Sheet feeding apparatus

Abstract: The present invention provides a sheet feeding apparatus comprising sheet containing means which containing sheets and removably mounted to a main body of the sheet feeding apparatus, separation means including convey means and a separation member urged against the convey means with predetermined separating pressure to separate the sheets fed out from the sheet containing means mounted on the body of the sheet feeding apparatus one by one, and pressure increasing means for increasing contact pressure between the convey means and the separation member above the predetermined separating pressure. Wherein the pressure increasing means increases the contact pressure until the mounting of the sheet containing means to the body of the sheet feeding apparatus is completed. Whereby, even if the sheet containing means is inserted into the sheet feeding apparatus vigorously, the sheets are prevented from entering between the convey means and the separation member, thereby preventing the poor sheet separation.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a sheet feeding apparatus for feeding a sheet used with an image forming apparatus such as an electrophotographic copying machine and the like. Related Background Art Nowadays, various information processing equipments have been proposed in dependence upon progress of information processing systems. Among them, recording apparatuses such as facsimiles, printers and the like have been widely used not only in offices but also in general homes. Fig. 7 is a sectional view of a facsimile system to which a conventional sheet feeding apparatus is applied. A cassette 142 to which recording sheets (sheet materials) S are housed is mounted to a predetermined position of the facsimile system, and there are provided a recording sheet separating portion 143 comprising a pick-up roller 143a and a separation piece 143b which serve to separate the recording sheets S one by one, a sheet supply roller pair 145 comprising a pair of feed rollers 145a, 145b for conveying the separated recording sheet Sa, a recording portion 144 comprising a sheet feed roller 146 and an ink jet cartridge 147 having an ink jet head and an ink tank, and a sheet discharge roller pair 148 comprising a pair of sheet discharge rollers 148a, 148b for discharging the recording sheet S on which an image was recorded. However, in the above-mentioned conventional art, in order to always contact the recording sheet stack S in the cassette 142 with the pick-up roller 143a, as shown in Fig. 8A, an intermediate plate 149 is always biased upwardly toward the pick-up roller. Further, an upper surface of a front wall 142a of the cassette 142 is positioned slightly lower than an upper surface of the sheet stack S. Thus, if the cassette 142 containing the recording sheets S is mounted to the predetermined position of the facsimile system vigorously, as shown in Fig. 8B, several recording sheets S positioned above the upper surface of the front wall 142a of the cassette are advanced forwardly by inertia force, thereby forcing down the separation piece 143b for separating the recording sheets S one by one and entering the recording sheets between the pick-up roller 143a and the separation piece 143b to cause poor separation. This is caused when separation pressure (contact pressure between the pick-up roller 143a and the separation piece 143b) for separating the recoding sheets S cannot prevent the recording sheets S from entering between the pick-up roller 143a and the separation piece 143b due to the great inertia force of the recording sheets S. From EP-A-0 204 227 a sheet feeding apparatus including a pick-up roller and a friction pad is known. When the cassette is mounted, the contact pressure between pick-up roller and friction pad is established. SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problem caused when a cassette is pushed into an image forming apparatus vigorously. That is to say, the object of the present invention is to prevent occurrence of a problem that poor sheet supply is caused by entering bundled sheets between a convey means and a separation member when the cassette is pushed into an image forming apparatus vigorously. According to the present invention, there is provided a sheet feeding apparatus comprising sheet containing means which can contain sheets and which can removably be mounted to a body of the sheet feeding apparatus, separation means including a convey means and a separation member urged against the convey means with predetermined separating pressure and adapted to separate the sheets fed out from the sheet containing means mounted on the body of the sheet feeding apparatus one by one, and pressure increasing means for increasing a contact pressure between the convey means and the separation member above the predetermined separating pressure, arranged so that the pressure increasing means increases the contact pressure until the mounting of the sheet containing means to the body of the sheet feeding apparatus is completed. Preferably, the pressure increasing means increases the contact pressure when the sheet containing means is shifted forwardly from a mounting position of the body of the sheet feeding apparatus in the mounting direction. With this arrangement, even if the sheet containing means is pushed into the sheet feeding apparatus vigorously, bundled sheets are prevented from entering between the convey means and the separation member. Consequently, occurrence of poor sheet supply can be prevented, thereby separating and feeding the sheets one by one without fail. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a perspective view of a facsimile system to which a sheet feeding apparatus according to a preferred embodiment of the present invention is applied; Fig. 2 is a sectional view of the facsimile system of Fig. 1; Fig. 3 is a perspective view of the sheet feeding apparatus; Figs. 4A to 4C are schematic views for explaining an operation of a recording sheet separating portion of the sheet feeding apparatus; Figs. 5A to 5C are schematic views showing a cassette mounting operation, according to another embodiment of the present invention; Figs. 6A to 6C are schematic views showing a recording sheet separating portion of a sheet feeding apparatus according to a further embodiment of the present invention; Fig. 7 is a sectional view of a facsimile system to which a conventional sheet feeding apparatus is applied; Figs. 8A and 8B are schematic views showing movement of sheets in the conventional sheet feeding apparatus. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be explained in connection with embodiments thereof with reference to the accompanying drawings. Fig. 1 is a perspective view of a facsimile system to which a sheet feeding apparatus according to a preferred embodiment of the present invention is applied and Fig. 2 is a sectional view of the facsimile system. Fig. 3 is a perspective view showing a separating portion of the sheet feeding apparatus. First of all, explaining the entire construction of the facsimile system with reference to Fig. 2, a body 1 of the system has an upper cover 1a inclined so that one end (left end in Fig. 2) of the cover is lower than the other end, thereby making the system compact. An original reading portion 2 provided at one end (left end in Fig. 2) of the facsimile system has an original insertion opening 3, and an original guide 5 slidable along a widthwise direction of an original D in order to regulate a side edge of the original at the original insertion opening 3. Further, in an original convey path of the original reading portion 2 (i.e. between the original insertion opening 3 and an original discharge opening 6 positioned below the left end of the upper cover 1a of the system body 1), there are arranged an ADF (automatic document feeder) portion 7 adapted to separate the originals D sent from the original guide 5 one by one and comprising an ADF roller 7a and an urging member 7b urged against the ADF roller 7a, a sheet feed portion 8 comprising a pair of feed rollers 8a, 8b for feeding the original separated at the ADF portion 7, an image sensor 9 of contact type acting as a reading means for reading image information on the original sent from the sheet feed portion 8, a CS roller 10 acting as a contacting means opposed to the image sensor 9 of contact type and adapted to convey the original while closely contacting the original D against the sensor 9 with a predetermined urging force at a reading position 9a, and a discharge portion 11 comprising a pair of discharge rollers 11a, 11b for discharging the original 4 (which was read) through the original discharge opening 6. Next, a reading operation of the facsimile system will be explained. After the originals D are set along the original guide 5, when a reading start signal is inputted by an operation switch, a drive motor (not shown) is driven to rotate the ADF roller 7a, feed roller 8a, discharge roller 11a and CS roller 10, with the result that the originals D are separated one by one at the ADF portion 7 and the separated original is sent to the sheet feed portion 8. When a tip end of the original D is detected by an original tip end detection sensor (DES), the drive motor is stopped to temporarily stop the ADF roller 7a, feed roller 8a, discharge roller 11a and CS roller 10. Then, a predetermined time period is elapsed, the drive motor is driven again to rotate the ADF roller 7a, feed roller 8a, discharge roller 11a and CS roller 10 again. After the rollers 7a, 8a, 11a, 10 are rotated, while the tip end of the original D is being conveyed to the reading position 9a of the sensor 9 of contact type, a peripheral surface (white as reference color) of the CS roller 10 is read by the sensor 9 of contact type. Then, when the tip end of the original D is sent to the reading position 9a of the sensor 9 of contact type, the image information on the original D is read. In this case, the original D is urged against the reading position 9a of the sensor 9 of contact type from the above by means of the CS roller 10 so that a reading line of the sensor 9 of contact type is aligned with a generatrix of the CS roller 10, with the result that the original D is not floating from the reading position 9a, thereby reading the image information with high accuracy. When the reading of the original D is finished in this way, the original D is sent to the discharge portion 11 by the CS roller 10 also acting as the original convey means and then is discharged out of the system through the sheet discharge opening 6 by the pair of discharge rollers 11a, 11b. In this way, the reading of the information on the single original is completed. If the original being read is jammed, as shown by the two dot and chain line in Fig. 2, the upper cover 1a is opened by rocking the cover around a fulcrum disposed near the sheet discharge opening. As a result, the urging member 7b, feed roller (back-up roller) 8b, CS roller 10 and discharge roller (back-up roller) 11b held by a member (not shown) attached to the upper cover 1a are shifted to positions shown by the two dot and chain line in Fig. 2 to open a sheet convey path. Accordingly, the jammed original D can easily be removed. Next, a construction of a recording portion will be explained. A recording portion 21 is provided at the other end (right end in Fig. 2) of the original reading portion 2 of the facsimile system 1. A cassette 23 acting as a containing means for containing recording sheet S as sheet materials is mounted to the facsimile system 1. Further, since a cassette cover 24 is made of transparent material, a remaining amount of recording sheets S can be ascertained without retracting the cassette 23 from the facsimile system 1. In the proximity of one end (right end in Fig. 2) of the recording sheet stack S, there are arranged a recording sheet separating portion 25 comprising a pick-up roller (convey means) 25a and separation piece (separation member) 25b urged against the pick-up roller 25a by a spring (not shown) or other elastic member such as a rubber member, a sheet feed portion 26 comprising a pair of feed rollers 26a, 26b for feeding the recording sheet S separated at the recording sheet separating portion 25, an ink jet cartridge (recording means) 27 for recording an image on the recording sheet S conveyed from the sheet feed portion 26, a convey roller 28 for conveying the recording sheet S to a position substantially opposed to the ink jet cartridge 27, and a sheet discharge portion 30 comprising a pair of discharge rollers 30a, 30b for discharging the recording sheet S on which the image was recorded through a recording sheet discharge opened 29. Next, a recording operation of the recording portion 21 will be explained. When the reading start signal is inputted by an operation switch after the original D is set along the original guide 5, or when an image receiving signal is inputted through a telephone line, the drive motor is driven to rotate the pick-up roller 25a to send the recording sheets S to the separation piece (separation member) 25b, where the recording sheets S are separated one by one by the separating portion 25 comprising the pick-up roller 25a and the separation piece 25b, and the separated recording sheet is sent to the sheet feed portion 26. Incidentally, the separation piece 25b is made of high friction material. Further, before the recording sheet S reaches the sheet feed portion 26, another drive motor is driven to rotate the feed roller 26a, convey roller 28 and discharge roller 30a, thereby conveying the recording sheet S. Then, a tip end of the recording sheet S is detected by a recording sheet tip end sensor (PE sensor) disposed between the feed roller 26a and the convey roller 28. After the tip end of the sheet is detected by the PE sensor, the recording sheet S is advanced by a predetermined distance and the recording is started by the ink jet cartridge. When the recording of the recording sheet S is finished, the recording sheet is discharged out of the facsimile system by the pair of discharge rollers 30a, 30b. In this way, the recording operation of the image information regarding the single recording sheet is completed. Further, as shown by the two dot and chain line, a record cover 31 can be opened around an upper end (Fig. 2) of the system so that the ink jet cartridge can easily be exchanged. Next, an operation for mounting the cassette 23 to the facsimile system 1 will be explained with reference to Fig. 3 which is a perspective view showing the separation piece 25b and therearound. The separation piece 25b is held by a support plate 25c rockable around a longitudinal axis m in directions d and e. On the other hand, a jam releasing plate 33 acting as a pressure increasing means is normally biased toward a direction a by a spring 32 to rotate the plate 33 around an axis n in a direction b, with the result that the support plate 25c is rotated by a bent portion 33b of the jam releasing plate in the direction d (Fig. 4A). As a result, the separation piece 25b is separated from the pick-up roller 25a, so that, if the recording sheet S is jammed between the separation piece and the pick-up roller, the sheet can easily be removed. Incidentally, although the support plate 25c is biased toward the direction e by springs 25e, since a spring force of the spring 32 is set to be greater than spring forces of the springs 25e, the separation piece 25b can be separated from the pick-up roller 25a. Then, after the cassette 23 is mounted to the facsimile system, when an urging piece 33c of the jam releasing plate 33 is pushed toward a direction X in opposition to the spring force of the spring 32, the jam releasing plate 33 is rotated around the axis in a direction c so that a bent portion 25d of the support plate 25c is urged by a bent portion 33a of the jam releasing plate 33 around the axis in the direction e, thereby increasing the contacting force between the pick-up roller 25a and the separation piece 25b. Consequently, even if the cassette 23 is inserted into the facsimile system vigorously, the separation piece 25b can be prevented from being pushed down by the bundled recording sheets S (Fig. 4B). However, in this condition, the cassette 23 is further advanced from a normal or proper mounting position. When the mounting of the cassette 23 to the facsimile system is completed, that is, when the operator releases his hand from the cassette 23, the cassette 23 is slightly returned to the proper mounting position (Fig. 4C) by the spring force of the spring 32. In this condition, the support plate 25c is not regulated by the jam releasing plate 33 to provide the predetermined separating pressure (contact pressure) between the pick-up roller 25a and the separation piece 25b, thereby enabling to separate the recording sheets S one by one properly. Incidentally, although the cassette 23 is biased toward a dismounting direction by the spring 32 at the mounting position, it is held in the mounting position by an appropriate regulating means (not shown). (Second Embodiment) In the above-mentioned first embodiment, while an example that the jam releasing plate 33 and the support plate 25c are mechanically shifted in synchronism with the movement (mounting movement) of the cassette 23 to temporarily increase the contact force between the pick-up roller 25a and the separation piece 25b so that, if the cassette 23 is inserted into the facsimile system vigorously, the separation piece 25b can be prevented from being pushed down by the bundled recording sheets S was explained, the same technical advantage can be obtained by using an electrical technique in place of the mechanical movement. That is to say, as shown in Figs. 5A to 5C, the presence/absence of the cassette 23 is detected by a micro-switch SW1, and a micro-switch SW2 detects whether the cassette 23 is mounted to the proper mounting position. On the basis of conditions of the micro-switches SW1, SW2, the separation piece 25b is pulled toward the pick-up roller 25a by a solenoid (pressure increasing means) 34, thereby controlling the contact pressure between the pick-up roller 25a and the separation piece 25b. Now, this electrical technique will be fully described. (1) When the cassette 23 is not mounted: As shown in Fig. 5A, when the micro-switches SW1, SW2 are both turned OFF, it is judged that the cassette is not mounted on the facsimile system. In this condition, the solenoid 34 is not operated, and the contact pressure f between the pick-up roller 25a and the separation piece is defined by a force F from the springs 25e ( f = F) (Fig. 6A). Incidentally, in this embodiment, even when the cassette 23 is not mounted, although the separation piece 25b is urged against the pick-up roller 25a due to the presence of the springs, the separation piece is not necessarily urged against the pick-up roller when the cassette is not mounted. (2) When the cassette 23 is mounted: As shown in Fig. 5B, when the micro-switch SW1 is turned ON and the micro-switch SW2 is turned OFF, it is judged that the casstte is mounted on the facsimile system. In this condition, the contact pressure f between the pick-up roller 25a and the separation piece 25b is defined by not only the force F from the springs but also a force f 1 (f= f 0 ) of the solenoid 34 for pulling the support plate 25c and accordingly the separation piece 25b toward the pick-up roller 25a in a direction g (f = F + f 0 ), with the result that, even if the cassette 23 is inserted into the facsimile system vigorously, the separation piece 25b can be prevented from being pushed down by the bundled recording sheets S (Fig. 6B) (3) When the mounting of the cassette 23 is completed: As shown in Fig. 5C, when the micro-switches SW1, SW2 are both turned ON, it is judged that the mounting of the cassette is completed. In this condition, the force f 1 of the solenoid 34 disappears (f 1 = f 0 ), and, thus, the contact pressure (separating pressure) f between the pick-up roller 25a and the separation piece 25b is kept to the optimum value (f = F) for separating the recording sheets S one by one (Fig. 6C). In this embodiment, the condition that the cassette 23 is not mounted (Fig. 6A) is the same as the condition that the mounting of the cassette 23 is completed (Fig. 6C). While the present invention was fully explained in connection with embodiments thereof, the present invention is not limited to such embodiments. For example, in the above-mentioned emodiments, while the present invention was applied to the separation means for separating the recording sheets one by one, the present invention may be applied to a separation means for separating originals or other sheets one by one. Further, in the above-mentioned embodiments, while an example that the supplying and separation of the sheets are effected by the pick-up roller was explained, the supplying and separation of the sheets may be effected by discrete rollers and the like. In addition, in the above-mentioned embodiments, while the separation piece was used as the separation means, in place of the separation piece, a reverse rotation roller (i.e. so-called retard roller) may be used.

Claims: A sheet feeding apparatus comprising: sheet containing means (23) containing sheets and removably mounted to a main body of the sheet feeding apparatus; separation means including convey means (25a) and a separation member (25b) urged against said convey means with predetermined separating pressure for separating the sheets fed out from said sheet containing means mounted on the main body of the sheet feeding apparatus one by one; and pressure increasing means (33; 34) for increasing contact pressure between said convey means (25a) and said separation member (25b) above the predetermined separating pressure, arranged so that said pressure increasing means increases the contact pressure until the mounting of said sheet containing means to the main body of the sheet feeding apparatus is completed. A sheet feeding apparatus according to claim 1, wherein said separation member (25b) is held by a support member (25c) in such a manner that said separation member can be abutted against and separated from said convey means (25a), and said separation member is urged against said convey means with said predetermined separating pressure by biasing said support member by means of a first elastic means (25e). A sheet feeding apparatus according to claim 2, wherein said pressure increasing means (33; 34) is operated as said sheet containing means is mounted to the main body of the sheet feeding apparatus. A sheet feeding apparatus according to claim 3, wherein said pressure increasing means has a rockable member (33) rockably provided, and, when said sheet containing means (23) is mounted to the main body of the sheet feeding apparatus, said sheet containing means urges one end of said rockable member to rock it, thereby regulating a movement of said separation member (25b) away from said convey means (25a) at the other end of said rockable member to thereby increase the contact pressure. A sheet feeding apparatus according to claim 2, wherein said pressure increasing means has a solenoid (34) for urging said separation member against said convey means, and said solenoid is energized on the basis of a detection signal from detection means (SW1, SW2) for detecting the mounting of said sheet containing means (23) to the main body of the sheet feeding apparatus, to increase an urging force by which said separation member (25b) is urged against said convey means (25a), thereby increasing the contact pressure. A sheet feeding apparatus according to claim 5, wherein said detection means has a first sensor (SW1) for detecting insertion of said sheet containing means (23) into the main body of the sheet feeding apparatus, and a second sensor (SW2) for detecting whether said sheet containing means is mounted to a predetermined position, and wherein said solenoid (34) is energized on the basis of detection of said first sensor and disenergized on the basis of detection of said second sensor. A sheet feeding apparatus according to claim 1, wherein said separation means (25b) is arranged in the proximity of a downstream end of said sheet containing means (23) when mounted to the body of the sheet feeding apparatus. A sheet feeding apparatus according to claim 1, wherein said convey means (25a) is abutted against an uppermost sheet among the sheets contained in said sheet containing means (23) to feed out the sheet or sheets. A sheet feeding apparatus according to claim 2, wherein said pressure increasing means (33; 34) increases the contact pressure when said sheet containing means is further shifted from a mounting position of the body of the sheet feeding apparatus in the mounting direction. A sheet feeding apparatus according to claim 9, wherein said pressure increasing means has a rockable member (33), and, when said sheet containing means (23) is further shifted from said mounting position of the body of the sheet feeding apparatus in the mounting direction, said sheet containing means urges one end of said rockable member to rock it in a first direction (c), thereby regulating a movement of said separation member away from said convey means (25a) by engaging the other end of said rockable member with said support member (25c) to increase the contact pressure. A sheet feeding apparatus according to claim 10, further comprising a second elastic means (32) for biasing said rockable member (33) to rotate it in a second direction (b) opposite to said first direction (c), and, said rockable member is rotated in said second direction as said sheet containing means (23) is dismounted from the body of the sheet feeding apparatus, said rockable member is engaged by said support member to separate said separation member and said convey means from each other in opposition to an elastic force of said first elastic means (25e). An image forming apparatus comprising: a sheet feeding apparatus according to any one of claims 1 to 11; and an image forming means for forming an image on the sheet fed out from said sheet feeding apparatus.

Inventors: NAGAHARA HIDEAKI, NAGAHARA, HIDEAKI, NAGAHARA, HIDEAKI, C/O CANON KABUSHIKI KAISHA
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1995
Main classification: G03G15
IPC codes: B65H1, B65H3, G03G15