JP4315039B2 - Fixing device - Google Patents

Description

  The present invention relates to a belt-type fixing device mounted on an image forming apparatus, and in particular, it is possible to obtain an optimum nip width according to the thickness of a sheet while having a simple configuration, and to have a sheet separation property. It relates to a good fixing device.

  Conventionally, there is an electrophotographic image forming apparatus that forms an image using toner. Such an image forming apparatus is equipped with a fixing device for fixing the transferred toner image on a sheet. There are two types of fixing devices, a two-roll type and a belt type, but the belt-type fixing device has attracted attention because of its merit that the nip width can be set wider than the two-roll type and the power consumption is low. Yes.

  As a conventional belt-type fixing device, for example, in JP-A-5-165357, as shown in FIG. 6, an endless fixing belt 103 rotatably supported by two large and small support rollers 101 and 102 is shown. In a fixing device that heats and fixes a toner image on a sheet when the sheet passes between the fixing belt 103 and the pressure roller 104, a support roller 102 is provided according to the type of the sheet to be used. The fixing device 100 has been proposed which is configured to move the position of the fixing belt 103 and change the contact width between the fixing belt 103 and the pressure roller 104.

  According to such a configuration, it is possible to select an optimum nip width corresponding to paper having various thicknesses, and it is possible to select fixing conditions according to the type of paper.

  In Japanese Patent Application Laid-Open No. 2003-5266, as shown in FIG. 7, the fixing roller 201, the heating roller 202, the fixing belt 203 stretched between both rollers, and the outer peripheral surface of the fixing belt 203 are contacted. In a belt fixing apparatus including a pressure roller 204 that forms a nip, the position of the fixing belt 203 is a position corresponding to an outlet separation portion of the nip formed by the fixing roller 201 and the pressure roller 204 via the fixing belt 203. A fixing device 200 having a configuration in which a fixing member 205 having a large curvature is provided on the inner side of the outlet separation portion has been proposed.

According to such a configuration, the separation radius is reduced to improve the separation performance, and the self-separation of the recording paper after fixing is performed without using separation means such as oil application, separation claw, separation guide plate and the like. That is, self-stripping becomes possible.
JP-A-5-165357 (Embodiments of the Invention [0019] to [0041], FIGS. 1 to 8) Japanese Patent Laying-Open No. 2003-5566 (Embodiments of the Invention [0050] to [0061], FIGS. 4 and 5)

  However, in the fixing device 100 described in Japanese Patent Laid-Open No. 6-115767, the position of the support roller 102 is moved in accordance with the type of paper to be used, and the contact width between the fixing belt 103 and the pressure roller 104 is changed. However, in order to drive the support roller 102, many components such as a motor, a cam, a holder, and a spring are required, and there is a problem that the configuration is complicated.

  Further, in the fixing device 200 of Japanese Patent Application Laid-Open No. 2003-5566, a fixing member 205 having a large curvature is pressed against the inside of the fixing belt 203 to self-separate the recording paper after fixing. On the other hand, there is a problem that the nip is uniformly increased and the image quality is deteriorated depending on the thickness of the paper. In addition, a sudden change in curvature due to the fixing member 205 places a burden on the fixing belt 203, leading to a problem of shortening the service life.

  The present invention has been made in view of the above problems, and can simplify the configuration and improve the assemblability by reducing the number of parts, and can obtain an optimum nip amount according to the thickness of the paper. An object of the present invention is to provide a fixing device that can perform separation and has good sheet separation.

To achieve the above object, a fixing device according to the present invention includes a fixing belt ring, a heating roller that is rotationally driven is provided to the fixing in the belt, and a backup roller that is provided outside the fixing belt, wherein A nip forming guide that is supported by a rotating shaft in a fixing belt and is provided to stretch the fixing belt with the heating roller, and is capable of forming a nip with respect to a sheet by pressing against the backup roller via the fixing belt. When the fixing belt outer surface and a tension roller which contact with the addition of tension, a fixing device provided with a, the outer peripheral surface of the nip forming guide, the skilled in contact with the fixing belt inner surface In addition to forming a contact surface, it is provided with means for controlling the rotation of the rotation shaft of the nip forming guide so as to selectively change the position of the contact surface .

Good Mashiku is a configuration in which prior to coating oil to the fixing belt by Kite emissions Deployment rollers, further wherein the tension roller, the amount of oil that is proportional to the level of tension to be added to be applied to the fixing belt In addition, the application of oil by the tension roller may be stopped by reducing the tension of the fixing belt when the fixing pressure release surface of the nip forming guide is selected.

According to the fixing device of the present invention, the large-diameter contact surface and the small-diameter contact surface formed to change the nip width in the nip formation guide , and the fixing pressure release surface formed to release the nip. Thus, with a simple configuration in which a plurality of contact surfaces are formed, an optimum nip width corresponding to the thickness of the paper can be obtained, and good paper separation can be exhibited.

  That is, when the toner image is fixed on the thick paper, by selecting a contact surface having a large radius of curvature, the nip width is increased and the fixing pressure is increased, so that the toner image has good fixability. On the other hand, since the thick paper itself has a strong stiffness, there is no problem in paper separation even if the curvature of the contact surface is large.

  In addition, when fixing a toner image on thin paper, by selecting a contact surface having a small radius of curvature, the separation of the paper is improved, while a small nip width and a small fixing pressure according to the paper thickness. can get.

The nip forming guide is provided with a fixing pressure release surface that releases the contact between the fixing belt and the backup roller, so that the durability of the fixing belt is deteriorated under high-temperature heating, the service life is shortened, and the fixed curvature is wrinkled. Can be prevented.

  When the oil is applied to the fixing belt by the tension roller, the oil can be supplied to the paper without separately adding an oil applying unit. Further, when the tension roller is configured to supply an amount of oil proportional to the tension level of the fixing belt, a large amount of oil can be automatically supplied to the thick paper, and a small amount of oil can be automatically supplied to the thin paper. During non-fixing, the oil supply can be stopped by selecting the fixing pressure release surface of the nip forming guide.

Hereinafter, a fixing device according to an embodiment of the present invention will be described. First, an image forming apparatus (printer) equipped with a fixing device according to the present embodiment will be described with reference to FIG.
FIG. 1 is a cross-sectional view illustrating the internal configuration of an image forming apparatus equipped with a fixing device according to an embodiment of the present invention. In FIG. 1, an image forming apparatus 1 is an electrophotographic tandem color image forming apparatus, and includes an image forming unit 2, an intermediate transfer belt unit 3, a paper feeding unit 4, and a duplex printing transport unit 5. It is.

  The image forming unit 2 has a configuration in which four image forming units 2M, 2C, 2Y, and 2K are arranged side by side in a multistage manner from right to left in FIG. Of these image forming units 2M, 2C, 2Y, and 2K, the three upstream image forming units 2M, 2C, and 2Y are magenta (M) and cyan (C), which are subtractive three primary colors, respectively. The monochromatic image is formed with yellow (Y) color toner, and the image forming unit 2K forms a monochrome image with black (K) toner mainly used for dark portions of characters and images.

  Each of the image forming units 2M, 2C, 2Y, and 2K has the same configuration except for the color of the toner stored in the toner container. Accordingly, the configuration of the black (K) image forming unit 2K will be described below as an example.

  The image forming unit 2K includes a photosensitive drum 21 at the bottom. The peripheral surface of the photosensitive drum 21 is made of, for example, an organic photoconductive material. A cleaner 22, a charger 23, an optical writing head 24, and a developing roller 26 of a developing unit 25 are arranged around the periphery of the photosensitive drum 21. The optical writing head 24 is separate from the image forming unit 2K. Further, the image forming unit 2K is configured to be able to be inserted and removed in the depth direction of the drawing by opening a front door (not shown) in front of the printer 1 (front side of the drawing).

  The developing unit 25 applies magenta (M), cyan (C), yellow (Y), or black (K) toner to the upper toner container as indicated by M, C, Y, and K in FIG. An intermediate portion is provided with a toner replenishing mechanism at a lower portion, a lower portion is provided with the above-described developing roller 26 at a side opening, a toner stirring member, a toner supply roller for supplying toner to the developing roller 26, a developing A doctor blade or the like for regulating the toner layer on the roller 13 to a constant layer thickness is provided.

  The intermediate transfer belt unit 3 includes a transfer belt 31 that extends in a substantially loop shape from substantially the left and right sides of the drawing at the center of the main body device, and circulates the transfer belt 31 in the counterclockwise direction of the drawing. A driving roller 32 to be moved and a driven roller 33 are provided.

  The transfer belt 31 directly transfers the toner image onto the belt surface (primary transfer) and conveys the toner image to the transfer position to the paper for further transfer (secondary transfer). The whole is called an intermediate transfer belt unit.

  The intermediate transfer belt unit 3 includes a belt position control mechanism 34 in the loop of the flat loop-shaped transfer belt 31. The belt position control mechanism 34 includes a primary transfer roller 35 made of a conductive foam sponge that presses against the lower peripheral surface of the photosensitive drum 21 via the transfer belt 31.

  The belt position control mechanism 34 includes three primary transfer rollers 35 corresponding to the three image forming units 2M, 2C, and 2Y of magenta (M), cyan (C), and yellow (Y) with a bowl-shaped support shaft. The image is transferred to the center at the same cycle, and one primary transfer roller 35 corresponding to the black (K) image forming unit 2K is rotated and moved at a rotation cycle different from the cycle of the three primary transfer rollers 35. The belt 31 is moved away from the photosensitive drum 21, and the full color mode (all four primary transfer rollers 35 are in contact with the transfer belt 31) and the monochrome mode (only the primary transfer roller 35 corresponding to the image forming unit 2K is the transfer belt). 31) and all non-transfer modes (all four primary transfer rollers 35 are separated from the transfer belt 31).

  In the intermediate transfer belt unit 3, a belt cleaner unit 36 is disposed further upstream of the uppermost image forming unit 2M in the belt moving direction on the upper surface portion, and is flat so as to be almost along the entire lower surface portion. A thin waste toner collecting container 37 is detachably disposed.

  The paper feed unit 4 includes two paper feed cassettes 41 arranged in two upper and lower stages. A paper take-out roller 42 and a paper feed are provided near the paper feed opening (right side in the drawing) of these paper feed cassettes 41, respectively. A roller 43, a separating roller 44, and a conveying roller pair 45 are arranged. In the sheet conveyance direction (vertical direction in the figure) of the conveyance roller pair 45, a secondary transfer roller 46 that is in pressure contact with the driven roller 33 via the transfer belt 31 is disposed, and a secondary transfer portion to the sheet is provided. Forming.

  A fixing device 60 according to the present embodiment is disposed downstream (upward in the drawing) of the secondary transfer portion, which will be described in detail later. Further downstream of the fixing device 60, a pair of discharge rollers 47 for discharging the fixed paper from the fixing device 60, and a pair of discharge rollers for discharging the discharged paper to a paper discharge tray 48 formed on the upper surface of the device. 49 is arranged.

  The duplex printing conveyance unit 5 includes a start return path 51a branched from the intermediate conveyance path between the carry-out roller pair 47 and the discharge roller pair 49 in the right lateral direction in the figure, an intermediate return path 51b bent downward from this, A terminal return path 51c that bends in the left lateral direction opposite to the above and eventually reverses the return sheet, and three return roller pairs 52a, 52b, and 52c arranged in the middle of these return paths are provided. . At the outlet of the end return path 51c, a pair of carry-in rollers 53 is disposed inside the main body.

  Next, the fixing device of this embodiment mounted on the image forming apparatus will be described with reference to the drawings. FIG. 2 is a cross-sectional view showing the fixing device according to the present embodiment, and FIG. 3 is an enlarged view showing a nip forming guide of the fixing device.

  In FIG. 2, the fixing device 60 of the present embodiment mainly includes a fixing belt 61, a heating roller 62, a nip forming guide 63, a backup roller 64, and a tension roller 65.

  The fixing belt 61 is stretched between the heating roller 62 and the nip forming guide 63 disposed on the inside thereof, and an appropriate tension is applied by pressing the tension roller 65 to a part thereof. In this embodiment, an electroformed belt having a thickness of 0.2 mm is used as the fixing belt 61, and the surface layer is seamlessly coated with 200 μm of silicon rubber.

  The heating roller 62 has a configuration in which the surface of the thin AL tube 62a is coated with Teflon (registered trademark), and a halogen heater 62b is disposed therein. The halogen heater 62b is a circular, halogen lamp, and is a clean, safe, small and light heat source that radiates most of the input power by converting it into infrared rays (heat). Further, since the halogen heater 62b uses a filament with a small heat capacity as a heat source, it can start radiating heat almost simultaneously with the power ON. When the halogen heater 62b emits light, the AL tube 62a is rapidly heated to continuously supply heat to the fixing belt 61.

  The nip forming guide 63 is a thick cylindrical body in which the surface of a columnar body made of a heat-resistant resin is coated with Teflon (registered trademark), and by contacting the outer peripheral surface thereof with the fixing belt 61, A nip for the paper is formed between the two.

  As shown in FIG. 3, on the outer peripheral surface of the nip forming guide 63, a concentric arc-shaped large diameter contact surface 63A, a small diameter contact surface 63B, and a fixing pressure release surface 63C are formed in stages. . By rotating the nip forming guide 63 in the forward and reverse directions by a driving means (not shown), the large diameter contact surface 63A, the small diameter contact surface 63B, and the fixing pressure release surface 63C are brought into contact with the fixing belt 61. As appropriate.

  The large diameter contact surface 63A is used for fixing thick paper and has a large radius of curvature and forms a large nip width to exert a large fixing pressure. In this embodiment, the nip width is set to about 10 mm, and the weight during fixing is set to about 300N. Further, when the large diameter contact surface 63A having a large protrusion amount toward the backup roller 64 is selected, a relatively large tension is applied to the fixing belt 61.

  The small diameter contact surface 63B is for fixing thin paper, has a small radius of curvature, forms a small nip width, and exhibits a small fixing pressure. In this embodiment, the nip width is set to about 6 to 7 mm, and the weight during fixing is set to about 200N. Further, when the small diameter contact surface 63B having a small protrusion amount toward the backup roller 64 is selected, a relatively small tension is applied to the fixing belt 61.

  The fixing pressure release surface 63C is intended to protect the fixing belt 61, and has the smallest radius of curvature and a small amount of protrusion toward the backup roller 64. Therefore, when the fixing pressure release surface 63C is selected. The contact between the fixing belt 61 and the backup roller 64 is released, and the fixing belt 61 is hardly tensioned.

  The rotating shaft 63a of the nip forming guide 63 is provided with a clutch mechanism (not shown), which rotates by receiving a control signal from a control unit such as a CPU and a driving force from the driving unit. The contact surface 63A, the small diameter contact surface 63B, and the fixing pressure release surface 63C are switched. Then, after switching to any of the large diameter contact surface 63A, the small diameter contact surface 63B, and the fixing pressure release surface 63C, the nip forming guide 63 is in a fixed state. Accordingly, the fixing belt 61 receives the driving force of the backup roller 64 and slides along the nip forming guide 63.

The backup roller 64 is a cylindrical roller for driving the fixing belt 61, and forms a nip when the nip forming guide 63 comes into contact with the fixing belt 61.
Here, depending on the type of toner used, it is necessary to apply oil to the fixing belt 61. For example, POP printing, which often uses thick paper, requires a large amount of oil. Conversely, for thin paper, if there is too much oil, the oil marks on the paper become conspicuous. There is a need. Therefore, in this embodiment, a function of applying an appropriate amount of oil to the tension roller 65 that applies tension to the fixing belt 61 is added.

  The tension roller 65 has a structure in which a multilayer paper impregnated with silicone oil is covered with a porous heat-shrinkable Teflon (registered trademark) tube, and an amount of oil proportional to the level of tension to be applied is fixed to the fixing belt. 61 is applied.

  That is, as described above, the tension applied to the fixing belt 61 by the large diameter contact surface 63A, the small diameter contact surface 63B, and the fixing pressure release surface 63C of the nip forming guide 63 has a proportional relationship of high → low → no. In proportion to this, the compression amount of the pressing spring 65a of the tension roller 65 also has a relationship of large → small → no.

  Therefore, when the large diameter contact surface 63A is selected, the tension roller 65 is pressed against the fixing belt 61 with a relatively strong force, and a large amount of oil is supplied. When the small diameter contact surface 63B is selected, the tension roller 65 is pressed against the fixing belt 61 with a relatively weak force, and a small amount of oil is supplied. Further, when the fixing pressure release surface 63C is selected, the supply of oil is stopped because the fixing belt 61 is not pushed back against the tension roller 65.

  Next, the operation of the fixing device 60 of the present embodiment described above will be described with reference to FIGS. FIG. 4 is a cross-sectional view showing a state where the nip forming guide of the fixing device is changed to a contact surface having a small radius of curvature. FIG. 5 is a cross-sectional view showing a state in which the nip forming guide of the fixing device is changed to a fixing pressure releasing surface. 2 already referred to shows a state in which the nip forming guide of the fixing device is changed to a contact surface having a large curvature radius.

  As described above, in the fixing device 60, the contact surface of the nip forming guide 63 can be selected according to the thickness of the paper, and the user manually selects either the thick paper mode or the thin paper mode in advance by manual setting. Alternatively, by auto setting, it is possible to automatically select either the thick paper mode or the thin paper mode by detecting the paper thickness during the conveyance process.

  When the sheet thickness is specified manually or automatically, the control unit outputs a control signal to operate the clutch mechanism and transmit the driving force of the driving unit to the rotating shaft 63a to thereby generate the nip forming guide 63. Rotate.

  Thereafter, based on a detection signal from a position detection means (not shown), the control unit stops the rotation of the nip forming guide 63, and either the large diameter contact surface 63A, the small diameter contact surface 63B, or the fixing pressure release surface 63C is detected. It is brought into contact with the fixing belt 61.

  When the toner image is fixed on the thick paper, as shown in FIG. 2, when the large diameter contact surface 63A having a large radius of curvature is brought into contact with the fixing belt 61, a large nip width is formed between the backup roller 64 and the sheet. A large fixing pressure is exhibited. Thereby, the fixability of the toner image is improved. On the other hand, since the thick paper itself is strong, there is no problem in the paper separation even if the curvature of the contact surface is large. At this time, the tension roller 65 is pressed against the fixing belt 61 with a relatively strong force, and a large amount of oil is supplied to the cardboard.

  When fixing a toner image on thin paper, as shown in FIG. 4, a small diameter contact surface 63 </ b> B having a small curvature radius is brought into contact with the fixing belt 61. Then, a small nip width is formed between the backup roller 64 and a small fixing pressure. Since the radius of curvature of the abutting surface is small, the sheet separation is good, while a small nip width and a small fixing pressure corresponding to the sheet thickness are obtained. Further, when switching to the small diameter contact surface 63B, the tension of the fixing belt 61 is lowered, so that the tension roller 65 is pressed against the fixing belt 61 with a relatively weak force, and a small amount of oil is supplied to the thin paper.

  When the fixing pressure releasing surface 63C is selected, as shown in FIG. 5, since the radius of curvature is the smallest, the contact between the fixing belt 61 and the backup roller 64 is released, and tension is hardly applied to the fixing belt 61. No state. As a result, it is possible to prevent the durability of the fixing belt 61 from being deteriorated under high-temperature heating, shortening the service life, and wrinkling with a constant curvature.

  At this time, since the fixing belt 61 is not pushed back against the tension roller 65, the supply of oil from the tension roller 65 is stopped. For example, in the non-job state of the image forming apparatus 1, unnecessary oil continues to be supplied. Inconveniences such as oil traces caused by oil accumulated between the nips and slipping of the paper can be eliminated.

In addition to the above-described non-job state of the image forming apparatus 1, the fixing pressure release surface 63 </ b> C may be used when a jam occurs or when the image forming apparatus 1 is marketed.
According to the fixing device 60 of this embodiment, the optimum nip width corresponding to the thickness of the sheet is obtained by a simple configuration in which the large diameter contact surface 63A and the small diameter contact surface 63B are formed on the nip forming guide 63. Can be obtained, and good paper separation can be exhibited.

  In particular, when switching from the thick paper mode to the thin paper mode, there are many cases in which the paper feed speed and the fixing temperature are changed, but in the case of the fixing device 60, the switching is completed only by switching the contact surface of the nip forming guide 63. In the thin paper mode, the curvature of the contact surface is small, so that the phenomenon that the toner printing surface of the thin paper is offset to the fixing belt 61 side is surely prevented, and the improvement of the thin paper separation and the stable conveyance are ensured. Image quality stability is also guaranteed.

  Since the fixing pressure release surface 63C for releasing the contact between the fixing belt 61 and the backup roller 64 is formed on the nip forming guide 63, the durability of the fixing belt 61 is deteriorated under high-temperature heating, the life is shortened, and the wrinkle of a constant curvature is provided. Can be prevented.

  With the configuration in which oil is applied to the fixing belt 61 by the tension roller 65, oil can be supplied to the paper without additional oil application means. Further, since the tension roller 65 supplies an amount of oil proportional to the tension level of the fixing belt 61, a large amount of oil can be automatically supplied to the thick paper and a small amount of oil can be automatically supplied to the thin paper. The oil supply can be stopped by selecting the fixing pressure release surface 63C of the nip forming guide 63. Further, since the minimum necessary oil corresponding to the scene is supplied, the durability of the tension roller 65 is also improved.

The fixing device of the present invention is not limited to the above-described embodiment. For example, in the present embodiment, the contact surface of the nip forming guide 63 is three types, that is , a large diameter contact surface 63A, a small diameter contact surface 63B, and a fixing pressure release surface 63C. A switchable configuration may be used.

  Further, the contact surface of the nip forming guide 63 is not limited to the concentric circular arc surface such as the large diameter contact surface 63A, the small diameter contact surface 63B, and the fixing pressure release surface 63C. It may be a curved surface based on.

1 is a cross-sectional view illustrating an internal configuration of an image forming apparatus equipped with a fixing device according to an embodiment of the present invention. FIG. 2 is a cross-sectional view showing a fixing device according to the present embodiment. FIG. 3 is an enlarged view showing a nip formation guide of the fixing device. FIG. 6 is a cross-sectional view illustrating a state where a nip forming guide of the fixing device is changed to a contact surface having a small radius of curvature. FIG. 4 is a cross-sectional view illustrating a state where a nip forming guide of the fixing device is changed to a fixing pressure release surface. FIG. 10 is a cross-sectional view showing a fixing device according to a conventional example. It is sectional drawing which shows the fixing device which concerns on another prior art example.

Explanation of symbols

1 Image forming device (printer)
2 Image forming unit 2M, 2C, 2Y, 2K Image forming unit 21 Photosensitive drum 22 Cleaner 23 Charger 24 Optical writing head 25 Developer 26 Developing roller 3 Intermediate transfer belt unit 31 Transfer belt 32 Drive roller 33 Driven roller 34 Belt Position control mechanism 35 Primary transfer roller 36 Belt cleaner unit 37 Waste toner collection container 4 Paper feed unit 41 Paper feed cassette 42 Paper take-out roller 43 Feed roller 44 Rolling roller 45 Conveying roller pair 46 Secondary transfer roller 47 Unloading roller pair 48 Ejection Paper tray 49 Paper discharge roller pair 5 Double-sided printing transport unit 51a Start return path 51b Intermediate return path 51c End return path 52a, 52b, 52c Return roller pair 53 Carry-in roller pair 60 Fixing device 61 Fixing belt 62 Heating roller 63 Nip forming guide 63A Large diameter contact surface 63B Small diameter contact surface 63C Fixing pressure release surface 64 Backup roller 65 Tension roller

Claims (3)

A fixing belt ring, a heating roller that is rotated provided in the fixing in the belt, and a backup roller that is provided outside the fixing belt, the axially supported by and fixing belt rotation axis by the fixing belt in A nip forming guide provided to be stretched by the heating roller and capable of forming a nip with respect to the sheet by being pressed against the backup roller via the fixing belt, and a tension for applying a tension by contacting the outer surface of the fixing belt A fixing device comprising a roller ,
The outer peripheral surface of the nip forming guide, the fixing belt inner surface abutting against the large径当contact surface formed so as to change the width of the nip and the small diameter abutting surface, and is formed so as to release the nip Forming a plurality of contact surfaces consisting of a fixing pressure release surface ,
Means for rotationally controlling the rotational axis of the nip forming guide to selectively change the position of the contact surface ;
A fixing device. Previous claim 1 Symbol mounting of the fixing device, characterized in that applying oil to the fixing belt by Kite emissions Deployment roller. The tension roller applies an amount of oil proportional to the level of tension to be applied to the fixing belt, and reduces the tension of the fixing belt when the fixing pressure release surface of the nip forming guide is selected. The fixing device according to claim 2 , wherein the application of oil by the tension roller is stopped.

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