Image forming apparatus

Abstract

To provide an image forming apparatus that can convey a recording medium subjected to skew correction to a fixing nip to prevent the occurrence of an abnormal image without reducing productivity.SOLUTION: An image forming apparatus comprises: an image carrier 115; a transfer roller 114 that forms a transfer nip N1; a fixing roller 122; a pressure roller 123 that forms a fixing nip N3; conveyance means 126 that conveys a recording medium P between the transfer nip N1 and the fixing nip N3; and skew correction means 125 that is provided to be contactable and separable with respect to the conveyance means 126 and is in contact with the conveyance means 126 to form a skew correction nip N2. The conveyance means 126 includes a conveyance belt 131 that is stretched over a plurality of rollers, and a suction device 132 that causes the recording medium P to be adsorbed onto a surface of the conveyance belt 131. After conveying the recording medium P toward the skew correction nip N2, the image forming apparatus causes the recording medium P subjected to skew correction to be adsorbed onto the conveyance belt and conveys the recording medium P to the fixing nip N3 in an attitude after the skew correction.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus. [Background technology]

[0002] Conventionally, when an image forming device such as a copier or printer prints a solid image (all solid, solid patch), wrinkle-like white areas (also called "worms") can occur from the center to the rear end of the paper (recording material, recording medium) in the printing direction.

[0003] This "worm" phenomenon occurs when the paper enters the fixing device with a sagging deviation or twist in the transport path within the device and is fixed. In other words, areas of the paper with a large sagging deviation or twist come into contact with the fixing member, causing unfixed toner on the paper to scatter, resulting in white spots.

[0004] The deflection deviation and twist of the paper are thought to be caused by the skew of the paper. To address this problem, a technique is known in which the leading edge of a sheet tilted relative to the sheet transport direction is abutted against an abutting member or a nip portion of a roller pair to correct the skew (for example, see Patent Document 1).

[0005] Patent Document 1 discloses an image forming apparatus having a control means for correcting the skew of the recording material in the fixing device, and then causing the fixing device to fix the image. It also describes that the skew of the recording material is corrected by stopping the rotation of the heating roller while urging the recording material downstream, and then abutting the recording material against the leading edge of the nip portion. Summary of the Invention [Problem to be solved by the invention]

[0006] When performing skew correction on the paper, it is important that fixing is performed in the skewed-corrected posture without causing skew again after the correction. As in the apparatus of Patent Document 1, it is considered that by performing the skew correction operation in the fixing device, it is possible to prevent image defects related to fixing such as abnormal images like the above-mentioned earthworms and wrinkles.

[0007] However, in the configuration of Patent Document 1, it is necessary to stop the rotation of the heating roller in order to perform skew correction, and there is a problem that productivity decreases. In addition, by driving the heating roller after skew correction to resume fixing, there is a possibility of occurrence of poor fixing due to insufficient heating. Similarly, when the paper passes in a state where the rotation of the roller is not stable immediately after driving, there is also a possibility of generating a jitter image (density unevenness).

[0008] Therefore, an object of the present invention is to provide an image forming apparatus that can transport a skew-corrected recording medium to a fixing nip without reducing productivity and suppress the occurrence of abnormal images.

Means for Solving the Problems

[0009] In order to solve the above problems, an image forming apparatus of the present invention includes an image carrier, a transfer roller that forms a transfer nip in contact with the image carrier, a fixing roller, a pressure roller that forms a fixing nip in contact with the fixing roller, a conveying unit that conveys a recording medium between the transfer nip and the fixing nip, and a skew correction unit that is provided so as to be able to contact and separate from the conveying unit and forms a skew correction nip in contact with the conveying unit. The conveying unit includes a conveying belt stretched over a plurality of rollers and a suction device that sucks the recording medium onto the surface of the conveying belt. After conveying the recording medium toward the skew correction nip, the skew-corrected recording medium is sucked onto the conveying belt, and the recording medium is conveyed to the fixing nip in the posture after skew correction. Then, the suction device starts suction after skew correction of the recording medium, and stops suction after the leading end in the conveyance direction of the recording medium has passed through the fixing nip. It is characterized by this.

Effects of the Invention

[0010] According to the present invention, it is possible to provide an image forming apparatus that can convey a skew-corrected recording medium to a fixing nip without reducing productivity and suppress the occurrence of abnormal images.

Brief Description of the Drawings

[0011]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Embodiments for Carrying Out the Invention

[0012] Hereinafter, the image forming apparatus of the present invention will be described with reference to the drawings. Note that the present invention is not limited to the embodiments shown below, and can be changed within the scope that those skilled in the art can conceive, such as other embodiments, additions, modifications, deletions, etc., and is included in the scope of the present invention as long as the functions and effects of the present invention are achieved in any aspect.

[0013] FIG. 1 is a schematic configuration diagram showing a laser printer as an example of an image forming apparatus to which the present invention is applied. The image forming apparatus shown in FIG. 1 (hereinafter also referred to as "printer") has a function as a copier that scans and reads a document, digitizes it, and copies it onto a recording medium. It also has a function of a so-called printer that prints image information handled by a computer or the like onto a recording medium.

[0014] In FIG. 1, the printer includes an image forming unit and a fixing device, and a paper feeding unit is arranged below and a reading unit is arranged above. Also, on the left side in the figure, a paper discharge tray 106 for discharging and storing the recording medium on which an image is formed is provided.

[0015] On the paper feeding tray 104 of the paper feeding unit, a recording medium (for example, paper, etc.) P1 is placed. A manual feed tray 105 is also provided, and the recording medium P2 can be stacked on the manual feed tray 105. The recording medium P1 passes through the separation pad 112 and is sent out from the paper feeding tray 104 by the rotation of the paper feeding roller 111, and is conveyed to the registration roller 113. Similarly, the recording medium P2 passes through the separation pad 109 and is sent out from the manual feed tray 105 by the rotation of the paper feeding roller 108, and is conveyed to the registration roller 113. In the figure, the recording medium after being conveyed to the registration roller 113 is represented by the symbol P3.

[0016] In the reading unit for reading a document, a scanner 103 for reading a document (not shown) placed on the contact glass 102 is provided. The image information is read as an image signal and subjected to image processing. Based on the image-processed signal, an electrostatic latent image is formed on the surface of the image carrier (hereinafter also referred to as "photoconductor") 115.

[0017] Around the photoconductor 115 constituting the image forming unit, a charging roller 116 for performing a charging process on the surface of the photoconductor 115, a developing roller 120 for visualizing the electrostatic latent image formed by exposing the surface of the photoconductor 115, and a cleaning means (cleaning blade) 117 for removing and recovering the residual toner on the photoconductor 115 are arranged. While the photoreceptor 115 is being rotationally driven counterclockwise, after being uniformly charged by the charging roller 116, it is irradiated with light whose intensity has changed based on image information by the exposure unit, and an electrostatic latent image is formed on the surface. The electrostatic latent image on the photoreceptor 115 is developed using toner as a developing substance by the developing roller 120, and a toner image as a visible image is formed on the photoreceptor 115. The toner is supplied from the toner bottle unit 137. The toner image is transferred to the recording medium P3 conveyed by the resist roller 113 at a position facing the transfer roller 114 as transfer conveyance means.

[0018] The recording medium P3 onto which the toner image has been transferred is fed into the fixing device 124 on the downstream side of its conveyance path. This fixing device 124 includes a fixing roller 122 and a pressure roller 123, and fixes the toner image on the recording medium. The recording medium on which the toner image has been fixed is discharged and stored in the discharge tray 106 by the discharge roller 136.

[0019] Photoelectric sensors (138, 139) are provided inside the apparatus on the upstream side of the resist roller 113 and on the downstream side of the fixing device 124, respectively. Also, a toner density sensor 121 and screws (119a, 119b) are provided on the upstream side of the resist roller 113.

[0020] Figs. 2 to 4 are diagrams schematically showing the conveyance path of the recording medium from the image forming unit (image carrier 115 and transfer roller 114) to the fixing device 124. As shown in Figs. 2 to 4, conveyance means 126 and skew correction means (skew correction roller) 125 are provided on the conveyance path. Also, a first sensor 127 for detecting the presence or absence of the recording medium P between the transfer roller 114 and the skew correction means 125 and a second sensor 128 for detecting the presence or absence of the recording medium P on the outlet side of the fixing nip N3 formed by the fixing roller 122 and the pressure roller 123 are provided on the conveyance path.

[0021] The image forming apparatus according to this embodiment includes an image carrier 115, a transfer roller 114 that contacts the image carrier 115 to form a transfer nip N1, a fixing roller 122, a pressure roller 123 that contacts the fixing roller 122 to form a fixing nip N3, a conveying unit 126 that conveys a recording medium P between the transfer nip N1 and the fixing nip N3, and a skew correction unit 125 that is provided so as to be able to contact and separate from the conveying unit 126 and forms a skew correction nip N2 by contacting the conveying unit 126. The conveying unit 126 includes a conveying belt 131 stretched over a plurality of rollers (a driving roller 129 and a driven roller 130), and a suction device 132 that sucks the recording medium P onto the surface of the conveying belt 131. After conveying the recording medium P toward the skew correction nip N2, the skew-corrected recording medium P is sucked onto the conveying belt 131, and the recording medium P is conveyed to the fixing nip N3 in the posture after skew correction.

[0022] According to the image forming apparatus of this embodiment, even when an unfixed toner image is on the recording medium P, the skew (skew) of the recording medium P can be corrected without disturbing the toner image, and the recording medium P can be conveyed to the fixing nip N3 by suction conveyance while maintaining the posture after skew correction. Since the driving of the rotating members related to the fixing device and conveyance is not stopped during skew correction, the occurrence of abnormal images due to skew can be suppressed without reducing productivity.

[0023] The skew correction unit 125 is preferably a roller member having at least a surface made of a fluororesin material. Examples of the fluororesin material include PFA (polytetrafluoroethylene). By using a roller member made of PFA, it is possible to prevent dirt due to adhesion and accumulation of scattered toner and prevent the formed image from being soiled.

[0024] The skew correction unit 125 is pressed against the driving roller 129 of the conveying unit 126 via the conveying belt 131 to form the skew correction nip N2. The leading end in the conveying direction of the conveyed recording medium P abuts against the skew correction nip N2, so that the leading end side is aligned and the skew is eliminated. The suction device 132 starts suction after the skew correction of the recording medium P, and stops suction after the leading end of the recording medium P in the conveyance direction passes through the fixing nip N3.

[0025] When the recording medium P is subjected to skew correction, the non-printing area (margin portion) at the leading end in the conveyance direction abuts on the skew correction nip N2. Thereby, skew correction can be performed without affecting the unfixed toner image on the recording medium P. The size of the non-printing area can be appropriately selected according to the purpose. For example, it can be an area with a width of 2 mm from the leading end.

[0026] Also, as shown in FIG. 3, there is a space S between the transfer roller 114 and the conveying means 126, and the deflection of the recording medium P caused by being blocked by the skew correction nip N2 during conveyance is accommodated in the space S. Thereby, skew correction can be performed without stopping the transfer roller 114, and productivity is not reduced.

[0027] Further, the image forming apparatus according to the present embodiment includes a first sensor 127 that detects the presence or absence of the recording medium P between the transfer roller 114 and the skew correction means 125, and a second sensor 128 that detects the presence or absence of the recording medium P on the outlet side of the fixing nip N3. Furthermore, it includes control means for performing operation control according to the detection results of the first sensor 127 and the second sensor 128. The control means controls the approach and separation of the skew correction means 125 with respect to the conveying means 126 and the on / off of the suction device 132 according to the detection results of the first sensor 127 and the second sensor 128. By appropriately controlling the approach and separation of the skew correction means 125 with respect to the conveying means 126 according to the detection results of the sensors, it is possible to prevent the occurrence of jams in the conveyance path of the recording medium and the occurrence of abnormal images caused by contamination of the toner image or the like.

[0028] When the first sensor 127 detects the recording medium P conveyed from the transfer nip N1, the skew correction means 125 presses against the drive roller 129 of the conveying means 126 via the conveying belt 131 and stops for a predetermined time (0.5 seconds in this embodiment) in a state where the skew correction nip N2 is formed. During that time, since the conveyance of the recording medium P continues, as shown in FIG. 3, deflection occurs and the leading end of the recording medium P is abutted against the skew correction nip N2 to be aligned, and the skew of the recording medium P is eliminated. After the elapse of the predetermined time, that is, after the skew correction is completed, the suction device 132 operates to suck the recording medium P and adsorb it in that posture on the conveying belt 131. The conveying means 126 guides the recording medium P to the fixing inlet guide 141 and conveys it to the fixing nip N2 while suppressing the flutter on the leading end side.

[0029] FIG. 5 is a schematic diagram showing an example of the conveying means 126. The conveying means 126 includes a conveying belt 131 stretched between a drive roller 129 and a driven roller 130, and a suction device 132 inside the conveying belt 131. The suction device 132 includes a fan 132a that generates an intake air for adsorbing the recording device P, and shutter members (a fixed shutter 133 and a movable shutter 134) for adjusting the intake air volume, and the intake air volume can be changed according to the thickness of the recording medium P.

[0030] Note that the conveying belt 131 only needs to be configured to adsorb the recording medium P by the intake air from the suction device 132. For example, a mode made of a breathable material, a mode made of a non-breathable material with ventilation holes formed, etc. can be mentioned.

[0031] The intake air volume can be adjusted by the movable shutter 134 that can change the air volume. In the suction device 132 shown in FIG. 5, when the movable shaft 135 and the cam 140 rotate, the movable shutter 134 opens and closes by a predetermined amount according to the rotation angle. The rotation amount of the cam 140 is appropriately set corresponding to the thickness (paper thickness) of the recording medium P. The paper thickness is input and set by the user using, for example, an operation panel provided in the apparatus.

[0032] FIG. 6 is a table showing the relationship among the paper thickness of the recording medium, the conveying force, and the opening / closing operation amount of the shutter member. When "plain paper 2" is set on the operation panel as the recording medium P to be conveyed, as shown in FIG. 6, the cam 140 rotates 90° clockwise, and the movable shutter 134 moves so as to close by 10 mm from the fully open state. As a result, the generated intake air volume becomes 10 m / sec. The conveying force obtained as a result of the above adjustment is about 0.24 N, and the recording medium P of "plain paper 2" can be conveyed while being firmly held. In this way, by making it possible to adjust the intake air volume and the conveying force according to the paper thickness, it is also possible to prevent the disturbance of the unfixed toner image due to insufficient suction.

[0033] FIG. 7 is a flowchart showing an example of the skew correction process by the image forming apparatus according to the above-described embodiment. First, the paper thickness of the recording medium to be used is set (step S001), and the shutter member (movable shutter 134) of the suction device 132 opens and closes according to the set paper thickness, and the intake air volume and the conveying force for sucking the recording medium P are adjusted (step S002). The input of the paper thickness is performed from an external input means (such as an operation panel). The relationship between the set paper thickness, the opening / closing operation amount of the shutter, the intake air volume, and the conveying force is as shown in the example of FIG. 6.

[0034] Image formation is started (step S003), and the recording medium P is conveyed (step S004). The conveyance path in the apparatus is as schematically shown in FIGS. 1 and 2 to 4.

[0035] A first sensor 127 disposed between the transfer roller 114 and the skew correction means 125 detects the presence or absence of the recording medium P (step S005). When the presence of the recording medium P is detected, the skew correction means 125 is brought into contact with the conveyor belt 131 of the conveying means 126 (in pressure contact with the driving roller 129 via the conveyor belt 131), thereby forming a skew correction nip N2 (step S006).

[0036] The skew correction nip N2 is maintained by the skew correction means 125 stopping for a predetermined time, during which the skew correction of the recording medium P is performed. It is determined whether the skew correction is completed, that is, whether a predetermined time (for example, 0.5 seconds) for stopping the skew correction means 125 has elapsed (step S007). After the elapse of the predetermined time, the suction of the suction device 132 is turned on to start sucking the recording medium (step S008).

[0037] Then, the skew correction means 125 is separated from the conveyor belt 131 (step S009) to enable the conveyance of the recording medium P. The recording medium P is conveyed to the fixing nip N3 while being adsorbed on the surface of the conveyor belt 131, that is, while maintaining the posture after skew correction (step S010).

[0038] Fixing of the toner image on the recording medium P in a state where the skew has been eliminated is performed in the fixing device 124 (step S011), and the recording medium P is discharged from the outlet of the fixing nip N3. When the recording medium P is detected by a second sensor 128 provided on the outlet side of the fixing nip N3 (step S012), the suction of the suction device 132 is turned off.

[0039] After the fixing is completed in the fixing device 124, the recording medium P is conveyed to the outside of the device and discharged (step S014).

[0040] As described above, according to the image forming apparatus of the present embodiment, it is possible to convey the skew-corrected recording medium to the fixing nip while maintaining the posture after correction without reducing productivity, and to suppress the occurrence of abnormal images.

Explanation of Symbols

[0041] 114 Transfer roller 115 Image carrier (photoreceptor) 120 Developing roller 122 Fusing roller 123 Pressing roller 124 Fusing device 125 Skew correction means (skew correction roller) 126 Conveying means 127 First sensor 128 Second sensor 129 Driving roller 130 Driven roller 131 Conveyor belt 132 Suction device 132a Fan 133 Shutter member (fixed shutter) 134 Shutter member (movable shutter) 141 Fusing inlet guide N1 Transfer nip N2 Skew correction nip N3 Fusing nip P Recording medium (paper)

Prior Art Documents

Patent Documents

[0042]

Patent Document 1

Claims

1. An image carrier, a transfer roller that contacts the image carrier to form a transfer nip, a fixing roller, a pressure roller that contacts the fixing roller to form a fixing nip, transport means for transporting a recording medium between the transfer nip and the fixing nip, skew correction means provided so as to be separable from and contact the transport means to form a skew correction nip, and comprising: the transport means includes a transport belt stretched over a plurality of rollers and a suction device for sucking the recording medium onto the surface of the transport belt, after transporting the recording medium toward the skew correction nip, the skew-corrected recording medium is sucked onto the transport belt, and the recording medium is transported to the fixing nip in the posture after skew correction, the suction device starts suction after skew correction of the recording medium, and stops suction after the leading end in the transport direction of the recording medium has passed through the fixing nip, an image forming apparatus characterized by this.

2. The image forming apparatus according to claim 1, wherein, during skew correction, a non-printing area at the leading end portion in the transport direction of the recording medium contacts the skew correction nip.

3. There is a space between the transfer roller and the transport means, The image forming apparatus according to claim 1 or 2, characterized in that the deflection of the recording medium caused by being blocked by the skew correction nip during transportation is accommodated in the space.

4. A first sensor for detecting the presence or absence of the recording medium between the transfer roller and the skew correction means, A second sensor for detecting the presence or absence of the recording medium on the outlet side of the fixing nip, Control means for performing operation control according to the detection results of the first sensor and the second sensor, and The control means controls the contact and separation of the skew correction means with respect to the transport means and the on / off of the suction device according to the detection results of the first sensor and the second sensor, the image forming apparatus according to any one of claims 1 to 3.

5. The transport means includes the suction device inside the transport belt, The suction device includes a fan that generates an intake air for sucking the recording medium and a shutter member that adjusts the intake air volume, and the intake air volume can be changed according to the thickness of the recording medium, the image forming apparatus according to any one of claims 1 to 4.

6. The image forming apparatus according to any one of claims 1 to 5, wherein the skew correction means is at least a roller member having a surface made of a fluororesin material.

7. An image carrier, a transfer roller that contacts the image carrier to form a transfer nip, a fixing roller, a pressure roller that contacts the fixing roller to form a fixing nip, transport means for transporting a recording medium between the transfer nip and the fixing nip, skew correction means that is provided so as to be able to contact and separate from the transport means and that contacts the transport means to form a skew correction nip, wherein the transport means includes a transport belt stretched over a plurality of rollers and a suction device that adsorbs the recording medium to the surface of the transport belt, after transporting the recording medium toward the skew correction nip, adsorbing the skew-corrected recording medium onto the transport belt, and transporting the recording medium to the fixing nip in the posture after skew correction, there is a space between the transfer roller and the transport means, An image forming apparatus, characterized in that the bending of the recording medium caused by being blocked by the skew correction nip during transportation is accommodated in the space.

8. An image carrier, a transfer roller that contacts the image carrier to form a transfer nip, a fixing roller, a pressure roller that contacts the fixing roller to form a fixing nip, transport means for transporting a recording medium between the transfer nip and the fixing nip, skew correction means that is provided so as to be able to contact and separate from the transport means and that contacts the transport means to form a skew correction nip, wherein the transport means includes a transport belt stretched over a plurality of rollers and a suction device that adsorbs the recording medium to the surface of the transport belt, after transporting the recording medium toward the skew correction nip, adsorbing the skew-corrected recording medium onto the transport belt, and transporting the recording medium to the fixing nip in the posture after skew correction, a first sensor that detects the presence or absence of the recording medium between the transfer roller and the skew correction means, a second sensor that detects the presence or absence of the recording medium on the outlet side of the fixing nip, control means for performing operation control according to the detection results of the first sensor and the second sensor, The image forming apparatus, characterized in that the control means controls the contact and separation of the skew correction means with respect to the transport means and the on / off of the suction device according to the detection results of the first sensor and the second sensor.

Images