Fixing device and image forming apparatus

Abstract

To allow a temperature detection member to appropriately perform temperature detection even when a conductive support member is reduced in size to reduce the size of a fixing member.SOLUTION: A fixing device 30 comprises: a hollow fixing member 31 that heat-fixes an image to a recording material P; an opposite member 32 that forms a fixing nip between the fixing member and the opposite member; a conductive support member 33 that is arranged in the hollow part of the fixing member and supports the fixing nip part of the fixing member; and a temperature detection member 40 that detects temperature. The conductive support member is provided with recesses or openings 33d at portions opposite to exposure conductive parts of the temperature detection member.SELECTED DRAWING: Figure 8

Description

[Technical field]

[0001] The present invention relates to a fixing device and an image forming apparatus. [Background technology]

[0002] Conventionally, a fixing device has been known that includes a hollow fixing member that heats and fixes an image onto a recording material, an opposing member that forms a fixing nip between the fixing member, a conductive support member that is disposed in the hollow portion of the fixing member and supports the fixing nip portion of the fixing member, and a temperature detection member that detects temperature.

[0003] For example, Patent Document 1 discloses a fixing device including an endless fixing belt as a fixing member, a pressure roller as an opposing member, and a metal stay (conductive support member) arranged on the inner circumferential side (hollow portion) of the fixing belt. The stay includes an upstream conductive support portion and a downstream conductive support portion in the recording material conveying direction, and supports a heater holder that holds a planar heater at each tip of these support portions, and supports the fixing nip portion of the fixing belt via the heater holder. The heater holder holds a heater on the fixing nip side, and holds a temperature detection member made of a thermistor on the opposite side to the fixing nip. The temperature detection member is arranged inside the stay, and detects the temperature of the heater through a through hole provided in the heater holder. Summary of the Invention [Problem to be solved by the invention]

[0004] In recent fixing devices, in order to reduce the size of the fixing member, there is a demand for reducing the size of the conductive support member disposed in the hollow portion of the fixing member. However, if the conductive support member is reduced in size, it becomes difficult for the temperature detection member to properly detect the temperature, and there is a risk that proper operation of the fixing device will be hindered. [Means for solving the problem]

[0005] In order to solve the above-mentioned problems, the present invention provides a fixing device including a hollow fixing member that heats and fixes an image on a recording material, a facing member that forms a fixing nip between the fixing member and a facing member, a conductive support member that is disposed in the hollow portion of the fixing member and supports a fixing nip portion of the fixing member, and a temperature detection member that detects temperature, The conductive support member includes an upstream conductive support portion disposed on the upstream side in the recording material transport direction and a downstream conductive support portion disposed on the downstream side in the recording material transport direction, the temperature detection member is disposed between the upstream conductive support portion and the downstream conductive support portion, and has a configuration in which two exposed conductive portions extending from a detection portion of the temperature detection member in a recording material width direction perpendicular to the recording material transport direction are arranged side by side in the recording material transport direction, and the upstream conductive support portion of the temperature detection member The recording medium conveying direction is arranged upstream of the recording medium conveying direction. Facing exposed conductive parts Open The mouth is provided The downstream conductive support portion has an opening at a position facing the exposed conductive portion of the temperature detection member that is disposed downstream in the recording material conveying direction. It is characterized by the fact that Effect of the Invention

[0006] According to the present invention, even if the conductive support member is made smaller in size in order to reduce the size of the fixing member, the temperature detection member can properly detect the temperature, and the fixing device can operate properly. [Brief description of the drawings]

[0007] [Figure 1] FIG. 1 is a schematic configuration diagram of a printer according to an embodiment. [Diagram 2] FIG. 2 is an explanatory diagram showing the configuration of a fixing device of the printer. [Diagram 3] FIG. 4 is an explanatory diagram showing the fixing device in an exploded state with a fixing belt removed. [Figure 4] FIG. 2 is a perspective view showing a belt module in the fixing device. [Diagram 5] FIG. 4 is an explanatory diagram showing the belt module in an exploded state (with the fixing belt removed). [Figure 6] FIG. 2 is an explanatory diagram showing an example of the configuration of a heater (in a state where an overcoat layer is formed) in the fixing device. [Figure 7] FIG. 4 is an explanatory diagram showing another example of the configuration of the heater (in a state where an overcoat layer is formed) in the fixing device. [Figure 8] 2 is a schematic diagram showing an internal configuration of a fixing belt in the fixing device. [Figure 9]1A is a perspective view showing an example of a thermostat in an identification device, and FIG. 1B is an explanatory diagram of the thermostat disposed in the internal space of the stay, as viewed from the detection unit side of the thermostat. [Figure 10] 1A is a side view showing the thermostat before and after it has been disposed in the internal space of the stay, and FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] Hereinafter, an embodiment in which the present invention is applied to a printer, which is an electrophotographic image forming apparatus, will be described. The image forming apparatus may be a printer, a copier, a facsimile, or a combination machine of these. In the present embodiment, a one-drum type image forming apparatus having one photosensitive drum is described, but a tandem type image forming apparatus having multiple photosensitive drums may be used. In the present embodiment, a direct transfer type image forming apparatus in which an image is directly transferred from a photosensitive drum to a sheet is described, but an intermediate transfer type image forming apparatus in which an image is directly transferred from a photosensitive drum to a sheet via an intermediate transfer body may be used.

[0009] FIG. 1 is a schematic diagram of a printer according to this embodiment. The printer of this embodiment includes a paper feeder 4, a pair of registration rollers 6, a photosensitive drum 8 as an image carrier, a transfer device 10, a fixing device 30, etc. The paper feeder 4 includes a paper feed tray 14 in which paper sheets P are stored in a stacked state, and a paper feed roller 16 that separates and sends out the paper sheets stored in the paper feed tray 14 one by one starting from the top sheet. The paper sheets P sent out by the paper feed roller 16 are temporarily stopped by the pair of registration rollers 6, and their positional deviation is corrected. The paper sheets P are then sent to the transfer nip N by the pair of registration rollers 6 at a timing synchronized with the rotation of the photosensitive drum 8, i.e., at a timing when the leading edge of the toner image formed on the photosensitive drum 8 coincides with a predetermined position of the leading edge of the paper sheets P in the transport direction.

[0010] Around the photosensitive drum 8, in the order of the rotation direction indicated by the arrow in the figure, there are arranged a charging roller 18 as a charging means, a mirror 20 constituting a part of an exposure device as a latent image forming means, a developing device 22 as a developing means having a developing roller 22a, a transfer device 10 as a transfer means, and a cleaning device 24 as a cleaning means having a cleaning blade 24a. The exposure light Lb irradiated via the mirror 20 is irradiated to an exposure portion 26 on the photosensitive drum 8 located between the charging roller 18 and the developing device 22, and is scanned.

[0011] When the photoconductor drum 8 starts to rotate, the surface of the photoconductor drum 8 is uniformly charged by the charging roller 18, and the exposure light Lb is irradiated and scanned by the exposure unit 26 based on the image information. As a result, an electrostatic latent image corresponding to the image information is formed on the surface of the photoconductor drum 8. This electrostatic latent image is moved to the developing device 22 by the rotation of the photoconductor drum 8, where toner is supplied and the electrostatic latent image is made visible, forming a toner image.

[0012] The toner image formed on the photosensitive drum 8 is transferred onto the paper P that has entered the transfer nip N at a predetermined timing by the application of a transfer bias by the transfer device 10. The paper P carrying the toner image is then transported toward the fixing device 30, where the toner image is fixed, and then discharged and stacked on a paper output tray.

[0013] Residual toner remaining on the photosensitive drum 8 that has not been transferred at the transfer nip N reaches the cleaning device 24 as the photosensitive drum 8 rotates, and is scraped off and cleaned by the cleaning blade 24a while passing through the cleaning device 24. Thereafter, the residual potential on the photosensitive drum 8 is removed by a charge removing means, and the photosensitive drum 8 is prepared for the next image forming process.

[0014] Next, the configuration and operation of the fixing device 30 of this embodiment will be described. FIG. 2 is an explanatory diagram showing the configuration of the fixing device 30 of the present embodiment. FIG. 3 is an explanatory diagram showing the fixing device 30 of this embodiment in an exploded state with the fixing belt removed.

[0015] 2, the fixing device 30 of this embodiment includes an endless fixing belt 31 as a fixing member, and a pressure roller 32 as an opposing member that forms a fixing nip SN between the fixing belt 31 and the pressure roller 32. The fixing device 30 has a first frame 30A and a second frame 30B that are joined to each other by screws or the like, and the fixing belt 31 and the pressure roller 32 are disposed within these frames 30A and 30B.

[0016] 3, the first frame 30A is composed of two side plates that support both end portions 32f of the core metal 32a of the pressure roller 32, and a bridge plate that connects these side plates. This first frame 30A may be formed by bending a single sheet of metal, or the two side plates and the bridge plate may be separate parts that are fastened together with screws or the like.

[0017] As shown in Fig. 3, each side plate of the first frame 30A has a notch 30a into which each end 32f of the core metal 32a of the pressure roller 32 is inserted, and a pressure bearing 32d made of a sliding bearing is fitted into these notches 30a. In this embodiment, the pressure bearing 32d is a sliding bearing, but it may be a ball bearing. As shown in Fig. 3, a pressure gear 32e is provided at one end of the pressure roller 32. The pressure gear 32e is connected to a drive gear provided on the printer body side and is driven to rotate.

[0018] In the fixing device 30, the pressure roller 32 is inserted into the notch 30a of the first frame 30A, and each end 32f of the core metal 32a of the pressure roller 32 is fitted into the pressure bearing 32d. This allows the pressure roller 32 to be rotatably supported by the first frame 30A. Following the pressure roller 32, a belt module including the fixing belt 31 is inserted into the notch 30a of the first frame 30A. Thereafter, the second frame 30B is placed on the first frame 30A so as to close the entrance of the notch 30a, and the first frame 30A and the second frame 30B are fastened together.

[0019] 3, a pressure spring (compression spring) 35 is provided as a biasing means between the second frame 30B and the belt module. The biasing force of the pressure spring 35 biases the belt module (fixing belt 31) toward the pressure roller 32, thereby forming a fixing nip between the fixing belt 31 and the pressure roller 32. The pressure spring 35 may bias the belt module directly, or may bias the belt module via a lever member. By interposing a lever member, a large pressure force can be obtained even with a weak biasing force due to the principle of leverage.

[0020] FIG. 4 is a perspective view showing a belt module in the fixing device 30 of the present embodiment. FIG. 5 is an explanatory diagram showing the belt module of the present embodiment in an exploded state (with the fixing belt removed). The belt module of this embodiment includes a heater holder 36, a heater 37 held by the heater holder 36, left and right flanges 38 provided at both ends of the belt module, and a stay 33 supporting the heater holder 36, all on the inner side (hollow portion) of the fixing belt 31.

[0021] As shown in FIG. 5, the heater holder 36 has a recess having substantially the same outer shape as the heater 37, and the heater 37 is fitted into the recess. The heater holder 36 is likely to become hot because it comes into contact with the heater 37, and is preferably made of a heat-resistant material. In addition, the heater holder 36 is preferably insulating and has as low a thermal conductivity as possible. Therefore, the heater holder 36 is preferably made of a heat-resistant resin material such as LCP or PEEK. If the heater holder 36 is made of such a heat-resistant resin, the heat transfer from the heater 37 to the heater holder 36 can be suppressed, and the heat from the heater 37 can be efficiently transferred to the fixing belt 31.

[0022] The stay 33 supports the back surface of the heater holder 36 (the surface opposite to the surface on which the heater 37 is arranged) and is a member having higher rigidity than the heater holder 36. As shown in FIG. 2, both ends of the stay 33 are supported by notches 30a provided in each side plate of the first frame 30A. The stay 33 firmly receives the pressing force from the pressure roller 32 and supports the heater holder 36 so that the heater holder 36 does not bend due to the pressing force. As a result, the belt portion of the fixing nip SN of the fixing belt 31 is supported by the stay 33 via the heater holder 36, and the fixing nip SN with the desired pressure can be formed.

[0023] 5, the stay 33 of this embodiment is composed of an upstream leg 33a arranged on the upstream side in the transport direction of the paper P, a downstream leg 33b arranged on the downstream side in the transport direction of the paper P, and a connecting portion 33c connecting these legs 33a and 33b. The stay 33 is formed, for example, by bending a single sheet metal so that the cross section perpendicular to the longitudinal direction has a U-shape. The stay 33 is arranged so that the tip of the upstream leg 33a and the tip of the downstream leg 33b abut against the back surface of the heater holder 36 over the longitudinal direction, and supports the heater holder 36 so that the heater holder 36 does not bend due to the pressing force from the pressure roller 32.

[0024] Flanges 38 provided at both ends of the belt module abut against the inner circumferential surface near both sides of the fixing belt 31 to support the fixing belt 31. In addition, when the fixing belt 31 meanders while it runs (rotationally drives), the flanges 38 abut against both sides of the fixing belt 31 to regulate the belt meandering.

[0025] In the belt module of this embodiment, the heater 37 and the heater holder 36, the heater holder 36 and the left flange 38, and the left flange 38 and the first frame 30A have positioning shapes for positioning them relative to each other in the longitudinal direction. The stay 33 fits into the left and right flanges 38 with some play (backlash). The right flange 38 is not provided with a positioning shape for the heater holder 36. This is to prevent the heater holder 36 from being strained even if it thermally expands relative to the first frame 30A.

[0026] FIG. 6 is an explanatory diagram showing an example of the configuration of the heater 37 (with an overcoat layer 39 formed) in this embodiment. FIG. 7 is an explanatory diagram showing another example of the configuration of the heater 37 (with an overcoat layer 39 formed) in this embodiment. The heater 37 of this embodiment includes heating element patterns 37a1 to 37a8 arranged on a heater base material 37b, a conductor pattern 37d having a resistance value smaller than that of the heating element patterns, and electrodes 37e and 37f. An overcoat layer 39, which is an insulating layer, is formed on the heater 37 so as to cover these elements.

[0027] As the material of the heater base material 37b, ceramics such as alumina and aluminum nitride, glass, mica, etc., which have excellent heat resistance and insulation, are preferable. Alternatively, an insulating material may be laminated on a conductive material such as metal. Among them, aluminum and stainless steel are preferable in terms of cost. Furthermore, materials with high thermal conductivity such as copper, graphite, and graphene can uniformize the temperature of the entire heater due to their high thermal conductivity, and are therefore more preferable in terms of improving image quality by improving fixing uniformity. For example, an alumina base material with a short side length of 8 mm, a long side length of 270 mm, and a thickness of 1.0 mm is used for the heater base material 37b of this embodiment.

[0028] The heating element patterns 37a1-37a8 are formed by, for example, applying a paste made of silver palladium (AgPd) and glass powder by screen printing or the like, and then firing the paste. The heating element patterns 37a1-37a8 are each set to have a resistance value of 80Ω at room temperature. The heating element patterns 37a1-37a8 may be made of a resistive material such as a silver alloy (AgPt) or ruthenium oxide (RuO2) in addition to the above-mentioned materials. The heating element patterns 37a1-37a8 of this embodiment are formed by screen printing the conductor pattern 37d and the electrodes 37e and 37f with silver (Ag) or silver palladium (AgPd), for example.

[0029] The overcoat layer 39 may be made of heat-resistant glass having a thickness of 75 μm. The overcoat layer 39 is formed to cover the heating element patterns 37a1-37a8 and the conductor pattern 37d on the heater base material 37b, and ensures insulation between the heating element patterns 37a1-37a8 and the heater surface. The overcoat layer 39 also ensures sliding performance with the inner circumferential surface of the fixing belt 31.

[0030] The heater 37 contacts and heats the fixing belt 31 on the overcoat layer 39 side, and increases the temperature of the fixing belt 31 by heat transfer.

[0031] As shown in Fig. 6 and Fig. 7, the heating element patterns 37a1-37a8 are divided in the longitudinal direction and electrically connected in parallel. The heating element patterns 37a1-37a8 are made of a material with a PTC (positive temperature coefficient of resistance) characteristic, and are characterized in that the resistance value increases (the heater output decreases) as the temperature increases. When fixing a paper P narrower than the range of the heating element patterns 37a1-37a8, the temperature increases in the heating element pattern portion on the outer side of the paper in the paper width direction (outside the heater 37 in the longitudinal direction) because the paper does not take heat, and the resistance value increases due to the above-mentioned characteristics. At this time, since the voltage applied to the heating element patterns 37a1-37a8 is constant, the output of the heating element pattern portion on the outer side of the paper decreases relatively, and the temperature increase in the heating element pattern portion is suppressed.

[0032] When the heating element patterns 37a1 to 37a8 are electrically connected in series, it becomes necessary to slow down the image formation speed (printing speed) during continuous image formation in order to suppress the temperature rise of the heating element pattern portion facing the outer side of the paper in the paper width direction. In contrast, by adopting the configuration of this embodiment, it becomes unnecessary to slow down the image formation speed in order to suppress the temperature rise of the heating element pattern portion, and productivity can be improved.

[0033] Furthermore, when the heating element patterns 37a1 to 37a8 are arranged in parallel in the longitudinal direction, it is necessary to provide a distance between the heating elements to ensure insulation between the heating elements, and the amount of heat generated decreases in the areas between the heating elements. Therefore, as shown in Fig. 6 and Fig. 7, it is preferable to arrange the heating element patterns so as to overlap each other in the longitudinal direction, thereby suppressing partial reduction in the amount of heat generated in the longitudinal direction.

[0034] The heat generating patterns 37a1 to 37a8 may be formed by folding back the heat generating material so as to obtain a desired output (resistance value).

[0035] The fixing device 30 of this embodiment will be described in further detail below. FIG. 8 is a schematic diagram showing the internal configuration of fixing belt 31 in fixing device 30 of the present embodiment. The fixing device 30 of this embodiment includes an endless fixing belt 31 as a fixing member, and a pressure roller 32 as an opposing member that forms a fixing nip SN between the fixing belt 31 and itself.

[0036] The fixing belt 31 is a member that heats and fixes a toner image (image) to a paper P. The fixing belt 31 of this embodiment has an outer diameter of 25 mm and a hollow base made of polyimide (PI) with a thickness of 40 μm to 120 μm. In order to increase durability and ensure releasability, a release layer made of fluorine-based resin such as PFA or PTFE with a thickness of 5 μm to 50 μm is formed on the outermost layer of the fixing belt 31. An elastic layer made of rubber or the like with a thickness of 50 μm to 500 μm may be provided between the base and the release layer. The base of the fixing belt 31 is not limited to polyimide, and may be a heat-resistant resin such as PEEK, or a metal base such as nickel (Ni) or SUS. In addition, a layer of polyimide, PTFE, or the like may be provided as a sliding layer on the inner peripheral surface of the fixing belt 31.

[0037] The pressure roller 32 of this embodiment has an outer diameter of 25 mm and is composed of a solid iron core 32a, an elastic layer 32b formed on the surface of the core 32a, and a release layer 32c which is the outermost layer. The elastic layer 32b is made of, for example, silicone rubber and has a thickness of, for example, 3.5 mm. The release layer 32c formed on the surface side of the elastic layer 32b can be a fluororesin layer having a thickness of, for example, about 40 μm in order to improve releasability.

[0038] As shown in FIG. 2, the heater holder is in contact with the rear surface of the heater base material 37b at two points that avoid the heating element patterns 37a1 to 37a8, thereby suppressing heat transfer from the heater 37 to the heater holder .

[0039] 8, in the fixing device 30 of this embodiment, a thermistor 34 serving as a temperature detection unit for detecting the temperature of the heater 37 is disposed inside the heater holder 36. Specifically, the thermistor 34 is disposed on the rear surface side (the surface opposite to the surface on which the heating element patterns 37a1-37a8 are disposed) of the heater base material 37b of the heater 37. The detected temperature of the thermistor 34 is sent to the temperature control unit 50.

[0040] The temperature control unit 50 controls a heater power supply 51 that supplies power to the heater 37 in accordance with the temperature detected by the thermistor 34, and performs fixing temperature control so that the temperature of the fixing belt 31 becomes a target temperature. The temperature control unit 50 can be configured by a microcomputer including a CPU, ROM, RAM, an I / O interface, etc. The temperature control unit 50 may control the temperature based only on the temperature detected by the thermistor 34, but may also take other parameters into consideration.

[0041] 8, the fixing device 30 of this embodiment also includes a thermostat 40 as another temperature detection member for detecting the temperature of the heater 37. The thermostat 40 is disposed in the internal space of the stay 33 (the space surrounded by the upstream leg 33a, downstream leg 33b, and connecting portion 33c of the stay 33 and the rear surface of the heater holder 36). The thermostat 40 is positioned in the longitudinal direction by fitting a detection portion 40a for detecting the temperature into an opening 36a provided in the heater holder 36. The thermostat 40 is positioned in the paper transport direction by sandwiching the thermostat 40 between the upstream leg 33a and downstream leg 33b of the stay 33.

[0042] Thermostat 40 is connected on the power path from heater power supply 51 to heater 37, and when the temperature of heater 37 rises above a predetermined upper limit temperature, thermostat 40 detects this and switches off the power supply from heater power supply 51 to heater 37. This controls the temperature of heater 37 so that it does not exceed the predetermined upper limit temperature, ensuring safety.

[0043] In order to reduce the size of the fixing belt 31, it is necessary to reduce the size of the stay 33, which is a conductive support member disposed in the hollow portion (the space surrounded by the inner circumferential surface of the endless fixing belt 31) of the fixing belt 31. If the dimensions of the stay 33 in the paper conveyance direction (the left-right direction in FIG. 8) and the pressure direction of the fixing nip (the up-down direction in FIG. 8) can be reduced, the circumferential length of the fixing belt 31 can be shortened, and the fixing belt 31 can be reduced in size.

[0044] 9(a) and 9(b), the thermostat 40 is usually configured such that the detection unit 40a and the two terminals 40b are exposed to the outside. As shown in FIG. 9(b), the thermostat 40 is installed in the internal space of the stay 33 with the wiring 40c connected to the two terminals 40b by soldering or the like. At this time, the two terminals 40b of the thermostat 40 are conductors and exposed, and therefore form exposed conductive parts.

[0045] Since such a thermostat 40 is disposed in the internal space of the stay 33, when the stay 33, which is a conductive support member, is made smaller, the distance between the exposed conductive portion (terminal 40b) of the thermostat 40 and the opposing portion of the stay 33 is shortened. For example, in the case of this embodiment, the distance between the upstream leg 33a and the downstream leg 33b of the stay 33 is narrowed to make the dimension of the stay 33 smaller in the paper conveying direction. In this case, as shown in FIG. 9(b), the distance L between the exposed conductive portion (terminal 40b) of the thermostat 40 and the opposing upstream leg 33a and downstream leg 33b of the stay 33 is shortened. In particular, when the thermostat 40 is sandwiched between the upstream leg 33a and downstream leg 33b of the stay 33, the exposed conductive portion (terminal 40b) of the thermostat 40 and the upstream leg 33a and downstream leg 33b of the stay 33 are closest to each other, and the distance L is very short.

[0046] Therefore, when the stay 33 is made smaller, a short circuit or the like is more likely to occur between the stay 33 and the exposed conductive portion (terminal 40b) of the thermostat 40, making it difficult for the thermostat 40 to properly detect the temperature. As a result, there is a risk that proper operation of the fixing device 30 (such as an operation of controlling the temperature so that the heater 37 does not exceed a predetermined upper limit temperature) may be hindered.

[0047] It is also possible to prevent the occurrence of the above-mentioned short circuit by interposing an insulating member between the exposed conductive portion (terminal 40b) of thermostat 40 and the opposing portion of stay 33. However, the thickness of the insulating member impedes the miniaturization of stay 33, and therefore the demand for miniaturization cannot be fully met.

[0048] 10(a) and 10(b), in this embodiment, openings 33d are provided in the locations of the stay 33 that face the exposed conductive portion (terminal 40b) of the thermostat 40. Specifically, when the thermostat 40 is installed in the internal space of the stay 33, openings 33d are provided in the upstream leg 33a and the downstream leg 33b of the stay 33 at locations that face the exposed conductive portion (terminal 40b) of the thermostat 40.

[0049] Providing such an opening 33d makes it possible to increase the distance (closest distance) between the exposed conductive portion (terminal 40b) of the thermostat 40 and the stay 33 even if the stay 33 is made compact. Therefore, even if the stay 33 is made compact, the occurrence of the above-mentioned short circuit can be suppressed.

[0050] Note that, here, the opening 33d which is a through hole is provided at the location of the stay 33 facing the exposed conductive portion (terminal 40b) of the thermostat 40, but this is not limiting, and for example, a recess may be provided at the opposing location. Specifically, when the thermostat 40 is installed in the internal space of the stay 33, recesses (dents) may be provided in the inner wall surface portions of the upstream leg 33a and downstream leg 33b of the stay 33 which face the exposed conductive portion (terminal 40b) of the thermostat 40.

[0051] In addition, in the present embodiment, the distance between the upstream leg 33a and the downstream leg 33b of the stay 33 is narrowed to reduce the dimension of the stay 33 in the paper transport direction, but the present invention is not limited to this. For example, the height (length in the pressure direction of the fixing nip) of the upstream leg 33a and the downstream leg 33b of the stay 33 may be shortened to reduce the dimension of the stay 33 in the pressure direction of the fixing nip. In this example, the connecting portion 33c of the stay 33 is close to the exposed conductive portion (terminal 40b) of the thermostat 40, so the opening 33d is provided in the connecting portion 33c.

[0052] In this embodiment, the opening 33d is provided in both the upstream leg 33a and the downstream leg 33b of the stay 33, but the opening 33d may be provided in only one of the legs 33a, 33b. For example, there may be a case where the thermostat 40 is arranged offset toward the upstream or downstream side in the paper transport direction in the internal space of the stay 33, or where the exposed conductive portion (terminal 40b) of the thermostat 40 is offset toward the upstream or downstream side in the paper transport direction. In this case, the opening 33d may be provided only in the leg 33a, 33b that is closer to the exposed conductive portion (terminal 40b) of the thermostat 40.

[0053] In this embodiment, the temperature detection member disposed in the internal space of the stay 33 is a thermostat 40 that is provided separately from the thermistor 34 for controlling the fixing temperature to a target temperature and is used to control the power supply to the heater 37 to be turned off when the upper limit temperature is exceeded. However, the temperature detection member disposed in the internal space of the stay 33 may be a temperature detection member used to control the fixing temperature to a target temperature.

[0054] The opening 33d in this embodiment may have any size and shape that can ensure a sufficient distance (closest distance) between the exposed conductive portion (terminal 40b) of the thermostat 40 and the stay 33 so that a short circuit or the like does not occur. However, when the opening 33d is provided with a function other than the function of preventing a short circuit or the like, the opening 33d may have a size larger than necessary or a shape different from necessary depending on the other function. Examples of the other function include a recess or opening that is used only when manufacturing the stay 33, a viewing window for viewing the thermostat 40 arranged in the internal space of the stay 33 from the outside of the stay 33, and a hole opened for weight reduction.

[0055] The above description is merely an example, and each of the following aspects provides unique effects. [First aspect] The first aspect is a fixing device 30 including a hollow fixing member (e.g., fixing belt 31) that heats and fixes an image onto a recording material (e.g., paper P), an opposing member (e.g., pressure roller 32) that forms a fixing nip between the fixing member, a conductive support member (e.g., stay 33) that is disposed in the hollow portion of the fixing member and supports the fixing nip portion of the fixing member, and a temperature detection member (e.g., thermostat 40) that detects temperature, wherein the conductive support member is provided with a recess or opening 33d at a position facing an exposed conductive portion (e.g., terminal 40b) of the temperature detection member. In a conventional fixing device, when the conductive support member disposed in the hollow portion of the fixing member is made smaller in size in order to make the fixing member smaller, the distance between the exposed conductive portion of the temperature detection member and the facing portion of the conductive support member facing it may become shorter. For example, when the temperature detection member is disposed inside the conductive support member, the closer the conductive support member is to the smaller the conductive support member, the shorter the closest distance between the exposed conductive portion of the temperature detection member and the conductive support member may become. Therefore, when the conductive support member is made smaller, a short circuit or the like is more likely to occur between the conductive support member and the exposed conductive portion of the temperature detection member, making it difficult for the temperature detection member to detect the temperature properly, and there is a risk that the proper operation of the fixing device may be hindered. In this case, if an insulating member is interposed between the exposed conductive portion of the temperature detection member and the facing portion of the conductive support member facing it, the occurrence of the above-mentioned short circuit or the like can be suppressed. However, the thickness of the insulating member hinders the miniaturization of the conductive support member, and therefore the demand for miniaturization cannot be fully met. In this embodiment, by providing a recess or an opening at the portion of the conductive support member facing the exposed conductive portion of the temperature detection member, the closest distance between the exposed conductive portion of the temperature detection member and the conductive support member can be made long even if the conductive support member is made small. Therefore, even if the conductive support member is made small, the occurrence of the above-mentioned short circuit is suppressed. Therefore, even if the conductive support member is made small in order to make the fixing member small, the temperature detection member can properly detect the temperature, and the fixing device can be operated properly.

[0056] [Second aspect] The second aspect is characterized in that, in the first aspect, the conductive support member comprises an upstream conductive support portion (e.g., upstream leg portion 33a) arranged upstream in the transport direction of the recording material, and a downstream conductive support portion (e.g., downstream leg portion 33b) arranged downstream in the transport direction, and the recess or the opening is provided in at least one of the upstream conductive support portion and the downstream conductive support portion. According to this, even if the length of the conductive support member in the recording material transport direction is shortened to make the conductive support member smaller, temperature detection by the temperature detection member can be performed properly, and the fixing device can be operated properly.

[0057] [Third aspect] A third aspect is characterized in that in the second aspect, the temperature detection member has the recess or the opening only in one of the upstream conductive support part and the downstream conductive support part, which is closer to the temperature detection member. This allows the number of recesses or openings to be formed in the conductive supporting member to be reduced.

[0058] [Fourth aspect] A fourth aspect is characterized in that in any one of the first to third aspects, the exposed conductive portion is a terminal portion (for example, terminal 40b) of the temperature detection member. According to this, even if the conductive support member is made smaller, it is possible to prevent a short circuit or the like from occurring between the terminal portion of the temperature detection member and the conductive support member.

[0059] [Fifth aspect] A fifth aspect is characterized in that in any one of the first to fourth aspects, the temperature detection member is a thermostat 40. Since the thermostat 40 has a relatively large dimension compared to other temperature detection members such as the thermistor 34, if the conductive support member in which it is placed is made smaller, a short circuit or the like is likely to occur between the conductive support member and the exposed conductive portion of the temperature detection member. Therefore, according to this embodiment, even if the temperature detection member is such a thermostat, it is possible to prevent a short circuit or the like from occurring between the terminal portion of the temperature detection member and the conductive support member.

[0060] [Sixth aspect] The sixth aspect is characterized in that in any of the first to fifth aspects, the recess or the opening is at least one of a recess or opening used during manufacturing, a viewing window for viewing the temperature detection member from the outside, and a hole opened for weight reduction. According to this, the recess or opening for preventing the occurrence of a short circuit or the like between the terminal portion of the temperature detection member and the conductive support member can also be used for other purposes.

[0061] [Seventh aspect] A seventh aspect is an image forming apparatus equipped with a fixing means for fixing an image formed on a recording material onto the recording material, characterized in that the fixing means is a fixing device according to any one of the first to sixth aspects. This makes it possible to provide an image forming apparatus in which the fixing device is miniaturized while still allowing the fixing device to operate properly. [Explanation of symbols]

[0062] 4: Paper feeder 6: Registration roller pair 8: Photoconductor drum 10: Transfer device 30: Fixing device 30A: First frame 30B: Second frame 30a: Notch 31: Fixing belt 32: Pressure roller 33: Stay 33a: Upstream leg 33b: Downstream leg 33c: Connecting part 33d: Opening 34: Thermistor 35: Pressure spring 36: Heater holder 36a: Opening 37: Heater 37a1~37a8: Heating element pattern 37b: Heater substrate 37d: Conductor pattern 37e,37f: Electrode 38: Flange 39: Overcoat layer 40: Thermostat 40a: Detection unit 40b: Terminal 40c: Wiring 50: Temperature control unit 51: Heater power supply 52: Switch [Prior art documents] [Patent documents]

[0063] [Patent Document 1] JP 2020-098311 A

Claims

1. a hollow fixing member that heats and fixes an image onto a recording material; a facing member that forms a fixing nip between the facing member and the facing member; a conductive support member disposed in the hollow portion of the fixing member and supporting a fixing nip portion of the fixing member; A fixing device including a temperature detection member that detects a temperature, the conductive support member includes an upstream conductive support portion disposed on the upstream side in a recording material transport direction and a downstream conductive support portion disposed on the downstream side in the recording material transport direction, the temperature detection member is disposed between the upstream-side conductive support portion and the downstream-side conductive support portion, and has a configuration in which two exposed conductive portions extending from a detection portion of the temperature detection member in a recording material width direction perpendicular to a recording material transport direction are arranged side by side in the recording material transport direction, an opening is provided in the upstream conductive support portion at a position facing an exposed conductive portion of the temperature detection member that is disposed upstream in a recording material conveying direction; a fixing device, wherein the downstream conductive support portion is provided with an opening at a position facing an exposed conductive portion of the temperature detection member that is disposed downstream in a recording material transport direction;

2. In the fixing device according to claim 1, The fixing device, wherein the exposed conductive portion is a terminal portion of the temperature detection member.

3. 3. The fixing device according to claim 1, The fixing device, wherein the temperature detection member is a thermostat.

4. 4. The fixing device according to claim 1, The opening is at least one of an opening used during manufacturing, a viewing window for viewing the temperature detection member from the outside, and a hole formed for weight reduction.

5. An image forming apparatus including a fixing unit for fixing an image formed on a recording material onto the recording material, 5. An image forming apparatus comprising the fixing device according to claim 1 as said fixing means.

Images