JP7594738B2 - Fixing device and image forming apparatus - Google Patents

Description

The present invention relates to a fixing device and an image forming device.

Image forming devices such as copiers and printers are equipped with a fixing device that fixes the toner image onto the paper.

Typically, a fixing device has a pair of rotating bodies that come into contact with each other, and by passing paper between the rotating bodies (the fixing nip), the paper is heated and pressurized, and the toner image on the paper is fixed.

In recent years, in order to save energy or shorten warm-up times, fixing devices have been developed that use a fixing belt, which has a smaller thermal capacity than a roller, as the rotating body. Furthermore, from the perspective of safety, this type of fixing device is provided with a temperature detection member such as a fuse or thermostat that detects the temperature of the heat source that heats the fixing belt. In the unlikely event that the temperature of the heat source rises excessively due to an abnormality such as a breakdown, the temperature detection member detects the temperature rise and cuts off the power to the heat source, stopping the heat source from generating heat.

In order for the temperature detection member to detect the temperature of the heat source with good responsiveness, it is preferable that the temperature detection member is placed close to the heat source. In particular, when the temperature detection member is placed in direct contact with the heat source, the responsiveness of the temperature detection member is good. However, on the other hand, if the temperature detection member is in direct contact with the heat source, the temperature of the heat source may be partially reduced due to the heat of the heat source being absorbed by the temperature detection member at the point of contact with the temperature detection member, which may cause unevenness in the fixing quality of the image.

To address this issue, the following Patent Document 1 (Patent Publication No. 4546233) proposes a configuration in which a resin spacer is interposed between the heat source and the temperature detection member. In this configuration, the spacer is interposed between the heat source and the temperature detection member, so that the temperature detection member is kept out of contact with the heat source, preventing a drop in the temperature of the heat source due to direct contact of the temperature detection member. On the other hand, if the temperature of the heat source rises excessively due to an abnormality, the resin spacer melts, and the molten resin fills the gap between the temperature detection member and the heat source, and the temperature detection member approaches the heat source. This makes it easier for the heat of the heat source to be transmitted to the temperature detection member via the molten resin, ensuring the responsiveness of the temperature detection member in the event of abnormal heating.

However, in a configuration using a resin spacer as described above, the resin is unlikely to be in a uniform melted state due to variations in thermal conductivity or melting temperature, and there is a risk that when the temperature of the heat source exceeds a predetermined temperature, the spacer may not be able to melt reliably and stop the heat generation of the heat source. Therefore, in order to improve the accuracy and reliability of the response of the temperature detection member, a configuration that replaces the resin spacer is required.

In order to solve the above problems, the present invention provides a fixing device comprising a rotatable endless fixing belt, a rotatable pressure member that contacts the outer peripheral surface of the fixing belt to form a fixing nip, a heat source that heats the fixing belt, a temperature detection member that detects the temperature of the heat source and stops the heat source from generating heat when the temperature of the heat source exceeds a predetermined temperature, and a metallic heat transfer member interposed between the heat source and the temperature detection member, wherein when the temperature of the heat source exceeds the predetermined temperature, the heat transfer member deforms and the contact area of the heat transfer member with both the temperature detection member and the heat source increases.

The present invention can improve the accuracy and reliability of the response of the temperature sensing component.

1 is a schematic configuration diagram of an image forming apparatus according to an embodiment of the present invention; FIG. 2 is a schematic configuration diagram of a fixing device according to the present embodiment. FIG. 1 is a diagram showing a configuration of a safety device according to a first embodiment of the present invention, illustrating a state of the safety device under normal circumstances. FIG. 2 is a diagram showing the configuration of the safety device according to the first embodiment of the present invention, illustrating the state of the safety device when abnormal heating occurs. FIG. 11 is a diagram showing a configuration of a safety device according to a second embodiment of the present invention, illustrating a state of the safety device under normal circumstances. FIG. 13 is a diagram showing the configuration of a safety device according to a second embodiment of the present invention, illustrating the state of the safety device when abnormal heating occurs. FIG. 13 is a diagram showing a configuration of a safety device according to a third embodiment of the present invention, illustrating a state of the safety device under normal circumstances. FIG. 13 is a diagram showing the configuration of a safety device according to a third embodiment of the present invention, illustrating the state of the safety device when abnormal heating occurs. FIG. 13 is a diagram showing a configuration of a safety device according to a fourth embodiment of the present invention, illustrating a state of the safety device under normal circumstances. FIG. 13 is a diagram showing the configuration of a safety device according to a fourth embodiment of the present invention, illustrating the state of the safety device when abnormal heating occurs. FIG. 13 is a diagram showing the configuration of a safety device according to a fifth embodiment of the present invention, illustrating the state of the safety device under normal circumstances. FIG. 13 is a diagram showing the configuration of a safety device according to a fifth embodiment of the present invention, illustrating the state of the safety device when abnormal heating occurs. FIG. 13 is a diagram showing the configuration of a safety device according to a sixth embodiment of the present invention, illustrating the state of the safety device under normal circumstances. FIG. 13 is a diagram showing the configuration of a safety device according to a sixth embodiment of the present invention, illustrating the state of the safety device when abnormal heating occurs.

The present invention will be described below with reference to the attached drawings. In each drawing for explaining the present invention, components such as parts and components having the same function or shape are given the same reference numerals as far as possible to distinguish them, and the description will be omitted after the first description.

Figure 1 is a schematic diagram of an image forming device according to one embodiment of the present invention.

As shown in FIG. 1, the image forming device 1 according to this embodiment is an electrophotographic printer that includes an image forming unit 2, a recording medium supply unit 3, a transfer unit 4, a fixing unit 5, and a recording medium discharge unit 6. The image forming device according to the present invention may be a printer, a copier, a facsimile, or a multifunction device that has two or three of these functions.

The image forming section 2 includes four imaging units 7Y, 7M, 7C, and 7K that form images, and an exposure device 8 that forms an electrostatic latent image on the surface of the photoconductor 10 of each imaging unit 7Y, 7M, 7C, and 7K. In addition to the photoconductor 10 as an image carrier, each of the four imaging units 7Y, 7M, 7C, and 7K includes a charging member 11 that charges the surface of the photoconductor 10, a developing device 12 that supplies developer to the surface of the photoconductor 10, and a cleaning member 13 that cleans the surface of the photoconductor 10. Each imaging unit 7Y, 7M, 7C, and 7K has the same configuration, except that it contains developers of different colors, yellow (Y), magenta (M), cyan (C), and black (K), which correspond to the color separation components of the color image. The exposure device 8 includes a light source, a polygon mirror, an f-θ lens, a reflecting mirror, and the like.

The recording medium supply unit 3 is provided with a paper feed tray 18 that stores paper P as a recording medium, and a paper feed roller 19 that feeds paper P one sheet at a time from the paper feed tray 18. The paper P stored in the paper feed tray 18 includes plain paper, thick paper, thin paper, postcards, envelopes, coated paper (coated paper or art paper, etc.), tracing paper, etc. In addition to paper, resin sheets such as overhead projector sheets may also be used as recording media.

The transfer section 4 is provided with a transfer device 14 that transfers an image onto paper P supplied from a paper feed tray 18. The transfer device 14 includes an intermediate transfer belt 15, a primary transfer roller 16, and a secondary transfer roller 17. The intermediate transfer belt 15 is an endless belt member that is stretched by a plurality of support rollers. Four primary transfer rollers 16 are provided on the inside of the intermediate transfer belt 15 corresponding to each photoconductor 10. Each primary transfer roller 16 contacts each photoconductor 10 via the intermediate transfer belt 15, thereby forming a primary transfer nip between the intermediate transfer belt 15 and each photoconductor 10. The secondary transfer roller 17 contacts the outer peripheral surface of the intermediate transfer belt 15 to form a secondary transfer nip.

The fixing section 5 is provided with a fixing device 20 that fixes an image onto the paper P. The fixing device 20 includes an endless fixing belt 21 and a pressure roller 22 as a pressure member. The fixing belt 21 and the pressure roller 22 are pressed against each other, forming a fixing nip between them.

The recording medium ejection section 6 is provided with a pair of ejection rollers 23 that eject the paper P outside the device.

Next, the printing operation of the image forming device will be explained with reference to FIG.

When an instruction to start a printing operation is given, the photoconductor 10 in each of the imaging units 7Y, 7M, 7C, and 7K starts to rotate, and the surface of the photoconductor 10 is charged to a uniform high potential by the charging member 11. Next, the exposure device 8 irradiates the surface of each photoconductor 10 with laser light based on the image information of the original document read by the original reading device or the print information instructed to be printed from the terminal. This reduces the potential of the area irradiated with the laser light, and an electrostatic latent image is formed on the surface of each photoconductor 10. Toner is then supplied from the developing device 12 to this electrostatic latent image, and a toner image is formed on each photoconductor 10.

The toner images formed on each photoconductor 10 reach the primary transfer nip (position of the primary transfer roller 16) as each photoconductor 10 rotates, and are transferred to the rotating intermediate transfer belt 15 so that they overlap one another. After the toner images are transferred, the toner remaining on each photoconductor 10 is removed by each cleaning member 13. The toner images transferred to the intermediate transfer belt 15 then reach the secondary transfer nip (position of the secondary transfer roller 17) as the intermediate transfer belt 15 rotates, and are transferred to the paper P.

This paper P is supplied from the recording medium supply unit 3. In the recording medium supply unit 3, after an instruction to start the printing operation is given, the paper feed roller 19 rotates, and paper P is sent out one sheet at a time from the paper feed tray 18. The sent-out paper P is then temporarily stopped by a pair of timing rollers 24, and then transported to the secondary transfer nip in time with the toner image on the intermediate transfer belt 15 reaching the secondary transfer nip. In this way, a full-color toner image is transferred onto the paper P.

The paper P with the transferred toner image is transported to the fixing unit 5. In the fixing unit 5, the paper P is conveyed while being sandwiched between the fixing belt 21 and the pressure roller 22, so that the toner image is fixed to the paper P. The paper P is then conveyed to the recording medium discharge unit 6, and is discharged outside the device by the paper discharge rollers 23. This completes the series of printing operations.

The basic configuration of the fixing device 20 according to this embodiment will be described below with reference to FIG. 2.

As shown in FIG. 2, the fixing device 20 according to this embodiment includes a fixing belt 21, a pressure roller 22, a heater 25, a heater holder 26, and a stay 27.

The fixing belt 21 is disposed on the unfixed image bearing surface of the paper P, and is a fixing member that fixes the unfixed image on the paper P. The fixing belt 21 is composed of an endless belt member, and is rotatably held by a pair of belt holding members inserted at both ends in the longitudinal direction. In other words, the fixing belt 21 is held by the pair of belt holding members in a so-called free belt state in which no tension is applied when the fixing belt 21 is not rotating. In addition, a heater 25 is disposed inside the fixing belt 21 as a heat source for heating the fixing belt 21.

The pressure roller 22 is a rotating body that contacts the outer peripheral surface of the fixing belt 21 to form the fixing nip 100. Specifically, the pressure roller 22 is composed of a core metal, an elastic layer made of foamed silicone rubber, silicone rubber, fluororubber, or the like provided on the surface of the core metal, and a release layer made of PFA, PTFE, or the like provided on the surface of the elastic layer. The pressure roller 22 is pressed toward the fixing belt 21 by a biasing member such as a spring, and is pressed against the outer peripheral surface of the fixing belt 21. As a result, the fixing nip 100 is formed between the fixing belt 21 and the pressure roller 22 (at the contact point).

The pressure roller 22 is configured to be rotated by a drive source provided in the image forming apparatus body. When the pressure roller 22 is rotated, the drive force is transmitted to the fixing belt 21, which rotates. The fixing belt 21 is then heated by the heater 25. When the temperature of the fixing belt 21 reaches a predetermined temperature (fixing temperature), as shown in FIG. 2, the paper P carrying the unfixed image is transported between the fixing belt 21 and the pressure roller 22 (fixing nip 100). As a result, the paper P is pressurized and heated as it passes through the fixing nip 100, and the unfixed image is fixed to the paper P.

The heater 25 is a plate-shaped heater having a substrate 30, a first insulating layer 31, a resistance heating element 32, and a second insulating layer 33. The heater 25 is arranged so as to extend across the longitudinal direction (paper width direction intersecting the paper conveying direction) of the fixing belt 21. The substrate 30 is made of a metal material such as stainless steel (SUS), iron, or aluminum. In addition to a metal material, ceramic or glass can also be used as the material of the substrate 30. The first insulating layer 31 and the second insulating layer 33 are made of a material such as heat-resistant glass, ceramic, or polyimide. The first insulating layer 31 is laminated on the surface of the substrate 30 on the fixing nip 100 side, and the second insulating layer 33 is laminated further on the fixing nip 100 side than the first insulating layer 31. In addition, when the substrate 30 is made of an insulating material such as ceramic, the first insulating layer 31 can be omitted. The resistance heating element 32 is a heating element interposed between the first insulating layer 31 and the second insulating layer 33. The resistive heating element 32 is formed, for example, by applying a paste made of a mixture of silver palladium (AgPd) and glass powder to the surface of the base material 30 by screen printing or the like, and then firing the base material 30. Alternatively, the resistive heating element 32 may be made of a resistive material such as a silver alloy (AgPt) or ruthenium oxide (RuO ₂ ).

The heater 25 is also positioned so as to contact the inner circumferential surface of the fixing belt 21 at the fixing nip 100. Therefore, when the fixing belt 21 rotates, the fixing belt 21 slides against the heater 25. At this time, a low-friction sheet or a lubricant such as grease may be interposed between the heater 25 and the fixing belt 21 to increase the sliding property of the fixing belt 21 against the heater 25.

The heater holder 26 is a heat source holding member that holds the heater 25 inside the fixing belt 21. The heater holder 26 is preferably made of a heat-resistant material because it is prone to becoming hot due to the heat from the heater 25. In particular, when the heater holder 26 is made of a heat-resistant resin with low thermal conductivity such as LCP or PEEK, the heat resistance of the heater holder 26 is ensured while heat transfer from the heater 25 to the heater holder 26 is suppressed, so that the fixing belt 21 can be heated efficiently.

The stay 27 is a reinforcing member disposed on the inside of the fixing belt 21. The stay 27 supports the surface of the heater holder 26 opposite the surface on the fixing nip 100 side, thereby preventing the heater holder 26 from bending due to the pressure of the pressure roller 22. This forms a fixing nip 100 of uniform width between the fixing belt 21 and the pressure roller 22. In addition, the stay 27 is preferably formed from an iron-based metal material such as SUS or SECC to ensure its rigidity.

In the fixing device described above, a control temperature detection member such as a thermistor is provided to maintain the temperature of the fixing belt at a predetermined temperature (fixing temperature) suitable for image fixing. The control temperature detection member detects the temperature of the heater, and the heater output is controlled based on the detected temperature, thereby maintaining the temperature of the fixing belt at the predetermined temperature.

In addition to the control temperature detection member, the fixing device is also provided with a temperature detection member as a safety device to prevent the heater from excessively increasing in temperature. For example, if the control temperature detection member breaks down and the heater temperature increases excessively, the safety device detects the increase in heater temperature and cuts off the power supply to the heater, causing the heater to stop generating heat.

In such a safety device, it is preferable to place the temperature detection member close to the heater in order to improve the responsiveness of the temperature detection member. However, if the temperature detection member is placed in direct contact with the heater to ensure good responsiveness, as mentioned above, there is a problem that the temperature of the heater will drop partially at the point of contact with the temperature detection member.

To address this problem, a method has been proposed in the past in which a resin spacer is interposed between the heater (heat source) and the temperature detection member; however, because the molten state of the resin is not uniform, there is a risk that the resin will not melt reliably and stop the heater from generating heat when the heater temperature exceeds a predetermined temperature. For this reason, the fixing device according to this embodiment employs the following configuration to improve the accuracy and reliability of the response of the safety device. The configuration of the safety device according to this embodiment will be described in detail below.

Figure 3 shows the configuration of the safety device according to this embodiment.

As shown in FIG. 3, the safety device 40 includes a thermostat 41 as a temperature detection member, a spring 42 as an elastic member, and a metal heat transfer member 43.

The thermostat 41 is a temperature detection member that cuts off the flow of electricity to the heater 25 when an excessive temperature rise in the heater 25 is detected. Specifically, the thermostat 41 is composed of a bimetal, a movable pin, a switch, and a case that houses these components. In FIG. 3, only the case of the thermostat 41 is shown. The bimetal is formed by bonding together two metal plates with different thermal expansion coefficients, and when the temperature of the bimetal rises above a predetermined operating temperature as the temperature of the heater 25 rises, the bimetal deforms due to the difference in thermal expansion between the metal plates. This deformation activates the movable pin, disconnecting the switch contacts and cutting off the flow of electricity to the heater 25.

The thermostat 41 and the heat transfer member 43 are housed in a through hole 26a provided in the heater holder 26 and are elastically biased toward the heater 25 by a spring 42. In this embodiment, the thermostat 41 and the heat transfer member 43 are formed in a circular shape when viewed from the biasing direction of the spring 42, so the through hole 26a is also formed in a circular shape (cylindrical). Note that the shapes of the thermostat 41, the heat transfer member 43, and the through hole 26a are not limited to being circular, and may be other shapes such as rectangular.

The heat transfer member 43 is formed by bonding two metal plates with different thermal expansion coefficients together, similar to the bimetal in the thermostat 41. Therefore, when the temperature of the heat transfer member 43 rises above a predetermined operating temperature as the temperature of the heater 25 rises, the heat transfer member 43 deforms due to the difference in thermal expansion of the metal plates that make up the heat transfer member 43. The metal plates that make up the heat transfer member 43 may be made of the same type of metal material as the bimetal in the thermostat 41, or may be made of a different type of metal material.

3 shows the state of the heat transfer member 43 when the temperature of the heater 25 is in a normal temperature state. In this state, the heat transfer member 43 is curved so as to be convex toward the heater 25, and the convex surface 43a (hereinafter referred to as the "lower surface") on the heater 25 side is in contact with the heater 25. In this embodiment, since the heat transfer member 43 is formed in a circular shape, the central portion (the center portion of the circular heat transfer member 43) 43a1 of the lower surface 43a of the heat transfer member 43 that protrudes toward the heater 25 and the surrounding portion are in contact with the heater 25. On the other hand, the surface 43b (hereinafter referred to as the "upper surface") of the heat transfer member 43 on the thermostat 41 side is formed as a concave surface with a concave central portion. Therefore, the annular edge portion 43b2 of the upper surface 43b of the heat transfer member 43 is in contact with the thermostat 41. In addition, in this embodiment, the diameter (width) d1 of the heat transfer member 43 is set smaller than the diameter (width) d2 of the thermostat 41 so that the edge 43b2 of the heat transfer member 43 comes into contact with the thermostat 41.

In contrast to the normal state described above, if the temperature of the heater 25 exceeds the predetermined temperature due to an abnormality, the heat transfer member 43 deforms due to the difference in thermal expansion, and the concave and convex surfaces of the heat transfer member 43 are reversed, as shown in FIG. 4. In other words, the lower surface 43a of the heat transfer member 43 becomes concave, and conversely, the upper surface 43b of the heat transfer member 43 becomes convex.

In this case, as shown in FIG. 4, the lower surface 43a, which is the concave surface of the heat transfer member 43, and particularly the annular edge portion 43a2, contacts the heater 25, and the central portion 43b1 (the center portion of the heat transfer member 43) and the adjacent portion of the upper surface 43b, which is the convex surface of the heat transfer member 43, contacts the thermostat 41.

In this embodiment, the thermostat 41 has a recess 41a formed in a concave shape following the convex shape of the heat transfer member 43. Therefore, in the state shown in FIG. 4, the convex upper surface 43b of the heat transfer member 43 comes into contact with the recess 41a of the thermostat 41.

In this manner, in this embodiment, when the temperature of the heater 25 exceeds a predetermined temperature due to an abnormality, the convex upper surface 43b of the heat transfer member 43 comes into contact with the concave portion 41a of the thermostat 41, and the contact area of the heat transfer member 43 with the thermostat 41 increases. That is, in the normal temperature state shown in FIG. 3, only the edge portion 43b2 of the upper surface (concave surface) 43b of the heat transfer member 43 comes into contact with the thermostat 41, whereas in the abnormal heating state shown in FIG. 4, the convex upper surface 43b of the heat transfer member 43 comes into contact with the concave portion 41a of the thermostat 41 over a wide area.

As a result, in the event of abnormal heating, the amount of heat transferred from the heater 25 to the thermostat 41 via the heat transfer member 43 increases. As a result, the temperature of the thermostat 41 rises rapidly in response to the temperature of the heater 25, and power to the heater 25 is immediately cut off. On the other hand, under normal circumstances, the contact area of the heat transfer member 43 with the thermostat 41 is small, and the amount of heat transferred from the heater 25 to the thermostat 41 via the heat transfer member 43 is also small, so the thermostat 41 does not operate and power to the heater 25 is maintained.

As described above, in this embodiment, by using a metal heat transfer member 43 that deforms due to differences in thermal expansion coefficients, the amount of heat transferred to the thermostat 41 during normal and abnormal heating can be adjusted while keeping the thermostat 41 from coming into direct contact with the heater 25. This prevents the temperature of the heater 25 from dropping due to the thermostat 41 coming into direct contact with the heater 25, and increases the amount of heat transferred to the thermostat 41 during abnormal heating, allowing the thermostat 41 to operate with good responsiveness. Furthermore, the metal heat transfer member 43 is more accurate and reliable in deformation due to temperature rise than a resin spacer. This allows the accuracy and reliability of the response of the thermostat 41 to be improved compared to conventional methods, improving reliability.

In particular, when the recess 41a of the thermostat 41 is formed with the same shape or the same curvature as the convex shape of the heat transfer member 43, the contact area of the heat transfer member 43 with the thermostat 41 can be increased more reliably, and the accuracy and reliability of the response of the thermostat 41 can be further improved. However, the recess 41a of the thermostat 41 and the convex shape of the heat transfer member 43 are not limited to being the same, and may be different shapes as long as a large contact area is ensured during abnormal heating. In addition, grease having thermal conductivity may be applied to at least one of the surface of the heat transfer member 43 that contacts the thermostat 41 (upper surface 43b) and the surface of the heat transfer member 43 that contacts the heater 25 (lower surface 43a). This can further improve the heat transfer from the heater 25 to the thermostat 41.

In addition, since a large heat capacity of the heat transfer member 43 causes the temperature of the heater 25 to drop partially, it is preferable that the heat transfer member 43 is formed thin. Specifically, as shown in FIG. 3, it is preferable that the thickness t1 between the surface (lower surface 43a) of the heat transfer member 43 on the heater 25 side and the surface (upper surface 43b) on the thermostat 41 side is set thinner than the thickness t2 between the surface (upper surface) of the heater 25 on the heat transfer member 43 side and the surface (lower surface) on the fixing belt 21 side. In this way, since the thickness t1 of the heat transfer member 43 is thinner than the thickness t2 of the heater 25, the heat capacity of the heat transfer member 43 is reduced, and the temperature drop of the heater 25 caused by the heat transfer member 43 coming into contact with the heater 25 can be reduced.

Next, an embodiment that is different from the above-mentioned embodiment (first embodiment) will be described. In the following explanation, the different parts will be mainly described, and the other parts will be omitted as they are basically the same as the above-mentioned embodiment.

Figures 5 and 6 are diagrams showing the configuration of a safety device according to a second embodiment of the present invention.

As shown in Fig. 5 and Fig. 6, in the safety device 40 according to the second embodiment, the unevenness of the heat transfer member 43 is reversed from that of the above-mentioned embodiment (first embodiment). That is, in the normal state shown in Fig. 5, the heat transfer member 43 is curved so as to be convex toward the thermostat 41, and in the abnormal heating state shown in Fig. 6, the heat transfer member 43 is curved so as to be convex toward the heater 25. Also, in this embodiment, unlike the above-mentioned embodiment, a convex portion 41b is formed on the surface of the thermostat 41 that faces the heat transfer member 43.

In the second embodiment configured in this manner, during normal operation as shown in FIG. 5, the convex upper surface 43b of the heat transfer member 43 comes into contact with the convex portion 41b of the thermostat 41. In other words, in this case, the convex surfaces of the heat transfer member 43 and the thermostat 41 come into contact with each other, reducing the contact area between them.

On the other hand, when the temperature of the heater 25 exceeds a predetermined temperature and abnormal heating occurs, as shown in FIG. 6, the concave and convex portions of the heat transfer member 43 are inverted, so that the concave upper surface 43b of the heat transfer member 43 comes into contact with the convex portion 41b of the thermostat 41. Therefore, in this case, the contact area between the heat transfer member 43 and the thermostat 41 becomes large.

In this way, even in the second embodiment, if the temperature of the heater 25 exceeds a predetermined temperature due to an abnormality, the unevenness of the heat transfer member 43 is inverted, thereby increasing the contact area of the heat transfer member 43 with the thermostat 41. This increases the amount of heat transferred from the heater 25 to the thermostat 41, so that electricity to the heater 25 is immediately cut off in the event of abnormal heating. On the other hand, under normal circumstances, the contact area of the heat transfer member 43 with the thermostat 41 is small and the amount of heat transferred from the heater 25 to the thermostat 41 is also small, so the thermostat 41 does not operate and electricity to the heater 25 is maintained.

In addition, in this embodiment, as in the above-described embodiment, a metal heat transfer member 43 is used, improving the accuracy and reliability of the response of the thermostat 41. In addition, in this embodiment, if the convex portion 41b of the thermostat 41 is formed to have the same shape or the same curvature as the concave shape of the heat transfer member 43, the contact area of the heat transfer member 43 with the thermostat 41 is more reliably increased, further improving the responsiveness of the thermostat 41. Note that the convex portion 41b of the thermostat 41 and the concave shape of the heat transfer member 43 do not necessarily have to match, and may have different shapes as long as a large contact area can be secured during abnormal heating.

Figures 7 and 8 are diagrams showing the configuration of a safety device according to a third embodiment of the present invention.

In the safety device 40 according to the third embodiment shown in Figs. 7 and 8, in addition to the configuration of the second embodiment shown in Figs. 5 and 6 described above, a recess 25a is formed on the surface of the heater 25 facing the heat transfer member 43.

In this way, in the third embodiment, the concave portion 25a is formed on the surface of the heater 25 facing the heat transfer member 43. Therefore, when the temperature of the heater 25 exceeds a predetermined temperature due to an abnormality, as shown in FIG. 8, the concave and convex portions of the heat transfer member 43 are inverted, and the convex lower surface 43a of the heat transfer member 43 comes into contact with the concave portion 25a of the heater 25. This increases the contact area of the heat transfer member 43 with the heater 25. Furthermore, in this state, the convex portion 41b of the thermostat 41 comes into contact with the concave upper surface 43b of the heat transfer member 43, as in the second embodiment described above. Therefore, the contact area of the heat transfer member 43 with the thermostat 41 also increases.

In this way, in the third embodiment, the contact area of the heat transfer member 43 with the heater 25 is increased in addition to the contact area of the heat transfer member 43 with the thermostat 41, so the amount of heat transferred from the heater 25 to the thermostat 41 during abnormal heating is further increased. This makes it possible to more effectively improve the responsiveness of the thermostat 41. Also, in this embodiment, if the recess 25a of the heater 25 is formed to have the same shape or the same curvature as the convex shape of the heat transfer member 43, the contact area of the heat transfer member 43 with the heater 25 is more reliably increased, so the responsiveness of the thermostat 41 is further improved. Note that the recess 25a of the heater 25 and the convex shape of the heat transfer member 43 do not have to match each other as long as a large contact area during abnormal heating can be ensured.

Figures 9 and 10 are diagrams showing the configuration of a safety device according to the fourth embodiment of the present invention.

9 and 10, in the safety device 40 according to the fourth embodiment, a convex portion 25b is formed on the surface of the heater 25 that faces the heat transfer member 43. In addition, in this embodiment, the shape of the heat transfer member 43 is not a curved cross-sectional shape as in the above-mentioned embodiments, but a broken line cross-sectional shape having a flat portion. In detail, the heat transfer member 43 has a flat portion 44 including its center, and an inclined portion 45 provided around the flat portion 44. The flat portion 44 is arranged parallel to the surface (plane) of the thermostat 41 that faces the heat transfer member 43, and the inclined portion 45 is arranged so as to be inclined with respect to the flat portion 44.

In the fourth embodiment having such a configuration, when the temperature of the heater 25 is in a normal temperature state, as shown in FIG. 9, the inclined portion 45 of the heat transfer member 43 is arranged so as to face the thermostat 41 side. That is, the heat transfer member 43 is arranged so as to be convex toward the heater 25. In addition, in this state, the flat portion 44 of the heat transfer member 43 contacts the convex portion 25b (flat surface) of the heater 25, and the tip of the inclined portion 45 of the heat transfer member 43, in other words, the edge portion 43b2 of the upper surface 43b of the heat transfer member 43, contacts the thermostat 41.

In contrast, when the temperature of the heater 25 exceeds a predetermined temperature, as shown in FIG. 10, the unevenness of the heat transfer member 43 is inverted, and the flat portion 44 of the heat transfer member 43 comes into contact with the thermostat 41. As a result, the contact area of the heat transfer member 43 with the thermostat 41 increases compared to the case where the tip of the inclined portion 45 comes into contact with the thermostat 41 (normal state) as shown in FIG. 9. Note that in this state, the flat portion 44 of the heat transfer member 43 comes into contact with the heater 25 in the same way as before the deformation of the heat transfer member 43, so the contact area of the heat transfer member 43 with the heater 25 basically does not change.

In this way, even in the fourth embodiment, the unevenness of the heat transfer member 43 is inverted, so that the contact area of the heat transfer member 43 with the thermostat 41 can be increased, and the amount of heat transferred from the heater 25 to the thermostat 41 during abnormal heating increases, allowing the power supply to the heater 25 to be immediately cut off. On the other hand, under normal circumstances, the contact area of the heat transfer member 43 with the thermostat 41 is small, and the amount of heat transferred from the heater 25 to the thermostat 41 is also small, so the thermostat 41 does not operate and the power supply to the heater 25 is maintained.

In addition, in this embodiment, as in the above-mentioned embodiments, a metal heat transfer member 43 is used, improving the accuracy and reliability of the response of the thermostat 41. Note that the heat transfer member 43 may have a curved cross-sectional shape as in the above-mentioned embodiments, rather than a shape having a flat portion 44. In that case, it is preferable to provide a concave portion formed following the convex shape of the heat transfer member 43 on the surface of the thermostat 41 facing the heat transfer member 43, so that a large contact area between the thermostat 41 and the heat transfer member 43 can be ensured during abnormal heating.

Figures 11 and 12 are diagrams showing the configuration of a safety device according to the fifth embodiment of the present invention.

As shown in Figures 11 and 12, in the safety device 40 according to the fifth embodiment, a recess 25c is formed on the surface of the heater 25 that faces the heat transfer member 43. This recess 25c is formed to a depth and width sufficient to accommodate the entire heat transfer member 43.

In this embodiment, in the normal state shown in FIG. 11, the heat transfer member 43 is arranged so as to be convex toward the thermostat 41, and the thermostat 41 is supported by the heat transfer member 43. Therefore, the thermostat 41 is held in a non-contact state with the heater 25.

On the other hand, in the event of abnormal heating as shown in FIG. 12, the unevenness of the heat transfer member 43 is reversed, causing the heat transfer member 43 to enter the recess 25c of the heater 25. In more detail, when the unevenness of the heat transfer member 43 is reversed, the thermostat 41 presses the heat transfer member 43 toward the heater 25 under the biasing force of the spring 42, causing the heat transfer member 43 to be pushed into the recess 25c while undergoing elastic deformation. As a result, the thermostat 41 comes into (direct) contact with the heater 25 without going through the heat transfer member 43.

In this way, in the fifth embodiment, if the temperature of the heater 25 exceeds a predetermined temperature due to an abnormality, the thermostat 41 comes into (direct) contact with the heater 25, and heat is transferred well from the heater 25 to the thermostat 41 via the contact point. As a result, in the event of abnormal heating, the thermostat 41 rises in temperature rapidly in response to the temperature of the heater 25, so the thermostat 41 operates with good responsiveness and immediately cuts off the flow of electricity to the heater 25. On the other hand, in normal operation, the thermostat 41 is held out of contact with the heater 25 by the heat transfer member 43, so that heat transfer from the heater 25 to the thermostat 41 is suppressed and the flow of electricity to the heater 25 is maintained.

In addition, in this embodiment, as in the above-described embodiment, a metal heat transfer member 43 is used, improving the accuracy and reliability of the response of the thermostat 41. Note that the shape of the heat transfer member 43 may be a curved cross-sectional shape rather than a broken line cross-sectional shape having flat portions as shown in Figures 11 and 12.

Figures 13 and 14 are diagrams showing the configuration of a safety device according to the sixth embodiment of the present invention.

As shown in Figures 13 and 14, the safety device 40 according to the sixth embodiment does not include a metal heat transfer member as described above, but instead includes magnetic bodies 46A and 46B that repel each other. One magnetic body 46A is provided in the thermostat 41, and the other magnetic body 46B is provided in the heater 25.

As shown in FIG. 13, in the normal state, the thermostat 41 is biased in a direction away from the heater 25 by the repulsive force between the magnetic bodies 46A and 46B, so that the thermostat 41 is held in a non-contact state with respect to the heater 25. In other words, the repulsive force of the magnetic bodies 46A and 46B and the biasing force of the spring 42 are set so that a gap is created between the thermostat 41 and the heater 25 when they are in balance. In this state, heat transfer from the heater 25 to the thermostat 41 is suppressed, so the thermostat 41 does not operate and electricity is maintained to the heater 25.

On the other hand, if the temperature of the heater 25 exceeds the predetermined temperature due to an abnormality, as shown in FIG. 14, the repulsive force between the magnetic bodies 46A and 46B disappears, and the thermostat 41 comes into (direct) contact with the heater 25. In detail, if the temperature of the heater 25 rises excessively, the temperature of the magnetic body 46B on the heater 25 side exceeds the so-called Curie point (the temperature at which magnetism is lost), and as a result, the magnetism of the magnetic body 46B on the heater 25 side disappears. As a result, the repulsive force (biasing force) between the magnetic bodies 46A and 46B also disappears, and the thermostat 41 is pushed by the biasing force of the spring 42 and comes into contact with the heater 25. As a result, heat is transferred well from the heater 25 to the thermostat 41, so that the temperature of the thermostat 41 rises rapidly following the temperature of the heater 25, and the current to the heater 25 is immediately cut off.

In this way, in the fifth embodiment, by using magnetic bodies 46A and 46B that lose their magnetism as the temperature rises, the thermostat 41 is kept out of direct contact with the heater 25 under normal conditions, while the thermostat 41 is brought into contact with the heater 25 under abnormal heating conditions, thereby increasing the amount of heat transferred to the thermostat 41. This makes it possible to prevent a drop in the temperature of the heater 25 due to the thermostat 41 coming into direct contact with the heater 25 under normal conditions, and to increase the amount of heat transferred to the thermostat 41 under abnormal heating conditions, thereby enabling the thermostat 41 to operate with good responsiveness. Furthermore, a configuration using such magnetic bodies 46A and 46B provides better accuracy and reliability in the response of the thermostat 41 than a configuration using a resin spacer, thereby improving reliability.

For example, ferrite magnets can be used as the magnetic bodies 46A and 46B. Ferrite magnets have a Curie point of about 450°C, which is within the temperature range that is the criterion for determining an abnormality in a heater, and are therefore suitable as the magnetic bodies 46A and 46B. Each of the magnetic bodies 46A and 46B may be an electromagnet in addition to a permanent magnet.

In addition, in this embodiment, the thermostat 41 is configured to contact the heater 25, but the thermostat 41 may simply approach the heater 25 without contacting it. In other words, the repulsive force (biasing force) between the magnetic bodies 46A and 46B decreases with an excessive temperature rise in the heater 25, so that even if the thermostat 41 approaches the heater 25, heat is transferred well from the heater 25 to the thermostat 41. Therefore, the temperature of the thermostat 41 rises in accordance with the temperature of the heater 25, and the power supply to the heater 25 can be cut off.

Although the embodiment of the present invention has been described above, the present invention is not limited to the above-mentioned embodiment, and various modifications can be made without departing from the spirit of the invention.

The present invention is not limited to a free-belt type configuration in which the fixing belt is rotatably held by a pair of belt holding members as shown in FIG. 2, but can also be applied to a configuration in which the fixing belt is stretched around multiple rollers, etc.

1 Image forming apparatus 20 Fixing device 21 Fixing belt 22 Pressure roller (pressure member)
25 Heater (heat source)
25a: recess 25b: protrusion 25c: recess 40: safety device 41: thermostat (temperature detection member)
41a: Concave portion 41b: Convex portion 43: Heat transfer member 46A: Magnetic body 46B: Magnetic body 100: Fixing nip d1: Diameter of heat transfer member d2: Diameter of thermostat t1: Thickness of heat transfer member t2: Thickness of heater

Patent No. 4546233

Claims (8)

a rotatable endless fixing belt;
a rotatable pressure member that contacts an outer peripheral surface of the fixing belt to form a fixing nip;
a heat source for heating the fixing belt;
a temperature detection member that detects the temperature of the heat source and stops the heat generation of the heat source when the temperature of the heat source exceeds a predetermined temperature;
a metal heat transfer member interposed between the heat source and the temperature detection member;
Equipped with
a heat transfer member that transfers heat to the temperature detection member and the heat source when the temperature of the heat source exceeds the predetermined temperature, and a contact area of the heat transfer member with both the temperature detection member and the heat source increases. a rotatable endless fixing belt;
a rotatable pressure member that contacts an outer peripheral surface of the fixing belt to form a fixing nip;
a heat source for heating the fixing belt;
a temperature detection member that detects the temperature of the heat source and stops the heat generation of the heat source when the temperature of the heat source exceeds a predetermined temperature;
a metal heat transfer member interposed between the heat source and the temperature detection member;
Equipped with
the heat transfer member has a convex surface having a convex central portion facing the temperature detection member or the heat source, and a concave surface having a concave central portion facing the opposite surface to the convex surface,
A fixing device characterized in that, when the temperature of the heating source exceeds the predetermined temperature, the heat transfer member deforms so that the convex and concave surfaces are inverted , thereby increasing the contact area of the heat transfer member with the temperature detection member. The fixing device according to claim 2 , wherein the temperature detection member has a concave portion that contacts the convex surface of the heat transfer member or a convex portion that contacts the concave surface of the heat transfer member when the temperature of the heating source exceeds the predetermined temperature . 4. The fixing device according to claim 2, wherein the heat source has a concave portion that contacts the convex surface of the heat transfer member when the temperature of the heat source exceeds the predetermined temperature, or a convex portion that contacts the concave surface of the heat transfer member . the heat transfer member is disposed such that the concave surface faces the temperature detection member when the temperature of the heat source is equal to or lower than the predetermined temperature,
5. The fixing device according to claim 2, wherein the heat transfer member is formed in a circular shape having a diameter smaller than that of the temperature detection member . A fixing device according to any one of claims 1 to 5, wherein a thickness between the surface of the heat transfer member facing the heating source and the surface of the temperature detection member is thinner than a thickness between the surface of the heat source facing the heat transfer member and the surface of the heat source facing the fixing belt . 7. The fixing device according to claim 1, wherein a thermally conductive grease is applied to at least one of a surface of the heat transfer member that contacts the temperature detection member and a surface of the heat transfer member that contacts the heating source . An image forming apparatus comprising the fixing device according to claim 1 .

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