CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

[0001] This application claims priority to Japanese Patent Application No. 2022-015874, filed on February 3, 2022, the entirety of which is incorporated by reference herein.

BACKGROUND

[0002] An image forming apparatus includes a fixing device which fixes a toner image to a sheet. The fixing device fixes the toner image to the sheet by heating and pressing the sheet with the toner image. A self-heating type fixing device includes a fixing belt having a heat generation resistor. The self-heating type fixing device heats the fixing belt by supplying electric power to the heat generation resistor and fixes a toner image to a sheet by conveying the sheet with the toner image along the heated fixing belt.

BRIEF DESCRIPTION OF THE DRAWINGS

[0003] FIG. l is a schematic diagram of an image forming apparatus, according to an example.

[0004] FIG. 2 is a schematic diagram of an example of a fixing device.

[0005] FIG. 3 is a partial cross-sectional view of a fixing belt.

[0006] FIG. 4 is a block diagram showing a functional configuration of a control device.

[0007] FIG. 5 is a flowchart showing a control method of the fixing device.

[0008] FIG. 6A is a diagram showing states of a detection switch and a power supply control switch in a preliminary detection operation.

[0009] FIG. 6B is a diagram showing the states of the detection switch and the power supply control switch in a power supply control operation. [0010] FIG. 7 is a timing chart showing an example of a change over time in electric power applied to a pair of sliding contacts.

[0011] FIG. 8 is a graph showing a relationship between a resistance and a gain of an impedance measurement device.

10012 ] FIG. 9 is a graph showing an example of a change over time of measured impedance.

[0013 [ FIG. 10 is a diagram showing a configuration of a control program stored in a recording medium.

[0014] FIG. 11 A is a schematic diagram showing an electrode and fixing rollers of a fixing device according to another example.

[0015] FIG. 1 IB is a schematic diagram of the fixing device of FIG. 11 A, shown with a control switch circuitry.

[0016] FIG. 12A is a schematic diagram showing an electrode and fixing rollers of a fixing device according to another example.

[0017] FIG. 12B is a schematic diagram of the fixing device of FIG. 12A, shown with a control switch circuitry.

[0018J FIG. 13 is a schematic diagram of a fixing device according to another example.

DETAILED DESCRIPTION

10019 [ In the following description, with reference to the drawings, the same reference numbers are assigned to the same components or to similar components having the same function, and overlapping description is omitted.

[0020] An image forming apparatus according to the present disclosure may be a printer, for example. This image forming apparatus includes a self-heating fixing device. The selfheating fixing device includes a fixing belt which includes a heat generation resistor generating heat by energization and a pair of electrodes electrically connected to the heat generation resistor, and is described further below. Electric power is supplied from a pair of sliding contacts which is in sliding contact with the pair of electrodes to the pair of electrodes of the fixing belt. When a distinct portion of the surfaces of the pair of electrodes is identified as including an irregularity or abnormality such as a scratch, a crack, or a dent, contact between the pair of electrodes and the pair of sliding contacts is prevented at the distinct portion identified where sparks (spark discharge) may occur if contact is maintained. Accordingly, the fixing device prevents the occurrence of sparks by temporarily interrupting the supply of electric power to the distinct portion of the pair of electrodes.

[00211 FIG. 1 is a diagram schematically showing an example of an image forming apparatus 1. The image forming apparatus 1 is an apparatus which forms a color image by using cyan, magenta, yellow, and black colors. The image forming apparatus 1 includes a conveying device 10 which conveys a sheet 5 as a print medium, a plurality of developing devices 20C, 20M, 20Y, and 20K which develop electrostatic latent images to form respective toner images, a transfer device 30 which secondarily transfers a toner image of each color to the sheet 5, a plurality of photoconductors 40C, 40M, 40Y, and 40K which form the electrostatic latent images on their respective surfaces, a fixing device 50 which fixes a layered toner image to the sheet 5, and a discharge device 60 which discharges the sheet 5. Any one of the of developing devices 20C, 20M, 20Y, and 20K may be referred to herein as "developing device 20", and any one of the photoconductors 40C, 40M, 40Y, and 40K may be referred to herein as "photoconductor 40". The conveying device 10, the developing devices 20C, 20M, 20 Y, and 20K, the transfer device 30, the photoconductors 40C, 40M, 40Y, and 40K, the fixing device 50, and the discharge device 60 are accommodated in a casing 15 of the image forming apparatus 1.

100221 The conveying device 10 conveys the sheet 5 corresponding to a print medium on which an image is to be formed along a conveying path 12. The sheet 5 is stacked and accommodated in a cassette 7 and is picked up and conveyed by a feeding roller 11. The conveying device 10 allows the sheet 5 to reach a transfer region 13 through the conveying path 12 at a timing at which the toner image to be transferred to the sheet 5 reaches the transfer region 13. [0023] The developing devices 20C, 20M, 20Y, and 20K are provided for the four respective colors and are positioned adjacent the photoconductors 40C, 40M, 40 Y, and 40K, respectively. Each developing device 20 includes a developing roller 45 which transfers a toner to the adjacent photoconductor 40. In the developing device 20, a two-component developer containing a toner and a carrier is used as the developer. That is, in the developing device 20, the toner and the carrier are adjusted to a targeted mixing ratio and are further mixed and stirred to disperse the toner, so that the developer is adjusted to have a targeted charge amount. This developer is carried on the developing roller 45. Then, when the developer is conveyed to a developing region facing the photoconductor 40 via a rotation of the developing roller 45, the toner contained in the developer carried on the developing roller 45 transfers to the electrostatic latent image formed on the peripheral surface of the photoconductor 40, so that the electrostatic latent image is developed to form a toner image.

|0024[ The transfer device 30 conveys the toner image formed by the developing device 20 to the transfer region 13 to transfer the toner image to the sheet 5. The transfer device 30 includes an intermediate transfer belt 31 that is an endless belt, a suspension roller 34 which tensions the intermediate transfer belt 31, idler rollers 35 and 36, a drive roller 37 which drives the intermediate transfer belt 31, primary transfer rollers 32C, 32M, 32Y, and 32K which interpose the intermediate transfer belt 31 between the primary transfer rollers 32C, 32M, 32Y, and 32K and the photoconductors 40C, 40M, 40 Y, and 40K, and a secondary transfer roller 33 which interpose the intermediate transfer belt 31 between the secondary transfer roller 33 and the drive roller 37. The respective toner images are primarily transferred from the photoconductors 40C, 40M, 40Y, and 40K onto the transfer belt 31. In the primary transfer, the toner images are sequentially layered onto the transfer belt 31 to form a single layered toner image. The transfer belt 31 conveys the layered toner image to the transfer region 13 where the layered toner image is secondarily transferred to the sheet 5.

[0025] The photoconductors 40C, 40M, 40Y, and 40K may also be referred to as electrostatic latent image carriers, photoconductor drums, and the like. The photoconductors 40C, 40M, 40Y, and 40K are provided for the respective four colors. The respective photoconductors 40 are provided along the moving direction of the intermediate transfer belt 31. The adjacent developing device 20, a charging device 41, an exposure device 42, and a cleaning device 43 are provided to face the photoconductor 40.

[0026] The charging device 41 is, for example, a charging roller which contacts the photoconductor 40 to charge the surface of the photoconductor 40 to a predetermined potential. The exposure device 42 exposes the surface of the photoconductor 40 having been charged by the charging device 41, to a light in response to the image to be formed on the sheet 5. Accordingly, a potential of a portion exposed by the exposure device 42 in the surface of the photoconductor 40 changes, so that an electrostatic latent image is formed. The image forming apparatus 1 includes toner tanks 18C, 18M, 18Y, and 18K that contain cyan toner, magenta toner, yellow toner, and black toner, respectively, to supply the developing devices 20C, 20M, 20Y, and 20K. The developing devices 20C, 20M, 20Y, and 20K develop the respective electrostatic latent images formed on the photoconductors 40C, 40M, 40Y, and 40K with the respective toners supplied from toner tanks 18C, 18M, 18Y, and 18K, so that a toner image is generated for each of the colors on the surfaces of the photoconductors 40C, 40M, 40Y, and 40K. The cleaning device 43 collects the toner remaining on the photoconductor 40 after the toner image formed on the photoconductor 40 is primarily transferred to the intermediate transfer belt 31.

[0027] The fixing device 50 conveys the sheet 5 with the transferred toner image through a fixing nip region 14, to fix the toner image to the sheet 5. The fixing device 50 is, for example, a self-heating fixing device and includes an endless fixing belt 51, a pressing roller 52 which is pressed against the outer peripheral surface of the fixing belt 51, a fixing roller 53 which is loosely inserted into the fixing belt 51, and a housing 58 which accommodates the fixing belt 51, the pressing roller 52, and the fixing roller 53. The fixing nip region 14 is formed between the fixing belt 51 and the pressing roller 52. When the sheet 5 passes through the fixing nip region 14, the toner image is melt-fixed (or fused) to the sheet 5.

[0028] The discharge device 60 includes discharge rollers 62 and 64 which discharge the sheet 5 to which the toner image has been fixed, to the outside of the image forming apparatus 1. [0029] FIG. 2 is a perspective view schematically showing the fixing device 50 according to an example. The fixing belt 51 of the fixing device 50 is a rotation body rotatable about a rotation axis. FIG. 3 is a partial cross-sectional view of the fixing belt 51 according to an example. The fixing belt 51 is a substantially cylindrical belt which is formed to be elastically deformable and has a layered structure in which an insulation layer 71, a heat generation resistor 72, an elastic layer 73, and a release layer 74 are layered in order form the inner peripheral side as shown in FIG. 3.

[0030] The insulation layer 71 of the fixing belt 51 is formed of an elastically deformable insulation material. The heat generation resistor 72 has a substantially cylindrical shape. A conductive filler is dispersed in the heat-resistant insulating resin on the heat generation resistor 72 to adjust the resistance value of the heat generation resistor 72 to a targeted resistance value. When electric power is applied to the heat generation resistor 72, a current flows to the heat generation resistor 72 to generate heat via Joule heating. Accordingly, the fixing belt 51 is heated by the heat generated by the heat generation resistor 72.

|0031| The elastic layer 73 covers the outer peripheral surface of the heat generation resistor 72 excluding the two end portions of the heat generation resistor 72. The release layer 74 covers the outer peripheral surface of the elastic layer 73.

[0032] The fixing belt 51 further includes a pair of electrodes 75 electrically connected to the heat generation resistor 72. The two electrodes 75 have a substantially annular shape, and are each provided at a portion of the heat generation resistor 72 exposed from the elastic layer 73, namely, at the two opposite end portions of the fixing belt 51, to extend along the outer peripheral surface of the heat generation resistor 72. The pair of electrodes 75 is formed of a conductive material such as metal. With reference to FIG. 3, the insulation layer 71, the heat generation resistor 72, the elastic layer 73, and the release layer 74 are layered in that order, in a region between the pair of electrodes 75 of the fixing belt 51, and the insulation layer 71, the heat generation resistor 72, and the pair of electrodes 75 are layered in that order, in a region in which the pair of electrodes 75 of the fixing belt 51 is disposed.

[0033] The fixing roller 53 has an outer diameter smaller than the inner diameter of the fixing belt 51 and is loosely inserted into the fixing belt 51. The fixing roller 53 includes a core metal 77 and an elastic layer 78. The core metal 77 is formed of, for example, a metal material and has a substantially columnar shape extending along a rotation axis 46 parallel to the rotation axis of the fixing belt 51. The two end portions of the core metal 77 include shaft portions 79 axially supported by the housing 58 of the fixing device 50. Thus, the fixing roller 53 is rotatable about the rotation axis 46. The elastic layer 78 may be formed of an elastically deformable material such as silicone rubber or fluororubber and is provided to cover the outer peripheral surface of the core metal 77.

[0034] The pressing roller 52 is disposed adjacent to the fixing belt 51 and is pressed against the fixing roller 53 through the fixing belt 51. Accordingly, the fixing nip region 14 is formed between the fixing belt 51 and the pressing roller 52. The pressing roller 52 includes, for example, a core metal 80, an elastic layer 81, and a release layer 82. The core metal 80 is formed of, for example, a metal material and extends along the rotation axis 48 parallel to the rotation axis 46. The two end portions of the core metal 77 are axially supported by, for example, the housing 58 of the fixing device 50. The elastic layer 81 is formed of an elastically deformable material such as silicone rubber or fluororubber and is provided to cover the outer peripheral surface of the core metal 80. The release layer 82 is formed of, for example, a resin composition such as a fluororesin and is provided to cover the outer peripheral surface of the elastic layer 81.

10035] The pressing roller 52 rotates about the rotation axis 48 by receiving a driving force from a driving motor. When the pressing roller 52 rotates, with the fixing belt 51 interposed between the pressing roller 52 and the fixing roller 53, the fixing belt 51 rotates in a following manner and the fixing roller 53 rotates about the rotation axis 46 in a following manner.

[0036] The fixing device 50 further includes a high-voltage power supply 54, a power supply control switch 55, a detection device 56, a pair of sliding contacts 65, and a control device 90. The pair of sliding contacts 65 may be, for example, a carbon brush formed of a conductive material that is electrically connected to the pair of electrodes 75. The pair of sliding contacts 65 is disposed to respectively face the pair of electrodes 75 at the fixed positions in the rotation direction of the fixing belt 51. Further, two opposite ends of a wiring (or circuitry wire) 84 are respectively connected to the pair of sliding contacts 65. The high- voltage power supply 54 and the power supply control switch 55 are connected in series to the wiring 84. The pair of sliding contacts 65 is in sliding contact with the pair of electrodes 75 so that when the fixing belt 51 rotates, the sliding contacts 65 slide along the rotating pair of electrodes 75, to supply electric power from the high-voltage power supply 54 to the fixing belt 51 via contact of the sliding contacts 65 with the pair of electrodes 75.

[0037] The high-voltage power supply 54 is a power supply which supplies electric power for generating heat from the heat generation resistor 72 to the fixing belt 51. In some examples, the high-voltage power supply 54 applies a voltage to the pair of electrodes 75 via the pair of sliding contacts 65. The high-voltage power supply 54 is an AC power supply and applies, for example, an AC voltage of 100 V to 240 V in effective value, to the pair of sliding contacts 65. When a voltage is applied from the high-voltage power supply 54 to the pair of electrodes 75, a current flows to the heat generation resistor 72 between the pair of electrodes 75 so that the fixing belt 51 is heated by Joule heating.

|0038| The power supply control switch 55 is connected to the wiring 84 between the high-voltage power supply 54 and one of the sliding contacts 65. The power supply control switch 55 controls the supply of electric power from the high-voltage power supply 54 to the fixing belt 51 or the stopping (or interruption) of the supply of electric power. For example, when the power supply control switch 55 is turned on, the high-voltage power supply 54 is electrically connected to the pair of sliding contacts 65 so that electric power is supplied from the high-voltage power supply 54 to the pair of sliding contacts 65. When the power supply control switch 55 is turned off, the electrical connection between the high-voltage power supply 54 and the pair of sliding contacts 65 is interrupted so that the supply of electric power from the high-voltage power supply 54 to the pair of sliding contacts 65 is stopped.

|0039| The detection device 56 measures the impedance between the pair of sliding contacts 65. As shown in FIG. 2, the detection device 56 includes a low-voltage power supply 91, an impedance measurement device 92, and a detection switch 93. The low- voltage power supply 91, the impedance measurement device 92, and the detection switch 93 are connected in series to a wiring (or circuitry wire) 86. The wiring 86 includes a pair of terminals, among which one terminal 86a of the wiring 86 is connected to the wiring 84 between the high-voltage power supply 54 and one sliding contact 65, and the other terminal 86b of the wiring 86 is connected to the wiring 84 between the power supply control switch 55 and the other sliding contact 65. Thus, the low-voltage power supply 91, the impedance measurement device 92, and the detection switch 93 are electrically connected in parallel to the high-voltage power supply 54 and the power supply control switch 55.

[0040] The low-voltage power supply 91 applies a voltage lower than the voltage of the high-voltage power supply 54 to the pair of sliding contacts 65 in order to measure the impedance between the pair of sliding contacts 65. The voltage applied from the low-voltage power supply 91 to the pair of sliding contacts 65 is a DC voltage which is low enough to prevent sparks occurring between the pair of sliding contacts 65 and the pair of electrodes 75 and is, for example, 5 V.

[0041] Further, when a voltage is applied from the low-voltage power supply 91 to the pair of sliding contacts 65, the impedance measurement device 92 measures the impedance between the pair of sliding contacts 65 on the basis of the magnitude of the voltage applied to the pair of sliding contacts 65. For example, the impedance measurement device 92 detects the impedance between the pair of sliding contacts 65 on the basis of the voltage applied to the pair of sliding contacts 65 and the current flowing through the wiring 86 by the use of Ohm's law. The impedance measurement device 92 may have a resistance value of 100 > or more. Since the impedance measurement device 92 has a resistance value of 100 > or more, it is possible to increase the gain of the detection device 56.

[0042] The detection switch 93 is provided between the low-voltage power supply 91 and the pair of sliding contacts 65 and controls the electrical connection between the low-voltage power supply 91 and the pair of sliding contacts 65. For example, when the detection switch 93 is turned on, the low-voltage power supply 91 is electrically connected to the pair of sliding contacts 65 so that a lower power is supplied to the pair of sliding contacts 65. At this time, the power supply control switch 55 is turned off. On the other hand when the detection switch 93 is turned off, the low-voltage power supply 91 is electrically disconnected from the pair of sliding contacts 65 so that the supply of electric power from the low-voltage power supply 91 to the pair of sliding contacts 65 is stopped.

[0043] The control device 90 may include a processor, a storage device, a communication device, an input device, a display device, and the like. The control device 90 is communicably connected to parts of the fixing device 50 to control the operation of each part. For example, the control device 90 transmits a control signal to the power supply control switch 55 and the detection switch 93 and switches the on/off states of the power supply control switch 55 and the detection switch 93. Further, the control device 90 controls the rotation of the pressing roller 52 by controlling the driving of the driving motor. The storage device of the control device 90 stores a control program in the form of data and/or instructions, to be executed by the processor to carry out various processes to operate the fixing device 50.

[0044] FIG. 4 is a block diagram illustrating a configuration of the control device 90. As shown in FIG. 4, the control device 90 includes an impedance acquisition unit 101, an identification unit 102, a control unit 103, and an output unit 104.

[0045] The impedance acquisition unit 101 receives the impedance between the pair of sliding contacts 65 measured by the impedance measurement device 92. The identification unit 102 identifies a distinct portion 120 of the pair of electrodes 75 (cf. FIG. 6A) where a scratch, a crack, a dent, and/or the like is formed on the surfaces of the pair of electrodes 75. The distinct portion 120 moves in the rotation direction of the fixing belt 51 in accordance with the rotation of the electrodes 75 of the fixing belt 51. When the distinct portion 120 is identified on the surfaces of the pair of electrodes 75, the pair of electrodes 75 and the pair of sliding contacts 65 are prevented from contacting the pair of electrodes 75 at the distinct portion 120, so that the electrical connection is temporarily interrupted. Accordingly, the impedance between the pair of sliding contacts 65 increases. Here, the identification unit 102 identifies a position in which the impedance measured by the impedance measurement device 92 exceeds a threshold value on the pair of electrodes 75, as the distinct portion 120.

[0046] That is, the distinct portion 120 represents a circumferential position of at least one electrode 75 of the pair of electrodes 75 and may include one or more surface regions on the electrodes 75 to be electrically disconnected from the pair of sliding contacts 65, due to scratches or other irregularities. The identification unit 102 stores information on the distinct portion 120 in a storage device 105. The information indicating the distinct portion 120 is, for example, information indicating the rotation angle (angle associated with a rotational position) of the fixing belt 51 corresponding to the distinct portion 120 or the detection timing associated with the distinct portion 120.

[0047] The control unit 103 controls the operation of the fixing device 50. For example, the control unit 103 controls the on/off states of the power supply control switch 55 and the detection switch 93. Namely, the control unit 103 turns off the power supply control switch 55 and turns on the detection switch 93 when the impedance between the pair of sliding contacts 65 is measured by the impedance measurement device 92. Accordingly, the supply of electric power from the high-voltage power supply 54 to the pair of sliding contacts 65 is interrupted and electric power is supplied from the low-voltage power supply 91 to the pair of sliding contacts 65. On the other hand, the detection switch 93 is turned off and the power supply control switch 55 is turned on when the fixing device 50 is operated to fix the toner image to the sheet 5 conveyed through the fixing nip region 14. Accordingly, the supply of electric power from the low-voltage power supply 91 to the pair of sliding contacts 65 is interrupted and electric power is supplied from the high-voltage power supply 54 to the pair of sliding contacts 65.

[0048] There may be a case in which sparks occur between the pair of sliding contacts 65 and the pair of electrodes 75 if electric power is supplied from the high-voltage power supply 54 to the pair of sliding contacts 65 when at least one of the sliding contacts 65 faces (and/or contacts) the distinct portion 120. When sparks occur, the fixing belt 51 or the peripheral element may be damaged, which may hinder the operation of the fixing device 50. Here, the control unit 103 controls the supply of electric power from the pair of sliding contacts 65 to the pair of electrodes 75 in order to prevent the occurrence of sparks in advance. Namely, the control unit 103 acquires the distinct portion 120 stored in the storage device 105 and is configured to supply electric power from the high-voltage power supply 54 to the pair of sliding contacts 65 by turning on the power supply control switch 55 when at least one of the sliding contacts 65 does not face the distinct portion 120 and to temporarily interrupt the supply of electric power from the high-voltage power supply 54 to the pair of sliding contacts 65 by turning off the power supply control switch 55 when at least one of the sliding contacts 65 faces the distinct portion 120. In other words, the control unit 103 controls the power supply control switch 55 so that the supply of electric power from the high-voltage power supply 54 to the fixing belt 51 is temporarily stopped when the fixing belt 51 is located at a rotational position in which electric power is supplied via the distinct portion 120. Further, the control unit 103 controls the power supply control switch 55 so that the supply of electric power from the high-voltage power supply 54 to the fixing belt 51 is restarted when the fixing belt 51 is located at a rotational position in which electric power is supplied via a portion excluding the distinct portion 120 in accordance with the rotation of the fixing belt 51 after the supply of electric power to the fixing belt 51 has been temporarily stopped. The rotational position indicates the rotation angle of the fixing belt 51 with respect to the reference rotation angle (or reference position) of the fixing belt 51.

10049] The output unit 104 displays various information to the display device. For example, the output unit 104 may output an alarm to the display device when the size of the surface region corresponding to the distinct portion 120 interrupting the electrical connection between the pair of electrodes 75 and the pair of sliding contacts 65 is greater than a reference size. The size of the surface region corresponding to the distinct portion 120 is, for example, a size (or a length) of the scratch on the surfaces of the pair of electrodes 75 in the rotation direction of the fixing belt. In some examples, when a duration (e.g., time length) during which the impedance becomes larger than the threshold value is measured and the measured duration is longer than a predetermined duration, the output unit 104 determines that the size of the surface region corresponding to the distinct portion 120 is larger than the reference size.

[0050] Next, a control method of the fixing device 50 according to an example, will be described with reference to FIG. 5. FIG. 5 is a flowchart showing a control method of the example of the fixing device 50. The respective operations shown in FIG. 5 are performed in such a manner that the control device 90 controls respective elements of the fixing device 50. As shown in FIG. 5, a control method according to an example, includes a preliminary detection operation STI of detecting the impedance between the pair of sliding contacts 65 and a power supply control operation ST2 of controlling the supply of electric power to the pair of sliding contacts 65.

[0051] The preliminary detection operation STI includes operations ST11 to ST17 which are described further below. In the preliminary detection operation STI, the control unit 103 of the control device 90 first turns off the power supply control switch 55 to stop the supply of electric power to the fixing belt 51 (cf. operation STI 1). Next, the control unit 103 drives the pressing roller 52 so that the fixing belt 51 rotates at a constant rotation speed (cf. operation ST 12). Next, the control unit 103 turns on the detection switch 93 (cf. operation STB).

10052] As shown in FIG. 6 A, when the power supply control switch 55 is turned off and the detection switch 93 is turned on, the supply of electric power from the high-voltage power supply 54 to the pair of sliding contacts 65 is stopped and electric power is supplied from the low-voltage power supply 91 to the pair of sliding contacts 65. When the electric power is supplied from the low-voltage power supply 91 to the pair of sliding contacts 65, a current I flows to the wiring 86 via one sliding contact 65, one electrode 75, the heat generation resistor 72, the other electrode 75, and the other sliding contact 65. The impedance measurement device 92 measures the impedance between the pair of sliding contacts 65 on the basis of the current I flowing through the wiring 86 and the voltage applied across the pair of sliding contacts 65 (cf. operation ST14). The impedance is measured continuously or periodically while rotating the fixing belt 51.

[0053] Additionally, when periodically measuring the impedance between the pair of sliding contacts 65, the impedance measurement device 92 measures the impedance at a cycle corresponding to the size of the distinct portion 120 to be detected. For example, when the rotation speed of the fixing belt 51 is 600 mm/s and the distinct portion 120 having a length of 0.08 mm or more in the rotation direction of the fixing belt 51 is detected, the impedance measurement device 92 measures the impedance at a sampling frequency of 8 kHz or more. Accordingly, since the detection peak becomes 0.08 mm or less, it is possible to appropriately detect the distinct portion 120 of the size to be detected. The impedance measurement device 92 outputs the measured impedance to the control device 90. The impedance acquisition unit 101 of the control device 90 acquires the impedance measured by the impedance measurement device 92.

[0054] FIG. 7 shows an example of a change over time in the impedance measured by the impedance measurement device 92. As shown in FIG. 6A, when the distinct portion 120 is formed on the surfaces of the pair of electrodes 75, the contact between the pair of sliding contacts 65 and the pair of electrodes 75 is reduced so as to increase the impedance at a timing at which at least one of the sliding contacts 65 faces (and/or contacts) the distinct portion 120 on the pair of electrodes 75. Here, the identification unit 102 identifies a position on the pair of electrodes 75 in which the measured impedance exceeds a threshold value as the distinct portion 120 (cf. operation STI 5). That is, the distinct portion 120 is a portion of the pair of electrodes 75 where the electrical contact area between the pair of electrodes 75 and the pair of sliding contacts 65 is reduced due to the surface irregularity (e.g., scratches, etc.) or the like formed on the surfaces of the pair of electrodes 75.

[0055] FIG. 8 shows a relationship between the resistance value of the impedance measurement device 92 and the gain of the detection device 56. The horizontal axis of the graph of FIG. 8 indicates the resistance value of the impedance measurement device 92 and the vertical axis of the graph indicates the detection voltage applied to the pair of sliding contacts 65 and the gain of the detection device 56. The gain of the detection device 56 corresponds to a ratio between the detection voltage (the detection voltage in the abnormal state) detected when the pair of sliding contacts 65 faces the distinct portion 120 and the detection voltage (the detection voltage in the normal state) when the pair of sliding contacts 65 does not face the distinct portion 120. As shown in FIG. 8, when the impedance measurement device 92 has a resistance value of 100 > or more, the gain of the detection device 56 reaches 20 dB or more. In this way, it is possible to locate the distinct portion 120 with a greater accuracy by setting the resistance value of the impedance measurement device 92 to 100 > or more.

[0056] The identification unit 102 stores the identified distinct portion 120 in the storage device 105 so that the distinct portion 120 is associated with a rotation angle (e.g., rotational position) of the fixing belt 51 (cf. operation ST16). For example, the identification unit 102 may set a rotation angle of the fixing belt 51 at which the reference point on the fixing belt 51 faces the pair of sliding contacts 65, as a reference rotation angle (e.g., OD) and may store a rotation angle of the distinct portion 120 relative to the reference rotation angle, in the storage device 105. In some examples, the storage device 105 may store a timing (distinct timing) at which the distinct portion 120 is detected relative to a rotation start timing of the fixing belt 51. The control unit 103 stores the rotation angle or timing of detecting the distinct portion 120 in the storage device 105 and then turns off the detection switch 93 (cf. operation ST17).

[0057] Next, the power supply control operation ST2 is performed. The power supply control operation ST2 includes operations ST21 to ST25 which are described further below. In the power supply control operation ST2, first, the control unit 103 determines whether or not at least one of the sliding contacts 65 faces the distinct portion 120 (cf. operation ST21). For example, the control unit 103 acquires the rotation angle of detecting the distinct portion 120 from the storage device 105 and determines that the pair of sliding contacts 65 faces the distinct portion 120 when the rotation angle of the fixing belt 51 matches the rotation angle acquired from the storage device 105. On the other hand, the control unit 103 determines that the pair of sliding contacts 65 does not face the distinct portion 120 when the rotation angle of the fixing belt 51 does not match the rotation angle acquired from the storage device 105.

[0058] When it is determined that at least one of the sliding contacts 65 does not face the distinct portion 120, the control unit 103 turns on the power supply control switch 55 (cf. operation ST22). As shown in FIG. 6B, when the power supply control switch 55 is turned on and the detection switch 93 is turned off, the supply of electric power from the low- voltage power supply 91 to the pair of sliding contacts 65 is stopped and electric power is supplied from the high-voltage power supply 54 to the pair of sliding contacts 65. When electric power is supplied from the high-voltage power supply 54 to the pair of sliding contacts 65, a current I flows to the wiring 84 via one sliding contact 65, one electrode 75, the heat generation resistor 72, the other electrode 75, and the other sliding contact 65. Joule heating is generated by the current i flowing through the heat generation resistor 72 of the fixing belt 51 and the fixing belt 51 is heated. The heated fixing belt 51 fixes the toner image to the sheet 5 by pressing and heating the sheet 5 conveyed through the fixing nip region 14 together with the pressing roller 52. [0059] On the other hand, when it is determined that at least one of the sliding contacts 65 faces the distinct portion 120, the control unit 103 turns off the power supply control switch 55 (cf. operation ST25). As a result, as shown in FIG. 7, the supply of electric power from the high-voltage power supply 54 to the pair of sliding contacts 65 is temporarily interrupted and the energization of the pair of sliding contacts 65 is temporarily stopped. Since the energization of the pair of sliding contacts 65 is stopped, the occurrence of sparks occurring between the pair of sliding contacts 65 and the pair of electrodes 75 is prevented when at least one of the sliding contacts 65 faces the distinct portion 120.

10060] The control of the power supply control switch 55 by the control unit 103 is continuously performed until the power supply control to the fixing belt 51 ends (cf. operation ST23). The control of the power supply control switch 55 is repeated at a cycle corresponding to the size of the distinct portion 120 to be detected. When the power supply control ends, the power supply control switch 55 is turned off by the control unit 103 (cf. operation ST24).

[0061] Additionally, the output unit 104 of the control device 90 may output an alarm to the display device when the size of the distinct portion 120 on the pair of electrodes 75 in the rotation direction of the fixing belt 51 is greater than a reference size. The output unit 104 measures, for example, a duration during which the impedance exceeds a threshold value and determines that the length of the distinct portion 120 is greater than the reference size when the measured duration is longer than a predetermined duration.

[0062] Further, when the plurality of distinct portions 120 are formed at the pair of electrodes 75, the output unit 104 may output an alarm to the display device when the cumulative size of the plurality of distinct portions 120 is larger than the reference size. For example, as shown in FIG. 9, it is assumed that the impedance measured during one rotation of the fixing belt 51 exceeds the threshold value three times and the time lengths exceeding the threshold value are Tl, T2, and T3, respectively. In this case, the output unit 104 outputs an alarm to the display device when it is determined that the total of the time lengths Tl, T2, and T3 exceeds a predetermined time length. Accordingly, it is possible to notify an operator that the cumulative size of the scratches formed on the surfaces of the pair of electrodes 75 is greater than the reference size.

[0063] Next, a control program 210 including instructions which can be executed by the processor of the control device 90, and a recording medium 220 storing the control program 210 will be described with reference to FIG. 10. FIG. 10 is a diagram showing a configuration of the control program 210 stored in the recording medium 220.

[0064] As shown in FIG. 10, the control program 210 includes a main module 200, an impedance acquisition module 201, an identification module 202, a control module 203, and an output module 204. The main module 200 controls the process related to the control device 90. The impedance acquisition module 201, the identification module 202, the control module 203, and the output module 204 may execute substantially the same functions as the impedance acquisition unit 101, the identification unit 102, the control unit 103, and the output unit 104.

[0065] The control program 210 is provided by data and instructions stored on a computer-readable non-transitory recording medium 220 such as a CD-ROM (Compact Disc Read Only Memory), a DVD-ROM (Digital Versatile Disc Read Only Memory), and/or a semiconductor memory. The control program 210 may be provided as a data signal via a network.

[0066] In the image forming apparatus 1, the fixing device 50, the control method, the control program 210, and the recording medium 220 described above, when at least one of the sliding contacts 65 faces the distinct portion 120 of the fixing belt 51, the power supply control switch 55 is operated and the supply of electric power from the high-voltage power supply 54 to the pair of sliding contacts 65 is interrupted. Thus, since the occurrence of sparks between the pair of sliding contacts 65 and the pair of electrodes 75 is suppressed, the damage of the pair of electrodes 75 can be prevented in advance. Further, when at least one of the sliding contacts 65 does not face the distinct portion 120 of the fixing belt 51, electric power is supplied from the high-voltage power supply 54 to the pair of sliding contacts 65. That is, the on/off state of the power supply control switch 55 is dynamically controlled so that electric power is supplied from the high-voltage power supply 54 to the fixing belt 51 when the fixing belt 51 is located at a rotational position in which electric power is supplied via a portion excluding the distinct portion 120 during one rotation (or one revolution) of the fixing belt 51, the supply of electric power from the high-voltage power supply 54 to the fixing belt 51 is temporarily stopped when the fixing belt 51 is rotated to a rotational position in which the distinct portion 120 contacts or faces the sliding contacts 65, and the supply of electric power from the high-voltage power supply 54 to the fixing belt 51 is restarted when the fixing belt 51 further rotates so that the sliding contacts 65 contact the fixing belt 51 at a rotational position excluding the distinct portion 120. In this way, since the power supply control switch 55 is dynamically controlled, it is possible to substantially continuously operate the fixing device 50 while suppressing the occurrence of sparks even with a surface irregularity at the distinct portion 120 of the pair of electrodes 75.

[0067] Although various examples have been described and shown herein, but it should be understood that other examples can be modified in their arrangement and details. All variations and modifications contained within the spirit and scope of the protected subject matter claimed herein are claimed.

[0068] For example, in the fixing device 50 shown in FIG. 2, the pair of electrodes 75 is provided at the two end portions of the fixing belt 51, but the pair of electrodes 75 may be provided at intermediate positions excluding the end portions of the fixing belt 51 according to other examples. FIGS. 11 A and 1 IB show a modified example of the fixing device. The fixing device shown in FIGS. 11 A and 1 IB includes a substantially cylindrical electrode 75 disposed to cover the outer peripheral surface of the heat generation resistor 72. The pair of sliding contacts 65 extending in parallel to the rotation axis of the fixing belt 51 comes into contact with the outer peripheral surface of the electrode 75. In this fixing device, when electric power is supplied from the high-voltage power supply 54 to the pair of sliding contacts 65, a current flows in the circumferential direction of the heat generation resistor 72 of the fixing belt 51 so that the fixing belt 51 generates heat. Even in such a configuration, it is possible to prevent the occurrence of sparks by interrupting the supply of electric power from the high-voltage power supply 54 to the pair of sliding contacts 65 when at least one of the sliding contacts 65 faces the distinct portion 120 of the fixing belt 51. [0069] FIGS. 12A and 12B show another modified example of the fixing device. This fixing device includes the pair of electrodes 75 having a substantially cylindrical shape and covering the inner peripheral surface and the outer peripheral surface of the heat generation resistor 72. The pair of sliding contacts 65 extend in parallel to the rotation axis of the fixing belt 51 and contact the pair of electrodes 75, respectively, covering the inner peripheral surface and the outer peripheral surface of the heat generation resistor 72. In this fixing device 50, when electric power is supplied from the high-voltage power supply 54 to the pair of sliding contacts 65, a current flows in the thickness direction of the heat generation resistor 72 of the fixing belt 51 so that the fixing belt 51 generates heat. Even in such a configuration, it is possible to suppress the occurrence of sparks by interrupting the supply of electric power from the high-voltage power supply 54 to the pair of sliding contacts 65 when at least one of the sliding contacts 65 faces the distinct portion 120 of the fixing belt 51.

10070] In the example shown in FIG. 2, the control device 90 locates the distinct portion 120 on the basis of the impedance measured by the detection device 56. In other examples, the control device 90 may locate the distinct portion 120 without using the impedance. For example, as shown in FIG. 13, the fixing device 50 may further include an imaging device 95 to acquire an image of the surfaces of the pair of electrodes 75. The control device 90 performs image processing on the image of the surfaces of the pair of electrodes 75 acquired by the imaging device 95 and identifies the distinct portion 120 from a difference in contrast or the like caused by the irregularities such as scratches, formed on the surfaces of the pair of electrodes 75. In this way, it is possible to prevent the damage of the pair of electrodes 75 in advance by suppressing the occurrence of sparks between the pair of sliding contacts 65 and the pair of electrodes 75 when the distinct portion 120 is identified as including a surface irregularity.

[0071] Additionally, the fixing device 50 may include a fixing roller (e.g., a solid roller) instead of the cylindrical fixing belt 51, as a rotatable rotation body. In this case, the control device 90 of the fixing device 50 dynamically controls the power supply control switch 55 so that the supply of electric power to the fixing roller via the distinct portion on the surface of the fixing roller is stopped and the supply of electric power to the fixing roller via a portion excluding the distinct portion on the surface of the fixing roller is allowed. Accordingly, it is possible to continuously operate the fixing device 50 while preventing the occurrence of sparks.

[0072] Further, in the example shown in FIG. 2, the power supply control switch 55 is provided between the high-voltage power supply 54 and the pair of electrodes 75 and controls the electrical connection between the high-voltage power supply 54 and the pair of electrodes 75. However, the power supply control switch 55 may control the operation of the high- voltage power supply 54 or the interruption of the operation thereof. For example, the power supply control switch 55 may be provided between a main power supply (for example, an external power supply) of the image forming apparatus 1 and the high-voltage power supply 54 and may be configured to temporarily stop the supply of electric power of the fixing belt 51 by stopping the operation of the high-voltage power supply 54 when at least one of the sliding contacts 65 faces the distinct portion 120 of the fixing belt 51 and to supply electric power to the fixing belt 51 by operating the high-voltage power supply 54 when neither of the sliding contacts 65 faces the distinct portion 120 of the fixing belt 51.

100731 Further, the fixing device 50 may in some example, not include the pair of sliding contacts 65. For example, the fixing device 50 may include a non-contact power supply device which supplies electric power to the pair of electrodes 75 in a non-contact manner instead of the pair of sliding contacts 65. Then, the power supply control switch 55 may control the operation of the non-contact power supply device or the stopping of the operation in response to the position of the distinct portion 120 on the pair of electrodes 75.

[0074] It is to be understood that not all aspects, advantages and features described herein may necessarily be achieved by, or included in, any one particular example. Indeed, having described and illustrated various examples herein, it should be apparent that other examples may be modified in arrangement and detail is omitted.