JPH0767996B2 - Paper feeder - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sheet feeding device, and more particularly to a sheet feeding device having an intermediate roller and a conveying roller on the upstream side and the downstream side of a registration roller, respectively. .

<Prior Art> Conventionally, there is provided a sheet feeding device having an intermediate roller on the upstream side of a registration roller. The intermediate roller conveys a sheet to the registration roller to cause a bend, and at the same time, to correct the leading edge of the sheet, It is possible to form a copy image on the paper by carrying the paper by the registration rollers in synchronism with the leading edge of the image formed on the surface of the photoconductor.

However, with this configuration, when the sheet is conveyed by the registration roller and the bending is eliminated, even if the intermediate roller can freely rotate, until the rotation of the intermediate roller becomes stable, Since a large amount of tension is applied instantaneously, slippage occurs and the leading edge of the paper is delayed. Especially, in the case of a copying machine in which paper feeding units such as paper feeding cassettes can be mounted in multiple stages, in the worst case, it is necessary to circulate a plurality of intermediate rollers by the conveying force given by the registration rollers. However, the above problems will be noticeable.

In consideration of such a problem, when the sheet is conveyed by the registration rollers, the deviation of the leading end is surely prevented by allowing the registration rollers to convey the sheet while the deflection of the sheet is completely preserved. A sheet feeding device is provided (see Japanese Patent Laid-Open No. 59-49561).

<Problems to be Solved by the Invention> With the paper feeding device described in the above publication, it is almost expected that the peripheral speed of the registration roller and the peripheral speed of the intermediate roller are equal when the product is actually commercialized. I can't. More specifically, in recent copying machines, it is common to use a DC motor as a drive source for driving a paper feed roller and an intermediate roller separately from a drive source for driving a photosensitive drum and the like. However, the peripheral speed of the intermediate roller tends to increase because the speed on the side receiving the driving force by the DC motor tends to increase, although it changes somewhat depending on the load condition.

Therefore, there is a problem in that so-called Z-folding occurs due to excessive bending of the paper.

In addition, since the paper is conveyed by the registration roller while holding the deflection, if the center side of the registration roller is made slightly larger in order to surely convey a large size paper (a driving side roller and a driven side roller by a spring). When the center side of the driven side roller has a slightly larger diameter so that the pressure contact force with and is uniform over the entire range), wrinkles are generated by carrying thin paper. There is also a problem.

This invention has been made in view of the above problems,
It is an object of the present invention to provide a sheet feeding device capable of preventing the leading edge of a sheet from slipping and Z-folding and also preventing wrinkles when a thin large size sheet is conveyed.

<Means for Solving Problems> A paper feeding device of the present invention for achieving the above object is
The paper sent from the paper feed section by the paper feed roller is conveyed to the registration roller by the intermediate roller, and this paper is conveyed by the registration roller at a predetermined timing, and by the conveyance roller installed between the registration roller and the photoconductor. Further, the sheet feeding device is configured to give a conveying force to the sheet, and the sheet is fed from a sheet feeding unit and a registration roller driving unit that drives the registration roller in synchronization with the leading edge of the image formed on the surface of the photoconductor. After the leading edge of the paper comes into contact with the registration roller, the intermediate roller is driven until a predetermined time elapses, thereby causing the paper to bend, and at a predetermined timing after the conveyance by the registration roller is started and at the intermediate time. After the paper reaches the conveyance roller from the timing that does not completely eliminate the deflection of the paper formed by the roller Those having an intermediate roller driving means for rotating the intermediate roller again until a predetermined timing.

However, it is preferable that the predetermined timing after the conveyance by the registration rollers is started is a timing at which the deflection of the sheet formed by the intermediate roller is not completely eliminated.

<Operation> In the case of the sheet feeding device having the above-described configuration, a conveying force is applied to the sheet sent from the sheet feeding section by the sheet feeding roller by the intermediate roller driven by the intermediate roller driving unit, and the leading end of the sheet is registered by the registration roller. And a predetermined amount of deflection is generated. Then, the registration roller driving means drives the registration roller in synchronization with the leading edge of the image formed on the surface of the photoconductor to start the conveyance of the paper, and the paper surely reaches the conveyance roller from a predetermined timing. The intermediate roller is driven by the intermediate roller driving means until a predetermined timing after that time, and a large tension is prevented from being applied to the paper. After that, the registration roller and the transport roller alone apply a predetermined tension to the paper. The paper can be fed in the closed state, and the phenomenon of wrinkling of the paper can be prevented.

In particular, by starting the intermediate roller after the registration roller, the sheet is conveyed by the registration roller and the intermediate roller in a state in which the bending is reduced to the extent that it cannot be eliminated. Therefore, even if there is a problem that the peripheral speed of the intermediate roller is higher than that of the registration roller, the deflection does not become too large, so that the so-called Z-fold of the sheet can be prevented from occurring. Further, since the bending of the paper is not completely eliminated, it is possible to reliably prevent a large tension from being applied to the paper instantaneously.

<Example> Hereinafter, detailed description will be given with reference to the accompanying drawings illustrating an example.

FIG. 2 is a schematic view showing an embodiment of the paper feeding device, in which the paper is selectively fed from the three-stage paper feeding cassettes (1a) (1b) (1c) as the paper feeding unit, and the photosensitive drum It can be conveyed toward (6).

More specifically, the paper cassettes (1a) of each stage
(1b) It has paper feed rollers (2a) (2b) (2c) that feed the paper stored in (1c) one by one, and further conveys the paper fed from the uppermost paper feed cassette (1a) Intermediate rollers (3a) and (3b), registration rollers (4) that further convey the paper conveyed by the intermediate rollers (3a) and (3b), and further conveyance force to the paper conveyed by the registration rollers (4). And a transport roller (5) that is constantly driven to rotate. Then, the paper fed from the second-stage paper feed cassette (1b) is directly fed to the intermediate roller (3b).
The sheet fed from the lowermost sheet feeding cassette (1c) is directly led to the registration roller (4). Incidentally, (7a), (7b) and (7c) are paper detection switches attached immediately before the intermediate rollers (3a) (3b) and the registration roller (4), respectively.

Among the above-mentioned components, the registration roller (4), the pre-transfer roller (5), and the photosensitive drum (6) are driven by the same drive source (not shown), and the registration roller (4) By mounting a clutch that controls the transmission of the driving force to the sheet, the secondary feeding of the sheet can be performed in synchronization with the leading edge of the image formed on the surface of the photosensitive drum (6).

The paper feed rollers (2a) (2b) (2c) and the intermediate rollers (3a) (3b) are driven by a drive source different from the above drive source, for example, a DC motor (not shown). By attaching a clutch that controls the transmission of driving force to the paper feed rollers (2a) (2b) (2c) and the intermediate rollers (3a) (3b), temporary paper feed can be performed.

FIG. 1 is a block diagram showing the electrical configuration of the paper feeding device. The registration roller clutch (72) is operated by inputting a document exposure start signal from an optical system (not shown), and rotation to the registration roller (4) is performed. The registration roller drive unit (71) for transmitting the force and the time required for the leading edge of the paper to reach the transport roller (5) have elapsed since the transmission of the rotational force to the registration roller (4) was started. A timing signal generator (73) that outputs a timing signal when
The clutch (75a) (75b) (75c) for the paper feed rollers is selectively operated by inputting a paper feed start signal from a control unit (not shown), and the paper feed rollers (2a) (2b) (2c) are selectively operated. For the intermediate roller for a predetermined time selectively by inputting the signals from the paper feed roller drive unit (74) for transmitting the rotational force to the roller and the switches (7a) (7b) (7c) and the timing signal And an intermediate roller drive unit (76) for selectively operating the clutches (77a, 77b) to selectively transmit the rotational force to the intermediate rollers (3a, 3b).

FIG. 3 is a time chart for explaining the operation of the sheet feeding device, in which the sheet is fed from the uppermost sheet feeding cassette (1a).
The case where the copying operation is continuously performed is shown.

The clutch (75a) is operated by the paper feed roller drive unit (74) at the timing when the print key of the copying machine is operated, and the predetermined time (the time from when the switch (7a) detects the paper until the predetermined time elapses) Only the paper feed roller (2a) is rotated to convey the paper until it comes into contact with the intermediate roller (3a) (see A in the figure). Next, intermediate roller drive unit (76)
The clutches (77a) (77b) are operated by and the intermediate time is reached for a predetermined time (from the time when the paper contacts the intermediate roller (3a) until the switch (7c) detects the paper and the predetermined time elapses). The rollers (3a) and (3b) are rotated so that the leading edge of the sheet comes into contact with the registration roller and is conveyed until a predetermined amount of deflection is formed (see B in the figure).

That is, the temporary feeding is completed by the above operation, and the timing for starting the secondary feeding is waited (see C in the figure).

The timing of starting the secondary paper feeding is the timing at which the exposure of the original is started by an optical system (not shown). First, the registration roller driving unit (71) operates the clutch (72) for a predetermined time (from the above timing, the switch (7c)
The sheet can be conveyed to the photosensitive drum 6 by rotating the registration roller (4) for a predetermined time after the sheet no longer detects the sheet (see D in the figure). Incidentally, since the carrying force of the carrying roller (5) is applied during the carrying operation, the paper can be carried reliably.

Further, at the time point when a predetermined time (the time when the flexure of the paper is not completely eliminated) has elapsed since the conveyance of the paper by the registration rollers (4) was started, the intermediate roller drive unit (7
The clutches (77a) and (77b) are operated by 6), and the intermediate rollers (3a) and (3b) are rotated for a predetermined time (time until the leading edge of the paper surely reaches the conveyance roller (5)),
By conveying the sheet with a certain amount of bending left, it is possible to reliably prevent delay of sheet feeding due to slip (see E in the figure). At this time, since the flexure is reduced by starting the intermediate roller after the registration roller is delayed, even if the peripheral speed of the intermediate roller is higher than that of the registration roller, the flexure will be too large. As a result, the so-called Z-fold of the paper can be prevented from occurring. After that, as indicated by F in the figure, the registration roller (4) and the conveyance roller (5) apply a conveyance force to the sheet, and the intermediate rollers (3a) and (3b) change the driving force from the rotational drive state. Since only the state where the transmission is cut off is shifted and the speed does not rise from the stopped state to the predetermined speed, the delay of the sheet feeding due to the slip does not occur.

The second sheet is fed in the same manner as above.

In the above embodiment, each predetermined time is not calculated by counting a single clock pulse, but the paper feed rollers (2a) (2b) (2c) and the intermediate roller (3a).
(3b) is calculated by counting clock pulses synchronized with the rotation speed of the DC motor, and the registration roller (4)
Is calculated by counting clock pulses synchronized with the rotation speed of the drive motor on the copying machine main body side. Therefore, even if the number of rotations of the drive motor and the DC motor of the main body of the copying machine is different, the operation amount per one clock pulse can be controlled to be constant, which is a disadvantage caused by using another drive source. Can be reliably solved.

The present invention is not limited to the above embodiment, and for example, at least a part of the control of the driving time can be performed by a switch. Further, it is possible to configure the paper feeding unit with a plurality of paper feeding trays built in the front of the copying machine so as to be drawn out (a so-called front loading system). In addition, various design changes can be made within the scope of the present invention.

<Advantages of the Invention> As described above, according to the present invention, when secondary sheet feeding is performed, it is possible to reliably prevent the deviation of the leading edge timing due to the slip of the sheet, and to prevent the occurrence of Z-fold due to excessive bending. There is a unique effect that it can be prevented and the phenomenon of wrinkles during secondary feeding can be surely prevented.

[Brief description of drawings]

FIG. 1 is a block diagram showing an electrical configuration of an embodiment of the paper feeding device, FIG. 2 is a schematic view showing an embodiment of the paper feeding device, and FIG. 3 is a timing chart. (1a) (1b) (1c) …… paper feed cassette, (2a) (2b) (2c) …… paper feed roller, (3a) (3b) …… intermediate roller, (4) …… registration roller, ( 5) ... conveying roller, (6) ... photosensitive drum, (71) ... registration roller driving section, (76) ... intermediate roller driving section

Claims (1)

[Claims] 1. A sheet fed from a sheet feeding section by a sheet feeding roller is conveyed by an intermediate roller to a registration roller, and the sheet is conveyed by a registration roller at a predetermined timing, and between the registration roller and a photoconductor. A sheet feeding device configured to further apply a sheet conveying force to a sheet by an attached sheet conveying roller, including a registration roller driving unit that drives a registration roller in synchronization with the leading edge of an image formed on the surface of a photoconductor, and a sheet feeding device. After the leading edge of the paper sent from the unit contacts the registration roller, the intermediate roller is driven until a predetermined time elapses, causing the paper to bend, and at a predetermined timing after the conveyance by the registration roller is started. And the sheet is not conveyed by the timing at which the deflection of the sheet formed by the intermediate roller is not completely eliminated. Sheet feeding apparatus, comprising an intermediate roller driving means again for rotating the intermediate roller to a subsequent predetermined timing has been reached.