MEDIUM

BACKGROUND

[0001] An image forming apparatus may form an image on a print medium and convey the print medium. The image forming apparatus may include an image carrier to carry a toner image on a print medium and a fixing device to fix the toner image to the print medium. The image carrier and the fixing device may be arranged along a conveyance route of the print medium. In the image forming apparatus, the print medium may adhere to the image carrier.

BRIEF DESCRIPTION OF DRAWINGS

[0002] Various examples will be described below by referring to the following figures.

[0003] FIG. 1 is a schematic view of an image forming apparatus according to an example.

[0004] FIG. 2 is an enlarged schematic view of a periphery of an image carrier, a fixing device, a conveyance state sensor unit, and a jam detection sensor in the image forming apparatus of FIG. 1 according to an example.

[0005] FIG. 3 is a schematic view showing a configuration of the conveyance state sensor unit of FIG. 2 according to an example.

[0006] FIG. 4 is a diagram showing detection signals of the conveyance state sensor unit and the jam detection sensor of FIG. 2 according to an example. [0007] FIG. 5 is a schematic view showing a state in which a print medium comes into contact with a movable portion of the conveyance state sensor unit of FIG. 3 according to an example.

[0008] FIG. 6 is a schematic view showing a state in which a print medium contacts a print medium return portion of the conveyance state sensor unit of FIG. 3 according to an example.

[0009] FIG. 7 is a schematic view of an actuator and a conveyance abnormality detection sensor of the conveyance state sensor unit of FIG. 3 according to an example.

[0010] FIG. 8 is a schematic view showing a conveyance state sensor unit and an actuator according to an example.

[0011] FIG. 9 is a schematic view showing a conveyance state sensor unit according to an example.

[0012] FIG. 10 is a schematic view showing a conveyance state sensor unit according to an example.

[0013] FIG. 11 is a schematic view describing movement of a print medium between an image carrier and a fixing device according to an example.

[0014] FIG. 12 is a diagram showing intensity of reflected light detected by a conveyance abnormality detection sensor according to an example.

[0015] FIG. 13 is a perspective view showing a photoreceptor unit of an image forming apparatus according to a comparative example.

DETAILED DESCRIPTION

[0016] Hereinafter, various examples will be described with reference to the drawings. However, the present disclosure may be implemented in several different forms and is not limited to the examples described hereinafter.

[0017] An image forming apparatus may include an image carrier to transfer a toner image to a print medium and a fixing device to fix the toner image to the print medium. The image carrier and the fixing device may be arranged along a conveyance route of the print medium. The image forming apparatus may include a conveyance state sensor unit to detect a conveyance state of the print medium in a conveyance route between the image carrier and the fixing device. The conveyance state sensor unit can detect the conveyance state of the print medium in the conveyance route between the image carrier and the fixing device by operating an actuator.

[0018] For example, the image forming apparatus may include a jam detection sensor which is disposed on a downstream side of the fixing device in the conveyance route. A detection time may be set for the jam detection sensor. The jam detection sensor may detect a jam of the print medium between the image carrier and the fixing device based on the print medium not being detected for the detection time. The image forming apparatus may include a control unit to delay the detection time of the jam detection sensor based on the print medium being detected by the conveyance state sensor unit. Based on the conveyance state of the print medium being abnormal in the conveyance route between the image carrier and the fixing device, the arrival of the print medium to the jam detection sensor may be delayed, in an example, the control unit is able to delay the detection time of the jam detection sensor in a situation in which the print medium is detected by the conveyance state sensor unit. In that case, the control unit may delay the detection time to compensate for the delay in arrival of the print medium to the jam detection sensor. Thus, it is possible to suppress an erroneous detection of a jam by the jam detection sensor by delaying the detection time of the jam detection sensor.

[0019] Hereinafter, various examples of an image forming apparatus will be described with reference to the drawings. In the description of the drawings, the same reference numerals are given to the same or corresponding elements, and overlapping descriptions are omitted as appropriate. The drawings may be partially simplified or exaggerated for easy understanding, and the dimensional ratios and the like are not limited to those described in the drawings.

[0020] FIG. 1 is a schematic view an image forming apparatus 1 according to an example. The image forming apparatus 1 may include a conveying device 10, an image carrier 20, a developing device 30, a transfer device 40, and a fixing device 50. The conveying device 10 is to convey a print medium 2 on which an image is formed. As an example, the print medium 2 may be paper. For example, the conveying device 10 may include a registration roller 11 and the print medium 2 may be conveyed to a transfer region, an example of which is to be described later, at a predetermined timing by the registration roller 11.

[0021] The image carrier 20 may be an electrostatic latent image carrier, a photosensitive drum, etc. The image carrier 20 is to form an electrostatic latent image to form a toner image. For example, the image forming apparatus 1 may include a charging device 21 and a cleaning device 23. The charging device 21 and the cleaning device 23 may be arranged at a position facing a surface 20b of the image carrier 20. The charging device 21 is to charge the surface 20b of the image carrier 20 to a predetermined potential.

[0022] The developing device 30 is to receive toner from a toner cartridge to form a toner image formed on the surface 20b of the image carrier 20. The developing device 30 may include a developing roller 31 to supply a toner to the surface 20b of the image carrier 20. Based on the developing roller 31 supplying toner to the surface 20b of the image carrier 20, an electrostatic latent image that is formed on the surface 20b of the image carrier 20 may be developed. Accordingly, a toner image corresponding to the electrostatic latent image, that is, a toner image corresponding to the image to be formed on the print medium 2 may be formed on the surface 20b of the image carrier 20.

[0023] The transfer device 40 is to transfer the toner image developed on the image carrier 20 by the developing device 30 to the print medium 2. As an example, the transfer device 40 may include a transfer roller 41. The transfer roller 41 may have, for example, an axis extending in parallel to the axis of the image carrier 20. A surface 41 b of the transfer roller 41 and the surface 20b of the image carrier 20 are to contact each other so that a transfer region is formed between the transfer roller 41 and the image carrier 20. The transfer roller 41 is to apply an electric field to the print medium 2 conveyed to the transfer region so that the toner image formed on the surface 20b of the image carrier 20 may be transferred to the print medium 2. The toner image may be transferred to the print medium 2 conveyed to the transfer region by the transfer roller 41 .

[0024] The cleaning device 23 is to collect toner remaining on the surface 20b of the image carrier 20 (i.e., toner that is not transferred to the print medium 2) as waste toner. The cleaning device 23 may include, for example, a blade 24. As the blade 24 scrapes off toner remaining on the surface 20b of the image carrier 20, the cleaning device 23 removes the toner from the image carrier 20 and collects the toner. The blade 24 may be fixed to a housing 3 of the image forming apparatus 1 to contact the surface 20b of the image carrier 20.

[0025] The fixing device 50 is to fix the toner image to the print medium 2 by passing the print medium 2 through a fixing nip region to heat and press the print medium. The fixing device 50 may indude a heating roller 51 to heat the print medium 2 and a pressing roller 52 to rotationally drive the heating roller 51 in a pressed state. The fixing nip region of the fixing device 50 may be formed between the heating roller 51 and the pressing roller 52.

[0026] FIG. 2 is an enlarged schematic view of a periphery of the image carrier 20, the fixing device 50, a conveyance state sensor unit 70, and a jam detection sensor 90 in the image forming apparatus 1of FIG. 1 according to an example.

[0027] As shown in FIG. 2, the image forming apparatus 1 may include, for example, a conveyance state sensor unit 70 (i.e., a first sensor unit) to detect the conveyance state of the print medium 2 in a conveyance route 4 between the image carrier 20 and the fixing device 50. The conveyance state sensor unit 70 may be disposed on the upstream side of the fixing device 50 in the conveyance route 4 of the print medium 2 and detect the conveyance state of the conveyance route 4 of the print medium 2.

[0028] For example, the image carrier 20 and the fixing device 50 may be arranged along a first direction D1 , which is an extension direction of the conveyance route 4. The image carrier 20 and the transfer roller 41 may be arranged along a second direction D2 intersecting the first direction D1. The conveyance state sensor unit 70 may be arranged along the conveyance route 4 and the second direction D2 between the image carrier 20 and the fixing device 50. The conveyance state sensor unit 70 may be provided at a position near the image carrier 20 as viewed from the conveyance route 4. In this case, the conveyance state sensor unit 70 can detect the print medium 2 that does not adhere to the surface 20b of the image carrier 20 but deviates from the conveyance route 4 toward the image carrier 20.

[0029] The conveyance state sensor unit 70 includes, for example, a conveyance abnormality detection sensor 71 to detect the adhesion of the print medium 2 to the image carrier 20 and an actuator 72 which may be operated in accordance with the conveyance state of the print medium 2 between the image carrier 20 and the fixing device 50. The conveyance abnormality detection sensor 71 is a sensor to detect the abnormality of the conveyance state of the print medium 2. The conveyance abnormality detection sensor 71 may be an optical sensor to irradiate light 71 b toward the surface 20b of the image carrier 20 and receive reflected light generated in accordance with the irradiation of the light 71 b. For example, the conveyance abnormality detection sensor 71 may be provided in advance and may be a density control optical sensor to control the density of the toner image of the surface 20b of the image carrier 20. In this case, the existing density control optical sensor can be efficiently used as the conveyance abnormality detection sensor 71. As an example, the conveyance abnormality detection sensor 71 may be a Color Toner Density (CTD) sensor. In this case, the conveyance abnormality detection sensor 71 may acquire light intensity as a voltage value. That is, the conveyance abnormality detection sensor 71 may acquire the intensity of the reflected light caused by the irradiation of the light 71 b onto the surface 20b of the image carrier 20 as a voltage value.

[0030] The conveyance abnormality detection sensor 71 is to detect the adhesion of the print medium 2 by irradiating the light 71 b toward the surface 20b of the image carrier 20 and receiving the reflected light from the print medium 2 adhering to the surface 20b. For example, the conveyance abnormality detection sensor 71 may detect that the print medium 2 does not adhere to the surface 20b based on irradiating the light 71 b toward the surface 20b of the image carrier 20 and receiving the reflected light from the surface 20b. The conveyance abnormality detection sensor 71 may detect that the print medium 2 adheres to the surface 20b based on irradiating the light 71b toward the surface 20b of the image carrier 20 and receiving the reflected light from the print medium 2. The intensity of the reflected light from the print medium 2 is smaller than the intensity of the reflected light from the surface 20b of the image carrier 20. Thus, the conveyance abnormality detection sensor 71 may detect that the print medium 2 adheres to the surface 20b by receiving the reflected light having intensity smaller than that of the reflected light from the surface 20b.

[0031] The actuator 72 may include, for example, a movable portion 73 that is to move while contacting the print medium 2 and a print medium return portion 74 that is to return the print medium 2 to the conveyance route 4. The conveyance state sensor unit 70 is to detect the abnormality of the conveyance state of the print medium 2 based on the movable portion 73 moving as the print medium 2 contacts the movable portion 73. The image forming apparatus 1 may include a control unit 80 to control each unit of the image forming apparatus 1 and the control unit 80 can communicate with the conveyance state sensor unit 70.

[0032] The control unit 80 is to detect the abnormality of the conveyance state of the print medium 2 in accordance with a decrease in intensity of the reflected light received by the conveyance abnormality detection sensor 71. For example, the image forming apparatus 1 may include a display unit 85 and the control unit 80 may display that the abnormality of the conveyance state of the print medium 2 occurs on the display unit 85 based on detecting the abnormality of the conveyance state of the print medium 2.

[0033] The movable portion 73 may include, for example, a first side 75 that may come into contact with the print medium 2, a second side 76 which extends from the first side 75 toward the image carrier 20, a shaft portion 77 which is located at the end portion on the side opposite to the second side 76 in the first side 75, and a support member 78 that supports the shaft portion 77 to be rotatable. The shaft portion 77 may extend in parallel to the axis of the image carrier 20 (i.e., a direction orthogonal to the paper surface of FIG. 2). The movable portion 73 is to rotate about the shaft portion 77. As an example, the movable portion 73 may have an L shape, in this case, the first side 75 and the second side 76 have a linear shape and the second side 76 extends in a direction intersecting the first side 75 from the end portion on the side of the image carrier 20 of the first side 75. The first side 75 extends from the shaft portion 77 toward the image carrier 20.

[0034] The movable portion 73 is to block the optical path of the light 71 b from the conveyance abnormality detection sensor 71 while moving in accordance with the contact of the print medium 2. For example, based on the print medium 2 contacting the first side 75, the first side 75 and the second side 76 rotate about the shaft portion 77 and the second side 76 blocks the optical path of the light 71b. In this case, the second side 76 is a light shield portion that is to block the optical path of the light 71b of the conveyance abnormality detection sensor 71 based on the print medium 2 contacting the first side 75. [0035] The conveyance state sensor unit 70 is to detect the abnormality of the conveyance state of the print medium 2 based on the movable portion 73 blocking the optical path from the conveyance abnormality detection sensor 71. For example, the inner wall of the second side 76 may be blackened. In that case, the intensity of the reflected light from the second side 76 in accordance with the irradiation of the light 71b of the conveyance abnormality detection sensor 71 is much smaller than the intensity of the reflected light from the print medium 2. For example, the conveyance abnormality detection sensor 71 may output an abnormal signal indicating the abnormality of the conveyance state based on the movable portion 73 moving and the second side 76 blocking the optical path of the light 71 b. The abnormal signal may include a signal indicating a voltage value decreased as the intensity of the reflected light is decreased based on the optical path being blocked by the movable portion 73. On the other hand, a normal signal may include a signal indicating a voltage value which is not decreased while the intensity of the reflected light is not decreased. The movable portion 73 may return to a position (i.e., an original position) in which the optical path of the light 71 b is not blocked while the print medium 2 does not contact the movable portion 73. At this time, the conveyance abnormality detection sensor 71 may output the normal signal. For example, the movabie portion 73 may return to an original position by gravity or may return to an original position by an urging force of a spring or the like.

[0036] For example, the print medium return portion 74 may extend from the movable portion 73 toward the fixing device 50. The print medium return portion 74 may be provided so that the print medium 2 contacting the actuator 72 returns to the conveyance route 4. The print medium return portion 74 extends from the shaft portion 77 toward the fixing device 50. As an example, the print medium return portion 74 may have a curved shape which is curved toward the conveyance route 4 as it goes away from the shaft portion 77. For example, the image forming apparatus 1 may include a frame 79 which is provided between the print medium return portion 74 and the fixing device 50 to guide the print medium 2 to the fixing device 50.

[0037] The image forming apparatus 1 may include a jam detection sensor 90 (i.e., a second sensor unit) which is located on the downstream side of the fixing device 50 in the conveyance route 4. For example, the control unit 80 may identify a jam of the print medium 2 by using the conveyance state sensor unit 70, which is the first sensor unit, and the jam detection sensor 90, which is the second sensor unit. A predetermined time may be set for the jam detection sensor 90, which is a time period during which the print medium 2 is to arrive at the jam detection sensor 90. The predetermined time may be an estimated arrival time for the print medium 2 to arrive at the jam detection sensor 90. The predetermined time may be, for example, an estimated time taken until the print medium 2 is to arrive at the jam detection sensor 90 through the conveyance route 4 after a sensor attached to the registration roller 11 (see FIG. 1) detects the print medium 2.

[0038] For example, the jam detection sensor 90 may detect that the print medium 2 is jammed between the image carrier 20 and the fixing device 50 based on the print medium 2 not arriving at the jam detection sensor 90 at the predetermined time. Based on the jam detection sensor 90 detecting the jam, for exampie, the jam detection sensor 90 may output a detection signai to the control unit 80. Based on the control unit 80 receiving the detection signal, for example, the control unit may display on the display unit 85 that the print medium 2 is jammed and stop the operation of the image forming apparatus 1 .

[0039] However, for example, based on the print medium 2 deviating from the conveyance route 4 in a situation in which the print medium 2 is not jammed between the image carrier 20 and the fixing device 50, there is a case in which the arrival of the print medium 2 at the jam detection sensor 90 may be delayed. In such a case, based on the jam detection sensor 90 detecting the jam, an erroneous detection is made. On the other hand, in the image forming apparatus 1 according to an example, the control unit 80 can suppress the erroneous detection by identifying the jam of the print medium 2 using the conveyance state sensor unit 70, which is the first sensor unit, and the jam detection sensor 90, which is the second sensor unit.

[0040] Hereinafter, an example of detection of the print medium 2 by the conveyance state sensor unit 70, the control unit 80, and the jam detection sensor 90 will be described. As shown in FIGS. 2, 3, and 4, a case is assumed in which the print medium 2 does not arrive at the jam detection sensor 90 at a predetermined time T1 while the print medium 2 deviates from the conveyance route 4.

[0041] FIG. 3 is a schematic view showing a configuration of the conveyance state sensor unit of FIG. 2 according to an example. FIG. 4 is a diagram showing detection signals of the conveyance state sensor unit and the jam detection sensor of FIG. 2 according to an example. FIG. 5 is a schematic view showing a state in which a print medium comes into contact with a movable portion of the conveyance state sensor unit of FIG. 3 according to an example. FIG. 6 is a schematic view showing a state in which a print medium contacts a print medium return portion of the conveyance state sensor unit of FIG. 3 according to an example.

[0042] As shown in FIGS. 4 and 5, based on the print medium 2 that deviates from the conveyance route 4 contacting the actuator 72, the movable portion 73 may rotate about the shaft portion 77 to block the optical path of the light 71 b of the conveyance abnormality detection sensor 71. Based on the optical path of the conveyance abnormality detection sensor 71 being blocked, the control unit 80 detects the abnormality of the conveyance state of the print medium 2 in accordance with a decrease in intensity of the reflected light received by the conveyance abnormality detection sensor 71 .

[0043] The control unit 80 may calculate a time A during which the movable portion 73 blocks the optical path of the conveyance abnormality detection sensor 71. The time A is a signal output time during which the conveyance abnormality detection sensor 71 outputs an abnormal signal based on the movable portion 73 moving in accordance with the contact of the print medium 2 with respect to the actuator 72 and the moved movable portion 73 (e.g., the second side 76) blocking the optical path of the light 71 b. The signal output time is a time until the conveyance abnormality detection sensor 71 starts to output a normal signal after the conveyance abnormality detection sensor 71 starts to output an abnormal signal and the movable portion 73 returns to an original position from the position at which the movable portion 73 blocks the optical path of the light 71 b. The control unit 80 may delay the predetermined time T1 to a predetermined time T2 by adding a signal output time A, during which an abnormal signal is output from the conveyance abnormality detection sensor / 1 , or a time kA, which is obtained by multiplying the time A, which is the signal output time, by a coefficient k, to the predetermined time T1 , which is the estimated arrival time at the jam detection sensor 90.

[0044] After the print medium 2 contacts the movable portion 73, the print medium 2 may move from the movable portion 73 to the print medium return portion 74 as shown in FIG. 6. At this time, the movable portion 73 may return to an original position. The print medium 2, which moves to the print medium return portion 74, may be guided to the print medium return portion 74 to face the conveyance route 4. The toner image may be fixed to the print medium 2, which returns to the conveyance route 4, at the fixing nip portion of the fixing device 50 and the print medium may arrive at the jam detection sensor 90 at the predetermined time T2. Accordingly, the erroneous detection of the jam of the jam detection sensor 90 may be avoided.

[0045] Next, various examples of the conveyance state sensor unit (i.e., the first sensor unit) will be described. FIG. 7 is a schematic view of the actuator

72 and the conveyance abnormality detection sensor 71 of the conveyance state sensor unit 70 of FIG. 3 according to an example. The conveyance state sensor unit 70 includes the conveyance abnormality detection sensor 71 and the actuator 72. In an example, the conveyance abnormality detection sensor 71 may be supported by a sensor support member 71c. The actuator 72 includes the movable portion 73 and the print medium return portion 74. The movable portion

73 includes the first side 75, the second side 76, and the shaft portion 77 and may rotate about the shaft portion 77 to block the optical path of the light 71b of the conveyance abnormality detection sensor 71.

[0046] FIG. 8 is a schematic view showing a conveyance state sensor unit 70A and an actuator according to an example.

[0047] The conveyance state sensor unit 70A includes a conveyance abnormality detection sensor 71 A, which may include a switch, and an actuator 72A. The conveyance abnormality detection sensor 71 A can communicate with the control unit 80 and output an abnormal signal to the control unit 80 based on being pressed by the actuator 72A. The conveyance abnormality detection sensor 71A may include, for example, a switch body 71 d, which is to be pressed by the actuator 72A in accordance with the abnormality of the conveyance state of the print medium 2, and a support portion 71 f, which supports the switch body 71 d on the sensor support member 71c.

[0048] The actuator 72A may include, for example, a movable portion 73A, which is to contact the conveyance abnormality detection sensor 71 A, a shaft portion 77A, which is to support the movable portion 73A to be rotatable, and a print medium return portion 74A, which extends from the shaft portion 77A to the side opposite to the movable portion 73A. The movable portion 73A extends in a linear shape from the shaft portion 77A toward the image carrier 20. The movable portion 73A includes a first surface 73b that is to press the conveyance abnormality detection sensor 71 A and a second surface 73c, which faces the side opposite to the first surface 73b.

[0049] The print medium 2 may contact the second surface 73c. Based on the print medium 2 contacting the second surface 73c, the movable portion 73A may rotate about the shaft portion 77A and the first surface 73b may press the conveyance abnormality detection sensor 71A (i.e., the switch body 71d). In that case, an abnormal signal may be output from the conveyance abnormality detection sensor 71 A to the control unit 80 and the abnormality of the conveyance state of the print medium 2 may be detected by the control unit 80. As described above, in the conveyance state sensor unit 70A shown in FIG. 8, the conveyance abnormality detection sensor 71A includes a switch which contacts the movable portion 73A based on the movable portion 73A moving and detects the abnormality of the conveyance state of the print medium 2 based on the movable portion 73A contacting the switch.

[0050] FIG. 9 is a schematic view showing a conveyance state sensor unit 70B according to an example.

[0051] As shown in FIG. 9, a conveyance state sensor unit 70B may include a weight 73f which is attached to the movable portion 73A. That is, the movable portion 73A may include a contact portion 73g, which is to contact the conveyance abnormality detection sensor 71 A corresponding to the switch, and the weight 73f, which may be fixed to the contact portion 73g. In the case of the conveyance state sensor unit 70B, the position of the movable portion 73A can be more reliably returned to an original position by the weight 73f based on the print medium 2 not contacting the movable portion. Thus, the behavior of the movable portion 73A can be made more stable.

[0052] FIG. 10 is a schematic view showing a conveyance state sensor unit 70C according to an example. As shown in FIG. 10, the conveyance state sensor unit 70C includes a conveyance abnormality detection sensor 71 C and an actuator 72C. The conveyance abnormality detection sensor 71 C may include, for example, a photointerrupter 71g and a sensor support member 71c that supports the photointerrupter 71g on the housing 3. The photointerrupter 71g may include, for example, a light emitting portion 71 h and a light receiving portion 71 k that is to receive light 71j from the light emitting portion 71 h.

[0053] The actuator 72C may include, for example, a movable portion 73C, the shaft portion 77.A, and the print medium return portion 74.A. The movable portion 73C is to move in accordance with the contact of the print medium 2 and block the optical path of the light 71 j of the photointerrupter 71g. The conveyance state sensor unit TOC is to detect the abnormality of the conveyance state of the print medium 2 based on the movable portion 73C blocking the optical path of the photointerrupter 71g. For example, the movable portion 73C may include an extension portion 73h, which extends from the shaft portion 77A toward the image carrier 20, and a protrusion portion 73j, which protrudes from the extension portion 73h toward the side opposite to the conveyance route 4.

[0054] The protrusion portion 73j may protrude from, for example, the middle portion of the extension portion 73h toward the conveyance abnormality detection sensor 71 C. The protrusion portion 73j may be a portion that is to block the optical path of the photointerrupter 71g based on the print medium 2 contacting the movable portion 73C so that the movable portion 73C moves. In this case, based on the print medium 2 contacting the movable portion 73C, the movable portion 73C is to move about the shaft portion 77A and the protrusion portion 73j is to enter between the light emitting portion 71 h and the light receiving portion 71 k to block the optical path of the light 71 j. Based on the optical path of the light 71 j being blocked, the conveyance abnormality detection sensor 71 C may output an abnormal signal in accordance with a decrease in intensity of the light 71 j received by the light receiving portion 71 k. Based on this abnormal signal being output to the control unit 80, the abnormality of the conveyance state of the print medium 2 may be detected by the control unit 80. As described above, in the examples shown in FIGS. 8 to 10, the conveyance abnormality detection sensor 71 , which is the density control optical sensor, can be omitted.

[0055] FIG. 11 is a schematic view describing movement of a print medium between an image carrier and a fixing device according to an example. FIG. 12 is a diagram showing intensity of reflected light detected by a conveyance abnormality detection sensor according to an example.

[0056] As described above, the image forming apparatus 1 may include the conveyance state sensor unit 70, the jam detection sensor 90, and the control unit 80 and can detect the print medium 2 deviating from the conveyance route 4 as shown in FIG. 11. FIG. 12 shows actual measured values in a voltage value chart measured by a CTD sensor, which is an example of the conveyance abnormality detection sensor 71. The conveyance abnormality detection sensor 71 shown in the example of FIG. 11 is a specular reflection sensor (KMEM008C manufactured by KODENSHI CORR), and the actuator 72 is made of black ABS resin. The inner surface of the second side 76 of the movable portion 73 is blackened and for example, a light absorbing sheet is attached. As the light absorbing sheet, Fine Shut pole manufactured by Koyo Orient Japan Co., Ltd. was used.

[0057] As shown in FIGS. 11 and 12, the print medium 2, which deviates from the conveyance route 4 and passes between the surface 20b of the image carrier 20 and the conveyance state sensor unit 70 (between 0 and a in FIGS. 11 and 12), is detected in such a manner that the reflected light of the conveyance abnormality detection sensor 71 becomes weaker than the reflected light from the surface 20b. Based on the conveyance abnormality detection sensor 71 being the CTD sensor, for example, the voltage value acquired by the conveyance abnormality detection sensor 71 due to the print medium 2 passing between the surface 20b and the conveyance state sensor unit 70 (the voltage value according to the intensity of the reflected light) is below the first threshold value V1. At this time, the voltage value acquired by the conveyance abnormality detection sensor 71 changes in accordance with the type of the print medium 2, for example, 1.3 V to 1.8 V. in that case, the control unit 80 detects that the print medium 2 moves between the surface 20b and the conveyance state sensor unit 70 in accordance with the voltage value acquired by the conveyance abnormality detection sensor

71 being below the first threshold value V1.

[0058] The print medium 2, which deviates from the conveyance route 4 and moves to the conveyance state sensor unit 70 (i.e., the print medium 2 moving between a and b in FIGS. 11 and 12), contacts the movable portion 73 of the actuator 72. At this time, the movable portion 73 moves in accordance with the contact of the print medium 2 with respect to the movable portion 73 and the movable portion 73 blocks the optical path of the light 71 b of the conveyance abnormality detection sensor 71. Based on the conveyance abnormality detection sensor 71 being the CTD sensor, the voltage value acquired by the conveyance abnormality detection sensor 71 due to the print medium 2 contacting the actuator

72 (i.e., the voltage value according to the intensity of the reflected light) is below the second threshold value V2, which is smaller than the first threshold value V1. At this time, the voltage value acquired by the conveyance abnormality detection sensor 71 may be, for example, 0.1 V, but, in a situation in which the inner surface of the second side 76 is blackened, the voltage value may be about 0 V. The control unit 80 detects that the print medium 2 contacts the actuator 72 based on the voltage value acquired by the conveyance abnormality detection sensor 71 being below the second threshold value V2.

[0059] The print medium 2, which deviates from the conveyance route 4 and moves between the conveyance state sensor unit 70 and the fixing device 50, contacts, for example, the frame 79. The print medium 2 may be guided to the fixing nip portion of the fixing device 50 by the frame 79. At this time, since the light 71 b of the conveyance abnormality detection sensor 71 is reflected from the surface 20b of the image carrier 20, the voltage value acquired by the conveyance abnormality detection sensor 71 is equal to or larger than the first threshold value V1. At this time, the voltage value acquired by the conveyance abnormality detection sensor 71 may be, for example, 3.0 V. The control unit 80 may detect that the print medium 2 is normally conveyed based on the voltage value acquired by the conveyance abnormality detection sensor 71 being equal to or larger than the first threshold value V1.

[0060] As described above, in the image forming apparatus 1 , the conveyance state sensor unit 70 and the control unit 80 can check the conveyance state of the print medium 2 between the image carrier 20 and the fixing device 50. Further, the control unit 80 may delay the estimated arrival time of the print medium 2 to the jam detection sensor 90 (i.e. , delay the predetermined time T1 to the predetermined time T2) in accordance with the signal output time A during which the conveyance abnormality detection sensor 71 outputs the abnormal signal based on the print medium 2 deviating from the conveyance route 4. Thus, the erroneous detection of the jam by the jam detection sensor 90 can be suppressed.

[0061] Next, an example of the image forming apparatus 1 will be described in comparison with an image forming apparatus 100 according to a comparative example. FIG. 13 is a perspective view showing a photoreceptor unit 110 of the image forming apparatus 100 according to a comparative example. The photoreceptor unit 110 includes an image carrier 120 and a plurality of separation claws 130 which separate the print medium adhering to the surface of the image carrier 120. On the other hand, the image forming apparatus 1 according to various examples includes the above-described conveyance state sensor unit 70, control unit 80, and jam detection sensor 90 and does not include the separation claw 130. In this way, the image forming apparatus 1 can eliminate the separation claw 130 by including the conveyance state sensor unit 70.

[0062] The image forming apparatus 1 according to various examples and the image forming apparatus 100 according to the comparative example were verified for occurrence of the jam of the print medium 2. First, a test was conducted in which the image forming apparatus 1 and the image forming apparatus 100 continuously printed sheets under an environment having a temperature of 22°C and a humidity of 55%. [0063] For the sheets, a sheet of 60 g/m ² was used. As a result of this test, in the image forming apparatus 100 according to the comparative example, a 1/5 kpv (one sheet out of 5000 sheets) jam was detected. On the other hand, no jam was detected in the image forming apparatus 1 according to the various examples. [0064] Further, a test was conducted in which the image forming apparatus 1 and the image forming apparatus 100 continuously printed sheets under a low- temperature and low-humidity environment having a temperature of 10°C and a humidity of 10%. For the sheets, sheets of 60 g/m ² and 70 g/m ² were used. As a result of this test, in the image forming apparatus 100 according to the comparative example, the jam of 5/2 kpV (five sheets out of 2000 sheets) was detected in the case of the sheet of 60 g/m ² and the jam of 3/2 kpV (three sheets out of 2000 sheets) was detected in the case of the sheet of 70 g/m ² . Some of the detected jams included erroneous detection.

[0065] In the image forming apparatus 1 according to various examples, no jam was detected in the case of the sheet of 70 g/m ² , but the jam of % kpV (one sheet out of 2000 sheets) was detected in the case of the sheet of 60 g/m ² . However, this jam was not erroneously detected. In this way, in the image forming apparatus 1 according to various examples, it was found that the jam can be reduced and the erroneous detection of the jam can be suppressed. Further, in the image forming apparatus 1 according to various examples, since the separation claw 130 is not included, an increase in cost relating to the components of the image forming apparatus 1 can be suppressed.

[0066] While examples have been shown and described, the disclosure is not limited to the aforementioned examples, and it is apparent that various modifications can be made without departing from the gist of the disclosure as claimed by the appended claims. Indeed, while various examples have been described and shown herein, it should be apparent that other examples may be modified in their arrangement and details. Also, it is intended that such modifications are not to be interpreted independently from the technical idea or prospect of the disclosure.