Image forming apparatus, operation control method

Abstract

To provide an image forming apparatus and an operation control method that can facilitate the removal of a sheet wrapped around a fixing member. [Solution] The image forming apparatus includes a stop processing unit that stops the image forming process if the sheet is not detected by the downstream sensor 46 within a predetermined specific time elapsed from the moment the leading edge of the sheet reaches the fixing nip P2 during the execution of the image forming process, and a rotation processing unit that reverses the fixing roller 41 by an amount of rotation corresponding to the difference between the specific distance and the length when the image forming process is stopped by the stop processing unit and the length of the sheet in the transport direction D6 is less than a specific distance that is longer than the product of the specific time and the transport speed of the sheet.

Description

Technical Field

[0001] The present invention relates to an image forming apparatus and an operation control method.

Background Art

[0002] An electrophotographic image forming apparatus includes a fixing unit that fixes a toner image transferred onto a sheet onto the sheet. The fixing unit includes a fixing member such as a fixing roller, and a pressing member such as a pressing roller that forms a fixing nip portion between the fixing member.

[0003] In the fixing unit, a winding jam may occur in which the sheet is wound around the fixing member. In contrast, when the winding jam occurs, an image forming apparatus that reversely rotates the fixing member so that the leading end of the sheet does not wind around the fixing member more than once is known as a related art (see Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] By the way, in the image forming apparatus according to the related art, after the reverse rotation of the fixing member, the trailing end of the sheet may not protrude upstream in the sheet conveyance direction from the fixing nip portion. Specifically, in the image forming apparatus according to the related art, when the length of the sheet in the conveyance direction is shorter than the circumferential length of the fixing member, after the reverse rotation of the fixing member, the trailing end of the sheet does not protrude upstream in the conveyance direction from the fixing nip portion.

[0006] When the aforementioned jamming occurs, if the rear end of the sheet does not protrude upstream from the fixing nip portion in the conveying direction (i.e., the rear end of the sheet is wrapped around the fixing member), it becomes difficult for the user to remove the sheet wrapped around the fixing member.

[0007] The object of the present invention is to provide an image forming apparatus and an operation control method that can facilitate the removal of a sheet wrapped around a fixing member. [Means for solving the problem]

[0008] An image forming apparatus according to one aspect of the present invention comprises a fixing member, a pressurizing member, a first detection unit, a stop processing unit, and a rotation processing unit. The fixing member is rotatably provided and contacts a sheet onto which a toner image has been transferred to fix the toner image to the sheet. The pressurizing member is rotatably provided opposite the fixing member and forms a fixing nip portion that pressurizes the sheet between itself and the fixing member. The first detection unit detects the sheet downstream of the fixing nip portion in the sheet transport path, passing through the fixing nip portion. The stop processing unit stops the image forming process if, during the execution of the image forming process to form an image on the sheet, the sheet is not detected by the first detection unit within a predetermined specific time elapsed from the moment the leading edge of the sheet in the transport direction reaches the fixing nip portion. The rotation processing unit rotates the fixing member in the reverse direction by an amount corresponding to the difference between the specific distance and the length, when the image forming process is stopped by the stop processing unit and the length of the sheet in the transport direction is less than a specific distance that is longer than the product of the specific time and the transport speed of the sheet.

[0009] An operation control method according to another aspect of the present invention is performed in an image forming apparatus comprising: a fixing member rotatably provided and in contact with a sheet onto which a toner image has been transferred to fix the toner image to the sheet; a pressing member rotatably provided opposite the fixing member and forming a fixing nip portion that pressurizes the sheet with respect to the fixing member; and a first detection unit that detects the sheet downstream of the fixing nip portion in the sheet transport path passing through the fixing nip portion in the sheet transport direction, and includes a stop step and a rotation step. In the stop step, if the sheet is not detected by the first detection unit within a predetermined specific time elapsed from the time the leading edge of the sheet in the transport direction reaches the fixing nip portion during the execution of the image forming process to form an image on the sheet, the image forming process is stopped. In the rotation step, if the image forming process is stopped by the stop step and the length of the sheet in the transport direction is less than a specific distance that is longer than the product of the specific time and the transport speed of the sheet, the fixing member is rotated in the reverse direction by an amount corresponding to the difference between the specific distance and the length. [Effects of the Invention]

[0010] According to the present invention, it is possible to easily remove the sheet that has become wrapped around the fixing member. [Brief explanation of the drawing]

[0011] [Figure 1] Figure 1 is a cross-sectional view showing the configuration of an image forming apparatus according to an embodiment of the present invention. [Figure 2] Figure 2 is a block diagram showing the system configuration of an image forming apparatus according to an embodiment of the present invention. [Figure 3] Figure 3 is a cross-sectional view showing the configuration of the image forming section of an image forming apparatus according to an embodiment of the present invention. [Figure 4] Figure 4 is a cross-sectional view showing the configuration of the fixing apparatus of an image forming apparatus according to an embodiment of the present invention. [Figure 5]Figure 5 is a flowchart showing an example of an operation control process performed in an image forming apparatus according to an embodiment of the present invention. [Modes for carrying out the invention]

[0012] The embodiments of the present invention will be described below with reference to the attached drawings. Note that the following embodiments are merely examples of the present invention and do not limit the technical scope of the present invention.

[0013] [Configuration of the image forming apparatus 100] First, the configuration of the image forming apparatus 100 according to an embodiment of the present invention will be described with reference to Figures 1 and 2.

[0014] For the sake of explanation, the vertical direction is defined as the up-down direction D1 when the image forming apparatus 100 is in a usable installation state (as shown in Figure 1). The front-to-back direction D2 is defined with the left side of the image forming apparatus 100 shown in Figure 1 as the front. The left-to-right direction D3 is defined with the front of the image forming apparatus 100 in the aforementioned installation state as the reference point.

[0015] The image forming apparatus 100 is a multifunction device having multiple functions, including a scanning function for reading an image from a document, a printing function for forming an image based on the image data, as well as a fax function and a copying function. The present invention may also be applied to image forming apparatuses such as printers, fax machines, and copiers.

[0016] As shown in Figures 1 and 2, the image forming apparatus 100 comprises an ADF (Auto Document Feeder) 1, an image reading unit 2, an image forming unit 3, a paper feeding unit 4, an operation display unit 5, a storage unit 6, and a control unit 7.

[0017] The ADF1 transports the document to be scanned by the scanning function. The ADF1 comprises a document setting section, multiple transport rollers, a document holder, and a paper output section.

[0018] The image reading unit 2 realizes the scanning function. The image reading unit 2 includes a document table, a light source, a plurality of mirrors, an optical lens, and a CCD (Charge Coupled Device).

[0019] The image forming unit 3 realizes the printing function. Specifically, the image forming unit 3 forms a color or monochrome image on a sheet supplied from the paper feeding unit 4 according to the electrophotographic method.

[0020] The paper feeding unit 4 supplies a sheet to the image forming unit 3. The paper feeding unit 4 includes a paper feed cassette, a manual feed tray, and a plurality of conveyance rollers.

[0021] The operation display unit 5 is the user interface of the image forming apparatus 100. The operation display unit 5 includes a display unit and an operation unit. The display unit displays various information according to a control instruction from the control unit 7. For example, the display unit is a display device such as a liquid crystal display. The operation unit inputs various information to the control unit 7 according to the user's operation. For example, the operation unit is an operation device including operation keys and a touch panel.

[0022] The storage unit 6 is a non-volatile storage device. For example, the storage unit 6 is a flash memory.

[0023] The control unit 7 comprehensively controls the image forming apparatus 100. As shown in FIG. 2, the control unit 7 includes a CPU 11, a ROM 12, and a RAM 13. The CPU 11 is a processor that executes various arithmetic processes. The ROM 12 is a non-volatile storage device in which information such as a control program for causing the CPU 11 to execute various processes is stored in advance. The RAM 13 is a volatile or non-volatile storage device used as a temporary storage memory (working area) for various processes executed by the CPU 11. The CPU 11 comprehensively controls the image forming apparatus 100 by executing various control programs stored in advance in the ROM 12.

[0024] Furthermore, the control unit 7 may be a separate control unit from the main control unit that comprehensively controls the image forming apparatus 100. Also, the control unit 7 may be composed of electronic circuits such as an integrated circuit (ASIC).

[0025] [Configuration of the image forming unit 3] Next, the configuration of the image forming unit 3 will be described with reference to Figures 1 to 4. Here, Figure 3 is a cross-sectional view showing the configuration of multiple image forming units 20, an intermediate transfer belt 26, and a secondary transfer roller 27. Figure 4 is a diagram showing the sheet transport path R1 via the fixing nip section P2. In Figure 4, the transport path R1 is shown as a dashed line. Also in Figure 4, the pressure rollers 42 positioned at intervals are shown as dashed lines.

[0026] As shown in Figure 1, the image forming unit 3 comprises four image forming units 20, an optical scanning device 25, an intermediate transfer belt 26, a secondary transfer roller 27, a fixing device 28, and a paper output tray 29.

[0027] Of the four image forming units 20, image forming unit 21 (see Figure 3) forms a yellow (Y) toner image. Of the four image forming units 20, image forming unit 22 (see Figure 3) forms a cyan (C) toner image. Of the four image forming units 20, image forming unit 23 (see Figure 3) forms a magenta (M) toner image. Of the four image forming units 20, image forming unit 24 (see Figure 3) forms a black (K) toner image. In other words, the image forming unit 3 forms an image on the sheet using each of the CMYK toners. As shown in Figures 1 and 3, the four image forming units 20 are arranged in the order of yellow, cyan, magenta, and black from the front side of the image forming apparatus 100 along the front-to-back direction D2.

[0028] As shown in Figure 3, each image forming unit 20 includes a photoreceptor drum 31, a charging roller 32, a developing device 33, a primary transfer roller 34, and a drum cleaning unit 35. Each image forming unit 20 also includes a toner container 36 as shown in Figure 1.

[0029] An electrostatic latent image is formed on the surface of the photoreceptor drum 31. For example, the photoreceptor drum 31 has a photosensitive layer formed of amorphous silicon. The photoreceptor drum 31 receives rotational driving force supplied from a motor (not shown) and rotates in the rotational direction D4 shown in Figure 3. In this way, the photoreceptor drum 31 transports the electrostatic latent image formed on its surface.

[0030] The charging roller 32 charges the surface of the photoreceptor drum 31 when a preset charging voltage is applied. For example, the charging roller 32 charges the surface of the photoreceptor drum 31 in a positive polarity. The surface of the photoreceptor drum 31, which has been charged by the charging roller 32, is irradiated with light based on image data emitted from the optical scanning device 25. As a result, an electrostatic latent image is formed on the surface of the photoreceptor drum 31.

[0031] The developing device 33 develops the electrostatic latent image formed on the surface of the photoreceptor drum 31. The developing device 33 comprises a pair of stirring members, a magnetic roller, and a developing roller. The pair of stirring members stir the developer contained inside the developing device 33. The developer contains toner and a carrier. As a result, the toner contained in the developer becomes positively charged through friction with the carrier contained in the developer. The magnetic roller draws up the developer stirred by the pair of stirring members and supplies the toner contained in the developer to the developing roller. The developing roller transports the toner supplied from the magnetic roller to a position opposite the photoreceptor drum 31. The developing roller also receives a preset developing bias voltage and supplies the toner transported to the opposite position to the photoreceptor drum 31. As a result, the electrostatic latent image formed on the surface of the photoreceptor drum 31 is made visible (developed). The developing device 33 is supplied with toner from a toner container 36.

[0032] The primary transfer roller 34 receives a preset primary transfer current and transfers the toner image formed on the surface of the photoreceptor drum 31 to the outer surface of the intermediate transfer belt 26. As shown in Figure 3, the primary transfer roller 34 is positioned opposite the photoreceptor drum 31, with the intermediate transfer belt 26 in between.

[0033] The drum cleaning unit 35 removes toner remaining on the surface of the photoreceptor drum 31 after the toner image has been transferred by the primary transfer roller 34.

[0034] The optical scanning device 25 emits light based on image data toward the surface of the photosensitive drum 31 of each image forming unit 20.

[0035] The intermediate transfer belt 26 is an endless belt member onto which the toner image formed on the surface of the photoreceptor drum 31 of each image forming unit 20 is transferred. The intermediate transfer belt 26 is stretched at a predetermined tension by a drive roller 26A (see Figure 3) and a tension roller 26B (see Figure 3). The intermediate transfer belt 26 rotates in the rotation direction D5 shown in Figure 3, as the drive roller 26A rotates in response to rotational driving force supplied from a motor (not shown). As a result, the intermediate transfer belt 26 transports the toner image formed on its outer surface to the secondary transfer position P1 (see Figure 3) by the secondary transfer roller 27. After the toner image has been transferred by the secondary transfer roller 27, the outer surface of the intermediate transfer belt 26 is cleaned by the belt cleaning device 26C shown in Figure 3.

[0036] The secondary transfer roller 27 receives a preset secondary transfer current and transfers the toner image transferred to the outer surface of the intermediate transfer belt 26 to the sheet supplied from the paper feeding unit 4. As shown in Figure 3, the secondary transfer roller 27 is positioned opposite the drive roller 26A, with the intermediate transfer belt 26 in between. The secondary transfer roller 27 is biased toward the drive roller 26A by a biasing member (not shown) so as to contact the intermediate transfer belt 26 with a predetermined nip pressure. At the secondary transfer position P1 (see Figure 3), where it contacts the intermediate transfer belt 26, the secondary transfer roller 27 transfers the toner image formed on the intermediate transfer belt 26 to the sheet. The sheet on which the toner image has been transferred at the secondary transfer position P1 is transported in the transport direction D6 (see Figure 1) toward the fixing nip unit P2 (see Figure 1).

[0037] The fixing device 28 fixes the toner image transferred to the sheet by the secondary transfer roller 27 to the sheet.

[0038] As shown in Figures 1 and 4, the fixing device 28 includes a fixing roller 41 and a pressure roller 42. The fixing device 28 also includes a drive unit 43 and a moving mechanism 44, as shown in Figure 2.

[0039] The fixing roller 41 is rotatably mounted and contacts the sheet onto which the toner image has been transferred to fix the toner image to the sheet. The fixing roller 41 is an example of a fixing member of the present invention. Note that the fixing member of the present invention is not limited to a roller shape.

[0040] The pressure roller 42 is rotatably mounted opposite the fixing roller 41. The pressure roller 42 also forms a fixing nip portion P2 (see Figures 1 and 4) that pressurizes the sheet between itself and the fixing roller 41. Specifically, the pressure roller 42 is mounted to be movable between a contact position (see Figure 4) where it is in contact with the fixing roller 41 and a separated position (see dashed line in Figure 4) separated from the contact position. The pressure roller 42 is also biased by a biasing member (not shown) in the direction toward the contact position from the separated position. The pressure roller 42 is an example of a pressure member of the present invention. Note that the pressure member of the present invention is not limited to a roller shape.

[0041] The drive unit 43 rotates the pressure roller 42 in the rotation direction D7 shown in Figure 4. The drive unit 43 is a motor. The drive unit 43 is rotatable in both forward and reverse directions.

[0042] The fixing roller 41 rotates in the rotational direction D8 shown in Figure 4, as the pressure roller 42 rotates in the rotational direction D7 by receiving rotational driving force supplied from the drive unit 43.

[0043] A heater (not shown) is provided inside the fuser roller 41. The heater heats the fuser roller 41 to a predetermined fixing temperature. When the fuser roller 41 is heated to the fixing temperature, the sheet passing through the fuser nip P2 is pressurized and heated. As a result, the toner image transferred to the sheet is fixed to the sheet.

[0044] The moving mechanism 44 moves the pressure roller 42 between the contact position and the separated position. For example, the moving mechanism 44 includes a motor and a cam that rotates in response to the rotational driving force supplied by the motor, thereby displacing the pressure roller 42 between the contact position and the separated position.

[0045] As shown in Figure 4, the sheet transport path R1, which passes through the fixing nip section P2, is provided with an upstream sensor 45 and a downstream sensor 46.

[0046] The upstream sensor 45 detects the sheet at a detection position P3 (see Figure 4) upstream of the fixing nip section P2 in the sheet transport direction D6 in the transport path R1. The detection position P3 is located between the secondary transfer position P1 (see Figure 1) and the fixing nip section P2 (see Figure 1) in the transport path R1. For example, the upstream sensor 45 is a reflective or transmissive optical sensor. The upstream sensor 45 is an example of the second detection unit of the present invention.

[0047] The downstream sensor 46 detects the sheet at a detection position P4 (see Figure 4) downstream of the fixing nip section P2 in the conveying direction D6 of the sheet in the conveying path R1. For example, the downstream sensor 46 is a reflective or transmissive optical sensor. The downstream sensor 46 is an example of the first detection unit of the present invention.

[0048] The output tray 29 receives a sheet on which the toner image has been fixed by the fuser unit 28.

[0049] Incidentally, in the fixing device 28, a jam can occur where the sheet wraps around the fixing roller 41. In response to this, an image forming apparatus is known as a related technology that reverses the rotation of the fixing roller 41 so that when the aforementioned jam occurs, the leading edge of the sheet does not wrap around the fixing roller 41 more than once.

[0050] In the image forming apparatus according to the aforementioned related technology, the rear end of the sheet may not protrude upstream of the sheet in the sheet transport direction D6 after the fixing roller 41 has rotated in the reverse direction. Specifically, in the image forming apparatus according to the aforementioned related technology, if the length of the sheet in the transport direction D6 is shorter than the circumference of the fixing roller 41, the rear end of the sheet may not protrude upstream of the sheet in the transport direction D6 after the fixing roller 41 has rotated in the reverse direction.

[0051] If the aforementioned jam occurs and the rear end of the sheet does not protrude upstream in the conveying direction D6 from the fixing nip P2 (i.e., the rear end of the sheet is wrapped around the fixing roller 41), it becomes difficult for the user to remove the sheet wrapped around the fixing roller 41.

[0052] In contrast, the image forming apparatus 100 according to the embodiment of the present invention makes it possible to easily remove the sheet wrapped around the fixing roller 41, as will be explained below.

[0053] [Configuration of Control Unit 7] Next, the configuration of the control unit 7 will be described with reference to Figure 2.

[0054] As shown in Figure 2, the control unit 7 includes a setting processing unit 51, a measurement processing unit 52, a stop processing unit 53, a rotation processing unit 54, a pressure reduction processing unit 55, and a notification processing unit 56.

[0055] Specifically, the ROM 12 of the control unit 7 contains pre-stored operation control programs that enable the CPU 11 to function as each of the aforementioned processing units. The CPU 11 then functions as each of the aforementioned processing units by executing the operation control programs stored in the ROM 12.

[0056] The operation control program may be recorded on a computer-readable recording medium such as a CD, DVD, or flash memory, and may be read from the recording medium and stored in a storage device such as the storage unit 6. Furthermore, some or all of the processing units included in the control unit 7 may be composed of electronic circuits. Also, the operation control program may be a program that causes multiple processors to function as individual processing units included in the control unit 7.

[0057] The setting processing unit 51 sets one of several predetermined speeds as the sheet transport speed in the image formation process where an image is formed on the sheet.

[0058] For example, the setting processing unit 51 displays a speed setting screen used for setting the transport speed on the operation display unit 5 in accordance with a predetermined operation on the operation display unit 5. The speed setting screen accepts a speed setting operation to set the transport speed to one of the fastest first speed, the second fastest second speed, or the slowest third speed. The setting processing unit 51 sets the transport speed in accordance with the speed setting operation.

[0059] The measurement processing unit 52 measures the elapsed time from the moment when the leading edge of the sheet in the transport direction D6 reaches the fixing nip portion P2 (see Figure 4) during the execution of the image forming process.

[0060] For example, the measurement processing unit 52 determines that the leading edge of the sheet in the transport direction D6 has reached the fixing nip section P2 when the time elapsed from the moment the leading edge of the sheet in the transport direction D6 is detected by the upstream sensor 45, and the time elapsed is calculated by dividing the distance L1 (see Figure 4) from the detection position P3 in the transport path R1 to the fixing nip section P2 by the transport speed.

[0061] The measurement processing unit 52 continues to measure time until the sheet is detected by the downstream sensor 46 or the image forming process is stopped by the stop processing unit 53.

[0062] The stop processing unit 53 stops the image forming process if, during the execution of the image forming process, the sheet is not detected by the downstream sensor 46 within a predetermined time period from the moment the leading edge of the sheet in the transport direction D6 reaches the fixing nip portion P2.

[0063] In other words, the stop processing unit 53 stops the image forming process when the time measured by the measurement processing unit 52 exceeds the specified time.

[0064] Here, the specified time is the time corresponding to the transport speed set by the setting processing unit 51, among a plurality of times (first time, second time, and third time) corresponding to a plurality of speeds (first speed, second speed, and third speed).

[0065] Specifically, the specified time is determined based on the time obtained by dividing the distance L2 (see Figure 4) from the fixing nip section P2 to the detection position P4 in the transport path R1 by the transport speed. More specifically, the specified time is the time obtained by adding a predetermined margin time to the time obtained by dividing the distance L2 by the transport speed.

[0066] In the image forming apparatus 100, if the time measured by the measurement processing unit 52 exceeds the specified time, it is determined that the jam has occurred.

[0067] When the image forming process is stopped by the stop processing unit 53, and the length of the conveying direction D6 on the sheet is less than a specific distance that is longer than the product of the specific time and the conveying speed of the sheet, the rotation processing unit 54 rotates the fixing roller 41 in the reverse direction by an amount of rotation corresponding to the difference between the specific distance and the length of the conveying direction D6 on the sheet.

[0068] Specifically, the rotation processing unit 54 rotates the fixing roller 41 in the opposite direction to the rotation direction D8 so that the sheet is transported in the opposite direction to the transport direction D6 by the difference between the specific distance and the length of the transport direction D6 in the sheet.

[0069] For example, the specified distance is a distance longer than the sum of the product and the distance L1 (see Figure 4) from the upstream sensor 45 to the fixing nip section P2 in the transport path R1.

[0070] For example, the specified distance is the sum of the product, the distance L1 (see Figure 4), and the distance the sheet moves due to inertia from the time the image forming process stops. Alternatively, the specified distance may be the sum of the product, the distance the sheet moves due to inertia from the time the image forming process stops, and the amount the sheet protrudes from the fixing nip portion P2, which allows the user to grasp the rear end of the sheet.

[0071] For example, the rotation processing unit 54 reverses the fixing roller 41 at a rotation speed corresponding to a predetermined specific speed among the multiple speeds, regardless of which of the multiple speeds the transport speed set by the setting processing unit 51 is. In other words, the reverse rotation time (reverse rotation amount) of the fixing roller 41 is the time obtained by dividing the difference between the specific distance and the length of the transport direction D6 on the sheet by the specific speed. By fixing the rotation speed during reverse rotation to the speed corresponding to the specific speed regardless of the transport speed, it becomes unnecessary to refer to the transport distance when calculating the reverse rotation amount, thus simplifying the calculation process for the reverse rotation amount.

[0072] For example, the specified speed is the slowest speed (the third speed) among the multiple speeds.

[0073] The length of the conveying direction D6 in the sheet may be set in advance by user operation on the operation display unit 5, or it may be measured using a sensor located upstream of the secondary transfer position P1 (see Figure 1) in the conveying path R1 in the conveying direction D6.

[0074] The pressure reduction unit 55 reduces the pressure at the fixing nip section P2 after the rotation unit 54 has finished reversing the rotation of the fixing roller 41.

[0075] For example, the depressurization unit 55 uses the moving mechanism 44 to move the pressure roller 42 from the contact position to the separated position.

[0076] The notification processing unit 56 notifies that the entanglement jam has occurred when the image forming process is stopped by the stop processing unit 53.

[0077] For example, the notification processing unit 56 causes the operation display unit 5 to display a message indicating that the aforementioned jamming has occurred.

[0078] Furthermore, the notification processing unit 56 notifies the upstream sensor 45 if the rear end of the sheet in the transport direction D6 is not detected by the upstream sensor 45 before the reverse rotation of the fixing roller 41 by the rotation processing unit 54 is completed.

[0079] For example, the notification processing unit 56 displays a message on the operation display unit 5 indicating that even when the fixing roller 41 is rotated in reverse, the rear end of the sheet could not be made to protrude from the fixing nip portion P2 to the upstream side in the transport direction D6.

[0080] The control unit 7 may perform a retry process if the upstream sensor 45 does not detect the rear end of the sheet in the transport direction D6 before the reverse rotation of the fixing roller 41 by the rotation processing unit 54 is completed. The retry process involves rotating the fixing roller 41 in the rotation direction D8 by the same amount as the reverse rotation amount of the fixing roller 41 by the rotation processing unit 54, and then rotating the fixing roller 41 in the opposite direction to the rotation direction D8 by the same amount as the reverse rotation amount of the fixing roller 41 by the rotation processing unit 54. The rotation speed of the fixing roller 41 during the execution of the retry process may be a speed corresponding to the aforementioned speed, but different from the specified speed.

[0081] [Motion control processing] The operation control method of the present invention will be described below with reference to Figure 5, along with an example of the procedure for operation control processing performed by the control unit 7 in the image forming apparatus 100. Here, steps S11, S12, etc. represent the numbers of the processing procedures (steps) performed by the control unit 7.

[0082] Furthermore, during the execution of the image forming process, the control unit 7 executes the motion control process each time the leading edge of the sheet in the transport direction D6 reaches the fixing nip portion P2.

[0083] <Step S11> First, in step S11, the control unit 7 starts measuring the elapsed time from the moment when the leading edge of the sheet in the transport direction D6 reaches the fixing nip section P2 (see Figure 4). The process in step S11 is performed by the measurement processing unit 52 of the control unit 7.

[0084] <Step S12> In step S12, the control unit 7 determines whether the leading edge of the sheet in the transport direction D6 has been detected by the downstream sensor 46.

[0085] Here, if the control unit 7 determines that a sheet has been detected by the downstream sensor 46 (Yes side of S12), it stops measuring the elapsed time during the process in step S11 and terminates the operation control process. If the sheet has not been detected by the downstream sensor 46 (No side of S12), the control unit 7 proceeds to step S13.

[0086] <Step S13> In step S13, the control unit 7 determines whether the elapsed time measured by the processing in step S11 exceeds the specified time.

[0087] Here, if the control unit 7 determines that the elapsed time measured by the process in step S11 exceeds the specified time (Yes side of S13), it stops measuring the elapsed time by the process in step S11 and moves the process to step S14. If the elapsed time measured by the process in step S11 does not exceed the specified time (No side of S13), the control unit 7 moves the process to step S12.

[0088] <Step S14> In step S14, the control unit 7 stops the image forming process. The process in step S14 is an example of a stop step in the present invention and is performed by the stop processing unit 53 of the control unit 7.

[0089] <Step S15> In step S15, the control unit 7 determines whether the length of the conveying direction D6 in the sheet is less than the specified distance.

[0090] Here, if the control unit 7 determines that the length of the sheet in the transport direction D6 is less than the specified distance (Yes side of S15), it proceeds to step S16. If the length of the sheet in the transport direction D6 is not less than the specified distance (No side of S15), the control unit 7 proceeds to step S17.

[0091] <Step S16> In step S16, the control unit 7 rotates the fixing roller 41 in the reverse direction by an amount corresponding to the difference between the specific distance and the length of the conveying direction D6 in the sheet. The process in step S16 is an example of the rotation step of the present invention and is performed by the rotation processing unit 54 of the control unit 7.

[0092] Specifically, the control unit 7 uses the drive unit 43 to rotate the fixing roller 41 at a rotational speed corresponding to the specified speed, for a time equal to the difference between the specified distance and the length of the conveying direction D6 on the sheet divided by the specified speed, in the opposite direction to the rotational direction D8.

[0093] <Step S17> In step S17, the control unit 7 reduces the pressure at the fixing nip section P2. The process in step S17 is performed by the pressure reduction processing unit 55 of the control unit 7. This makes it easier for the user to remove the sheet wrapped around the fixing roller 41.

[0094] <Step S18> In step S18, the control unit 7 notifies that the jam has occurred. The processing in step S18 is performed by the notification processing unit 56 of the control unit 7.

[0095] Specifically, the control unit 7 causes the operation display unit 5 to display a message indicating that the aforementioned jamming has occurred.

[0096] Furthermore, if the upstream sensor 45 does not detect the rear end of the sheet in the transport direction D6 before the reverse rotation of the fixing roller 41 by the processing in step S16 is completed, the control unit 7 displays a message on the operation display unit 5 indicating that even if the fixing roller 41 is rotated in reverse, the rear end of the sheet could not be made to protrude upstream of the fixing nip P2 in the transport direction D6. This allows the user to recognize that the sheet is wrapped around the fixing roller 41.

[0097] Thus, in the image forming apparatus 100, if the image forming process stops due to the occurrence of the jam, and the length of the sheet in the transport direction D6 is less than the specified distance, the fixing roller 41 is rotated in the reverse direction by an amount corresponding to the difference between the specified distance and the length of the sheet in the transport direction D6. This makes it possible to make the rear end of the sheet in the transport direction D6 protrude upstream of the fixing nip P2 in the transport direction D6, regardless of the size of the sheet. Therefore, it is possible to easily remove the sheet that has become entangled in the fixing roller 41.

[0098] [Notes on the invention] The following is an overview of the invention extracted from the above-described embodiments. Note that each configuration and processing function described below can be selected and combined as desired.

[0099] <Note 1> An image forming apparatus comprising: a fixing member rotatably provided and in contact with a sheet onto which a toner image has been transferred to fix the toner image to the sheet; a pressing member rotatably provided opposite the fixing member and forming a fixing nip portion that pressurizes the sheet with respect to the fixing member; a first detection unit that detects the sheet downstream of the fixing nip portion in the sheet transport path passing through the fixing nip portion in the sheet transport direction; a stop processing unit that stops the image forming process if the sheet is not detected by the first detection unit within a predetermined specific time elapsed from the moment the leading edge of the sheet in the transport direction reaches the fixing nip portion during the execution of an image forming process to form an image on the sheet; and a rotation processing unit that reverses the rotation of the fixing member by an amount corresponding to the difference between the specific distance and the length when the image forming process is stopped by the stop processing unit and the length of the sheet in the transport direction is less than a specific distance that is longer than the product of the specific time and the transport speed of the sheet.

[0100] <Note 2> The image forming apparatus according to Appendix 1, further comprising a pressure reduction processing unit that reduces the pressure at the fixing nip portion after the completion of the reverse rotation of the fixing member by the rotation processing unit.

[0101] <Note 3> The image forming apparatus according to Appendix 1 or 2, further comprising a second detection unit that detects the sheet upstream of the fixing nip portion in the transport path in the transport direction, wherein the specific distance is longer than the sum of the product and the distance from the second detection unit to the fixing nip portion in the transport path, and the image forming apparatus further comprising a notification processing unit that notifies the second detection unit if the rear end of the sheet in the transport direction is not detected by the second detection unit before the reverse rotation of the fixing member by the rotation processing unit is completed.

[0102] <Note 4> An image forming apparatus according to any one of the appendices 1 to 3, comprising a setting processing unit that sets one of a predetermined number of speeds as the transport speed in the image forming process, wherein the specific time is the time corresponding to the transport speed set by the setting processing unit from among a number of times corresponding to the number of speeds.

[0103] <Note 5> The rotation processing unit rotates the fixing member in the reverse direction at a predetermined specific speed among the multiple speeds, regardless of which of the multiple speeds the transport speed set by the setting processing unit is, as described in Appendix 4 of the image forming apparatus.

[0104] <Note 6> An operation control method performed in an image forming apparatus comprising: a fixing member rotatably provided and in contact with a sheet onto which a toner image has been transferred to fix the toner image to the sheet; a pressing member rotatably provided opposite the fixing member and forming a fixing nip portion that pressurizes the sheet with respect to the fixing member; and a first detection unit that detects the sheet downstream of the fixing nip portion in the sheet transport path passing through the fixing nip portion, the operation control method comprising: a stop step in which, during the execution of an image forming process to form an image on the sheet, the sheet is not detected by the first detection unit within a predetermined specific time elapsed from the timing when the leading edge of the sheet in the transport direction reaches the fixing nip portion; and a rotation step in which, when the image forming process is stopped by the stop step and the length of the sheet in the transport direction is less than a specific distance that is longer than the product of the specific time and the transport speed of the sheet, the fixing member is rotated in the reverse direction by an amount of rotation corresponding to the difference between the specific distance and the length. [Explanation of symbols]

[0105] 1 ADF 2 Image reading unit 3 Image forming unit 4 Paper feed section 5 Operation display section 6 Memory section 7 Control Unit 20 Image forming unit 25 Optical scanning device 26 Intermediate transfer belt 27 Secondary transfer roller 28 Fixing device 29 Paper output tray 41 Fixing roller 42 Pressure rollers 43 Drive unit 44 Moving mechanism 45 Upstream sensor 46 Downstream Sensor 51 Setting Processing Unit 52 Measurement Processing Unit 53 Stop Processing Unit 54 Rotation Processing Unit 55. Reduced pressure processing section 56 Notification Processing Unit 100 Image forming apparatus

Claims

1. A fixing member is provided that is rotatably mounted and comes into contact with a sheet on which a toner image has been transferred, to fix the toner image onto the sheet. A pressing member is provided rotatably opposite the fixing member and forms a fixing nip portion that presses the sheet between itself and the fixing member, A first detection unit detects the sheet downstream of the fixing nip in the sheet transport path, which passes through the fixing nip; During the execution of the image forming process in which an image is formed on the sheet, if the sheet is not detected by the first detection unit within a predetermined specific time elapsed from the moment when the leading edge of the sheet in the transport direction reaches the fixing nip portion, the image forming process is stopped by the first detection unit. When the image forming process is stopped by the stop processing unit, and the length of the sheet in the transport direction is less than a specific distance that is longer than the product of the specific time and the transport speed of the sheet, the rotation processing unit rotates the fixing member in the reverse direction by an amount of rotation corresponding to the difference between the specific distance and the length, An image forming apparatus equipped with the following features.

2. The system includes a pressure reduction unit that reduces the pressure at the fixing nip portion after the reverse rotation of the fixing member by the rotation unit is completed. The image forming apparatus according to claim 1.

3. The transport path includes a second detection unit that detects the sheet upstream of the fixing nip portion in the transport direction, The specified distance is a distance longer than the sum of the product and the distance from the second detection unit to the fixing nip unit in the transport path. The image forming apparatus is The system includes a notification processing unit that notifies the user if the second detection unit does not detect the rear end of the sheet in the transport direction before the reverse rotation of the fixing member by the rotation processing unit is completed. The image forming apparatus according to claim 1 or 2.

4. The system includes a setting processing unit that sets one of a predetermined number of speeds as the transport speed in the image forming process, The specified time is the time corresponding to the transport speed set by the setting processing unit, among a plurality of times corresponding to the plurality of speeds. The image forming apparatus according to claim 1 or 2.

5. Regardless of which of the multiple speeds the transport speed set by the setting processing unit is, the rotation processing unit reverses the rotation of the fixing member at a predetermined specific speed among the multiple speeds. The image forming apparatus according to claim 4.

6. An operation control method performed in an image forming apparatus comprising: a fixing member rotatably provided and in contact with a sheet onto which a toner image has been transferred to fix the toner image to the sheet; a pressing member rotatably provided opposite the fixing member and forming a fixing nip portion that pressurizes the sheet with respect to the fixing member; and a first detection unit that detects the sheet downstream of the fixing nip portion in the sheet transport path passing through the fixing nip portion in the sheet transport direction, wherein the first detection unit detects the sheet downstream of the fixing nip portion in the sheet transport direction, During the execution of the image forming process in which an image is formed on the sheet, if the sheet is not detected by the first detection unit within a predetermined specific time elapsed from the moment when the leading edge of the sheet in the transport direction reaches the fixing nip portion, the image forming process is stopped. If the image forming process is stopped by the stop step, and the length of the sheet in the transport direction is less than a specific distance that is longer than the product of the specific time and the transport speed of the sheet, a rotation step is performed to rotate the fixing member in the reverse direction by an amount of rotation corresponding to the difference between the specific distance and the length. A method for controlling operation that includes this.

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