Image forming apparatus

Abstract

To improve productivity and prevent attachment of toner to a cover to prevent the occurrence of paper jam or dirt on an image.SOLUTION: An image forming apparatus E has: an image heating device A1 including a fixing belt 1, a pressure roller 2 that is in contact with the fixing belt 1 to form a nip part N, and a cover 8 that is provided extending in an axial direction of the pressure roller 2 and covers the fixing belt 1 in a circumferential direction; and a sheet detection member having an inlet flag 10 that is in contact with a back face Sb of a sheet S, and an urging unit 30 that urges the inlet flag 10 from the back face Sb toward a front face Sf. The cover 8 includes a recess 8a that is provided recessed to separate from the inlet flag 10 in an urging direction F5 in which the urging unit 30 urges the inlet flag from the back face Sb to the front face Sf.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to an image forming apparatus such as a copying machine, a printer, a fax machine, or a multifunction machine having a plurality of these functions, which is provided with an image heating device that heats an image formed on a sheet. [Background technology]

[0002] Conventionally, in image forming devices such as electrophotographic devices or electrostatic recording devices, an unfixed toner image is formed on a sheet, and the formed toner image is heated and pressurized by an image heating device (fixing device), thereby fixing the toner image to the sheet.

[0003] Patent Document 1 discloses an image forming apparatus that includes a slack sensor for detecting slack in a sheet at the entrance side where a sheet on which an unfixed toner image is formed enters a fixing device. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2016-161703 A Summary of the Invention [Problem to be solved by the invention]

[0005] A configuration is known in which a sensor is disposed upstream of the fixing device in the sheet conveying direction, as in the fixing device of Patent Document 1. In addition, in order to improve the productivity of the image forming device, it is important that the heat of the fixing device is efficiently applied to the sheet. Therefore, a configuration has been proposed in which the image forming device is provided with a cover that prevents the heat of the heating rotor from diffusing to the surroundings and escaping. In an image forming apparatus using the above-mentioned sensor and cover, the sensor may come into contact with a sheet, causing unfixed toner on the sheet to adhere to the cover. If this occurs repeatedly, the toner may accumulate on the cover, causing paper jams or image stains.

[0006] An object of the present invention is to provide an image forming apparatus capable of improving productivity and suppressing the occurrence of sheet jams or image stains by suppressing adhesion of toner to the cover. [Means for solving the problem]

[0007] The image forming apparatus of the present invention is an image forming apparatus that forms an image on a sheet, and is equipped with a heating rotor that heats an unfixed toner image on a sheet, a pressure rotor that forms a nip portion by abutting with the heating rotor, and a cover extending in the axial direction of the pressure rotor and covering the circumferential direction of the heating rotor, and is characterized in that the image forming apparatus has a fixing device that fixes the unfixed toner image on the sheet to the sheet, and a sheet detection member that is arranged upstream of the nip portion in the sheet conveying direction and detects the sheet, wherein the sheet detection member has an abutment portion that abuts against the back surface of the sheet when the surface of the sheet that contacts the heating rotor at the nip portion is the front surface and the surface of the sheet that contacts the pressure rotor at the nip portion is the back surface, and a biasing portion that biases the abutment portion from the back surface toward the front surface, and the cover has a recess that is recessed so as to move away from the abutment portion in the biasing direction in which the biasing portion biases from the back surface to the front surface. Effect of the Invention

[0008] According to the present invention, it is possible to improve productivity, and also to suppress the occurrence of sheet clogging or image stains by suppressing adhesion of toner to the cover. [Brief description of the drawings]

[0009] [Figure 1] 1 is a schematic diagram of an image forming apparatus according to a first embodiment of the present invention. [Diagram 2] 1 is a schematic cross-sectional view of an image heating device of an image forming apparatus according to a first embodiment of the present invention. [Diagram 3]1 is a schematic front view of an image heating device of an image forming apparatus according to a first embodiment of the present invention. [Figure 4] 11 is a schematic cross-sectional view of an image heating device of an image forming apparatus according to a second embodiment of the present invention. FIG. [Diagram 5] 11 is a schematic front view of an image heating device of an image forming apparatus according to a second embodiment of the present invention. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, the embodiments will be described in detail with reference to the drawings.

[0011] (Embodiment 1) <Configuration of Image Forming Apparatus> The configuration of an image forming apparatus E according to the first embodiment of the present invention will be described in detail with reference to Fig. 1 and Fig. 2. Fig. 2 is a view of an image heating apparatus A1 seen from the same direction as Fig. 1.

[0012] The image forming apparatus E forms an image on a sheet S. Here, the sheet S is a medium on which an image is formed by the image forming apparatus E, and is, for example, regular paper, thick paper, envelopes, postcards, stickers, resin sheets, OHP film, glossy paper, etc. Examples of the image forming apparatus E here include an electrophotographic laser beam printer using an image heating device, and a tandem type intermediate transfer type full color printer.

[0013] Specifically, the image forming apparatus E includes image forming units PY, PM, PC, and PK, a sheet conveying mechanism 9, an entrance flag 10, a biasing unit 30, a secondary transfer cleaner 24T, an intermediate transfer belt 26, and primary transfer rollers 27Y, 27M, 27C, and 27K. The image forming apparatus E also includes a secondary transfer opposing roller 28, a secondary transfer roller 29, a cassette 31, a feed roller 32, a registration roller 33, and an image heating device A1. Here, the entrance flag 10 and the biasing unit 30 constitute a sheet detection member that detects the sheet S. Note that the sheet conveying mechanism 9, the entrance flag 10, and the biasing unit 30 are omitted from FIG. 1.

[0014] The image forming units PY, PM, PC, and PK are arranged along the intermediate transfer belt 26. The image forming unit PY forms a yellow image. The image forming unit PM forms a magenta image. The image forming unit PC forms a cyan image. The image forming unit PK forms a black image. The image forming units PY, PM, PC, and PK each include photosensitive drums 21Y, 21M, 21C, and 21K, and charging rollers 22Y, 22M, 22C, and 22K. The image forming units PY, PM, PC, and PK each include developing devices 23Y, 23M, 23C, and 23K, cleaners 24Y, 24M, 24C, and 24K, and exposure devices 25Y, 25M, 25C, and 25K.

[0015] The photosensitive drums 21Y, 21M, 21C, and 21K are rotated by a driving force from a driving source (not shown).

[0016] The charging rollers 22Y, 22M, 22C, and 22K uniformly charge the surfaces of the photosensitive drums 21Y, 21M, 21C, and 21K.

[0017] The developing devices 23Y, 23M, 23C, and 23K develop the electrostatic images written on the photosensitive drums 21Y, 21M, 21C, and 21K to form toner images on the photosensitive drums 21Y, 21M, 21C, and 21K.

[0018] The cleaners 24Y, 24M, 24C, and 24K remove the residual toner from the surfaces of the photosensitive drums 21Y, 21M, 21C, and 21K.

[0019] The exposure devices 25Y, 25M, 25C, and 25K irradiate and scan the photosensitive drums 21Y, 21M, 21C, and 21K with a laser beam, thereby writing electrostatic images of images onto the uniformly charged photosensitive drums 21Y, 21M, 21C, and 21K.

[0020] The sheet conveying mechanism 9 conveys the sheet S conveyed by the secondary transfer opposing roller 28 and the secondary transfer roller 29 to the image heating device A1.

[0021] The entrance flag 10, which serves as a contact portion, is provided between the sheet conveying mechanism 9 and the image heating device A1, and is disposed upstream of the nip portion N of the image heating device A1, which will be described later, in the conveying direction of the sheet S (hereinafter simply referred to as the "conveying direction").

[0022] When the sheet S is not passing through, the entrance flag 10 is biased by the biasing unit 30 to be in a first position shown by a solid line in Fig. 2. When the sheet S is passing through, the entrance flag 10 abuts against the sheet S and is pressed by the sheet S against the biasing force of the biasing unit 30 to be in a second position shown by a dashed line in Fig. 2. The entrance flag 10 is rotatable between the first position and the second position. The rotation distance Y when the entrance flag 10 rotates between the first position and the second position is exemplified as 7 mm here.

[0023] The entrance flag 10 abuts against the back surface Sb of the sheet S, where the surface of the sheet S that contacts the fixing belt 1 of the image heating device A1 at the nip portion N is defined as the front surface Sf, and the surface of the sheet S that contacts the pressure roller 2 of the image heating device A1 at the nip portion N is defined as the back surface Sb.

[0024] The urging unit 30 is disposed upstream of the nip portion N in the conveying direction, and urges the entrance flag 10, which is in contact with the back surface Sb of the sheet S, from the back surface Sb toward the front surface Sf of the sheet S. The urging unit 30 is provided outside the conveying path of the sheet S from the sheet conveying mechanism 9 to the image heating device A1.

[0025] The secondary transfer cleaner 24T collects the toner remaining on the intermediate transfer belt 26 during the secondary transfer.

[0026] An endless resin belt is used for the intermediate transfer belt 26. The intermediate transfer belt 26 is stretched around three rollers including a secondary transfer opposing roller 28. On the intermediate transfer belt 26, the toner images primarily transferred by the primary transfer rollers 27Y, 27M, 27C, and 27K are synthesized to form a toner image T.

[0027] The primary transfer rollers 27Y, 27M, 27C, and 27K transfer the toner images formed on the photosensitive drums 21Y, 21M, 21C, and 21K onto the intermediate transfer belt 26 in a multi-transfer manner and a primary transfer manner by applying a voltage thereto.

[0028] The secondary transfer opposing roller 28 and the secondary transfer roller 29, in a nip portion formed by their contact with each other, perform secondary transfer of the toner image T formed on the intermediate transfer belt 26 onto the sheet S conveyed by the registration roller 33. The secondary transfer opposing roller 28 and the secondary transfer roller 29 convey the sheet S, onto which the toner image has been secondarily transferred, to a sheet conveying mechanism 9.

[0029] The cassette 31 stores sheets S therein.

[0030] The feeding roller 32 takes out the sheets S stored in the cassette 31 one by one and feeds them to the registration rollers 33 .

[0031] The registration roller 33 temporarily holds the sheet S fed by the feed roller 32, and then conveys the sheet S to the secondary transfer opposing roller 28 and the secondary transfer roller 29 in accordance with the timing of conveying the toner image T on the intermediate transfer belt 26.

[0032] The image heating device A1 is a fixing device that uses heat to melt and fuse the unfixed toner image T transferred onto the sheet S transported by the secondary transfer opposing roller 28 and the secondary transfer roller 29 onto the sheet S, and also applies pressure to fix the toner image T onto the sheet S. The image heating device A1 transports the sheet S, on which the unfixed toner image T has been fixed, to a discharge mechanism (not shown) for discharging the sheet S outside the main body of the image forming apparatus E. The configuration of the image heating device A1 will be described in detail later.

[0033] In the image forming apparatus E having the above configuration, a control unit (not shown) detects the passing timing of the sheet S based on the detection result of an optical sensor (not shown) that detects the state of the entrance flag 10, and controls the operating speed and timing of the sheet transport mechanism 9. The control unit also detects a jam of the sheet S based on the detection result of the optical sensor.

[0034] <Configuration of image heating device> The configuration of the image heating device A1 included in the image forming apparatus E according to the first embodiment of the present invention will be described in detail with reference to Fig. 2 and Fig. 3. Fig. 3 is a view of the image heating device A1 as seen from the front (the right side of Fig. 2).

[0035] Here, the front of the image heating apparatus A1 is the surface seen from the inlet side of the image heating apparatus A1 for the sheet S, and the back of the image heating apparatus A1 is the surface seen from the outlet side of the sheet S, opposite the front. Also, the left and right of the image heating apparatus A1 are the left and right when the image heating apparatus A1 is seen from the front.

[0036] The image heating device A1 has a fixing belt 1, a pressure roller 2, a pad holder 3, a stay 4, a magnetic shielding core 5, an exciting coil 6, an outer magnetic core 7, and a cover 8.

[0037] The fixing belt 1, which serves as a heating rotator, rotates in the direction of arrow R1 in Fig. 2 (clockwise in Fig. 2) following the rotation of the pressure roller 2. The fixing belt 1 comes into contact with the pressure roller 2 to form a nip portion N together with the pressure roller 2. The fixing belt 1 conveys the sheet S, which is conveyed to the nip portion N by a sheet conveying mechanism 9, together with the pressure roller 2 from upstream to downstream in the conveying direction of the sheet S (from left to right in Fig. 2), and heats the unfixed toner image T on the sheet S.

[0038] The pressure roller 2 as a pressure rotating body rotates in the direction of the arrow R2 in Fig. 2 (counterclockwise in Fig. 2) when driven by a drive source (not shown). The pressure roller 2 conveys the sheet S conveyed to the nip portion N by the sheet conveying mechanism 9 from upstream to downstream in the conveying direction while sandwiching the sheet S together with the fixing belt 1, and pressurizes the unfixed toner image T on the sheet S.

[0039] The fixing belt 1 and the pressure roller 2 heat and pressurize the unfixed toner image T on the sheet S at the nip portion N, thereby fixing the unfixed toner image T to the sheet S.

[0040] The pad holder 3 presses the fixing belt 1 against the pressure roller 2 by a pressure force from a stay 4 .

[0041] The stay 4 applies a predetermined pressure to the fixing belt 1 via the pad holder 3 by the biasing force of a biasing member (not shown).

[0042] The magnetic shielding core 5 is disposed inside the fixing belt 1. The magnetic shielding core 5 has the same characteristics as the outer magnetic core 7. The magnetic shielding core 5 is disposed above the stay 4 along the axial direction of the fixing belt 1 (the direction perpendicular to the paper surface in FIG. 2 and the left-right direction in FIG. 3) (hereinafter simply referred to as the "axial direction"). The magnetic shielding core 5 shields the magnetic flux so that the magnetic flux that is guided by the outer magnetic core 7 and penetrates the fixing belt 1 does not act on the stay 4 and cause abnormal heating of the stay 4.

[0043] The exciting coil 6, which serves as a coil, is made of a litz wire long and shaped like a boat bottom, and is disposed along the outer circumferential surface of the fixing belt 1 so as to face the outer circumferential surface of the fixing belt 1. The exciting coil 6 is provided on a part of the circumferential direction of the fixing belt 1 between the upper side of the inlet side and the upper side of the outlet side of the sheet S of the fixing belt 1. The exciting coil 6 is spaced from the fixing belt 1 by a distance of 1.5 mm, and is also spaced apart from the fixing belt 1 by a constant distance. The exciting coil 6 generates an alternating magnetic field by passing a high-frequency current of 20 to 50 kHz by a power supply device (not shown), which induces heat in the Ni base layer of the fixing belt 1 and heats the fixing belt 1.

[0044] The outer magnetic core 7 is a member for inducing the AC magnetic field generated by the exciting coil 6 to act on the fixing belt 1 with high efficiency, and is preferably made of a material having high magnetic permeability and low residual magnetic flux density. Ferrite is exemplified here as the material for forming the outer magnetic core 7.

[0045] The cover 8 has a thickness of 0.5 mm and is made of an insulating material. The cover 8 is an insulating member that insulates the exciting coil 6 from the surroundings, and is also a heat radiation suppressing member that is provided to suppress heat radiation from the surface of the fixing belt 1 to the outside and improve thermal efficiency. The surface of the cover 8 is spaced 1.0 mm from the surface of the fixing belt 1, and is also spaced at a constant distance. The cover 8 extends in the axial direction and covers the fixing belt 1 in the circumferential direction.

[0046] The cover 8 has a recess 8a recessed at a circumferential end 8b facing the entrance flag 10 so as to be away from the entrance flag 10 in a biasing direction F5 in which the biasing unit 30 biases the entrance flag 10, which abuts against the back surface Sb of the sheet S, from the back surface Sb to the front surface Sf. The cover 8 has the recess 8a at, for example, the center of the end 8b in the axial direction. The configuration of the recess 8a will be described in detail later.

[0047] The image heating device A1 having the above configuration is a roller-driven (tensionless) fixing device in which the fixing belt 1 is rotated by the pressure roller 2. The image heating device A1 is also an induction heating fixing device in which the fixing belt 1 is directly heated from the outside by the magnetic flux from the excitation coil 6.

[0048] <Configuration and effect of the recessed part of the cover> The configuration and effect of the recess 8a of the cover 8 of the image heating device A1 of the image forming apparatus E according to the first embodiment of the present invention will be described in detail with reference to FIGS. 2 and 3. FIG.

[0049] The cover 8 has a recess 8a having a depth D1 [mm] in the direction parallel to the conveying direction and a width W1 [mm] in the axial direction. The recess 8a has a shape in which the width gradually narrows in the recessed direction. As shown in Fig. 3, the range in the axial direction in which the recess 8a is provided in the cover 8 includes the tip of the inlet flag 10 in the direction facing the recess 8a.

[0050] By providing the recess 8a at the end 8b of the cover 8 in this manner, it is possible to increase the distance between the cover 8 and the entrance flag 10. This makes it possible to prevent unfixed toner T on the sheet S, which has been flicked away by the entrance flag 10, from adhering to the cover 8, thereby making it possible to prevent toner from accumulating on the cover 8.

[0051] Here, the air flow in the image heating apparatus A1 will be described in detail.

[0052] As the fixing belt 1 and pressure roller 2 rotate, air flows in the directions of arrows F1 and F2 in Fig. 2 and Fig. 3. Note that arrows F1 and F2 in Fig. 3 indicate directions from the front side to the back side of the paper in Fig. 3 along the outer circumferential surface of the fixing belt 1 or pressure roller 2. Also, arrows F3 and F4 indicate directions from the front side to the back side of the paper in Fig. 3.

[0053] 3, the winds flowing in the directions of the arrows F1 and F2 draw in the surrounding air at both ends in the axial direction and escape to the outside in the axial direction before entering the nip portion N. On the other hand, near the conveyance entrance of the cover 8 for the sheet S, the winds flow in the directions of the arrows F3 and F4 so as to be drawn into the nip portion N.

[0054] At this time, the wind speed of the wind flowing in the direction of arrow F4 at the recess 8a so as to be drawn into the nip portion N becomes faster than the wind speed of the wind flowing in the direction of arrow F3 in the axial direction on both sides of the recess 8a (wind speed of arrow F3 < wind speed of arrow F4).

[0055] As a result, the unfixed toner T bounced off by the entrance flag 10 is less likely to stay in the recess 8a, and the adhesion of the unfixed toner T bounced off by the entrance flag 10 to the cover 8 can be suppressed. As a result, the deposition of toner on the cover 8 can be suppressed.

[0056] According to the study of the inventor, the depth D1 of the recess 8a is preferably 3 mm or more (D1≧3mm), and 5 mm is exemplified here. When the depth D1 of the recess 8a is less than 3 mm, the above effects cannot be obtained sufficiently. Also, the upper limit value of the depth D1 of the recess 8a is not particularly limited as long as the functions of the excitation coil 6, the outer magnetic core 7, and the cover 8 are not impaired and the uniformity of the temperature of the fixing belt 1 is not impaired.

[0057] Also, the width W1 of the recess 8a is preferably larger than the width X1 of the entrance flag 10 and within a range that does not significantly reduce the wind speed of the wind in the direction of arrow F4. Here, the width X1 is the axial width at the tip of the entrance flag 10 in the direction facing the cover 8. Specifically, according to the study of the inventor, the width W1 is preferably X1[mm]<W1[mm]≦X1 + 20[mm], and more preferably X1[mm]<W1[mm]≦X1 + 10[mm]. For example, when the width X1 of the entrance flag 10 is 4 mm, the width W1 of the recess 8a is 8 mm. Here, the width W1 is the width of the tip of the recess 8a in the recessed direction, which has the smallest width and gradually narrows in the recessed direction.

[0058] When W1 is less than or equal to X1, the distance between the cover 8 and the entrance flag 10 cannot be increased, so there is a possibility that the above effects cannot be obtained sufficiently. Also, when W1[mm] is larger than X1 + 20[mm], the wind speed of the recess 8a cannot be increased, so there is a possibility that the above effects cannot be obtained sufficiently.

[0059] Also, in the direction opposite to the cover 8 with respect to the entrance flag 10, the shortest distance Z1 [mm] between the entrance flag 10 located at the first position not in contact with the sheet S and the cover 8 in the case where the recess 8a is not provided is exemplified as 14 mm here. Toner deposition is likely to occur in a configuration where the distance between the cover 8 and the entrance flag 10 is short. Specifically, according to the inventor's study, it is likely to occur in a configuration where Z1 [mm] ≤ 5Y [mm]. Therefore, it is effective to provide the recess 8a in a configuration where the shortest distance Z1 [mm] is 5 times or less the rotation distance Y.

[0060] In the present embodiment, a recess 8a is provided in the cover 8 so as to be recessed away from the entrance flag 10 in the biasing direction F5 in which the biasing portion 30 biases from the back surface Sb to the front surface Sf. Thereby, productivity can be improved, and by suppressing the adhesion of toner to the cover 8, it is possible to suppress the occurrence of jamming of the sheet S or image contamination.

[0061] Also, in the present embodiment, a recess 8a is provided whose width gradually narrows in the recessed direction. Thereby, on the side opposite to the recessed direction of the recess 8a of the cover 8, the distance from the entrance flag 10 can be made sufficiently large, so that it is possible to suppress the deposition of toner on the cover 8.

[0062] In the present embodiment, the recess 8a has a width W1 such that X1 [mm] < W1 [mm] ≤ X1 + 20 [mm], but it is not limited to this, and a recess 8a having an arbitrary width W1 larger than X1 [mm] may be provided in the cover 8. Even in this case, since the distance between the cover 8 and the entrance flag 10 can be increased, it is possible to suppress the deposition of toner.

[0063] Also, in the present embodiment, a recess 8a whose width gradually narrows in the recessed direction is provided, but it is not limited to this, and a recess having the same width in the recessed direction may be provided, or a recess having an arbitrary shape may be provided.

[0064] (Embodiment 2) The configuration of the image forming apparatus according to the second embodiment of the present invention is the same as that shown in FIG. 1, and therefore a description thereof will be omitted.

[0065] <Configuration of image heating device> The configuration of the image heating device A2 included in the image forming apparatus according to the second embodiment of the present invention will be described in detail with reference to FIGS.

[0066] In addition, in Figs. 4 and 5, parts having the same configuration as those in Figs. 2 and 3 are given the same reference numerals, and the description thereof will be omitted.

[0067] The image heating device A 2 includes a pressure roller 2 , a pad holder 3 , a stay 4 , a heating roller 11 , a halogen heater 12 , a fixing belt 13 , a tension roller 14 , a cover 15 , and a nip pad 16 .

[0068] The pressure roller 2 as a pressure rotating body rotates in the direction of arrow R2 in Fig. 4 (counterclockwise in Fig. 4) when driven by a drive source (not shown). The pressure roller 2 conveys the sheet S conveyed to the nip portion N by the sheet conveying mechanism 9 from upstream to downstream in the conveying direction while sandwiching the sheet S together with the fixing belt 13, and pressurizes the unfixed toner image T on the sheet S.

[0069] The pad holder 3 presses the fixing belt 13 against the pressure roller 2 via the nip pad 16 by the pressure force from the stay 4 .

[0070] The stay 4 applies a predetermined pressure to the fixing belt 13 via the pad holder 3 and the nip pad 16 by the biasing force of a biasing member (not shown).

[0071] The heating roller 11 is made of metal and is provided so as to surround the halogen heater 12. The heating roller 11 transfers heat from the halogen heater 12 to the fixing belt 13.

[0072] The halogen heater 12 is a heat source and heats the inner circumferential surface of the fixing belt 13 via the heating roller 11 .

[0073] The fixing belt 13 as a heating rotator rotates in the direction of arrow R1 in Fig. 4 (clockwise in Fig. 4) following the rotation of the pressure roller 2, so that the heat of the inner peripheral surface heated by the heating roller 11 is transferred to the outer peripheral surface. The fixing belt 13 forms a nip portion N together with the pressure roller 2 by contacting the pressure roller 2. The fixing belt 13 conveys the sheet S conveyed to the nip portion N by the sheet conveying mechanism 9 from upstream to downstream in the conveying direction (from left to right in Fig. 4) together with the pressure roller 2, and heats the unfixed toner image T on the sheet S.

[0074] The fixing belt 13 and the pressure roller 2 heat and pressurize the unfixed toner image T on the sheet S at the nip portion N, thereby fixing the unfixed toner image T to the sheet S.

[0075] The tension roller 14 contacts the inner peripheral surface of the fixing belt 13. The tension roller 14 applies tension to the fixing belt 13 and controls the position in the axial direction (the direction perpendicular to the paper surface in FIG. 4 and the left-right direction in FIG. 5).

[0076] The cover 15 is made of a resin having heat resistance and heat insulation properties. The cover 15 is a heat radiation suppressing member provided to suppress heat radiation from the surface of the fixing belt 13 to the outside and improve thermal efficiency. A metal sheet (not shown) having a luster for reflecting infrared rays toward the fixing belt 13 is provided on the inner surface of the cover 15 facing the fixing belt 13. The cover 15 extends in the axial direction, is disposed facing the fixing belt 13, and is provided on a part of the fixing belt 13 in the circumferential direction.

[0077] The cover 15 has a recess 15a recessed at a circumferential end 15b facing the entrance flag 10 so as to be away from the entrance flag 10 in a biasing direction F5 in which the biasing unit 30 biases the entrance flag 10, which abuts against the back surface Sb of the sheet S, from the back surface Sb to the front surface Sf. The cover 15 has the recess 15a at, for example, the center in the axial direction of the end 15b facing the entrance flag 10. The configuration of the recess 15a will be described in detail later.

[0078] The nip pad 16 presses the fixing belt 13 against the pressure roller 2 by a pressure force from the stay 4 via the pad holder 3 .

[0079] <Configuration and effect of the recessed part of the cover> The configuration and effect of the recess 15a of the cover 15 of the image heating device A2 of the image forming apparatus according to the first embodiment of the present invention will be described in detail with reference to FIGS.

[0080] The cover 15 has a recess 15a having a depth D2 [mm] in the direction parallel to the conveying direction and a width W2 [mm] in the axial direction. The recess 15a has a shape in which the width gradually narrows in the recessed direction. In the axial direction, the range in which the recess 15a is provided in the cover 15 includes the tip of the inlet flag 10 in the conveying direction.

[0081] By providing recess 15a at end 15b of cover 15 in this manner, the distance between cover 15 and entrance flag 10 can be increased. This makes it possible to prevent unfixed toner on sheet S, which has been flicked away by entrance flag 10, from adhering to cover 15, thereby preventing toner accumulation. Note that the air flow in image heating device A2 is the same as the air flow in image heating device A1, and therefore a description thereof will be omitted.

[0082] The wind speed flowing through recess 15a in the direction of arrow F4 is faster than the wind speed flowing in the direction of arrow F3 in both left and right portions of recess 15a in the axial direction (wind speed of arrow F3<wind speed of arrow F4).

[0083] As a result, the toner bounced off by the entrance flag 10 is less likely to stay in the recess 15a, and the adhesion of the toner bounced off by the entrance flag 10 to the recess 15a can be suppressed, so that the deposition of the toner can be suppressed.

[0084] The depth D2 of the recess 15a is exemplified as 15 mm here. Also, the width W2 of the recess 15a is preferably larger than the width X2 of the entrance flag 10 and within a range that does not significantly reduce the wind speed of the wind in the direction of arrow F4. Here, the width X2 is the axial width at the tip in the direction facing the cover 15 of the entrance flag 10. Specifically, the width W2 is preferably X2 [mm] < W2 [mm] ≦ X2 + 20 [mm], and more preferably X2 [mm] < W2 [mm] ≦ X2 + 10 [mm]. For example, when the width X2 of the entrance flag 10 is 5 mm, the width W2 of the recess 15a is 8 mm.

[0085] When W2 is less than or equal to X2, the distance between the cover 15 and the entrance flag 10 cannot be increased, so there is a risk that the above effects cannot be obtained sufficiently. Also, when W2 [mm] is larger than X2 + 10 [mm], the wind speed in the recess 15a cannot be increased, so there is a risk that the above effects cannot be obtained sufficiently. Here, the width W2 is the width of the tip of the recess 15a in the recessed direction where the width gradually narrows in the recessed direction.

[0086] Also, in the direction facing the entrance flag 10 and the cover 15, the shortest distance Z2 (mm) between the entrance flag 10 located at the first position not in contact with the sheet S and the cover 15 when the recess 15a is not provided is exemplified as 6 mm here. Toner deposition is likely to occur in a configuration where the distance between the cover 15 and the entrance flag 10 is close, specifically, in a configuration where Z2 (mm) ≦ 5Y (mm). Therefore, providing the recess 15a is effective in a configuration where the shortest distance Z2 [mm] is 5 times or less the rotation distance Y.

[0087] In this embodiment, the recess 15a is formed so that the width gradually narrows in the recess direction. This allows the distance between the cover 15 and the inlet flag 10 to be sufficiently large on the opposite side of the recess direction of the cover 15, thereby preventing toner from accumulating on the cover 15.

[0088] In this embodiment, recesses 15a are provided with a width that gradually narrows in the recessed direction, but this is not limited to the above, and recesses of the same width in the recessed direction may be provided, or recesses of any shape may be provided. [Explanation of symbols]

[0089] A1 Image heating device A2 Image heating device E. Image forming equipment PC image forming section PK image forming section PM image forming section PY image forming section 1 Fixing belt 2 Pressure roller 5 Magnetic shielding core 6 Excitation coil 7 Outer magnetic core 8 Cover 8a Recess 8b end 10 Entrance Flag 11 Heating roller 12 Halogen heater 13 Fixing belt 15 Cover 15a Recess 15b End 30 Pressurizing section

Claims

1. An image forming apparatus for forming an image on a sheet, a fixing device including a heating rotor that heats an unfixed toner image on a sheet, a pressure rotor that forms a nip portion by contacting the heating rotor, and a cover that extends in an axial direction of the pressure rotor and covers a circumferential direction of the heating rotor, and fixes the unfixed toner image on the sheet to the sheet; a sheet detection member disposed upstream of the nip portion in a sheet conveying direction and configured to detect the sheet; having The sheet detection member is a surface of the sheet that contacts the heating rotator at the nip portion is defined as a front surface, and a surface of the sheet that contacts the pressure rotator at the nip portion is defined as a back surface, the sheet has an abutting portion that abuts against the back surface of the sheet, and a biasing portion that biases the abutting portion from the back surface toward the front surface, The cover is a recess that is recessed so as to be away from the abutment portion in a biasing direction in which the biasing portion biases the surface from the back surface, 1. An image forming apparatus comprising:

2. The length of the recess in the recessed direction is 3 mm or more.

2. The image forming apparatus according to claim 1,

3. The length of the recess in the axial direction is greater than the length of the abutment portion in the axial direction.

3. The image forming apparatus according to claim 1, wherein the first and second electrodes are arranged in a first direction.

4. The abutment portion is a fixing device that is rotatable between a first position and a second position, and that rotates from the first position to the second position by contacting with a sheet that is conveyed to the fixing device; a shortest distance between the contact portion located at the first position in the biasing direction of the contact portion and the cover and the cover in a case where the recess is not provided is 5 times or less of a rotation distance when the contact portion rotates between the first position and the second position; 3. The image forming apparatus according to claim 1, wherein the first and second electrodes are arranged in a first direction.

5. A coil for inductively heating the heating rotor is provided. The cover is An insulating member that insulates the coil from the surroundings.

3. The image forming apparatus according to claim 1, wherein the first and second electrodes are arranged in a first direction.

6. The cover is It is made of resin, 3. The image forming apparatus according to claim 1, wherein the first and second electrodes are arranged in a first direction.

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