Patent Application
20090079125
The present invention relates to a sheet supply device for supplying a sheet and an image forming apparatus having the sheet supply device.
In a conventional image forming apparatus such as a printer, a copier, a facsimile, and the likes, a sheet supply device is provided for supplying a sheet to an image forming unit for forming an image on the sheet.
When the sheet supply device is a retard separation type as a sheet separation type, a separation supply unit is disposed on a sheet pick up side of a medium tray storing a medium for separating and supplying the medium one by one. The separation supply unit includes a retard separation unit for separating the medium thus picked up. The retard separation unit includes a sheet supply roller to be pressed against the medium for picking up the medium; a transportation roller; and a separation roller abutting against the transportation roller.
The separation roller of the retard separation unit generates torque in a direction of returning the medium backward. When only one medium is supplied, the separation roller follows and rotates in a sheet supply direction through friction between the medium and the separation roller. When more than two media are supplied, the separation roller generates a medium separation function and applies brake to the media with the torque, thereby supplying only one medium.
In Patent Reference, a double supply regulating unit (a primary separation unit) is separately disposed between a sheet supply roller and a retard separation unit (a secondary separation unit). The double supply regulating unit (the primary separation unit) separates a leading edge of a medium picked up with the sheet supply roller. The retard separation unit (the secondary separation unit) includes a guide member for guiding the medium, and has a function of preventing a plurality of media from being supplied to the retard separation unit.
In an electro-photography printer as an image forming apparatus, there has been a demand for reducing energy consumption and a space, thereby making it necessary to reduce a size of the electro-photography printer. On the other hand, it is necessary to print on various types of media according to various applications. Accordingly, it is necessary to improve a function capable of transporting various types of media.
In particular, in an electro-photography printer capable of printing a color image, it is necessary to print on a medium having a large thickness. When the sheet supply device disclosed in Patent Reference supplies a medium having a large thickness, however, the primary separation unit may be excessively deformed due to stiffness of the medium, so that the primary separation unit thus deformed interferes with the secondary separation unit disposed on a downstream side in a medium transportation direction.
To this end, rigidity of the primary separation unit may be increased. Alternatively, the primary separation unit may be disposed sway from the secondary separation unit, so that the primary separation unit can stably separate the medium without interfering with the secondary separation unit even when the primary separation unit is deformed. However, when the primary separation unit is disposed sway from the secondary separation unit, it is necessary to increase a size of the image forming apparatus.
In view of the problems described above, an object of the present invention is to provide a sheet supply device and an image forming apparatus capable of solving the problems. In the invention, it is possible to stably separate a medium without interfering with a secondary separation unit even when a primary separation unit is excessively deformed due to stiffness of the medium.
Further objects of the invention will be apparent from the following description of the invention.
According to the present invention, a sheet supply device includes a first separation unit for applying a transportation load to a medium supplied from a stored state with a sheet supply member to separate the medium, and a second separation unit disposed on a downstream side of the first separation unit for separating the medium passing through the first separation unit. The first separation unit is disposed outside an extension area of the second separation unit in a medium transportation direction.
In the present invention, the first separation unit is disposed outside the extension area of the second separation unit in the medium transportation direction. That is, the first separation unit is disposed at a position not overlapping with the second separation unit with respect to the medium transportation direction. Accordingly, even when the first separation unit is deformed due to stiffness of the medium, it is possible to properly separate the medium without interfering with the second separation unit and increasing a size of an image forming apparatus.
a) and 5(b) are schematic views showing an operation of the sheet supply device according to the second embodiment of the present invention;
Hereunder, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following description, an electro-photography printer will be explained as an image forming apparatus.
A first embodiment of the present invention will be explained.
As shown in
In the embodiment, the medium tray 4 is provided for supplying a long medium, a thin medium, a thick medium, or a narrow medium, that the medium cassette 2 cannot handle. The medium cassette 4 is attached to the electro-photography printer 1 in a foldable manner. A pressing spring 13 is disposed below a distal end portion of a placing plate 12.
In the embodiment, the sheet supply unit 5 constitutes a sheet supply device for supplying the medium P placed on the medium tray 4 to the image forming unit 6. The sheet supply unit 5 includes a sheet supply roller 14, a transportation roller 15, and a separation roller 16. A configuration of the sheet supply unit 5 will be explained later in more detail.
In the embodiment, a transportation path 17 is connected to the sheet supply unit 5 and extends to the image forming unit 6. A sheet supply sensor 18, a print timing adjusting member 19, and a writing timing sensor 20 are disposed along the transportation path 17. The print timing adjusting member 19 is formed of a pair of rollers.
In the embodiment, the image forming unit 6 includes photosensitive drums 21K, 21Y, 21M, and 21C for forming toner images in black, yellow, magenta, and cyan, respectively, on the medium P to form a color image thereon. Further, the image forming unit 6 includes a transfer belt unit 22 and the likes for forming an image on the medium P through an electro-photography process. The medium P is synchronized to an image forming operation of the image forming unit 6 with the print timing adjusting member 19, so that an image is formed on one side of the medium P. Afterward, the medium P is transported to the fixing unit 7 disposed on a downstream side of the image forming unit 6.
In the embodiment, the fixing unit 7 includes a pair of rollers 23 and 24 pressed against with each other with a specific pressure. Heaters 25 and 26 are disposed inside the rollers 23 and 24 for heating, respectively. A transportation path 8 is connected to the fixing unit 7. A transportation detection sensor 27, a pair of transportation rollers 28, and a pair of discharge rollers 29 are disposed along the transportation path 8. The transportation rollers 28 and the discharge rollers 29 transport and discharge the medium P outside the electro-photography printer 1 through the transportation path 8 after fixing.
In the embodiment, each of the first separation units 31 is formed of a thin metal plate (a stainless steel plate with a thickness of 0.2 mm) having a fixed portion 33 fixed to a main frame of the electro-photography printer 1; a vertical portion 34 extending vertically from the fixed portion 33; and an inclined portion 35 extending obliquely and upwardly from the vertical portion 34 in the medium transportation direction. A friction member 36 is attached to a surface of the inclined portion 35.
In the embodiment, the friction member 36 is disposed at a position abutting against the leading edge of the medium P, so that the friction member 36 applies a transportation load to the medium P thus supplied to separate the leading edge of the medium P and guide the medium P toward a downstream side in the transportation direction. The friction member 36 is formed of a rubber piece made of, for example, EPDM (Ethylene-Propylene Diene Monomer).
As shown in
In the embodiment, a plurality of transportation guides 38 is disposed above the first separation units 31, so that the transportation guides 38 and the first separation units 31 form the transportation path 17 of the medium P. The transportation guides 38 are formed of a resin or a plastic in a rib shape, and have bottom portions 38a arranged such that a vertical space of the transportation path 17 gradually decreases from a point near the sheet supply roller 14 toward a downstream side of the second separation unit 32.
As shown in
In the embodiment, the top portions 37 of the first separation units 31 contact with the medium P at positions different from that of the second separation unit 32 in a vertical direction, thereby causing the medium P to bend or sag. The distance L is determined according to a sagging shape of the medium P in a direction perpendicular to the transportation direction.
When the distance L is small, the sagging shape of the medium P is bent by a large angle between the first separation units 31 and the second separation unit 32. Accordingly, when the medium P has high stiffness, an excessive force is applied to the separation roller 16 downwardly, so that it is difficult to efficiently separate the medium P with the second separation unit 32.
When the distance L increases, on the other hand, it is necessary to arrange the first separation units 31 within a transportation range (in a width direction) of the medium P having a minimum size that the sheet supply unit 5 can handle. In the embodiment, the distance L is set 10 mm. Note that the sheet supply roller 14 is disposed within a width range substantially the same as that of the transportation roller 15 and the separation roller 16 in a direction (a lateral direction in
In the embodiment, a drive system (not shown) drives the transportation roller 15 of the second separation unit 32. The separation roller 16 is provided with a torque limiter 40 for generating a brake force to be applied to the medium P. The torque limiter 40 is disposed to be freely rotatable and not rotate spontaneously. A supporting shaft fixed in a rotational direction supports the torque limiter 40.
An operation of the electro-photography printer 1 will be explained next. First, an operation of forming an image on the medium P will be explained. As shown in
When the sheet supply sensor 18 detects the medium P supplied from the sheet supply unit 5, the print timing adjusting member 19 synchronizes the medium P with an image forming process (not shown) of the image forming unit 6. Further, the writing timing sensor 20 detects the leading edge of the medium P, and the medium P is transported to the image forming unit 6.
In the image forming unit 6, the toner images in each color are formed on the photosensitive drum 21K, 21Y, 21M, and 21C. The toner images are then transferred to the medium P transported with the transfer belt unit 22. After the toner image in cyan is transferred, the medium P is sent to the fixing unit 7.
In the fixing unit 7, the heaters 25 and 26 heat the rollers 23 and 24, so that the toner images are fixed to the medium P through heat and pressure. After the toner images are fixed to the medium P in the fixing unit 7, the transportation detection sensor 27 detects the medium P passing therethrough. The transportation rollers 28 transport the medium P through the discharge transportation path 8, and the discharge rollers 29 discharge the medium P outside the electro-photography printer 1, thereby completing the printing operation.
An operation of the sheet supply unit 5 will be explained next. As shown in
As described above, the first separation units 31 are disposed outside the second separation unit 32. Further, the top portions 37 of the first separation units 31 are situated above the contact point between the transportation roller 15 and the separation roller 16 of the second separation unit 32 in the vertical direction. Accordingly, the medium P bends or sags both in the transportation direction thereof and the direction (the width direction of the medium P) perpendicular to the transportation direction. In
In the embodiment, when a plurality of the media P is transported, a space is created between the media P due to the sagging thereof. Accordingly, it is possible to reduce a frictional force between the media P. That is, a plurality of the media P is transported to the second separation unit 32 with the space therebetween. Accordingly, it is possible to securely separate the media P with the second separation unit 32.
In the embodiment, a medium transportation force Ff is generated through a drive force of the transportation roller 15 and a frictional force μr between the medium P and the transportation roller 15. When only a single medium P is transported to the second separation unit 32, the medium transportation force Ff becomes smaller than a brake force Ft of the separation roller 16 generated with the torque limiter 40 for stopping the medium P (Ff>Ft). Accordingly, the torque limiter 40 and the separation roller 16 follow the medium P and rotate in the transportation direction, thereby transporting the medium P to the sheet supply sensor 18 on the downstream side.
When two media, i.e., a medium P1 and a medium P2, are transported to the second separation unit 32, the medium transportation force Ff is generated through the drive force of the transportation roller 15 and a frictional force μr between the medium P1 abutting against the transportation roller 15 and the transportation roller 15. Further, the torque limiter 40 generates the brake force Ft of the separation roller 16 for stopping the medium P2 abutting against the separation roller 16.
In this case, the medium transportation force Ff and the brake force Ft are sufficiently larger than a frictional force Fpp between the medium P1 abutting against the transportation roller 15 and the medium P2 abutting against the separation roller 16 (Ff, Ft>>F μp). Accordingly, only the medium P1 abutting against the transportation roller 15 is transported to the sheet supply sensor 18 on the downstream side, and the medium P2 abutting against the separation roller 16 is not transported.
In the embodiment, when the sheet supply roller 14 transports the medium P and the leading edge of the medium P abuts against the friction members 36 of the first separation units 31, the friction members 36 may sag or bend in an arrow direction A shown in
When the sheet supply sensor 18 (refer to
As described above, in the embodiment, the first separation units 31 are disposed outside the extension area of the second separation unit 32 in the medium transportation direction. Accordingly, when the medium P having high stiffness is transported and the first separation units 31 are deformed excessively upon abutting against the medium P, it is possible to prevent the first separation units 31 from interfering with the second separation unit 32. As a result, it is possible to stably separate and supply the medium P without increasing a size of the electro-photography printer 1.
Further, when a plurality of the media P is transported to the first separation units 31, the media P sag in the transportation direction and the perpendicular direction thereof, and a space is created between the media P. Accordingly, it is possible to securely separate the media P with the second separation unit 32.
In the embodiment described above, the friction members 36 of the first separation units 31 are formed of the rubber piece made of EPDM, and are not limited thereto. A material with a high friction coefficient such as a cork price, a felt, and a sponge may be used. Further, the first separation units 31 may not be provided with the friction members 36, and may be provided with an inclined surface instead for applying a transportation load.
In the embodiment described above, the second separation unit 32 is a separate roller type formed of the transportation roller 15 and the separation roller 16. Instead of the separation roller 16, the second separation unit 32 may be a separation pad type using a separation pad, or any other separation types using a frictional separation method.
A second embodiment of the present invention will be explained next.
As shown in
In the second embodiment, different from the first embodiment, transportation guides 52 are provided above the first separation units 31. The transportation guides 52 have lower portions 52a extending in substantially a horizontal direction such that a minimum space d of the transportation path 17 between the first separation units 31 and the transportation guides 52 satisfies the following relationship:
tmax<d<3×tmax
where tmax is a maximum thickness of the medium P that the sheet supply unit 51 can handle. When the maximum thickness tmax of the medium P is 0.4 mm, the space d is set, for example, 1.0 mm.
As described above, the transportation guides 52 have the lower portions 52a extending in substantially the horizontal direction, and the lower portions 52a may be slightly inclined as far as the minimum space d of the transportation path 17 between the first separation units 31 and the transportation guides 52 satisfies the above relationship.
Note that the maximum thickness tmax of the medium P may be set according to a maximum thickness of the medium P that the image forming unit 6 can transfer the image thereto or the fixing unit 7 can fix the image thereto. It is preferred to determine the maximum thickness tmax of the medium P according to a maximum thickness of the medium P that the electro-photography printer 1 as a whole can handle.
An operation of supplying a medium Pmax having a maximum thickness that the sheet supply unit 51 can handle will be explained next.
When the sheet supply roller 14 supplies a plurality of media Pmax having the maximum thickness as a media bundle, the transportation guides 52 regulate an upper surface of the media bundle as shown in
In the embodiment, the friction members 36 of the first separation units 31 and the transportation guides 52 form a transportation path 54 having a wedge shape. Accordingly, the media Pmax at a lower portion of the media bundle abuts against the inclined surfaces of the friction members 36 and are prevented from proceeding further. As a result, as shown in
In the embodiment, the second separation unit 32 does not drive the separation roller 16, i.e., the sheet supply unit 51 is a so-called semi-retard type. Accordingly, when two media P are supplied to the second separation unit 32, it is possible to efficiently separate the media P.
As described above, in the embodiment, the transportation guides 52 and the first separation units 31 are arranged such that the minimum space d therebetween satisfies the following relationship:
tmax<d<3×tmax
where tmax is a maximum thickness of the medium P that the sheet supply unit 51 can supply. Accordingly, it is possible to pass one or two media Pmax through between the first separation units 31 and the transportation guides 52, thereby making it possible to efficiently separate the media P with the second separation unit 32.
A third embodiment of the present invention will be explained next.
As shown in
In the third embodiment, different from the second embodiment, transportation guides 62 are provided above the first separation units 31. The transportation guides 62 have lower portions for guiding the leading edge of the medium P toward a nip portion 62 between the transportation roller 15 and the separation roller 16, i.e., the transportation guides 62 have lower portions having an inclined shape inclined toward the nip portion 62.
In the embodiment, the transportation guides 62 have lower top portions 62a situated above the nip portion 63 between the transportation roller 15 and the separation roller 16. More specifically, the lower top portions 62a situated above the nip portion 63 by 0.5 mm.
In the embodiment, when the sheet supply roller 14 supplies the medium P, the friction members 36 of the first separation units 31 separate the leading edge of the medium P. Then, the transportation guides 62 guide the medium P toward the nip portion 63 between the transportation roller 15 and the separation roller 16 of the second separation unit 32 (toward a position lower than the upper most position of the first separation units 31). Accordingly, it is possible to easily bend the medium P on the downstream side of the first separation units 31, thereby transporting the medium P the second separation unit 32 smoothly.
As described above, in the embodiment, the transportation guides 62 are provided for guiding the leading edge of the medium P toward the nip portion 62 of the second separation unit 32. Accordingly, it is possible to easily bend the medium P on the downstream side of the first separation units 31, thereby reducing friction between the media P upon transporting a plurality of the media P.
A fourth embodiment of the present invention will be explained next.
As shown in
In the fourth embodiment, different from the third embodiment, transportation guides 72 are provided above the first separation units 31. The transportation guides 72 have lower portions for guiding the medium P. More specifically, each of the lower portions has a first guide portion (a horizontal portion) 72a facing the friction members 36 of the first separation units 31 and extending in a horizontal direction; a second guide portion (an inclined portion) 72b for smoothly guiding the leading edge of the medium P toward a nip portion 72 of the second separation unit 32 on the downstream side of the first separation units 31 in the medium transportation direction; and a curved portion 72c formed between the first guide portion 72a and the second guide portion 72b.
In the embodiment, the curved portion 72c is situated on the downstream side of the first separation units 31 at a position on an outer circumference of the transportation roller 15 of the second separation unit 32 or slightly outside thereof. The transportation guides 72 have lower top portions 72d situated at a position slightly above the nip portion 73 of the second separation unit 32. More specifically, the curved portions 72c are situated outside the outer circumference of the transportation roller 15 by 0.2 mm, and the lower top portions 72d of the transportation guides 72 are situated above the nip portion 73 by 1.0 mm.
In the embodiment, when the sheet supply roller 14 supplies the medium P, the friction members 36 of the first separation units 31 separate the leading edge of the medium P. After the medium P passes through the first separation units 31, the first guide portions 72a of the transportation guides 72 guide the medium P. When the leading edge of the medium P reaches the curved portions 72c, a transportation load increases. Accordingly, when a plurality of the media P is transported, the curved portions 72c separate the leading edges of the media P.
After the medium P passes through the curved portions 72c, the second guide portions 72b of the transportation guides 72 guide the medium P toward the nip portion 72 of the second separation unit 32. Then, after the second separation unit 32 separates and supplies the medium P, an image is formed on the medium P through the process described above, and the medium P is discharged outside the electro-photography printer 1.
As described above, in the embodiment, the curved portions 72c of the transportation guides 72 are arranged to face the first separation units 31 on the downstream side thereof. When the medium P passes through the curved portions 72c, the transportation load increases, so that the curved portions 72c separate the leading edges of the media P. Accordingly, before the medium P reaches the second separation unit 32, the leading edge of the medium P is separated twice, thereby preventing the second separation unit 32 from transporting a plurality of the media P. As a result, it is possible to securely separate the media P with the second separation unit 32, thereby improving a separation capability of the sheet supply unit 71.
In the embodiment, the first guide portions 72a of the transportation guides 72 extend substantially in the horizontal direction, and may be inclined. The features in the fourth embodiment may be combined with the features in the second embodiment.
In the embodiments described above, the present invention is applied to the electro-photography printer as the image forming apparatus, and may be applicable to other device, for example, a copier, a facsimile, and a multifunction product having a sheet supply device for supplying a medium such as a cut sheet. The image forming unit 6 is not limited to the electro-photography method, and is applicable to other method such as an ink jet method. The present invention is further applicable to an original supply device of an image reading apparatus.
The disclosure of Japanese Patent Application No. 2007-248442, filed on Sep. 26, 2007, is incorporated in the application by reference.
While the invention has been explained with reference to the specific embodiments of the invention, the explanation is illustrative and the invention is limited only by the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2007-248442 | Sep 2007 | JP | national |
