JP7613225B2 - Heating unit - Google Patents

Description

The present invention relates to a heating unit used in a fixing device of an image forming apparatus.

Conventionally, a heating unit is known that includes a plate-shaped heater and a holder that supports the heater (see Patent Document 1). In this technology, the heater is positioned in the longitudinal direction by abutting one end of the heater against a rib formed at one longitudinal end of the holder. Also, taking into account thermal expansion of the heater in the longitudinal direction, a gap is provided between the other end of the heater and the other end of the holder.

JP 2018-54898 A

However, in conventional technology, one end of the heater is simply pressed against the rib of the holder, so when the heater repeatedly heats up and stops, causing it to thermally expand and contract in the longitudinal direction, there is a risk that the heater will shift to the other end of the holder. When this phenomenon of the heater shifting position occurs, there is a risk that the positions of the power supply terminal on the heater and the connector connected to the power supply terminal will shift, resulting in poor contact.

Therefore, the present invention aims to suppress misalignment of the heater caused by repeated thermal expansion and contraction of the heater, thereby suppressing misalignment of the power supply terminal.

In order to solve the above-mentioned problems, the heating unit of the present invention comprises a substrate, a resistive heating element supported on the substrate, a heater having a power supply terminal electrically connected to the resistive heating element and located at one end of the substrate in the longitudinal direction, an endless belt having an inner surface in contact with a nip surface of the heater and rotating around the heater, a holder supporting the heater, and a heat conductive member located between the holder and a back surface of the heater opposite the nip surface, the heat conductive member having a higher thermal conductivity than the substrate.
The holder has a first position restriction portion that faces one end of the substrate in the longitudinal direction.
The heat conducting member has a second position restricting portion that faces the other end of the substrate in the longitudinal direction.

With this configuration, the second position restriction portion of the heat conductive member can restrict the position of the board from shifting toward the other end in the longitudinal direction due to repeated thermal expansion and contraction, thereby preventing the position of the power supply terminal from shifting.

The heat conducting member may also have a base portion that contacts the back side of the heater, and the second position restriction portion may protrude from the other end of the base portion in the longitudinal direction.

This configuration allows the heat conduction member and the substrate to have a simpler configuration than, for example, a structure in which a hole is formed in the other end of the heat conduction member and a protrusion that fits into the hole is provided on the other end of the substrate.

The length by which the second position restriction portion protrudes from the other end of the base portion in the longitudinal direction may be less than the thickness of the substrate.

This configuration prevents the second position restriction part from interfering with the belt.

The holder also has a third position restricting portion for positioning the heat conductive member in the longitudinal direction, and the distance from the first position restricting portion to the third position restricting portion is Lp, the length of the substrate in the longitudinal direction is Lb, the linear expansion coefficient of the substrate is α1, and the linear expansion coefficient of the heat conductive member is α2,
Lp≦{1-(α1/α2)}×Lb
Lp may be set so as to satisfy the following formula.

With this configuration, the amount of expansion of the substrate can be made equal to or less than the amount of expansion of the thermally conductive member, so that the other end of the substrate can be prevented from being pressed against the second position restriction portion during thermal expansion, and damage to the substrate or thermally conductive member can be prevented.

The longitudinal length of the heat conducting member may be longer than the longitudinal length of the resistive heating element.

This configuration allows the heater temperature to be uniform throughout the entire area in the longitudinal direction where the resistive heating element is arranged.

The substrate may be made of ceramics made of aluminum oxide, and the heat conducting member may be a plate-shaped member made of aluminum.

With this configuration, the specific heat of the substrate and the specific heat of the thermally conductive member can be set to similar values, making design easier since only the linear expansion coefficient needs to be considered when positioning the thermally conductive member in the longitudinal direction relative to the substrate.

According to the present invention, it is possible to suppress the misalignment of the heater caused by repeated thermal expansion and contraction of the heater, and therefore to suppress the misalignment of the power supply terminal.

FIG. FIG. 1A is a diagram showing the surface on which the resistive heating element of the heater is arranged, FIG. 1B is a diagram showing the heater and the heat conductive member from the back side of the heater, and FIG. 1C is a cross-sectional view of the heating unit taken in the longitudinal direction. 4A is an enlarged view of one end portion in the longitudinal direction of the heating unit, and FIG. 4B is an enlarged view of the other end portion in the longitudinal direction of the heating unit. 1A to 1C are diagrams showing, in an exaggerated manner, the states of a substrate and a heat conductive member during thermal expansion and contraction.

The heating unit 1 according to the embodiment is used in a fixing device of an image forming apparatus, a device for transferring foil by heat, etc. As shown in FIG. 1, the heating unit 1 includes a belt 3, a heater 10, a holder 20, a heat conductive member 30, and a pressure roller 40.

The pressure roller 40 sandwiches the belt 3 between itself and the heater 10. The pressure roller 40 has a cylindrical shaft 41 and a cylindrical roller portion 42. The shaft 41 is made of, for example, metal. The roller portion 42 is made of, for example, rubber. The roller portion 42 covers a portion of the shaft 41. The roller portion 42 contacts the belt 3. One of the holder 20 and the pressure roller 40 is biased toward the other. In the following description, the direction in which one of the holder 20 and the pressure roller 40 is biased is also referred to as the biasing direction.

The belt 3 is endless and 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 peripheral surface 3A and an inner peripheral surface 3B. The outer peripheral surface 3A contacts the pressure roller 40 or the sheet to be heated. The inner peripheral surface 3B contacts the heater 10.

The heater 10 has a substrate 11, a resistance heating element 12 supported by the substrate 11, and a cover 13. The substrate 11 is a long and narrow rectangular plate of ceramic made of aluminum oxide. The heater 10 is a so-called ceramic heater. The resistance heating element 12 is formed by printing on one side of the substrate 11. As shown in FIG. 2(a), in this embodiment, two resistance heating elements 12 are provided. The two resistance heating elements 12 are each long in the longitudinal direction of the heater 10 (hereinafter, the longitudinal direction of the heater 10 is simply referred to as the "longitudinal direction") and are arranged parallel to each other and spaced apart in the lateral direction perpendicular to the longitudinal direction. A conductor 19A is connected to one end 12A of each resistance heating element 12, and a power supply terminal 18 is provided at each end of the conductor 19A to supply power to the resistance heating element 12.

The power supply terminal 18 is electrically connected to the resistance heating element 12 via a conductor 19A. The power supply terminal 18 is located at one end 11E of the substrate 11 in the longitudinal direction.

The other ends 12B of the resistive heating elements 12 are connected to each other by conductive wires 19B. The number of resistive heating elements 12 is not particularly limited. Alternatively, a resistive heating element having a larger heat generation amount at the longitudinal center than at the longitudinal ends and a resistive heating element having a larger heat generation amount at the longitudinal ends than at the longitudinal center may be provided, and the heat generation distribution in the longitudinal direction may be adjusted by individually controlling each resistive heating element.

As shown in FIG. 1, the cover 13 covers the resistance heating element 12. The cover 13 is made of, for example, glass. The heater 10 has a nip surface 15 that contacts the inner circumferential surface 3B of the belt 3, and a back surface 16 opposite the nip surface 15.

The holder 20 is a member that supports the heater 10. The holder 20 has a support portion 21 and a guide portion 22. The support portion 21 has a plate shape that corresponds to the shape of the heater 10. The guide portions 22 are provided at both ends of the support portion 21 in the short direction. Each guide portion 22 has a guide surface 22G that runs along the inner circumferential surface 3B of the belt 3. The guide portion 22 has multiple guide ribs 22A aligned in the longitudinal direction.

The heat conducting member 30 is a member that conducts heat in the longitudinal direction of the heater 10 to make the temperature of the heater 10 uniform in the longitudinal direction. The heat conducting member 30 is a plate-shaped member that is located between the back side 16 of the heater 10 and the support part 21 of the holder 20. When the heating unit 1 sandwiches a sheet, which is an object to be heated, between the belt 3 and the pressure roller 40, the heat conducting member 30 is sandwiched between the heater 10 and the support part 21. The heat conducting member 30 has a heater side 31A that contacts the back side 16 of the heater 10, and an opposite side 31B opposite the heater side 31A. The opposite side 31B contacts the support part 21.

The thermal conduction member 30 is a member whose thermal conductivity in a direction parallel to the heater side surface 31A (hereinafter simply referred to as the "planar direction") is greater than the thermal conductivity in the planar direction of the substrate 11. In this embodiment, the thermal conduction member 30 is made of aluminum.

2(a) and (b), one end 12A and the other end 12B of the resistance heating element 12 are located outside the maximum width W1 of the sheet that can be used in the heating unit 1 in the longitudinal direction, and inside one end 30A and the other end 30B of the heat conducting member 30. In other words, in the longitudinal direction, the length of the heat conducting member 30 is longer than the length of the resistance heating element 12.

In the longitudinal direction, the length of the substrate 11 is longer than the length of the heat conduction member 30. One end 30A of the heat conduction member 30 is located inside one end 11A of the substrate 11 in the longitudinal direction. The other end 30B of the heat conduction member 30 is located outside the other end 11B of the substrate 11 in the longitudinal direction.

As shown in Figures 2(c) and 3, the heat transfer member 30 has a plate-shaped base portion 31 that contacts the back surface 16 of the heater 10, and a second position regulating portion 32. For convenience, the resistive heating element 12, cover 13, and belt 3 are omitted from Figure 2(c). For convenience, the resistive heating element 12 and cover 13 are omitted from Figure 3.

The base portion 31 has the heater side surface 31A and the opposite surface 31B described above. The base portion 31 has the other end portion 31C including the other end portion 30B of the heat conductive member 30. The second position restricting portion 32 protrudes from the other end portion 31C of the base portion 31 in the biasing direction and faces the other end portion 11B of the substrate 11 in the longitudinal direction. The second position restricting portion 32 is disposed so as to be in approximate contact with the other end portion 11B of the substrate 11, and restricts the other end portion 11B of the substrate 11 from moving in the other longitudinal direction. Here, "approximate contact" includes contact, as well as a slight gap between the other end portion 11B and the second position restricting portion 32.

The length by which the second position restricting portion 32 protrudes from the other end 31C of the base portion 31 is smaller than the thickness of the substrate 11. In other words, the second position restricting portion 32 is farther from the pressure roller 40 in the biasing direction than the surface F1 of the substrate 11 on the pressure roller 40 side.

The support portion 21 of the holder 20 has a first surface 21A and a second surface 21B which are the surfaces on the heater 10 side, and a step surface 21C connecting the first surface 21A and the second surface 21B. The first surface 21A and the second surface 21B are perpendicular to the biasing direction. The step surface 21C is perpendicular to the longitudinal direction. The first surface 21A contacts the heat conductive member 30 to support the heat conductive member 30. The second surface 21B contacts one end 11E of the substrate 11 to support one end 11E of the substrate 11.

In the longitudinal direction, the length of the first surface 21A is longer than the length of the heat conducting member 30. In the longitudinal direction, the length of the heat conducting member 30 is longer than the length of the roller portion 42 of the pressure roller 40. The roller portion 42 is located within the range of the heat conducting member 30 in the longitudinal direction.

The second surface 21B is located at a different position in the longitudinal direction from the first surface 21A. More specifically, the second surface 21B is located on one side of the longitudinal direction relative to the first surface 21A.

The second surface 21B is located closer to the heater 10 than the first surface 21A. The size of the step surface 21C in the biasing direction is approximately the same as the thickness of the base portion 31 of the heat conduction member 30. It is desirable that the size of the step surface 21C in the biasing direction be equal to or greater than the thickness of the base portion 31.

The holder 20 further has a first position restricting portion 23 and a third position restricting portion 24. The first position restricting portion 23 protrudes in the biasing direction from one end of the second surface 21B in the longitudinal direction and faces one end 11A of the substrate 11 in the longitudinal direction. The substrate 11 is positioned so that one end 11A is in contact with the first position restricting portion 23.

The third position restricting portion 24 is a portion for positioning the heat conductive member 30 in the longitudinal direction. The third position restricting portion 24 protrudes from the first surface 21A and is inserted into a hole H1 formed in a predetermined position in the longitudinal direction of the base portion 31 of the heat conductive member 30. The size by which the third position restricting portion 24 protrudes from the first surface 21A is smaller than the thickness of the base portion 31. Note that a convex portion may be formed at the short end of the heat conductive member 30, and a concave portion into which this convex portion fits may be formed in the holder 20, and the concave portion may be used as the third position restricting portion. The relationship between the convex portion and the concave portion may also be reversed. A protrusion protruding from the opposite surface 31B of the base portion 31 toward the first surface 21A may be provided, and a concave portion into which this protrusion fits may be formed in the first surface 21A, and the concave portion may be used as the third position restricting portion.

The distance Lp from the first position restriction portion 23 to the third position restriction portion 24 is set so as to satisfy the following formula.
Lp≦{1-(α1/α2)}×Lb
Lb: length of substrate 11 in the longitudinal direction α1: linear expansion coefficient of substrate 11 α2: linear expansion coefficient of heat conductive member 30 In this embodiment, the linear expansion coefficient of aluminum oxide constituting substrate 11 is approximately 7.2×10 ⁻⁶ /K. The linear expansion coefficient of aluminum constituting heat conductive member 30 is approximately 23.9×10 ⁻⁶ /K.

By setting the distance Lp in this manner, the amount of longitudinal expansion ΔLb of the substrate 11 is equal to or less than the amount of expansion Δ(Lb-Lp) of the portion (Lb-Lp) of the heat conductive member 30 from the third position restriction portion 24 to the other end 30B.

The heating unit 1 further includes a connector 50 for supplying electricity to the heater 10. The connector 50 includes a connector body 51 made of resin or the like, and two connection terminals 52 made of a conductive material such as metal.

The connection terminals 52 are made of elastic metal plates. The two connection terminals 52 are arranged at a distance from each other in the longitudinal direction of the heater 10. The connection terminals 52 are connected to the power supply terminal 18 of the heater 10.

The connector body 51 is roughly U-shaped when viewed from the longitudinal direction. The connector body 51 sandwiches one longitudinal end of the heater 10 and one longitudinal end of the holder 20 in the biasing direction. The connector 50 is attached to the heater 10 and one end of the holder 20 from one side of the heater 10 in the short direction.

Next, the assembly of the heater 10, holder 20, and heat conduction member 30 of the heating unit 1 of this embodiment will be described. First, the heat conduction member 30 is placed on the first surface 21A of the holder 20. At this time, the third positioning portion 24 is inserted into the hole H1 of the base portion 31 to position the heat conduction member 30 in the longitudinal direction. One end 30A of the heat conduction member 30 has a gap with respect to the step surface 21C of the support portion 21 that can allow thermal expansion of the heat conduction member 30.

Next, the heater 10 is placed on the second surface 21B of the holder 20. At this time, the heater 10 is placed on the second surface 21B with one end 11A of the substrate 11 abutting against the first position restriction portion 23, and the other end 11B of the substrate 11 is placed on one side in the longitudinal direction of the second position restriction portion 32. This assembles the heater 10 and the heat conductive member 30 to the holder 20.

Next, the state of the substrate 11 and the thermally conductive member 30 during thermal expansion or contraction will be described.
4(a) , when the temperature of the heating unit 1 rises and the substrate 11 and the heat conductive member 30 thermally expand in the longitudinal direction, as shown in FIG 4(b), the other end 11B of the substrate 11 moves to the other side in the longitudinal direction together with the second position restricting portion 32 of the heat conductive member 30. At this time, the distance Lp from the first position restricting portion 23 to the third position restricting portion 24 is set so that Lp≦{1-(α1/α2)}×Lb, and thus the other end 11B of the substrate 11 moves together with the second position restricting portion 32 without being pressed against it.

4(b) from the state of FIG. 4(b) when the temperature of the heating unit 1 drops and the substrate 11 and the heat conductive member 30 shrink in the longitudinal direction, as shown in FIG. 4(c), both ends of the substrate 11 in the longitudinal direction may shrink to approach the center in the longitudinal direction. In this case, one end 11A of the substrate 11 in the longitudinal direction may move in a direction away from the first position restricting portion 23. On the other hand, since the heat conductive member 30 is positioned in the longitudinal direction by the third position restricting portion 24, it shrinks with the position of the hole H1 as the base point. That is, both ends of the heat conductive member 30 in the longitudinal direction shrink to approach the position of the hole H1. Therefore, the second position restricting portion 32 moves due to the shrinkage of the heat conductive member 30, and the substrate 11 is pressed toward the first position restricting portion 23 by the moving second position restricting portion 32, so that one end 11A of the substrate 11 can be prevented from moving away from the first position restricting portion 23 as shown in FIG. 4(a). Therefore, the second position regulation portion 32 of the heat conductive member 30 can regulate the position of the substrate 11 from shifting toward the other end in the longitudinal direction due to repeated thermal expansion and contraction.

As described above, the following effects can be obtained in this embodiment.
The second position regulating portion 32 of the heat conductive member 30 can regulate the position of the substrate 11 to the other end in the longitudinal direction due to repeated thermal expansion and contraction, thereby preventing the position of the power supply terminal 18 from shifting.

Since the second position restriction portion 32 protrudes from the other longitudinal end portion 31C of the base portion 31, the heat conduction member 30 and the substrate 11 can be configured more simply than, for example, a structure in which a hole is formed in the other end portion of the heat conduction member and a protrusion that fits into the hole is provided on the other end portion of the substrate.

As shown in FIG. 3(b), the length by which the second position regulating portion 32 protrudes from the other end 31C of the base portion 31 is smaller than the thickness of the substrate 11, so that the second position regulating portion 32 can be prevented from interfering with the belt 3.

By setting the distance Lp from the first position restricting portion 23 to the third position restricting portion 24 so as to satisfy the formula Lp≦{1-(α1/α2)}×Lb, the longitudinal expansion amount ΔLb of the substrate 11 can be made equal to or less than the expansion amount Δ(Lb-Lp) of the portion (Lb-Lp) on the other end side of the heat conductive member 30. This makes it possible to prevent the other end 11B of the substrate 11 from being pressed against the second position restricting portion 32 during thermal expansion, thereby preventing damage to the substrate 11 or the heat conductive member 30.

The longitudinal length of the heat conducting member 30 is longer than the longitudinal length of the resistive heating element 12, so the temperature of the heater 10 can be made uniform throughout the entire area in which the resistive heating element 12 is arranged in the longitudinal direction.

By constructing the substrate 11 from a ceramic made of aluminum oxide and the heat conducting member 30 from a plate-shaped member made of aluminum, the specific heat of the substrate 11 and the specific heat of the heat conducting member 30 can be made close to each other, so that only the linear expansion coefficients α1 and α2 need to be considered when determining the longitudinal positioning of the heat conducting member 30 relative to the substrate 11, making the design easier.

The present invention is not limited to the above embodiment, but can be used in various forms, as exemplified below.

In the above embodiment, the thermally conductive member 30 is made of one sheet-like member, but it may be made of a combination of multiple sheet-like members. In this case, the multiple sheet-like members may be different from each other in terms of material, thermal conductivity, shape, etc., or may be the same as each other.

In the above embodiment, the substrate 11 of the heater 10 is made of a long and narrow rectangular ceramic plate, but it may be made of a long and narrow rectangular metal plate such as stainless steel as long as it has a lower thermal conductivity than the heat conducting member 30. The heat conducting member may be made of an aluminum alloy, copper, etc.

The elements described in the above embodiments and variations may be implemented in any combination.

REFERENCE SIGNS LIST 1 heating unit 3 belt 3B inner peripheral surface 10 heater 11 substrate 11A one end 11B other end 11E one end 12 resistance heating element 15 nip surface 16 back side surface 18 power supply terminal 20 holder 23 first position restriction portion 30 heat conductive member 32 second position restriction portion

Claims (5)

a heater including a substrate, a resistance heating element supported by the substrate, and a power supply terminal electrically connected to the resistance heating element, the power supply terminal being located at one end of the substrate in a longitudinal direction;
an endless belt having an inner circumferential surface in contact with the nip surface of the heater and rotating around the heater;
A holder for supporting the heater;
a heat conductive member located between the holder and a rear surface of the heater opposite to the nip surface, the heat conductive member having a higher thermal conductivity than the substrate;
the holder has a first position restricting portion that faces one end of the substrate in the longitudinal direction , and a third position restricting portion for positioning the heat conductive member in the longitudinal direction ,
the heat conducting member has a second position restricting portion that faces the other end of the substrate in the longitudinal direction,
Let Lp be the distance from the first positional restriction portion to the third positional restriction portion, Lb be the length of the substrate in the longitudinal direction, α1 be the linear expansion coefficient of the substrate, and α2 be the linear expansion coefficient of the heat conductive member,
Lp≦{1-(α1/α2)}×Lb
A heating unit characterized in that Lp is set so as to satisfy the following formula . the thermally conductive member has a base portion in contact with the back surface of the heater,
The heating unit according to claim 1 , wherein the second position restriction portion protrudes from the other end of the base portion in the longitudinal direction. The heating unit according to claim 2, characterized in that the length by which the second position regulating portion protrudes from the other end of the base portion in the longitudinal direction is smaller than the thickness of the substrate. 4. The heating unit according to claim 1 , wherein a length of the heat conducting member in the longitudinal direction is longer than a length of the resistance heating element in the longitudinal direction. The substrate is made of a ceramic material made of aluminum oxide,
5. The heating unit according to claim 1 , wherein the heat conducting member is a plate-like member made of aluminum.

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