JP2001348129A - Paper feeder and image forming apparatus - Google Patents

Abstract

(57) [Problem] To stabilize paper transportability during paper feeding even when a small motor is used as a driving source of a paper feeding system. When a registration roller is driven in synchronization with an operation of an image forming unit (S7), a sheet feeding roller is driven again (S8), so that even when a small-capacity motor is used as a driving source, conveyance is performed. The paper is conveyed with the force applied. In this case, a single sheet feeding end time at which the rear end of the sheet reaches the sheet feeding roller (Y in S9) is set according to the length of the sheet, and the feeding is performed at the single sheet feeding end time. The paper roller is stopped (S10). Therefore, it is possible to accurately set the stop timing of the re-driven paper feed roller according to the length of the paper, thereby reliably feeding the paper to be fed, and feeding the next layer of paper in a stacked manner. This can prevent the occurrence of jams due to the above.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sheet feeding apparatus and an image forming apparatus for feeding a sheet fed from a sheet feeding section by a registration roller with the timing of operation of an image forming section.

[0002]

2. Description of the Related Art In a paper feeding device used in an image forming apparatus, a sheet fed by a sheet feeding roller is temporarily stopped by a nip portion of a registration roller in order to keep a position of an image to be output on the sheet. The sheet is sent out by driving a registration roller in synchronization with the progress of the printing.
When the registration roller is driven, the trailing end of the sheet is located at the sheet feeding section, and the sheet feeding roller is in a state where no driving force is applied even if the sheet feeding roller is rotated by friction with the sheet.

In this case, the conveyance of the sheet is not always stable due to the resistance applied to the sheet. In particular, when a small-sized and small-capacity motor is used as a driving source of a paper feeding system for cost reduction, the stability of sheet conveyance tends to be deteriorated.

[0004] For this reason, Japanese Patent Application Laid-Open No. 9-2269 discloses
As described in Japanese Patent Publication No. 85, a proposal has been made in which a sheet feeding roller is rotated at the same time as a registration roller is driven to supplement a conveying force. In this case, the timing for stopping the paper feed roller is set according to the difference in the thickness of the paper.

[0005]

Problems to be Solved by the Invention
The proposal described in Japanese Patent Laid-Open Publication No. 5 (1999) -2005 can compensate for the conveying force when a small motor is used as a drive source. But,
If the length of the paper to be used changes, the timing for stopping the paper feed roller changes, causing a problem. Specifically, when the paper to be used is long, the paper feed roller is stopped before the rear end of the paper reaches the paper feed roller, and the subsequent conveyance force is reduced. Conversely, if the paper is short, the paper feed roller is driven even if the trailing edge of the paper passes the paper feed roller, so that the paper of the next layer is fed, causing a jam.

SUMMARY OF THE INVENTION It is an object of the present invention to stabilize sheet transportability during sheet feeding even when a small motor is used as a driving source of a sheet feeding system.

[0007]

According to a first aspect of the present invention, there is provided a sheet feeding device including a sheet feeding unit for storing sheets, a sheet feeding roller for feeding sheets in the sheet feeding unit to an image forming unit, and a sheet feeding command. Paper feed driving means for driving the paper feed roller each time a signal is output,
A registration roller disposed between the image forming unit and the sheet feeding roller; a registration driving unit that drives the registration roller in synchronization with the operation of the image forming unit; A sheet feeding end time setting means for setting a sheet feeding end time at which the rear end of the sheet reaches the sheet feeding roller in accordance with a designated sheet length; and Re-driving means for re-driving the paper feed roller only during a period up to the end of single-sheet feeding.

Therefore, when the paper feed command signal is output, the paper feed roller is driven, and the paper in the paper feed unit is fed to the registration roller. When the registration roller is driven in synchronization with the operation of the image forming unit, the sheet feeding roller is driven again, so that the sheet is conveyed in a state where the conveying force is supplemented. In this case, the sheet feeding end time when the rear end of the sheet reaches the sheet feeding roller is set according to the length of the sheet, and the sheet feeding roller is stopped at the sheet feeding end time.

According to a second aspect of the present invention, in the sheet feeding apparatus according to the first aspect, there is provided a sheet length detecting means for detecting a length of a sheet actually fed, and the sheet feeding end timing setting means is provided. Sets the sheet feeding end timing based on the sheet length detected by the sheet length detecting means.

Therefore, the setting of the single sheet feeding end timing for stopping the sheet feeding roller re-driven when the registration roller is driven is based on the length of the sheet actually fed.

According to a third aspect of the present invention, in the paper feeder according to the second aspect, the sheet length detecting means is provided only for the first sheet fed first when a plurality of print sheets are designated. The sheet length is detected, and the sheet length is recognized as the second and subsequent sheet lengths.

Therefore, the operation of detecting the length of the sheet and updating the data for the setting of the sheet feeding end time is as follows.
This is considered when the first sheet is fed, and the second and subsequent sheets can be omitted.

According to a fourth aspect of the present invention, there is provided the sheet feeding device according to the second aspect, further comprising a sheet feeding unit reset determination unit configured to determine whether a sheet is reset in the sheet feeding unit, The detecting means detects the sheet length only for the first sheet fed first when it is recognized that the sheet feeding section has been reset as a result of the judgment of the sheet feeding section reset setting judging means, The sheet length is recognized as the second and subsequent sheet lengths.

Therefore, the operation of detecting the length of the sheet and updating the data for setting the sheet feeding end time is as follows.
When recognizing the state in which the sheet feeding unit is reset, the first sheet fed first is regarded as feeding the first sheet, and the second and subsequent sheets can be omitted.

According to a fifth aspect of the present invention, there is provided the image forming apparatus according to the first aspect.
5. The sheet feeding device according to any one of claims 1 to 4, and an image forming unit that outputs an image to a sheet fed by the sheet feeding device.

Therefore, when the registration roller is driven, the paper feed roller is re-driven to reliably feed the paper to be fed, and the jam caused by feeding the next layer of paper in an overlapping manner. An image forming apparatus capable of preventing occurrence can be provided.

[0017]

FIG. 1 shows a first embodiment of the present invention.
This will be described with reference to FIG. FIG. 1 is a vertical sectional front view showing a schematic internal configuration of an image forming apparatus in which a paper feeding device is mounted, FIG. 2 is a block diagram schematically showing an electrical connection configuration, and FIG. 3 is a flowchart showing a paper feeding operation.

As shown in FIG. 1, a housing 1 of the image forming apparatus
The image forming section 2 is provided at the center of the image forming section. The image forming section 2 is formed by arranging a charging roller 4, a writing unit 5, a developing unit 6, a transfer roller 7, and a cleaning unit 8 around a photoreceptor 3.
In the image forming unit 2, the photosensitive member 3 is uniformly charged by the charging roller 4, and the charged portion is scanned by a laser beam modulated according to image data by the optical writing unit 5 to form an electrostatic latent image. The electrostatic latent image is formed, developed by the developing unit 6, the developed image on the photoconductor 3 is transferred to paper by the transfer roller 7, and the remaining toner on the photoconductor 3 is cleaned by the cleaning unit 8.

In the paper transport path 9 passing between the photosensitive member 3 and the transfer roller 7, heat and pressure are applied during the transport of the paper passing through the transfer roller 7 to fix the toner on the paper. A unit 10 is provided.

Further, on the downstream side of the paper transport path 9, a paper discharge path 1 connected to a paper discharge tray 11 formed on the housing 1 is provided.
2 and a reversing passage 13, and a switching claw 14 for switching the paper discharge path is rotatably provided at the branch point. Further, below the photoreceptor 3, there is provided a double-sided unit 15 for re-feeding the sheet, which has been inverted and returned from the inversion path 13, again toward the image forming unit 2.

Further, on one side of the housing 1, a manual feed tray 16 and a paper feed roller 17 for feeding the paper inserted into the manual feed tray 16 to the image forming section 2 are provided.

Next, the configuration of the sheet feeding device 18 of the present invention will be described. A paper feed tray 19 which is a paper feed unit for storing a large number of papers in a stacked state is detachably mounted below the housing 1. At the top of the paper feed tray 19, the paper feed tray 1
9 through the paper feed path 20 to the paper transport path 9 described above.
A paper feed roller 21 that feeds the paper is rotatably provided. Further, a paper feed roller 21 and the photosensitive member 3
Are provided between the pair of registration rollers 22. A registration sensor 30a is arranged near the registration roller 22 on the paper feed roller 21 side.

Next, an outline of the electrical connection configuration will be described with reference to FIG. A main control unit 23 having a microcomputer configuration is provided. The main control unit 23 includes a writing unit 5, a fixing unit 10, a double-sided unit 15, a high-voltage driving unit 24, a driver 26 for driving a motor 25, and a driver 28 for driving a paper feed clutch 27. , Controller 29,
Various sensors 30 and an operation panel 31 are connected.

Here, the high-voltage driving section 24 is a means for driving a portion requiring a high-voltage power supply, such as the charging roller 4, the developing unit 6, and the transfer roller 7 arranged around the photosensitive member 3. The motor (main motor) 25 is a driving source for a rotating system such as the photoconductor 3 and the fixing unit 10, and the rotational force is also transmitted to the paper feed roller 21 via the paper feed clutch 27.

The controller 29 has a function of an interface connected to a host computer (not shown), and further has a function of giving image data editing, image data transfer, and image formation instructions to the main control unit 23. Have.

Although not shown, the various sensors 30 are temperature sensors for outputting a signal corresponding to the temperature of the fixing unit 10 and the like, and are arranged in the paper transport path 9 and the paper feed path 20 to output signals according to the transport state of the paper. Paper sensor,
It includes a tray sensor that outputs a signal in accordance with the state of insertion / removal of the paper feed tray 19, a paper end sensor that outputs a signal in accordance with the presence or absence of paper in the paper feed tray 19, the registration sensor 30a shown in FIG. The registration sensor 30a
Since it is for recognizing the state in which the leading edge of the sheet has reached the nip portion of the registration roller 22, it is desirable to arrange the paper as close as possible to the registration roller 22 in order to increase the detection accuracy.

An operation panel 31 includes a display unit (not shown) for indicating an operation state, a number key for inputting the number of prints, and the like.
A mode setting key for setting a print mode, a start key for starting printing, and the like are provided. Although the image forming apparatus in FIG. 1 illustrates only one paper feed tray 19, it is assumed that a plurality of paper feed trays 19 are provided. A paper size specification key for specifying the size is provided.

The main control unit 23 controls the mechanical load in the image forming apparatus, writes an image by the writing unit 5, monitors the paper transport state based on the output of the various sensors 30, and the state of other parts, and sets a preset program. The operation of each unit is controlled by using.

The processing of the paper feeding operation in such a configuration will be described with reference to the flowchart shown in FIG. In addition,
When the power is turned on, the motor 25 always rotates. Printing is started when the operator presses a start key on an operation panel (not shown). Paper feeder 18
, The ON signal of the start key is a sheet feed command signal. When it is determined that printing is started by pressing the start key (Y in S1), the paper feed clutch 27 is turned on (S2), and the paper feed roller 21 is rotated. This allows
The uppermost sheet in the sheet feed tray 19 is fed by the sheet feed roller 21. This step S2 realizes a paper feed driving unit for driving the paper feed roller 21.

When the registration sensor 30a is turned on by this paper feeding (Y in S3), it is recognized that the leading end of the paper has reached the vicinity of the nip portion of the registration roller 22, but the paper feeding clutch 27 is not immediately turned off. After a delay of a predetermined time allowing for a margin is inserted (S4), the paper feed clutch 27 is turned off to stop the paper feed roller 21 (S5). By adding this delay, the sheet is fed a little extra to create a bend, and the sheet is stretched by its own waist strength to strike the leading end against the nip portion of the stopped registration roller 22. Thus, the leading edge of the sheet is aligned at right angles to the sheet feeding direction.

During this time, writing of an image on the photosensitive member 3 is prepared under the control of the controller 29. When the preparation is completed, writing of an electrostatic latent image on the photosensitive member 3 by the writing unit 5 and writing by the developing unit 6 are performed. Start development. When this state is recognized as the start of image formation by the monitoring of the CPU of the main control unit 23 (Y in S6), the registration is started in synchronization with this (S7). That is, the registration roller 22 is driven to feed the sheet toward the photoconductor 3. This step S7 realizes a registration driving unit for driving the registration roller 22.

When the paper feed clutch 27 is turned on again (S8) in synchronization with the registration start (S7), the paper feed roller 21 is driven again. As a result, the sheet is reliably sent out toward the photoconductor 3 by the conveying force of the registration roller 22 and the conveying force of the sheet feeding roller 21.

When it is recognized that the rear end of the fed sheet reaches the sheet feed roller 21 (S9 / Y), the sheet feeding clutch 27 is turned off. (S10), the paper feed roller 21 is stopped.

In the present embodiment, the paper size to be used can be recognized by a method such as pressing a paper size designation key on the operation panel 31. The position of the registration roller 21 and the positions of the registration roller 22 and the registration sensor 30a are known from the configuration of the apparatus, and the peripheral speeds of the paper supply roller 21 and the registration roller 22 are also known. Then, the sheet feeding end time when the rear end of the sheet reaches the sheet feeding roller 21 is set in advance. By storing the set value of the sheet feed end time as a table in the storage medium of the sheet main control unit 23 for each sheet having a different sheet length, a sheet feed end time setting unit is realized. The set value is set as the time from when the paper feed roller 21 is driven again until the rear end of the paper reaches the paper feed roller 21,
By counting this time, it is possible to recognize in step S9 whether or not the rear end of the sheet has reached the sheet feed roller 21.

Here, steps S8 and S10
Implements re-driving means for re-driving the paper feed roller 21 only during a period from the time when the registration roller 22 is driven to the time when one sheet is fed.

As described above, when the registration roller 22 is driven, the sheet feeding roller 21 is driven again, so that the sheet can be conveyed with the conveying force supplemented. In this case, the sheet feeding end time when the rear end of the sheet reaches the sheet feeding roller 21 is set according to the length of the sheet, and the sheet feeding roller 21 can be stopped at the sheet feeding end time. Therefore, it is possible to reliably feed the paper to be fed, and to prevent the occurrence of a jam caused by feeding the paper of the next layer in an overlapping manner.

The position where the rear end of the sheet reaches the feed roller 21, which is a position for determining the timing for stopping the re-driven feed roller 21, is determined immediately after the rear end of the sheet passes through the feed roller 21. Is most desirable, but there is no practical problem if it is in the vicinity.

Next, a second embodiment of the present invention will be described with reference to FIG. The same portions as those described in the above embodiment are denoted by the same reference numerals, and description thereof is omitted.
Also, regarding the processing of each step of the flowchart in FIG. 4, the same processing as that of the above-described embodiment will be briefly described.

In this example, in order to print a plurality of sheets, the number of prints is set by operating a number key on the operation panel 31. Also, regarding the paper size, the operation panel 31
This is an example of designation by operating the paper size designation key above. In printing, the operator presses the start key in the same manner as in the above embodiment. When it is determined that printing is started by operating the start key (S11).
(Y), the paper feed clutch 27 is turned on (S12), and the paper feed roller 21 is rotated. Thereby, the paper feed tray 19
The uppermost sheet is fed by the feed roller 21.
This step S12 implements a paper feed driving unit for driving the paper feed roller 21.

When the registration sensor 30a is turned on by this paper feeding (Y in S13), it is recognized that the leading end of the paper has reached the vicinity of the nip portion of the registration roller 22, but the paper feeding clutch 27 is not immediately turned off. Then, a delay of a certain time is allowed with a margin (S14).
Then, the paper feed clutch 27 is turned off to stop the paper feed roller 21 (S15). By inserting this delay, the sheet is slightly extra-conveyed to create a bend, and the leading end of the sheet strikes the nip portion of the stopped registration roller 22.

When the start of image formation is recognized (Y in S16), the registration is started in synchronization with this (S1).
7). That is, the registration roller 22 is driven to feed the sheet toward the photoconductor 3. This step S17 realizes registration driving means for driving the registration roller 22.

Next, it is determined whether or not the sheet to be printed is the first sheet (S18). This determination can be made by adding the number of fed sheets to the counter each time a sheet is fed and referring to the data of the counter. If it is determined that the sheet is the first sheet (Y in S18), measurement of the length of the currently fed sheet is started (S19). In this measurement, the time elapsed from the time when the registration roller 22 was driven (S17) to the time when the rear end of the sheet passed the registration sensor 30a and the registration sensor 30a was turned off (Y in S20) was measured. The calculation can be performed based on the measurement time. That is,
The length of the sheet can be calculated by adding the distance between the registration roller 22 and the registration sensor 30a to the product of the measurement time and the peripheral speed (known) of the registration roller 22. The sheet length is determined by this calculation (S21). This determination processing also includes processing for storing the calculated paper length data in the storage medium of the main control unit 23. Steps S19 and S21
Implements a sheet length detecting unit that detects the length of the sheet to be fed.

Next, in the present embodiment, it is determined whether or not the stored paper length data matches the paper size designated by operating the paper size designation key on the operation panel 31 (S22). If the result of the determination in step S22 is inconsistent (N in S22), an error is displayed on the display unit on the operation panel 31 (S23). If it is determined that they match (Y in S22), the sheet feed end time is set based on the sheet length data determined in step S21, and the set value is stored in the storage medium of the main control unit 23 (S24). ).

This step S24 realizes a sheet feeding end time setting means for setting the sheet feeding end time based on the sheet length detected by the sheet length detecting means, that is, the actually detected sheet length. . More specifically, the sheet feeding end timing indicating the timing at which the trailing edge of the sheet reaches the sheet feeding roller 21 is based on the state in which the leading end of the sheet abuts on the nip portion of the registration roller 22 and the deflection is formed. Then, based on the detected paper length, the paper feed roller 21 and the registration roller 22
The remaining length from the paper feed roller 21 to the rear end of the paper is obtained by subtracting the distance between the paper feed roller 21 and the amount of deflection of the paper. A time divided by (equivalent and known) is obtained, and this time is set as a re-driving time in which the sheet feeding roller 21 is stopped after being re-driven.

When the number of prints is set to a plurality, the sheet length of the first sheet is measured only.
Alone to the photoconductor 3.

When it is determined that the sheet is the second or subsequent sheet (S18)
N), the length of the second sheet is detected in order to recognize the length of the first sheet as the length of the second sheet and apply the end timing of feeding one sheet based on the length of the second sheet. Instead, when the paper feed clutch 27 is turned on again in synchronization with the registration start (S17), the paper feed roller 21 is driven again (S25). As a result, the sheet is reliably sent out toward the photoconductor 3 by the conveying force of the registration roller 22 and the conveying force of the sheet feeding roller 21.

When it is recognized that the trailing end of the fed paper has reached the paper feed roller 21 (S
26, Y), in other words, when the above-mentioned re-driving time has elapsed since the re-driving of the paper feed roller 21, the paper feed clutch 27 is turned off (S27), and the paper feed roller 21 is stopped. The processing in steps S25 to S27 is the same as the processing described in steps S8 to S10 in FIG. Here, step S25,
Step S27 implements a re-driving unit that re-drives the sheet feeding roller 21 only during a period from the time when the registration roller 22 is driven to the time when the sheet feeding is completed.

As described above, when the registration roller 22 is driven, the sheet feeding roller 21 is driven again, so that the sheet can be conveyed in a state where the conveying force is supplemented.

Further, in the present embodiment, the length of the actually fed paper is detected, and the sheet feeding end timing is set based on the detected length of the paper. The timing for stopping the paper feed roller 21 can be set more accurately in accordance with the length of the sheet. Therefore, the reliability of paper feeding accuracy can be further improved.

Further, when the number of prints is specified to be plural,
The operation of detecting the sheet length and updating the data for setting the sheet feeding end timing is considered when the first sheet is fed, so that the printing time for the second sheet and thereafter becomes longer. Can be prevented.

Further, the paper feed roller 21 is driven again only when the paper size designated by operating the paper size designation key on the operation panel 31 and the paper length of the actually fed paper match. In this case, an error message can be displayed if they do not match. If the size of the actually fed paper does not match the specified paper size,
Can be avoided.

Next, a third embodiment of the present invention will be described with reference to FIG. The same portions as those described in the above embodiment are denoted by the same reference numerals, and description thereof is omitted.
Regarding the processing of each step of the flowchart in FIG. 5, the same processing as in the above-described embodiment will be briefly described.

Also in this embodiment, in order to print a plurality of sheets, the number of prints is set by operating the number keys on the operation panel 31. The size of the paper is also designated by operating the paper size designation key on the operation panel 31. In printing, the operator presses the start key in the same manner as in the above embodiment. When the output of the start key is monitored and it is determined that the printing is not to be started because the start key is not pressed (N in S31),
It is determined whether or not the paper feed tray 19 has been reset (S
32). This step S32 implements a sheet feeding unit reset determination unit.

Since resetting the paper feed tray 19 may involve replacing sheets of different sizes, the possibility is checked in step S12. As described above, the various sensors 30 include a tray sensor that outputs a signal in accordance with the state of insertion and removal of the paper feed tray 19 and a paper end sensor that outputs a signal in accordance with the presence or absence of paper in the paper feed tray 19. As described above, in step S32, it is determined whether or not the paper feed tray 19 has been detached from the history of the on / off state of the tray sensor, and the presence or absence of paper in the paper feed tray 19 is determined based on the signal of the paper end sensor. When the paper tray 19 is detached and the presence of paper is also recognized, it is determined that the paper feed tray 19 has been reset (Y in S32). In this state, since the paper size is unknown, the flag is reset (S3).
3), the initial state.

When it is determined that printing is started by operating the start key (Y in S31), the paper feed clutch 27 is turned on (S34), and the paper feed roller 21 is rotated. Thus, the uppermost sheet in the sheet feed tray 19 is fed by the sheet feed roller 21. This step S34 implements a paper feed driving unit for driving the paper feed roller 21.

When the registration sensor 30a is turned on by this paper feeding (Y in S35), it is recognized that the leading end of the paper has reached the vicinity of the nip portion of the registration roller 22, but the paper feeding clutch 27 is not immediately turned off. The delay of a certain period of time is entered with some margin (S36).
Then, the paper feed clutch 27 is turned off to stop the paper feed roller 21 (S37). By inserting this delay, the sheet is slightly extra-conveyed to create a bend, and the leading end of the sheet strikes the nip portion of the stopped registration roller 22.

When the start of image formation is recognized (Y in S38), the registration is started in synchronization with this (S3).
9). That is, the registration roller 22 is driven to feed the sheet toward the photoconductor 3. This step S39 implements registration driving means for driving the registration roller 22.

Next, it is determined whether or not the flag has been reset (S40). In the first sheet feeding after the sheet feeding tray 19 is reset, the sheet is in the initial state, and the process proceeds to step S33
Since the flag has been reset in step (1), it is determined that the flag has been reset (Y in S40), and the flag is set (S41).

Next, measurement of the length of the currently fed sheet is started (S42). In this measurement, the time elapsed from the time when the registration roller 22 was driven (S39) to the time when the trailing edge of the sheet passed the registration sensor 30a and the registration sensor 30a was turned off (Y in S43) was measured. Calculation is performed based on the measurement time to determine the paper length (S4).
4) Yes. This calculation is the same as the processing described as the processing in steps S19 and S21 in FIG. Steps S42 and S44 in FIG. 5 realize a sheet length detecting unit that detects the length of the sheet to be fed.

Next, in the present embodiment, it is determined whether or not the stored paper length data matches the paper size specified by operating the paper size specification key on the operation panel 31 (S45). If the result of the determination in step S45 is a mismatch (N in S45), an error is displayed on the display unit on the operation panel 31 (S46). If it is determined that they match (Y in S45), the sheet feed end time is set based on the sheet length data determined in step S44, and the set value is stored in the storage medium of the main control unit 23 (S47). ).

This step S47 implements a sheet feeding end time setting means for setting the sheet feeding end time based on the sheet length detected by the sheet length detecting means, that is, the actually detected sheet length. Although specifically, it is the same as the processing performed in step S24 in FIG.

The sheet length of the first sheet after the sheet feeding tray 19 is reset is measured only. The sheet reaching the nip portion of the registration roller 22 is only the registration roller 22 and the photosensitive member 3 Transport to

After the paper tray 19 is reset, the sheet length is measured, and the sheet feeding end timing is set, the flag should be set unless the paper tray 19 is reset. . Therefore, in the next printing, it is determined in step S40 that the flag is set (S40).
40 N). In this case, the length of the second sheet is not detected in order to recognize the length of the first sheet as the length of the second sheet and apply the one sheet feeding end timing based on the length of the second sheet. ,
Feed clutch 2 at registration start (S39)
7 is turned on again (S48), the paper feed roller 21 is driven again. As a result, the sheet is reliably sent out toward the photoconductor 3 by the conveying force of the registration roller 22 and the conveying force of the sheet feeding roller 21.

When it is recognized that the trailing end of the fed paper has reached the paper feed roller 21 (S
49, Y), in other words, when the above-described re-driving time has elapsed since the re-driving of the paper feed roller 21, the paper feed clutch 27 is turned off (S50), and the paper feed roller 21 is stopped. The processing in steps S48 to S50 is the same as the processing described in steps S8 to S10 in FIG. Here, step S48,
Step S50 realizes a re-driving unit that re-drives the sheet feeding roller 21 only during a period from the time when the registration roller 22 is driven to the time when one sheet feeding is completed.

As described above, when the registration roller 22 is driven, the sheet feeding roller 21 is driven again, so that the sheet can be conveyed in a state where the conveying force is supplemented.

In this embodiment, the paper feed tray 19
Each time the paper is reset, the length of the paper actually fed is detected, and the end timing of single-sheet feeding is set based on the detected paper length. Accordingly, the timing for stopping the sheet feeding roller 21 can be set more accurately. Therefore, the reliability of paper feeding accuracy can be further improved.

Further, unless the sheet feeding tray 19 is reset, the operation of detecting the sheet length and updating the data is not performed for setting the sheet feeding end timing. It can be prevented from becoming longer.

[0068]

According to the first aspect of the present invention, when the registration roller is driven in synchronization with the operation of the image forming section, the paper supply roller is driven again, so that the driving source of the paper supply system is provided. Even if a small motor is used, the paper can be transported in a state where the transport force is supplemented. In this case, the sheet feeding end time at which the trailing end of the sheet reaches the sheet feeding roller is set according to the length of the sheet, and the sheet feeding roller is stopped at the sheet feeding end time. It is possible to accurately set the stop time of the re-driven paper feed roller according to the length, which ensures that the paper to be fed is fed, and that the next layer of paper is fed one on top of the other. The occurrence of jams that occur can be prevented.

According to the second aspect of the present invention, in the paper feeding apparatus according to the first aspect, the length of the paper actually fed is detected, and the one-sheet feeding is completed based on the detected paper length. Since the timing is set, it is possible to set the single-sheet feeding end timing for stopping the sheet feeding roller re-driven when the registration roller is driven, based on the length of the sheet actually fed. Therefore, the reliability of paper feeding accuracy can be further improved.

According to the third aspect of the present invention, in the paper feeder according to the second aspect, the detection of the sheet length for setting the sheet feeding end timing is performed when a plurality of print sheets are designated. This is performed only for the first sheet fed to the printer, so that it is possible to prevent the printing time of the second and subsequent sheets from becoming longer.

According to the fourth aspect of the present invention, in the paper feeding apparatus according to the second aspect, the detection of the sheet length for setting the sheet feeding end timing is recognized as a state where the sheet feeding unit is reset. Since the printing is performed only for the first sheet fed first, the subsequent printing time can be prevented from becoming long unless the sheet feeding unit is reset.

According to a fifth aspect of the present invention, since the image forming apparatus includes the sheet feeding device according to any one of the first to fourth aspects, when the registration roller is driven, the sheet feeding roller is driven again to feed the sheet. It is possible to provide an image forming apparatus capable of reliably feeding sheets to be printed and preventing occurrence of a jam caused by feeding sheets of the next layer in a stacked manner.

[Brief description of the drawings]

FIG. 1 is a vertical sectional front view showing a schematic internal configuration of an image forming apparatus in which a sheet feeding device according to a first embodiment of the present invention is mounted.

FIG. 2 is a block diagram schematically showing an electrical connection configuration.

FIG. 3 is a flowchart illustrating a sheet feeding operation.

FIG. 4 is a flowchart illustrating a sheet feeding operation according to a second embodiment of the present invention.

FIG. 5 is a flowchart illustrating a sheet feeding operation according to a third embodiment of the present invention.

[Explanation of symbols]

2 Image forming unit 18 Paper feeding device 19 Paper feeding unit 21 Paper feeding roller 22 Registration roller 31 Paper size specifying means S2, S12, S34 Paper feeding driving means S7, S17, S39 Registration driving means S8, S10, S25, S27, S48 , S50 Re-driving means S24, S47 Single sheet feeding end timing setting means S32 Sheet feeding section reset setting determining means

 ──────────────────────────────────────────────────続 き Continued on front page F term (reference) 2H072 AA01 AA14 AA22 AB06 3F102 AA01 AB01 BA02 BB02 DA08 EA03 FA08 3F343 FA02 FB01 FC13 FC15 GA01 GB01 GC01 GD01 JD09 KB04 KB06 KB20 LA04 LA16 LC25 MA03 MA36 MC10 MC17 MC23

Claims (5)

[Claims] A paper feed unit for storing paper; a paper feed roller for feeding paper in the paper feed unit to an image forming unit; and a paper feed roller driven each time a paper feed command signal is output. Paper feed driving means; a registration roller disposed between the image forming unit and the paper feed roller; a resist driving means for driving the registration roller in synchronization with the operation of the image forming unit; A sheet feeding end time setting means for setting a sheet feeding end time at which a rear end of a sheet fed by a roller reaches the sheet feeding roller in accordance with a designated sheet length; and the registration roller And a re-driving means for re-driving the paper feed roller only during a period from the time when is driven to the time when the one-sheet feeding is completed. 2. A sheet length detecting means for detecting a length of a sheet actually fed, wherein the sheet feeding end timing setting means is based on the sheet length detected by the sheet length detecting means. 2. The sheet feeding device according to claim 1, wherein the sheet feeding end time is set. 3. The paper length detecting means detects the paper length of only the first paper fed first when the number of prints is designated to be plural, and determines the paper length for the second and subsequent papers. 3. The paper feeding device according to claim 2, wherein the paper feeding device recognizes the length. 4. A sheet feeding unit reset determining unit for determining whether the sheet feeding unit has been reset, and wherein the sheet length detecting unit determines the sheet length based on a result of the determination by the sheet feeding unit resetting unit. 3. The sheet length of only the first sheet fed first when it is recognized that the sheet feeding unit has been reset, and the sheet length is recognized as the second and subsequent sheet lengths. Paper feeder. 5. An image forming apparatus, comprising: the sheet feeding device according to claim 1; and an image forming unit that outputs an image to a sheet fed by the sheet feeding device.