35B is disposed at a position corresponding to the holder opening 25B, namely, the position corresponding to the second thermistor 50B.
As illustrated in
The second heat conductive members 45, 46 are members configured to uniformize the temperature at portions where the second heat conductive members 45, 46 are in contact with the heater 10 by conducting heat in the planar direction and configured to conduct heat from the heater 10 to the temperature sensor (the thermistor 50 or the energization interrupting member 60) quickly.
The second heat conductive member 45 is a sheet-like member, and includes a second heater-side surface 45F facing the heater 10 side and a second opposite surface 45R located on an opposite side of the second heater-side surface 45F.
As illustrated in
As illustrated in
In the embodiment, sizes of the second heat conductive members 45A, 45B, and 46 are smaller than a size of the first heat conductive member 30. Then, the second heat conductive member 45A is located inside the first opening 35A. The second heat conductive member 45B is located inside the first opening 35B. The second heat conductive member 46 is located inside the second opening 36.
The second heat conductive members 45, 46 are members in which a heat conductivity in the planar direction is higher than the heat conductivity in the planar direction of the substrate 11. A material of the second heat conductive members 45, 46 is not particularly limited. For example, metals such as aluminum, aluminum alloys, and copper having high heat conductivities can be adopted. A thickness of each of the second heat conductive members 45, 46 is not particularly limited either. For example, a film-like member thinner than 0.1 mm and a plate-like member thicker than 1 mm may be adopted as the second heat conductive members 45, 46. It is preferable that the thickness of each of the second heat conductive members 45, 46 is 0.03 mm to 3 mm.
Sizes of the second heat conductive members 45, 46 in the short-side direction orthogonal to the longitudinal direction are larger than a size of the resistance heating element 12 in the short-side direction. Then, the second heat conductive members 45, 46 are located between the two resistance heating elements 12 in the short-side direction.
The second heat conductive members 45, 46 have better heat conductivities at least in the thickness direction than the first heat conductive member 30. Therefore, a heat conductivity from the heater 10 to the second opposite surfaces 45R, 46R is better than a heat conductivity from the heater 10 to the first opposite surface 32. In this case, the good heat conductivity does not mean that a heat conductivity of the material of the second heat conductive members 45, 46 is merely high, but means that heat is conducted quickly including the thickness of the second heat conductive members 45, 46. For example, in a case where the first heat conductive member 30 and the second heat conductive members 45, 46 have the same thickness as illustrated in
The second heat conductive member 46 has protruding portions 46B, each of which is an example of a second protrusion, protruding toward the energization interrupting member 60 in the thickness direction as illustrated in
As illustrated in
As illustrated in
As illustrated in
As illustrated in
It is preferable that the first openings 35A, 35B become small as long as the second heat conductive members 45A, 45B can be disposed. For example, a size of each of the first openings 35A, 35B in the longitudinal direction is preferably 1.5 times or less of a size of each of the second heat conductive members 45A, 45B in the longitudinal direction. A size of each of the first openings 35A, 35B in the short-side direction is preferably 1.5 times or less of a size of each of the second heat conductive members 45A, 45B in the short-side direction. A size of each of the second heat conductive members 45A, 45B in the planar direction is equivalent to the urging member 52 as an example. It is preferable that a width of each of the second heat conductive members 45A, 45B is larger than a width of one resistance heating element 12 in the short-side direction. It is preferable that the width of each of the second heat conductive members 45A, 45B is larger than a distance of the two adjacent resistance heating elements 12 in the short-side direction.
As illustrated in
It is preferable that the second opening 36 becomes small as long as the second heat conductive member 46 can be disposed. For example, a size of the second opening 36 in the longitudinal direction is preferably 1.5 times or less of a size of the second heat conductive member 46 in the longitudinal direction. A size of the second opening 36 in the short-side direction is preferably 1.5 times or less of a size of the second heat conductive member 46 in the short-side direction. As an example, a size of the second heat conductive member 46 in the planar direction is equivalent to a size of the detector 62. It is preferable that a width of the second heat conductive member 46 is larger than the width of one resistance heating element 12 in the short-side direction. It is preferable that the width of the second heat conductive member 46 is larger than the distance of the two adjacent resistance heating elements 12 in the short-side direction.
As illustrated in
Then, one ends 12A and the other ends 12B of the resistance heating elements 12 are located on outer sides of the maximum width W1 and on an inner side of one end portion 38A and the other end portion 38B of the first heat conductive member 30 in the longitudinal direction. That is, a length of the first heat conductive member 30 is longer than a length of the resistance heating element 12 in the longitudinal direction.
The one end portion 38A and the other end portion 38B of the first heat conductive member 30 are located on outer sides of the one ends 12A and the other ends 12B of the resistance heating element 12 and on an inner side of one end 11A and the other end 11B of the substrate 11 in the longitudinal direction. That is, a length of the substrate 11 is longer than the length of the first heat conductive member 30 in the longitudinal direction.
Operations and effects of the above heating unit 1 will be explained.
The thermistor 50 is in contact with the second opposite surface 45R of the second heat conductive member 45, and the energization interrupting member 60 is in contact with the second opposite surface 46R of the second heat conductive member 46. The second heat conductive members 45, 46 have better heat conductivity in the thickness direction than the first heat conductive member 30; therefore, the thermistor 50 and the energization interrupting member 60 have good response with respect to the temperature of the heater 10.
On the other hand, if the thermistor 50 and the energization interrupting member 60 are in contact with the back surface 16 of the heater 10 directly, they may be affected by temperature unevenness due to disposition of the resistance heating elements 12. For example, in a case where the thermistor 50 and the energization interrupting member 60 are in contact with portions each corresponding to a portion located between the adjacent two resistance heating elements 12 in the short-side direction on the back surface 16, it may be difficult to detect an accurate temperature. However, the thermistor 50 and the energization interrupting member 60 are in contact with the second opposite surfaces 45R, 46R of the second heat conductive members 45, 46 which are different members from the first heat conductive member 30 without directly being in contact with the back surface 16 of the heater 10 in the embodiment; therefore, temperature unevenness due to disposition of the resistance heating elements 12 can be uniformed by the second heat conductive members 45, 46. Accordingly, it is possible to detect the accurate temperature by the thermistor 50 and the energization interrupting member 60.
The end ranges AE1, AE2 are portions in which the temperatures of the end ranges AE1, AE2 are easily increased since heat is not deprived by the sheet with the minimum width W2 when the sheet with the minimum width W2 is heated. When the temperatures at the end ranges AE1, AE2 are increased, heat of the heater 10 is transmitted through the first heat conductive member 30 and the second heat conductive members 45B, 46 and flows from the end ranges AE1, AE2 to the range inside the minimum width W2. Here, if the second heat conductive members 45B, 46 do not exist, heat does not flow in the longitudinal direction from the end ranges AE1, AE2 to the range inside the minimum width W2, however, since the second heat conductive members 45B, 46 are provided in the embodiment, heat conduction performance at the end ranges AE1, AE2 is not largely affected. Accordingly, it is possible to suppress temperature increase at end portions in the longitudinal direction of the heater 10.
Since the heat conductivity from the heater 10 to the second opposite surface 46R is better than the heat conductivity from the heater 10 to the first opposite surface 32, it is possible to detect the accurate temperature by the thermistor 50 and the energization interrupting member 60 while securing response of the thermistor 50 and the energization interrupting member 60 with respect to the temperature of the heater 10.
Since the length of the first heat conductive member 30 is longer than the length of the resistance heating element 12, it is possible to uniform the temperature of the heater 10 in the entire range in which the resistance heating elements 12 are disposed in the longitudinal direction of the heater 10.
Since the second thermistor 50B is disposed so as to detect the temperature at a position in the end range AE1, it is possible to detect temperature increase in the end range AE1 by the second thermistor 50B.
Since the energization interrupting member 60 is disposed so as to detect the temperature at the position in the end range AE2, it is possible to detect temperature increase in the range AE2 by the energization interrupting member 60.
Since the second heat conductive member 45 is engaged with the protruding portions 53B of the thermistor 50, it is possible to be properly positioned the second heat conductive member 45 with respect to the thermistor 50.
Since the protruding portions 46B of the second heat conductive member 46 are engaged with the energization interrupting member 60, it is possible to be properly positioned the second heat conductive member 46 with respect to the energization interrupting member 60. It is preferable that a thickness of the energization interrupting member 60 is 0.03 mm to 3 mm.
The embodiment of the present disclosure has been explained above. The present disclosure is not limited to the above embodiment and can be achieved by being modified suitably.
For example, a second heat conductive member 40 may be larger than the openings (the first openings 35A, 35B) of the first heat conductive member 30 as in a heating unit 1B illustrated in
Also in this modification, the graphite sheet which is the anisotropic heat conductive member can be adopted as the second heat conductive member 40 as an example.
A sheet-like third heat conductive member 70 may be further provided between the heater 10 and the first heat conductive member 30 and between the heater 10 and the second heat conductive member 45 as in a heating unit 1C illustrated in
The third heat conductive member 70 is, for example, an anisotropic heat conductive member in which a heat conductivity in a direction parallel to the third heater-side surface 70F is higher than a heat conductivity in a direction orthogonal to the third heater-side surface 70F, and the third heat conductive member is the graphite sheet as an example.
A method for positioning the second heat conductive member may be different from one in the above embodiment.
For example, instead of the protruding portions of the thermistor 50, a second heat conductive member 245 may have protruding portions 245B, each of which is an example of a second protrusion, at both ends in the longitudinal direction of the second heat conductive member 245, and the protruding portions 245B may be engaged with both end portions of the film 53 in the thermistor 50 as illustrated in
Instead of the protruding of the second heat conductive member, the energization interrupting member 60 may have protruding portions 61A at both ends in the longitudinal direction of the energization interrupting member 60, and the protruding portions 61A may be engaged with both end portions of a second heat conductive member 246 as illustrated in
Not only the second heat conductive member 245 has the protruding portions 245B protruding toward the thermistor 50 as in the modification illustrated in
Moreover, the energization interrupting member 60 may be disposed so as to detect the temperature at a position in the range in which the sheet with the minimum width W2 usable in the heating unit 1 can pass as in a modification illustrated in
The numbers of the temperature sensors and the energization interrupting members are not limited. Only one temperature sensor may be provided and three or more temperature sensors may be provided. Two or more energization interrupting members may be provided and it is possible that no energization interrupting member is provided. Only the first thermistor 50A may be in contact with the second opposite surface 45R of the second heat conductive member 45. For example, the second thermistor 50B and the energization interrupting member 60 may be in contact with the first opposite surface 32 of the first heat conductive member 30 or the back surface 16 of the heater 10.
In the above embodiment, each of the first heat conductive member 30, the second heat conductive members 45, 46, and the third heat conductive member 70 is formed of one sheet-like member; however, each of them may be formed of a combination of a plurality of sheet-like members. In the latter case, the material, heat conductivity, and the shape of the plurality of sheet-like members may be different from one another and may be the same as one another.
In the above embodiment, the substrate 11 of the heater 10 is formed of the long rectangular plate made of ceramic; however, the substrate 11 may be formed of a long rectangular plate made of metal such as stainless steel, which has a heat conductivity lower than that of the heat conductive member 30.
In the above embodiment, the opening is a through hole formed at a position apart from an outline of the heat conductive member; however, the opening may have a cutout shape.
Respective components explained in the above embodiment and modification examples may be arbitrarily combined to achieve the disclosure.
Number | Date | Country | Kind |
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2021-004688 | Jan 2021 | JP | national |