Fixing device having feed control switch

Abstract

To continuously operate a fixing device while preventing the occurrence of spark.SOLUTION: An image forming apparatus according to an aspect comprises: a rotatable rotating body; a power source that supplies power to the rotating body; a feed control switch 55 that controls supply of power from the power source to the rotating body or stop of the supply of power; and a control unit that controls the feed control switch so that when the rotating body reaches a rotation position where power is supplied via a specific portion on the surface of the rotating body, the supply of power from the power source to the rotating body is temporarily stopped, and when the rotating body reaches the rotation position where power is supplied via a portion excluding the specific portion in association with the rotation of the rotating body after the temporary stop of the supply of power, the supply of power from the power source to the rotating body is resumed.SELECTED DRAWING: Figure 2

Description

[Background technology]

[0001] An image forming apparatus includes a fixing device that fixes a toner image onto paper. The fixing device fixes the toner image onto the paper by applying heat and pressure to the paper onto which the toner image has been transferred. One type of fixing device is a self-heating fixing device that includes a fixing belt with a heating resistor. The self-heating fixing device heats the fixing belt by supplying power to the heating resistor, and fixes the toner image onto the paper by passing the paper onto which the toner image has been transferred through the heated fixing belt. [Brief explanation of the drawings]

[0002] [Figure 1] FIG. 1 is a schematic diagram of an exemplary imaging device that can be used to implement various examples disclosed herein. [Figure 2] FIG. 1 is a diagram illustrating an exemplary fixing device. [Figure 3] FIG. 2 is a partial cross-sectional view of a fixing belt. [Figure 4] FIG. 2 is a block diagram showing the functional configuration of a control device. [Figure 5] 10 is a flowchart illustrating a method for controlling the fixing device. [Figure 6] FIG. 10A is a diagram showing the states of the detection switch and the power supply control switch in the pre-detection step, and FIG. 10B is a diagram showing the states of the detection switch and the power supply control switch in the power supply control step. [Figure 7] 10 is a timing chart showing an example of a change over time in power applied to a pair of sliding contacts. [Figure 8] FIG. 10 is a diagram showing the relationship between the resistance value and the gain of the impedance measuring device. [Figure 9] FIG. 10 is a diagram showing an example of changes in measured impedance over time. [Figure 10] FIG. 2 is a diagram showing the functional configuration of a control program recorded on a recording medium. [Figure 11] FIG. 10 is a diagram schematically illustrating a modification of the fixing device. [Figure 12] FIG. 10 is a diagram schematically illustrating another modified example of the fixing device. [Figure 13] FIG. 10 is a diagram schematically illustrating another modified example of the fixing device. DETAILED DESCRIPTION OF THE INVENTION

[0003] An exemplary fixing device and an image forming apparatus including the fixing device will be described below with reference to the drawings. In the description based on the drawings, identical elements or elements having identical functions will be assigned the same reference numerals, and redundant description will be omitted. The drawings may be partially simplified or exaggerated for ease of understanding, and the dimensional ratios, angles, etc. are not limited to those shown in the drawings.

[0004] The image forming apparatus according to the present disclosure is, for example, a printer or other image forming apparatus. This image forming apparatus includes a self-heating fixing device. As described below, the self-heating fixing device has a fixing belt including a heating resistor that generates heat when energized and a pair of electrodes electrically connected to the heating resistor. Power is supplied to the pair of electrodes of the fixing belt from a pair of sliding contacts that slide against the pair of electrodes. If the surfaces of the pair of electrodes have a specific portion with an abnormality such as a scratch, crack, or dent, the pair of electrodes and the pair of sliding contacts may not be in contact with each other at the location of the specific portion, potentially causing a spark (spark discharge). The exemplary fixing device temporarily stops the supply of power to the specific portion to prevent sparks from occurring.

[0005] FIG. 1 is a diagram illustrating an exemplary image forming apparatus. The image forming apparatus 1 illustrated in FIG. 1 is an apparatus for forming a color image using the colors cyan, magenta, yellow, and black. The image forming apparatus 1 includes a conveying device 10 that conveys a print medium, namely, paper 5; multiple developing devices 20C, 20M, 20Y, and 20K that develop electrostatic latent images (hereinafter, referred to as "developing devices 20" unless it is necessary to distinguish between the individual components); a transfer device 30 that performs a second transfer of the toner images of each color onto the paper 5; multiple photoconductors 40C, 40M, 40Y, and 40K (hereinafter, referred to as "photoconductors 40" unless it is necessary to distinguish between the individual components); a fixing device 50 that fixes the laminated toner image onto the paper 5; and a discharge device 60 that discharges the paper 5. The conveying device 10 , the developing device 20 , the transfer device 30 , the photosensitive member 40 , the fixing device 50 and the discharge device 60 are housed in a housing 15 of the image forming apparatus 1 .

[0006] Conveying device 10 conveys paper 5, which is a print medium on which an image is formed, on conveying path 12. Paper 5 is stored in a stack in cassette 7, and is picked up and conveyed by paper feed roller 11. Conveying device 10 causes paper 5 to reach transfer area 13 via conveying path 12 at the timing when the toner image to be transferred onto paper 5 reaches transfer area 13.

[0007] Developing devices 20C, 20M, 20Y, and 20K are provided for each color. Each developing device 20 includes a developing roller 45 that carries toner on the photoconductor 40. The developing device 20 uses a two-component developer containing toner and carrier. That is, the toner and carrier are mixed in a desired ratio in the developing device 20, and then mixed and stirred to uniformly disperse the toner and provide the developer with an optimal charge. This developer is carried by the developing roller 45. When the developer is transported to the development area facing the photoconductor 40 by the rotation of the developing roller 45, the toner contained in the developer carried by the developing roller 45 moves to the electrostatic latent image formed on the circumferential surface of the photoconductor 40, developing the electrostatic latent image.

[0008] The transfer device 30 transports the toner image formed by the developing device 20 to a transfer area 13 where the toner image is secondarily transferred onto the paper 5. The transfer device 30 includes an intermediate transfer belt 31, which is an endless belt onto which the toner image is primarily transferred from the photosensitive member 40, a tension roller 34 that tensions the intermediate transfer belt 31, idler rollers 35 and 36, a drive roller 37 that drives the intermediate transfer belt 31, primary transfer rollers 32C, 32M, 32Y, and 32K that respectively sandwich the intermediate transfer belt 31 together with the photosensitive members 40C, 40M, 40Y, and 40K, and a secondary transfer roller 33 that sandwiches the intermediate transfer belt 31 together with the drive roller 37.

[0009] The photoconductors 40C, 40M, 40Y, and 40K are also called electrostatic latent image carriers, photoconductor drums, etc. The photoconductors 40C, 40M, 40Y, and 40K are provided for each color. Each photoconductor 40 is provided along the direction of movement of the intermediate transfer belt 31. A developing device 20, a charging device 41, an exposure unit 42, and a cleaning device 43 are provided around the photoconductor 40.

[0010] The charging device 41, which is, for example, a charging roller in contact with the photoreceptor 40, uniformly charges the surface of the photoreceptor 40 to a predetermined potential. The exposure unit 42 exposes the surface of the photoreceptor 40, which has been charged by the charging device 41, to light in accordance with the image to be formed on the paper 5. This changes the potential of the portion of the surface of the photoreceptor 40 exposed by the exposure unit 42, forming an electrostatic latent image. The developing devices 20C, 20M, 20Y, and 20K develop the electrostatic latent image formed on the photoreceptor 40 with toner supplied from toner tanks 18C, 18M, 18Y, and 18K, which are provided opposite the respective developing devices 20, to generate a toner image. The toner tanks 18C, 18M, 18Y, and 18K are filled with cyan, magenta, yellow, and black toner, respectively. The cleaning device 43 collects toner remaining on the photoreceptor 40 after the toner image formed on the photoreceptor 40 is primarily transferred to the intermediate transfer belt 31.

[0011] The fixing device 50 fixes the toner image, which has been secondarily transferred from the intermediate transfer belt 31 to the paper 5, onto the paper 5 by passing the paper 5 through the fixing nip area 14. The fixing device 50 is, for example, a self-heating fixing device, and includes an endless fixing belt 51, a pressure roller 52 that is in pressure contact with the outer peripheral surface of the fixing belt 51, a fixing roller 53 that is loosely fitted into the fixing belt 51, and a housing 58 that houses the fixing belt 51, the pressure roller 52, and the fixing roller 53. A fixing nip area 14 is formed between the fixing belt 51 and the pressure roller 52. When the paper 5 passes through the fixing nip area 14, the toner image is fused and fixed to the paper 5.

[0012] The discharge device 60 includes discharge rollers 62 and 64 for discharging the paper 5 onto which the toner image has been fixed by the fixing device 50 to the outside of the device.

[0013] Fig. 2 is a perspective view schematically illustrating an exemplary fixing device 50. The fixing belt 51 of the fixing device 50 is a rotating body that can rotate around a rotation axis. Fig. 3 is a partial cross-sectional view of the exemplary fixing belt 51. The fixing belt 51 is an elastically deformable belt having a substantially cylindrical shape, and as shown in Fig. 3, has a layered structure in which an insulating layer 71, a heating resistor 72, an elastic layer 73, and a release layer 74 are layered in this order from the inner periphery.

[0014] The insulating layer 71 of the fixing belt 51 is made of an elastically deformable insulating material. The heating resistor 72 has a substantially cylindrical shape. The heating resistor 72 is made of a heat-resistant insulating resin with conductive fillers dispersed therein, and the resistance of the heating resistor 72 is adjusted to a desired resistance value. When power is applied to the heating resistor 72, a current flows through the heating resistor 72, generating Joule heat. The heat generated by the heating resistor 72 heats the fixing belt 51.

[0015] The elastic layer 73 covers the outer peripheral surface of the heating resistor 72 except for both end portions of the heating resistor 72. The release layer 74 covers the outer peripheral surface of the elastic layer 73.

[0016] The fixing belt 51 further includes a pair of electrodes 75 electrically connected to the heating resistor 72. The pair of electrodes 75 are generally annular and are provided on the portion of the heating resistor 72 exposed from the elastic layer 73, i.e., on both ends of the fixing belt 51, and extend along the outer circumferential surface of the heating resistor 72. The pair of electrodes 75 are made of a conductive material such as metal. That is, as shown in FIG. 3 , an insulating layer 71, the heating resistor 72, the elastic layer 73, and a release layer 74 are laminated in this order in the region of the fixing belt 51 between the pair of electrodes 75, and an insulating layer 71, the heating resistor 72, and the pair of electrodes 75 are laminated in this order in the region of the fixing belt 51 where the pair of electrodes 75 are located.

[0017] The fixing roller 53 has an outer diameter smaller than the inner diameter of the fixing belt 51 and is loosely fitted in the fixing belt 51. The fixing roller 53 has a core 77 and an elastic layer 78. The core 77 is made of, for example, a metal material and has a generally cylindrical shape extending along a rotation axis 46 that is parallel to the rotation axis of the fixing belt 51. Shafts 79 that are journaled on the housing 58 of the fixing device 50 are provided at both ends of the core 77. Therefore, the fixing roller 53 is rotatable around the rotation axis 46. The elastic layer 78 is made of an elastically deformable material such as silicone rubber or fluororubber and is provided to cover the outer peripheral surface of the core 77.

[0018] The pressure roller 52 is disposed adjacent to the fixing belt 51 and is pressed against the fixing roller 53 via the fixing belt 51. This forms a fixing nip region 14 between the fixing belt 51 and the pressure roller 52. The pressure roller 52 includes, for example, a core metal 80, an elastic layer 81, and a release layer 82. The core metal 80 is made of, for example, a metal material and extends along a rotation axis 48 parallel to the rotation axis 46. Both ends of the core metal 80 are journaled, for example, by the housing 58 of the fixing device 50. The elastic layer 81 is made 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 made of, for example, a resin composition such as a fluororesin, and is provided to cover the outer peripheral surface of the elastic layer 81.

[0019] The pressure roller 52 receives a driving force from the drive motor and rotates around the rotation axis 48. When the pressure roller 52 rotates with the fixing belt 51 sandwiched between the pressure roller 52 and the fixing roller 53, the fixing belt 51 is rotated, and the fixing roller 53 is rotated around the rotation axis 46.

[0020] The fixing device 50 further includes a high-voltage power supply 54, a power supply control switch 55, a detection unit 56, a pair of sliding contacts 65, and a control device 90. The pair of sliding contacts 65 are, for example, carbon brushes made of a conductive material, and are electrically connected to a pair of electrodes 75. The pair of sliding contacts 65 are disposed opposite the pair of electrodes 75 at positions fixed in the rotation direction of the fixing belt 51. Both ends of a wiring 84 are connected to the pair of sliding contacts 65, respectively. The high-voltage power supply 54 and the power supply control switch 55 are connected in series to the wiring 84. When the fixing belt 51 rotates, the pair of sliding contacts 65 come into sliding contact with the pair of electrodes 75, supplying power from the high-voltage power supply 54 to the fixing belt 51 via the pair of electrodes 75.

[0021] High-voltage power supply 54 is a power supply that supplies power to fixing belt 51 for causing heating resistor 72 to generate heat. For example, high-voltage power supply 54 applies a voltage to a pair of electrodes 75 via a pair of sliding contacts 65. High-voltage power supply 54 is an AC power supply, and applies an AC voltage of, for example, an effective value of 100 V or more and 240 V or less to the pair of sliding contacts 65. When voltage is applied from high-voltage power supply 54 to the pair of electrodes 75, a current flows through heating resistor 72 between the pair of electrodes 75, and Joule heat heats fixing belt 51.

[0022] The power supply control switch 55 is connected to the wiring 84 between the high-voltage power supply 54 and one of the pair of sliding contacts 65. The power supply control switch 55 controls whether or not to supply power from the high-voltage power supply 54 to the fixing belt 51. For example, when the power supply control switch 55 is turned on, the high-voltage power supply 54 and the pair of sliding contacts 65 are electrically connected, and power is supplied from the high-voltage power supply 54 to the pair of sliding contacts 65. On the other hand, 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 cut off, and the supply of power from the high-voltage power supply 54 to the pair of sliding contacts 65 is stopped.

[0023] The detection unit 56 measures the impedance between the pair of sliding contacts 65. As shown in FIG. 2 , the detection unit 56 includes a low-voltage power supply 91, an impedance measuring device 92, and a detection switch 93. The low-voltage power supply 91, the impedance measuring device 92, and the detection switch 93 are connected in series to a wire 86. The wire 86 has a pair of terminals. One terminal 86a of the wire 86 is connected to the wire 84 between the high-voltage power supply 54 and one of the sliding contacts 65, and the other terminal 86b of the wire 86 is connected to the wire 84 between the power supply control switch 55 and the other sliding contact 65. Therefore, the low-voltage power supply 91, the impedance measuring 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.

[0024] 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, for example, 5 V, that is low enough not to cause sparks between the pair of sliding contacts 65 and the pair of electrodes 75.

[0025] Furthermore, the impedance measuring device 92 measures the impedance between the pair of sliding contacts 65 based on the magnitude of the voltage applied to the pair of sliding contacts 65 when a voltage is applied to the pair of sliding contacts 65 from the low-voltage power supply 91. For example, the impedance measuring device 92 uses Ohm's law to detect the impedance between the pair of sliding contacts 65 based on the voltage applied to the pair of sliding contacts 65 and the current flowing through the wiring 86. Here, the impedance measuring device 92 may have a resistance value of 100 Ω or more. When the impedance measuring device 92 has a resistance value of 100 Ω or more, the gain of the detection unit 56 is increased.

[0026] 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 and the pair of sliding contacts 65 are electrically connected, and a weak amount of 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 and the pair of sliding contacts 65 are electrically disconnected, and the supply of power from the low-voltage power supply 91 to the pair of sliding contacts 65 is stopped.

[0027] The control device 90 includes a processor, a storage device, a communication device, an input device, a display device, etc. The control device 90 is communicably connected to each part of the fixing device 50 and controls the operation of each part of the fixing device 50. For example, the control device 90 sends control signals to the power supply control switch 55 and the detection switch 93 to switch the power supply control switch 55 and the detection switch 93 on and off. The control device 90 also controls the drive of the drive motor to control the rotation of the pressure roller 52. The storage device of the control device 90 stores control programs for causing the processor to execute various processes executed in the fixing device 50.

[0028] The functional configuration of the control device 90 will be described with reference to Fig. 4. Fig. 4 is a block diagram showing the functional configuration of the control device 90. As shown in Fig. 4, the control device 90 includes, as functional components, an impedance acquisition unit 101, an identification unit 102, a control unit 103, and an output unit 104. The operation of each functional unit of the control device 90 will be described in detail in the description of the control method to be given later, so here, the function of each functional unit will be briefly described.

[0029] 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 specific portion 120 of the pair of electrodes 75 (see FIG. 6A). The specific portion 120 is a portion on the surface of the pair of electrodes 75 where scratches, cracks, dents, or the like are formed, and moves in the rotational direction of the fixing belt 51 as the fixing belt 51 rotates. If the specific portion 120 is present on the surface of the pair of electrodes 75, the pair of electrodes 75 and the pair of sliding contacts 65 are out of contact at the portion where the specific portion 120 is formed, and the electrical connection is interrupted. This increases the impedance between the pair of sliding contacts 65. Therefore, the identification unit 102 identifies, as the specific portion 120, a position on the pair of electrodes 75 where the impedance measured by the impedance measurement device 92 is greater than a threshold value.

[0030] That is, the specific portion 120 represents the circumferential position of at least one of the pair of electrodes 75, and more specifically refers to one or more surface areas on the electrode 75 where electrical connection to the pair of sliding contacts 65 has been interrupted due to scratches or the like. The identification unit 102 stores information indicating the identified specific portion 120 in the storage device 105. The information indicating the specific portion 120 is, for example, information indicating the rotation angle (angular position) of the fixing belt 51 corresponding to the specific portion 120, or information indicating the timing at which the specific portion 120 was detected.

[0031] The control unit 103 controls the operation of each unit of the fixing device 50. For example, the control unit 103 controls the on / off of the power supply control switch 55 and the detection switch 93. More specifically, when the impedance measuring device 92 measures the impedance between the pair of sliding contacts 65, the control unit 103 turns off the power supply control switch 55 and turns on the detection switch 93. This blocks the supply of power from the high-voltage power supply 54 to the pair of sliding contacts 65 and allows the supply of power from the low-voltage power supply 91 to the pair of sliding contacts 65. On the other hand, when a toner image is to be fixed on the paper 5 passing through the fixing nip region 14, the control unit 103 turns off the detection switch 93 and turns on the power supply control switch 55. This blocks the supply of power from the low-voltage power supply 91 to the pair of sliding contacts 65 and allows the supply of power from the high-voltage power supply 54 to the pair of sliding contacts 65.

[0032] Here, if power is supplied from the high-voltage power supply 54 to the pair of sliding contacts 65 when at least one of the pair of sliding contacts 65 faces the specific portion 120, sparks may occur between the pair of sliding contacts 65 and the pair of electrodes 75. If sparks occur, the fixing belt 51 or its surrounding components may be damaged, which may interfere with the operation of the fixing device 50. Therefore, the control unit 103 controls the supply of power from the pair of sliding contacts 65 to the pair of electrodes 75 to prevent sparks from occurring. More specifically, the control unit 103 acquires the specific portion 120 stored in the storage device 105, and when at least one of the pair of sliding contacts 65 does not face the specific portion 120, turns on the power supply control switch 55 to supply power from the high-voltage power supply 54 to the pair of sliding contacts 65. When at least one of the pair of sliding contacts 65 faces the specific portion 120, the control unit 103 turns off the power supply control switch 55 to temporarily cut off the supply of power from the high-voltage power supply 54 to the pair of sliding contacts 65. In other words, when fixing belt 51 reaches a rotational position where power is supplied via specific portion 120, control unit 103 controls power supply control switch 55 to temporarily stop the supply of power from high-voltage power supply 54 to fixing belt 51. Furthermore, after the supply of power to fixing belt 51 has been temporarily stopped, control unit 103 controls power supply control switch 55 to resume the supply of power from high-voltage power supply 54 to fixing belt 51 when fixing belt 51, as fixing belt 51 rotates, reaches a rotational position where power is supplied via portions other than specific portion 120. Note that the rotational position is the rotational angle of fixing belt 51 with respect to a reference rotational angle.

[0033] The output unit 104 outputs various information to a display device. For example, the output unit 104 outputs an alarm to the display device when the size of the surface area corresponding to the specific portion 120 that interrupts the electrical connection between the pair of electrodes 75 and the pair of sliding contacts 65 is larger than a reference size. The size of the surface area corresponding to the specific portion 120 is, for example, the size of a scratch on the surface of the pair of electrodes 75 in the rotational direction of the fixing belt. For example, the output unit 104 measures the length of time during which the impedance is greater than a threshold, and determines that the size of the surface area corresponding to the specific portion 120 is larger than the reference size when the measured length of time is longer than a predetermined length of time.

[0034] Next, an exemplary control method for the fixing device 50 will be described with reference to Fig. 5. Fig. 5 is a flowchart showing the exemplary control method for the fixing device 50. The steps shown in Fig. 5 are executed by the control device 90 controlling the components of the fixing device 50. As shown in Fig. 5, the exemplary control method includes a pre-detection step ST1 for measuring impedance between the pair of sliding contacts 65 and a power supply control step ST2 for controlling power supply to the pair of sliding contacts 65.

[0035] The pre-detection step ST1 includes steps ST11 to ST17, which will be described later. In the pre-detection step ST1, first, the control unit 103 of the control device 90 turns off the power supply control switch 55 to stop power supply to the fixing belt 51 (step ST11). Next, the control unit 103 drives the pressure roller 52 to rotate the fixing belt 51 at a constant rotation speed (step ST12). Next, the control unit 103 turns on the detection switch 93 (step ST13).

[0036] As shown in FIG. 6A, by turning off the power supply control switch 55 and turning on the detection switch 93, the power supply from the high-voltage power supply 54 to the pair of sliding contacts 65 is stopped, and power is supplied from the low-voltage power supply 91 to the pair of sliding contacts 65. When power from the low-voltage power supply 91 is supplied to the pair of sliding contacts 65, a current I flows through the wiring 86 via one sliding contact 65, one electrode 75, the heating resistor 72, the other electrode 75, and the other sliding contact 65. The impedance measuring device 92 measures the impedance between the pair of sliding contacts 65 based on the current I flowing through the wiring 86 and the voltage applied between the pair of sliding contacts 65 (step ST14). The impedance measurement is performed continuously or periodically while the fixing belt 51 is rotating.

[0037] When measuring the impedance between a pair of sliding contacts 65 periodically, the impedance measuring device 92 measures the impedance at a period corresponding to the size of the specific portion 120 to be detected. For example, when the rotation speed of the fixing belt 51 is 600 mm / s and a specific portion 120 having a length of 0.08 mm or more in the rotation direction of the fixing belt 51 is to be detected, the impedance measuring device 92 measures the impedance at a sampling frequency of 8 kHz or more. This results in a detection pitch of 0.08 mm or less, allowing the specific portion 120 of the size to be detected to be properly detected. The impedance measuring device 92 outputs the measured impedance to the control device 90. The impedance acquiring unit 101 of the control device 90 acquires the impedance measured by the impedance measuring device 92.

[0038] 7 shows an example of the change over time in impedance measured by the impedance measuring device 92. As shown in FIG. 6(a), when a specific portion 120 is formed on the surface of the pair of electrodes 75, the pair of sliding contacts 65 and the pair of electrodes 75 are partially out of contact with each other when at least one of the pair of sliding contacts 65 faces the specific portion 120 on the pair of electrodes 75, and the impedance increases. Therefore, the identifying unit 102 identifies as the specific portion 120 a position on the pair of electrodes 75 where the measured impedance is greater than a threshold value (step ST15). In other words, the specific portion 120 is a part of the pair of electrodes 75 where the electrical connection between the pair of electrodes 75 and the pair of sliding contacts 65 is interrupted due to a scratch or the like formed on the surface of the pair of electrodes 75.

[0039] FIG. 8 shows the relationship between the resistance value of the impedance measuring device 92 and the gain of the detection unit 56. The horizontal axis of the graph in FIG. 8 represents the resistance value of the impedance measuring device 92, and the vertical axis of the graph represents the detection voltage applied to the pair of sliding contacts 65 and the gain of the detection unit 56. The gain of the detection unit 56 is the ratio of the detection voltage (detection voltage in an abnormal state) detected when the pair of sliding contacts 65 faces the specific portion 120 to the detection voltage (detection voltage in a normal state) detected when the pair of sliding contacts 65 does not face the specific portion 120. As shown in FIG. 8, when the impedance measuring device 92 has a resistance value of 100 Ω or more, the gain of the detection unit 56 is 20 dB or more. In this way, by setting the resistance value of the impedance measuring device 92 to 100 Ω or more, it is possible to identify the specific portion 120 with high accuracy.

[0040] The identifying unit 102 associates the identified specific portion 120 with the rotation angle of the fixing belt 51 and stores the association in the storage device 105 (step ST16). For example, the identifying unit 102 may set the rotation angle of the fixing belt 51 at which a reference point on the fixing belt 51 faces the pair of sliding contacts 65 as a reference rotation angle (0°), and store in the storage device 105 the rotation angle at which the specific portion 120 is detected, using the reference rotation angle as a base point. Note that the timing at which the specific portion 120 is detected (specific timing) may be stored in the storage device 105 using the timing at which the fixing belt 51 starts to rotate as a reference. After storing the rotation angle or timing at which the specific portion 120 is detected in the storage device 105, the control unit 103 turns off the detection switch 93 (step ST17).

[0041] Next, the power supply control step ST2 is performed. The power supply control step ST2 includes steps ST21 to ST25, which will be described later. In the power supply control step ST2, first, the control unit 103 determines whether or not at least one of the pair of sliding contacts 65 faces the specific portion 120 (step ST21). For example, the control unit 103 acquires the rotation angle at which the specific portion 120 is detected from the storage device 105, and determines that the pair of sliding contacts 65 faces the specific 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, when the rotation angle of the fixing belt 51 does not match the rotation angle acquired from the storage device 105, the control unit 103 determines that the pair of sliding contacts 65 does not face the specific portion 120.

[0042] If it is determined that at least one of the pair of sliding contacts 65 does not face the specific portion 120, the control unit 103 turns on the power supply control switch 55 (step 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 power supply from the low-voltage power supply 91 to the pair of sliding contacts 65 is stopped, and power is supplied from the high-voltage power supply 54 to the pair of sliding contacts 65. When power is supplied from the high-voltage power supply 54 to the pair of sliding contacts 65, a current i flows through the wiring 84 via one sliding contact 65, one electrode 75, the heating resistor 72, the other electrode 75, and the other sliding contact 65. The current i flows through the heating resistor 72 of the fixing belt 51, generating Joule heat, which heats the fixing belt 51. The heated fixing belt 51, together with the pressure roller 52, presses and heats the paper 5 passing through the fixing nip region 14, thereby fixing a toner image on the paper 5.

[0043] On the other hand, when it is determined that at least one of the pair of sliding contacts 65 faces the specific portion 120, the control unit 103 turns off the power supply control switch 55 (step ST25). As a result, as shown in Fig. 7, the power supply from the high-voltage power supply 54 to the pair of sliding contacts 65 is temporarily cut off, and the current to the pair of sliding contacts 65 is temporarily stopped. By stopping the current to the pair of sliding contacts 65, it is possible to prevent sparks from occurring between the pair of sliding contacts 65 and the pair of electrodes 75 when at least one of the pair of sliding contacts 65 faces the specific portion 120.

[0044] The control of the power supply control switch 55 by the control unit 103 continues until the power supply control to the fixing belt 51 is completed (step ST23). The control of the power supply control switch 55 is repeatedly performed at a period corresponding to the size of the specific portion 120 to be detected. When the power supply control is completed, the control unit 103 turns off the power supply control switch 55 (step ST24).

[0045] The output unit 104 of the control device 90 may output a warning to the display device when the size of the specific portion 120 on the pair of electrodes 75 in the rotation direction of the fixing belt 51 is larger than a reference size. For example, the output unit 104 measures the length of time during which the impedance is larger than a threshold, and determines that the length of the specific portion 120 is larger than the reference size when the measured length of time is longer than a preset length of time.

[0046] Furthermore, if multiple specific portions 120 are formed on the pair of electrodes 75, the output unit 104 may output an alarm to the display device when the cumulative size of the multiple specific portions 120 is larger than the reference size. For example, as shown in FIG. 9, assume that the impedance measured during one rotation of the fixing belt 51 exceeds the threshold three times, and the times during which the threshold is exceeded are T1, T2, and T3, respectively. In this case, the output unit 104 outputs an alarm to the display device when it determines that the sum of the times T1, T2, and T3 exceeds a predetermined time. This allows the operator to be notified that the cumulative size of scratches formed on the surfaces of the pair of electrodes 75 is larger than the reference size.

[0047] Next, a control program 210 including instructions executable by the processor of the control device 90 and a recording medium 220 that stores the control program 210 will be described with reference to Fig. 10. Fig. 10 is a diagram showing the configuration of the control program 210 recorded on the recording medium 220.

[0048] 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 is a part that performs overall control of processing related to the control device 90. Functions realized by executing the impedance acquisition module 201, the identification module 202, the control module 203, and the output module 204 are similar to the functions of the impedance acquisition unit 101, the identification unit 102, the control unit 103, and the output unit 104 described above, respectively.

[0049] The control program 210 is provided by 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), or a semiconductor memory. The control program 210 may also be provided as a data signal over a network.

[0050] In the image forming apparatus 1, fixing device 50, control method, control program 210, and recording medium 220 described above, when at least one of the pair of sliding contacts 65 faces the specific portion 120 of the fixing belt 51, the power supply control switch 55 is activated to cut off the supply of power from the high-voltage power supply 54 to the pair of sliding contacts 65. This prevents sparks from occurring between the pair of sliding contacts 65 and the pair of electrodes 75, thereby preventing damage to the pair of electrodes 75. Furthermore, when at least one of the pair of sliding contacts 65 does not face the specific portion 120 of the fixing belt 51, power is supplied from the high-voltage power supply 54 to the pair of sliding contacts 65. That is, during one rotation of the fixing belt 51, when the fixing belt 51 is in a rotation position where power is supplied via parts other than the specific part 120, power is supplied to the fixing belt 51 from the high-voltage power supply 54, and when the fixing belt 51 reaches a rotation position where power is supplied via the specific part 120 as the fixing belt 51 rotates, the supply of power from the high-voltage power supply 54 to the fixing belt 51 is temporarily stopped, and when the fixing belt 51 further rotates and reaches a rotation position where power is again supplied via parts other than the specific part 120, the supply of power from the high-voltage power supply 54 to the fixing belt 51 is resumed. By dynamically controlling the power supply control switch 55 in this way, even when the specific part is present in the pair of electrodes 75, the fixing device 50 can be continuously operated while suppressing the occurrence of sparks.

[0051] It is to be understood that not all aspects, advantages, and features described herein are necessarily achieved or included in any one particular example or embodiment. Indeed, while various examples have been described and illustrated herein, it should be apparent that other examples can be modified in arrangement and detail. We claim all modifications and variations that fall within the spirit and scope of the subject matter claimed herein.

[0052] For example, in the fixing device 50 shown in FIG. 2, a pair of electrodes 75 is provided at both ends of the fixing belt 51. However, the pair of electrodes 75 may be provided at positions other than both ends of the fixing belt 51. FIGS. 11(a) and 11(b) show modified examples of the fixing device. The fixing device shown in FIGS. 11(a) and 11(b) includes a substantially cylindrical electrode 75 arranged to cover the outer circumferential surface of the heating resistor 72. A pair of sliding contacts 65 extending parallel to the rotation axis of the fixing belt 51 abuts against the outer circumferential surface of the electrode 75. In this fixing device, when power is supplied from the high-voltage power supply 54 to the pair of sliding contacts 65, a current flows circumferentially through the heating resistor 72 of the fixing belt 51, causing the fixing belt 51 to generate heat. Even with this configuration, when at least one of the pair of sliding contacts 65 faces a specific portion 120 of the fixing belt 51, the supply of power from the high-voltage power supply 54 to the pair of sliding contacts 65 is cut off, thereby preventing sparks from occurring.

[0053] 12(a) and 12(b) show another modified example of the fixing device. This fixing device includes a pair of electrodes 75 having a substantially cylindrical shape that cover the inner and outer circumferential surfaces of the heating resistor 72. A pair of sliding contacts 65 extend parallel to the rotational axis of the fixing belt 51 and abut against the pair of electrodes 75 that cover the inner and outer circumferential surfaces of the heating resistor 72, respectively. In this fixing device 50, when 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 heating resistor 72 of the fixing belt 51, causing the fixing belt 51 to generate heat. Even with this configuration, when at least one of the pair of sliding contacts 65 faces a specific portion 120 of the fixing belt 51, the supply of power from the high-voltage power supply 54 to the pair of sliding contacts 65 is cut off, thereby preventing sparks from occurring.

[0054] In the example shown in FIG. 2, the control device 90 identifies the specific portion 120 based on the impedance measured by the detection unit 56, but the control device 90 may identify the specific portion 120 without using the impedance. For example, as shown in FIG. 13, the fixing device 50 may further include an imaging unit 95 that captures 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 unit 95, and identifies the specific portion 120 based on a difference in contrast caused by scratches formed on the surfaces of the pair of electrodes 75, etc. Even when the specific portion 120 is identified in this way, it is possible to suppress the occurrence of sparks between the pair of sliding contacts 65 and the pair of electrodes 75, and prevent damage to the pair of electrodes 75.

[0055] The fixing device 50 may include a fixing roller having a substantially cylindrical shape as a rotatable rotating body instead of the fixing belt 51 having a substantially cylindrical shape. 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 power to the fixing roller via a specific portion on the surface of the fixing roller is stopped and the supply of power to the fixing roller via portions of the surface of the fixing roller other than the specific portion is permitted. This allows the fixing device 50 to operate continuously while preventing the occurrence of sparks.

[0056] 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, but the power supply control switch 55 may also control the activation or deactivation of the high-voltage power supply 54. For example, the power supply control switch 55 may be provided between the main power supply (e.g., an external power supply) of the image forming apparatus 1 and the high-voltage power supply 54, and may deactivate the high-voltage power supply 54 to temporarily stop the supply of power to the fixing belt 51 when at least one of the pair of sliding contacts 65 faces the specific portion 120 of the fixing belt 51, and may activate the high-voltage power supply 54 to supply power to the fixing belt 51 when at least one of the pair of sliding contacts 65 does not face the specific portion 120 of the fixing belt 51.

[0057] Furthermore, the fixing device 50 does not necessarily have to include the pair of sliding contacts 65. For example, the fixing device 50 may include a contactless power supply device that supplies power to the pair of electrodes 75 in a contactless manner, instead of the pair of sliding contacts 65. The power supply control switch 55 may control activation or deactivation of the contactless power supply device depending on the position of the specific portion 120 on the pair of electrodes 75.

Claims

1. A rotatable rotor; A power source for supplying power to the rotating body; a power supply control switch that controls the supply or stop of power supply from the power source to the rotating body; a control device that controls the power supply control switch so that when the rotating body reaches a rotational position where power is supplied via a specific portion on the surface of the rotating body, the supply of power from the power source to the rotating body is temporarily stopped, and when, as the rotating body rotates, the rotating body reaches a rotational position where power is supplied via a portion other than the specific portion, the supply of power from the power source to the rotating body is resumed; An image forming apparatus comprising:

2. 2. The image forming apparatus according to claim 1, wherein the rotating body includes a fixing belt having a heating resistor that receives electric power to generate heat and a pair of electrodes electrically connected to the heating resistor.

3. a pair of sliding contacts that are in sliding contact with the pair of electrodes; 3. The image forming apparatus according to claim 2, wherein the power source supplies power to the pair of electrodes through a pair of sliding contacts.

4. A detection unit for measuring an impedance between the pair of sliding contacts is further provided, The image forming apparatus according to claim 3 , wherein the control device specifies, as the specific portion, a position on the pair of electrodes of the fixing belt where the impedance becomes greater than a threshold value.

5. The detection unit is a low voltage power supply that applies a voltage lower than that of the power supply to the pair of sliding contacts; an impedance measuring device that measures an impedance between the pair of sliding contacts based on a voltage applied between the pair of sliding contacts by application of the voltage from the low-voltage power supply; a detection switch that controls an electrical connection between the low voltage power supply and the pair of sliding contacts; The image forming apparatus according to claim 4 .

6. the low voltage power supply and the impedance measuring device are electrically connected in parallel to the power supply; 6. The image forming apparatus according to claim 5, wherein the control device controls the power supply control switch so that the supply of power from the power source to the pair of sliding contacts is stopped when the impedance measuring device measures the impedance between the pair of sliding contacts.

7. An imaging unit that images the surfaces of the pair of electrodes, The image forming apparatus according to claim 2 , wherein the control device identifies the specific portion by performing image processing on the image of the surfaces of the pair of electrodes acquired by the imaging unit.

8. The heating resistor has a substantially cylindrical shape, The pair of electrodes has a substantially annular shape extending at both ends of the heating resistor, the specific portion represents a circumferential position of at least one of the pair of electrodes, 4. The image forming apparatus according to claim 3, wherein the pair of sliding contacts face the pair of electrodes at positions fixed in a rotational direction of the fixing belt.

9. the control device has a storage device that stores an angular position of the pair of electrodes in a circumferential direction of the fixing belt corresponding to the identified specific portion, The image forming apparatus according to claim 2 , wherein the control device controls the power supply control switch based on the angular positions of the pair of electrodes stored in the storage device.

10. the control device has a storage device that stores a specific timing corresponding to a timing at which the specific portion is detected, The image forming apparatus according to claim 2 , wherein the control device controls the power supply control switch based on the specific timing stored in the storage device.

11. A rotatable rotor; A power source for supplying power to the rotating body; a power supply control switch that controls the supply or stop of power supply from the power source to the rotating body; a control device that controls the power supply control switch so that when the rotating body reaches a rotational position where power is supplied via a specific portion on the surface of the rotating body, the supply of power from the power source to the rotating body is temporarily stopped, and when, as the rotating body rotates, the rotating body reaches a rotational position where power is supplied via a portion other than the specific portion, the supply of power from the power source to the rotating body is resumed; A fixing device comprising:

12. The fixing device according to claim 11 , wherein the rotating body includes a fixing belt having a heating resistor which receives electric power to generate heat and a pair of electrodes electrically connected to the heating resistor.

13. a pair of sliding contacts that are in sliding contact with the pair of electrodes; The fixing device according to claim 12 , wherein the power source supplies power to the pair of electrodes through a pair of sliding contacts.

14. A detection unit for measuring an impedance between the pair of sliding contacts is further provided, The fixing device according to claim 13 , wherein the control device specifies, as the specific portion, a position on the pair of electrodes of the fixing belt where the impedance becomes greater than a threshold value.

15. the control device includes a memory device that stores a plurality of specific portions that cause the measured impedance to be greater than a threshold, the plurality of specific portions corresponding to one or more surface areas of the pair of electrodes that interrupt an electrical connection between the pair of electrodes and the pair of sliding contacts; The fixing device according to claim 14 , wherein the control device outputs a warning when a size of the one or more surface areas is larger than a reference size.

Images