Image forming device

Abstract

To provide a configuration that can detect a loop of a sheet and that can improve accuracy of detecting a sheet remaining in a fixing device 9.SOLUTION: A sheet detection unit 50 is arranged between a secondary transfer unit and a fixing film 91 and a pressure roller 92 and can detect a sheet. The sheet detection unit 50 has a flag 51 that moves in contact with the sheet, a loop detection sensor S1, and a remaining sheet detection sensor S2. When the flag 51 moves to a first position, the loop detection sensor S1 detects that the sheet conveyed by the secondary transfer unit and the fixing film 91 and pressure roller 92 forms a loop. When the flag 51 moves to a second position different from the first position, the remaining sheet detection sensor S2 detects that a sheet remains in a fixing device 9. Such a sheet detection unit 50 is removably attached to an image forming apparatus body together with the fixing device 9.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus such as a copier, printer, facsimile, or a multifunction machine having multiple functions of these. [Background technology]

[0002] In an image forming apparatus, an image formed on an image carrier such as a photosensitive drum or an intermediate transfer belt is transferred to a sheet in a transfer unit, and the sheet with the transferred image is transported to a fixing device where the image is fixed to the sheet. At this time, a loop is formed in the sheet to prevent the sheet from pulling against each other between the transfer unit and the fixing device, and the sheet transport speed between the transfer unit and the fixing device is controlled by detecting this loop with a sensor (Patent Document 1). Patent Document 1 also discloses that a loop sensor for detecting the loop is used to detect a sheet remaining in the fixing device. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-233372 Summary of the Invention [Problem to be solved by the invention]

[0004] As described above, in the configuration described in Patent Document 1, the loop detection unit also detects residual sheets, but to detect small-sized sheets, it is necessary to position the contact portion of the loop detection unit that comes into contact with the sheet as close as possible to the entrance of the nip portion of the fixing device. On the other hand, in order to detect the amount of deformation of the sheet, loop detection requires that the contact portion be brought into contact with the sheet upstream of the position where residual sheet detection is performed.

[0005] SUMMARY OF THE INVENTION An object of the present invention is to provide a configuration capable of detecting a loop in a sheet and improving the accuracy of detecting a sheet remaining in a fixing device. [Means for solving the problem]

[0006] One aspect of the present invention is a recording medium conveying device including: a transfer unit that transfers a toner image onto a recording material; a rotatable first rotating body having a heat source; a second rotating body that forms a nip portion by contacting the outer circumferential surface of the first rotating body, the second rotating body applying heat and pressure to fix the toner image while nipping and conveying the recording material together with the first rotating body; a control unit that controls the rotation speed of the second rotating body; and a contact portion that is arranged downstream of the transfer unit and upstream of the nip portion in the conveying direction of the recording material and is capable of coming into contact with the recording material, the contact portion entering a conveying path along which the recording material is conveyed. do a first position, and a second position where the recording material is moved from the first position by contacting the contact portion when the recording material passes through the conveying path; The contact portion Evacuate did Second position and , third position and a first detection unit that detects whether the contact member is located at the second position; The aforementioned a second detection unit that detects whether the sensor is located at a third position; Equipped with The aforementioned 3rd position When the contact member is located at the second position, if a force is applied to the contact portion from the recording material passing through the conveyance path, the contact portion is further away from the first position than the second position. The position is moved to , the control unit When the second detection unit does not detect that the position of the contact member is at the third position during conveyance of the recording material, the rotation speed of the second rotating body is set to a first speed, and when the second detection unit detects that the position of the contact member is at the third position, the rotation speed of the second rotating body is set to a second speed that is faster than the first speed. The image forming apparatus is characterized by the above. [Effects of the Invention]

[0007] According to the present invention, the accuracy of detecting a sheet remaining in the fixing device can be improved by using a configuration that can detect a loop in the sheet. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a schematic diagram illustrating the configuration of an image forming apparatus according to a first embodiment. [Figure 2] FIG. 1 is a cross-sectional view showing a schematic configuration of a fixing device according to a first embodiment. [Figure 3]FIG. 4 is a diagram showing a state in which a loop of a sheet is detected according to the first embodiment. [Figure 4] FIG. 4 is a diagram showing a state in which a remaining sheet is detected according to the first embodiment. [Figure 5] 6 is a flowchart of a sheet loop detection operation according to the first embodiment. [Figure 6] 6 is a flowchart of a remaining sheet detection operation according to the first embodiment. [Figure 7] FIG. 10 is a diagram showing a state in which a remaining sheet is detected according to a comparative example. [Figure 8] FIG. 10 is a diagram showing a state in which a loop of a sheet is detected according to a comparative example. [Figure 9] 10A and 10B are diagrams illustrating a state in which the sheet is looped and a state in which the sheet is unlooped, respectively, according to the second embodiment. [Figure 10] 10A is a diagram illustrating a state in which a remaining sheet detection flag contacts the trailing edge of a remaining sheet, and FIG. 10B is a diagram illustrating a state in which a remaining sheet is detected by a remaining sheet detection unit according to a second embodiment. [Figure 11] 10A and 10B are diagrams showing the relationship between a sheet conveyance path and a nip portion according to a second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] First Embodiment The first embodiment will be described with reference to Figures 1 to 6. First, the schematic configuration of an image forming apparatus according to this embodiment will be described with reference to Figure 1.

[0010] [Image forming equipment] The image forming apparatus 100 of this embodiment is an electrophotographic tandem-type full-color printer equipped with four image forming units Pa, Pb, Pc, and Pd, each having a photosensitive drum 3a, 3b, 3c, and 3d as a photosensitive member. The image forming apparatus 100 forms a toner image (image) on a sheet (recording material) in response to an image signal from a document reader (not shown) connected to the image forming apparatus main body 100A or a host device such as a personal computer connected to the image forming apparatus main body 100A for communication purposes. Examples of the sheet include paper, plastic film, and cloth. The image forming units Pa, Pb, Pc, and Pd form yellow, magenta, cyan, and black toner images, respectively.

[0011] The four image forming units Pa, Pb, Pc, and Pd included in the image forming apparatus 100 have substantially the same configuration except for the different developing colors. Therefore, only the image forming unit Pa will be described as a representative, and descriptions of the other image forming units will be omitted.

[0012] As shown in FIG. 1, the image forming unit Pa is provided with a cylindrical photosensitive member, i.e., a photosensitive drum 3a, as an image carrier. The photosensitive drum 3a is driven to rotate in the direction of the arrow in the figure. Around the photosensitive drum 3a, a charging roller 2a as a charging means, a developing device 1a, a primary transfer roller 6a as a transfer means, and a cleaning device 4a as a cleaning means are arranged. Above the photosensitive drum 3a in the figure, an exposure device (laser scanner in this embodiment) 5a as an exposure means is arranged.

[0013] Below each image forming unit in FIG. 1, an image carrier that carries an image and an endless intermediate transfer belt 20 that serves as an intermediate transfer body are disposed. The intermediate transfer belt 20 is stretched around a plurality of rollers 13, 14, and 15 and configured to move (rotate) in the direction of arrow A. Specifically, the intermediate transfer belt 20 rotates when the drive roller 13 is driven to rotate by a motor (not shown). The intermediate transfer belt 20 carries and transports a toner image that has been primarily transferred onto the intermediate transfer belt 20, as will be described later. A secondary transfer outer roller 11 serving as a transfer member is disposed at a position facing the secondary transfer inner roller 14, one of the rollers that stretch the intermediate transfer belt 20, across the intermediate transfer belt 20, and forms a secondary transfer unit T2 that transfers the toner image on the intermediate transfer belt 20 to a sheet P. That is, the outer secondary transfer roller 11 conveys the sheet while nipping it between itself and the intermediate transfer belt 20 at the secondary transfer portion T2, and transfers the toner image on the intermediate transfer belt 20 (on the image carrier) onto the sheet P. A fixing device 9 is disposed downstream of the secondary transfer portion T2 in the sheet conveying direction.

[0014] A cassette 10 containing sheets P is disposed at the bottom of the image forming apparatus 100. The sheet P fed from the cassette 10 is transported toward registration rollers 12 by a feed roller (not shown). The leading edge of the sheet P then strikes the registration rollers 12, which are in a stopped state, forming a loop and correcting any skew of the sheet P. Thereafter, the registration rollers 12 start to rotate in synchronization with the toner image on the intermediate transfer belt 20, and the sheet P is transported to the secondary transfer unit T2.

[0015] A process for forming, for example, a four-color full-color image using the image forming apparatus 100 configured as described above will now be described. First, when the image forming operation starts, the surface of the rotating photosensitive drum 3a is uniformly charged by the charging roller 2a. Next, the photosensitive drum 3a is exposed to laser light corresponding to an image signal emitted from the exposure device 5a. As a result, an electrostatic latent image corresponding to the image signal is formed on the photosensitive drum 3a. The electrostatic latent image on the photosensitive drum 3a is visualized by toner contained in the developing device 1a as a developer, becoming a visible image.

[0016] The toner image formed on the photosensitive drum 3a is primarily transferred onto the intermediate transfer belt 20 at a primary transfer section formed between the photosensitive drum 3a and a primary transfer roller 6a disposed across the intermediate transfer belt 20. At this time, a primary transfer bias is applied to the primary transfer roller 6a. Toner remaining on the surface of the photosensitive drum 3a after the primary transfer (transfer residual toner) is removed by a cleaning device 4a.

[0017] This operation is performed sequentially in each image forming unit for yellow, magenta, cyan, and black, and the four color toner images are superimposed on the intermediate transfer belt 20. Thereafter, in synchronization with the timing of the formation of the toner images, the sheet P stored in the cassette 10 is transported to the secondary transfer unit T2. Then, by applying a secondary transfer bias to the outer secondary transfer roller 11, the four color toner images on the intermediate transfer belt 20 are secondarily transferred all at once onto the sheet P. Any toner that was not transferred in the secondary transfer unit T2 and remains on the intermediate transfer belt 20 is removed by an intermediate transfer belt cleaner 24.

[0018] Next, the sheet P is conveyed to the fixing device 9 via the belt conveying device 30. The belt conveying device 30 is, for example, a conveying belt that attracts and conveys the sheet P, and is arranged between the secondary transfer portion T2 and the fixing device 9. The belt conveying device 30 is arranged to feed the sheet P discharged from the secondary transfer portion T2 into the fixing device 9 while assisting its conveying posture. In this embodiment, the belt conveying device 30 is formed by a belt stretched between rollers, but it may also be configured with only a guide member that guides the sheet P. The sheet P that has passed through the secondary transfer portion T2 is handed over to the belt conveying device 30 and conveyed to the fixing device 9 by the belt conveying device 30. Note that the belt conveying device 30 may be omitted, and the sheet P that has passed through the secondary transfer portion T2 may be conveyed directly to the fixing device 9.

[0019] The fixing device 9 includes a pair of rotating bodies, a fixing film 91 (first rotating body) and a pressure roller 92 (second rotating body), and the fixing film 91 and the pressure roller 92 form a fixing nip portion. When a sheet P with a toner image transferred thereon passes through the fixing nip portion of the fixing device 9, the sheet P is heated and pressurized. The toner on the sheet is then melted and mixed, and fixed to the sheet P as a full-color image. The sheet P is then discharged outside the machine by a discharge roller.

[0020] On the other hand, when forming images on both sides of the sheet P (double-sided printing), the sheet P is switched back to the switchback conveying path 17 by switching the switching member 16, and further, the sheet P is conveyed to the double-sided conveying path 19 by the conveying rollers 18. The sheet P is conveyed from the double-sided conveying path 19 in an inverted state to the registration rollers 12, and a toner image is formed on the back side of the sheet P in the same manner as described above. This completes the series of image forming processes.

[0021] In addition, the image forming apparatus 100 of this embodiment can also form a monochrome or multi-color image, such as a monochrome black image, using image forming units for a desired monochrome color or several of the four colors.

[0022] The image forming apparatus 100 is also provided with an operation panel S as an operation unit, which includes various buttons and operation switches operated by the user, and a display unit that displays messages to the user and errors such as jam occurrence. The image forming apparatus 100 also has a plurality of sheet detection sensors that can detect sheets. Of these sheet detection sensors, the post-registration sensor 21 is a sensor that detects that the leading edge of the sheet P has reached the registration rollers 12. The post-secondary transfer sensor 22 is a sensor that detects that the leading edge of the sheet P has passed through the secondary transfer unit T2. The discharge sensor 23 is a sensor that detects the sheet P on the side of the fixing device 9 where the sheet P is discharged.

[0023] Signals from these sensors are sent to the control unit 110. The control unit 110 receives signals from various sensors including these sheet detection sensors and controls each unit. It also controls the entire image forming apparatus 100 according to input job information such as the number of sheets to be imaged and the type of sheet P, and performs image formation. The control unit 110 has a CPU (Central Processing Unit), ROM (Read Only Memory), and RAM (Random Access Memory). The CPU controls each unit by reading programs corresponding to control procedures stored in the ROM. The RAM also stores working data and input data, and the CPU performs control by referring to the data stored in the RAM based on the aforementioned programs, etc.

[0024] [Fusing device] The fixing device 9 will be described in detail with reference to Fig. 2. The fixing device 9 includes a fixing film 91 as a fixing member and a pressure roller 92 as a pressure member. The fixing film 91 includes a heating member for heating the inside. (heat source) 102 is disposed inside the fixing film 91, and heats the fixing film 91 to a predetermined temperature. A stay 104 is disposed inside the fixing film 91 so as to pass through it, and a support member 105 that supports the heating member 102 is urged toward the pressure roller 92 via the stay 104 by an urging member such as a spring (not shown). As a result, a fixing nip N is formed between the fixing film 91 and the pressure roller 92 for nipping and transporting the sheet P.

[0025] The heating member 102 is, for example, a plate-shaped ceramic heater, and is arranged in the fixing nip portion N. That is, the heating member 102 is supported by a support member 105 so as to face the pressure roller 92 with the fixing film 91 interposed therebetween. The fixing film 91 rotates in accordance with the pressure roller 92 as the pressure roller 92 is driven to rotate. The fixing film 91 and the pressure roller 92 are arranged inside a housing 90.

[0026] That is, the fixing device 9 includes a housing 90, a fixing film 91 and a pressure roller 92 as a pair of rotating bodies disposed inside the housing 90, an entrance guide 93, and a sheet detection unit 50. The housing 90 has openings at the entrance and exit for the sheet P, and is internally provided with the fixing film 91, the pressure roller 92, the entrance guide 93, and the sheet detection unit 50. The entrance guide 93 is disposed between the entrance of the housing 90 and the fixing nip N, and guides the sheet P, which enters through the entrance of the housing 90 and carries an unfixed toner image, to the entrance of the fixing nip N. The sheet P guided along the entrance guide 93 is heated and pressurized while being nipped and conveyed between the fixing film 91 and the pressure roller 92 in the fixing nip N. This fixes the toner image to the sheet P. The sheet detection unit 50 serves both as a loop detection sensor that detects the formation of a loop in the sheet P and as a residual sheet detection sensor that detects the presence of a sheet remaining in the fixing device 9. A detailed description will be given later.

[0027] The fixing device 9 is also equipped with a fixing motor M whose rotation speed is variable, which drives the pressure roller 92 to rotate. The control unit 110 can control the conveyance speed of the sheet P at the fixing nip N by controlling the rotation speed of the fixing motor M. In the fixing device 9 of this embodiment, the pair of rotating bodies forming the fixing nip N is configured with the fixing film 91 and the pressure roller 92, but the configuration of the pair of rotating bodies is not limited to this. For example, both of the pair of rotating bodies may be rollers, or both may be endless belts stretched by multiple rollers. Furthermore, one may be an endless belt and the other a roller. The heating method is also not limited to the ceramic heater described above. For example, a halogen heater may be disposed within the roller, or an IH (electromagnetic induction heating) configuration may be used.

[0028] [Sheet detection unit] Next, the configuration of the sheet detection unit 50 will be described with reference to FIG. 2. The sheet detection unit 50 is disposed between the secondary transfer unit T2 and the fixing film 91 and pressure roller 92, and is capable of detecting a sheet. Specifically, the sheet detection unit 50 is disposed between the belt conveying device 30 as a pre-fixing conveying unit and the fixing nip N. The sheet detection unit 50 includes a flag 51 as a moving member and a swinging member, a first sensor, and a second sensor. Sa and Loop detection sensor (Second detection unit) S1, 2nd Sen Sa and Residual sheet detection sensor (First detection unit) S2. The flag 51 moves in contact with the sheet. In this embodiment, the flag 51 is a swinging member that can swing around a rotation shaft 50a that serves as the swing center.

[0029] As a contact member The flag 51 has a contact portion 52, a first flag portion 53, and a second flag portion 54 that can come into contact with the sheet. The contact portion 52 is positioned so that its tip is closer to the fixing nip portion N (the nip portion side) than the center of the swing, and is biased by a spring (not shown) in the direction opposite to the pressing direction of the sheet P. Specifically, the sheet detection unit 50 is positioned below the entrance guide 93. The entrance guide 93 is, for example, a plate-shaped member with an opening or a notch formed therein so that the flag 51 can pass through. The contact portion 52 protrudes upward from the opening or notch. When the contact portion 52 comes into contact with the sheet P conveyed from the belt conveying device 30, the contact portion 52 is pressed downward by the sheet P, causing the contact portion 52 to rotate counterclockwise in FIG. 2 around the pivot shaft 50a. A spring (not shown) biases the contact portion 52 to rotate clockwise in FIG. 2.

[0030] The flag 51 as described above can be positioned at a first position, a second position, and a third position. The first position is a position where the contact portion 52 enters the conveying path along which the sheet is conveyed, and the second position is a position where the sheet comes into contact with the contact portion 52 when passing through the conveying path, and the third position is a position where the sheet comes out of the first position and enters the third position. The contact portion 52The third position is a position where the contact portion 52 is further away from the first position than the second position when a force is applied to the contact portion 52 from a sheet passing through the conveyance path while the flag 51 is located at the second position. Moved to Specifically, the first flag portion 53 and the second flag portion 54 are provided so as to protrude from the rotation shaft 50a at positions different from the contact portion 52, and are capable of swinging together with the contact portion 52 around the rotation shaft 50a. The first flag portion 53 and the second flag portion 54 are disposed at positions with different phases in the rotation direction about the rotation shaft 50a, and the contact portion 52, the first flag portion 53, and the second flag portion 54 swing around the rotation shaft 50a while maintaining their respective phase positions. The first flag portion 53 is provided at a position where it can be detected by the loop detection sensor S1, and the second flag portion 54 is provided at a position where it can be detected by the residual sheet detection sensor S2.

[0031] The loop detection sensor S1 detects that the flag 51 is 3 When the flag 51 is moved to the second transfer position, the residual sheet detection sensor S2 detects that the sheet conveyed by the secondary transfer portion T2, the fixing film 91, and the pressure roller 92 forms a loop. 3 When the loop detection sensor S1 moves to a second position different from the first position, it detects that a sheet remains in the fixing device 9. The loop detection sensor S1 and the remaining sheet detection sensor S2 are each a photointerrupter in which a light emitting portion and a light receiving portion are arranged opposite each other. That is, the flag blocks the light emitted from the light emitting portion. do This makes it possible to detect the rotational positions of the first flag portion 53 and the second flag portion 54. Signals detected by the loop detection sensor S1 and the remaining sheet detection sensor S2 are sent to the control unit 110, and the control unit 110 performs control based on these signals as described below.

[0032] [Loop detection and residual sheet detection] Next, loop detection and residual sheet detection in this embodiment will be described with reference to FIGS. 3 and 4. FIG. 3 shows a state in which loop detection is being performed by the sheet detection unit 50. FIG. 3 shows a state L1 in which a loop occurs in the sheet P due to a difference in sheet conveyance speed between the belt conveyance device 30 and the fixing device 9, and a state L2 in which the loop is eliminated. The belt conveyance device 30 is designed to convey the sheet at approximately the same speed as the sheet conveyance speed at the secondary transfer portion T2. ​​Similarly, the sheet conveyance speed at the fixing device 9 is also designed to convey the sheet at approximately the same speed. However, in the fixing device 9, the fixing film 91 is rotated by the rotation of the pressure roller 92. The fixing film 91 rotates in response to the rotation of the pressure roller 92. This causes a slight slip between the pressure roller 92 and the fixing film 91. This causes an error in the belt rotation speed. The same applies to the belt conveyance device 30. Therefore, the sheet conveyance speed at the fixing device 9 may differ from the sheet conveyance speed at the secondary transfer portion T2. Therefore, if the sheet conveying speed in the fixing device 9 is slower than the sheet conveying speed in the belt conveying device 30, a loop in which the sheet bends occurs between the fixing device 9 and the belt conveying device 30, and no pulling of the sheet occurs between the fixing device 9 and the secondary transfer portion T2. ​​On the other hand, if the sheet conveying speed in the fixing device 9 is faster than the sheet conveying speed in the belt conveying device 30 in a state where no loop is formed, pulling of the sheet occurs between the fixing device 9 and the secondary transfer portion T2, and there is a risk of misalignment of the transferred image occurring at the secondary transfer portion T2.

[0033] Therefore, in this embodiment, the loop detection sensor S1 is arranged so that the first flag portion 53 can be detected when the sheet P has looped. That is, when the contact portion 52 of the flag 51 is in contact with the sheet P in the state L2 (broken line), the first flag portion 53 does not block the light of the loop detection sensor S1. On the other hand, when the contact portion 52 comes into contact with the sheet P in the state L1, it swings counterclockwise and 3 When the first flag portion 53 is positioned at the position (solid line), the first flag portion 53 blocks light from the loop detection sensor S1 (the sensor is turned ON).

[0034] In FIG. 3, flag 51 is 3 When the second flag unit 54 is positioned at the position (solid line), the second flag unit 54 blocks light from the residual sheet detection sensor S2 (the sensor turns ON). Therefore, when both the loop detection sensor S1 and the residual sheet detection sensor S2 turn ON, the control unit 110 determines that a loop of the sheet P has formed between the belt conveying device 30 and the fixing nip N. Note that the positions of the second flag unit 54 and the residual sheet detection sensor S2 may be set so that the residual sheet detection sensor S2 does not turn ON in this state.

[0035] 4 shows a state in which the sheet detection unit 50 is detecting a remaining sheet. If a sheet P remains in the fixing nip N during a jam, the contact portion 52 of the flag 51 comes into contact with the trailing edge of the remaining sheet P, causing the flag 51 to rotate counterclockwise to the second position (solid line). The second flag unit 54 then blocks the remaining sheet detection sensor S2 (the sensor is turned ON). At this time, the first flag unit 53 does not block the loop detection sensor S1. Therefore, the control unit 110 determines that the loop detection sensor S1 is OFF and the remaining sheet detection sensor S2 is ON, and that a sheet remains in the fixing nip N. The dashed line indicates a state in which the contact portion 52 of the flag 51 does not detect the sheet P. That is, the position indicated by the dashed line in FIG. 4 indicates the first position.

[0036] In this case, if a sheet remains in the fixing nip N and the fixing device 9 is heated without detecting the remaining sheet, the toner in the fixing nip N may melt, causing the remaining sheet to stick to the fixing film 91, which may cause malfunction of the fixing device 9. For this reason, a method is generally used in which a sheet remaining in the fixing nip is detected by a sensor disposed on the conveyance path of the fixing device. The closer the sensor disposed before (upstream) and the sensor disposed after (downstream) the fixing nip are to the fixing nip, the more likely it is that a remaining sheet with a short length in the conveyance direction will be detected.

[0037] Therefore, in the case where the sheet detection unit 50 detects both the loop of the sheet and the remaining sheet in the fixing nip, as in the present embodiment, it is preferable that the flag 51 be disposed as close as possible to the fixing nip N. If the tip of the contact portion 52 of the flag 51 is disposed in a position close to the entrance of the fixing nip N, even if a sheet with a short length in the conveyance direction remains in the fixing nip N, it becomes easier to detect this remaining sheet.

[0038] Therefore, in this embodiment, the loop detection sensor S1 is set to the flag 51. 3 In order to detect that the sheet has formed a loop when the sheet is moved to the position, the remaining sheet detection sensor S2 is set to the flag 51. 3 The flags 51 are arranged so that if the flag 51 is moved to a second position different from the first position, it can detect whether a sheet remains in the fixing device 9. Therefore, loop detection and remaining sheet detection can be performed when the flag 51 is in a position suitable for remaining sheet detection and a position suitable for loop detection, respectively. Therefore, the accuracy of detecting sheet loops and detecting sheets remaining in the fixing device can be improved with a single flag 51 without increasing the number of parts.

[0039] In this embodiment, the sheet detection unit 50 is detachably attached to the image forming apparatus main body 100A as one unit with the fixing device 9. The sheet detection unit 50 is disposed inside the housing 90 of the fixing device 9. Specifically, the rotation shaft 50a of the flag 51 is supported directly on the frame of the fixing device 9 or on an entrance guide 93 provided on the frame. The fixing film 91 and the pressure roller 92 are also supported on this frame.

[0040] By making the sheet detection unit 50 detachable integrally with the fixing device 9 in this way, it becomes easier to bring the contact portion 52 of the flag 51 close to the fixing nip portion N. In other words, if the sheet detection unit 50 and the fixing device 9 were configured to be detachable separately from the image forming apparatus main body 100A, multiple parts would be interposed between the support portion for the contact portion 52 of the flag 51 and the support portions for the fixing film 91 and the pressure roller 92. For this reason, the positional relationship between the contact portion 52 and the fixing film 91 and the pressure roller 92 must be specified taking into account the tolerances of these multiple parts, making it difficult to bring the contact portion 52 close to the fixing nip portion N.

[0041] On the other hand, by making the sheet detection unit 50 detachable integrally with the fixing device 9 as in this embodiment, the number of parts present between the support portion for the contact portion 52 of the flag 51 and the support portions for the fixing film 91 and the pressure roller 92 can be reduced. This reduces the number of parts requiring tolerance considerations, making it easier to bring the contact portion 52 closer to the fixing nip N. In particular, by supporting the rotation shaft 50a of the flag 51, the fixing film 91, and the pressure roller 92 on a common frame, it becomes easier to ensure the positional relationship between the contact portion 52 of the flag 51 and the fixing nip N, making it easier to bring the contact portion 52 closer to the fixing nip N. Note that even if the rotation shaft 50a is supported on the entrance guide 93 provided on the frame, the number of parts increases due to the presence of the entrance guide 93, but it is easier to bring the contact portion 52 closer to the fixing nip N than if the rotation shaft 50a were supported at a location other than the components of the fixing device 9. As a result, even if the length of the sheet remaining in the fixing nip portion N is short, the remaining sheet can be easily detected by the flag 51, and the configuration capable of detecting the loop of the sheet can improve the detection accuracy of the sheet remaining in the fixing device 9.

[0042] In the above description, the sheet detection unit 50 has two sensors, S1 and S2, but the number of sensors may be increased to improve the accuracy of flag position detection. In the above description, the flag 51 has two flag portions (light-shielding portions) (first flag portion 53 and second flag portion 54) for detection by a photointerrupter, but the flag 51 may have only one flag portion. That is, one flag portion may be configured to shield S1 and S2 from light. In the above description, the remaining sheet detection sensor S2 is used to detect remaining sheets, but it may also be used as a second loop detection sensor that detects a loop state different from the state detected by the loop detection sensor S1.

[0043] [Loop Control] Here, we will explain loop control, which detects the loop state of a sheet using the above-mentioned sheet detection unit 50 and controls the sheet conveying speed of the fixing device 9. When the loop detection sensor S1 does not detect a loop of the sheet during sheet conveyance, the control unit 110 sets the sheet conveying speed by the fixing film 91 and the pressure roller 92 to a first speed. On the other hand, when the loop detection sensor S1 detects a loop of the sheet, the control unit 110 sets the sheet conveying speed by the fixing film 91 and the pressure roller 92 to a second speed that is faster than the first speed.

[0044] That is, when the sheet is not looped, the control unit 110 slows down the rotation speed of the fixing motor M that drives the pressure roller 92, thereby reducing the speed at which the sheet is conveyed by the fixing film 91 and the pressure roller 92 to be lower than the speed at which the sheet is conveyed by the belt conveying device 30. This causes a loop to be formed in the sheet conveyed between the belt conveying device 30 and the fixing nip N. On the other hand, when the sheet is looped, the control unit 110 increases the rotation speed of the fixing motor M that drives the pressure roller 92, thereby making the speed at which the sheet is conveyed by the fixing film 91 and the pressure roller 92 higher than the speed at which the sheet is conveyed by the belt conveying device 30. This ensures the sheet conveyance speed without making the sheet loop too large.

[0045] Such loop control in this embodiment will be specifically described with reference to the flowchart in Fig. 5. First, when a job is started, a sheet P is fed from the cassette 10 and conveyed toward the registration rollers 12 (S101). Next, an image is formed in each image forming unit in synchronization with the sheet feeding, and the image is transferred to the sheet P conveyed from the registration rollers 12 at the secondary transfer unit T2 (S102). In this way, The image The sheet P onto which the image has been transferred is conveyed by the rotation of the secondary transfer portion T2 and the belt conveying device 30, and reaches the fixing device 9.

[0046] At this time, the conveying speed of the fixing device 9 (the sheet conveying speed by the fixing film 91 and the pressure roller 92) is set to VL (first speed) which is 2% slower than the sheet conveying speed at the secondary transfer portion T2. ​​As a result, as the conveyance of the sheet P progresses, a loop of the sheet is formed between the belt conveying device 30 and the fixing nip portion N of the fixing device 9.

[0047] Then, the control unit 110 determines whether a loop is formed in the sheet from the status of the sheet detection unit 50 (S103). Specifically, it determines whether the sheet P passes through the fixing nip N in a state where the output of the loop detection sensor S1 is off, i.e., in a state where the sheet P does not form a loop, or whether the sheet P passes through the fixing nip N in a state where a loop is formed between the belt conveying device 30 and the fixing nip N (the output of the loop detection sensor S1 is on).

[0048] If the sheet P passes through the fixing nip N without forming a loop (No in S103), the rotation of the fixing motor M is controlled to set the conveying speed of the fixing device 9 to VL (first speed) (S104). That is, if the sheet conveying speed of the fixing device is VL, this VL is maintained, and if the sheet conveying speed of the fixing device is VH (described below), the sheet conveying speed of the fixing device is reduced from VH to VL.

[0049] On the other hand, if a loop is formed in the sheet in S103 (Yes in S103), the rotation of the fixing motor M is controlled for a certain time h to set the conveying speed of the fixing device 9 to VH (second speed), which is 2% faster than the sheet conveying speed at the secondary transfer portion T2 (S105). That is, the sheet P is conveyed at the sheet conveying speed of the fixing device 9 at VH for a certain time h (0.5 seconds in this embodiment) to eliminate the sheet loop. Thereafter, the controls of S103 to S105 are repeated until the post-secondary transfer sensor 22 detects that the trailing edge of the sheet P has passed through the secondary transfer portion T2 (S106). Note that the loop detection sensor may be configured to determine that a loop exists if the sensor signal remains on for a certain time (e.g., 0.1 seconds) to prevent erroneous detection.

[0050] [Residual sheet detection control] Next, a description will be given of residual sheet detection control, which uses the sheet detection unit 50 to detect a sheet remaining in the fixing nip N and notify an error. When the sheet detection unit 50 detects a sheet when the apparatus is powered on, the control unit 110 outputs a message indicating that a sheet remains in the fixing device 9. That is, when the image forming apparatus 100 is powered on, if the residual sheet detection sensor S2 is on, the control unit 110 displays an error message indicating that a sheet remains in the fixing device 9 on the operation panel S. The control unit 110 may also output the error message to an external terminal, such as a personal computer, connected to the image forming apparatus 100. Furthermore, even if the residual sheet detection sensor S2 is not on, if the loop detection sensor S1 is on, the control unit 110 may display an error message indicating that a sheet remains in the fixing device 9 on the operation panel S.

[0051] The remaining sheet detection control of this embodiment will be specifically described with reference to the flowchart in Fig. 6. Fig. 6 is a flowchart illustrating the process of detecting remaining sheets P when the image forming apparatus 100 is powered on and when the image forming apparatus 100 is in an idle state where no print job is being executed. When the image forming apparatus 100 is powered on, the control unit 110 checks whether the remaining sheet detection sensor S2 is on, i.e., whether it is detecting a sheet P (S201). If the remaining sheet detection sensor S2 is on (Yes in S201), the control unit 110 determines that a remaining sheet exists in the fixing device 9 and notifies the user of an error indicating the presence of a remaining sheet (S202).

[0052] On the other hand, in S201, if the remaining sheet detection sensor S2 does not detect a sheet P when the power is turned on (No in S201), the process proceeds to normal initialization processing, reception of an image formation job, and execution processing of the image formation job (S203). Note that an image formation job is an operation from the start of image formation based on a print signal (image formation signal) for forming an image on a sheet to the completion of image formation. The initialization processing is a preparatory operation before the image formation operation, in which the rotation of the photosensitive drum is started and various voltages are sequentially started up and various voltages are adjusted, and is what is known as pre-rotation processing.

[0053] Next, the control unit 110 determines whether the image forming job is in a standby state where the image forming job is not being executed (S204). If the image forming job is in a standby state (Yes in S204), the process proceeds to S201, where a determination is made as to whether there are any remaining sheets, in the same manner as when the power is turned on as described above, and whether to notify the user of a jam error. If the image forming job is not in a standby state in S204 (No in S204), the process returns to S203 and continues normal processing. This makes it possible to determine whether there are any remaining sheets P when the sheet P is not being conveyed.

[0054] In this embodiment, a configuration in which two contact portions are provided on one flag (moving member) enables loop detection and residual detection, which reduces the number of parts compared to a configuration in which loop detection and residual detection are performed using independent flags (moving members).

[0055] <Second embodiment> The second embodiment will be described with reference to Figures 7 to 11. In the first embodiment described above, a configuration was described in which both a sheet with a loop formed therein and a sheet remaining in the fixing device 9 were detected at the tip of the contact portion 52 of the flag 51. In contrast, in this embodiment, a sheet with a loop formed therein and a sheet remaining in the fixing device 9 are detected at two different points of the flag 51A.

[0056] [Comparative Example] First, a comparative example shown in Figures 7 and 8 will be described. As described above, in residual sheet detection, if the leading edge of contact portion 52 of flag 51 catches on the trailing edge of the sheet remaining in fixing nip portion N, the residual sheet can be detected. Therefore, it is desirable that the leading edge of contact portion 52 be located close to fixing nip portion N.

[0057] However, as shown in the comparative example in Figure 7, if the flag 51 is extended from the pivot shaft 50a to bring the leading edge of the contact portion 52 closer to the fixing nip N in an attempt to improve the detection performance of the residual sheet, the following problem may occur. That is, as shown in Figure 8, if the leading edge of the contact portion 52 is brought closer to the fixing nip N, the loop detection will be performed in an area where there is little difference in the trajectory between a state L1 where a loop has occurred in the sheet near the fixing nip N and a state L2 where the loop has been eliminated. This may make it impossible to distinguish between a slight change in behavior during the transport of the sheet P and the occurrence of a loop.

[0058] [Configuration of this embodiment] Therefore, in this embodiment, as shown in FIGS. 9(a) to 10(b), the leading end of the flag 51A of the sheet detection unit 50A is bent, and the bent portion 52b is used as the loop detection position and the leading end 52a is used as the residual sheet detection position, thereby achieving both loop detection performance and residual sheet detection performance. That is, the sheet detection unit 50A of this embodiment differs from the first embodiment in the shape of the flag 51A. Similar to the first embodiment, the sheet detection unit 50A includes a first flag portion 53, a second flag portion 54, a loop detection sensor S1, and a residual sheet detection sensor S2. The flag 51A of this embodiment has a bent portion 52b, which is bent so that the leading end 52a is bent in the direction extending from the pivot shaft 50a, which serves as the swing center. The bent portion 52b is a first contact portion for detecting the formation of a loop, and the leading end 52a is a second contact portion for detecting the presence of a sheet remaining in the fixing device 9.

[0059] The bent portion 52b of the flag 51A is arranged so that it is closest to the conveying path at the position where the loop detection sensor S1 is switched on by the first flag portion (light blocking portion) 53 provided on the flag 51A, that is, at the position where the loop is detected. 3 When flag 51A is positioned at the position indicated by the solid line (position indicated by the solid line in FIG. 9A, position where it is in contact with sheet P in the L1 state), bent portion 52b is positioned closer to the path along which the sheet is transported than leading edge 52a. This makes it possible to detect a loop using bent portion 52b, and to detect a residual sheet using leading edge 52a (when it is in contact with sheet P remaining in fixing nip N in FIG. 10B). As a result, even if the leading edge of flag 51A is brought closer to fixing nip N to improve residual sheet detection performance, it is possible to prevent a decrease in loop detection performance. This will be described in detail below.

[0060] [Loop detection and remaining sheet detection] Next, a loop detection operation and a remaining sheet detection operation performed by the sheet detection unit 50A of this embodiment will be described with reference to FIGS. 9(a) to 10(b).

[0061] When a sheet P passes over the entrance guide 93, the flag 51A of the sheet detection unit 50A is pressed by the sheet P and rotates around the rotation shaft 50a. A rotation force is applied to the flag 51A by a rotation spring (not shown) in the direction opposite to the pressing force of the sheet P (clockwise direction in FIGS. 9(a) and 9(b) and 10(a) and 10(b)).

[0062] The tip 52a of the flag 51A that is pressed against the sheet P is 20 The belt conveying device 30 is arranged to be rotatable between a state L1 (FIG. 9(a)) in which a loop occurs due to the difference in the conveying speed of the sheet P conveyed by the belt conveying device 30 and the conveying speed of the sheet P conveyed by the fixing device 9, and a state L2 (FIG. 9(b)) in which the loop is eliminated. The belt conveying device 30 is designed to convey the sheet at approximately the same speed as the sheet conveying speed at the secondary transfer portion T2. ​​Similarly, the sheet conveying speed at the fixing device 9 is also designed to convey the sheet at approximately the same speed. However, the fixing device 9 rotates the pressure roller 92, causing the fixing film 91 to rotate. The fixing film 91 rotates in response to the rotation of the pressure roller 92, causing a slight slip between the pressure roller 92 and the fixing film 91. This causes an error in the rotation speed of the fixing film 91. The same is true for the belt conveying device 30. Therefore, the sheet conveying speed at the fixing device 9 may differ from the sheet conveying speed at the secondary transfer portion T2.

[0063] When the secondary transfer portion T2 and the fixing nip portion N simultaneously nip and convey the sheet, and the sheet conveying speed in the fixing device 9 becomes faster than the sheet conveying speed in the secondary transfer portion T2, the fixing device 9 pulls the sheet, and the desired area on the sheet is not conveyed. The image There is a risk that the image may not be transferred (misaligned transfer). To prevent this misalignment, a loop detection sensor detects the amount of loop in the sheet and controls the sheet conveyance speed in the fixing device. The details are described below.

[0064] The loop detection sensor S1 is configured to turn ON when it blocks light from the loop detection sensor S1 and to turn OFF when it transmits light through the loop detection sensor S1. Therefore, as shown in Fig. 9(a), the position of the first flag portion 53 is defined so that when the bent portion 52b of the flag 51A reaches the position of state L1 where a loop has occurred, the first flag portion 53 turns ON the loop detection sensor S1.

[0065] 9(b), when the loop of the sheet is released, the first flag portion 53 transmits light from the loop detection sensor S1, and the loop detection sensor S1 turns OFF. Then, the sheet conveying speed of the fixing device 9 is reduced, and the loop is formed again.

[0066] 10(a), if a sheet P remains in the fixing nip N due to a jam or the like, the trailing edge of the sheet P is detected by the leading edge 52a of the flag 51A. In this embodiment, even if a small-sized sheet, such as a postcard or envelope, with a length of about 150 mm in the sheet conveyance direction remains in the fixing nip N, the leading edge 52a of the flag 51A is extended to the vicinity of the entrance of the fixing nip N so that the remaining sheet can be detected.

[0067] Next, as shown in FIG. 10(b), if a sheet P remains in the fixing nip N due to a jam or other reason, the sheet P follows the direction of the nip surface of the fixing nip N, causing the trailing edge of the sheet P to move downward from the dashed line position to the solid line position. Then, the leading edge 52a in contact with the trailing edge of the sheet P rotates counterclockwise, and the second flag portion 54 blocks the light from the residual sheet detection sensor S2. Even in this state, the first flag portion 53 does not block the light from the loop detection sensor S1. When the second flag portion 54 blocks the light from the residual sheet detection sensor S2, the residual sheet detection sensor S2 turns ON, and it is detected that a sheet P remains in the fixing nip N.

[0068] In the above description, a loop detection position and a remaining sheet detection position are provided by providing a bent portion 52b on the flag 51A, but it is also possible to provide a loop detection portion (first contact portion) and a remaining sheet detection portion (second contact portion) on the flag by using a configuration in which a convex portion is provided in the middle of the flag instead of the bent portion 52b, or by using a configuration in which the flag is bifurcated.

[0069] 11, the fixing nip N is located on the sheet conveying path of the belt conveying device 30 disposed upstream of the fixing device 9. A virtual line extending from It is preferable to arrange the fixing nip portion N so that the downstream side of the fixing nip portion N is inclined at an angle θ relative to L3 so as to move away from the flag 51A. Traces When extended to the exit of the fixing nip N, the exit of the fixing nip N is longer than the entrance of the fixing nip N. Virtual Line The sheet conveying direction in the fixing nip N is changed so as to move away from L3. Virtual Line It is preferable to tilt the flag 51A with respect to L3. As a result, the sheet remaining in the fixing nip N is held in the fixing nip N with the flag 51A tilted downward, making it easier to detect the remaining sheet by the flag 51A. It is preferable to set θ in the range of 0 to 40 degrees.

[0070] <Other embodiments> In the above embodiment, the movable member detected by the loop detection sensor S1 and the residual sheet detection sensor S2 is a swingable member, namely, a flag 51. However, the movable member may be configured to slide by contacting a sheet in addition to swinging. For example, the movable member may be arranged to be movable in the vertical direction in Figures 3 and 4, and the loop detection sensor S1 and the residual sheet detection sensor S2 may be arranged above and below. In this case, if the loop detection sensor S1 is arranged below the residual sheet detection sensor S2, both loop detection and residual sheet detection can be performed by a single movable member, as in the case shown in Figures 3 and 4.

[0071] In the above embodiment, an intermediate transfer method has been described in which a toner image is transferred from the intermediate transfer belt 20 as an image carrier to a sheet, but the present invention can also be applied to a direct transfer method in which a toner image is transferred directly from a photosensitive drum to a sheet. In this case, the photosensitive drum corresponds to the image carrier. [Explanation of symbols]

[0072] P... Sheet N Fixing nip (nip) S···Operation Panel S1: Loop detection sensor (first sensor) S2: Residual sheet detection sensor (second sensor) T2: Secondary transfer unit (transfer unit) 9. Fixing device 11. Secondary transfer outer roller (transfer member) 20. Intermediate transfer belt (image carrier) 30 Belt conveying device (conveying section) 50, 50A... Sheet detection unit 50a Rotation axis (swing center) 51, 51A... Flag (moving member, swinging member) 52... Contact part 52a...Tip (second contact part) 52b...Bending part (first contact part) 53 First flag section 54 Second flag section 90... Enclosure 91 Fixing film (rotating body) 92 Pressure roller (rotating body) 100 Image forming device 100A Image forming device main body 110 Control unit

Claims

1. a transfer section that transfers a toner image onto a recording material; a first rotor that is rotatable and has a heat source; a second rotating body that forms a nip portion by contacting an outer peripheral surface of the first rotating body, and that applies heat and pressure to a recording material while sandwiching and conveying the recording material together with the first rotating body to fix the toner image; a control unit that controls the rotation speed of the second rotating body; a contact member disposed downstream of the transfer portion and upstream of the nip portion in the recording material conveying direction, the contact member having a contact portion capable of coming into contact with the recording material, the contact member being movably provided at a first position where the contact portion enters a conveying path along which the recording material is conveyed, a second position where the contact portion retracts from the first position as the recording material comes into contact with the contact portion when the recording material passes through the conveying path, and a third position; a first detection unit that detects whether the contact member is located at the second position; a second detection unit that detects whether the contact member is located at the third position, the third position is a position where, when the contact member is located at the second position and a force is applied to the contact portion from the recording material passing through the conveyance path, the contact portion moves to a position farther away from the first position than the second position, When the second detection unit does not detect that the position of the contact member is at the third position during conveyance of the recording material, the control unit sets the rotation speed of the second rotating body to a first speed, and when the second detection unit detects that the position of the contact member is at the third position, the control unit sets the rotation speed of the second rotating body to a second speed that is faster than the first speed. An image forming apparatus characterized by:

2. When the recording material forms a loop, the second detection unit detects that the contact member is located at the third position during image formation.

2. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

3. a fixing device having the first rotating body and the second rotating body, The contact member, the first detection unit, and the second detection unit are detachable from the image forming apparatus main body together with the fixing device.

3. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

4. an entrance guide that guides the recording material conveyed from the transfer portion to an entrance of the nip portion; The contact member is provided on the inlet guide.

4. The image forming apparatus according to claim 1, wherein the image forming apparatus comprises: a first fixing member;

5. the contact member has a tip end and a swing center, and is swingable around the swing center; The tip end is located closer to the nip portion than the swing center.

5. The image forming apparatus according to claim 1, wherein the image forming apparatus comprises: a first fixing member;

6. The contact member has a first contact portion for detecting that the recording material has formed a loop, and a second contact portion for detecting that the recording material remains in the nip portion.

6. The image forming apparatus according to claim 5,

7. When the contact member is located at the first position, the second contact portion is closer to the nip portion than the first contact portion.

7. The image forming apparatus according to claim 6, wherein the image forming apparatus is a recording medium.

8. the contact member has a bent portion bent such that the tip end portion is bent in a direction extending from the swing center, the bent portion is the first contact portion, The tip portion is the second contact portion.

8. The image forming apparatus according to claim 7,

9. a conveying section that conveys a recording material between the transfer section and the nip section, When a line extending from a conveyance path of the recording material conveyed by the conveying section is taken as a virtual line, the direction in which the recording material is conveyed at the nip portion is inclined with respect to the virtual line so that the exit of the nip portion is farther from the virtual line than the entrance of the nip portion.

9. The image forming apparatus according to claim 1, wherein the image forming apparatus comprises: a first fixing member;

10. The contact member is given a rotational force by a rotation spring in a direction opposite to the direction in which the force is given from the recording material.

10. The image forming apparatus according to claim 1, wherein the image forming apparatus comprises: a first fixing member;

11. The contact member is disposed so as to intersect with the inlet guide.

5. The image forming apparatus according to claim 4.

12. When the contact member is located at the first position, the tip portion is located above the nip portion in a direction perpendicular to the conveying direction of the recording material.

6. The image forming apparatus according to claim 5,

Images