Patent Application
20250130519
This disclosure relates to an image forming apparatus that forms an image on a sheet.
According to Japanese Patent Laid-Open No. 2005-181507, a loop detection sensor for determining whether or not a loop that a transfer portion and a fixing roller form on a sheet has reached a predetermined amount is proposed. The loop detection sensor includes a mechanical flag that pivots when coming into contact with the sheet, and a photointerrupter that can transition between a light-blocking state and a light-transmitting state when the mechanical flag pivots.
In addition, according to Japanese Patent Laid-Open No. 2007-041188, an image forming apparatus in which two light transmissive type loop detection sensors are disposed between a secondary transfer portion and a fixing unit is proposed. The image forming apparatus includes an actuator that pivots upon contact with the sheet, and the actuator has two projections that can each block optical axes of the two loop detection sensors. These two loop detection sensors output an OFF signal when the optical axis is blocked by the projection and an ON signal when the optical axis is unobstructed. This image forming apparatus can detect four types of the loop amounts based on the combination of the signals from these two loop detection sensors.
Incidentally, the sheet used in the image forming apparatus includes various types such as thin paper, standard paper, and thick paper. Then, an appropriate loop amount is known to vary according to the type of the sheet. However, in Japanese Patent Laid-Open No. 2005-181507, since the loop detection sensor can detect only a single type of the loop amount, it is difficult to control the loop amount (bending amount) in accordance with the various types of the sheets.
In addition, the image forming apparatus described in Japanese Patent Laid-Open No. 2007-041188 necessitates positioning each of the two loop detection sensors and the actuator equipped with the two projections to prevent detection errors, and, thereby, the configuration is complicated.
According to one aspect of the present invention, an image forming apparatus includes a transfer portion configured to convey a sheet while nipping the sheet and configured to transfer a toner image onto the sheet, a fixing unit configured to convey the sheet while nipping the sheet and configured to fix the toner image transferred by the transfer portion on the sheet, a detection unit arranged between the transfer portion and the fixing unit in a sheet conveyance direction and configured to detect a bending amount of the sheet nipped by the transfer portion and the fixing unit, and a control unit configured to control a conveyance speed of the sheet conveyed by the fixing unit based on a detection result of the detection unit. The detection unit includes a pivot portion configured to pivot when pressed by the sheet nipped by the transfer portion and the fixing unit, and a rotary encoder configured to output a pulse signal in accordance with a pivot amount of the pivot portion.
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
The image forming unit 140 is an electrophotographic unit of an intermediate transfer tandem method in which image forming stations Y, M, C, and Bk forming toner images of four colors are arranged along an intermediate transfer belt 145.
The sheet S is stored in a cassette 111 disposed in a lower part of the apparatus body 101, and is fed by the sheet feed unit 110 one sheet at a time. For the sheet feed unit 110, for example, a unit including a feed roller that feeds the sheet, and a separation roller that is arranged to come into contact with the feed roller to apply a friction force on the sheet S to separate other sheets S from the sheet S is used. To be noted, as the sheet S, serving as the recoding material, diverse sheets with varying sizes and materials can be used, and the sheet S includes paper such as standard paper and thick paper, a plastic film, cloth, a surface treated sheet material such as coated paper, specially shaped sheet material such as an envelope and index paper, and the like.
The sheet S fed from the sheet feed unit 110 is corrected for skew by a skew correction unit 120, and is conveyed toward a transfer nip 130 in a timing that synchronizes with a toner image formation process by the image forming unit 140. The transfer nip 130, serving as a transfer portion, is a nip portion formed between a secondary transfer inner roller 131 and a secondary transfer outer roller 132, which substantially face each other across an intermediate transfer belt 145 and conveys the sheet S while nipping the sheet S.
In parallel with the conveyance process of the sheet S to the transfer nip 130 described above, the image forming unit 140 performs the toner image formation process. Each of the image formation stations Y, M, C, and Bk of the image forming unit 140 includes a photosensitive drum 141 that is a drum shaped image bearing member (electrophotographic photosensitive member), a charge unit such as a charge roller, and a developing unit 143, serving as a developing unit. In addition, the image forming unit 140 includes an exposing unit 142 arranged below the four photosensitive drums 141. In the toner image formation process, the charge unit uniformly charges a surface of the photosensitive drum 141, and the exposing unit 142 exposes the photosensitive drum 141 based on a signal of image information to be formed and writes an electrostatic latent image on the surface of the photosensitive drum 141. This electrostatic latent image is developed by toner supplied from the developing unit 143, and becomes a monochromatic toner image. Thereby, the toner images of four colors i.e., yellow, magenta, cyan, and black are formed on the surfaces of the four photosensitive drums 141.
The intermediate transfer belt 145 is rotatably driven in a counter-clockwise direction in
The sheet S that has passed through the transfer nip 130 is conveyed to the fixing unit 150. The fixing unit 150 includes a fixing roller 155 that incorporates a heater, and a pressing roller 156 that comes into contact with the fixing roller 155 with a predetermined pressure force. The fixing roller 155 is driven by a drive source such as a motor, not shown, and the pressing roller 156 is rotatably driven by the fixing roller 155. While nipping and conveying the sheet S at a fixing nip formed by the fixing and pressing rollers 155 and 156, the fixing unit 150 applies heat and pressure to the toner image on the sheet S. Thereby the toner melts, and, after passing through the fixing nip, is secured to produce the image fixed on the sheet S.
The sheet S that has passed through the fixing unit 150 is guided by a first guide member 151 to either a path toward a first sheet discharge roller pair 160 or a path toward a second sheet discharge roller pair 161. In a case of performing the image formation on both sides of the sheet S, the sheet S on whose first surface the image has been formed is guided toward the second sheet discharge roller pair 161 by the first guide member 151, and is conveyed toward the outside of the apparatus by the second sheet discharge roller pair 161. When a trailing edge of the sheet S in a conveyance direction has passed through a second guide member 152, the second sheet discharge roller 161 reverses the conveyance direction of the sheet S, and sends the sheet S to a duplex conveyance path 180. During a reverse operation by the second sheet discharge roller pair 161, a part of the sheet S protruding outside of the apparatus body 101 is supported by a second sheet discharge tray 171. After the skew correction and a timing adjustment, by passing through the transfer nip 130 and the fixing unit 150, the image is formed on a second surface of the sheet S that has again reached the skew correction unit 120 via the duplex conveyance path 180.
In a case of discharging the sheet S, the sheet S sent from the fixing unit 150 is guided to the first sheet discharge roller pair 160 by the first guide member 151, and is discharged outside of the apparatus body 101 by the first sheet discharge roller pair 160. A first sheet discharge tray 170 is disposed on the top of the apparatus body 101, and the sheet S discharged by the first sheet discharge roller pair 160 is supported on the first sheet discharge tray 170. Upper surfaces of the first and second sheet discharge trays 170 and 171 are inclined upward toward downstream sides in the sheet conveyance direction. The sheet S supported on the first or second sheet discharge tray 170 or 171 slides upstream in the sheet conveyance direction by its own weight following an inclination of the first or second sheet discharge tray 170 or 171. Alignment surfaces extending in the vertical direction are disposed on upstream sides of the first and second sheet discharge trays 170 and 171 in a sheet discharge direction. When the trailing edge of the sheet S that slides along the inclination of the first or second sheet discharge tray 170 or 171 abuts against the alignment surface, a position of a sheet bundle supported on the first or second sheet discharge tray 170 or 171 is aligned.
Incidentally, the image forming apparatus 100 includes the image reading apparatus 102 mounted on the top of the apparatus body 101. The image reading apparatus 102 includes a platen glass on which a document is placed, and an image sensor that reads an image of the document via the platen glass. In addition, the image reading apparatus 102 includes an auto document feeder for feeding the document set on a document tray one sheet at a time and reading the image by the image sensor. The image forming apparatus 100 of this embodiment utilizes a configuration of a so-called in-drum discharge type, in which an in-drum sheet discharge space 190 for the sheet S is arranged between the image forming unit 140 and the image reading apparatus 102 in the vertical direction. In comparison with a configuration in which the sheet discharge space is arranged on a side of the apparatus body 101 by disposing the first sheet discharge tray 170 on the side of the apparatus body 101, the configuration of the in-drum discharge type offers an advantage that, for example, it is possible to reduce an area occupied by the image forming apparatus 100 when viewed from the above.
In addition, the image forming unit 140 described above is an example of an image forming unit, and, for example, it is acceptable to use an electrophotographic unit of a direct transfer method that directly transfers the toner image formed on the photosensitive drums onto the sheet without using an intermediate transfer member.
Next, a detection unit 200 arranged between the transfer and fixing nips 130 and 157 in the sheet conveyance direction D1 and a configuration around the detection unit 200 will be described.
As illustrated in
The conveyance guide 210, serving as a guide member, is constituted by a first guide portion 210a, a second guide portion 210b, and a third guide portion 210c. These first, second, and third guide portions 210a, 210b, and 210c may be formed either integrally or separately with respect to each other. The first guide portion 210a supports a plurality of driven rollers 250 that are rotatably driven by coming into sliding contact with the non-image surface of the sheet S. As illustrated in
The conveyance guide 210 does not linearly guide the sheet S between the transfer and fixing nips 130 and 157, and, as illustrated by a dashed line in
As illustrated in
The detection unit 200 is arranged substantially in a central position between the transfer and fixing nips 130 and 157 in the sheet conveyance direction D1, and can accurately detect the bending amount of the sheet S. In addition, since the detection unit 200 is arranged in the central portion in the loop formation space SP in the width direction, the detection unit 200 can detect the bending amount of the sheet ranging from the smallest to the largest size that the image forming apparatus 100 can use.
As illustrated in
The first flag spring 202, serving as a first urging member, is constituted by, for example, a torsion coil spring, and a coil portion of the first flag spring 202 is supported by the first pivot shaft 203. Then, the first end portion extending in one direction from the coil portion of the first flag spring 202 is secured to the spring supporting portion 201c, and a second end portion extending in the other direction from the coil portion is secured to a fixing member of the apparatus body 101. By such a first flag spring 202, the first flag 201 is urged in a F1 direction, serving as a first pivot direction, around the first pivot shaft 203 as a center.
As illustrated in
As illustrated in
As illustrated in
In a case where a force in the F1 direction applied to the first flag 201 by the sheet S is designated as F31, when the detection unit transitions to the detection state, the condition F20<F30+F31 is satisfied. Then, as illustrated is
The first and second flags 201 and 205 stop when an urging force F11 by the first flag spring 202, an urging force F21 by the second flag spring 251, and the force F31 by the sheet S satisfy the condition F21=F11+F31 at the contact point T. Positions where the first and second flags 201 and 205 stop after they each have pivoted from the standby positions are designated as the detection positions.
As described above, the second flag 205 pivots from the standby position to the detection position in synchronization with the pivot of the first flag 201 upon being pressed by the sheet S. These first and second flags 201 and 205 constitute a pivot portion 240 that pivots upon being pressed by the sheet S. Then, the sensor 207 can detect a pivot amount of the second flag 205 from the standby position to the detection position. For example, the sensor 207 is constituted from a photointerrupter including a light emitting element and a light receiving element, and the rotary encoder 260 of a photoelectric type is constituted by the sensor 207 and the detected portion 205b formed in the second flag 205. The light emitting element of the photointerrupter is constituted from, for example, a light emitting diode, and the light receiving element is constituted from, for example, a phototransistor.
In a case where the rotary encoder 260 is a transmissive type encoder, the detected portion 205b includes a plurality of slits that allow light emitted from the light emitting element to pass through. In a case where the rotary encoder 260 is a reflection type encoder, the detected portion 205b includes a plurality of concave-convex structures or slits that can either reflect or not reflect the light emitted from the light emitting element. The light receiving element of the sensor 207 outputs a current corresponding to an amount of received light, and a waveform forming circuit within the rotary encoder 260 converts a waveform of the current into a pulse signal, which is then output as a voltage signal. In other words, the rotary encoder 260 reads the number of the plurality of concave-convex structures or slits corresponding to a pivot amount of the pivot portion 240, and outputs the pulse signal.
As described above, since the rotary encoder 260 outputs the pulse signal according to the pivot amount of the second flag 205 that pivots in conjunction with the first flag 201, the detection unit 200 can detect the bending amount of the sheet. To be noted, the resolution of the rotary encoder 260 can be set arbitrarily, and the rotary encoder 260 of the detection unit 200 can detect at least equal to or more than three loop amounts of the sheet S.
Next, the bending amount control (loop amount control) of the sheet S by a control unit 300 will be described.
In this embodiment, the conveyance speed of the sheet S by the fixing nip 157 is set to be slightly slower than a conveyance speed of the sheet S by the transfer nip 130. Therefore, the sheet S conveyed by the transfer nip 130 is conveyed to gradually bend after reaching the fixing nip 157. This is indicated in a first region X1 in
Then, in a case where the control unit 300 determines that, based on the detection result of the detection unit 200, the bending amount of the sheet S has reached a bending amount (L1) suitable for the thin paper, as illustrated in a second region Y1 in
As described above, based on the detection result of the detection unit 200, the control unit 300 controls the fixing unit 150 such that the bending amount, which is set according to a type of the sheet S, is formed on the sheet S for at least predetermined duration. In
To be noted, the thin paper is a sheet whose grammage is, for example, 52 to 59 grams per square meter (g/m2), the standard paper is a sheet whose grammage is, for example, 64 to 105 g/m2, and the thick paper is a sheet whose grammage is, for example, 106 to 300 g/m2.
Incidentally, if the intermediate transfer belt 145 receives an external force from the sheet S at the transfer nip 130 when primarily transferring the image from the photosensitive drum 141 onto the intermediate transfer belt 145, there is a risk that a position of the toner image transferred from the photosensitive drum 141 onto the intermediate transfer belt 145 may be misaligned. Because of this, sometimes, image defects caused by color misregistration occur in a full color toner image which is completed by superimposing the toner images of four colors. Therefore, it is preferable that the external force from the sheet S, which is nipped by the transfer and fixing nips 130 and 157, is not exerted onto the intermediate transfer belt 145.
In addition, if a posture of the sheet S is unstable at a position upstream of the fixing nip 157 in the sheet conveyance direction D1, wrinkles sometimes occur in the sheet S during the passage of the sheet S through the fixing nip 157. In addition, when the sheet S nipped by the transfer and fixing nips 130 and 157 enters a tensioned state, the unfixed image on the sheet S may sometimes become distorted when the trailing edge of the sheet S passes through roller pairs located upstream of the transfer nip 130 in the sheet conveyance direction D1. To prevent such image defects and wrinkles in the sheet described above, there is an appropriate bending amount according to such as the type, size, and stiffness of the sheet S.
For example, generally, a stiffer sheet produces a greater reaction force when bent, and increases the external force exerted onto the intermediate transfer belt 145 from the sheet S. Therefore, in this embodiment, it is possible to perform the bending amount control to achieve such that, by respectively setting to target the values L1, L2, and L3 for the thin paper, standard paper, and thick paper as the bending amount, the bending amount is appropriate in accordance with the type of the sheet. That is, in a case of conveying the sheet S of a first stiffness, the control unit 300 controls the conveyance speed of the sheet S by the fixing nip 157 such that the bending amount of the sheet S becomes a first bending amount. In addition, in a case of conveying the sheet S of a second stiffness that is lower than the first stiffness, the control unit 300 controls the conveyance speed of the sheet S by the fixing nip 157 such that the bending amount of the sheet S becomes a second bending amount, which is larger than the first bending amount.
Thereby, even when conveying various types of sheets, it is possible to suppress the image defects and the wrinkles in the sheet. Then, the reason why it is possible to control the bending amount of sheet S to target different values according to the type of the sheet S is because the rotary encoder 260 can output the pulse signal corresponding to the pivot amount of the second flag 205 and can detect the bending amount of the sheet S in real-time and with high accuracy.
To be noted, while, in this embodiment, as described above, the target bending amount is set at three levels of L1, L2, and L3, it is not limited to this. For example, it is acceptable to set equal to or more than four levels of the bending amount according to the type, size, and stiffness of the sheet.
Here, using
As illustrated in
The flag 305 is urged in the arrow C direction by a flag spring, not shown, and is positioned at the standby position by abutting against a stopper, not shown. That is, the flag 305 is always attempting to return to the standby position by a predetermined urging force applied by the flag spring. This predetermined urging force applied by the flag spring becomes resistance with respect to the sheet S that presses the flag 305.
In particular, since, in a section between the transfer and fixing nips 130 and 157, the conveyance guide 210 is disposed only on the non-image surface side, there is a risk that, depending on the stiffness of the sheet S, a force to push the flag 305 may be insufficient and it may not be possible to detect the bending amount of the sheet S. Especially, there is a risk that the sheet, such as the thin paper, whose stiffness is relatively low, may not be able to push the flag 305 from the standby position while resisting the urging force of the flag spring, and detection errors by the detection unit 400 may occur.
With this configuration, the sheet S that presses the first flag 201 can apply pressure to the first flag 201 with a minimal amount of force. That is, the force F31 received by the first flag 201 from the sheet S, which is required to pivot the first flag 201 from the standby position in the F1 direction is sufficiently small. In other words, a resistance force that the sheet S, which comes into contact with the first flag 201, receives from the first flag 201 when pressing the first flag 201 is small, and, even in a case of the low stiffness sheet, such as the thin paper, can reliably press the first flag 201. Therefore, it is possible to reduce the detection errors by the detection unit 200.
As described above, in this embodiment, since the detection unit 200 that includes the rotary encoder 260 detects the bending amount of the sheet S at the plurality of levels, with a simple configuration, it is possible to control the bending amount in accordance with the various types of the sheets. In addition, since the rotary encoder 260 is configured to be relatively small in size, it is possible to improve the freedom of disposition.
In addition, since the first flag 201 is urged by the first flag spring 202 in the same direction as the direction in which the first flag 201 pivots when pressed by the sheet S, the sheet S can press the first flag 201 from the standby position with the minimal force. Therefore, for example, even if the sheet S is the thin paper having low stiffness, it is possible to reduce the detection errors by the detection unit 200, and it is possible to satisfactorily perform the bending amount control.
Further, since the first and second flags 201 and 205 are urged to come into contact with each other by the urging forces of the first and second flag springs 202 and 251, these first and second flags 201 and 205 are always in contact with each other. Therefore, the pivot of the first flag 201 is immediately transmitted to the second flag 205, and, by detecting the pivot amount of the second flag 205, the sensor 207 can accurately detect the bending amount of the sheet S.
To be noted, while, in the image forming apparatus of this embodiment, a conveyance path from the sheet feed unit 110 to the first and second sheet discharge roller pairs 160 and 161 extends along the vertical direction, it is not limited to this. For example, this disclosure can be applied to an image forming apparatus in which at least part of a conveyance path conveys the sheet S in the horizontal direction.
In addition, while, in this embodiment, the fixing unit 150 is constituted by the fixing roller 155 and the pressing roller 156, it is not limited to this. For example, instead of the fixing roller 155, it is acceptable to apply an endless belt or a film that incorporates a heater, or is acceptable to apply a belt that possesses a heat generation layer heated by electromagnetic induction.
In addition, while the detection unit 200 includes two flags, namely the first and second flags 201 and 205, it is acceptable to include equal to or more than three flags. Further, as illustrated in the comparative example in
In addition, while, in this embodiment, the stopper 204 is arranged to abut against the first flag 201, it is not limited to this. For example, the stopper 204 may be arranged to abut against the second flag 205. That is, it is acceptable if the stopper 204 positions the first and second flags 201 and 205 at their respective standby positions by abutting against either one of the first and second flags 201 and 205. In addition, instead of the stopper 204 illustrated in
In addition, if the urging forces of the first and second flag springs 202 and 251 are balanced in their natural states and the first and second flags 201 and 205 are retained at the standby positions, the stopper 204 can be omitted.
In addition, while, in this embodiment, when pressed by the first flag 201 that pivots in the arrow B direction (F1 direction), the second flag 205 pivots in the arrow C direction that is opposite to the arrow B direction (F1 direction), it is not limited to this. For example, when pressed by the first flag 201 that pivots in the arrow B direction (F1 direction), the second flag 205 may pivot in a direction that is the same as the arrow B direction (F1 direction). In this case, the second flag spring 251 urges the second flag 205 in the arrow C direction.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Application No.2023-181412, filed Oct. 20, 2023, which is hereby incorporated by reference herein in its entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2023-181412 | Oct 2023 | JP | national |
