EP4617788A1

EP4617788A1 - Fixing device and image forming apparatus incorporating the same

Info

Publication number: EP4617788A1
Application number: EP25156283.1A
Authority: EP
Inventors: Yoshikuni Sasaki; Seiji Saitoh; Jun Okamoto
Original assignee: Ricoh Co Ltd
Current assignee: Ricoh Co Ltd
Priority date: 2024-03-15
Filing date: 2025-02-06
Publication date: 2025-09-17
Also published as: JP2025141402A; CN120652766A

Abstract

A fixing device (20) includes a planar heater (24), a fixing belt (21) heated by the planar heater (24), a pressure rotator (31) pressing one face of the planar heater (24) via the fixing belt (21), a holder (23) holding the planar heater (24), a heat sensitive element (40) facing another face of the planar heater (24), a biasing member (47) biasing the heat sensitive element (40) against the planar heater (24), a stay (30) holding the holder (23) and accommodating the biasing member (47) in the stay (30), and an interlocking portion (41a, 47a, 47b, and 48). The stay (30) has a through hole (30a). The interlocking portion (41a, 47a, 47b, and 48) has a portion in the through hole (30a) and changes a posture according to a change in a posture of the biasing member (47) in the stay (30).

Description

BACKGROUND

Technical Field

The present disclosure relates to a fixing device including a planar heater and an image forming apparatus including the fixing 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

One type of fixing device in an image forming apparatus such as a copier or a printer in the related art uses a planar heater (a resistive heat generator) as a heating device to heat a fixing belt. (For example, see Japanese Unexamined Patent Application Publication No. 2022-140086 )
Specifically, Japanese Unexamined Patent Application Publication No. 2022-140086 discloses the fixing device including a fixing belt, a pressure roller as a pressure rotator, a planar heater that is pressed against the pressure roller via the fixing belt, a holder (that is a heater holder) to hold the planar heater, a stay to hold and reinforce the holder, and a heat sensitive element such as a thermostat or a thermistor to detect the temperature of the planar heater or the excessive temperature rise of the planar heater. As a driver drives and rotates the pressure roller, the fixing belt rotates in accordance with the rotation of the pressure roller by friction therebetween generated at a fixing nip. A controller controls the temperature of the planar heater based on the temperature detected by the heat sensitive element. The planar heater heats the fixing belt. A sheet bearing a toner image is conveyed to a fixing nip, and heat and pressure in the fixing nip fix the toner image onto the sheet.
Japanese Unexamined Patent Application Publication No. 2022-140086 discloses a technique of forming an opening in a side face of the stay to prevent a short circuit between the stay and the thermostat and downsize the stay.
The fixing device known in the art includes a biasing member such as a compression spring to bias the heat sensitive element such as the thermostat or the thermistor against the planar heater. The biasing member is typically disposed inside the stay. As a result, checking whether the biasing member is assembled to the stay in a correct posture is difficult.

SUMMARY

An object of the present disclosure is to solve the above-described problem and provide a fixing device and an image forming apparatus in which a worker can easily check whether the biasing member to bias the heat sensitive element against the planar heater is assembled to the stay in the correct posture. In order to achieve this object, there is provided a fixing device according to claim 1. Advantageous embodiments are defined by the dependent claims.
The present disclosure described herein provides a fixing device including a planar heater, a fixing belt, a pressure rotator, a holder, a heat sensitive element, a biasing member, a stay, and an interlocking portion. The planar heater heats the fixing belt. The pressure rotator presses one face of the planar heater via the fixing belt to form a fixing nip through which a sheet is conveyed. The holder holds the planar heater. The heat sensitive element faces another face of the planar heater. The biasing member biases the heat sensitive element against the planar heater. The stay holds the holder and accommodates the biasing member in the stay. The stay has a through hole. The interlocking portion has a portion in the through hole and changes a posture according to a change in a posture of the biasing member in the stay.
According to one aspect of the present disclosure, the fixing device and the image forming apparatus in which the worker can easily check whether the biasing member to bias the heat sensitive element against the planar heater is assembled to the stay in the correct posture can be 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 schematic diagram illustrating an overall configuration of an image forming apparatus;
FIG. 2 is a diagram illustrating a configuration of a fixing device incorporated in the image forming apparatus of FIG. 1;
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 a 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 schematic diagram illustrating a configuration of a biasing member biasing a thermistor against a planar heater;
FIG. 7 is a schematic diagram illustrating a configuration of a biasing member biasing a thermistor against a planar heater in a fixing device according to a comparative example;
FIG. 8 is a schematic diagram illustrating a configuration of a biasing member biasing a thermistor against a planar heater in a fixing device according to a first modification;
FIG. 9 is a schematic diagram illustrating a configuration of a biasing member biasing a thermistor against a planar heater in a fixing device according to a second modification;
FIG. 10 is a schematic diagram illustrating a configuration of a biasing member biasing a thermistor against a planar heater in a fixing device according to a third modification;
FIGS. 11A to 11D are schematic diagrams each illustrating a configuration of a biasing member biasing a thermistor against a planar heater in a fixing device according to a fourth modification; and
FIG. 12 is a schematic diagram illustrating a configuration of a biasing member biasing a thermistor against a planar heater via another member.

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. FIG. 1 is a schematic diagram of an overall configuration of the image forming apparatus 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. Image forming processes including a charging process, an exposure process, a developing process, a primary transfer process, and a cleaning process are performed on an outer circumferential surface of each of the photoconductor drums 5Y, 5M, 5C, and 5K, forming yellow, magenta, cyan, and black toner images on the photoconductor drums 5Y, 5M, 5C, and 5K, respectively.
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. 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 a lower portion of the body of the image forming apparatus 1 through a conveyance path disposed in a right side portion of the body of the image forming apparatus 1, which includes a feed roller 97, a registration roller pair 98, and a fixing device 20.
Specifically, the sheet feeder 12 contains a stack of multiple sheets P such as sheets of paper stacked on one on 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 a 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 from the fixing device 20, and an ejection roller pair 99 ejects the sheet P to the outside of the image forming apparatus through an ejection opening A. The sheets P are ejected one by one from the ejection opening A by the ejection roller pair 99 and 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.
In addition, the image forming apparatus 1 includes a duplex printing conveyance path to convey the sheet P after a single-sided printing toward the secondary transfer nip in order to print images on both sides of the sheet P.
The image forming apparatus 1 includes an opening-and-closing cover 110 including a part of the duplex printing conveyance path. The opening-and-closing cover 110 is rotatable about a support shaft 110a. Opening the opening-and-closing cover 110 exposes the fixing device 20 and enables the fixing device 20 to be attached to and detached from the body of the image forming apparatus 1.
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 planar heater 24 as a heating unit (heat source), the pressure roller 31 as a pressure rotator, a thermistor 40 as a heat sensitive element, a bracket 41 to hold the thermistor 40, a compression spring 47 as a biasing member.
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, flexible endless belt driven to rotate counterclockwise in FIG. 2, that is, in a rotation direction 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 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 fluoro-rubber. 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 formation of an orange peel image on the sheet P.
The release layer of the fixing belt 21 has a thickness in a range 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 toner image on the sheet P from the fixing belt 21.
In the present embodiment, the fixing belt 21 includes the elastic layer. However, the fixing belt 21 may not include the elastic layer. In this case, the fixing belt includes the base layer and the release layer as a surface layer formed on the base layer.
Inside the loop of the fixing belt 21, the planar heater 24, a holder 23, a stay 30, the thermistor 40, the bracket 41, and the compression spring 47 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 (a heat source) to heat the fixing belt 21.
In the present embodiment, 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 stay 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 stay 30 holding the planar heater 24 and the holder 23 in the width direction via flanges 42 (see FIG. 3). The stay 30 also holds (in other words, accommodates) the compression spring 47, which is described below in detail.
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 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 thermistor 40. The thermistor 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 thermistor 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 thermistor 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. Both ends of the housing 43 of the fixing device 20 in the width direction hold the flanges 42, respectively so that the flanges 42 can slide and move in a direction in which the fixing belt 21 supported by the flanges 42 forms 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 according to the present embodiment 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 stay 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 stay 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 stay 30 is assembled to the housing 43 (or the holder 23) by screw fastening or other fasteners. The stay 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 stay 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 largely 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), or 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.
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 nip (the 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 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. 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.
Thereafter, 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 guided by a guide plate and conveyed in a direction indicated by an arrow Y10. The sheet P enters the fixing nip formed between the fixing belt 21 and the pressure roller 31 that are in pressure contact.
The planar heater 24 heats the fixing belt 21. The planar heater 24 and the holder 23 are reinforced by the stay 30 and pressed against the pressure roller 31. The heat in the fixing belt 21 and the pressure between the planar heater 24 and the pressure roller 31 fix the toner image on the surface of the sheet P. 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 surface facing the inner circumferential surface of the fixing belt 21 in the fixing nip. At least the front surface 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 surface of the base 25. Similarly, the conductor patterns 27 are also formed on the front surface 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.
The planar heater 24 has one face forming the fixing nip and the other face opposite that one face. Specifically, the pressure roller 31 as the pressure rotator presses the above-described one face via the fixing belt 21 to form the fixing nip. The other face is the upper face of the planar heater 24 in FIG. 6. As illustrated in FIGS. 6 to 11D, the thermistor 40 in each of the present embodiment and modifications is the heat sensitive element (a temperature detector) that is in direct contact with the other face of the planar heater 24. However, as illustrated in FIG. 12, the thermistor 40 may be in indirect contact with the other face of the planar heater 24 via another member such as a thermal equalizing plate 46.
The compression spring 47 as the biasing member biases the thermistor 40 in a direction in which the thermistor 40 abuts against the planar heater 24 (i.e., the direction toward the right side in FIG. 2 and the direction downward in FIG. 6), which is described in detail below.
In the present embodiment, the thermistor 40 (and the compression spring 47) is disposed at one position on the center portion of the planar heater 24 in the width direction, but the number and the position of the thermistor 40 are not limited to this.
The following describes the configuration and operation of the fixing device 20 in detail, which is characteristic of the image forming apparatus 1 according to the present embodiment.
As described above with reference to FIGS. 2 and 6, the fixing device 20 according to the present embodiment includes the planar heater 24 extending in the width direction, the fixing belt 21 heated by the planar heater 24, the pressure roller 31 as the pressure rotator, and the holder 23 holding the planar heater over the width direction. The pressure roller 31 is in pressure contact with the planar heater 24 via the fixing belt 21 to form the fixing nip through which the sheet P is conveyed.
The planar heater 24 has one face forming the fixing nip and the other face opposite to the one face. The other face is the left side face of the planar heater 24 in FIG. 2 and the upper face of the planar heater 24 in FIG. 6. The fixing device 20 includes the thermistor 40 as the heat sensitive element that is in direct contact or indirect contact with the other face of the planar heater 24.
In addition, the fixing device 20 includes the compression spring 47 as the biasing member and the stay 30. The compression spring 47 biases the thermistor 40 (the heat sensitive element) against the planar heater 24. The stay 30 supports the holder 23 and accommodates the compression spring 47.
Specifically, as illustrated in FIG. 6, the stay 30 is a metal plate bent to have a substantially U-shaped cross section and is formed to be fitted into a recess formed in the holder 23 that holds the planar heater 24. The thermistor 40 held by a bracket 41 and the compression spring 47 are disposed inside the stay 30.
The holder 23 has a hole to set the thermistor 40 that contacts the planar heater 24, which is a loose hole having a slight gap between the thermistor 40 and the holder 23.
The bracket 41 is made of resin and has a recess. The thermistor 40 is fitted into the recess and held by the bracket 41. The bracket 41 includes a column 41a (in other words, a boss) that protrudes in a direction away from the thermistor 40. The column 41a is inserted into an inner peripheral portion of one end of the compression spring 47 (that is a lower end of the compression spring 47 in FIG. 6).
The other end of the compression spring 47 (the upper end of the compression spring 47 in FIG. 6) is in contact with the ceiling face of the stay 30 that is also the inner face of the stay 30 (the upper wall face of the inner face of the stay 30 in FIG. 6). As a result, the compression spring 47 is held inside the stay 30 between the ceiling face of the stay 30 and a face of the bracket 41 (the upper face of the bracket 41 in FIG. 6 in which the base of the column 41a is located). A distance from the ceiling face of the stay 30 to the face of the bracket 41 is designed to be smaller than the free length of the compression spring 47.
The compression spring 47 (the biasing member) in the fixing device 20 according to the present embodiment includes a hook-shaped portion 47a (in other words, an end portion having a processed shape) serving as an interlocking portion that interlocks with a change in the posture of the compression spring 47 held inside the stay 30. The stay 30 has a through hole 30a formed in the ceiling face of the stay 30. The hook-shaped portion 47a protrudes from the through hole 30a.
Specifically, the hook-shaped portion 47a as the interlocking portion is a portion formed as a part of the compression spring 47 (the biasing member). The hook-shaped portion 47a is made by bending the other end of the compression spring 47 (in other words, the tip of the compression spring 47) to have a substantially rectangular hook shape (in other words, processing the end shape). The hook-shaped portion is smaller than the inner diameter of the spring body of the compression spring 47 (in other words, the spring inner diameter of the compression spring 47). The hook-shaped portion 47a is disposed so as to protrude outward from the inside of the stay 30 via the through hole 30a. In other words, the hook-shaped portion 47a has a protruding portion protruding from the stay 30 through the through hole 30a.
The change in the posture of the spring body of the compression spring 47 (for example, due to installation failure such as buckling, oblique arrangement, or missing) changes the posture of the hook-shaped portion 47a as the interlocking portion, which causes the hook-shaped portion 47a not to correctly protrude from the stay 30. In other words, when the hook-shaped portion 47a correctly protrudes from the through hole 30a, the compression spring 47 is correctly set in the stay 30 without being buckled, obliquely arranged, or missing.
FIG. 7 illustrates a fixing device according to a comparative example. As illustrated in FIG. 7, the fixing device according to the comparative example includes a compression spring 147 not including the interlocking portion and a stay 130 not having the through hole in the ceiling face of a stay 130. In this case, an assembling operation error is likely to cause an abnormal setting of the compression spring 147 inside the stay 130 as illustrated in FIG. 7. The worker cannot check the above-described setting failure of the compression spring 147 inside the stay 130 from the outside of the stay 130. As a result, the worker assembles a subassembly with the setting failure to the fixing device 20, and the fixing process is performed. In such a case, the thermistor 40 is not brought into contact with the planar heater 24 with a correct contact force or at a correct contact position, and the fixing temperature control based on the detection result of the thermistor 40 is not performed under normal operating conditions, so that a problem such as a fixing failure occurs.
In contrast, the fixing device according to the present embodiment enables the worker to easily check whether the compression spring 47 is correctly set in the stay 30 and whether the buckling, oblique arrangement, or missing does not occur, reducing the occurrence of the above-described problem.
With reference to FIG. 6, the hole diameter M of the through hole 30a in the stay 30 is designed to be larger than the outer radius N of the hook-shaped portion 47a as the interlocking portion of the compression spring 47 (M > N). The above-described configuration can reduce a disadvantage that the hook-shaped portion 47a contacts the edge of through hole 30a to change the spring force of the compression spring 47 (the biasing force) from a target value compared to a configuration in which the hole radius M of the through hole 30a is equal to the outer diameter N of the hook-shaped portion 47a as the interlocking portion (M = N).
With reference to FIG. 2, the protrusion amount of the hook-shaped portion 47a as the interlocking portion of the compression spring 47 is determined so that the hook-shaped portion 47a does not contact the inner circumferential surface of the fixing belt 21. In other words, a sufficient clearance is set between the tip of the hook-shaped portion 47a protruding from the stay 30 and the inner circumferential surface of the fixing belt 21 facing the tip of the hook-shaped portion 47a. Specifically, the protruding amount that is a distance from the tip of the hook-shaped portion 47a to an outer face of the stay 30 having the through hole 30a is smaller than a distance from the inner circumferential surface of the fixing belt 21 to the outer face having the through hole 30a. The above-described configuration prevents the hook-shaped portion 47a from coming into sliding contact with the fixing belt 21 and damaging the fixing belt 21 and the compression spring 47.
The following describes a first modification.
As illustrated in FIG. 8, the fixing device 20 according to the first modification includes the compression spring 47 including the protruding portion protruding from the stay 30 through the through hole 30a. The portion serves as the interlocking portion that protrudes in conjunction with the change in the posture of the compression spring 47.
Specifically, the compression spring 47 includes a folding-back-processing portion 47b made by folding back a spring wire of the one end of the compression spring 47 (that is the lower end of the compression spring 47 in FIG. 8) toward the other end of the compression spring 47. The folding-back-processing portion serves as the interlocking portion. The folding-back-processing portion 47b protrudes outward from the inside of the stay 30 through the through hole 30a to form the protruding portion. The above-described configuration enables the worker to easily check whether the compression spring 47 is assembled in the correct posture inside the stay 30.
The following describes a second modification.
As illustrated in FIG. 9, the fixing device 20 according to the second modification includes a cap 48 serving as an attachment attached to the other end of the compression spring 47 as the biasing member. The cap 48 protrudes from the stay 30 through the through hole 30a. The cap 48 functions as the interlocking portion that protrudes in conjunction with the change in the posture of the compression spring 47.
Specifically, the cap 48 as the attachment has a shaft made of resin. One end of the shaft is fitted into the inner peripheral portion of the compression spring 47. The cap 48 has a flange formed at the center of the cap 48 in the vertical direction of FIG. 9. The flange has an outer diameter larger than the hole diameter of the through hole 30a. The flange determines the position of the compression spring 47 in the biasing direction of the compression spring 47 (that is the vertical direction in FIG. 9). The other end of the shaft of the cap 48 protrudes outside the stay 30 through the through hole 30a to form the protruding portion, and the cap 48 functions as the interlocking portion. The above-described configuration enables the worker to easily check whether the compression spring 47 is assembled in the correct posture inside the stay 30.
The following describes a third modification.
As illustrated in FIG. 10, the fixing device 20 according to the third modification includes the bracket 41 holding the thermistor 40 as the heat sensitive element and the column 41a protruding from the bracket 41 as a part of the bracket 41. The column 41a protrudes from the stay 30 through the through hole 30a and is inserted into the inner peripheral portion of the compression spring 47. As a result, the bracket 41 functions as the interlocking portion that protrudes in conjunction with the change in the posture of the compression spring 47.
Specifically, as illustrated in FIG. 10, the column 41a extends from the upper face of the bracket 41 upward, is inserted into the entire region of the inner peripheral portion of the compression spring 47, and further protrudes to the outside of the stay 30 via the through hole 30a to form the protruding portion. The above-described configuration enables the worker to easily check whether the compression spring 47 is assembled in the correct posture inside the stay 30.
The following describes a fourth modification.
As illustrated in FIG. 11A, the fixing device 20 according to the fourth modification includes the compression spring 47 including the hook-shaped portion 47a. The hook-shaped portion 47a serves as the interlocking portion that interlocks with the change in the posture of the compression spring 47 in the stay 30. In other words, the hook-shaped portion 47a as the interlocking portion changes the posture according to the change in the posture of the compression spring 47 in the stay 30. The hook-shaped portion 47a does not protrude from the stay 30 through the through hole 30a. The hook-shaped portion 47a is positioned inside the through hole 30a.
In other words, the hook-shaped portion 47a of the compression spring 47 in the fourth modification is different from the hook-shaped portion 47a illustrated in FIG. 6. The hook-shaped portion 47a of the compression spring 47 is loosely inserted into the through hole 30a so as to interfere with the edge of the through hole 30a without completely protruding outward from the stay 30 through the through hole 30a.
Even in such a case, visually checking whether the hook-shaped portion 47a is positioned in the through hole 30a enables the worker to easily check whether the compression spring 47 is not buckled, not obliquely arranged, does not become a missing component, and is correctly set in the stay 30.
FIG. 11B illustrates a modification corresponding to FIG. 8, and the folding-back-processing portion 47b as the interlocking portion is positioned in the through hole 30a.
FIG. 11C illustrates a modification corresponding to FIG. 9, and the cap 48 (the attachment) as the interlocking portion is positioned in the through hole 30a.
FIG. 11D illustrates a modification corresponding to FIG. 10, and the column 41a as the interlocking portion is positioned in the through hole 30a.
The above-described configurations as illustrated in FIGS. 11B to 11D enable the worker to easily check whether the compression spring 47 is correctly set in the stay 30 and whether the buckling, oblique arrangement, or missing does not occur.
As described above, the fixing device 20 according to the present embodiment in the image forming apparatus 1 includes the planar heater 24 extending in the width direction, the fixing belt 21 heated by the planar heater 24, the pressure roller 31 as the pressure rotator, and the holder 23 holding 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 through which the sheet P is conveyed. The planar heater 24 has the one face forming the fixing nip and the other face opposite to the one face. The fixing device 20 includes the thermistor 40 as the heat sensitive element facing the other face of the planar heater 24. The thermistor 40 may be in direct contact with the other face of the planar heater 24 or may be in indirect contact with the other face of the planar heater 24. In addition, the fixing device 20 includes the compression spring 47 as the biasing member that biases the thermistor 40 in the direction toward the planar heater 24 and the stay 30 that supports the holder 23 and accommodates the compression spring 47 in the stay 30. The compression spring 47 includes the hook-shaped portion 47a. The hook-shaped portion 47a serves as the interlocking portion that interlocks with the change in the posture of the compression spring 47 held inside the stay 30. In other words, the hook-shaped portion 47a changes the posture according to the change in the posture of the compression spring 47 in the stay 30. The hook-shaped portion 47a has a portion positioned inside the through hole 30a and protrudes outward from the stay 30 through the through hole 30a.
The above-described configuration enables easy checking of whether the compression spring 47 as the biasing member that biases the thermistor 40 as the heat sensitive element against the planar heater 24 is assembled to the stay in the correct posture.
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 a pressure rotator.
In the above-described present embodiment and modifications, the thermistor 40 is in direct or indirect contact with the other face of the planar heater 24 opposite to the one face forming the fixing nip and is used as the heat sensitive element, but the thermostat may be used as the heat sensitive element. A non-contact type thermistor or a non-contact type thermopile facing the other face of the planar heater 24 opposite to the one face forming the fixing nip with a gap therebetween may be used as the heat sensitive element.
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.
In the present description, the term "sheet" is defined as any sheet-like recording medium including all conveyed objects, such as general paper, coated paper, label paper, overhead projector (OHP) transparency, or a film sheet.
Aspects of the present disclosure are, for example, as follows.

(First Aspect)

In a first aspect, a fixing device includes a planar heater, a fixing belt, a pressure rotator, a holder, a heat sensitive element, a biasing member, a stay, and an interlocking portion. The planar heater extends in a width direction. The fixing belt is heated by the planar heater. The pressure rotator is pressed against the planar heater via the fixing belt to form a nip through which a sheet is conveyed. The holder holds the planar heater. The planar heater has one face forming the nip and another face opposite to the one face. The heat sensitive element is in direct or indirect contact with or faces the other face. The biasing member biases the heat sensitive element in a direction in which the heat sensitive element approaches the planar heater. The stay supports the holder and holds the biasing member. The interlocking portion interlocks with a change in posture of the biasing member held inside the stay. The interlocking portion has a portion that protrudes from the stay to the outside via a through hole of the stay or a portion that is positioned in the through hole.

(Second Aspect)

In a second aspect, the interlocking portion in the fixing device according to the first aspect is a portion formed as a part of the biasing member.

(Third Aspect)

In a third aspect, the interlocking portion in the fixing device according to the first aspect is an attachment attached to the biasing member.

(Fourth Aspect)

In a fourth aspect, the fixing device according to the first aspect further includes a bracket holding the heat sensitive element, and the interlocking portion is a column protruding as a part of the bracket. The column is inserted into an inner peripheral portion of a compression spring serving as the biasing member.

(Fifth Aspect)

In a fifth aspect, a hole diameter of the through hole in the fixing device according to any one of the first to fourth aspects is larger than an outer diameter of the interlocking portion.

(Sixth Aspect)

In a sixth aspect, a protrusion amount of the interlocking portion in the fixing device according to any one of the first to fifth aspects is determined so that the interlocking portion does not come into contact with the inner circumferential surface of the fixing belt.

(Seventh Aspect)

In a seventh aspect, the heat sensitive element in the fixing device according to any one of the first to sixth aspects is a thermistor or a thermostat.

(Eighth Aspect)

In an eighth aspect, an image forming apparatus includes the fixing device according to any one of the first to seventh aspects
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 fixing device (20) comprising:
a planar heater (24);

a fixing belt (21) heated by the planar heater (24);

a pressure rotator (31) pressing one face of the planar heater (24) via the fixing belt (21) to form a fixing nip through which a sheet is conveyed;

a holder (23) holding the planar heater (24);

a heat sensitive element (40) facing another face of the planar heater (24);

a biasing member (47) biasing the heat sensitive element (40) against the planar heater (24);

a stay (30) holding the holder (23) and accommodating the biasing member (47) in the stay, the stay (30) having a through hole (30a); and

an interlocking portion (41a, 47a, 47b, and 48) having a portion in the through hole (30a), the interlocking portion to change a posture according to a change in a posture of the biasing member (47) in the stay (30).
The fixing device (20) according to claim 1,
wherein the interlocking portion (41a, 47a, 47b, and 48) has a protruding portion protruding from the stay (30) through the through hole (30a).
The fixing device according to claim 2,
wherein a protruding amount of the protruding portion of the interlocking portion (41a, 47a, 47b, and 48) from the through hole of the stay (30) is smaller than a distance from an inner circumferential surface of the fixing belt (21) to an outer face of the stay (30) having the through hole (30).
The fixing device (20) according to any one of claims 1 to 3,
wherein the heat sensitive element (40) is in direct contact with said another face of the planar heater (24).
The fixing device (20) according to any one of claims 1 to 3,
wherein the heat sensitive element (40) is in indirect contact with said another face of the planar heater (24).
The fixing device (20) according to any one of claims 1 to 5,
wherein the biasing member (47) includes the interlocking portion (41a, 47a, 47b, and 48).
The fixing device (20) according to any one of claims 1 to 5,
wherein the interlocking portion (41a, 47a, 47b, 48) includes an attachment (48) attached to the biasing member (47) and protruding from the stay (30) through the through hole (30a).
The fixing device (20) according to any one of claims 1 to 5, further comprising
a bracket (41) holding the heat sensitive element (40),

wherein the biasing member (47) includes a compression spring (47),

the interlocking portion (41a, 47a, 47b, and 48) includes a column (41a) protruding from the bracket (41) and inserted into an inner peripheral portion of the compression spring (47).
The fixing device (20) according to any one of claims 1 to 8,
wherein a hole diameter of the through hole (30a) is larger than an outer diameter of the interlocking portion (41a, 47a, 47b, and 48).
The fixing device (20) according to any one of claims 1 to 9,
wherein the heat sensitive element (40) includes a thermistor (40) or a thermostat.
An image forming apparatus comprising
the fixing device according to any one of claims 1 to 10.