Heating unit

A heating unit includes a heater, an endless belt, a holder, a heat conductive sheet, and a connector including a connecting terminal connected to a supply terminal. The connector is configured to hold a first end of the heater in the longitudinal direction and a first end of the holder in the longitudinal direction. The holder includes a first surface supporting the heat conductive member, and a second surface supporting the first end of the heater. The second surface is located at a position nearer to the heater than the first surface in a direction orthogonal to the substrate. A height of a step formed between the first surface and the second surface is greater than a thickness of the heat conductive member.

CROSS REFERENCE TO RELATED APPLICATION

The present application claims priority from Japanese Patent Application No. 2021-029496, which was filed on Feb. 26, 2021, the disclosure of which is herein incorporated by reference in its entirety.

BACKGROUND

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 heater and a pressure roller. The fixing device includes a supporter supporting the heater, a heat conductive member disposed between the heater and the supporter and having a sheet shape, a connector configured to supply electricity to the heater.

A first end of the heater in a longitudinal direction protrudes more than the heat conductive member. A supply terminal is provided at the first end of the heater in the longitudinal direction to which a terminal of the connector is connected. The supporter includes a first surface supporting the heat conductive member and a second surface supporting the first end of the heater in the longitudinal direction.

SUMMARY

Incidentally, in the above described fixing device, in a case where a thickness of the heat conductive member is greater than a dimension of a step between the first surface and the second surface, there is a possibility of connection fault caused by large variations of contact pressure between the terminal of the connector and the supply terminal, since a space is formed between the first end of the heater in the longitudinal direction and the second surface.

An aspect of the disclosure relates to a heating unit capable of suppressing the variations of the contact pressure between the terminal of the connector and the supply terminal from being increased.

In one aspect of the disclosure, a heating unit includes a heater including a substrate, a resistance heating element provided on the substrate, and a supply terminal disposed at a first end of the substrate in a longitudinal direction of the heater, the supply terminal being electrically conducted with the resistance heating element, an endless belt configured to rotate around the heater, a holder supporting the heater, a heat conductive sheet located between the heater and the holder, the heat conductive sheet having a heat conductivity greater than that of the substrate, and a connector including a connecting terminal connected to the supply terminal, the connector being configured to hold a first end of the heater in the longitudinal direction and a first end of the holder in the longitudinal direction. The holder includes a first surface located on a heater side and supporting the heat conductive sheet, and a second surface located on the heater side and supporting the first end of the heater, the second surface being located at a position different from a position of the first surface and nearer to the heater than the first surface in a direction orthogonal to the substrate. A height of a step formed between the first surface and the second surface is greater than a thickness of the heat conductive sheet.

EMBODIMENTS

A heating unit1according 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 inFIG.1, the heating unit1includes a belt3, a heater10, a holder20, a heat conductive member30, and a pressure roller40as an example of a pressure member.

The belt3is interposed between the pressure roller40and the heater10. The pressure roller40includes a shaft41having a column shape and a roller42having a cylinder shape. The shaft41is made of, for example, metal and the like. The roller42is made of, for example, rubber and the like. The roller42covers a part of the shaft41. The roller42is in contact with the belt3. One of the holder20and the pressure roller40is urged toward the other of the holder20and the pressure roller40. In the following description, a direction in which one of the holder20and the pressure roller40is urged will be referred to as “urging direction”.

The belt3is an endless belt, which is made of metal or resin. The belt3rotates around the heater10while being guided by the holder20. The belt3has an outer circumferential surface and an inner circumferential surface. The outer circumferential surface comes into contact with the pressure roller40or a sheet to be heated. The inner circumferential surface is in contact with the heater10.

The heater10includes a substrate11, resistance heating elements12supported by the substrate11, and a cover13. The substrate11is formed of a long rectangular plate made of ceramic. The heater10is a so-called ceramic heater. The resistance heating elements12are formed on one surface of the substrate11by printing. As illustrated inFIG.2A, two resistance heating elements12are provided in the embodiment. The two resistance heating elements12are respectively disposed so as to extend in a longitudinal direction of the heater10(hereinafter the longitudinal direction of the heater10is referred to merely as “longitudinal direction”) and so as to be spaced apart from each other in parallel in a short-side direction orthogonal to the longitudinal direction. A conducting wire19A is connected to a first end12A of each of the resistance heating elements12, and a supply terminal18for supplying power is provided at an end portion of the conducting wire19A of each of the resistance heating elements12.

The supply terminal18is electrically conducted with each of the resistance heat elements12through the conducting wire19A. Each of the supply terminals18is located at a first end portion11E of the substrate11in the longitudinal direction.

Second ends12B of the resistance heating elements12are connected to each other by a conducting wire19B. The number of the resistance heating elements12is not particularly limited. The resistance heating elements may be configured such that a resistance heating element in which a heat generation amount at the center in the longitudinal direction is greater than a heat generation amount at end portions in the longitudinal direction and a resistance heating element in which the heat generation amount at end portions in the longitudinal direction is greater than the heat generation amount at the center in the longitudinal direction are provided, and such that a heat generation distribution in the longitudinal direction is regulated by individually controlling each of the resistance heating elements.

As illustrated inFIG.1, the cover13covers the resistance heating elements12. The cover13is made of, for example, glass. The heater10includes a nip surface15which is in contact with the inner circumferential surface of the belt3and a back surface16located on an opposite side to the nip surface15.

The holder20is a member supporting the heater10. The holder20includes a support portion21and guide portions22. The support portion21has a plate shape corresponding to a shape of the heater10. The guide portions22are provided at both ends of the support portion21in the short-side direction. Each of the guide portions22has a guide surface22G extending along the inner circumferential surface of the belt3. The guide portions22have a plurality of guide ribs22A arranged in the longitudinal direction.

The heat conductive member30is a member configured to uniformize the temperature of the heater10in the longitudinal direction by conducting heat in the longitudinal direction of the heater10. The heat conductive member30is a sheet-like member, and is located between the back surface16of the heater10and the support portion21of the holder20. When the sheet as a heating target is interposed between the belt3of the heating unit1and the pressure roller40, the heat conductive member30is interposed between the heater10and the support portion21. The heat conductive member30includes a heater-side surface31which is in contact with the back surface16of the heater10, and an opposite surface32located on an opposite side to the heater-side surface31. The opposite surface32is in contact with the support portion21.

The heat conductive member30is a member in which a heat conductivity in a direction parallel to the heater-side surface31(hereinafter referred to merely as “planar direction”) is higher than a heat conductivity of the substrate11in the planar direction. A material of the heat conductive member30is not particularly limited. For example, metals such as aluminum, aluminum alloys, and copper having high heat conductivities can be adopted.

As illustrated inFIG.2AandFIG.2B, the first ends12A and the second ends12B of the resistance heating elements12are located on outer sides of a range in which the sheet with a maximum width W1usable in the heating unit1passes and on an inner side of a first end38A and a second end38B of the heat conductive member30in the longitudinal direction. That is, a length of the heat conductive member30is longer than a length of the resistance heating element12in the longitudinal direction.

Moreover, the first end38A and the second end38B of the heat conductive member30are located on outer sides of the first ends12A and the second ends12B of the resistance heating element12and on an inner side of a first end11A and a second end11B of the substrate11in the longitudinal direction. That is, a length of the substrate11is longer than the length of the heat conductive member30in the longitudinal direction. The above described supply terminals18are disposed at positions spaced apart from the first end38A of the heat conductive member30in the longitudinal direction.

As illustrated inFIG.2C, the support portion21of the holder20includes a first surface21A, a second surface21B, and a third surface21C, each of which is a surface located on a side of the heater10. The support portion21further includes a first step face21D connecting the first surface21A and the second surface21B, and a second step face21E connecting the first surface21A and the third surface21C. Each of the first surface21A, the second surface21B and the third surface21C is orthogonal to the urging direction. Each of the first step face21D and the second step face21E is orthogonal to the longitudinal direction. The holder20further includes a first opposed portion23opposed to the second surface21B at a first end of the holder20in the longitudinal direction, and a second opposed portion24opposed to the third surface21C at a second end of the holder20in the longitudinal direction. The first surface21A supports the heat conductive member30so as to be in contact with the heat conductive member30. The second surface21B supports the first end portion11E of the substrate11so as to be in contact with the first end portion11E of the substrate11. The third surface21C supports a second end portion11F of the substrate11so as to be in contact with the second end portion11F of the substrate11. The first opposed portion23holds the substrate11in a state in which the first end portion11E of the substrate11is nipped between the second surface21B and the first opposed portion23. The second opposed portion24holds the substrate11in a state in which the second end portion11F is nipped between the third surface21C and the opposed portion24. It is noted that the resistance heat elements12, the cover13and the belt3are not illustrated inFIG.2CandFIG.3, as a matter of convenience.

In the longitudinal direction, a length of the first surface21A is longer than the length of the heat conductive member30. In the longitudinal direction, the length of the heat conductive member30is longer than a length of the roller42of the pressure roller40. The roller42is located in a range in which the heat conductive member30is positioned in the longitudinal direction. That is, the roller42is located between the first end38A and the second end38B of the heat conductive member30in the longitudinal direction.

The second surface21B and the third surface21C are located at positions different from a position of the first surface21A in the longitudinal direction. More specifically, the second surface21B is located at the position on a first side with respect to the first surface21A in the longitudinal direction. The third surface21C is located at the position on a second side with respect to the first surface21A in the longitudinal direction.

The second surface21B and the third surface21C are disposed at the positions nearer to the heater10than the first surface21A in a direction orthogonal to the first surface21A. The second surface21B and the third surface21C are a same position in the direction orthogonal to the first surface21A. That is, a distance between the second surface21B and the heater10is the same as a distance between the third surface21C and the heater10in the direction orthogonal to the first surface21A. As illustrated inFIG.3, a length of step L1between the first surface21A and the second surface21B is greater than a thickness L2of the heat conductive member30. It is preferable that the thickness L2of the heat conductive member30is 0.2 mm to 0.3 mm, and an example of the thickness L2of the heat conductive member30is 0.3 mm. It is preferable that the length of step L1between the first surface21A and the second surface21B is 0.4 mm to 0.5 mm, and an example of the length of step L1between the first surface21A and the second surface21B is 0.4 mm. It is preferable that the length of step L1is 0.1 mm to 0.2 mm greater than the thickness L2, and, for example, the length of step L1is 0.1 mm greater than the thickness L2. It is noted that the deformed substrate11is illustrated inFIG.2andFIG.3so as to exaggerate a difference between the length of step L1and the thickness L2for convenience, however, in fact, the substrate11rarely deforms, since the difference between the length of step L1and the thickness L2is very small so that a crack of the substrate11of the heater10does not occurs.

The heating unit1further includes a connector50configured to supply electricity to the heater10. As illustrated inFIG.4, the connector50includes a connector body51made of resin and the like, and two connecting terminals52made of conductive material such as metal.

The connecting terminals52are made of metal plates having elasticity. Each of the connecting terminals52is connected to the supply terminal18of the heater10(SeeFIG.3). The two connecting terminals52are arranged with a space therebetween in the longitudinal direction of the heater10.

The connector body51includes a base portion51A having a rectangular parallelepiped shape, a first extending portion51B extending in a direction directed from the base portion51A toward the heater10, and a second extending portion51C extending in the direction directed from the base portion51A toward the heater10. The first extending portion51B includes the connecting terminals52. The first extending portion51B and the second extending portion51C are arranged with a space therebetween in a direction orthogonal to the nip surface15(SeeFIG.1). The first extending portion51B (more specifically, the connecting terminals52) and the second extending portion51C hold a first end of the heater10in the longitudinal direction and the first end of the holder20in the longitudinal direction from an upper side and a lower side of the heater10and the holder20. In other words, the first end of the heater10in the longitudinal direction and the first end of the holder20in the longitudinal direction are interposed between the first extending portion51B and the second extending portion51C in the direction orthogonal to the nip surface15. The connector50is mounted to the first end of the heater10and the first end of the holder20in the longitudinal direction from a first side of the heater10in the short-side direction.

As described above, it is possible to achieve the following effects in the present embodiment.

Since the length of step L1between the first surface21A and the second surface21B is greater than the thickness L2of the heat conductive member30, it is possible that the first end of the heater10is in surface contact with the second surface21B. Accordingly, it is possible to suppress variations of a contact pressure between the connecting terminal52and the supply terminal18from being increased when the connector50is mounted to the heater10and the holder20.

Since the length of the heat conductive member30in the longitudinal direction is greater than the length of the resistance heat element12in the longitudinal direction, it is possible to uniformize the temperature of the heater10in an entire range in which the resistance heat element12is disposed.

Since the length of the first surface21A in the longitudinal direction is greater than the length of the heat conductive member30in the longitudinal direction, even if the heat conductive member30thermally expands in the longitudinal direction due to the heater10, it is possible to suppress the heat conductive member30from interfering the first step face21D or the second step face21E.

Since the heat conductive member30is made of aluminum or aluminum alloys so that the heat conductivity of the heat conductive member30increases, it is possible to more properly uniformize the temperature of the heater10in the longitudinal direction.

Since the length of the heat conductive member30in the longitudinal direction is greater than the length of the roller42of the pressure roller40in the longitudinal direction, it is possible to hold the heat conductive member30and the heater10between the pressure roller40and the holder20without a space in a state in which one of the pressure roller40and the holder20is urged toward the other of the pressure roller40and the holder20. Accordingly, it is possible to suppress the heat conductive member30from moving between the holder20and the heater10.

It is noted that the present disclosure is not limited to the above embodiment and various modification can be adopted as described below.

In the above described embodiment, the two supply terminals are disposed at the first end portion of the heater in the longitudinal direction, however, this disclosure is not limited to this configuration. For example, a plus terminal of the two supply terminals may be disposed at the first end portion of the heater in the longitudinal direction and a minus terminal of the two supply terminals may be disposed at a second end portion of the heater in the longitudinal direction. In this case, two connectors may be respectively disposed at the first end portion and the second end portion of the heater in the longitudinal direction.

In the above described embodiment, the step face is a face orthogonal to the longitudinal direction, however, this disclosure is not limited to this configuration. The step face may be an inclined face inclining with respect to the longitudinal direction.

In the above embodiment, the heat conductive member30is formed of one sheet-like member, however, the heat conductive member30may be formed of a combination of a plurality of sheet-like members. In this case, materials, heat conductivities, and shapes 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 substrate11of the heater10is formed of the long rectangular plate made of ceramic, however, the substrate11may be formed of a long rectangular plate, as long as a heat conductivity of which is less than that of the heat conductive member30, made of metal such as stainless steel.

Respective components explained in the above embodiments and modifications may be arbitrarily combined to achieve the disclosure.