Patent Publication Number: US-10788775-B2

Title: Fixing device and image forming apparatus including same

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This patent application is based on and claims priority pursuant to 35 U.S.C. § 119(a) to Japanese Patent Application No. 2019-012938, filed on Jan. 29, 2019, in the Japan Patent Office, the entire disclosure of which is incorporated by reference herein. 
     BACKGROUND 
     Technical Field 
     Aspects of the present disclosure relate to a fixing device and an image forming apparatus including the fixing device. 
     Related Art 
     A fixing device in an electrophotographic image forming apparatus includes: a heating device such as a fixing roller having a built-in heater; and a temperature detector such as a thermistor that controls a fixing temperature. The fixing device (fixing unit) is often attachable to/detachable from the image forming apparatus for the purposes of: improving a paper jam handling property; and replacing a unit. The heating device and the temperature detector supply electric power from an apparatus body to the heater and transmit a detection temperature of a thermistor element portion to a controller of the apparatus body by connection between terminal portions at a drawer connector. The terminal portions are provided on the fixing device and the image forming apparatus body side of the drawer connector, respectively. 
     However, in a conventional drawer connector, defective contact such as increase in electrical resistance or defective electrical continuity has occurred sometimes. The defective contact is caused as follows: when a metal-plated layer of a terminal contact portion is exposed to high-temperature and high-humidity conditions and subjected to abrasion by fine sliding motions of a fixing device at the time of attachment/detachment of the fixing device or vibration during operation of an apparatus body, the metal-plated layer of the terminal contact portion is peeled off, and nickel plating on an underlying layer is exposed, and then the terminal portion is oxidized. As a result, a detection error of a thermistor detection temperature is caused. 
     SUMMARY 
     In an aspect of the present disclosure, there is provided a fixing device that includes a fixing member, at least one temperature detector, and a device-side drawer connector. The at least one temperature detector is configured to detect a temperature of the fixing member, the at least one temperature detector including a plurality of lead wires. The device-side drawer connector has a terminal portion configured to fit with a terminal portion of a body-side drawer connector of an image forming apparatus body to connect the plurality of lead wires of the at least one temperature detector to the image forming apparatus body. The device-side drawer connector is configured to branch a signal wire of the plurality of lead wires of the at least one temperature detector into a plurality of systems. A plurality of earth wires of the plurality of lead wires of the at least one temperature detector is short-circuited to each other. 
     In an aspect of the present disclosure, there is provided an image forming apparatus including the fixing device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The aforementioned and other aspects, features, and advantages of the present disclosure would be better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein: 
         FIG. 1  is a schematic configuration diagram of a printer according to an embodiment of the present disclosure; 
         FIG. 2  is a schematic configuration diagram of a drawer connector according to an embodiment of the present disclosure; 
         FIG. 3  is a diagram illustrating an exemplary temperature detection circuit of a fixing device according to an embodiment of the present disclosure; 
         FIG. 4  is a diagram illustrating details of increasing a wire to a plurality of wires at a thermistor portion; 
         FIG. 5  is a diagram illustrating details of a connector fitting portion in a drawer connector portion; 
         FIG. 6  is a diagram illustrating a measuring device that measures resistance at a contact place of the drawer connector portion; and 
         FIG. 7  is a schematic configuration diagram of a drawer connector according to a comparative example. 
     
    
    
     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. 
     DETAILED DESCRIPTION 
     In describing embodiments illustrated in the drawings, specific terminology is employed for the sake of clarity. However, the disclosure of this patent 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 operate in a similar manner and achieve similar results. 
     Although the embodiments are described with technical limitations with reference to the attached drawings, such description is not intended to limit the scope of the disclosure and all of the components or elements described in the embodiments of this disclosure are not necessarily indispensable. 
     Referring now to the drawings, embodiments of the present disclosure are described below. In the drawings for explaining the following embodiments, the same reference codes are allocated to elements (members or components) having the same function or shape and redundant descriptions thereof are omitted below. 
     Hereinafter, a color laser printer (hereinafter also simply referred to as “printer”) that is an image forming apparatus according to an embodiment of the present disclosure will be described.  FIG. 1  is a schematic configuration diagram of a printer according to the present embodiment. This printer includes a tandem image former including four image forming devices of yellow, cyan, magenta, and black which are arranged side by side. In the tandem image former, image forming devices  101 Y,  101 C,  101 M, and  101 K as individual toner image forming devices are sequentially arranged from the left in the drawing. Here, suffixes Y, C, M, and K of the respective reference signs represent members of yellow, magenta, cyan, and black, respectively. Additionally, the individual image forming devices  101 Y,  101 C,  101 M, and  101 K of the tandem image former include charging devices, developing devices  10 Y,  10 C,  10 M, and  10 K, photoconductor cleaning devices, and the like which are arranged respectively around drum-shaped photoconductors  21 Y,  21 C,  21 M, and  21 K as latent image bearers. The printer includes, in an upper portion of the printer, toner bottles  2 Y,  2 C,  2 M, and  2 K respectively filled with toner of the respective colors of yellow, cyan, magenta, and black. The developing devices  10 Y,  10 C,  10 M, and  10 K are supplied with predetermined supply amounts of the toner respectively from the toner bottles  2 Y,  2 C,  2 M, and  2 K through conveyance paths provided in the image forming apparatus. 
     Additionally, an optical writing unit  9  as a latent image forming device is provided below the tandem image former. The optical writing unit  9  includes a light source, a polygon mirror, an f-θ lens, a reflection mirror, and the like, and irradiates the surfaces of the respective photoconductors  21  with laser light while scanning the surfaces with the laser light based on image data. 
     Additionally, an intermediate transfer belt  1  of an endless belt type is provided as an intermediate transferor immediately above the tandem image former. The intermediate transfer belt  1  is passed around support rollers  1   a  and  1   b , and a drive motor as a driving source is connected to a rotation shaft of the support roller  1   a  functioning as a drive roller among these support rollers. When this drive motor is driven, the intermediate transfer belt  1  is rotationally moved in a counterclockwise direction in the drawing, and also the support roller  1   b  that can be driven is rotated. The intermediate transfer belt  1  includes, on an inner side of the intermediate transfer belt, primary transfer devices  11 Y  11 C,  11 M, and  11 K to transfer, onto the intermediate transfer belt  1 , the toner images on the photoconductors  21 Y,  21 C,  21 M, and  21 K. 
     Additionally, the intermediate transfer belt  1  includes a secondary transfer roller  4  as a secondary transfer device more on a downstream side than the primary transfer devices  11 Y,  11 C,  11 M, and  11 K in the driving direction of the intermediate transfer belt  1 . The support roller  1   b  is arranged on an opposite side of the secondary transfer roller  4  while interposing the intermediate transfer belt  1 , and functions as a pressing member. Additionally, a sheet tray  8 , a sheet feeding roller  7 , a registration roller  6 , and the like are provided. Further provided are a fixing device  5  and an output roller pair  3  at a downstream portion of the secondary transfer roller  4  in an advancing direction of a recording medium S on which the toner image has been transferred by the secondary transfer roller  4 . The fixing device  5  fixes the image on the recording medium S. 
     Next, operation of the printer will be described. The photoconductors  21 Y,  21 C,  21 M, and  21 K are respectively rotated in the individual image forming devices, and the surfaces of the photoconductors  21 Y,  21 C,  21 M, and  21 K are first uniformly charged by charging devices  17 Y  17 C,  17 M, and  17 K along with the rotation of the photoconductors  21 Y,  21 C,  21 M, and  21 K. Subsequently, writing laser light is emitted from the optical writing unit  9  based on image data to form electrostatic latent images on the photoconductors  21 Y,  21 C,  21 M, and  21 K. After that, the toner is made to adhere by the developing devices  10 Y,  10 C,  10 M, and  10 K, and the electrostatic latent images are visualized to form respective monochromatic images of yellow, cyan, magenta, and black on the respective photoconductors  21 Y,  21 C,  21 M, and  21 K. Additionally, the support roller  1   a  as the drive roller is rotationally driven by the drive motor provided in the image forming apparatus to rotationally drive the other support roller  1   b  as a driven roller and the secondary transfer roller  4 , and rotationally convey the intermediate transfer belt  1 . Then, the visible images are sequentially transferred onto the intermediate transfer belt  1  at the primary transfer devices  11 Y,  11 C,  11 M, and  11 K. Thus, a composite color image is formed on the intermediate transfer belt  1 . The surfaces of the photoconductors  21 Y,  21 C,  21 M, and  21 K after the image transfer have residual toner removed by the respective photoconductor cleaning devices to prepare for image formation again. 
     Further, a leading edge of the recording medium S is fed out from the sheet tray  8  by the sheet feeding roller  7 , conforming to timing of image formation. Then, the recording medium S is conveyed to the registration roller  6  and stopped temporarily. Subsequently, the recording medium S is conveyed between the secondary transfer roller  4  and the intermediate transfer belt  1 , conforming to the timing of image forming operation. Here, the intermediate transfer belt  1  and the secondary transfer roller  4  form a so-called secondary transfer nip while sandwiching the recording medium S, and the toner image on the intermediate transfer belt  1  is secondarily transferred onto the recording medium S at the secondary transfer roller  4 . 
     After the image transfer, the recording medium S is sent to the fixing device  5 , and the recording medium S is conveyed and nipped at a nip portion formed by a fixing member  51  and a pressure member  52  to heat and pressurize the toner image on the recording medium S and fix the toner image on the recording medium S. The fixing member  51  has a surface kept at a predetermined temperature, and the pressure member  52  faces the fixing member  51  and is pressed against the fixing member  51 . Furthermore, the recording medium S ejected from the nip portion is separated by a separator and then ejected from the output roller pair  3  to the outside of the apparatus. On the other hand, the intermediate transfer belt  1  after the image transfer has residual toner remaining on the intermediate transfer belt  1 , and the residual toner is removed by an intermediate transferor cleaning device  12  to prepare again for image formation by the tandem image former. 
       FIG. 7  is a schematic configuration diagram of a drawer connector according to a comparative example. A drawer connector  55  includes a fixing device side connector  55 U and a body-side connector  55 H and is arranged between a fixing device  5  and an apparatus body (image forming apparatus body)  50 . The fixing device side connector  55 U is installed on the fixing device  5 , and the body-side connector  55 H is installed on the apparatus body  50 . A central thermistor  15  (hereinafter also referred to as the thermistor  15 ) and an end-portion thermistor  16  (hereinafter also referred to as the thermistor  16 ) are temperature detectors, and each of the thermistors includes two lead wires. Specifically, the central thermistor  15  includes the two lead wires of a signal wire  15   a  and an earth wire  15   b , and the end-portion thermistor  16  includes the two lead wires of a signal wire  16   a  and an earth wire  16   b . The central thermistor  15  is arranged at a center in a longitudinal direction of the fixing device  5 , and the end-portion thermistor  16  is arranged at an end portion in the longitudinal direction of the fixing device  5 . 
     The signal wires  15   a  and  16   a  and the earth wires  15   b  and  16   b  of the thermistors  15  and  16  are connected to the fixing device side connector  55 U on the fixing device  5  side of the drawer connector  55  via a relay connector, or directly connected to the fixing device side connector  55 U. Thus, the signal wires  15   a ,  16   a  and the earth wires  15   b ,  16   b  are each connected to one terminal in the fixing device side connector  55 U of the drawer connector  55 . 
     On the other hand, terminals corresponding to the terminals of the fixing device side connector  55 U side are also provided on the body-side connector  55 H side of the apparatus body  50  side. The drawer connector  55  is a snap-in connector including a pair of male and female connectors. Therefore, when the fixing device  5  is set in the apparatus body  50 , the terminal of the signal wire  15   a  and the terminal of the earth wire  15   b  are connected in a pair and the terminal of the signal wire  16   a  and the terminal of the earth wire  16   b  are connected in a pair, and a contact of one system (signal path) is formed by each of the pairs. A place where a terminal of the body-side connector  55 H and a terminal of the fixing device side connector  55 U are in contact with each other is a contact. 
       FIG. 2  is a schematic configuration diagram of a drawer connector according to an embodiment of the present disclosure. A central thermistor  15  and an end-portion thermistor  16  are temperature detectors that detect a temperature of the fixing member  51 . Each of the thermistors includes two lead wires. Specifically, the central thermistor  15  includes the two lead wires of a signal wire  15   a  and an earth wire  15   b , and the end-portion thermistor  16  includes the two lead wires of a signal wire  16   a  and an earth wire  16   b . Here, a system in each of the signal wire  15   a  of the thermistor  15  and the signal wire  16   a  of the thermistor  16  is branched into a plurality of systems at a portion of the fixing device side connector  55 U of the fixing device  5 . Then, the respective signal wires  15   a  and  16   a  are connected to the terminals or the signal wires  15   c  and  16   c  added by the system increase from one system to two systems. Additionally, the two earth wires  15   b  and  16   b  of the thermistors  15  and  16  are mutually short-circuited by a short-circuit wire  17 . With this configuration, even in a case where defective contact occurs at one contact out of a plurality of contacts at the terminal portions of the signal wires and the terminal portions of the earth wires, another signal wire and another earth wire each of which has a secured contact prevents defective electrical continuity at the terminal portions. Thus, occurrence of a temperature detection error of the temperature detectors can be suppressed. The body-side connector  55 H also includes terminals of branched signal wires in a manner corresponding to the terminals of the fixing device side connector  55 U of the fixing device  5  to connect the signal wires on the apparatus body side. Thus, compared to the comparative example, the number of lead wires of the signal wires  15   c  and  16   c  and the short-circuit wire  17  are added in the present embodiment, and the contacts (signal paths) of the plurality of systems (the two systems in the present embodiment) are formed in the drawer connector  55 . However, the number of signal paths is not limited to the two systems, and signal paths of three or more systems may also be formed. Also, one temperature detector that detects a temperature of the fixing member  51  may be provided. 
     Accordingly, the fixing device  5  according to the present embodiment is the fixing device including one or a plurality of thermistors  15  and  16  as the temperature detectors that detect the temperature of the fixing member  51 . The lead wire in each of the thermistors is connected by mutual fitting between the terminal portion on the fixing device  5  side and the terminal portion on the apparatus body  50  side at the drawer connector  55 . The system in each of the signal wires  15   a  and  16   a  of the thermistors  15  and  16  is branched into the plurality, of systems at the portion of the drawer connector  55 , and the plurality of earth wires  15   b  and  16   b  is short-circuited to each other. 
       FIG. 3  is a diagram illustrating an exemplary temperature detection circuit of the fixing device according to an embodiment of the present disclosure. The thermistors  15  and  16  as the temperature detectors provided in the fixing device  5  include a thermistor element  54   a  where a resistance value is changed by change in a temperature. The thermistors detect a temperature of the fixing member  51  based on the change in the resistance value. Here, a thermistor is used as the temperature detector, but the temperature detector is not limited to the thermistor. The thermistors  15  and  16  have current flowing through the drawer connector  55  from a controller  61  of a control board  60  provided in the apparatus body  50 . Further, the controller  61  detects voltage that is changed by the change in the resistance at the thermistor element  54   a , and controls energization of the heating member  53  to control the temperature of the fixing member  51 . 
       FIG. 4  is a diagram illustrating details of increasing a wire to a plurality of wires at a thermistor portion. The signal wire  15   a  of the central thermistor  15  is branched into the signal wire  15   a  and the signal wire  15   c  at the fixing device side connector  55 U and the body-side connector  55 H at a fitting portion between the fixing device side connector  55 U of the fixing device  5  and the body-side connector  55 H of the apparatus body  50  side. The branched signal wires are reverted to the one signal wire  15   a  on the apparatus body  50  side. Similarly, the signal wire  16   a  of the end-portion thermistor  16  is also branched into the signal wire  16   a  and the signal wire  16   c  at the fixing device side connector  55 U and the body-side connector  55 H. The branched signal wires are reverted to the one signal wire  16   a  on the apparatus body  50  side. 
     On the other hand, the earth wire  15   h  of the central thermistor  15  and the earth wire  16   b  of the end-portion thermistor  16  are short-circuited between the fixing device side connector  55 U and the body-side connector  55 H and between the central thermistor  15  and the end-portion thermistor  16  by the short-circuit wire  17 . The short-circuit wire  17  may be arranged between the fixing device side connector  55 U and the body-side connector  55 H, may be arranged between the central thermistor  15  and the end-portion thermistor  16 , or may be arranged between the fixing device side connector  55 U, the body-side connector  55 H, and the apparatus body  50 . 
       FIG. 5  is a diagram illustrating details of a connector fitting portion at a drawer connector portion. Each of the signal wires  15   a  and  16   a  of the above-described thermistors  15  and  16  has the number of systems increased from one system to two systems at the fixing device side connector  55 U and the body-side connector  55 H of the drawer connector  55  by relay connectors  31  and  32 . One wire is increased to a plurality of wires by each of the relay connectors  31  and  32 . Additionally, the earth wires  15   b  and  16   b  of the thermistors  15  and  16  are short-circuited by the relay connector  31  at the fixing device side connector  55 U of the drawer connector  55 . Since such a relay connector is provided, a conventional thermistor can be used as it is. The signal wires  15   c  and  15   a  of the central thermistor  15  are connected at terminal portions A 1  and A 2  of the fitting portion (connecting portion) between the fixing device side connector  55 U of the fixing device  5  side and the body-side connector  55 H of the apparatus body  50  side. Similarly, the signal wires  16   c  and  16   a  of the end-portion thermistor  16  are connected at terminal portions B 1  and B 2 . Additionally, the earth wires  15   b  and  16   b  of the central thermistor  15  and the end-portion thermistor  16  are connected at terminal portions G 1  and G 2 , and the earth wires  15   b  and  16   b  are short-circuited by the short-circuit wire  17 . 
     Furthermore, branching of each of the signal wires  15   a  and  16   a  and short-circuiting of the earth wires  15   b  and  16   b  in the fixing device side connector  55 U of the fixing device  5  side are achieved via: a relay board provided in the fixing device  5 ; and the relay connector  31  provided in the relay board. Specifically, each of the signal wires  15   a  and  16   a  has the number of systems increased from the one system to the two systems, and the earth wires  15   b  and  16   b  are short-circuited by the short-circuit wire  17 . Since the relay board is thus provided in the fixing device  5 , each of the signal wires  15   a  and  16   a  can be branched by the relay connector  31  and the lead wires (wiring harness) provided in the relay board. Furthermore, assembling work efficiency can be improved. Furthermore, branching of each of the signal wires  15   a  and  16   a  at the body-side connector  55 H of the apparatus body  50  side and short-circuiting of the earth wires  15   b  and  16   b  are achieved via a relay board provided in the apparatus body  50  and the relay connector  32  provided in the relay board. 
       FIG. 6  is a diagram illustrating a measuring device that measures resistance at a contact place of the drawer connector portion. The fixing device  5  includes the measuring devices (resistance measuring instruments) that measure resistance R 1 , R 2 , R 3 , and R 4  at contact portions of the terminal portions on each of the fixing device  5  side and the apparatus body  50  side of terminal portions A 1 , A 2 , B 1 , and B 2  of the signal wires of the fixing device side connector  55 U and the body-side connector  55 H. Detection of resistance abnormality with the measuring devices enables detection of defective contact at the drawer connector  55 . In a case where the measuring devices detect R 1 ≠R 2  or R 3 ≠R 4 , it is possible to determine whether one of the two signal wires connected to each of the terminal portions A 1 , A 2 , B 1 , and B 2  is disconnected or resistance abnormality has occurred. Since a system of a signal wire or terminal is increased to a plurality of systems, even when defective contact occurs at one of the terminal portions A 1  and A 2 , a risk of erroneous temperature detection is eliminated because: the other terminal portion keeps electrical continuity; or defective contact occurs at both of the terminal portions at the same time with extremely little possibility. 
     Furthermore, a versatile thermistor as conventionally used can be used as it is, and the configuration of the present embodiment can be achieved by adding the relay connectors  31  and  32  to increase the number of signal wires. Therefore, a high development cost for a new component can be suppressed. Similarly, the earth wires can be short-circuited by adding the relay connectors (in other words, a system of each earth wire is increased to a plurality of earth wires). Therefore, space saving can also be achieved. 
     Moreover, in a case where resistance abnormality is detected as a result of resistance measurement at terminal portions of signal wires of the drawer connector  55 , a notification to prompt a user to attach and detach the fixing device  5  relative to the apparatus body  50  can be displayed on an operation panel of the image forming apparatus. Thus, the resistance abnormality at the terminal portion of the drawer connector  55  is detected and the user is made to attach and detach the fixing device relative to the apparatus body  50 . As a result, a foreign substance, such as an oxide generated at the terminal portion of the drawer connector and causing defective contact, can be removed by a wiping effect to restore the terminal portion/contact portion. 
     As described above, according to an embodiment of the present disclosure, each thermistor includes the two lead wires as in a conventional thermistor, and the lead wires are separated into the signal wire and the earth wire. Each signal wire is branched at the drawer connector of the fixing device, and the branched signal wires are connected to the terminals obtained by the system increase from one system to two systems. On the other hand, earth wires of the thermistors are short-circuited to each other. The body-side connector also includes the terminals of the branched signal wires in a manner corresponding to the terminals of the fixing device side connector. The branched signal wires are connected on the body side. Thus, in the present embodiment, the contacts (signal paths) of the two systems (the plurality of systems) are formed in the drawer connector. 
     Numerous additional modifications and variations are possible in light of the above teachings. It is therefore to be understood that, within the scope of the above teachings, the present disclosure may be practiced otherwise than as specifically described herein. With some embodiments having thus been described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the scope of the present disclosure and appended claims, and all such modifications are intended to be included within the scope of the present disclosure and appended claims. 
     Any one of the above-described operations may be performed in various other ways, for example, in an order different from the one described above. Each of the functions of the described embodiments may be implemented by one or more processing circuits or circuitry. Processing circuitry includes a programmed processor, as a processor includes circuitry. A processing circuit also includes devices such as an application specific integrated circuit (ASIC), digital signal processor (DSP), field programmable gate array (FPGA), and conventional circuit components arranged to perform the recited functions.