Patent Application
20210107755
This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2019-188294 filed Oct. 15, 2019.
The present disclosure relates to a sheet transport device and an image forming apparatus.
Image forming apparatuses that feed sheets from a sheet tray and form images on both sides of the sheets are known. Such an image forming apparatus may form images on both sides of long sheets. To form images on both sides of a sheet, the sheet needs to be reversed after an image is formed on a front side thereof. Therefore, when images are to be formed both sides of a long sheet, a space having a length corresponding to the length of the long sheet is required to enable reversal of the sheet. A gap below the sheet tray may be used as this space. Even when the specifications of an image forming apparatus are such that the image forming apparatus is capable of forming images on both sides of long sheets, sheets of normal lengths are often used, and sheets of shorter lengths may also be used. One of the problems of such an image forming apparatus is how to prevent short sheets that are being subjected to an image forming operation from becoming separated from a sheet transport mechanism by accident and slipping into the gap below the sheet tray.
Accordingly, Japanese Unexamined Patent Application Publication No. 2017-142365 proposes a gate mechanism disposed at an intermediate position of a sheet transport path connected to a gap below a sheet tray. The gate mechanism includes a gate that is opened manually or by a solenoid only when images are to be formed on both sides of a long sheet.
Aspects of non-limiting embodiments of the present disclosure relate to a sheet transport device and an image forming apparatus including a gate structure that does not need to be opened or closed and that prevents a sheet that has been separated from a sheet transport mechanism from sliding into a gap.
Aspects of certain non-limiting embodiments of the present disclosure overcome the above disadvantages and/or other disadvantages not described above. However, aspects of the non-limiting embodiments are not required to overcome the disadvantages described above, and aspects of the non-limiting embodiments of the present disclosure may not overcome any of the disadvantages described above.
According to an aspect of the present disclosure, there is provided a sheet transport device including a sheet storage unit that stores a sheet and that is disposed in a housing having a bottom plate such that a gap is provided between the sheet storage unit and the bottom plate, the gap extending horizontally; a sheet transport unit that feeds the sheet from the sheet storage unit and transports the fed sheet along a transport passage including a reversing transport path along which the sheet is transported downward and then upward to reverse the sheet front to back, the reversing transport path extending vertically and being connected to the gap; and a first gate unit that prevents passage of the sheet that has entered the reversing transport path when the sheet free falls and allows passage of the sheet when the sheet receives a sheet transport driving force from the sheet transport unit.
An exemplary embodiment of the present disclosure will be described in detail based on the following figures, wherein:
An exemplary embodiment of the present disclosure will now be described.
An image forming apparatus 10 illustrated in
Four image forming engines 30Y, 30M, 30C, and 30K are disposed in an upper section of the housing 11 of the image forming apparatus 10. The image forming engines 30Y, 30M, 30C, and 30K form toner images by using yellow (Y), magenta (M), cyan (C), and black (K) toners, respectively.
An intermediate transfer belt 31 is disposed directly below the image forming engines 30Y, 30M, 30C, and 30K. The intermediate transfer belt 31 is wrapped around plural rollers 32a, 32b, and 32c and rotates in the direction of arrows A. The toner images of the respective colors formed by the image forming engines 30Y, 30M, 30C, and 30K are successively transferred onto the intermediate transfer belt 31 in a superposed manner by the operations of first transfer devices 33Y, 33M, 33C, and 33K. The toner images that have been transferred onto the intermediate transfer belt 31 are transported by the rotation of the intermediate transfer belt 31, and are transferred onto a sheet transported at a suitable timing by the operation of a second transfer device 34. The toner images that have been transferred onto the sheet are fixed to the sheet by being heated and pressed by a fixing device 35. The sheet on which an image composed of the fixed toner images is formed is finally discharged onto the sheet output tray 12.
The image forming apparatus 10 also includes a controller 40. The controller 40 controls the overall operation of the image forming apparatus 10 including the operations of forming the toner images with the image forming engines 30Y, 30M, 30C, and 30K, transferring the toner images onto the intermediate transfer belt 31, transferring the toner images onto the sheet, and transporting the sheet.
A sheet transport passage will now be described. The sheet transport passage is provided with many transport members including transport rollers or the like and gates for switching the path along which the sheet is transported. However,
In an image forming operation, a sheet is fed leftward in
The sheet transported upward in the direction of arrow C is transported in the direction of arrows D, which is opposite to the direction of arrows B. An image is formed on the sheet while the sheet is being transported in the direction of arrows D.
After the toner images are transferred onto the sheet by the operation of the second transfer device 34 and fixed to the sheet by the operation of the fixing device 35 so that an image composed of the fixed toner images is formed on the sheet, the sheet is transported in the direction of arrow E and discharged onto the sheet output tray 12 if the operation mode is not a double-sided printing mode in which images are to be formed on both sides of the sheet.
The image forming apparatus 10 also includes a manual feed tray 13, and the sheet may also be fed from the manual feed tray 13. When the sheet is to be fed from the manual feed tray 13, the sheet is placed on the manual feed tray 13. The sheet on the manual feed tray 13 is pulled in the direction of arrow F, and is transported in the direction of arrows D. After that, the sheet is transported along the same transport path as that in the case where the sheet is fed from one of the sheet trays 20.
In the double-sided printing mode in which images are formed on both sides of the sheet, the sheet is transported along transport paths described below.
First, an image is formed on a front side of the sheet. Similar to the above-described case, to form an image on the front side of the sheet, the sheet is fed leftward in
The sheet having the image formed on the front side thereof moves in the direction of arrow G instead of being transported in the direction of arrow E, and is transported downward in the direction of arrow H by the transport rollers 51. Then, the sheet is further transported downward in the direction of arrows I by the transport rollers 52.
The transport rollers 52 are capable of rotating in forward and reverse directions, and start to rotate in the reverse direction while an upper end of the sheet that is transported downward in the direction of arrows I is still above the transport rollers 52. In the case where the sheet used in the current image forming process has a short length in a transporting direction in which the sheet is transported, the sheet is in a position such that the sheet hangs down from the transport rollers 52 when the reverse rotation is started.
In the case where the length of the sheet is greater than the height of the transport rollers 52 from a bottom plate 111 of the housing 11, the sheet is in a position described below.
A gap S is formed between the lowermost sheet tray 21 among the sheet trays 20 disposed in the housing 11 and the bottom plate 111 of the housing 11. The transport path that extends downward from the transport rollers 52 is connected to the gap S. Therefore, the sheet that is long in the transporting direction is transported downward in the direction of arrows I, and a leading end portion of the sheet enters the gap S and is transported in the direction of arrow J.
The transport rollers 52 start to rotate in the reverse direction while the upper end of the sheet that is transported downward is still above the transport rollers 52. Accordingly, when the sheet is long, the lower end portion of the sheet is transported in the direction of arrow K, and then transported upward in the direction of arrows L. Then, the sheet is transported in the direction of arrow M, and then transported by the transport rollers 53 in the direction of arrow N, which is opposite to the direction of arrows D, in a region below the transport path in the direction of arrows D. The transport path according to the present exemplary embodiment along which the sheet is transported in the direction of arrows I and the direction of arrow J and that is connected to the gap S corresponds to an example of a reversing transport path according to the present disclosure. The structure that includes the above-described transport paths including the reversing transport path and that transports the sheet corresponds to an example of a sheet transport unit according to the present disclosure. A gate unit 60 is provided on the reversing transport path at a position slightly above the bottom plate 111 of the housing 11. The gate unit 60 will be described below.
The sheet transported in the direction of arrow N is transported in the direction of arrow O and enters the transport path in the direction of arrows D. By this time, the front and back sides of the sheet are reversed, so that toner images are transferred onto the back side of the sheet when the sheet moves in the direction of arrows D. The toner images that have been transferred onto the back side of the sheet are fixed to the back side of the sheet by the fixing device 35. Thus, images are formed on both front and back sides of the sheet. The sheet having images formed on both sides thereof moves in the direction of arrow E, and is discharged onto the sheet output tray 12.
Assume that a sheet having an image formed on the front side thereof moves in the directions of arrows G, H, and I in the double-sided printing mode and that the upper end thereof passes through the transport rollers 52 and falls in the direction of arrows I. This occurs when, for example, there is a trouble in the sequence, such as a slight delay in starting the reverse rotation of the transport rollers 52, or when the length of the actual sheet is shorter than the length of the designated sheet due to a user error in setting sheets.
As described above, the sheet is transported by the transport rollers 51 in the direction of arrow H, and is received and continuously transported by the transport rollers 52. The transport rollers 52 transport the sheet in the direction of arrows I, and then rotate in the reverse direction to transport the sheet in the direction of arrows L. Then, the sheet is transported in the direction of arrow M, and is received and continuously transported by the transport rollers 53. When the sheet that is used is long, the trailing end of the sheet that is received and continuously transported by the transport rollers 53 may be unable to leave the transport rollers 52 before the leading end of the next sheet that is transported by the transport rollers 51 reaches the transport rollers 52. In this exemplary embodiment, the transport rollers 52 are composed of two rollers that nip the sheet therebetween in a releasable manner. More specifically, when the two rollers are opened so that a gap is provided therebetween, the sheet freely moves through the gap between the rollers. At the time when the trailing end of the previous sheet leaves the transport rollers 52, the next sheet is still transported by the transport rollers 51. After the trailing end of the previous sheet leaves the transport rollers 52, the transport rollers 52 are closed to receive the next sheet from the transport rollers 51 and continuously transport the next sheet in the direction of arrows I. In the present exemplary embodiment, the above-described sequence is used to increase the productivity of the image forming operation. However, since the transport rollers 52 are opened and closed, there may be a higher risk that a sheet will pass through the gap between the transport rollers 52 and fall. The two rollers that constitute the transport rollers 52 correspond to an example of a pair of sheet driving portions according to the present disclosure.
When the sheet that has fallen is relatively long, only a portion of the sheet slides into the gap below the sheet tray 21, and an upper portion of the sheet remains in the transport path that extends in the vertical direction. Since the housing 11 has a door 14 on a wall surface along the transport path that extends in the vertical direction, the sheet that has fallen may be taken out by opening the door 14. However, if the gate unit 60 described below is not installed and a short sheet, such as a postcard-sized sheet, is used, the sheet may slip into the gap S below the sheet tray 21 over the entire length thereof.
If the sheet that has slipped into the gap S is not removed, there is a risk that the next sheet will come into contact with the sheet in the gap S and be wrinkled or bent. Therefore, when a sheet slips into the gap S, that sheet needs to be removed. If the sheet tray 21 is configured to be capable of being pulled out of and removed from the housing by the user, the user may remove the sheet as long as the user is aware that the sheet has slipped into the gap S. However, when a large number of large sheets are stacked on the sheet tray 21, removal of the sheet tray 21 is not easy and may be dangerous for the user. Therefore, in the present exemplary embodiment, the sheet tray 21 is not configured to be removable by the user. In addition, the bottom of the housing 11 is blocked by the bottom plate 111 for safety reasons, for example, to prevent fire. Therefore, once a sheet slips into the gap S, it becomes necessary to call a maintenance person. Accordingly, in the present exemplary embodiment, the gate unit 60 is disposed on the reversing transport path at a position above the bottom plate 111 of the housing 11 to prevent a sheet from slipping into the gap S.
As illustrated in
The gate unit 60A is positioned to face the curved guide portion 71 at the bottom of the guide wall 70A. The gate unit 60A includes a gate member 61 made of a resin and a spring member 62 that presses the gate member 61 against the curved guide portion 71 of the guide wall 70A. In the present exemplary embodiment, the contact point between the gate member 61 and the guide wall 70A is on the curved guide portion 71, that is, at a position upstream of a horizontal surface of the bottom plate 111 in a downstream region in the transporting direction of the sheet transported to the reversing transport path by the transport rollers 52.
In
The spring member 62 presses the gate member 61 against the guide wall 70A (curved guide portion 71) with a force strong enough to prevent the gate member 61 from being opened by a force applied by the sheet that free falls.
Referring to
Thus, the gate member 61 has a function of stopping the free falling sheet and allowing passage of the sheet receiving a transport driving force from the transport rollers 52.
The momentum of the free falling sheet is reduced by the curved guide portion 71. When the momentum of the falling sheet is reduced, passage of the sheet may be prevented simply by pressing the gate member 61 against the curved guide portion 71 with a weak force. The sheet that passes the gate member 61 has an image formed on the front side thereof that faces the guide wall 70A. Therefore, when the gate member 61 is pressed against the guide wall 70A with a strong force, there is a risk that the image will be damaged. Accordingly, the gate unit 60A is disposed at the curved guide portion 71, where the momentum of the falling sheet is reduced, so that the force with which the gate member 61 is pressed may be reduced. The gate member 61 corresponds to an example of a pressing member according to the present disclosure. The gate unit 60A corresponds to an example of a first gate unit according to the present disclosure. The curved guide portion 71 of the guide wall 70A corresponds to a curved guide portion of the present disclosure.
According to the gate unit 60B of the second example, the gate member 63 is elastically deformed to generate a pressing force applied to the guide wall 70A. Therefore, no additional spring member is required to press the gate member 63. Thus, the gate unit has a simpler structure.
According to the gate unit 60C of the third example, the roller that serves as the gate member 64 freely rotates. Therefore, damage to the sheet that passes the roller is further reduced.
In the above-described first to third examples, the guide wall 70A includes the curved guide portion 71 below a portion thereof that vertically extends. The curved guide portion 71 is disposed between the vertically extending portion and the bottom plate 111 of the housing that guides the sheet in a horizontal direction. However, an inclined surface may be provided instead of the curved guide portion 71.
The guide wall 70A that defines the reversing transport path illustrated in
The first curved surface 721 is a guide surface that bends the sheet by guiding the front side of the sheet that is opposite to the back side facing toward the sheet tray 20 (leftward in
The reversing transport path of the second example illustrated in
The curved guide portion 72 of the guide wall 70B provided on the reversing transport path of the second example illustrated in
In the second example illustrated in
When not only the end portions of the sheet P in the width direction but also the central portion of sheet P is shaped as described above, buckling of the sheet P is even less likely to occur. Therefore, the risk that the sheet P will buckle and fail to pass the gate member 61 may be further reduced.
Although an example of the guide wall 70A is illustrated in each of
The reversing transport path illustrated in
For example, assume that a somewhat long sheet that receives a transport driving force from the transport rollers 52 is transported downward and that the leading end thereof has passed the first gate unit 60. At this time, assume that the transport rollers 52 are opened due to any reason, such as noise, and the sheet starts to free fall. In such a case, since the sheet has already passed the gate unit 60, the sheet that has started to free fall does not stop and continues to fall. If the sheet is sufficiently long, even when the leading end portion of the free falling sheet slips into the gap S, the trailing end portion of the sheet appears when the door 14 illustrated in
In the example illustrated in
In the present exemplary embodiment, three examples of a gate unit according to the present disclosure have been described: an example in which the gate member 61 made of a resin is used, an example in which the gate member 63 composed of a PET film is used, and an example in which the gate member 64 composed of a roller is used. However, the gate unit according to the present disclosure is not limited to these examples, and may have any structure as long as the gate unit prevents passage of a sheet when the sheet free falls and allows passage of the sheet when the sheet receives a transport driving force.
Although an image forming apparatus that forms an image by an electrophotographic method and a sheet transport device installed in the image forming apparatus are described, the image forming apparatus according to the present disclosure may be an image forming apparatus that forms an image by a method other than the electrophotographic method, such as an inkjet method. Also, the sheet transport device according to the present disclosure may be a sheet transport device installed in an image forming apparatus that forms an image by a method other than the electrophotographic method. Also, the sheet transport device according to the present disclosure may be applied to a sheet transport device installed in an apparatus that is other than an image forming apparatus and in which a sheet needs to be reversed.
The foregoing description of the exemplary embodiment of the present disclosure has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure to the precise forms disclosed. Obviously, many modifications and variations will be apparent to practitioners skilled in the art. The embodiment was chosen and described in order to best explain the principles of the disclosure and its practical applications, thereby enabling others skilled in the art to understand the disclosure for various embodiments and with the various modifications as are suited to the particular use contemplated. It is intended that the scope of the disclosure be defined by the following claims and their equivalents.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2019-188294 | Oct 2019 | JP | national |
