Patent Application
20190302657
The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile device and the like that adopts an electrophotographic system or an electrostatic recording system.
Hitherto, an image forming apparatus of an electrophotographic system is known that adopts a method where toner image formed on an image bearing member such as a photosensitive drum is primarily transferred to an intermediate transfer member, and thereafter, the primarily transferred toner image is secondarily transferred to a sheet serving as a recording medium. This type of image forming apparatus uses an intermediate transfer belt as an intermediate transfer member, and toner image is transferred to the sheet at a transfer nip portion formed between the intermediate transfer belt and a transfer roller. In this type of image forming apparatus, a problem is known where impact occurs when the sheet conveyed to the intermediate transfer belt or the transfer nip portion enters and passes the same, and image is disturbed by the impact and quality of the product is deteriorated. Various proposals have been made as techniques to reduce such impact by moving a guide member that guides the sheet to the transfer nip portion.
An image forming apparatus is known, as disclosed in Japanese Patent Application Laid-Open Publication No. 2012-185454, in which a pair of guide members for guiding a sheet to a transfer nip portion is arranged in an opposite manner and one of the guide members, i.e., swing guide member, arranged on an intermediate transfer belt side is designed to move in swinging motion. According to this image forming apparatus, when a leading edge of a sheet enters the transfer nip portion, the swing guide member is positioned in a direction oriented along the intermediate transfer belt to suppress impact that occurs when the leading edge of the sheet abuts against the intermediate transfer belt. Further, when a trailing edge of the exists the swing guide member, the swing guide member is positioned so as to push the trailing edge of the sheet outward from the intermediate transfer belt side to prevent the trailing edge of the sheet from bouncing on the intermediate transfer belt when being released from the swing guide member.
Further, an image forming apparatus is known, as disclosed in Japanese Patent Application Laid-Open Publication No. 2015-31897, in which two guide members for guiding a sheet to a transfer nip portion is arranged side by side in a conveyance direction, each of the two guide members formed movably and swingably. According to this image forming apparatus, respective guide members are moved and swung in response to sheet type to form an appropriate conveyance path for each sheet type. For example, if a sheet having a high stiffness is conveyed, the respective guide members are moved upstream and swung to reduce the angle formed by the guide members, thereby forming a conveyance path that allows the sheet to move as straight as possible. If a sheet having a low stiffness is conveyed, the respective guide members are moved downstream and swung to increase the angle formed by the guide members, thereby forming a conveyance path that allows the sheet to be conveyed toward the transfer nip portion at a vicinity of the transfer nip portion.
In order to minimize the impact that occurs when the leading edge of a sheet enters the transfer nip portion, it is preferable that the sheet enters the transfer nip portion at an angle that is as small as possible with respect to a nip line of the transfer nip portion. The nip line of the transfer nip portion refers to a line that passes the transfer nip portion and that is perpendicular to a straight line connecting respective centers of a roller pair that forms the transfer nip portion. In other words, it is preferable to have the sheet enter the transfer nip portion from a vicinity of the intermediate transfer belt on an upstream side of the transfer nip portion in the sheet conveyance direction. However, since a conveyance mechanism that conveys the sheet to the transfer nip portion must be arranged so as not to interfere with the intermediate transfer belt, the conveyance path from the conveyance mechanism to the transfer nip portion is inevitably curved. If there is an extreme curved portion in the conveyance path, jamming of sheets becomes a problem. Especially if the sheet is a thin sheet having low stiffness, sheet jamming tends to occur at the curved portion. Therefore, if a curved portion is formed on the conveyance path with the aim to suppress shock that occurs when a thick paper enters the transfer nip portion, risk of conveyance failure of thin paper increases. Therefore, it was difficult to realize both suppression of shock during entry of thick paper to the transfer portion and suppression of conveyance failure of thin paper.
However, according to the image forming apparatus disclosed in above-described Japanese Patent Application Laid-Open Publication No. 2012-185454, the swing guide member is positioned along the intermediate transfer belt when the leading edge of the sheet enters the transfer nip portion, regardless of the stiffness of the sheet. Therefore, the conveyance path is curved greatly even when thin paper is conveyed, which may cause conveyance failure of the thin paper. Further, according to the image forming apparatus disclosed in above-described Japanese Patent Application Laid-Open Publication No. 2015-31897, a conveyance path close to a straight line is formed to minimize conveyance resistance when conveying a sheet having a high stiffness, such as thick paper. Therefore, the direction of entry of the sheet to the transfer nip portion may deviate greatly from the direction along the intermediate transfer belt and inclination of the direction of entry of the sheet to the transfer nip portion with respect to the intermediate transfer belt may be increased, by which the impact generated when the leading edge of the sheet enters the transfer nip portion may become greater. Furthermore, the conveyance path is curved if a sheet such as thin paper having a low stiffness is conveyed. However, a sheet having a low stiffness such as thin paper tends to be bent at the curved portion and may cause sheet jamming. It was difficult to realize both suppression of occurrence of impact at the transfer nip portion when conveying thick paper and suppression of sheet jamming when conveying thin paper.
The present invention provides an image forming apparatus capable of realizing both suppression of occurrence of impact at the transfer nip portion when conveying a sheet such as thick paper having a high stiffness and suppression of sheet jamming when conveying a sheet such as thin paper having a low stiffness.
According to one aspect of the present invention, an image forming apparatus includes a rotatable belt member configured to bear a toner image, a first stretch roller configured to stretch the belt member, a second stretch roller configured to stretch the belt member at a position adjacent to the first stretch roller on an upstream side in a direction of rotation of the belt member, a rotary member that is in contact with an outer circumferential surface of the belt member, the rotary member configured to nip the belt member with the first stretch roller and form a transfer nip portion where toner image is transferred from the belt member to a recording material while conveying the recording material between the belt member and the rotary member, a conveyance roller that is arranged upstream of the transfer nip portion in a conveyance direction of the recording material, the conveyance roller configured to form a conveyance nip portion that conveys the recording material and delivers the recording material to the transfer nip portion, a pressing member positioned upstream of the transfer nip portion in the conveyance direction and downstream of the conveyance nip portion in the conveyance direction, the pressing member configured to move between a first position and a second position, the second position at which the pressing member projects to a conveyance path of the recording material than the first position and presses a first surface of the recording material opposed to a second surface of the recording material facing the belt member, a driving source configured to drive the pressing member, and a control unit configured to control the driving source. The control unit controls the driving source such that the pressing member is positioned at the first position if a basis weight of the recording material conveyed to the transfer nip portion is equal to or smaller than a predetermined value and the pressing member is positioned at the second position if the basis weight of the recording material conveyed to the transfer nip portion is greater than the predetermined value.
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
Now, a first embodiment of the present invention will be described in detail with reference to
As illustrated in
The image forming unit 40 includes a drum cartridge 50, a developing apparatus 20, a toner container 42, a laser scanner 43, an intermediate transfer unit 44, a secondary transfer portion 30 and a fixing unit 46. The image forming unit 40 can form an image on a sheet fed from a registration roller pair 4 of the sheet conveyance unit based on image information. The image forming apparatus 1 according to the present embodiment corresponds to full-color image, and includes drum cartridges 50y, 50m, 50c and 50k corresponding to yellow (y), magenta (m), cyan (c) and black (k), which have the same configuration and are disposed independently. Similarly, toner containers 42y, 42m, 42c and 42k also correspond to yellow (y), magenta (m), cyan (c) and black (k), which have the same configuration and are disposed independently. Therefore, identifiers corresponding to the respective colors are added to the end of reference numbers for the respective components of four colors in
The toner container 42 is a cylindrical bottle in which toner is stored, for example, and arranged above each drum cartridge 50 via a toner hopper. The laser scanner 43 exposes a surface of a photosensitive drum 51 charged by a charge roller 52 and forms an electrostatic latent image on the surface of the photosensitive drum 51.
The drum cartridge 50 is a photosensitive unit formed as a unit and attached detachably to the apparatus body 10. The drum cartridge 50 includes a photosensitive drum, i.e., image bearing member, 51 capable of bearing a toner image and rotating, a charge roller 52 and a cleaning blade not shown. The photosensitive drum 51, the charge roller 52, the developing apparatus 20 and a developing sleeve 24 are also provided independently and having the same configuration for each of the four colors of yellow (y), magenta (m), cyan (c) and black (k).
The photosensitive drum 51 includes a photosensitive layer formed to have negative charged polarity on a surface of an outer circumference of an aluminum cylinder, and the photosensitive drum 51 rotates at a predetermined processing speed, i.e., peripheral speed. The charge roller 52 contacts the surface of the photosensitive drum 51 and charges the surface of the photosensitive drum 51 to a uniform negative dark potential, for example. After charging the surface of the photosensitive drum 51, an electrostatic latent image is formed based on image information using the laser scanner 43. The photosensitive drum 51 bears the electrostatic latent image being formed and rotates, and the image is developed using toner by the developing sleeve 24 of the developing apparatus 20. The developed toner image is primarily transferred to an intermediate transfer belt 44b described later. The surface of the photosensitive drum 51 after primary transfer is destaticized by a pre-exposure unit not shown.
The intermediate transfer unit 44 is arranged above the drum cartridges 50y, 50m, 50c and 50k. The intermediate transfer unit 44 includes a plurality of rollers such as a drive roller 44a, a driven roller, serving as a second stretch roller, 44d, and a plurality of primary transfer rollers 44y, 44m, 44c and 44k, and an intermediate transfer belt, serving as a belt member, 44b that is wound around the rollers and capable of rotating. The driven roller 44d stretches the intermediate transfer belt 44b at a position adjacent to a secondary transfer inner roller 32 described later on an upstream side in a rotation direction of the intermediate transfer belt 44b. In the present embodiment, the secondary transfer inner roller 32 is arranged at a position projected larger than the driven roller 44d with respect to a direction in which the secondary transfer inner roller 32 presses the intermediate transfer belt 44b horizontally.
The portion stretched between the secondary transfer inner roller 32 and the driven roller 44d of the intermediate transfer belt 44b is referred to as a flat portion, i.e., stretched portion, 44f. The primary transfer rollers 44y, 44m, 44c and 44k are arranged opposed to the photosensitive drums 51y, 51m, 51c and 51k, respectively, abutting against the intermediate transfer belt 44b and primarily transferring toner images formed on the photosensitive drums 51 to the intermediate transfer belt 44b. Primary transfer bias is applied to the intermediate transfer belt 44b, by which toner images formed on the photosensitive drums 51 are primarily transferred at the primary transfer portion. The intermediate transfer belt 44b is capable of bearing toner image and rotating.
The intermediate transfer belt 44b is an endless belt having a three-layer structure composed, from an inner side, of a resin layer, an elastic layer and a surface layer. The resin layer has a thickness of 70 to 100 μm and is composed of resin material such as polyimide and polycarbonate. The elastic layer has a thickness of 200 to 250 μm and is composed of elastic material such as urethane rubber and chloroprene rubber. The surface layer has a thickness of 5 to 10 μm and is composed of material that reduces adhesion force of toner to the surface of the intermediate transfer belt 44b and facilitates transfer of toner to the sheet at a transfer nip portion 33 of the secondary transfer portion 30. Specifically, one type of resin material, such as polyurethane, polyester or epoxy resin, can be used. In another example, a material that reduces surface energy and improves lubricity, such as powder or particles of fluororesin, dispersed in elastic material, such as elastic rubber or elastomer, can be used.
The secondary transfer portion 30 includes a secondary transfer outer roller, serving as roller, 31 and a secondary transfer inner roller, serving as first stretch roller, 32. The secondary transfer portion 30 secondarily transfers the toner image on the intermediate transfer belt 44b to a sheet by having secondary transfer bias applied at the transfer nip portion 33 formed by the secondary transfer outer roller 31 and the intermediate transfer belt 44b. The secondary transfer outer roller 31 forms the transfer nip portion 33 that conveys the sheet with the intermediate transfer belt 44b and where toner image is transferred from the intermediate transfer belt 44b to the sheet. The secondary transfer outer roller 31 constitutes an elastic layer formed of rubber or sponge for forming the transfer nip portion 33. The secondary transfer inner roller 32 is provided on an inner circumferential side of the intermediate transfer belt 44b and holds the intermediate transfer belt 44b in a stretched manner with the secondary transfer outer roller 31. In the present embodiment, by having DC voltage of positive polarity applied to the secondary transfer outer roller 31 from a power supply not shown, the secondary transfer portion 30 forms a transfer electric field of toner image as secondary transfer bias between the secondary transfer outer roller 31 and the secondary transfer inner roller 32 being connected to ground potential. The direction of discharge of the sheet conveyed from the transfer nip portion 33 is a nip line direction Dn of the intermediate transfer belt 44b and the secondary transfer outer roller 31 (refer to
The fixing unit 46 includes a fixing roller 46a and a pressure roller 46b, and by nipping and conveying a sheet between the fixing roller 46a and the pressure roller 46b, the toner image transferred to the sheet is heated, pressed and fixed to the sheet.
As illustrated in
Next, an image forming operation according the image forming apparatus 1 having the above-described configuration will be described. In a state where the image forming operation is started, the photosensitive drum 51 rotates and the surface thereof is charged by a charge roller 52. Then, laser beam is irradiated to the photosensitive drum 51 from the laser scanner 43 based on image information, and electrostatic latent image is formed on the surface of the photosensitive drum 51. The electrostatic latent image is developed by toner by the developing apparatus 20 and visualized as toner image, and the toner image is transferred to the intermediate transfer belt 44b.
Meanwhile, in parallel with the toner image forming operation, the sheet conveyance unit is activated and the sheet is conveyed to the secondary transfer portion 30 by the registration roller pair 4 at a matched timing with the toner image on the intermediate transfer belt 44b. Toner image is transferred from the intermediate transfer belt 44b to the sheet and the sheet is conveyed to the fixing unit 46, where unfixed toner image is heated and pressed and fixed to the surface of the sheet, and then the sheet is discharged from the apparatus body 10.
Next, a configuration for conveying the sheet to the secondary transfer portion 30 will be described in detail with reference to
As illustrated in
A sheet guide mechanism 6 that guides sheet S1 or S2 conveyed from the registration roller pair 4 to the secondary transfer portion 30 is provided between the registration roller pair 4 and the secondary transfer portion 30. The sheet guide mechanism 6 includes an inner guide portion 60 and an outer guide portion 70 that are arranged opposed to one another. The inner guide portion 60 is disposed at a side close to the intermediate transfer belt 44b than the outer guide portion 70. The outer guide portion 70 is provided on a side more distant from the intermediate transfer belt 44b than the inner guide portion 60.
The inner guide portion 60 includes an inner upstream guide 61 and an inner downstream guide, i.e., guide member, 62 arranged continuously along the sheet conveyance path. The inner upstream guide 61 is approximately plate shaped and arranged upstream of the inner downstream guide 62 in the sheet conveyance direction Ds. The inner downstream guide 62 is arranged downstream of the inner upstream guide 61 in the sheet conveyance direction Ds, and a surface of the inner downstream guide 62 opposite to the conveyance surface is arranged to face the intermediate transfer belt 44b. The intermediate transfer belt 44b has a flat, planar portion 44f stretched across the secondary transfer inner roller 32 and the driven roller 44d. The inner downstream guide 62 is approximately plate shaped and arranged along the planar portion 44f of the intermediate transfer belt 44b, and the inner downstream guide 62 is arranged in an inclined manner with respect to the planar portion 44f such that the transfer nip portion 33 side approximates the planar portion 44f. The inner downstream guide 62 is arranged so that a downstream edge portion in the sheet conveyance direction Ds contacts the planar portion 44f arranged upstream of the transfer nip portion 33 before reaching the transfer nip portion 33.
The inner downstream guide 62 guides the sheets S1 and S2 in a second direction D2 by having the sheet S1 or S2 conveyed by the registration roller pair 4 abut against the inner downstream guide 62 at an upstream side of the transfer nip portion 33 in the sheet conveyance direction Ds. The second direction D2 is a direction where the angle formed between the nip line direction Dn is a second angle θ2, and the second angle θ2 is set smaller than the first angle θ1 of the first direction D1 in which the sheets S1 and S2 are conveyed by the registration roller pair 4. That is, the inner downstream guide 62 is arranged upstream of the transfer nip portion 33 in the sheet conveyance direction Ds and downstream of the conveyance nip portion 4n in the sheet conveyance direction Ds. By having a transfer surface Sa of the sheet S on which toner is transferred abut against the inner downstream guide 62, the inner downstream guide 62 guides the sheet S to the planar portion 44f of the intermediate transfer belt 44b. In other words, the inner downstream guide 62 guides the sheet S to the intermediate transfer belt 44b by having the transfer surface Sa of the sheet S which opposes to the intermediate transfer belt 44b abut against the inner downstream guide 62.
The outer guide portion 70 includes an outer upstream guide 71 and an outer downstream guide, serving as pressing member, 72 which are arranged continuously along the sheet conveyance path. The outer upstream guide 71 is approximately plate shaped and arranged upstream of the outer downstream guide 72 in the sheet conveyance direction Ds, opposing to the inner upstream guide 61. The inner upstream guide 61, the inner downstream guide 62 and the outer upstream guide 71, excluding the outer downstream guide 72, are arranged in a fixed manner with respect to the apparatus body 10.
The sheet guide mechanism 6 includes, at an intermediate portion in the sheet conveyance direction Ds, a curved portion 6a that changes paths from the conveyance direction of the registration roller pair 4, i.e., first direction D1, to the conveyance direction of the secondary transfer portion 30, i.e., second direction D2, that is, a direction along the planar portion 44f of the intermediate transfer belt 44b. The curved portion 6a is positioned in the vicinity of a joint between the inner upstream guide 61 and the inner downstream guide 62, and a joint between the outer upstream guide 71 and the outer downstream guide 72.
In the present embodiment, when viewed from a rotational axis direction of the registration roller pair 4 as illustrated in
The outer downstream guide 72 serving as the pressing member is approximately plate shaped and arranged downstream of the outer upstream guide 71 in the sheet conveyance direction Ds. The outer downstream guide 72 is arranged upstream of the transfer nip portion 33 in the sheet conveyance direction Ds and downstream of the conveyance nip portion 4n in the sheet conveyance direction Ds and arranged to oppose to at least a portion of the inner downstream guide 62. The outer downstream guide 72 is a swing member configured swingably about a swing shaft 73 disposed along the rotational axis direction of each roller of the registration roller pair 4, and the outer downstream guide 72 is urged by an eccentric cam 75 via a tension coil spring 74 composed for example of a torsion coil spring and retained in a state abutted against the eccentric cam 75. The outer downstream guide 72 includes a pressure edge portion 72a that is curved to an outer side in the sheet conveyance path at an upstream side in the sheet conveyance direction Ds.
The outer downstream guide 72 is rotatable about the swing shaft 73 between a first position and a second position that is closer to the inner downstream guide 62 than the first position by the rotation of the eccentric cam 75. That is, the outer downstream guide 72 is capable of moving to the first position and the second position by swinging motion. The outer downstream guide 72 is positioned closer to the driven roller 44d when it is positioned at the second position than at the first position. That is, in a state where the outer downstream guide 72 is positioned at the first position, the distance from the driven roller 44d is a first distance, and in a state where it is positioned at the second position, the distance from the driven roller 44d is a second distance that is shorter than the first distance. The eccentric cam 75 is driven to rotate by the drive motor 15 such as a stepping motor (refer to
As illustrated in
As illustrated in
If basis weight of the sheet conveyed to the transfer nip portion 33 is equal to or smaller than a predetermined value, the control unit 3 controls the driving source so that the position of the outer downstream guide 72 is positioned at the first position. If basis weight of the sheet conveyed to the transfer nip portion 33 is greater than the predetermined value, the control unit 3 controls the driving source so that the outer downstream guide 72 is positioned at the second position. Further according to the present embodiment, if basis weight of the sheet conveyed to the transfer nip portion 33 is greater than the predetermined value, the control unit 3 controls the driving source so that the outer downstream guide 72 is positioned at the first position before the downstream edge portion St of the sheet reaches the outer downstream guide 72. Further, if basis weight of the sheet conveyed to the transfer nip portion 33 is greater than the predetermined value, the control unit 3 controls the driving source so that the outer downstream guide 72 is positioned at the second position after the downstream edge portion St of the sheet has reached the outer downstream guide 72 and before the downstream edge portion St reaches the transfer nip portion 33. Also, if basis weight of the sheet conveyed to the transfer nip portion 33 is greater than the predetermined value, the control unit 3 controls the driving source so that the outer downstream guide 72 is positioned at the second position after the downstream edge portion St of the sheet has passed an opposing position which the outer downstream guide 72 opposes and before the downstream edge portion St reaches the transfer nip portion 33.
Next, the operation of the image forming apparatus 1 described above will be described in detail. When type of sheet or thickness of sheet is entered through an operation unit or the like, the control unit 3 determines whether the sheet on which image is being formed is a thick paper having a basis weight greater than a predetermined value and executes a thick paper mode based on the determination. If basis weight of the sheet S2 conveyed through the registration roller pair 4 is greater than the predetermined value, the control unit 3 executes the thick paper mode. If basis weight of the sheet S1 conveyed through the registration roller pair 4 is equal to or smaller than the predetermined value, the control unit 3 positions the outer downstream guide 72 at the first position without executing the thick paper mode.
When the thick paper mode is executed, the image forming apparatus 1 operates as follows. At first, conveyance of the sheet S2 is started by driving the registration roller pair 4. The control unit 3 detects that the downstream edge portion St of the sheet S2 being conveyed has passed the sheet detection sensor 13. After elapse of a predetermined time after detection, the control unit 3 activates the drive motor 15 and moves the outer downstream guide 72 from the first position to the second position. Start time of the predetermined time is set to when the downstream edge portion St of the sheet S2 passes the sheet detection sensor 13. The predetermined time is a period of time that starts at the start time and ends when the drive motor 15 is activated to move the outer downstream guide 72 to the second position after the downstream edge portion St of the sheet S2 has abutted against the inner downstream guide 62 and before the downstream edge portion St reaches the transfer nip portion 33. The predetermined time is stored in the ROM 35 and set according to conveyance speed. That is, in the thick paper mode, before the sheet S2 conveyed by the registration roller pair 4 abuts against the inner downstream guide 62, the control unit 3 sets the outer downstream guide 72 to the first position. Further, in the thick paper mode, after the sheet S2 conveyed by the registration roller pair 4 abuts against the inner downstream guide 62 and before the sheet S2 reaches the transfer nip portion 33, the control unit 3 moves the outer downstream guide 72 from the first position to the second position. Thereby, speed reduction, i.e., impact, caused by the downstream edge portion St of the sheet S2 entering the transfer nip portion 33 is reduced and conveyance load is minimized. Thereby, when a high stiffness sheet such as thick paper is conveyed, suppression of impact caused at the intermediate transfer belt 44b or the transfer nip portion 33 and suppression of conveyance resistance can both be realized.
Further, after the sheet S2 passes the transfer nip portion 33 and before the conveyance of a subsequent sheet is started by the operation of the registration roller pair 4, the control unit 3 activates the drive motor 15 and moves the outer downstream guide 72 from the second position to the first position. If forming of image to sheets is performed continuously, the control unit 3 repeats the above-described sequence of operations.
In order to verify the effect of the image forming apparatus 1 of the above-described embodiment, structure analysis simulation by finite element method was performed. As illustrated in
In
Further, as illustrated in
Next, speed fluctuation of the intermediate transfer belt 44b will be described. Speed fluctuation of the intermediate transfer belt 44b is acquired using the simulation model illustrated in
It is assumed that speed reduction of the intermediate transfer belt 44b occurs by to the following process. At first, when the downstream edge portion St of the sheet enters the transfer nip portion 33, a task of deforming and moving the secondary transfer outer roller 31 according to the thickness of the sheet occurs. Further, there may be a case where the direction of entry of the sheet to the transfer nip portion 33 is angled with respect to a straight line direction, i.e., nip line direction Dn, which is a direction perpendicular to the straight line having connected the centers of the drive roller 44a and the secondary transfer outer roller 31. In this case, when the downstream edge portion St enters the transfer nip portion 33, a task of curving the sheet toward the nip line direction Dn occurs. According to these tasks, drive load of the intermediate transfer belt 44b occurs. According to the increase of load, speed reduction of driving source of the drive roller 44a that drives the intermediate transfer belt 44b occurs.
Meanwhile, according to the image forming apparatus 1 of the present embodiment, occurrence of drive load of the intermediate transfer belt 44b can be suppressed by executing the thick paper mode. The mechanism will be described in detail with reference to
As illustrated in
As illustrated in
Next, the loads caused by conveyance of sheets S1 and S2 are compared between a case where the above-described thick paper mode is executed and the outer downstream guide 72 is moved and a case where the outer downstream guide 72 is fixed to the second position.
As described, according to the image forming apparatus 1 of the present embodiment, the control unit 3 executes the thick paper mode if the basis weight of the sheet S conveyed by the registration roller pair 4 is greater than a predetermined value. In the thick paper mode, the control unit 3 sets the position of the outer downstream guide 72 to the first position before the sheet S2 conveyed by the registration roller pair 4 abuts against the inner downstream guide 62. That is, the control unit 3 sets the outer downstream guide 72 to the first position before the sheet conveyed by the registration roller pair 4 passes the curved portion 6a, or the outer downstream guide 72, of the conveyance path. Further, the control unit 3 moves the outer downstream guide 72 from the first position to the second position after the conveyed sheet S2 abuts against the inner downstream guide 62 and before the sheet S2 reaches the transfer nip portion 33. In other words, in the thick paper mode, the control unit 3 moves the outer downstream guide 72 from the first position to the second position while the sheet conveyed by the registration roller pair 4 passes the curved portion 6a, or outer downstream guide 72, of the conveyance path and before the sheet reaches the transfer nip portion 33. Thereby, the speed reduction, i.e., impact, caused when the downstream edge portion St of the sheet S2 enters the transfer nip portion 33 can be reduced, and conveyance load can be minimized. Therefore, occurrence of impact and conveyance resistance of the intermediate transfer belt 44b and the transfer nip portion 33 can both be suppressed when conveying high stiffness sheets S2 such as thick paper.
According further to the image forming apparatus 1 of the present embodiment, if the basis weight of the sheet S1 conveyed by the registration roller pair 4 is equal to or smaller than the predetermined value, the control unit 3 sets the position of the outer downstream guide 72 to the first position without executing the thick paper mode. Thereby, in a state where the sheet being conveyed is the sheet S1 having low stiffness, the present embodiment enables to suppress occurrence of sheet jam caused by the outer downstream guide 72 moving to the second position and increasing the curve of the conveyance path. In the sheet S1 having low stiffness, even if the sheet S1 abuts against the intermediate transfer belt 44b at a sharp angle with the outer downstream guide 72 set at the first position, the impact that occurs when the sheet abuts against the intermediate transfer belt 44b is small, such that fluctuation of speed of the intermediate transfer belt 44b rarely occurs.
The image forming apparatus 1 according to the above-described embodiment was described based on a case where the pressing member is the outer downstream guide 72 which is approximately plate shaped and a position of the whole body is displaced to the first position and the second position, but the present invention is not restricted to this example. For example, the pressing member may also be a roller that is displaced to the first position and the second position, as illustrated in
Further, the image forming apparatus 1 of the above-described embodiment was described based on a case where the outer downstream guide 72 is switched between the first position and the second position during conveyance of thick paper, but the present invention is not restricted thereto. For example, in a case where a thick paper having a basis weight that is greater than the predetermined value is conveyed, the outer downstream guide 72 can be constantly fixed to the second position. Meanwhile, if the basis weight of the sheet is equal to or smaller than the predetermined value, the outer downstream guide 72 can be positioned at the first position. That is, a configuration can be adopted where the position of the outer downstream guide 72 is switched according to the basis weight of the sheet.
Next, a second embodiment of the present invention will be described in detail with reference to
In the present embodiment, the sheet guide mechanism 6 includes an inner guide portion 60 and an outer guide portion 70, a part of which are mutually opposed to one another. The inner guide portion 60 includes an inner upstream guide 61 that is arranged at a position opposed to an outer upstream guide 71 of the outer guide portion 70. A secondary transfer inner roller 32 corresponds to a first stretch roller that stretches the intermediate transfer belt 44b. Further, a driven roller 44d corresponds to a second stretch roller that stretches the intermediate transfer belt 44b at a position adjacent to the secondary transfer inner roller 32 on an upstream side in the rotation direction of the intermediate transfer belt 44b. The portion of the intermediate transfer belt 44b stretched between the secondary transfer inner roller 32 and the driven roller 44d is formed as a planar portion, i.e., stretched portion, 44f.
The secondary transfer outer roller, i.e., rotary member, 31 is disposed on the outer circumferential side of the intermediate transfer belt 44b and nips the intermediate transfer belt 44b with the secondary transfer inner roller 32. Further, the secondary transfer outer roller 31 forms a transfer nip portion 33 where toner image is transferred from the intermediate transfer belt 44b to the sheet while conveying the sheet between the intermediate transfer belt 44b. Further, a registration roller pair, i.e., conveyance roller, 4 conveys the sheet toward the planar portion 44f of the intermediate transfer belt 44b upstream of the transfer nip portion 33 in the sheet conveyance direction Ds. In the present embodiment, the registration roller pair 4 conveys the sheet toward a driven roller 44d that stretches the planar portion 44f (refer to
An outer downstream guide, i.e., pressing portion, 72 is arranged to face at least a part of the planar portion 44f, and formed movably between a first position and a second position that is closer to the planar portion 44f than the first position. That is, the outer downstream guide 72 adopts a configuration capable of changing positions by rotation of an eccentric cam 75 between the first position where the curved portion 6a has a shallow curve, as illustrated in
In the thick paper mode, the control unit 3 sets the position of the outer downstream guide 72 to the first position before the sheet conveyed by the registration roller pair 4 abuts against the planar portion 44f. That is, the control unit 3 sets the position of the outer downstream guide 72 to the first position before the sheet conveyed by the registration roller pair 4 passes the curved portion 6a, or outer downstream guide 72, of the conveyance path. Further, the control unit 3 moves the outer downstream guide 72 from the first position to the second position after the sheet conveyed by the registration roller pair 4 abuts against the planar portion 44f and before it reaches the transfer nip portion 33. In other words, in the thick paper mode, the control unit 3 moves the outer downstream guide 72 from the first position to the second position while the sheet conveyed by the registration roller pair 4 passes the curved portion 6a, or outer downstream guide 72, of the conveyance path and before the sheet reaches the transfer nip portion 33.
As illustrated in
During execution of the thick paper mode, as illustrated in
After elapse of a predetermined time after the sheet detection sensor 13 has detected the downstream edge portion St of the sheet S2, as illustrated in
As for the operation of the image forming apparatus 1 of the present embodiment, similar to the first embodiment, the control unit 3 executes the thick paper mode if the basis weight of the sheet S2 conveyed by the registration roller pair 4 is greater than a predetermined value. Further, if the basis weight of the sheet S2 conveyed by the registration roller pair 4 is equal to or smaller than the predetermined value, the control unit 3 sets the position of the outer downstream guide 72 to the first position without executing the thick paper mode.
In the thick paper mode, the control unit 3 sets the outer downstream guide 72 to the first position before the sheet S2 conveyed by the registration roller pair 4 abuts against the planar portion 44f. Further, in the thick paper mode, the control unit 3 moves the outer downstream guide 72 from the first position to the second position after the sheet S2 conveyed by the registration roller pair 4 abuts against the planar portion 44f and before the sheet reaches the transfer nip portion 33. Further, the control unit 3 activates the drive motor 15 and moves the outer downstream guide 72 from the second position to the first position after the sheet S2 has passed the transfer nip portion 33 and before a subsequent sheet S2 is started to be conveyed by driving the registration roller pair 4. In forming images continuously to sheets S2, the control unit 3 repeatedly performs the above-described set of operations. Thereby, the speed reduction, i.e., impact, caused when the downstream edge portion St of the sheet S2 enters the transfer nip portion 33 can be reduced, and conveyance load can be minimized. Therefore, occurrence of impact and conveyance resistance of the intermediate transfer belt 44b and the transfer nip portion 33 can both be suppressed while conveying the high stiffness sheet S2 such as thick paper.
Now, in order to verify the effect of the image forming apparatus 1 of the above-described embodiment, structure analysis simulation by finite element method is performed, similar to the first embodiment. In
Further, as illustrated in
Next, speed fluctuation of the intermediate transfer belt 44b will be described. Speed fluctuation of the intermediate transfer belt 44b is acquired using the simulation model illustrated in
Next, the loads caused by conveyance of sheets S1 and S2 are compared between a case where the above-described thick paper mode is executed and where the thick paper mode is not executed.
Also according to the image forming apparatus 1 of the present embodiment, in the thick paper mode, the control unit 3 sets the position of the outer downstream guide 72 to the first position before the sheet S2 conveyed by the registration roller pair 4 abuts against the planar portion 44f Further, the control unit 3 moves the outer downstream guide 72 from the first position to the second position after the conveyed sheet S2 abuts against the planar portion 44f and before it reaches the transfer nip portion 33. Thereby, the speed reduction, i.e., impact, caused when the downstream edge portion St of the sheet S2 enters the transfer nip portion 33 can be reduced, and conveyance load can be minimized. Therefore, occurrence of impact and conveyance resistance of the intermediate transfer belt 44b and the transfer nip portion 33 can both be suppressed when conveying high stiffness sheets S2 such as thick paper.
According to the image forming apparatus 1 of the present embodiment, the sheet S2 contacts the planar portion 44f before entering the transfer nip portion 33, so that the sheet S2 is arranged further along the intermediate transfer belt 44b and the downstream edge portion St of the sheet enters the nip in a direction close to the nip line direction Dn. Therefore, the present embodiment exerts an effect of further minimizing the speed reduction, i.e., impact, during entry.
Further according to the image forming apparatus 1 of the present embodiment, the registration roller pair 4 conveys the sheet S2 toward the driven roller 44d that stretches the planar portion 44f. Therefore, deflection of the belt that occurs when the sheet S2 abuts against the planar portion 44f can be suppressed, and therefore, speed fluctuation of the intermediate transfer belt 44b can be suppressed. Since the position in which the sheet S2 abuts against the planar portion 44f is separated from the transfer nip portion 33, there is a distance from where the sheet abuts against the planar portion 44f to where the sheet is nipped by the transfer nip portion 33, and the curvature of the sheet S2 is gentle. Therefore, the resistance received from the sheet S2 when nipping the sheet S2 by the transfer nip portion 33 can be reduced, and speed reduction of the intermediate transfer belt 44b can be suppressed.
Next, a third embodiment of the present invention will be described in detail with reference to
The secondary transfer portion 130 includes the secondary transfer inner roller, i.e., first stretch roller, 132 and a secondary transfer belt unit 80. The secondary transfer inner roller 132 abuts against an inner side surface of the intermediate transfer belt 44b. The secondary transfer belt unit 80 includes a secondary transfer outer roller, serving as roller, 131, a conveyance surface formation roller 82, a tension roller 83, a driving roller 84, and a secondary transfer belt, serving as rotary member or second belt member, 85 that is wound around these rollers and rotated. The secondary transfer belt 85 is driven by the driving roller 84 and rotates in the direction of the arrow. A transfer nip portion 133 is formed at an area where the intermediate transfer belt 44b and the secondary transfer belt 85 are pressed by the secondary transfer inner roller 132 and the secondary transfer outer roller 131. That is, the secondary transfer inner roller 132 nips the intermediate transfer belt 44b and the secondary transfer belt 85 with the secondary transfer outer roller 131. The secondary transfer belt unit 80 causes the secondary transfer belt 85 to bear a sheet S2 and pass through the transfer nip portion 133. The use of the secondary transfer belt 85 enables the sheet S2 to be separated easily from the intermediate transfer belt 44b after transfer of toner image at the transfer nip portion 133, and the sheet S2 can be conveyed stably to the fixing unit 46.
A secondary transfer power supply 86 having a variable output current is connected to the secondary transfer outer roller 131 (refer to
A sheet guide mechanism 6 that guides the sheet S2 conveyed from the registration roller pair 4 toward the secondary transfer portion 30 is provided between the registration roller pair 4 and the secondary transfer portion 130. The sheet guide mechanism 6 according to the present embodiment only differs from that of the first embodiment in that the sheet conveyance direction Ds is different, and the components are the same, so that the same reference numbers are assigned to the same components and detailed descriptions thereof are omitted.
Also according to the image forming apparatus 101 of the present embodiment, in the thick paper mode, the control unit 3 positions the outer downstream guide 72 to the first position before the sheet S2 conveyed by the registration roller pair 4 abuts against the inner downstream guide 62. Further, after the conveyed sheet S2 has been abutted against the inner downstream guide 62 and before the sheet S2 reaches the transfer nip portion 133, the control unit 3 moves the outer downstream guide 72 from the first position to the second position. Thereby, the speed reduction, i.e., impact, caused when the downstream edge portion St of the sheet S2 enters the transfer nip portion 133 can be reduced, and conveyance load can be minimized. Therefore, occurrence of impact and conveyance resistance of the intermediate transfer belt 44b and the transfer nip portion 133 can both be suppressed when conveying high stiffness sheets S2 such as thick paper.
Further according to the image forming apparatus 101 of the present embodiment, occurrence of impact at the transfer nip portion 133 formed by the intermediate transfer belt 44b and the secondary transfer belt 85 can be suppressed. Therefore, speed reduction and increase of conveyance load of not only the intermediate transfer belt 44b but also the secondary transfer belt 85 can be suppressed, and occurrence of impact and conveyance resistance can both be suppressed even in the secondary transfer belt 85.
The second embodiment has illustrated a case where the inner downstream guide 62 is not provided, and the third embodiment has illustrated a case where a horizontal path system is adopted in which the sheets are conveyed approximately horizontally in the secondary transfer portion 130, but these embodiments can also be combined.
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. 2018-060696, filed Mar. 27, 2018, which is hereby incorporated by reference herein in its entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2018-060696 | Mar 2018 | JP | national |
