Patent Application
20110241285
This application claims the benefit of Japanese Patent Application No. 2010-086464, filed Apr. 2, 2010, which is hereby incorporated by reference herein in its entirety.
1. Field of the Invention
present invention relates to a sheet feeding apparatus and an image forming apparatus, and more particularly, to control of a lowering speed when a sheet stacking plate on which sheets are stacked is lowered.
2. Description of the Related Art
A conventional image forming apparatus such as a printer, a facsimile machine or a copying machine is provided with a sheet feeding apparatus which separates an uppermost one of a plurality of sheets accommodated in a sheet cassette and feeds the separated sheet. The sheet feeding apparatus has a sheet cassette and a sheet stacking plate provided in the sheet cassette such that the sheet stacking plate can be lifted and lowered, and sheets are stacked and supported on the sheet stacking plate. When a sheet is fed and an upper surface of the sheet is lowered, the sheet stacking plate is lifted so that the height of the uppermost sheet is maintained in such a range that the sheet can be fed.
In the image forming apparatus having such a conventional sheet feeding apparatus, when sheets are added or a sheet jam is handled, the sheet cassette is pulled out from an apparatus body. When the sheet cassette is pulled out, support of a lift mechanism is released and the sheet stacking plate is lowered (drops) by its own weight, but noise (impulsive sound) is generated in some cases due to impact that results when the lift mechanism is lowered. Especially when a large amount of sheets is stacked on the sheet stacking plate, a loud impulsive sound is generated.
Hence, as countermeasures against noise which is generated when the sheet stacking plate is lowered, it is proposed to slow down a lowering speed of the sheet stacking plate using a damper (see Japanese Patent Laid-Open No. 8-127434). By slowing the lowering speed of the sheet stacking plate in this manner, it is possible to moderate the impact received by the sheet stacking plate and to reduce the noise.
A chipped-tooth gear 42 is provided on a side surface of the sheet stacking plate 35, and a damper gear 51 is provided on an inner wall surface of the sheet cassette 34. The chipped-tooth gear 42 includes a gear portion 42a which meshes with the damper gear 51, and a chipped-tooth portion 42b which is located below the gear portion 42a and which cannot mesh with the damper gear 51.
However, when the amount of stacked sheets P is small, the sheet stacking plate 35 turns upward and with this, the chipped-tooth gear 42 is also lifted and the damper gear 51 comes to a position facing the chipped-tooth portion 42b of the chipped-tooth gear 42. That is, the damper gear 51 and the chipped-tooth gear 42 are not connected to each other. Therefore, if the sheet cassette 34 is pulled out when the number of stacked sheets is small, the lowering speed of the sheet stacking plate 35 immediately after the sheet cassette 34 is pulled out becomes fast. Thereafter, if the gear portion 42a of the chipped-tooth gear 42 and the damper gear 51 mesh with each other during the lowering motion of the sheet stacking plate 35, the lowering speed of the sheet stacking plate 35 becomes slow by the damper gear 51.
The conventional sheet feeding apparatus and image forming apparatus include a sheet presence/absence sensor which detects the presence or absence of sheets on the sheet stacking plate by inserting a sensor arm into an opening formed in the sheet stacking plate. If the sheet presence/absence sensor detects that sheets have run out, a user pulls out the sheet cassette from the image forming apparatus body to supply sheets.
At that time, if the sensor arm is inserted into the opening of the sheet stacking plate, there is an adverse possibility that the sheet stacking plate and the sensor arm interfere with each other when the sheet cassette is pulled out. Therefore, according to the conventional apparatus, when the sheet cassette is pulled out, the lowering speed of the sheet stacking plate is set to be fast immediately after the sheet cassette is pulled out, but the lowering speed of the sheet stacking plate can be fast only when the number of sheets stacked on the sheet stacking plate is small, and when a large number of sheets are stacked, the above-described problem cannot be solved.
Further, when a sheet jam occurs, the sheet cassette 34 is pulled out from the image forming apparatus body, but when the sheet cassette 34 is pulled out, the sensor arm is in contact with the uppermost sheet on the sheet stacking plate. When the sheet jam occurs, not only the sensor arm but also a feeding roller located above the sheet stacking plate are in contact with uppermost one of the sheets.
In such as case, if the sheet cassette is pulled out, and the sensor arm and the feeding roller rub against the uppermost sheet, there is the possibility of the roller surface being scarred or the sheet being damaged by the uppermost curled up stacked sheet. For this reason, when the sheet cassette is pulled out, it is necessary to increase the lowering speed of the sheet stacking plate but according to the conventional configuration, the lowering speed of the sheet stacking plate can be increased only when the number of sheets stacked on the sheet stacking plate is small, and the above-described problem cannot be solved when a large amount of sheets are stacked.
That is, according to the conventional configuration using the chipped-tooth gear, the lowering speed of the sheet stacking portion cannot be changed midstream depending upon a position (amount of sheets) of the sheet stacking portion when the cassette is pulled out. It is not possible to increase the speed immediately after the sheet stacking portion is lowered when the cassette is pulled out irrespective of the amount of sheets. If a plurality of dampers or chipped-tooth gears are provided, the above-described problem can be solved, but this increases costs and the problem can be solved only in stages.
The present invention has been accomplished in view of the circumstances, and provides a sheet feeding apparatus and an image forming apparatus capable of increasing a speed when a sheet stacking portion is lowered until the sheet stacking portion is lowered by a predetermined amount irrespective of an amount of stacked sheets.
The present invention provides a sheet feeding apparatus comprising, a sheet accommodating portion which can be brought into and out from an apparatus body, a sheet stacking portion, provided on the accommodating portion, on which is stacked sheets, a lift mechanism which pushes up the sheet stacking portion to a range where uppermost one of the sheets stacked on the sheet stacking portion can be fed, a driving portion provided in the apparatus body, and a damper portion provided on the sheet accommodating portion, wherein the lift mechanism can be engaged with and disengaged from the driving portion, and if the engagement between the lift mechanism and the driving portion is released, the lift mechanism lowers the sheet stacking portion, the damper portion is engaged with the lift mechanism, and if the engagement between the lift mechanism and the driving portion is released, the damper portion exerts damper effect on the lift mechanism to reduce a lowering speed of the sheet stacking portion, and wherein the damper portion does not exert the damper effect on the lift mechanism until the sheet stacking portion is lowered by a predetermined amount after the engagement between the lift mechanism and the driving portion is released.
According to the invention, a damper effect is not exerted on the sheet stacking portion until the sheet stacking portion is lowered by a predetermined amount and therefore, it is possible to increase the speed when the sheet stacking portion is lowered until the sheet stacking portion is lowered by the predetermined amount irrespective of an amount of stacked sheets.
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
Embodiments of the present invention will be described in detail with reference to the drawings.
In
The image forming portion 1B is a drum full-color image forming portion, and includes a laser scanner 10, and four process cartridges 11 which form toner images of four colors, i.e., yellow (Y), magenta (M), cyan (C) and black (K). Each of the process cartridges 11 includes a photosensitive drum 12, a charging device 13 which is a charging portion, a development device 14 which is a development unit, and a cleaner (not illustrated) which is a cleaning unit. The image forming portion 1B includes an intermediate transfer unit 1C disposed above the process cartridges 11.
The intermediate transfer unit 1C includes an intermediate transfer belt 16 which is wound around a driving roller 16a and a tension roller 16b and which rotates in the direction of arrow. The intermediate transfer unit 1C includes primary transfer rollers 19 which are provided inside of the intermediate transfer belt 16 and which abut against the intermediate transfer belt 16 at locations opposed to the photosensitive drums 12.
Positive transfer bias is applied to the intermediate transfer belt 16 by the primary transfer rollers 19, so that negative toner images of the respective colors on the photosensitive drums are sequentially transferred onto the intermediate transfer belt 16 in a multilayer manner. A secondary transfer roller 17 constituting a secondary transfer portion is provided at a location opposed to the driving roller 16a of the intermediate transfer unit 1C, and the secondary transfer roller 17 transfers the color image formed on the intermediate transfer belt onto sheets P.
A fixing portion 20 is disposed on an upper portion of the secondary transfer roller 17, and a pair of first discharge rollers 25a, a pair of second discharge rollers 25b and a two-sided reversing portion 1D which is a reverse discharge portion are disposed at upper and left portions of the fixing portion 20. The two-sided reversing portion 1D includes a pair of reverse rollers 22 which are sheet reverse conveying rollers capable of normally and reversely rotating, and a re-conveying passage R for conveying again, to the image forming portion 1B, a sheet having an image formed on its one of surfaces.
Next, an image forming operation of the printer 1 having the above-described configuration will be described. The image reading apparatus 2 reads image information of an original, this image information is subjected to image processing and then, the image information is converted into an electric signal and the electric signal is transmitted to the laser scanner 10 of the image forming portion 1B. Image information is input to the image forming portion 1B from an external device such as a personal computer in some cases. The image forming portion 1B scans surfaces of the photosensitive drums 12 of the process cartridges 11 by laser light which is emitted from the laser scanner 10 and which corresponds to image information of color components of yellow, magenta, cyan, and black. With this operation, a surface of each of the photosensitive drums 12 uniformly bears predetermined polarity and potential by the charging device 13, and the surface is sequentially exposed, and electrostatic latent images of yellow, magenta, cyan, and black are sequentially formed on the photosensitive drums of the process cartridges 11.
Thereafter, the electrostatic latent images are developed and visualized by each toner of yellow, magenta, cyan, and black, and the toner images on the photosensitive drums are sequentially transferred onto the intermediate transfer belt 16 in the multilayer manner by primary transfer bias applied to the primary transfer rollers 19. With this operation, the toner image is formed on the intermediate transfer belt 16.
Simultaneously with this toner image forming operation, sheets P are sent out from the sheet feeding apparatus 30 and then, the sheets P are conveyed to a pair of registration rollers 49. Skew feeding of the sheets P is corrected by the pair of registration rollers 49, and the sheets P are conveyed to a secondary transfer portion including the driving roller 16a and the secondary transfer roller 17 such that a position of the sheets P and the toner images on the intermediate transfer belt match with each other by the secondary transfer portion. Thereafter, the toner images are collectively transferred onto the sheets P by secondary transfer bias applied to the secondary transfer roller 17 by the secondary transfer portion.
Next, the sheets P onto which the toner image is transferred is conveyed to the fixing portion 20, the sheets P are heated and pressurized in the fixing portion 20, toner of respective colors is melted and mixed, and fixed as a color image on the sheets P. Thereafter, the sheets P to which the image is fixed are discharged to a stacking portion 23 by the pair of first discharge rollers 25a. When images are to be formed on both surfaces of the sheet, after the sheet having an image on its one surface passes through the fixing portion 20, a pair of reverse rollers 22 reversely rotates, the sheets P are conveyed to the re-conveying passage R by reverse rotation and then, the sheets P are conveyed to the pair of registration rollers 49 again. An image is formed on the back surface, and stacked on the stacking portion 23 by the pair of first discharge rollers 25a.
The pair of separating conveying rollers 32 and 33 separates an uppermost sheet P1 of sheets sent out by the feeding roller 31, and conveys the sheet P1 to the pair of registration rollers 49. As the sheet feeding operation proceeds, the sheets P on the sheet stacking plate 35 are reduced, and according to the reduction of sheets, control is performed to lift the sheet stacking plate 35 so that the sheet surface comes to such a height that the sheet can be fed. If sheets on the sheet stacking plate 35 run out and the sheet presence/absence sensor 36 detects this, a controlling portion (not illustrated) stops the sheet feeding operation, a message that sheets should be supplied is displayed on a panel. If a user is informed that sheets run out, the user pulls out the sheet cassette 34 and supplies sheets.
As illustrated in
If the sheet cassette 34 is attached to the printer body, the driving input gear 41 and the sector gear 42 are engaged (meshed) with each other, and if the driving input gear 41 rotates and the sector gear rotates, the lifter plate 43 upwardly turns integrally with the sector gear 42. With this, the sheet stacking plate 35 moves to the range where a sheet can be fed. If the engagement between the sector gear 42 and the driving input gear 41 is released when the sheet cassette 34 is pulled out from the printer body. Therefore, the lift mechanism 40 loses a force for supporting the sheet stacking plate 35, the sheet stacking plate 35 is lowered.
In
Next, an operation of the lift mechanism 40 having the above-described configuration will be described with reference to
Thereafter, sheets are sequentially sent out by the feeding roller 31, and if the amount of sheets on the sheet stacking plate 35 is reduced, the driving input gear 41 rotates, and the lifter plate 43 is upwardly turned through the sector gear 42. If all of sheets are fed and sheets on the sheet stacking plate run out as illustrated in
With this, the user pulls out the sheet cassette 34 from the printer body 1A and supplies sheets. When the sheet cassette 34 is pulled out from the printer body 1A, the meshed state with the driving input gear 41 which is a driving source is released, and then, the sector gear 42 loses the ability to support the sheet stacking plate 35. Therefore, the sheet stacking plate 35 is lowered by its own weight as illustrated in
As illustrated in
The shaft 54a of the gear portion 54 of the damper gear 51 is rotatably supported by a support member (not illustrated) provided on the cassette body. The shaft 52a which is a rotation shaft of the damper resistance member 52 is rotatably supported by a later-described shaft hole 38 illustrated in
In this embodiment, as illustrated in
According to this configuration, if the damper gear 51 is rotated, the damper resistance member 52 integrally rotates with the gear portion 54 within a range of the space 53, i.e., a range of the predetermined angle E°, and if the damper resistance member 52 exceeds the predetermined angle E°, the rotation is limited by the projection 38a. By providing the space 53 in the shaft 52a in this manner, the damper gear 51 can rotate in a state having no damper effect in the rotation direction by rotation of the predetermined angle E°. In this embodiment, the space 53 and the projection 38a constitute a rotation-restricting portion. If the sheet stacking plate 35 is lowered by a predetermined amount, the rotation-restricting portion restricts rotation of the damper resistance member 52 such that the gear portion 54 slides with respect to the damper resistance member 52.
This predetermined angle E° is set in the following manner. As illustrated in
Hence, when the sheet cassette 34 is pulled out, it is necessary to lower the sheet stacking plate 35 by an amount more than an entering amount (size L) of the sheet presence/absence sensor flag 36a into the opening 35b. That is, the predetermined angle E° is set to such a value that when the sheet cassette 34 is pulled out, the sheet stacking plate 35 is lowered fast to a position where the sheet presence/absence sensor flag 36a is not caught at an edge of the opening 35b.
Next, an operation of the damper gear 51 having the above-described configuration when the sheet cassette 34 is attached to the printer body 1A will be described. If the sheet cassette 34 is attached to the printer body 1A, the driving input gear 41 and the sector gear 42 mesh with each other, a driving force is transmitted from the driving input gear 41 to the sector gear 42, and the gear portion 54 of the damper gear 51 rotates in the direction of arrow D illustrated in
At an initial stage of rotation of the driving input gear 41 and the damper gear 51, the projection 38a and the space 53 have a positional relation as illustrated in
Next, an operation of the damper gear 51 when the sheet cassette 34 is pulled out from the printer body 1A will be described. If the sheet cassette 34 is pulled out forward of the printer body, a driving connection between the driving input gear 41 and the sector gear 42 is cut off. With this, the sector gear 42 and the lifter plate 43 turn in the direction of arrow F illustrated in
At the same time, the damper gear 51 which is driving-connected to the sector gear 42 rotates in the direction of arrow H. Here, if the damper gear 51 rotates in this manner, in an initial stage of rotation, the projection 38a and the space 53 have a positional relation as illustrated in
That is, since the space 53 constituting an idling rotation region is provided in the shaft 52a of the damper resistance member 52, the sheet stacking plate 35 is lowered to the position illustrated in
According to this configuration, when the sheet cassette is pulled out, the idling rotation state in which there is no damper effect which gives resistance to the lowering operation of the sheet stacking plate 35 is established immediately after the driving connection of the driving input gear 41 with respect to the sector gear 42 is released and therefore, the lowering speed of the sheet stacking plate 35 is increased. After the damper resistance member 52 is rotated by the predetermined angle E° and lowered by a predetermined amount, the lowering speed of the sheet stacking plate 35 is reduced by the damper effect.
As described above, in this embodiment, the lowering speed of the sheet stacking plate 35 can be increased immediately after the driving connection of the driving portion (input gear 41) is released, and the lowering speed of the sheet stacking plate 35 can be reduced by the damper effect after the damper resistance member 52 rotates by the predetermined angle E°. With this, the lowering speed of the sheet stacking plate 35 can be increased immediately after the driving connection of the driving portion is released irrespective of the stacking amount of sheets of the sheet stacking plate 35, i.e., irrespective of a lifting position of the sheet stacking plate 35.
As a result, it is possible not only to prevent noise caused when the sheet stacking plate 35 is lowered, but also to prevent the sheet presence/absence sensor and the feeding roller from being damaged. Further, since the chipped-tooth gear is used like the conventional technique, it is possible to delete meshing failure peculiar to the chipped-tooth gear, and to delete impulsive sound caused at the time of meshing. Further, if the chipped-tooth gear is used, it is necessary to strictly manage the size precision of shape because the shape is varied due to a molding machine, and the molding precision is required, so that if the chipped-tooth gear is not used, cost can be reduced.
In the above description, the space is provided in the damper resistance member 52 of the damper gear 51, a projection 38a is provided on the shaft hole 38 formed in the side wall surface of the cassette body 34A, and the projection 38a is provided on the shaft hole 38, but the present invention is not limited to these configurations. For example, a space may be provided on one of the shaft 52a of the damper resistance member 52 and the shaft hole 38 of the cassette body 34A, and the projection 38a which moves in the space and which rotates the damper resistance member 52 integrally with the gear portion 54 by the predetermined angle may be provided on the other one. That is, the space may be formed in the shaft hole formed in the outer wall surface of the side plate of the cassette body, and the projection may be formed on the damper resistance member which is axially supported by the shaft hole.
Next, a second embodiment of the invention having such configurations will be described.
According to such configuration, like the above-described first embodiment, a driving input gear rotates immediately after the sheet cassette 34 is inserted into the printer body, and when the sheet stacking plate is to be lifted, the projection 64 of the shaft 62 move to a position (A) from a position (B) in
When the sheet cassette is pulled out, if the damper gear (damper resistance member) rotates in the direction of arrow illustrated in
In the second embodiment, since the projection 64 which moves in the space is provided on the shaft 62 of the damper resistance member, the moving angle E′° of the space can be changed depending on the shape of the shaft hole 63. According to this configuration, in device models having different using conditions, diversion usability of the damper gear is enhanced. For example, in order to change a lowering amount of the sheet stacking plate in a state where there is no damper effect, the damper gear is changed in the first embodiment, but in the second embodiment, since the shape of the shaft hole 63 is changed. Since cassettes are different in every device model in many cases, it is easy to change a shape of a hole when a new device is produced. In this case, it is possible to enhance the diversion usability even if a damper gear is not produced for every different device.
In the above description, a tandem type vertical sheet conveying type color laser beam printer is illustrated, but the present invention is not limited to this. The invention can also be applied to a horizontal sheet conveying type image forming apparatus and a monochrome laser beam printer. Further, a cassette type sheet stacking apparatus was used, but even if the invention is utilized for a deck type sheet stacking apparatus capable of stacking a large amount of sheets, the same effect can be obtained. The invention is not limited to the sheet stacking plate, and the invention can be utilized when it is necessary to increase a lowering speed of a stacked object immediately after a releasing operation.
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. 2010-086464, filed Apr. 2, 2010, which is hereby incorporated by reference herein in its entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2010-086464 | Apr 2010 | JP | national |
