EP4641312A1

EP4641312A1 - Heating conveyance device and image forming apparatus

Info

Publication number: EP4641312A1
Application number: EP25168250.6A
Authority: EP
Inventors: Yasunori Ishigaya; Keitaro Shoji; Yuma Matsumoto
Original assignee: Ricoh Co Ltd
Current assignee: Ricoh Co Ltd
Priority date: 2024-04-24
Filing date: 2025-04-03
Publication date: 2025-10-29
Also published as: JP2025166791A

Abstract

A heating conveyance device (19) includes a fixing device (20) and a conveyance guide (110, 130). The fixing device (20) includes a fixing rotator (21, 22), a heater (24, 35, 50), and a pressure rotator (31) pressed against the fixing rotator (21, 22) to form a fixing nip through which a sheet (P) is conveyed in a conveyance direction. The conveyance guide (110, 130) guides the sheet (P) fed from the fixing nip to an ejection port (A, B). In a cross section orthogonal to the width direction, the fixing device (20) ejects the sheet (P) from an exit (N2) of the fixing nip to the conveyance guide in the conveyance direction (S) inclined concerning a vertical line (H) passing through the exit (N2). The ejection port (A, B) is disposed at one side of the virtual vertical line (H), and the conveyance direction (S) is inclined toward another side.

Description

BACKGROUND

Technical Field

The present disclosure relates to a heating conveyance device that heats and conveys a sheet and an image forming apparatus including the heating conveyance device, such as a copier, a printer, a facsimile machine, or a multifunction peripheral having at least two of copying, printing, and facsimile functions.

Related Art

An image forming apparatus such as a copier or a printer includes a fixing device and a conveyance guide such as a conveyance guide plate. The fixing device ejects a sheet. The conveyance guide guides the ejected sheet to an ejection port through a conveyance path curved in a predetermined direction. Thus, the sheet is ejected from the ejection port to the outside of the image forming apparatus. (see, for example, Japanese Unexamined Patent Application Publication No. 2015-34079 )
The sheet ejected from the ejection port in the image forming apparatus is largely bent and has a large curl. As a result, the appearance and stacking properties of the ejected sheets are poor.

SUMMARY

The present disclosure is made to solve the above-described problems, and an object of the present disclosure is to provide a heating conveyance device that is less likely to cause the large curl in the sheet ejected from the ejection port and an image forming apparatus including the heating conveyance device. In order to achieve this object, there is provided the heating conveyance device according to claim 1 and the image forming apparatus including the heating conveyance device. Advantageous embodiments are defined by the dependent claims.
The present disclosure described herein provides the heating conveyance device including a fixing device and a conveyance guide. The fixing device includes a fixing rotator, a heater, and a pressure rotator. The heater heats the fixing rotator and extends in a width direction. The pressure rotator is pressed against the fixing rotator to form a fixing nip through which a sheet is conveyed in a conveyance direction intersecting the width direction. The fixing nip has an entrance and an exit. The conveyance guide guides the sheet fed from the fixing nip to an ejection port. In a cross section orthogonal to the width direction, the fixing device ejects the sheet from the exit to the conveyance guide in the conveyance direction. The conveyance direction is inclined with respect to a virtual vertical line passing through the exit and extending in a vertical direction. The ejection port is disposed at one side of the virtual vertical line (H), and the conveyance direction (S) is inclined toward another side (opposite to the one side) of the virtual vertical line (H).
According to one aspect of the present disclosure, the heating conveyance device in which the large curl is unlikely to occur in the sheet ejected from the ejection port is provided, and the image forming apparatus including the heating conveyance device is provided.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of embodiments of the present disclosure and many of the attendant advantages and features thereof can be readily obtained and understood from the following detailed description with reference to the accompanying drawings, wherein:

FIG. 1 is a diagram illustrating an overall configuration of an image forming apparatus;
FIG. 2 is a diagram illustrating a configuration of a fixing device;
FIG. 3 is a schematic cross-sectional view of the fixing device of FIG. 2 to illustrate parts extending in a width direction;
FIG. 4 is a schematic cross-sectional view of a fixing belt and flanges of the fixing device of FIG. 3 in a cross-section perpendicular to the surface of the paper on which FIG. 3 is drawn;
FIG. 5A is a front view of a planar heater;
FIG. 5B is a side cross-sectional view of the planar heater of FIG. 5A;
FIG. 6 is a cross-sectional view of a thermostat;
FIG. 7 is a diagram illustrating a configuration of a heating conveyance device;
FIG. 8 is a diagram illustrating a configuration of a heating conveyance device according to a comparative example;
FIG. 9 is a timing chart illustrating control timings of a fixing device to start printing;
FIG. 10 is a flowchart illustrating control performed by an image forming apparatus;
FIG. 11 is a diagram illustrating a configuration of a fixing device according to a first modification;
FIG. 12 is a diagram illustrating a configuration of a heating conveyance device according to a second modification;
FIG. 13 is a diagram illustrating a configuration of a heating conveyance device according to a third modification;
FIG. 14 is a diagram illustrating a configuration of a fixing device according to a fourth modification; and
FIG. 15 is a diagram illustrating a configuration of a fixing device according to a fifth modification.

The accompanying drawings are intended to depict embodiments of the present disclosure and should not be interpreted to limit the scope thereof. The accompanying drawings are not to be considered as drawn to scale unless explicitly noted. Also, identical or similar reference numerals designate identical or similar components throughout the several views.

DETAILED DESCRIPTION

In describing embodiments illustrated in the drawings, specific terminology is employed for the sake of clarity. However, the disclosure of this specification is not intended to be limited to the specific terminology so selected and it is to be understood that each specific element includes all technical equivalents that have a similar function, operate in a similar manner, and achieve a similar result.
Referring now to the drawings, embodiments of the present disclosure are described below. As used herein, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.
Embodiments of the present disclosure are described below in detail with reference to the drawings. Like reference signs are assigned to identical or equivalent components and a description of those components may be simplified or omitted.
A description is given of an overall configuration and operations of an image forming apparatus 1 with reference to FIG. 1.
As illustrated in FIG. 1, the image forming apparatus 1 is a tandem-type color printer. The image forming apparatus 1 includes a bottle housing 101 in an upper portion of the image forming apparatus 1. The bottle housing 101 accommodates four toner bottles 102Y, 102M, 102C, and 102K containing fresh yellow, magenta, cyan, and black toners, respectively. The four toner bottles 102Y, 102M, 102C, and 102K are detachably attached to the bottle housing 101 for replacement.
Under the bottle housing 101, an intermediate transfer unit 85 is disposed. Facing an intermediate transfer belt 78 of the intermediate transfer unit 85, image forming devices 4Y, 4M, 4C, and 4K are arranged side by side to form toner images of yellow, magenta, cyan, and black, respectively.
The image forming devices 4Y, 4M, 4C, and 4K include photoconductor drums 5Y, 5M, 5C, and 5K, respectively. Each of the photoconductor drums 5Y, 5M, 5C, and 5K is surrounded by a charger 75, a developing device 76, a cleaner 77, and a discharger. The image forming apparatus 1 includes a controller 60. The controller 60 controls various parts to perform image forming processes including a charging process, an exposure process, a developing process, a primary transfer process, and a cleaning process on an outer circumferential surface of each of the photoconductor drums 5Y, 5M, 5C, and 5K and form yellow, magenta, cyan, and black toner images on the photoconductor drums 5Y, 5M, 5C, and 5K.
A motor drives and rotates the photoconductor drums 5Y, 5M, 5C, and 5K clockwise in FIG. 1. The chargers 75 uniformly charge the surfaces of the photoconductor drums 5Y, 5M, 5C, and 5K, which is referred to as the charging process.
After the charging process, the charged outer circumferential surface of each of the photoconductor drums 5Y, 5M, 5C, and 5K reaches an irradiation position at which an exposure device 3 irradiates and scans the photoconductor drums 5Y, 5M, 5C, and 5K with laser beams L, and irradiating and scanning the photoconductor drums 5Y, 5M, 5C, and 5K with the laser beams L forms electrostatic latent images according to yellow, magenta, cyan, and black image data in the exposure process.
After the exposure process, the irradiated and scanned outer circumferential surface of each of the photoconductor drums 5Y, 5M, 5C, and 5K reaches a developing position at which the developing device 76 is disposed opposite each of the photoconductor drums 5Y, 5M, 5C, and 5K, and the developing device 76 develops the electrostatic latent image formed on the respective photoconductor drums 5Y, 5M, 5C, and 5K, thus forming yellow, magenta, cyan, and black toner images on the photoconductor drums 5Y, 5M, 5C, and 5K in the developing process.
After the developing process, the yellow, magenta, cyan, and black toner images formed on the photoconductor drums 5Y, 5M, 5C, and 5K reach primary transfer nips formed between the photoconductor drums 5Y, 5M, 5C, and 5K and the intermediate transfer belt 78 by four primary transfer bias rollers 79Y, 79M, 79C, and 79K pressed against the four photoconductor drums 5Y, 5M, 5C, and 5K via the intermediate transfer belt 78, respectively, and the yellow, magenta, cyan, and black toner images are primarily transferred onto the intermediate transfer belt 78 in a primary transfer process. After the primary transfer process, residual toner failed to be transferred onto the intermediate transfer belt 78 remains on the photoconductor drums 5Y, 5M, 5C, and 5K slightly.
After the primary transfer process, the residual toner on each of the photoconductor drums 5Y, 5M, 5C, and 5K reaches a cleaning position at which the cleaner 77 is disposed opposite each of the photoconductor drums 5Y, 5M, 5C, and 5K, and a cleaning blade of the cleaner 77 mechanically collects the residual toner from each of the photoconductive drums 5Y, 5M, 5C, and 5K in the cleaning process.
Finally, the cleaned outer circumferential surface of each of the photoconductor drums 5Y, 5M, 5C, and 5K reaches a discharging position at which the discharger is disposed opposite each of the photoconductor drums 5Y, 5M, 5C, and 5K, and the discharger eliminates residual potential from each of the photoconductor drums 5Y, 5M, 5C, and 5K.
Thus, a series of image forming processes performed on the photoconductor drums 5Y, 5M, 5C, and 5K is finished.
The yellow, magenta, cyan, and black toner images formed on the photoconductor drums 5Y, 5M, 5C, and 5K in the developing process are primarily transferred onto an outer circumferential surface of the intermediate transfer belt 78 such that the yellow, magenta, cyan, and black toner images are superimposed on the intermediate transfer belt 78. Thus, a color toner image is formed on the intermediate transfer belt 78.
The intermediate transfer unit 85 includes the intermediate transfer belt 78, the four primary transfer bias rollers 79Y, 79M, 79C, and 79K, a secondary transfer backup roller 82, a cleaning backup roller 83, a tension roller 84, and an intermediate transfer belt cleaner 80. The intermediate transfer belt 78 is stretched taut across and supported by the three rollers, that is, the secondary transfer backup roller 82, the cleaning backup roller 83, and the tension roller 84. One of the three rollers, that is, the secondary transfer backup roller 82 drives and rotates the intermediate transfer belt 78 in a rotation direction indicated by an arrow in FIG. 1.
The four primary transfer bias rollers 79Y, 79M, 79C, and 79K sandwich the intermediate transfer belt 78 together with the four photoconductor drums 5Y, 5M, 5C, and 5K, respectively, thus forming the four primary transfer nips between the intermediate transfer belt 78 and the photoconductor drums 5Y, 5M, 5C, and 5K. Each of the primary transfer bias rollers 79Y, 79M, 79C, and 79K is applied with a primary transfer bias having a polarity opposite the polarity of the electric charge of toner.
The intermediate transfer belt 78 is moved in the direction indicated by the arrow in FIG. 1 and sequentially passes through the primary transfer nips formed by the primary transfer bias rollers 79Y, 79M, 79C, and 79K. The yellow, magenta, cyan, and black toner images on the photoconductor drums 5Y, 5M, 5C, and 5K are primarily transferred to and superimposed on the intermediate transfer belt 78, thereby forming the color toner image.
Subsequently, the intermediate transfer belt 78 bearing the color toner image reaches a position opposite a secondary transfer roller 89. At the position, the secondary transfer backup roller 82 and the secondary transfer roller 89 nip the intermediate transfer belt 78 therebetween to form a secondary transfer nip. The four color toner image formed on the intermediate transfer belt 78 is transferred onto the sheet P conveyed to the position of the secondary transfer nip. At this time, untransferred toner that is not transferred onto the sheet P remains on the surface of the intermediate transfer belt 78. The intermediate transfer belt 78 reaches a position opposite the intermediate transfer belt cleaner 80. At the position, the intermediate transfer belt cleaner 80 collects the untransferred toner from the intermediate transfer belt 78.
Thus, a series of transfer processes performed on the surface of the intermediate transfer belt 78 is completed.
The sheet P conveyed through the secondary transfer nip is conveyed from a sheet feeder 12 disposed in the lower portion of the body of the image forming apparatus 1 through a conveyance path disposed in the right side portion of the body of the image forming apparatus 1, which includes a feed roller 97, a registration roller pair 98, a fixing device 20, and conveyance guide plates 110.
Specifically, the sheet feeder 12 contains a stack of multiple sheets P such as sheets of paper stacked on top of one another. As the feed roller 97 is rotated counterclockwise in FIG. 1, the feed roller 97 feeds a top sheet P from the stack in the sheet feeder 12 to a roller nip between the registration roller pair 98.
As the registration roller pair 98 stops rotating temporarily, the leading end of the sheet P stops moving at the roller nip of the registration roller pair 98. Subsequently, the registration roller pair 98 is rotated to convey the sheet P to the secondary transfer nip, timed to coincide with the arrival of the color toner image on the intermediate transfer belt 78. Thus, the desired color toner image is transferred onto the sheet P.
Subsequently, the sheet P, onto which the color toner image is transferred at the secondary transfer nip, is conveyed to the position of the fixing device 20. In the fixing device 20, a fixing belt 21 and a pressure roller 31 apply heat and pressure to the sheet P to fix the transferred color toner image on the sheet P, which is referred to as a fixing process.
The sheet P is sent out from the fixing device 20. The conveyance guide plates 110 as the conveyance guide guides the sheet P to be conveyed toward the ejection port A. The sheet P is ejected to the outside of the image forming apparatus through the ejection port A by an ejection roller pair 99. The sheets P ejected one by one from the ejection port A by the ejection roller pair 99 are sequentially stacked as output images on a stacker 100.
Thus, a series of image forming processes (a printing operation) performed by the image forming apparatus 1 is completed.
A heating conveyance device 19 in the present embodiment to heat and convey the sheet P includes the fixing device 20 and the conveyance guide plates 110 serving as the conveyance guide, which is described in detail below.
As described above, the image forming apparatus 1 includes the conveyance path from the sheet feeder 12 to the ejection port A. The conveyance path is disposed on one side (the right side in FIG. 1) of the body of the image forming apparatus 1 and forms a substantially C-shaped conveyance path. Forming such a substantially C-shaped conveyance path stabilizes the conveyance and ejection of the sheet P.
With reference to FIGS. 2 to 6, the following describes a configuration and operation of the fixing device 20 incorporated in the image forming apparatus 1.
The fixing device 20 conveys the sheet P (bearing an unfixed toner image) while heating the sheet P. With reference to FIGS. 2 to 4, the fixing device 20 includes the fixing belt 21 as a fixing rotator, a reinforcement 30, a planar heater 24 as a heater, the pressure roller 31 as a pressure rotator, a thermostat 40 (a bimetal type thermostat).
The fixing belt 21 is an endless belt disposed in contact with an outer circumferential surface of the pressure roller 31 and driven to rotate by rotation of the pressure roller 31. The fixing belt 21 is a thin and flexible endless belt driven to rotate counterclockwise as indicated by an arrow in FIG. 2. The fixing belt 21 includes a base layer having an inner circumferential surface (i.e., a sliding contact surface of the fixing belt 21 sliding over the planar heater 24), an elastic layer coating the base layer, and a release layer coating the elastic layer, which define a total thickness of the fixing belt 21 not greater than 1 mm.
The base layer of the fixing belt 21 has a thickness in a range of from 30 µm to 50 µm and is made of metal, such as nickel or stainless steel, or resin such as polyimide.
The elastic layer of the fixing belt 21 has a thickness of 100 µm to 300 µm and is made of rubber such as silicone rubber, silicone rubber foam, or fluororubber. The elastic layer absorbs slight surface asperities of the fixing belt 21 at a fixing nip formed between the fixing belt 21 and the pressure roller 31, facilitating even heat conduction from the fixing belt 21 to the color toner image on the sheet P and thereby preventing the formation of an orange peel image on the sheet P.
The release layer of the fixing belt 21 has a thickness in a range of from 5 µm to 50 µm and is made of material such as tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), polytetrafluoroethylene (PTFE), polyimide, polyether imide, and polyether sulfone (PES). The release layer facilitates separation or peeling-off of toner of the color toner image on the sheet P from the fixing belt 21.
Inside the loop of the fixing belt 21, the planar heater 24, a holder 23, the reinforcement 30, and the thermostat 40 are disposed
The planar heater 24 is disposed so as to extend in a width direction that is a direction perpendicular to the surface of the paper on which FIG. 2 is drawn, the lateral direction in each of FIGS. 3 and 4, and the vertical direction in FIG. 5. The planar heater 24 contacts the inner circumferential surface of the fixing belt 21. The planar heater 24 is pressed against the pressure roller 31 via the fixing belt 21 to form the fixing nip through which the sheet P is conveyed. The planar heater 24 is disposed inside the loop formed by the fixing belt 21 such that the inner circumferential surface of the fixing belt 21 slides over the planar heater 24. Pressing the planar heater 24 against the pressure roller 31 via the fixing belt 21 forms the fixing nip between the fixing belt 21 and the pressure roller 31, through which the sheet P is conveyed. As described above, the planar heater 24 functions as a nip formation pad that is a member forming the fixing nip. The planar heater 24 may include a surface layer or a sheet made of low friction material such as PTFE on the surface of the planar heater 24 to reduce sliding friction between the fixing belt 21 and the planar heater 24.
In addition, the planar heater 24 includes a resistor pattern 26 (see FIGS. 5A and 5B) formed on a portion that is in sliding contact with the inner circumferential surface of the fixing belt 21. A power supply supplies electric power to the resistor pattern 26 serving as a resistive heat generator, and the resistor pattern 26 generates heat according to the resistance of the resistor pattern 26 to heat the fixing belt 21. As described above, the planar heater 24 also functions as a heater (heating body) that heats the fixing belt 21.
The fixing nip in the fixing device 20 has a flat shape in FIG. 2 but may have a curved shape (for example, a concave along the curvature of the pressure roller 31).
The holder 23 holds the planar heater 24. The holder 23 has a recess, and the planar heater 24 is fitted into the recess to hold the planar heater 24 in the width direction.
The reinforcement 30 holds the holder 23 holding the planar heater 24. The fixing device 20 includes a housing 43. The housing 43 holds both ends of the reinforcement 30 holding the planar heater 24 and the holder 23 in the width direction via flanges 42 (see FIG. 3).
As described above, the planar heater 24 (the resistor pattern 26) disposed inside the loop of the fixing belt 21 directly heats the fixing belt 21. The outer circumferential surface of the fixing belt 21 heated by the planar heater 24 heats the color toner image on the sheet P.
The output of the planar heater 24 is controlled based on the temperature of the planar heater 24 detected by the thermostat 40. The thermostat 40 directly contacts the planar heater 24 (or indirectly contacts the planar heater 24 via another member). The fixing device 20 in the present embodiment does not include a temperature sensor that directly detects the surface temperature of the fixing belt 21. Controlling the temperature of the planar heater 24 by using the thermostat 40 indirectly controls the surface temperature of the fixing belt 21 (a fixing temperature) to be a desired temperature.
The configuration and operation of the planar heater 24 and the thermostat 40 are described below in more detail with reference to FIGS. 5A, 5B, and 6.
With reference to FIG. 4, a pair of flanges 42 guides ends of the inner circumferential surface of the fixing belt 21 in the width direction of the fixing belt 21 such that the fixing belt 21 maintains a substantially cylindrical posture. Specifically, the two flanges 42 are made of a heat-resistant resin material and are held by both sides of the housing 43 in the width direction of the housing 43 of the fixing device 20 so that the flanges 42 can slide and move along both sides in a direction forming the fixing nip. Each of the flanges 42 includes a guide 42a and a stopper. The guides 42a hold the fixing belt 21 to maintain the substantially cylindrical posture of the fixing belt 21. The stopper restricts motion or skew of the fixing belt 21 in the width direction of the fixing belt 21.
As illustrated in FIG. 3, the fixing device 20 includes pressing levers 52 of a pressing device 51. The pressing levers press the flanges 42 such that the fixing belt 21, the planar heater 24, and the holder 23 press the pressure roller 31. The flanges 42 are disposed to support both ends of the loop of the fixing belt 21 in the width direction except for portions facing both ends of the fixing nip so that the planar heater 24 can form the fixing nip. The inner circumferential surface of the fixing belt 21 is loosely contacted only by the planar heater 24 and the flanges 42 at respective ends of the fixing belt 21 in the width direction thereof. No other component, such as a belt guide, contacts the inner circumferential surface of the fixing belt 21 to guide the fixing belt 21 as it rotates.
The fixing device 20 includes the reinforcement 30 that is disposed inside the loop of the fixing belt 21 so as to be in contact with the pressure roller 31 via the holder 23, the planar heater 24, and the fixing belt 21. The reinforcement 30 reinforces the planar heater 24 forming the fixing nip (and the holder 23), enhancing the mechanical strength of the holder 23 and the planar heater 24. The reinforcement 30 is assembled to the holder 23 (or the housing 43) by screw fastening or other fasteners. The reinforcement 30 receiving the pressure from the pressure roller 31 via the holder 23, the planar heater 24, and the fixing belt 21 prevents a disadvantage that the pressure from the pressure roller 31 largely deforms the planar heater 24 (and the holder 23) at the fixing nip. Preferably, the reinforcement 30 is made of metal having an increased mechanical strength, such as stainless steel or iron, to achieve the above-described function.
The holder 23 may be made of resin or metal. Preferably, the holder 23 is made of resin that has rigidity to prevent the holder 23 from bending even if the holder 23 receives pressure from the pressure roller 31, and the resin preferably has heat resistance and thermal insulation. The resin may be liquid crystal polymer (LCP), polyamide imide (PAI), polyether sulfone (PES), polyphenylene sulfide (PPS), polyether nitrile (PEN), and polyether ether ketone (PEEK). In the present embodiment, liquid crystal polymer (LCP) is used as the material of the holder 23.
With reference to FIG. 2, the pressure roller 31 as the pressure rotator includes a cored bar 32 (serving as an axial portion) and an elastic layer 33 coating the cored bar 32. The pressure roller 31 is driven and rotated clockwise in FIG. 2 by a drive motor 95.
The cored bar 32 of the pressure roller 31 has a hollow structure made of metal.
The elastic layer 33 of the pressure roller 31 is made of material such as silicone rubber foam, silicone rubber, or fluororubber. A thin release layer made of PFA or PTFE may be disposed on the surface of the elastic layer 33. The pressure roller 31 is pressed against the fixing belt 21 to form a desired fixing nip between the fixing belt 21 and the pressure roller 31. As illustrated in FIG. 3, a gear 45 is attached to the pressure roller 31 and engages a driving gear of the drive motor 95 so that the pressure roller 31 is driven and rotated clockwise in FIG. 2, that is, a direction indicated by the arrow in FIG. 2. Both ends of the pressure roller 31 in the width direction of the pressure roller 31 are rotatably supported by the housing 43 of the fixing device 20 through bearings.
A description is provided of a regular fixing process to fix the toner image on the sheet P, which is performed by the fixing device 20 having the construction described above.
Turning on a power switch on the body of the image forming apparatus 1 supplies power to the planar heater 24, and the motor starts driving and rotating the pressure roller 31 clockwise in FIG. 2, that is, in the direction indicated by the arrow in FIG. 2. Due to driving and rotating the pressure roller 31, friction between the pressure roller 31 and the fixing belt 21 at the fixing nip rotates the fixing belt 21 in a direction indicated by an arrow in FIG. 2.
After the fixing belt 21 rotates, the sheet P is fed from the sheet feeder 12, and the color toner image is transferred onto the sheet P at the position of the secondary transfer roller 89. As a result, the sheet P bears an unfixed color image. As illustrated in FIG. 2, the sheet P bearing the unfixed toner image is conveyed in a direction indicated by an arrow Y10 while the sheet P is guided by a guide plate and enters the fixing nip formed between the fixing belt 21 and the pressure roller 31 pressed against the fixing belt 21.
The toner image is fixed on the surface of the sheet P under heat from the fixing belt 21 heated by the planar heater 24 and pressure exerted from the planar heater 24 (and the holder 23) and the pressure roller 31 pressed against the planar heater 24 reinforced by the reinforcement 30. After the toner image is fixed on the surface of the sheet P, the sheet P is sent out from the fixing nip and conveyed in a direction indicated by an arrow Y11 in FIG. 2.
With reference to FIGS. 5A and 5B, the planar heater 24 includes a base 25, the resistor patterns 26 (the resistive heat generators), conductor patterns 27 (relay portions), and power supply electrodes 28 as electrodes.
The base 25 has a front face facing the inner circumferential surface of the fixing belt 21 in the fixing nip. At least the front face of the base 25 is made of an insulative material. In the present embodiment, the base 25 is entirely made of the insulative material (aluminum nitride (AlN) in the present embodiment).
The resistor patterns 26 are formed on the front face of the base 25. Similarly, the conductor patterns 27 are also formed on the front face of the base 25.
A current flows through the resistor pattern 26 (that is, energizing the resistor pattern 26), the resistance of the resistor pattern 26 generates heat, and the resistor pattern 26 functions as the resistive heat generator. The resistor pattern 26 is formed by applying and screen-printing a paste prepared to have a desired resistance value to the surface of the base 25 and baking the paste after screen-printing.
Each of the conductor patterns 27 electrically couples the resistor patterns 26 or couples the resistor pattern 26 to the power supply electrode 28 to function as the relay portion that flows the current input from the power supply electrode 28 to the resistor pattern 26. The conductor pattern 27 is formed by applying and screen-printing a paste having high conductivity to the surface of the base 25 and baking the paste after screen-printing.
The power supply electrode 28 is electrically coupled to the conductor pattern 27 and is formed to couple to a connector that is an external terminal. Accordingly, even when the surface layer having electrical insulating properties and low friction properties is formed on the entire surface of the planar heater 24, a part of the surface layer over the power supply electrode 28 is removed to expose the power supply electrode 28 and supply power to the power supply electrode 28.
The power supply electrode 28 is made of a silver-based material such as silver (Ag) or silver palladium (AgPd) in order to reduce heat generation due to energization. In the present embodiment, the power supply electrode 28 is formed by screen-printing the material on the surface of the base 25 and baking the material after screen-printing.
With reference to FIG. 6, the thermostat 40 in the present embodiment is the bimetal type thermostat including a cap 401, a bimetal 402, a pin 403, a first contact 404, a second contact 405, a spring 406, a terminal 407, an attachment 408, a case 409.
In the bimetal type thermostat 40, the planar heater 24 (the resistor pattern 26) that is a target object in which the temperature is detected contacts the cap 401, and the bimetal 402 receives heat from the cap 401. If the temperature of the bimetal 402 exceeds a predetermined temperature, the bimetal 402 deforms and pushes the pin 403. Under normal operating conditions, the pushing force of the spring 406 pushes the second contact 405 to be in contact with the first contact 404. When the pin 403 is pushed as described above, the first contact 404 and the second contact 405 are separated from each other, which cuts off a current flow via the terminal 407. Since the current flow is cut off, the controller 60 determines that an excessive temperature rise occurs in the planar heater 24.
As described above, the thermostat 40 also functions as a safety device to prevent an excessive temperature rise in the planar heater 24.
Since a mechanical force acting on the bimetal changes the temperature of the deformation of the bimetal 402, the length of the pin 403 is set to a length that does not press the bimetal 402.
In the present embodiment, the thermostats 40 are disposed at three positions, i.e., the center portion and both end portions in the width direction, but the number and the installation positions are not limited to this.
With reference to FIG. 5, the fixing device 20 in the present embodiment includes a thermal equalizer 48. The thermal equalizer 48 contacts the planar heater 24 and uniforms heat generated in the planar heater 24 (particularly, uniforms heat in the width direction). The thermal equalizer 48 may be a sheet made of a high thermal conductive material such as metal or carbon. Placing the thermal equalizer 48 on the planar heater 24 reduces the disadvantage that conveying the sheet having a size in the width direction smaller than the length M of the planar heater 24 (the resistor pattern 26) in the width direction increases the temperature of the planar heater 24 in a non-sheet passing region in which the sheet P does not pass and causes temperature unevenness in the width direction. Accordingly, placing the thermal equalizer 48 on the planar heater 24 reduces the curl (the curl in the width direction) of the sheet P caused by the above-described temperature unevenness after the fixing process.
The following describes the configuration and operation of the heating conveyance device 19 in detail, which is characteristic of the image forming apparatus 1 according to the present embodiment.
The heating conveyance device 19 heats and conveys the sheet P and includes the fixing device 20 and the conveyance guide plates 110 as the conveyance guide.
As described above with reference to FIG. 2, the fixing device 20 includes the planar heater 24 as the heater extending in the width direction, the fixing belt 21 as the fixing rotator heated by the planar heater 24, the pressure roller 31 as the pressure rotator, and the thermostat 40 directly or indirectly contacting the planar heater 24. The pressure roller 31 is in pressure contact with the planar heater 24 via the fixing belt 21 to form the fixing nip. In other words, the pressure roller 31 is pressed against the fixing belt 21 to form the fixing nip through which the sheet P is conveyed in a conveyance direction intersecting the width direction.
With reference to FIG. 7 and FIG. 1, the heating conveyance device 19 in the image forming apparatus 1 in the present embodiment includes conveyance guide plates 110 as the conveyance guide to guide the sheet P sent out from the fixing nip in the fixing device 20 toward the ejection port A. The conveyance guide functions as a correction member that corrects a curl of the sheet P.
Specifically, the conveyance guide includes a pair of conveyance guide plates 110 disposed downstream of the fixing device 20 and upstream of the ejection port A (the ejection roller pair 99). One of the pair of conveyance guide plates 110 faces the front face of the sheet P to be conveyed. The front face of the sheet P faces the fixing belt 21 when the sheet P passes through the fixing nip. The other one of the pair of conveyance guide plates 110 faces the back face of the sheet P to be conveyed. The back face of the sheet P faces the pressure roller 31 when the sheet P passes through the fixing nip. The conveyance guide plates 110 form a sheet conveyance path that bends (or curves) from the lower right side to the upper left side in FIG. 7 (and FIG. 1). After the fixing process, the conveyance guide plates 110 bend the sheet P and guide the sheet P to the ejection port A. In other words, the sheet P is bent along a direction defined by the conveyance guide plates bent or curved.
The shape of the conveyance guide plate 110 is not limited to the shape illustrated in FIG. 7. For example, the conveyance guide plate 110 may be formed of only a curved guide plate or may be formed of only a flat guide plate.
FIG. 7 is a diagram illustrating the configuration of the heating conveyance device 19 in the image forming apparatus 1 in a cross section orthogonal to the width direction. As illustrated in FIG. 7, the fixing nip in the fixing device 20 has an entrance N1 and an exit N2, and the image forming apparatus 1 is configured such that the conveyance direction of the sheet P fed from the exit N2, which is a direction of a virtual straight line S in FIG. 7, is directed to the right side in FIG. 7 that is a region opposite a region including the ejection port A with respect to a virtual vertical line H passing through the exit N2 of the fixing nip.
Specifically, the fixing belt 21 as the fixing rotator is disposed closer to the ejection port A than the pressure roller 31 as the pressure rotator in the fixing device 20. In other words, the fixing belt 21 is disposed the left side of the pressure roller 31 in FIG. 7. In addition, the fixing device 20 is configured to send the sheet P obliquely upward from the fixing nip in FIG. 7. The sheet P is sent out from the fixing nip along a direction of a virtual straight line S connecting the entrance N1 and the exit N2 of the fixing nip. The direction of the virtual straight line S is obliquely upward. When viewed in the cross section orthogonal to the width direction, the virtual straight line S is inclined to a side away from the ejection port A with respect to the virtual vertical line H extending in the vertical direction. In other words, in the cross section orthogonal to the width direction, the fixing device 20 ejects the sheet from the exit N2 to the conveyance guide 110 in the conveyance direction, and the conveyance direction is inclined with respect to the virtual vertical line H passing through the exit N2 and extending in the vertical direction. The ejection port A is disposed at one side of the virtual vertical line H, and the conveyance direction is inclined toward another side opposite to the one side of the virtual vertical line H. In other words, the position of the exit N2 of the fixing nip is above the horizontal line passing through the center of the pressure roller 31, and the direction of the fixing nip in the vicinity of the exit N2 is from the lower left to the upper right in FIG. 7.
In the present specification, the virtual straight line S is defined as the straight line simply connecting the entrance N1 and the exit N2 of the fixing nip even if the fixing nip in the fixing device 20 does not have a flat shape but has a curved shape (for example, a concave shape along the radius of curvature of the pressure roller 31).
The conveyance guide plate 110 extends from the vicinity of the exit N2 of the fixing nip toward the downstream side in a sheet conveyance direction substantially in parallel to the virtual straight line S, then is inclined at an angle θ (which is referred to as a contact angle) formed with the virtual straight line S, and extends downstream toward the ejection port A.
FIG. 8 is a diagram illustrating a configuration of a heating conveyance device including a fixing device 200 according to a comparative example. As illustrated in FIG. 8, a virtual straight line S' passing through the entrance N1 and the exit N2 of the fixing nip in the fixing device 200 extends vertically upward. Compared with the virtual straight line S', the virtual straight line S passing through the entrance N1 and the exit N2 of the fixing nip in FIG. 7 is inclined obliquely upward to the right in FIG. 7. As a result, the angle θ1 (the contact angle) formed by the virtual straight line S and the conveyance guide plate 110 in FIG. 7 is smaller than an angle θ' (a contact angle) in the comparative example illustrated in FIG. 8 (that is, θ1 < θ').
The sheet P sent out from the fixing nip has a high temperature and is cooled from the high temperature. In this process, moisture is evaporated from the back side of the sheet (the toner image is not fixed onto the back side of the sheet), and the back side of the sheet shrinks, which causes the curl of the sheet.
However, immediately after the sheet P is sent out from the fixing nip, the sheet P collides with the conveyance guide plate 110 at a relatively shallow angle θ1 (that is the contact angle) while the sheet P is still hot. The back side of the sheet P contacts the conveyance guide plate 110, and the sheet P is conveyed along the conveyance guide plate 110. Since the sheet P is bent at a position at which the sheet P collides with the conveyance guide 110 and is conveyed along the conveyance guide plate 110, the curl of the sheet P is finally corrected, and the sheet P is ejected from the ejection port A. In particular, the image forming apparatus 1 according to the present embodiment includes the substantially C-shaped conveyance path as described above that enables installing the conveyance guide plate 110 that can easily correct the curl. As a result, the configuration according to the present embodiment is useful.
The above-described configuration reduces the curl of the sheet P ejected from the ejection port A and stacked on the stacker 100, which enhances the appearance and stacking property.
The sheet P is conveyed along the conveyance guide plate 110 and nipped and ejected by the ejection roller pair 99. The ejection roller pair 99 may pull the sheet P while the sheet P is nipped by the ejection roller pair 99 and the fixing nip. For example, setting the rotational speed of the ejection roller pair 99 to be faster than the conveyance speed of the sheet P fed from the exit N2 of the fixing nip enables the ejection roller pair 99 to pull the sheet while the sheet P is nipped by the ejection roller pair 99 and the fixing nip. In addition, the heating conveyance device 19 (and the image forming apparatus 1) may include a bent section 110a as the correction member changing the conveyance direction of the sheet P sent out from the exit N2 of the fixing nip to the direction toward the ejection port A. In other words, the bent section 110a changes the conveyance direction of the sheet P from the other side to the one side of the virtual vertical line H toward the ejection port A in the cross section orthogonal to the width direction.
The bent section 110a as the correction member is a part of the conveyance guide plate 110 of the conveyance guide and faces the front face of the sheet P onto which the toner image is fixed. The bent section 110a as the correction member extends downstream from the vicinity of the exit N2 of the fixing nip and is bent at a predetermined angle. The bent section 110a is between the fixing device 20 and the ejection port A.
The bent section 110a serving as the correction member bends the sheet P fed from the exit N2 of the fixing nip within a range of 90 to 100 degrees in the direction toward the ejection port A.
The above-described configuration can reduce the curl (in other words, the bending) of the sheet P after the sheet P is conveyed along the conveyance guide 110.
The bent section 110a in the present embodiment is a part of the conveyance guide plate 110 of the conveyance guide but may be another component that imparts a reverse curl to the sheet P immediately after the sheet is sent out from the fixing nip (for example, an angular claw formed so as to protrude toward the conveyance path). Alternatively, the bent section 110a may be configured by a rotator that is unlikely to scrape the toner image on the front face of the sheet P.
With reference to FIG. 7, the thermostat 40 is disposed to face the pressure roller 31 as the pressure rotator via the planar heater 24.
Specifically, the thermostat 40 is disposed to be inclined with respect to the vertical direction together with the planar heater 24. The thermostat 40 applies a pressing force to the planar heater 24 in a direction indicated by a white arrow substantially orthogonal to the virtual straight line S in FIG. 7 (that is also a direction inclined obliquely downward with respect to the horizontal direction). The thermostat 40 is pressed against the pressure roller 31 via the planar heater 24.
As a result, a gravity component acts on the bimetal 402 (see FIG. 6) of the thermostat 40 in a direction in which the bimetal approaches and contacts the cap 401 (see FIG. 6), which is different from the fixing device 200 in the comparative example including the thermostat 40 and the planar heater 24 that are arranged in the vertical direction as illustrated in FIG. 8. The above-described gravity component causes the bimetal 402 to be likely to come into contact with the cap 401 even if the bimetal 402 is loosely held in the case 409 of the planar heater 24 and can prevent erroneous detection (that is a decrease in detection accuracy regarding detection of an excessive temperature rise of the planar heater 24) caused by a gap between the cap 401 and the bimetal 402.
As a result, the above-described configuration can accurately detect an excessive temperature rise in the planar heater 24 (in other words, a heat source runaway) and interrupt the power supply to the planar heater 24 at an appropriate timing based on the detection result.
As described above with reference to FIG. 2, controlling the temperature of the planar heater 24 by using the thermostat 40 indirectly controls the surface temperature of the fixing belt 21 (the fixing temperature) in the fixing device 20.
In other words, the fixing temperature is not directly controlled based on the detection result of the temperature sensor that directly detects the surface temperature of the fixing belt 21 but is indirectly controlled based on the detection result of the thermostat 40.
Specifically, the thermostat 40 that detects the temperature of the planar heater 24 higher than a predetermined range determines that the fixing temperature of the fixing belt 21 is higher than a predetermined range and cuts off the power supplied to the planar heater 24. In contrast, the thermostat 40 that detects the temperature of the planar heater 24 lower than the predetermined range determines that the fixing temperature of the fixing belt 21 is lower than the predetermined temperature range and supplies the power to the planar heater 24.
Maintaining the surface temperature of the fixing belt 21 (the fixing temperature) to be as low as possible with good responsiveness effectively reduces the amount of the curl generated in the sheet P after the fixing process. However, setting the contact angle θ between the virtual straight line S and the conveyance guide plate 110 to be large corrects the curl and is unlikely to cause the curl as described above. Even if indirectly controlling the fixing temperature based on the detection result of the thermostat 40 decreases the responsiveness of the temperature control, the contact angle θ set to be large can sufficiently cancel the curl caused by the decreased responsiveness of the temperature control. Removing the temperature sensor that directly detects the surface temperature of the fixing belt 21 from the fixing device can reduce the cost of the fixing device 20. Instead of the above-described control using the thermostat 40, a temperature sensor may detect the temperature of the planar heater 24, and the controller 60 may control the power supply to the planar heater 24 based on the detection results of the temperature sensor.
As illustrated in FIG. 7, the fixing device 20 includes the pressure roller 31 as the pressure rotator having the outer diameter smaller than the outer diameter of the fixing belt 21 as the fixing rotator.
Reducing the outer diameter of the pressure roller 31 as the pressure rotator reduces the thermal capacity of the pressure roller, which saves the energy consumed by the fixing device 20. In addition, reducing the diameter of the pressure roller 31 reduces the cost and size of the fixing device 20.
However, reducing the diameter of the pressure roller 31 reduces the nip width of the fixing nip, which increases the amount of the curl generated in the sheet P after the fixing process. However, setting the contact angle θ between the virtual straight line S and the conveyance guide plate 110 to be large corrects the curl and is unlikely to cause the curl as described above. The contact angle θ set to be large can sufficiently cancel the increase in the amount of the curl caused by the reduced nip width.
With reference to FIG. 9, control timings in the fixing device 20 are described. The controller 60 controls the planar heater 24 as the heater to start heating the fixing belt 21 before the start of the printing operation without rotating the fixing belt 21 as the fixing rotator and the pressure roller 31 as the pressure rotator.
Specifically, when a user operates a personal computer coupled to the image forming apparatus 1 to send a print command to the controller 60 in the image forming apparatus 1, receiving the print command becomes the trigger to supply power to the planar heater 24 and start heating the fixing belt 21 (to start a warming-up mode). At this time, the controller 60 does not drive the drive motor 95 (see FIG. 2) that drives and rotates the pressure roller 31, and the fixing belt 21 and the pressure roller 31 stop rotating. Therefore, the pressure roller 31 does not receive heat from the fixing belt 21 over the total circumference. The controller 60 starts driving the drive motor 95 when the controller 60 controls the sheet feeder 12 to feed the sheet P to actually start the printing operation (the fixing process).
The above-described control can shorten the time for driving the drive motor 95 to be smaller than a control in which the print command is the trigger to start driving the drive motor 95 during the warming-up mode. As a result, the above-described control can save the energy consumed by the image forming apparatus and shorten the recovery time.
However, stopping driving of the drive motor 95 during the warming-up mode does not sufficiently heat the pressure roller 31 over the total circumference, which increases the amount of the curl generated in the sheet P after the fixing process. However, setting the contact angle θ between the virtual straight line S and the conveyance guide plate 110 to be large corrects the curl and is unlikely to cause the curl as described above. The contact angle θ set to be large can sufficiently cancel the increase in the amount of the curl caused by stopping driving of the drive motor 95 during the warming-up mode.
With reference to FIG. 10, control regarding a sheet size in the present embodiment is described. As illustrated in FIG. 10, when the fixing device continuously conveys sheets P each having a size in the width direction shorter than a length M of the resistor pattern 26 of the planar heater 24 (see FIG. 5) by a predetermined value or more (for example, sheets P each having a size equal to or smaller than 210 mm in the width direction corresponding to a length of the shorter side of A4 size), the controller 60 performs the control reducing the number of sheets P conveyed per unit time (the number of printed sheets) to be smaller a number of sheets conveyed per unit time when the fixing device continuously conveys sheets P each having a size other than the above-described size (for example, sheets P each having a size larger than 210 mm in the width direction corresponding to a length of the shorter side of A4 size).
In other words, the controller performs a low-speed printing mode at a lower printing speed than that of a regular printing mode when the fixing device conveys the sheet P having a sufficiently small length in the width direction with respect to the length M of the resistor pattern 26 of the planar heater 24 in the width direction.
This is because performing regular printing mode to continuously print the sheets having the above-described small sizes is likely to increase the fixing temperature of a non-sheet passing region in the fixing nip compared to a sheet passing region, and the sheet P after the fixing process is likely to curl. Reducing the number of sheets P conveyed per unit time (the number of printed sheets) to be smaller than that of the regular printing mode when the sheets P having the above-described small size are continuously printed increases the time for heat transfer from the non-sheet passing region to the sheet passing region, which is unlikely to cause the curl in the sheet P after the fixing process.
In detail, as illustrated in FIG. 10, the controller 60 determines whether the size of the sheet P in the width direction is equal to or smaller than a predetermined value W (step S1) based on the data of the sheet input by the user after the controller receives the print command. If the controller 60 determines that the size of the sheet P in the width direction is not equal to or smaller than the predetermined value W, the controller performs the regular printing mode (step S2). In contrast, if the controller 60 determines that the size of the sheet P in the width direction is equal to or smaller than the predetermined value W, the controller performs the low-speed printing mode (step S3).
The following describes a first modification.
As illustrated in FIG. 11, the fixing device 20 according to the first modification includes the holder 23 holding the planar heater 24 and having an entrance portion adjacent to the entrance N1 of the fixing nip and an exit portion adjacent to the exit N2 of the fixing nip, and the exit portion protrudes toward the pressure roller 31 as the pressure rotator as compared with the entrance portion.
Specifically, the holder 23 according to the first modification has the recess, and the planar heater 24 having a substantially plate-shape is fitted into the recess when viewed in a cross section orthogonal to the width direction. In the cross section orthogonal to the width direction, the holder 23 has an entrance protrusion portion adjacent to the entrance N1 and an exit protrusion portion 23a adjacent to the exit N2, and the protrusion amount of the exit protrusion portion 23a protruding toward the pressure roller 31 is longer than the protrusion amount of the entrance protrusion portion protruding toward the pressure roller 31.
In the above-described configuration, the sheet P sent out from the fixing nip receives a curl correction force at each of two positions that are in the exit N2 of the fixing nip and the conveyance guide plate 110. As a result, the above-described configuration further reduces the amount of the curl generated in the sheet ejected from the ejection port A. Note that the sheet P is sent out from the exit N2 of the fixing nip in the direction indicated by the arrow in FIG. 11 that is the same direction as the direction indicated by the virtual straight line S in FIG. 7.
The following describes a second modification.
As illustrated in FIG. 12, the heating conveyance device 19 in the second modification includes a moving mechanism 120 that adjusts the angle θ1 at which the conveyance guide plate 110 of the conveyance guide is inclined toward the ejection port A.
Specifically, the moving mechanism 120 includes a motor mechanism and rotates one of the pair of conveyance guide plates 110 about a rotation shaft. The sheet P sent out from the fixing nip collides with one of the pair of conveyance guide plates 110 that is rotated by the moving mechanism 120.
The controller 60 determines whether the basis weight of the sheet P, which is input by the user or included in print data, is equal to or larger than a predetermined value Z (in other words, whether the sheet P is a thick sheet). When the controller 60 determines that the basis weight of the sheet P to be conveyed is equal to or larger than the predetermined value Z (in other words, the thick sheet), the controller 60 controls the moving mechanism 120 to adjust the angle θ1 (the contact angle) formed by the conveyance guide plate 110 to be larger than the angle θ1 when the sheet P having a basis weight smaller than the predetermined value Z (in other words, a sheet of plain paper or a thin sheet) is conveyed.
Specifically, when the thin sheet P thinner than the thick sheet is conveyed, the controller 60 controls the moving mechanism 120 to rotate the conveyance guide plate 110 so that the contact angle becomes θ1 (the position indicated by the solid line in FIG. 12). In contrast, when the thick sheet P is conveyed, the controller 60 controls the moving mechanism 120 to rotate the conveyance guide plate 110 so that the contact angle becomes larger than θ1 (the position indicated by the broken line in FIG. 12).
The thick sheet P collides with the conveyance guide plate 110 and is bent toward the direction opposite the direction of the curl caused by the evaporation of the moisture from the back side of the sheet P. In other words, the thick sheet P is bent so that the front face of the sheet onto which the toner image is fixed has a depressed center and raised edges. In the thick sheet P, a deformation amount caused by the conveyance guide plate is too large. The thick sheet ejected from the ejection port A is likely to have the curl having the depressed center in the front face of the thick sheet P. Setting the contact angle to be larger than θ1 for the thick sheet having high stiffness can prevent a conveyance failure in addition to reducing the curl.
The following describes a third modification.
As illustrated in FIG. 13, the image forming apparatus 1 in the third modification includes other conveyance guide plates 130 as another conveyance guide to guide the sheet P fed from the fixing nip to another ejection port B. In the following description, the conveyance guide plates 110 as the conveyance guide are referred to as first conveyance guide plates 110 as a first conveyance guide, and the other conveyance guide plates 130 as said another conveyance guide are referred to as second conveyance guide plates 130 as a second conveyance guide. The ejection port A is referred to as a first ejection port A, and said another ejection port B is referred to as a second ejection port B. An angle θ2 formed by the virtual straight line S and the second conveyance guide plate 130 that serves as the second conveyance guide to guide the sheet P to the second ejection port B is larger than the angle θ1 formed by the virtual straight line S and the first conveyance guide plate 110 that serves as the first conveyance guide to guide the sheet P to the first ejection port A (θ2 > θ1). The second conveyance guide plate 130 of the second conveyance guide is inclined in the clockwise direction in FIG. 13 with respect to the first conveyance guide plate 110 of the first conveyance guide.
Specifically, the first conveyance guide plate 110 includes a movable guide plate 111 as a switching part between the first conveyance guide plate 110 and the second conveyance guide plate 130, and the image forming apparatus 1 includes a driver to drive the movable guide plate 111 to rotate about a support shaft 111a.
When the fixing device conveys the sheet P having a basis weight smaller than the predetermined value Z, such as a sheet of plain paper or the thin sheet, the first conveyance guide plates 110 guide the sheet P sent out from the fixing nip to the first ejection port A to eject the sheet P from the first ejection port A to the outside of the image forming apparatus. At this time, the movable guide plate 111 is rotated to the position indicated by the broken line in FIG. 13 to form the angle θ1. The movable guide plate 111 as the switching part is rotated to the position indicated by the broken line in FIG. 13 to switch the conveyance path and guide the sheet P to the first ejection port A. At this time, the virtual straight line S and the movable guide plate 111 at the position indicated by the broken line in FIG. 13 forms the angle θ1. The back face of the sheet P sent out from the fixing nip collides with the movable guide plate 111. Subsequently, the sheet P is conveyed while the sheet P is in contact with the movable guide plate 111. Bending the sheet P at the position at which the sheet P collides with the movable guide plate 111 and conveying the sheet P along the first guide plate 110 reduces the curl occurred in the sheet P.
In contrast, when the fixing device conveys the sheet P having the basis weight equal to or larger than the predetermined value Z, such as the thick sheet, the second conveyance guide plates 130 guide the sheet P sent out from the fixing nip to the second ejection port B to eject the sheet P from the second ejection port B to the outside of the image forming apparatus. The movable guide plate 111 as the switching part is rotated to the position indicated by the solid line in FIG. 13 to switch the conveyance path to the second conveyance guide plates 130 and guide the sheet P to the second ejection port B. At this time, the virtual straight line S and the second guide plate 130 form the angle θ2 (θ2 > θ1). Conveying the thick sheet P along the second conveyance guide plate 130 that forms the contact angle θ2 larger than the angle θ1 can prevent a conveyance failure in addition to reducing the curl.
The thick sheet P collides with the conveyance guide plate 110 and is bent toward the direction opposite the direction of the curl caused by the evaporation of the moisture from the back side of the sheet. In other words, the thick sheet is bent so that the front face of the sheet onto which the toner image is fixed has a depressed center and raised edges. In the thick sheet, a deformation amount caused by the conveyance guide plate is too large, and the thick sheet ejected from the ejection port A is likely to have the curl having the depressed center in the front face of the thick sheet. To prevent the above disadvantage, using the second conveyance guide plate 130 that sets the increased contact angle θ1 when the thick sheet P is conveyed weakens the external force caused by the collision between the second conveyance guide plate 130 and the thick sheet P and reduces the above-described curl in the thick sheet P.
The following describes a fourth modification.
As illustrated in FIG. 14, the fixing device 20 in the fourth modification is a heater roller type fixing device and includes a fixing roller 22 as the fixing rotator and a halogen heater 35 as the heater.
Specifically, the fixing roller 22 as the fixing rotator has a multilayer structure and includes a cored bar having a hollow structure made of metal such as stainless steel and a coating layer including an elastic layer and a release layer that are laminated on the cored bar.
The fixing roller 22 as the fixing rotator is pressed against the pressure roller 31 as the pressure rotator to form the fixing nip.
The elastic layer of the coating layer of the fixing roller 22 is made of elastic material such as fluororubber, silicone rubber, or silicone rubber foam. The release layer of the coating layer of the fixing roller 22 is made of, for example, perfluoroalkoxy alkane (PFA).
The halogen heater 35 as the heater is fixed inside the loop of the fixing roller 22 that is the hollow portion.
The fixing device 20 configured as described above operates as follows.
When the image forming apparatus 1 is powered on, the alternating current voltage is applied from the power source in the body of the image forming apparatus 1 to the halogen heater 35.
In response to a print command (a print request) input, a drive motor as a drive mechanism starts rotating the fixing roller 22 clockwise in FIG. 14, and the pressure roller 31 starts rotating counterclockwise in FIG. 14 in accordance with the clockwise rotation of the fixing roller 22. After the fixing roller 22 and the pressure roller 31 start rotating, the sheet P is fed from the sheet feeder 12, and the toner image is transferred from the photoconductor drum 1 onto the sheet P at the position of the transfer roller 9. As a result, the sheet P bears the toner image, but the toner image is not fixed to the sheet P, that is an unfixed image. The sheet P bearing the unfixed image (that is the toner image) is conveyed in a direction indicated by the arrow in FIG. 14 and enters the fixing nip between the fixing roller 22 and the pressure roller 31 pressed against the fixing roller 22. The toner image is fixed onto the surface of the sheet P under heat from the fixing roller 22 and pressure exerted from the fixing roller 22 and the pressure roller 31. The sheet P, on which the toner image is fixed, is conveyed from the fixing nip in the direction indicated by an arrow in FIG. 14 according to the rotation of the fixing roller 22 and the pressure roller 31.
The image forming apparatus 1 including the fixing device 20 configured as described above also includes the conveyance guide plates 110 as the conveyance guide to bend the sheet P sent out from the fixing nip of the fixing device 20 in a predetermined direction and guide the sheet P toward the ejection port A, which is the same as the image forming apparatus illustrated in FIG. 7. When viewed in the cross section orthogonal to the width direction, the virtual straight line S passes through the entrance N1 and the exit N2 of the fixing nip of the fixing device 20, extends toward a sheet conveyance direction in which the sheet P is conveyed, and is inclined to a side away from the ejection port A. As a result, the above-described configuration is unlikely to cause a large curl generated in the sheet ejected from the ejection port A.
The following describes a fifth modification.
As illustrated in FIG. 15, the fixing device 20 in the fifth modification does not include the planar heater 24 and is not a heater heating type fixing device including the heater 35 but is an electromagnetic induction type fixing device including an electromagnetic induction coil 50 disposed so as to face the outer peripheral face of the fixing belt.
Specifically, the fixing device 20 according to the fifth modification also includes the nip formation pad 37, which is not the planar heater, as in the fixing device 20 illustrated in FIG. 2.
The fixing device 20 according to the fifth modification includes the electromagnetic induction coil 50 (an induction heating unit) as the heater. The electromagnetic induction coil 50 causes electromagnetic induction to heat the fixing belt 21 in the fifth modification.
The electromagnetic induction coil 50 includes a litz wire, which is a bundle of thin wires, extending in the width direction so as to cover a part of the fixing belt 21 and integrally formed with a core and a coil guide. The coil guide is made of resin having high heat resistance and holds the core and the electromagnetic induction coil 50.
The core is a semi-cylindrical member made of ferromagnetic material (having a relative magnetic permeability of about 1000 to 3000) such as ferrite. A center core and a side core are disposed to form an efficient magnetic flux toward the fixing belt 21. The core is disposed so as to face the electromagnetic induction coil 50 extending in the width direction.
In addition to the base layer, the elastic layer, and the release layer that are described with reference to FIG. 2, the fixing belt 21 includes a heat generating layer. The electromagnetic induction coil 50 generates heat in the heat generation layer due to electromagnetic induction. For example, the heat generation layer may be formed between the elastic layer and the release layer, or the base layer may be used as the heat generation layer. As the material of the heat generation layer, nickel, stainless steel, iron, copper, cobalt, chromium, aluminum, gold, platinum, silver, tin, palladium, or an alloy of some of these metals can be used.
The fixing device 20 configured as described above operates as follows.
When the fixing belt 21 rotates in the direction indicated by the arrow in FIG. 15, the fixing belt 21 is heated at a position facing the electromagnetic induction coil 50. Specifically, flowing a high-frequency alternating current through the electromagnetic induction coil 50 forms magnetic lines of force around the fixing belt 21 so as to be alternately switched in both directions.
At this time, an eddy current is generated in the surface of the heat generation layer of the fixing belt 21, and the eddy current and the electrical resistance of the heat generation layer itself generate Joule heat. The Joule heat generated by the electromagnetic induction heating heats the heat generation layer and heats the fixing belt 21.
In the example of FIG. 15, the electromagnetic induction coil 50 is disposed so as to face the outer circumferential surface of the fixing belt, but the electromagnetic induction coil 50 may be disposed so as to face the inner circumferential surface of the fixing belt.
The image forming apparatus 1 including the electromagnetic induction type fixing device 20 configured as described above also includes the conveyance guide plates 110 as the conveyance guide to bend the sheet P sent out from the fixing nip of the fixing device 20 in a predetermined direction and guide the sheet P toward the ejection port A, which is the same as the image forming apparatus illustrated in FIG. 7. When viewed in the cross section orthogonal to the width direction, the virtual straight line S passes through the entrance N1 and the exit N2 of the fixing nip of the fixing device 20, extends toward a sheet conveyance direction in which the sheet P is conveyed, and is inclined to a side away from the ejection port A. As a result, the above-described configuration is unlikely to cause a large curl generated in the sheet ejected from the ejection port A.
As described above, the heating conveyance device 19 of the image forming apparatus 1 in the present embodiment includes the fixing device 20. The fixing device 20 includes the planar heater 24 as the heater, the fixing belt 21 as the fixing rotator, and the pressure roller 31 as the pressure rotator. The planar heater 24 heats the fixing belt 21. The pressure roller 31 is pressed against the fixing belt 21 to form the fixing nip through which the sheet P is conveyed. In addition, the heating conveyance device 19 includes the conveyance guide plates 110 as the conveyance guide to guide the sheet P sent out from the fixing nip of the fixing device 20 toward the ejection port A. When viewed in the cross section orthogonal to the longitudinal direction of the planar heater 24 that is the width direction, the image forming apparatus 1 is configured such that the sheet P sent out from the exit N2 of the fixing nip is directed to the region opposite the region including the ejection port A with respect to the virtual vertical line H passing through the exit N2 of the fixing nip in the fixing device 20.
As a result, the above-described configuration is unlikely to cause a large curl generated in the sheet ejected from the ejection port A.
The above-described present embodiment and modifications are applied to the image forming apparatus 1 including the fixing device 20 using the pressure roller 31 as the pressure rotator. However, the present disclosure is also applicable to an image forming apparatus including a fixing device that uses a pressure belt as the pressure rotator.
The conveyance guide in the present embodiment includes the conveyance guide plate 110 having the plate shape and being made of a metal plate, but the present disclosure is not limited to this. As long as the conveyance guide has a guide face guiding a sheet, the conveyance guide, for example, may not have the plate shape and may be made of a resin material having a thickness.
In the present embodiment, the present disclosure is applied to the image forming apparatus 1 in which the sheet P is conveyed in the vertical direction but may be applied to an image forming apparatus in which the sheet P is conveyed in the horizontal direction. In this case, when viewed in the cross section orthogonal to the width direction, the virtual straight line S is inclined to a side away from the ejection port A with respect to the virtual horizontal line extending in the horizontal direction.
In the present embodiment, the present disclosure is applied to the heating conveyance device 19 installed in the image forming apparatus 1, but the heating conveyance device to which the present disclosure is applied is not limited to this. The present disclosure may be applied to, for example, a heating conveyance device installed in a drying device of an inkjet image forming apparatus, a heating conveyance device installed in a laminating device.
The above-described configurations also provide similar effects to those of the above-described embodiment and the modifications.
Note that the present disclosure is not limited to the above-described embodiments and modifications, and it is apparent that the above-described embodiments and modifications can be appropriately modified within the scope of the technical idea of the present disclosure in addition to what is suggested in the above-described embodiments and modifications.
The number, position, and shape of the components described above are not limited to the embodiment and modifications described above. Desirable number, position, and shape can be determined to perform the present disclosure.
Aspects of the present disclosure may be, for example, as follows.

(First Aspect)

In a first aspect, a heating conveyance device includes a fixing device and a conveyance guide. The fixing device includes a fixing rotator, a heater, and a pressure rotator. The heater heats the fixing rotator and extends in a width direction. The pressure rotator is pressed against the fixing rotator to form a fixing nip through which a sheet is conveyed in a conveyance direction intersecting the width direction. The fixing nip has an entrance and an exit. The conveyance guide guides the sheet fed from the fixing nip to an ejection port. In a cross section orthogonal to the width direction, the fixing device ejects the sheet from the exit to the conveyance guide in the conveyance direction. The conveyance direction is inclined with respect to a virtual vertical line passing through the exit and extending in a vertical direction. The ejection port is disposed at one side of the virtual vertical line, and the conveyance direction is inclined toward another side opposite to the one side of the virtual vertical line.

(Second Aspect)

In a second aspect, the heating conveyance device according to the first aspect further includes a bent section to change the conveyance direction from the another side to the one side of the virtual vertical line toward the ejection port in the cross section.

(Third Aspect)

In a third aspect, the conveyance guide in the heating conveyance device according to the second aspect includes the bent section between the fixing device and the ejection port.

(Fourth Aspect)

In a fourth aspect, the fixing device in the heating conveyance device according to any one of the first to third aspects includes a planar heater as the heater extending in the width direction, a fixing belt as the fixing rotator heated by the planar heater, the pressure rotator pressed against the planar heater via the fixing belt to form the fixing nip, and a thermostat disposed to contact the planar heater and face the pressure rotator via the planar heater.

(Fifth Aspect)

In a fifth aspect, the fixing device in the heating conveyance device according to the fourth aspect includes a holder holding the planar heater, the holder has an entrance portion adjacent to an entrance of the fixing nip and an exit portion adjacent to the exit of the fixing nip, and the exit portion protrudes toward the pressure rotator as compared with the entrance portion.

(Sixth Aspect)

In a sixth aspect, an outer diameter of the pressure rotator is smaller than an outer diameter of the fixing rotator in the heating conveyance device according to any one of the first to fifth aspects.

(Seventh Aspect)

In a seventh aspect, the heating conveyance device according to any one of the first to sixth aspects further includes another conveyance guide to guide the sheet fed from the fixing nip to another ejection port, and an angle formed by the conveyance direction and the conveyance guide is different from an angle formed by the conveyance direction and said another conveyance guide.

(Eighth Aspect)

In an eighth aspect, the heating conveyance device according to the seventh aspect further includes a switching part to convey the sheet fed from the fixing nip toward any one of the conveyance guide and said another conveyance guide.

(Ninth Aspect)

In a ninth aspect, the fixing device in the heating conveyance device according to any one of the fourth to eighth aspects includes a thermal equalizer that contacts the planar heater and uniforms heat generated in the planar heater.

(Tenth Aspect)

In a tenth aspect, an image forming apparatus includes the heating conveyance device according to any one of the first to ninth aspects.

(Eleventh Aspect)

In an eleventh aspect, the image forming apparatus according to the tenth aspect includes a controller to input a basis weight of the sheet, and the conveyance guide includes a portion inclined toward the ejection port at an adjustable angle. The controller is configured to determine whether the basis weight is equal to or greater than a predetermined value. In order to convey the sheet having the basis weight equal to or larger than the predetermined value, the controller is configured to adjust the angle to be larger than an angle to convey the sheet having the basis weight smaller than the predetermined value.
The above-described embodiments are illustrative and do not limit the present invention. Thus, numerous additional modifications and variations are possible in light of the above teachings. For example, elements and/or features of different illustrative embodiments may be combined with each other and/or substituted for each other within the scope of the present invention.

Claims

A heating conveyance device (19) comprising:
a fixing device (20) including:
a fixing rotator (21, 22); and

a heater (24, 35, 50) to heat the fixing rotator (21, 22), the heater extending in a width direction;

a pressure rotator (31) pressed against the fixing rotator (21, 22) to form a fixing nip through which a sheet (P) is conveyed in a conveyance direction intersecting the width direction, the fixing nip having an entrance and an exit; and

a conveyance guide (110, 130) to guide the sheet (P) fed from the fixing nip to an ejection port (A, B),

wherein, in a cross section orthogonal to the width direction,

the fixing device (20) ejects the sheet from the exit (N2) to the conveyance guide in the conveyance direction (S),

the conveyance direction (S) is inclined with respect to a virtual vertical line (H) passing through the exit (N2) and extending in a vertical direction (H),

the ejection port is disposed at one side of the virtual vertical line (H), and

the conveyance direction (S) is inclined toward another side opposite to the one side of the virtual vertical line (H).
The heating conveyance device (19) according to claim 1, further comprising
a bent section (110a, 130a) to change the conveyance direction from the another side to the one side of the virtual vertical line (H) toward the ejection port (A, B) in the cross section.
The heating conveyance device (19) according to claim 2,
wherein the conveyance guide (110, 130) includes the bent section (110a, 130a) between the fixing device (20) and the ejection port (A, B).
The heating conveyance device (19) according to any one of claims 1 to 3, wherein the fixing device (20) includes:
a planar heater (24) as the heater (24, 35, 50) extending in the width direction;

a fixing belt (21) as the fixing rotator (21, 22) heated by the planar heater (24);

the pressure rotator (31) pressed against the planar heater (24) via the fixing belt (21) to form the fixing nip; and

a thermostat (40) disposed to contact the planar heater (24) and face the pressure rotator (31) via the planar heater (24).
The heating conveyance device (19) according to claim 4,
wherein the fixing device (20) includes a holder (23) holding the planar heater (24), the holder (23) has an entrance portion adjacent to an entrance (N1) of the fixing nip and an exit portion (23a) adjacent to the exit (N2) of the fixing nip, and

the exit portion (23a) protrudes toward the pressure rotator (31) as compared with the entrance portion.
The heating conveyance device (19) according to any one of claims 1 to 5, wherein an outer diameter of the pressure rotator (31) is smaller than an outer diameter of the fixing rotator (21, 22).
The heating conveyance device (19) according to any one of claims 1 to 6, further comprising
another conveyance guide (130) to guide the sheet (P) fed from the fixing nip to another ejection port (B),

wherein an angle (θ1) formed by the conveyance direction (S) and the conveyance guide (110) is different from an angle (θ2) formed by the conveyance direction (S) and said another conveyance guide (130).
The heating conveyance device (19) according to claim 7, further comprising
a switching part (111) to convey the sheet (P) fed from the fixing nip toward any one of the conveyance guide (110) and said another conveyance guide (130).
The heating conveyance device (19) according to any one of claims 4 to 8,
wherein the fixing device (20) includes a thermal equalizer (48) that contacts the planar heater (24) and uniforms heat generated in the planar heater (24).
An image forming apparatus (1) comprising the heating conveyance device (19) according to any one of claims 1 to 9.
The image forming apparatus (1) according to claim 10, further comprising a controller (60) to input a basis weight of the sheet (P),
wherein the conveyance guide (110, 130) includes a portion inclined toward the ejection port (A, B) at an adjustable angle, and

the controller (60) is configured to:
determine whether the basis weight is equal to or greater than a predetermined value; and,

in order to convey the sheet (P) having the basis weight equal to or larger than the predetermined value, adjust the angle to be larger than an angle to convey the sheet (P) having the basis weight smaller than the predetermined value.