BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to a sheet conveyance apparatus configured to convey a sheet and an image forming apparatus provided with the sheet conveyance apparatus.
Description of the Related Art
Conventionally, an image forming apparatus configured to form an image on a sheet is provided with an openable and closable member so that a sheet conveyance path can be opened when a sheet is jammed. The openable and closable member is openable and closable with respect to a main body of the apparatus, and the openable and closable member is held in a closed position by locking a hook portion to a locking portion. If the hook portion is not securely locked to the locking portion, the image forming apparatus does not operate normally. Therefore, Japanese Patent Application Laid-Open No. 2013-221970 proposes to prevent incomplete locking of the hook portion to the locking portion by restricting a rotation of the hook portion by abutting the hook portion to a restricting member when the openable and closable member is closed. Japanese Patent Application Laid-Open No. 2010-197895 discloses that a locking member fixed to a sliding member which can slide vertically to the openable and closable member can be locked to a locking protrusion. The locking protrusion is provided with a rotary member. When the openable and closable member is closed, the locking member is pushed by the rotary member of the locking protrusion, and the sliding member is lowered smoothly, so that incomplete locking between the locking member and the locking protrusion can be prevented.
Recently, the demand for long paper and thick paper has been increasing. Especially, when long thick paper is jammed in the sheet conveyance apparatus, it is not easy to remove jammed long thick paper from the sheet conveyance apparatus because the long thick paper is hard and large in size. To improve jam clearance performance, it is necessary to increase an open space of the sheet conveyance path. For this purpose, it is necessary to make the openable and closable member larger. Further, in order to prevent incomplete locking of the hook portion of the openable and closable member, it is necessary to increase a rigidity of the openable and closable member. Further, when the sheet conveyance apparatus has a registration roller, a secondary transfer roller or a decurler in addition to a conveyance roller, it is necessary to further increase the rigidity of the openable and closable member of the sheet conveyance apparatus. Therefore, the openable and closable member becomes larger, and a weight of the openable and closable member increases. However, the increase in the size and weight of the openable and closable member greatly increases the user's operating force required when operating the openable and closable member, and reduces the operability of the openable and closable member.
SUMMARY OF THE INVENTION
According to an embodiment of the present invention, a sheet conveyance apparatus comprises: a pair of conveyance rollers having a first conveyance roller and a second conveyance roller and configured to convey a sheet in a sheet conveyance direction; a support member configured to support the first conveyance roller; an openable and closable member configured to support the second conveyance roller and pivotable with respect to the support member so as to make the second conveyance roller contact with and separate from the first conveyance roller; a locking protrusion provided on the support member; and a locking member provided to be pivotable with respect to the openable and closable member and lockable to the locking protrusion so as to hold the openable and closable member in a closed position in which the openable and closable member is closed with respect to the support member so that the second conveyance roller contacts the first conveyance roller, wherein the locking protrusion or a part of the locking protrusion to which the locking member locks is rotatable.
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a cross-sectional view of a printer.
FIG. 2A, FIG. 2B, FIG. 2C, FIG. 2D, and FIG. 2E are explanatory views of a duplex conveyance unit.
FIG. 2F is a view showing a front hook and a rear hook.
FIG. 2G is a view showing a rotation regulating portion.
FIG. 2H is a view showing a bearing roller.
FIG. 3A, FIG. 3B, FIG. 3C, and FIG. 3D are explanatory views of a locking mechanism configured to hold a duplex lower guide in a closed position.
FIG. 4 is a view showing a relationship between an elapsed time and a force applied to a handle.
FIG. 5 is a cross-sectional view of a duplex conveyance unit of a second embodiment.
FIG. 6 is an explanatory view showing a locking mechanism of a second embodiment.
FIG. 7A and FIG. 7B are explanatory views of a decurler.
FIG. 8 is a flowchart showing a control operation of a cam drive motor performed by CPU.
DESCRIPTION OF THE EMBODIMENTS
Hereinafter, an image forming apparatus including a sheet conveying apparatus according to the embodiment will be described with reference to the drawings. It should be noted that dimensions, materials, shapes, relative arrangements, etc. of components described below are not intended to limit the scope of the present invention to those only, unless otherwise specified.
First Embodiment
Image Forming Apparatus
The first embodiment will be described below. FIG. 1 is a cross-sectional view of a printer 1. As an example of an image forming apparatus, the printer 1 is an electrophotographic full-color laser beam printer. The printer 1 has an image forming unit 90 and a discharge accessory 120 as a downstream apparatus of the image forming unit 90. The image forming unit 90 is connected to the discharge accessory 120. The image forming unit 90 forms an image on a sheet as a recording medium and passes the sheet on which the image is formed to an inlet roller pair 121 provided in the discharge accessory 120.
The image forming unit 90 includes a feeding unit 10, a drawing unit 20, a registration unit 30, an image forming section 100, a fixing unit 52, and a branch conveyance unit 60. The image forming unit 90 further includes a decurler unit 110, a reversing conveyance unit 80 serving as a reversing conveyance portion, a duplex conveyance unit 70, and a duplex conveyance unit 71. The drawing unit 20, the registration unit 30, the branch conveyance unit 60, the decurler unit 110, the reversing conveyance unit 80, and the duplex conveyance units 70 and 71 function as a sheet conveyance apparatus configured to convey a sheet.
The image forming section 100 includes four process cartridges 99Y, 99M, 99C, and 99K configured to form toner images of four colors: yellow (Y), magenta (M), cyan (C), and black (K); and exposure devices 93Y, 93M, 93C, and 93K. The four process cartridges 99Y, 99M, 99C, and 99K have the same configuration except that the colors of the toner images to be formed are different. Therefore, the configuration of the process cartridge 99Y and the image formation process by the process cartridge 99Y will be described, and the description of the process cartridges 99M, 99C, and 99K will be omitted. The process cartridge 99Y includes a photosensitive drum 91, a charging roller 96, a developing device 92, and a cleaner 95. The photosensitive drum 91 is constituted by coating an organic photoconductive layer on an outer periphery of an aluminum cylinder, and is rotated counterclockwise by a drive motor (not shown).
The image forming unit 90 is provided with an intermediate transfer belt 40 under the photosensitive drum 91. The intermediate transfer belt 40 is wound around a tension roller 41, a drive roller 42, and a secondary transfer inner roller 43. The intermediate transfer belt 40 is rotated in a rotation direction indicated by the arrow T by the drive roller 42. Primary transfer rollers 45Y, 45M, 45C, and 45K are provided inside the intermediate transfer belt 40. The primary transfer rollers 45Y, 45M, 45C, and 45K are disposed opposite to the photosensitive drums 91 through the intermediate transfer belt 40 to form primary transfer portions T1 between the photosensitive drums 91 and the intermediate transfer belt 40. A secondary transfer outer roller 44 is provided on the outside of the intermediate transfer belt 40. The secondary transfer outer roller 44 is disposed opposite to the secondary transfer inner roller 43 through the intermediate transfer belt 40 to form a secondary transfer portion T2 between the secondary transfer outer roller 44 and the intermediate transfer belt 40.
The fixing unit 52 has a fixing roller pair 54 and a before-fixation guide 53 configured to guide the sheet S to a nip of the fixing roller pair 54. The feeding unit 10 has a lift plate 11 configured to lift and lower while stacking the sheet S thereon, a pickup roller 12 configured to feed the sheet S stacked on the lift plate 11, and a pair of separation rollers 13 configured to separate the fed sheet S one by one.
Next, an image forming operation of the printer 1 configured in this manner will be described. The charging roller 96 uniformly charges the surface of the photosensitive drum 91 rotating in the counterclockwise direction with a predetermined polarity and potential. When an image signal is input from an external device (not shown) such as a personal computer to the exposure device 93Y, a laser beam modulated according to the image signal is emitted from the exposure device 93Y. The laser beam is irradiated on the uniformly charged surface of the photosensitive drum 91 of the process cartridge 99Y through a mirror 94 to form an electrostatic latent image on the surface of the photosensitive drum 91. The electrostatic latent image formed on the surface of the photosensitive drum 91 is developed with yellow (Y) toner by the developing device 92, and a yellow (Y) toner image is formed on the surface of the photosensitive drum 91.
Similarly, the photosensitive drums 91 of the process cartridges 99M, 99C, and 99K are irradiated with laser lights from the exposure devices 93M, 93C, and 93K, respectively, to form electrostatic latent images on the surfaces of the photosensitive drums 91, respectively. The electrostatic latent images formed on the photosensitive drums 91 are developed with respective color toners by the developing devices 92 to form magenta (M), cyan (C), and black (K) toner images. The toner images of respective colors formed on the photosensitive drums 91 are transferred onto the intermediate transfer belt 40 by the primary transfer rollers 45Y, 45M, 45C, and 45K at the primary transfer portions T1, respectively. The image formation process of each color is performed at the timing of superposing the toner image onto the upstream toner image transferred on the intermediate transfer belt 40. The toners remaining on the surfaces of the photosensitive drums 91 are recovered by the cleaners 95. The toner image on the intermediate transfer belt 40 is conveyed to the secondary transfer portion T2 by rotation of the intermediate transfer belt 40 in the rotation direction indicated by the arrow T.
In parallel with the image forming process, the sheet S is fed from the feeding unit 10, and the sheet S is conveyed to the registration unit 30 by the drawing unit 20. A skew feed of the sheet S is corrected by the registration unit 30, and the sheet S is conveyed to the secondary transfer portion T2 at a predetermined conveying timing. When the secondary transfer bias is applied to the secondary transfer outer roller 44, the toner images of four colors on the intermediate transfer belt 40 are transferred onto the sheet S at the secondary transfer portion T2. The toner remaining on the surface of the intermediate transfer belt 40 is recovered by a belt cleaner 46.
The sheet S on which the toner image is transferred is conveyed to the fixing unit 52 by an after-transfer guide 47 and a before-fixation conveyance portion 51. The sheet S is guided to the nip of the fixing roller pair 54 of the fixing unit 52 by the before-fixation guide 53. The fixing roller pair 54 heats and pressurizes the sheet S to fuse the toner. Thus, a full-color image firmly adheres (is fixed) to the sheet S. A path selection of whether the sheet S that has passed through the fixing unit 52 is conveyed to the decurler unit 110 or the reversing conveyance unit 80 is performed by the branch conveyance unit 60. It should be noted that the branch conveyance unit 60 and the reversing conveyance unit 80 can reverse the sheet S so that the first surface (front side) of the sheet S on which the image is formed faces downward, and convey the sheet S to the decurler unit 110.
In a case in which an image is formed only on one side of the sheet S, the sheet S is conveyed from the branch conveyance unit 60 to the decurler unit 110. In the decurler unit 110, the curl of the sheet S is corrected by a small diameter hard roller and a large diameter soft roller. The sheet S that has passed through the decurler unit 110 is conveyed to the inlet roller pair 121 of the discharge accessory 120. The discharge accessory 120 perform a processing on the sheet S, and thereafter discharges the sheet S to a discharge tray 130 by a discharge roller 122.
In a case in which images are formed on both sides of the sheet S, the sheet S on which an image is formed on the first surface (front side) is conveyed to the reversing conveyance unit 80 by the branch conveyance unit 60. The reversing conveyance unit 80 switches back the sheet S, and the sheet S is conveyed from the reversing conveyance unit 80 to the duplex conveyance units 70 and 71 and further conveyed to the registration unit 30. A toner image is transferred to the second surface (back side) of the sheet in the secondary transfer portion T2, and a full-color image firmly adhere (is fixed) to the second surface (back side) of the sheet S by the fixing unit 52. The sheet S on which images are formed on both surfaces is conveyed to the decurler unit 110 by the branch conveyance unit 60, and discharged to the discharge tray 130 via the discharge accessory 120.
Duplex Conveyance Unit
FIG. 2A, FIG. 2B, FIG. 2C, FIG. 2D, and FIG. 2E are explanatory views of the duplex conveyance unit 70. The duplex conveyance unit 70 is provided with a duplex path 330 (conveyance path) through which the sheet S is conveyed. The duplex path 330 is defined by at least a pair of conveyance guides. In the embodiment, the pair of conveyance guides comprises a duplex upper guide 331 and a duplex lower guide 332. The duplex upper guide 331 (support member) is fixed to the main body of the image forming unit 90. The duplex lower guide 332 (openable and closable member) is pivotal about a lower guide pivot shaft 338 (pivotal axis) with respect to the duplex upper guide 331.
FIG. 2E is a cross-sectional view of the duplex conveyance unit 70. The duplex conveyance unit 70 has at least a pair of conveyance rollers. In the embodiment, the duplex conveyance unit 70 has a plurality of pairs of conveyance rollers. The duplex conveyance unit 70 has a first pair of duplex conveyance rollers 210, a second pair of duplex conveyance rollers 220, a third pair of duplex conveyance rollers 230, and a fourth pair of duplex conveyance rollers 240. However, the number of pairs of conveyance rollers is not limited to this, and may be one pair, two pairs, three pairs, or five pairs or more. As shown in FIG. 2E, the duplex upper guide 331 supports duplex conveyance drive rollers 211, 221, 231, and 241 (first conveyance rollers). The duplex lower guide 332 supports driven rollers 212, 222, 232, and 242 (second conveyance rollers). The duplex conveyance drive roller 211 and the driven roller 212 constitute the first pair of duplex conveyance rollers 210. The duplex conveyance drive roller 221 and the driven roller 222 constitute the second pair of duplex conveyance rollers 220. The duplex conveyance drive roller 231 and the driven roller 232 constitute the third pair of duplex conveyance rollers 230. The duplex conveyance drive roller 241 and the driven roller 242 constitute the fourth pair of duplex conveyance rollers 240. The driven rollers 212, 222, 232, and 242 are pressed (urged) by springs 213, 223, 233, and 243 (urging units) to the duplex conveyance drive rollers 211, 221, 231, and 241, respectively.
FIG. 2A is a view showing the duplex conveyance unit 70 as viewed in a direction orthogonal to the sheet conveyance direction CD. As shown in FIG. 2A, the duplex lower guide 332 comprises a duplex lower front frame 333, a duplex lower left frame 334, a duplex lower rear frame 335, a duplex lower right frame 336, and a duplex lower reinforcing frame 337. The duplex lower guide 332 functions as an openable and closable member configured to pivot about the lower guide pivot shaft 338 (pivotal axis) to take a closed position P1 and an open position P2. In the closed position P1, the duplex lower guide 332 takes a position in which the duplex lower guide 332 is closed with respect to the duplex upper guide 331 as shown in FIG. 2A. In the open position P2, the duplex lower guide 332 takes a position in which the duplex lower guide 332 is open with respect to the duplex upper guide 331 as shown in FIG. 2B.
The lower guide pivot shaft 338 is provided at one end portion 332a of the duplex lower guide 332 in the sheet conveyance direction CD. A handle shaft 341 (pivot shaft) is rotatably provided at the other end portion 332b opposite to the one end portion 332a of the duplex lower guide 332 in the sheet conveyance direction CD. In the sheet conveyance direction CD, the one end portion 332a of the duplex lower guide 332 is located upstream, and the other end portion 332b of the duplex lower guide 332 is located downstream. The lower guide pivot shaft 338 and the handle shaft 341 are disposed in parallel to a width direction WD (FIG. 3D) orthogonal to the sheet conveyance direction CD.
FIG. 3A, FIG. 3B, FIG. 3C, and FIG. 3D are explanatory views of a locking mechanism 300 configured to hold the duplex lower guide 332 in the closed position P1. The locking mechanism 300 has a handle 340, the handle shaft 341, a front hook 342 (locking member), a rear hook 343 (locking member), a rotation regulating portion 344, a front hook fixing shaft 345, and a rear hook fixing shaft 346. In the width direction WD orthogonal to the sheet conveyance direction CD, the handle 340 is fixed to a handle fixing portion 341a provided at one end portion 341e of the handle shaft 341. The front hook 342 and the rear hook 343 are respectively provided at both ends (341e, 341f) of the handle shaft 341. The front hook 342 and the rotation regulating portion 344 are provided on the one end portion 341e of the handle shaft 341. The front hook 342 is attached to the handle shaft 341 so as to be pivotable within a predetermined pivotal range. The rotation regulating portion 344 is fixed to the handle shaft 341. On the other end portion 341f opposite to the one end portion 341e of the handle shaft 341, the rear hook 343 is attached to the handle shaft 341 so as to be pivotable within a predetermined pivotal range. In the width direction WD, the one end portion 341e of the handle shaft 341 is positioned on the front side of the image forming unit 90, and the other end portion 341f is positioned on the rear side.
FIG. 2F is a view showing the front hook 342 and the rear hook 343. The front hook 342 and the rear hook 343 will be described with reference to FIG. 2F. The front hook 342 and the rear hook 343 are formed in such a shape that their ends are bent so that they can be engaged (contacted) with the front hook fixing shaft 345 and the rear hook fixing shaft 346, respectively. Since the front hook 342 and the rear hook 343 have similar structures, the front hook 342 will be described in the description of FIG. 2F, and the reference numerals of the rear hook 343 will be noted in parentheses, and the description of the rear hook 343 will be omitted. Two mounting portions 342k (343k) provided on the front hook 342 (343) are fitted onto the handle shaft 341 so that the front hook 342 (343) is pivotably attached to the handle shaft 341. The front hook 342 (343) is provided with a hole portion 342g (343g) between the two mounting portions 342k (343k). The handle shaft 341 is provided with two hook rotation regulating portions 341b (341c) protruding in radial directions. The two hook rotation regulating portions 341b (341c) are disposed in the hole portion 342g (343g). The hole portion 342g (343g) is provided with rotation regulating portions 342h (343h) which can abut against the hook rotation regulating portions 341b (341c) of the handle shaft 341. When the front hook 342 (343) is rotated with respect to the handle shaft 341, the rotation regulating portions 342h (343h) abut against the hook rotation regulating portions 341b (341c) to regulate the rotation of the front hook 342 (343) within the predetermined range.
The front hook 342 (343) is provided with a slope portion 342a (343a), a hook tip end portion 342b (343b), and a locking portion 342c (343c). The duplex upper guide 331 is provided with the front hook fixing shaft 345 (346) (locking protrusion) to which the front hook 342 (343) engages. In the embodiment, the front hook fixing shaft 345 (346) is a shaft member formed in a cylindrical shape. A bearing roller 345a (346a) is provided at a tip end portion of the front hook fixing shaft 345 (346). In the embodiment, the bearing roller 345a (346a) is a rotary member formed in an annular shape as a part of the front hook fixing shaft 345 (346). When the duplex lower guide 332 is in the closed position P1, the locking portion 342c (343c) of the front hook 342 (343) locks to the bearing roller 345a (346a) of the front hook fixing shaft 345 (346). With respect to the handle shaft 341, a spring mounting portion 342e (343e) is provided at an end portion opposite to the locking portion 342c (343c) of the front hook 342 (343). A front hook spring 342f (343f) (urging unit) is provided between the spring mounting portion 342e (343e) and the duplex lower guide 332. The front hook spring 342f (343f) urges the front hook 342 (343) in a direction in which the locking portion 342c (343c) locks to the bearing roller 345a (346a) of the front hook fixing shaft 345 (346).
FIG. 2G is a view showing the rotation regulating portion 344. As shown in FIG. 2G, the rotation regulating portion 344 is fixed to a handle rotation regulating fixing portion 341d of the handle shaft 341. The rotation regulating portion 344 is provided with a regulating protrusion 344a. The duplex lower front frame 333 is provided with a rotation regulating hole 333a. The regulating protrusion 344a is movable within a predetermined range within the rotation regulating hole 333a.
FIG. 2A shows an operation when the handle 340 is rotated in a direction indicated by the arrow A to open the duplex lower guide 332. At this time, the front hook spring 342f (343f) mounted on the spring mounting portion 342e (343e) of the front hook 342 (343) applies a reaction force (urging force) to the handle 340 against a rotational force by which the user rotates the handle 340. When the handle 340 is rotated in the direction of the arrow A, the hook rotation regulating portion 341b (341c) engages with the rotation regulating portion 342h (343h) as shown by the dashed line in FIG. 2F to rotate the front hook 342 (343) in the direction of the arrow A. As a result, the front hook 342 (343) is disengaged from the front hook fixing shaft 345 (346), the duplex lower guide 332 is opened, and the duplex lower guide 332 is assumed in the open position P2 as shown in FIG. 2B. The direction of the arrow A in which the handle 340 is pivoted to release the locking between the front hook 342 (343) and the front hook fixing shaft 345 (346) is the same as the direction in which the duplex lower guide 332 is pivoted from the closed position P1 to the open position P2. Therefore, the user can perform releasing the locking between the front hook 342 (343) and the front hook fixing shaft 345 (346) and pivoting the duplex lower guide 332 from the closed position P1 to the open position P2 by one operation of the handle 340 in the direction of the arrow A.
FIG. 2B shows an operation when the user holds the handle 340 and attempts to close the duplex lower guide 332 in a direction indicated by the arrow B. When the handle 340 is rotated in the direction of the arrow B, the regulating protrusion 344a of the rotation regulating portion 344 attached to the handle shaft 341 abuts against an inner surface of the rotation regulating hole 333a provided in the duplex lower front frame 333 (FIG. 2G). Thus, the rotation of the handle 340 with respect to the duplex lower guide 332 is regulated at a predetermined rotation position. Therefore, the user can close the duplex lower guide 332 by holding the handle 340 without further rotation of the handle 340 with respect to the duplex lower guide 332. At this time, a force required for the user to lift the entire duplex lower guide 332 is a force Ft (operation force) applied to the handle 340 in a region α of FIG. 4. FIG. 4 is a view showing a relationship between an elapsed time from a time when the user starts the closing operation of the duplex lower guide 332 by holding the handle 340 and the force Ft applied to the handle 340.
FIG. 2C shows that the slope portion 342a (343a) of the front hook 342 (rear hook 343) is in contact with the bearing roller 345a (346a) of the front hook fixing shaft 345 (346) on the way the duplex lower guide 332 is being closed. By the contact between the slope portion 342a (343a) and the bearing roller 345a (346a), the front hook 342 (rear hook 343) is rotated clockwise. Since the hole portion 342g (343g) has a play or an allowance with respect to the hook rotation regulating portion 341b (341c), the front hook 342 (rear hook 343) can be rotated with respect to the duplex lower guide 332 to compress the front hook spring 342f (343f). The reaction force of the compressed front hook spring 342f (343f) acts on the handle 340. At this time, a force required for the user to lift the entire duplex lower guide 332 is the force Ft applied to the handle 340 in a region β of FIG. 4. The shape of the slope portion 342a (343a) of the front hook 342 (the rear hook 343) is specified so that the force Ft applied to the handle 340 in the region β of FIG. 4 is as constant and small as possible.
FIG. 2D shows that the hook tip end portion 342b (343b) of the front hook 342 (the rear hook 343) is in contact with the bearing roller 345a (346a) of the front hook fixing shaft 345 (346) on the way the duplex lower guide 332 is further being closed. Since the front hook 342 (the rear hook 343) is urged by the front hook spring 342f (343f) in the direction in which the front hook 342 (the rear hook 343) is rotated in the counterclockwise direction, the urging force of the front hook spring 342f (343f) acts to lift the duplex lower guide 332. At this time, the force required for the user to lift the entire duplex lower guide 332 is the force Ft applied to the handle 340 in a region γ of FIG. 4. When the duplex lower guide 332 is moved in the closing direction, the locking portion 342c (343c) of the front hook 342 (343) is locked to the bearing roller 345a (346a) by the urging force of the front hook spring 342f (343f), and the force Ft applied to the handle 340 decreases rapidly. However, when the driven rollers 212, 222, 232, and 242 of the duplex lower guide 332 are pressed against the duplex conveyance drive rollers 211, 221, 231, and 241, the force Ft applied to the handle 340 increases.
Eventually, the front hook 342 (343) is drawn to the front hook fixing shaft 345 (346) by the urging force of the front hook spring 342f (343f), and the duplex lower guide 332 is completely closed as shown in FIG. 2E. At this time, the force required for the user to lift the entire duplex lower guide 332 is the force Ft applied to the handle 340 in a region δ of FIG. 4, which becomes 0 (zero).
FIG. 3A is a cross-sectional view of a state on the way the duplex lower guide 332 is being closed as viewed from the left side of the image forming unit 90. The handle 340 is located on the front side of the image forming unit 90. When the duplex lower guide 332 are pushed up in the direction of the arrow B, the slope portion 342a of the front hook 342 and the slope portion 343a of the rear hook 343 come into contact with the bearing roller 345a of the front hook fixing shaft 345 and the bearing roller 346a of the rear hook fixing shaft 346, respectively. These contacts compress the front hook spring 342f of the front hook 342 and the rear hook spring 343f of the rear hook 343. At this time, a reaction force Ff acts on the front hook 342 in the gravitational direction by the bearing roller 345a of the front hook fixing shaft 345, and a reaction force Fr acts on the rear hook 343 in the gravitational direction by the bearing roller 346a of the rear hook fixing shaft 346. The duplex lower guide 332 is deformed by a deformation amount D1 in a direction indicated by the arrow C by a weight G of the duplex lower guide 332 and the reaction forces Ff and Fr.
FIG. 3B shows a state in which the hook tip end portion 342b of the front hook 342 and the hook tip end portion 343b of the rear hook 343 contact the bearing roller 345a of the front hook fixing shaft 345 and the bearing roller 346a of the rear hook fixing shaft 346, respectively. A reaction force Ff′ from the bearing roller 345a acts on the hook tip end portion 342b of the front hook 342, which is urged by the urging force of the front hook spring 342f, in the direction of closing the duplex lower guide 332. A reaction force Fr′ from the bearing roller 346a acts on the hook tip end portion 343b of the rear hook 343, which is urged by the urging force of the hook spring 342r, in the direction of closing the duplex lower guide 332. The duplex lower guide 332 is deformed by a deformation amount D2 by the weight G of the duplex lower guide 332 and the reaction forces Ff′ and Fr′. The deformation amount of the duplex lower guide 332 is reduced from the deformation amount D1 to the deformation amount D2.
FIG. 3C shows a state when the locking portion 342c of the front hook 342 latches to the bearing roller 345a of the front hook fixing shaft 345 by the locking portion 342c being drawn to the bearing roller 345a. At this time, the driven rollers 212, 222, 232, and 242 are in a state of pressing the duplex conveyance drive rollers 211, 221, 231, and 241. A reaction force Ff″ from the bearing roller 345a acts on the locking portion 342c of the front hook 342 in the direction of closing the duplex lower guide 332. A reaction force Fr″ from the bearing roller 346a acts on the hook tip end portion 343b of the rear hook 343, which is urged by the urging force of the hook spring 342r, in the direction of closing the duplex lower guide 332. The duplex lower guide 332 is deformed by a deformation amount D3 by the weight G of the duplex lower guide 332 and the reaction forces Ff″ and Fr″. At this time, the rear hook 343 needs to lift the entire duplex lower guide 332 by a deformation amount D3 by only the reaction force Fr″ in the closing direction from the bearing roller 346a caused by the urging force of the rear hook spring 343f, and latch onto the rear hook fixing shaft 346.
Here, if the spring force of the rear hook spring 343f is increased, the reaction force Fr when the rear hook spring 343f is compressed is increased. If so, the force Ft applied to the handle 340 will be increased in the region β of FIG. 4. Further, if a rigidity of the duplex lower guide 332 is increased in order to reduce the deformation amount D3, the weight G of the duplex lower guide 332 is increased. If so, the force Ft applied to the handle 340 will be increased in all regions of FIG. 4. Therefore, in the embodiment, as shown in FIG. 2H, the bearing roller 346a is attached to the tip end portion of the rear hook fixing shaft 346. When the hook tip end portion 343b of the rear hook 343, which is rotated in a direction of the arrow E by the urging force UF of the rear hook spring 343f, comes into contact with the bearing roller 346a, the bearing roller 346a is rotated. As a result, even if the spring force of the rear hook spring 343f is small, the bearing roller 346a can be rotate in the direction of the arrow E′ in FIG. 2H, so that latching failure of the locking portion 343c of the rear hook 343 with respect to the bearing roller 346a can be prevented.
FIG. 3D shows a state in which the locking portion 343c of the rear hook 343 is drawn to the bearing roller 346a of the rear hook fixing shaft 346 and the locking portion 343c latches to the bearing roller 346a in a case in which the spring force of the rear hook spring 343f is sufficient. In the embodiment, by attaching the bearing roller 345a to the tip end portion of the front hook fixing shaft 345 in the same manner, the spring force of the front hook spring 342f can be reduced and the reaction force Ff can be further suppressed. According to the embodiment, the reaction forces Ff and Fr can be suppressed by the bearing rollers 345a and 346a and the force Ft applied to the handle 340 can be reduced, thereby greatly improving the user's operability.
The spring force of the rear hook spring 343f can be reduced while preventing the latch failure by means of the bearing roller 346a attached to the tip end portion of the rear hook fixing shaft 346 to be contacted with the rear hook 343. Since it is not necessary to increase the rigidity of the duplex lower guide 332, the duplex lower guide 332 can be reduced in weight. Thus, the force applied to the handle 340 can be suppressed. According to the embodiment, the operability of the duplex lower guide 332 can be improved.
Second Embodiment
The second embodiment will be described below. In the second embodiment, the same structures as in the first embodiment will be denoted by the same reference numerals, and the description thereof will be omitted. The printer 1 as the image forming apparatus in the second embodiment is the same as in the first embodiment, and the description thereof will be omitted. A duplex conveyance unit 170 of the second embodiment differs from the duplex conveyance unit 70 of the first embodiment in that a decurler 350 (a de-curling machine) is provided as a curl correcting device configured to correct the curl of the sheet S. Hereinafter, the duplex conveyance unit 170 as the sheet conveyance apparatus of the second embodiment will be described.
Duplex Conveyance Unit
FIG. 5 is a cross-sectional view of the duplex conveyance unit 170 of the second embodiment. The duplex conveyance unit 170 is provided with the first pair of duplex conveyance rollers 210, the second pair of duplex conveyance rollers 220, the third pair of duplex conveyance rollers 230, and the fourth pair of duplex conveyance rollers 240 from upstream to downstream in the sheet conveyance direction CD. The duplex conveyance unit 170 is provided with the decurler 350 downstream of the first pair of duplex conveyance rollers 210 in the sheet conveyance direction CD.
The duplex upper guide 331 is provided with a decurler drive shaft 351 (first conveyance roller). The duplex lower guide 332 is rotatably provided with a pressing arm 355 (pressing unit). The pressing arm 355 is rotatably provided with a sponge roller 352 (second conveyance roller). The shaft portion 353 of the sponge roller 352 is supported by the pressing arm 355 through a bearing 354. The pressing arm 355 is rotatably supported by a shaft 355a provided on the duplex lower guide 332. One end portion of the pressing arm 355 is in contact with a pressing cam 356 (pressing force adjustment unit). The pressing cam 356 is rotatably attached to a cam shaft 357 provided in the duplex lower guide 332. The pressing cam 356 presses the pressing arm 355 and presses the sponge roller 352 against the decurler drive shaft 351.
A cam drive motor 358 and a cam phase sensor 359 are connected to the cam shaft 357. The cam drive motor 358 and the cam phase sensor 359 are electrically connected to a CPU (central processing unit) 360. The CPU 360 controls the cam drive motor 358 based on a detection result of the cam phase sensor 359 to rotate the pressing cam 356 to adjust an inroad amount of the decurler drive shaft 351 into the sponge roller 352.
Since the duplex lower guide 332 is provided with the sponge roller 352, the pressing arm 355, the pressing cam 356, and the cam drive motor 358, the weight of the duplex lower guide 332 is heavier than that of the first embodiment. Therefore, the weight applied to the handle 340 when the user operates the handle 340 to open and close the duplex lower guide 332 is increased. FIG. 6 is an explanatory view of the locking mechanism 300 of the second embodiment. In order to reduce the weight of the duplex lower guide 332 applied to the handle 340, an auxiliary suspension spring 347 (opening and closing auxiliary unit) is provided between the duplex lower rear frame 335 of the duplex lower guide 332 and the duplex upper guide 331. When the duplex lower guide 332 is opened, the auxiliary suspension spring 347 urges the duplex lower guide 332 in the closing direction. However, the urging force of the auxiliary suspension spring 347 is a small force Fa so that the duplex lower guide 332 can be fully opened.
FIG. 6 is a cross-sectional view taken from the left side of the image forming unit 90 of a state on the way in which the duplex lower guide 332 is closed. The handle 340 is located on the front side of the image forming unit 90. When the duplex lower guide 332 are pushed up in the direction of the arrow B, the slope portion 342a of the front hook 342 and the slope portion 343a of the rear hook 343 come into contact with the bearing roller 345a of the front hook fixing shaft 345 and the bearing roller 346a of the rear hook fixing shaft 346, respectively. These contacts compress the front hook spring 342f of the front hook 342 and the rear hook spring 343f of the rear hook 343. At this time, the reaction force Ff acts on the front hook 342 in the gravitational direction by the bearing roller 345a of the front hook fixing shaft 345, and the reaction force Fr acts on the rear hook 343 in the gravitational direction by the bearing roller 346a of the rear hook fixing shaft 346. In addition, the force Fa of the auxiliary suspension spring 347 acts on the duplex lower guide 332 in a direction opposite to the gravity. The duplex lower guide 332 deforms by a deformation amount D in the direction of the arrow C by the weight G of the duplex lower guide 332, the reaction forces Ff and Fr, and the force Fa of the auxiliary suspension spring 347. The other configuration is the same as that of the first embodiment, and the rear hook 343 is drawn to the bearing roller 346a at the tip end portion of the rear hook fixing shaft 346 by the spring force of the rear hook spring 343f, and latches to the rear hook fixing shaft 346.
FIG. 7A and FIG. 7B are explanatory views of the decurler 350. FIG. 7A shows a state in which the sponge roller 352 is pressed by the decurler drive shaft 351 and the inroad amount of the decurler drive shaft 351 to the sponge roller 352 is maximum. FIG. 7B shows a state in which the pressing cam 356 is rotated and the inroad amount of the decurler drive shaft 351 into the sponge roller 352 is minimum.
FIG. 8 is a flowchart showing a control operation of the cam drive motor 358 performed by the CPU 360. The CPU 360 controls the cam drive motor 358 based on the detection signal of the cam phase sensor 359 to control the inroad amount of the decurler drive shaft 351 into the sponge roller 352. In the embodiment, an opening/closing sensor 370 configured to detect the opening/closing of the duplex lower guide 332 is provided. A detection signal of the opening/closing sensor 370 is transmitted to the CPU 360. When the CPU 360 detects that an opening operation of the duplex lower guide 332 has started based on the detection signal of the opening/closing sensor 370, the CPU 360 performs opening/closing processing instructions (S1). Based on the detection signal from the opening/closing sensor 370, the CPU 360 determines whether or not the opening operation of the duplex lower guide 332 has been completed and the duplex lower guide 332 has been in the open state (S2). In a case in which the duplex lower guide 332 is not in the open state (NO in S2), the CPU 360 repeats S2. In a case in which the duplex lower guide 332 is in the open state (YES in S2), the CPU 360 performs initialization control of the decurler 350 (S3). The CPU 360 controls the cam drive motor 358 to rotate the pressing cam 356 to move the pressing arm 355 to an initial position in a direction in which the pressing force of the sponge roller 352 against the decurler drive shaft 351 is loosened. The pressing force of the sponge roller 352 against the decurler drive shaft 351 is reduced or released. Thus, the inroad amount of the decurler drive shaft 351 into the sponge roller 352 when the duplex lower guide 332 is closed can be minimized or reduced to 0 (zero).
After the jam clearance of the sheet S, the user grasps the handle 340 and closes the duplex lower guide 332. Since the pressing arm 355 is positioned at the initial position by the initialization control, the inroad amount of the decurler drive shaft 351 into the sponge roller 352 when the duplex lower guide 332 is closed is minimized or 0 (zero), and the reaction force is reduced. Therefore, the reaction force Fr″ required in the closing direction of the rear hook 343 by the rear hook spring 343f can be reduced. The rear hook 343 can securely draw the rear hook fixing shaft 346 and securely latch the locking portion 343c of the rear hook 343 to the bearing roller 346a of the rear hook fixing shaft 346.
Based on the detection signal of the opening/closing sensor 370, the CPU 360 determines whether or not the duplex lower guide 332 is in the closed state (S4). In a case in which the duplex lower guide 332 is not in the closed state (NO in S4), the CPU 360 repeats S4. In a case in which the duplex lower guide 332 is in the closed state (YES in S4), the CPU 360 adjusts the inroad amount of the decurler 350 (S5). The CPU 360 makes the cam drive motor 358 rotate the pressing cam 356 to adjust the inroad amount of the decurler drive shaft 351 into the sponge roller 352 to a set value. The pressing force of the sponge roller 352 against the decurler drive shaft 351 is held at a predetermined value. The set value of the inroad amount may be previously set by the user or may be set according to the type of the sheet S. The CPU 360 ends the control operation of the cam drive motor 358.
In the embodiment, the CPU 360 determines whether the duplex lower guide 332 is in the closed state or the open state based on the detection signal of the opening/closing sensor 370. However, the CPU 360 may determine whether the duplex lower guide 332 is in the closed state or the open state based on a detection signal of a cover opening/closing sensor configured to detect an opening/closing of a cover of the main body of the image forming unit 90. The CPU 360 may also determine whether the duplex lower guide 332 is in the closed state or the open state based on the user's input operation to an operation screen of an operation portion of the printer 1.
According to the embodiment, even if the weight of the duplex lower guide 332 is increased, the bearing roller 346a attached to the tip end portion of the rear hook fixing shaft 346 and the auxiliary suspension spring 347 can prevent the latch failure even if the spring force of the rear hook spring 343f is small. Moreover, since it is not necessary to increase the rigidity of the duplex lower guide 332 as a structure in order to prevent the latch failure, the weight of the duplex lower guide 332 can be reduced accordingly. Therefore, the increase of the force Ft applied to the handle 340 can be prevented, and the operability of the handle 340 by the user can be greatly improved. According to the embodiment, the operability of the duplex lower guide 332 can be improved.
In the embodiment, the bearing rollers 345a and 346a, which are rotatable, are provided at the tip end portions of the front hook fixing shaft 345 and the rear hook fixing shaft 346, respectively. However, the entire front hook fixing shaft 345 and the entire rear hook fixing shaft 346 may be rotatable. In the embodiment, the inroad amount of the sponge roller 352 is set to be variable, but the same effect can be obtained even if the driven rollers 212, 222, 232, and 242 are configured to come in contact with or separate from the duplex conveyance drive rollers 211, 221, 231, and 241.
In the first embodiment and the second embodiment, the laser printer using the electrophotographic method is exemplified as an example of the image forming apparatus provided with the sheet conveyance apparatus. However, the image forming apparatus may be, for example, a copying machine, a facsimile machine, a multifunction printer, or a multifunction peripheral.
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. 2022-174525, filed Oct. 31, 2022, which is hereby incorporated by reference herein in its entirety.
Patent Application
20240140746
