JPH05193782A - Paper sheet feeding device - Google Patents

Abstract

PURPOSE:To increase the number of image-formed paper sheets per unit time without increasing a conveyance speed by keeping a distance between sheets to the necessary minimum limit when paper sheets are continuously fed by an image forming device, such as a duplicator. CONSTITUTION:A paper sheet sensor 5 and a member 6 by which the rear end part of a preceding paper sheet is separated away from the sensor 5 are arranged in a paper sheet feed route running from a paper sheet feed part 30 to a photo-sensitive body 10. The forward end of a subsequent paper sheet is positioned by the sensor 5 while the rear end part of the preceding paper sheet is lifted by means of the separating member 6. Thereafter, the rear end of the preceding paper sheet is released from lifting action and conveyance is executed in a state that a distance between the preceding and subsequent sheets is held at a constant value.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a feeding device for cut sheets such as transfer sheets of an image forming apparatus.

[0002]

2. Description of the Related Art As a feeding device for recording paper such as transfer paper in an image forming apparatus such as an electrophotographic copying machine, a facsimile, a laser printer, a device having a structure shown in FIG. 28 is generally used. In this apparatus, the uppermost sheet of the sheet bundle stacked on the sheet feeding unit 30 is sufficiently fed out from the front edge of the sheet bundle after the trailing edge of the preceding sheet, and then the pickup roller 1 rotates once to separate the separation claw 2 And is sent out to the grip roller 12.

The sheet sent out is registered in the registration sensor 13
Based on the timing at which the leading edge is detected in step S1, the roller is once abutted against the stopped registration roller 14, and in this state, the image forming apparatus waits until image formation starts.

The registration roller is rotated in synchronism with the start of image formation, and is sent to a transfer portion composed of the photoconductor 10 and the transfer / separation charger 9.

During this period, the preceding sheet and the sheet to be fed always maintain a sufficient sheet interval and do not overlap each other.

In this example, the separating claw method is illustrated as the sheet separating method, but there are various methods such as the friction pad method and the FRR method.

In any case, the separated sheets are fed to the transfer section at a constant interval by the feeding device having the above structure.

In the conventional analog type copying machine, since the scanning time of the original is intervened every time an image is formed on the sheet, the sheet interval must be necessarily large. In a page printer or plain paper facsimile, image processing time is required to perform the next print, and the idea of shortening the sheet interval has not been taken up.

However, with the advent of digital copying machines and the speeding up and efficiency of image processing apparatuses installed in printers and facsimiles, it has become desirable to minimize the sheet interval if possible.

In order to reduce the sheet interval, the conventional method has the following problems. At the registration rollers, after the conveyance of the preceding sheet is completed, it temporarily stops,
Since the operation of abutting the leading edge of the succeeding sheet and then starting the conveyance in synchronization with image formation is performed, a sufficient sheet interval is required to perform these controls. In order to avoid such a problem, complication of the apparatus is inevitable, such as a configuration in which a registration roller and a transfer roller are provided in the transfer section and the registration roller is rotated along the trailing edge of the sheet.

In the sheet feeding side sheet conveyance to the registration rollers, variations in sheet stacking position, variations in sheet conveyance speed of each roller and changes with time, variations in position of each roller, slip between sheet and roller, inside sheet conveyance path Due to the bending of the sheet, the error of the sheet detecting means, and the like, the sheet interval greatly varies. Therefore, in order to stably perform continuous image formation, it is necessary to make the sheet interval after the registration roller wider than the variation on the sheet feeding side. Particularly, in the friction pad system and the FRR system, the variation of the sheet stacking position is so large that it is necessary to consider the variation of 20 to 30 mm.

As a device for feeding sheets continuously with a sheet interval as small as possible, Japanese Patent Laid-Open Nos. 60-82542 and 60-62 are available.
In Japanese Patent No. 87359, a pair of registration rollers is fed in a stacked state and a pair of registration rollers arranged in front of an image forming unit reverses one roller with a constant torque as in the FRR separation device. There is disclosed a so-called stream-feed-type feeding device that continuously drives sheets by driving in the direction without opening a sheet interval at all.

However, as is clear from the problem in putting the FRR separating device into practical use, the separating operation of the registration roller portion is largely changed and pushed back because the separating roller constantly repeats rotation and inversion. The leading edge position of the succeeding sheet varies greatly. For this reason, even if such an apparatus is manufactured, variations in sheet spacing are large, and positional deviation (registration deviation) between the image and the sheet occurs, which makes it impossible to put into practical use.

Further, since the sheet is not abutted against the registration roller in the stopped state, skew occurs.

Further, since there is no sheet interval, it is difficult to detect the occurrence of jam.

Japanese Unexamined Patent Publication No. 63-8756 discloses a method of performing copying without opening a sheet interval by alternately switching two sets of registration rollers and a feeding path.

Although this method can reliably feed the sheet with the conventional control accuracy, it has a complicated structure and is costly. In addition, there is a drawback that the device becomes large.

Further, in Japanese Patent Laid-Open No. 176232/1988, sheets are continuously fed with a certain superposition defined by roller positions in a sheet feeding section, and speeds of a pickup roller and a conveying roller are increased. An apparatus is disclosed in which the difference is used to just eliminate the overlay.

However, this device is very difficult to realize because it is necessary to keep all the positions where the sheets are stacked, the positions of the rollers, and the conveying speed by the rollers, all with high precision.

It is generally known that the conveying speed of rollers such as pickup rollers changes over time due to wear, but no solution to the deviation of the sheet interval that occurs at that time is disclosed.

[0021]

SUMMARY OF THE INVENTION The present invention provides a minimum required sheet interval with high accuracy and continuously feeds and forms an image so that the continuous image forming speed (unit: It is possible to improve the number of images formed per hour), eliminate the wasteful life of the image forming portion typified by the photoconductor in the sheet interval portion, and realize the reduction in running cost due to the longer life. An object of the present invention is to provide a possible sheet feeding device.

[0022]

A sheet feeding apparatus of the present invention for solving the above-mentioned problems is a sheet feeding apparatus for continuously feeding cut sheets at a predetermined interval and is conveyed on a feeding path. Detecting means for detecting the edge of the sheet, and the trailing edge separating means for separating the trailing edge of the preceding sheet from the above-mentioned sheet detecting means outside the detectable area of the sheet detecting means. The leading edge of the trailing sheet is positioned by the sheet detecting means while the trailing edge portion of the preceding sheet is separated by the separating means, and then the sheet detecting means of the trailing edge portion of the preceding sheet is Is released so that the distance between the trailing edge of the preceding sheet and the leading edge of the trailing sheet is kept constant and the sheets are conveyed.

[0023]

Since the sheet feeding apparatus of the present invention is constructed as described above, the trailing edge of the preceding sheet is trailed while the trailing edge of the preceding sheet is separated from the sheet conveying path to the outside of the detectable area of the sheet detecting means. Positioning of the leading edge of the sheet is completed by the sheet detection means, then the separation of the trailing edge of the preceding sheet is resolved, and the preceding sheet and the succeeding sheet are conveyed at the same conveyance destination, thereby reducing the sheet interval to the minimum. The sheet can be continuously fed.

Various problems other than the above and means for solving the problems related to the above structure will be clarified by the description of the embodiments described in detail below with reference to the drawings.

[0025]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a diagram showing the construction of a sheet feeding apparatus according to an embodiment of the present invention.

A pickup roller 1 having an open circular cross section is provided in the vicinity of the front end of the upper surface of the sheet bundle placed on the sheet feeding unit 30. The circumferential surface of the pickup roller 1 is pressed against the upper surface of the sheet by being rotated by a stepping motor (not shown). In addition, the sheets are separated and fed one by one from the top of the sheet bundle by the separation claws 2 provided at both front end corners of the upper surface of the sheet bundle.

In the sheet feeding path from the sheet feeding section 30 to the transfer section between the photoconductor 10 and the transfer / separation charger 9, the registration sensor 3, the timing roller pair 4, and the reflection type sheet detecting means are arranged in this order from the upstream side. A timing sensor 5 such as an optical sensor, rear end separating means 6 and 7 for lifting the rear end of the preceding sheet to a non-operation area of the timing sensor 5, and a transport roller 8 are provided.

The registration sensor 3 is an optical sensor for detecting that the trailing edge of the sheet is sufficiently separated from the leading edge of the sheet bundle of the sheet feeding section 15. The timing roller 4 can freely control the rotation speed and the rotation direction by a stepping motor or the like (not shown).

In the present embodiment, the rear end separating means is composed of a crank 7 and a push-up member 6 whose base end is connected to the crank 7 and extends in the paper feed width direction.
The rear end separating means is composed of a solenoid and a push-up member connected to the solenoid, a combination of a groove having an open circular cross section and a pressing member having a cross section that fits the groove, and electrostatic attraction means. Various configurations such as suction means by negative pressure, and spraying means by air flow can be used. These will be described in detail later.

Next, the operation of continuously feeding sheets at a constant interval using this feeding device will be described with reference to the operation explanatory diagram sequentially shown in FIG. 2 and the timing chart shown in FIG. It should be noted that the numbers (a), (b), ... (G), (h) of the titles of the respective operations shown in FIG. 3 and (a), (b) ,. ... (g),
The time points of (h) correspond to each other.

(A) Detecting the trailing edge of the sheet 1: The registration sensor 3 detects that the trailing edge of the preceding top sheet (sheet 1) of the stacked uppermost sheet (sheet 2) is sufficiently separated. Then, the pick-up roller 1 makes one rotation to pass over the separation claw 2 and be separated. In this state, the rotation of the crank 50 is stopped, and the push-up member 52 is stopped at the home position, that is, at the position where the tip 52a of the push-up member is below the transport guide surface 11, as shown in the figure. Therefore, normal sheet conveyance is not hindered.

(B) Start of rear end lifting / Registration of sheet 2: The timing roller 4 is temporarily stopped on the basis of the timing when the leading edge of the sheet 2 is detected by the registration sensor 3. As a result, the leading edge of the sheet 2 is abutted against the timing roller 4 that is stopped, and the parallelism (skew) of the leading edge is corrected. At the same time, the crank 50 is started to rotate (the rotation direction is clockwise in the figure).

(C) Feeding of the sheet 2: When the crank 50 rotates, the connected push-up member 52 is guided by the sliding guide portion 11a to rise, and the tip 5 of the push-up member 5 is fed.
2a appears above the conveyance guide surface 11 and lifts the rear end portion from the lower surface side of the sheet 1 being conveyed. As a result, the rear end of the sheet 1 is separated from the timing sensor 5, the timing sensor 5 is released from the detection state of the rear end of the sheet 1, and the front end of the sheet 2 can be detected. At the same time, the timing roller resumes the conveyance at the conveyance speed of the photoconductor 10 and the transport roller 8, that is, the speed Vf higher than the conveyance speed V _{0 of} the sheet 1, and the sheet is placed on the lower surface side of the rear end of the lifted sheet 1. Feed the tip of 2.

(D) Detection of the leading edge of the sheet 2: When the leading edge of the sheet 2 is detected by the timing sensor 5, the timing roller 4 is stopped again. At this time as well, the rear end of the sheet 1 is separated upward by the lifting member 52, but at this time, the distance between the rear end of the sheet 1 and the front end of the sheet 2 is reduced to an overlapping state. The image formation on the sheet 2 can be started immediately after the image formation on the sheet 1 is completed.

(E) Seat 2 tip alignment: crank 50
As the rotation proceeds, the lifting member 52 begins to descend. The timing roller 4 reverses at a slow speed Vs to accurately align the leading edge of the sheet 2 with the upstream side of the timing sensor 5. By this operation, the position of the sheet 2 can be positioned more accurately than in the state of d.

(F) Sheet superposition: The rotation of the crank 50 progresses and stops after one rotation, and the lifting member 52 connected also stops at the home position. Since the leading end 52a of the lifting member is below the conveyance guide surface 11 at this time, the rear end of the separated sheet 1 falls onto the conveyance guide surface 11, and the trailing end of the sheet 1 becomes the leading end of the sheet 2. ..

(G) Sheet spacing adjustment: The timing roller 4 restarts the feeding of the sheet 2 at the same transport speed V ₀ as the photoconductor 10 and the transport roller 8 in synchronization with the progress of image formation. If the sheet 1 and the sheet 2 are image-formed at a required minimum distance, the sheet interval appears at a distance corresponding to this with high accuracy, so that the sheet interval can be adjusted with high accuracy.

(H) Realization of continuous sheet feeding: The sheet 2 is conveyed to the transfer section with the sheet interval kept as it is, and high-speed and wasteless image formation is realized.

Thereafter, the operations of (a) to (g) are repeated in succession with the sheets 3, 4 ... Can be realized.

FIG. 4 shows a control block diagram of the image forming apparatus having the configuration of FIG.

In response to the print command from the external device (host computer) 15, the controller 16 sends the image information to the image forming apparatus. The main body control device 17 in the image forming apparatus is composed of a CPU, a ROM, a RAM and the like, and takes in signals from the registration sensor 3, the timing sensor 5 and the like to control the drive circuit. A pickup roller ON / OFF clutch 24, a stepping motor 25, a transport motor 26, a rear end lifter drive motor 27, and the like are connected to the drive circuit to convey the sheet. The operation panel 28 includes a plurality of switches, L
An ED, an LCD, etc. can be used to make various settings of the image forming apparatus.

The controller develops the image information received from the external device 15 and sends a print start command to the image forming apparatus 15 when the development of one page is completed. In the case of image information over a plurality of pages, similar processing is successively performed.

By feeding paper in a state where the trailing edge of the preceding sheet and the leading edge of the following sheet are overlapped with each other in advance, the registration operation of the sheet feeding operation (b) is omitted. Alternatively, even if the low-speed reverse sheet feeding of (e) is omitted, the sheet interval can be made smaller than in the conventional case, and continuous feeding can be performed. The sheet feeding operation in that case will be described below with reference to the sequential explanatory diagram of FIG. 5 and the timing chart of FIG.

(A) Start feeding of sheet 2: The uppermost stacked sheet (sheet 2) is the preceding sheet (sheet 1)
The pickup roller 1 makes one rotation before the trailing edge of the sheet is separated from the upper portion of the stacked sheet bundle, and the separation roller 2 passes over the separating claw 2 to separate the sheet, so that the sheet is fed in the state where the trailing edge and the leading edge overlap.

(B) Start of trailing edge lifting: After the leading edge of the sheet 2 is gripped by the timing roller 4, the trailing edge lifters 6 and 7 are activated to start lifting the trailing edge of the sheet 1.

(C) Movement of sheet 2 at constant speed: The rear end of the sheet 1 is lifted, the timing sensor 5 is released from the detection state of the rear end of the sheet 1, and the front end of the sheet 2 can be detected. The sheet 2 continues to be conveyed at the speed V ₀ .

(D) Detection of the leading edge of the sheet 2: When the leading edge of the sheet 2 is detected by the timing sensor 5, the timing roller 4 is stopped.

(E) Resumption of conveyance of sheet 2: The feeding of the sheet 2 is resumed at the speed V ₀ in synchronization with the progress of image formation. If the image formation between the sheet 1 and the sheet 2 is performed with a required minimum distance, the sheet interval will appear accurately with a distance corresponding to this.

(F) Release of sheet separation: After that, the trailing edge lifter 6 is completely lowered, and the separation after the end of the sheet 1 is released.

(G) Realization of continuous sheet feeding: The sheet 2 is conveyed to the transfer portion while keeping the sheet interval, and high-speed and waste-free image formation is realized. After that, high-speed and efficient image formation continues in succession with sheets 3, 4 ...

When a reflection type optical sensor is used as the sheet detecting means as the timing sensor 5, in order to prevent erroneous detection of the trailing edge pushed up by the lifter of the preceding sheet, the following structure is adopted. Is appropriate.

FIG. 7 shows an example of the configuration. In the figure, the rear end lifter 6 is a plate-like member that projects in the vicinity of the reflection-type optical sensor 5, and the rear end of the sheet is configured to reliably retract from the detection range of the reflection-type optical sensor 5 by the plate-like member 6. There is.

Further, an antireflection sheet 29 such as black felt or black paper is attached to the surface of the plate member 6 on the reflection type optical sensor 5 side to prevent erroneous detection of the plate member 6 itself.

Further, the reflection type optical sensor 5 is usually placed in a direction in which a straight line connecting the light emitting portion and the light receiving portion is orthogonal to the conveying direction. This has the effect of facilitating the positioning of the detection position, but in this example, the detection positions are intentionally arranged in the parallel direction, and the possibility that the rear end lifter 6 overhangs and the malfunction of the reflection type optical sensor is reduced. By placing them in the parallel direction, it becomes difficult to form an optical path that reflects light by hitting the overhanging part of the rear end lifter by an angle corresponding to the inward angle of the optical axes of the light emitting part and the light receiving part. Reduce.

Since the variation in the positional accuracy of the detection position of the optical sensor 5 depends only on the mounting accuracy, if a means for adjusting this is provided, the mounting direction will not be particularly disadvantageous since it is different from the conventional one. Moreover, many of these adjusting means are conventionally mounted.

Furthermore, the possibility of erroneous detection is minimized by tilting the sensor itself so that one of the optical axes of the rear end lifter 6 and the light emitting portion of the optical sensor 5 and the light receiving portion that are overhanging are parallel to each other. I have a limit.

With this structure, the rear end portion lifter 6 of the seat is
Since it is possible to prevent malfunction even if the sheet detecting means 5 is arranged very close to each other, it is possible to downsize the apparatus.

The rear end separating means shown in FIG. 7 is composed of a crank 7 arranged on the lower surface side of the sheet conveying path and a pushing-up member 6 connected to the crank 7 by a pin 6a, and is provided on a sheet conveying guide surface 11. Sliding guide part 11 of lifting member
Although the push-up member 6 is guided by a and reciprocated, the rotation center of the crank 7 is further downstream than the sliding guide portion 11a of the push-up member in the sheet conveying direction (that is, in FIG. 7). The crank 7 is provided on the left side and rotates in the counter direction (that is, clockwise in FIG. 7) with respect to the sheet conveying direction.

Therefore, the lifting of the sheet is started (see FIG. 2).
In (c)), the lifting member 6 forms a shallow approach angle with respect to the conveyance guide surface 11, and therefore the leading end 6b of the lifting member contacts the sheet at a shallow angle, so that the surface of the sheet is not damaged. Further, since the lifting member 6 is inclined so as to cut off between the sheet detecting means 5 and the preceding sheet, the antireflection sheet 29 such as black felt or the like.
The effect of eliminating the erroneous detection of the preceding sheet can be obtained in combination with the sticking of.

When the sheet is descending ((e) of FIG. 2), the lifting member 6 makes a deep angle with the conveyance guide surface 11, and the leading end 6b of the lifting member is quickly lowered below the conveyance guide surface 11. Be in a position.

In this way, the trailing edge separating means operates promptly, so that it is possible to continuously feed sheets with the sheet interval minimized.

Below, examples of various configurations of the sheet trailing edge portion separating means other than the above will be described.

The sheet trailing edge separating means shown in FIG. 8 is composed of a solenoid 60 arranged on the lower surface side of the sheet conveying path and a pushing-up member 62 connected thereto. The drawing shows the OFF state of the solenoid 60, and the pushing-up member 62 is in the home position by the elastic force of the spring 61. At this time, the front end 62a of the pushing-up member is below the conveyance guide surface 11 and does not interfere with normal sheet conveyance.

Further, as in the case of using the crank described with reference to FIG. 7, the advancing angle of the pushing-up member 62 with respect to the seat is inclined toward the seat upstream direction.

When the solenoid 60 is turned on, the push-up member 62 has a force stronger than the elastic force of the spring 61 for returning to the home position.
A force acts in the direction in which 2 moves away from the solenoid 60. Therefore, as shown in FIG.
3, the tip end 62a of the pushing-up member is guided by the conveyance guide portion 63 and ascends, and the tip end 62a of the pushing-up member appears above the conveyance guide surface 11 so that the rear end of the sheet 1 being conveyed. Part from the bottom side.

At this time, since the lifting member 62 forms a shallow approach angle with respect to the conveyance guide surface 11, the leading end 62a of the lifting member contacts the sheet at a shallow angle, so that the sheet surface is not damaged. Also, the lifting member 62
By attaching an antireflection sheet such as black felt to the surface of the sheet detecting means side so that light is less likely to be reflected, the effect of eliminating false detection of the preceding sheet can also be obtained.
This is similar to the trailing edge separating means shown in FIG.

In the sheet rear end separating means shown in FIG. 10, a pushing member 70 having a width equal to or larger than the sheet width is formed in the width direction on the upper surface of the conveying guide 11 by a driving means (not shown). By pushing the sheet from the upper side of the sheet, the rear end of the sheet is lifted by the strain of the sheet itself to separate the sheet. Figure 1
0 indicates a state in which the pushing member 70 is at the home position, and the lower end 70a is located above the conveyance guide surface 11 and does not interfere with normal sheet conveyance.

As shown in FIG. 11, when the pushing member 70 descends, the leading end 70b of the pushing member 70 pushes the sheet into the truncated circular groove surface 11b of the conveyance guide. Since the sheet can be surely bent R at right angles to the conveying direction, the rigidity of the sheet increases in the direction orthogonal to the conveying direction, and the rear end is reliably separated.

As a result, the trailing edge of the preceding sheet is separated from the timing sensor 5, the timing sensor 5 is released from the detection state of the trailing edge of the preceding sheet, and the leading edge of the succeeding sheet can be detected.

Ends of the pushing-up member of the rear end separating means shown in FIGS. 7 and 8 and the pushing member of the rear end separating means shown in FIG. Therefore, it is desirable to take measures to reduce friction with the seat.

12 (a), (b), and (c) are shown in FIG.
It is an example of friction reducing means for the tip of the pushing member of the rear end part separating means. In (a), a roller 71 that is loosely fitted in the groove having a circular cross section is provided at the tip of the pushing member so as to be rotatable with respect to the sheet.

In (b), the tip portion of the pushing member 70 is coated with a tetrafluoroethylene resin 72. Further, in (c), the tetrafluoroethylene resin tape 73 is attached instead of the coating. As a result, the friction at the tip of the pushing member is reduced, it is prevented that the sheet conveying speed is affected, and stable sheet conveying becomes possible.

It goes without saying that the friction reduction measures shown in FIGS. 12A, 12B and 12C can also be applied to the push-up members 6 and 62 shown in FIGS.

FIG. 13 shows an example of the structure of still another sheet rear end portion separating means. In the figure, the sheet rear end portion separating means is configured to separate the sheet rear end portion by electrostatic attraction by the charging means. That is, the charging electrode 80 is provided above the transport guide surface 11 so as to be housed in the charging case 81. In front of the transport roller 8, a conductive static elimination brush 82 is provided as a static elimination means and is connected to the ground 83.

Normally, the charging electrode 80 is not energized, and the preceding sheet is conveyed along the conveyance guide surface 11 without any hindrance.

When the upper surface of the sheet 1 is sufficiently charged by energizing the charging electrode 80, the sheet is attracted to the charging case 81 side by the electrostatic force as shown in FIG. The charged sheet is neutralized by the static elimination brush 82 before the transport roller 8. It is not necessary to connect the ground 83 to the static elimination brush 82 when static elimination of the sheet is not required.

As a result, the trailing edge of the preceding sheet is separated from the timing sensor 5, the timing sensor 5 is released from the detection state of the trailing edge of the preceding sheet, and the leading edge of the trailing sheet can be detected.

Next, an example of the trailing edge separating means for adsorbing the trailing edge of the sheet by the air flow to separate the trailing edge of the sheet from the sheet conveying surface will be described with reference to FIG.
In this embodiment, as shown in FIG. 15, a suction box 91 is provided above the conveying path on the downstream side of the sheet detecting means in the sheet conveying path to be a negative pressure by the suction fan 90 over the entire conveying width. ing. The lower end surface of the suction box 91 is provided with slit-shaped openings 92 or a large number of small holes arranged in rows.

When the intake fan 90 is off, the suction box 9
The pressure in 1 is kept at atmospheric pressure, and no upward airflow is generated in the lower part, so that the sheet is conveyed along the conveyance guide surface 11.

When the rear end of the seat is separated, by driving the intake fan 90 as shown in FIG. 16, the inside of the suction box 91 becomes a negative pressure, and the atmosphere is sucked through the opening 92 such as a slit or a small hole. An upward airflow is generated between the upper surface of the rear end of the sheet and the rear end of the sheet rises, and the sheet is conveyed while being adsorbed by the opening surface of the suction box 91.

If the distance between the opening of the suction box and the upper surface of the sheet is large, the sheet is difficult to be adsorbed. Therefore, the suction box can be moved up and down, and once lowered to adsorb the sheet, it is raised to a predetermined position. You may do it.

Finally, the trailing edge separating means for blowing the air flow blown from the lower side of the sheet conveying path to the lower surface of the sheet to separate the trailing edge of the sheet upward will be described with reference to FIG. In this device, an openable and closable air nozzle 100 extending in the width direction is arranged below a slit 11c provided over the entire width of the sheet conveyance guide surface 11. Air nozzle 10
0 ejects the air sent by the fan 101, and when the air nozzle 100 is opened, the air flow blows on the lower surface of the sheet to lift the sheet. Since the air nozzle 100 is normally closed and no air flow is generated, the sheet is conveyed along the conveyance guide 11.

When the rear end of the sheet is to be lifted, the air nozzle 100 is opened to blow an air flow on the lower surface of the rear portion of the preceding sheet to separate the rear portion of the sheet above the conveying surface.

The feeding operation for continuously feeding the sheets at the minimum necessary interval by using the various sheet rear end separating means described above is performed by the rear end separating portion composed of the crank and the pushing-up member. The feeding device having the means is similar to that described in detail with reference to FIGS. 2 and 3.

By the way, when the sheet feeding device of the image forming apparatus having the above-described structure performs the operation for minimizing the sheet interval, the noise generated by the trailing edge separating means and the frequent shift noise generated by the timing roller driving section are generated. However, it may have an adverse effect in the usage environment. In order to reduce the above noise, a normal feeding mode for continuously feeding a sheet with a relatively wide sheet interval is provided without operating the rear edge separating means. It is preferable that the sheet intervalless feeding mode in which the means is operated to keep the sheet interval at a minimum and the sheet is continuously fed can be arbitrarily selected by the operation unit or the like.

The carrying state in the normal feeding mode in that case will be described.

FIG. 19 is a time chart of each part when the sheet is conveyed in the normal feeding mode.

With reference to FIGS. 1 and 19, the registration sensor 3 indicates that the uppermost sheet of the sheet bundle stacked on the sheet feeding unit 30 has been sufficiently separated from the trailing edge of the preceding sheet.
Then, the pickup roller 1 is rotated once to pass over the separation claw 2 to be separated.

The fed-out sheet is once abutted against the timing roller 4 which is stopped based on the timing when the leading edge of the sheet is detected by the registration sensor 3 and is obliquely fed (skew).
After the correction is made, the timing roller is rotated at the same circumferential speed as the conveyance speed Vo of the photoconductor 10 and the transport roller 8 to restart the conveyance.

When the leading edge of the sheet is detected by the timing sensor 5, the timing roller 4 is stopped.

Next, the timing roller 4 is reversed at a slow speed Vs and is accurately aligned with the upstream side of the timing sensor 5. The position may be immediately upstream of the sensor or may be adjusted in advance by a distance corresponding to the sheet interval.

By this operation, the sheet can be positioned with extremely high accuracy. After that, the sheet feeding is restarted at the speed Vo in synchronization with the progress of image formation.

As described above, in the normal feeding mode,
Since the rear end separating means is not operated, noise generated during operation can be eliminated. Further, the transport speed by the timing roller is as high as Vf in the sheet-less feeding mode, but is relatively slow as Vo in the normal feeding mode, so that the frequent shift noise of the timing roller is reduced. be able to.

When the noise generated by the rear end separating means or the frequent shift noise generated by the timing roller driving unit has an inconvenient influence under the use environment, the user can arbitrarily feed the paper without the inter-sheet feeding using the operation panel or the like. Since you can stop the mode and select the normal paper feed mode, you can operate comfortably with the operation mode that matches the usage environment. Further, the selection is not limited to the operation panel and the like, and may be selected by a command from an external device (host computer).

When a subsequent sheet feeding start command is sent after a lapse of a certain period of time with respect to the preceding sheet feeding operation and the sheets cannot be overlaid in time, use FIG. It is not necessary to perform the series of sheet interval control operations described above. Therefore, in this case, do not automatically separate the trailing edge of the leading sheet,
It is possible to reduce the noise generated by the rear end portion separating means and the frequent shift noise generated by the timing roller driving portion.

FIG. 20 shows a time chart and FIG. 21 shows a flow chart in that case.

In FIG. 20, when the interval between the feeding start command ST1 for the preceding sheet and the feeding start command ST2 for the following sheet is a predetermined interval (T1), the feeding is performed in the sheetless feeding mode. Is going. (First half of time chart) The interval (T2) between ST2 and the subsequent sheet feeding start command ST3 is longer than the predetermined interval by a certain time or more (ΔT). At this time, the normal feeding mode is set. Are being delivered. (First Half of Time Chart) By the way, depending on the image forming apparatus, there is a sheet transfer path provided with a transfer path switching means such as a fork gate so that the sheet transfer path can be selected from any of a plurality of paths. FIG. 22 shows an example of such an image forming apparatus.

In the image forming apparatus shown in FIG. 22, two paper discharge paths are prepared, and this switching is performed by the fork gate 31. Further, the sheet conveyed in the direction of arrow A by the fork gate 32 is
At that time, the direction is reversed and the sheet is fed again to the timing roller 4 to form an image and print on both sides.

The fork gate is driven by a solenoid (not shown) or the like to switch the transport path.
However, with this conventional method, it takes some time to switch, and when the preceding sheet and the following sheet do not specify the same paper discharge path or the same paper feed path, that is, the fork gate in the conveyance path. If there is a transport path switching means such as the above, switching cannot be performed normally if the sheet interval is too narrow.

Therefore, as shown in the flowchart of FIG. 23, when the same sheet feeding path and discharging path as the preceding sheet are not selected, the normal feeding mode is automatically selected and the sheet interval is widened. The above problem can be solved by sending it by hand.

By the way, when controlling the paper feeding operations (b) and (c) described with reference to FIG.
Even if the feeding start command for the subsequent seat is slightly delayed,
In order to maintain the sheet-less sheet feed mode as much as possible, the sheet interval becomes the target interval in accordance with the timing of the instruction to start the feeding of the succeeding sheet with respect to the feeding operation of the preceding sheet. The transport speed may be calculated and the timing roller (4) may be driven. (The feed speed is variable.) In addition, even if the target sheet interval cannot be obtained even with the maximum transport speed, the timing roller is driven with the maximum transport speed to allow the sheet spacing. It is desirable to perform control so that the contraction is as short as possible.

The details will be described with reference to FIGS. 24 and 25.

FIG. 25 shows changes in the feed speed of the timing roller 4. The solid line is a predetermined timing chart when the feeding start command is continuously received (see FIG. 3). The broken line shows an example when the feeding start command of the succeeding sheet is delayed with respect to the preceding sheet.

If the start timing of the timing roller 4 is delayed by t ₃ because the instruction to start the feeding of the succeeding sheet is delayed, V is set to recover the delay.
fr is calculated, and the timing roller is driven at this speed. At this time, the following relationship holds.

Vf · t ₁ = Vfr · t ₂ = l ₁ Vf: Feeding speed of the timing roller when continuously receiving the feeding start command Vfr: Feeding of the timing roller when the succeeding sheet is delayed Speed t ₁ : Timing roller driving time at speed Vf t ₂ : Timing roller driving time at speed Vfr t ₃ : Timing roller start delay time with respect to predetermined timing l ₁ : Conveyance path length between timing roller and timing sensor As described above, if the sheet is conveyed at the speed Vfr, the sheet interval can be maintained at a predetermined interval. Also, when Vfr exceeds the maximum speed that the timing roller 4 can feed in the calculation (when the succeeding sheets cannot catch up and the predetermined sheet interval cannot be achieved), the driving is performed at the maximum speed.
Sheet spacing can be reduced as much as possible.

By changing the feeding speed of the pickup roller 1 and feeding at a high speed, it is possible to maintain a predetermined sheet interval even at a timing which is further delayed.

The carrying speed of the timing roller 4 can be selected stepwise, and the carrying speed is set in accordance with the timing at which the feeding start command for the succeeding sheet is sent with respect to the feeding operation for the preceding sheet. It is also possible to select and change the driving time to perform control so as to obtain a predetermined sheet interval.

For example, in the embodiment shown in FIG. 26, the conveyance speed of the timing roller 4 is set to two stages, and high speed conveyance (> V) is performed.
The sheet interval is controlled by changing the period during which f) and constant speed conveyance (= Vf) are selected. Similarly to the apparatus of claim 4, even when the high-speed conveyance is performed at a rate of 100% and the desired sheet interval cannot be obtained, the timing roller is driven by the high-speed conveyance to allow the sheet interval. The control is performed so that it is shortened as much as possible.

The details will be described with reference to FIGS. 24 and 26.

FIG. 26 shows the feed speed of the timing roller. A solid line is a predetermined timing chart when the print start command is continuously received (see FIG. 3), and a broken line shows an example when the feeding start command is delayed. If the start timing of the timing roller is delayed by t ₃ because the instruction to start feeding the subsequent sheet is delayed, for example, the sheet is conveyed at a speed Vft higher than Vf for a certain period of time to catch up, and catches up. After that, the sheet interval is kept constant by conveying the sheet at a predetermined speed Vf. At this time, the following relationship holds.

Vf · t ₁ = Vfr · t ₄ + Vf · t ₅ = l ₁ Vfr: Re-high speed sent by the timing roller (> Vf) t ₄ : Timing roller driving time at speed Vft t ₅ : After catching up Driving Time of Timing Roller at Speed Vf As described above, by calculating the time t ₄ for transporting at the speed Vft and driving the timing roller 4, it is possible to maintain a predetermined sheet interval.

Further, in calculation, the speed is Vft and all the time (t
₁ -t ₃₎ sheet not catch up to the trailing even drive the timing roller, even if it can not achieve a predetermined sheet interval, and drives all the time with the speed Vft, can shorten the sheet interval as possible.

Further, if the feeding speed of the pickup roller 1 is also set in stages and the feeding is performed in the high speed mode, the predetermined sheet interval can be maintained even at the later timing.

When selecting the conveyance speed of the timing roller, if the high speed conveyance is selected first and then the conveyance speed slower than that is selected, the leading edge detection accuracy of the sheet can be improved. Can be improved. The above-described configuration is effective because the leading edge detection is more accurate when the sheet conveyance speed is slower.

In the image forming apparatus configured as shown in FIG. 1, when the jam is detected while the trailing edge separating means 6 and 7 are in the middle of operation, the trailing edge separating means operates regardless of interruption of the conveying operation. The control may be performed so that the operation of the trailing edge portion separating means is continued until the state where the operation is not performed.

When the user removes the jammed paper, if the trailing edge lifters 6 and 7 pop out in the transport path, there is a risk that the jam processing will be difficult to perform or the trailing edge lifter will be damaged. The problem is solved by doing

FIG. 27 shows the flowchart.

[0118]

(1) According to the present invention described in claims 1, 2 and 3, it is possible to form a continuous image in which the sheet interval is shortened to a necessary minimum, and the continuous image can be formed without increasing the sheet conveying speed. It is possible to improve the forming speed, eliminate unnecessary waste of the life of the image forming portion represented by the photoconductor at the sheet interval portion, and reduce the running cost by extending the life.

(2) According to the invention described in claim 4, the occurrence of a defect such as a jam of the preceding sheet can be promptly detected even when the sheet interval is minimized as much as possible. It is possible to provide a highly reliable feeding device.

(3) According to the invention described in claim 5, it is possible to provide a low-cost and highly reliable feeding device with a simple structure.

(4) According to the inventions of claims 7, 8 and 9, in the case of carrying out the invention of claim 1, since the leading edge of the sheet can be reliably detected, no malfunction occurs. A highly reliable feeding device can be realized.

Further, since the sheet detecting means can be constructed in a small size, downsizing and cost reduction of the entire apparatus can be realized.

(5) According to the invention described in claim 8, since the rear end separating means of the seat is composed of the crank and the pushing-up member connected to the crank, the separating operation can be easily realized by the rotational movement. ..

(6) According to the ninth aspect of the invention, in the above-mentioned sheet rear end spacing means, when the lifting member is raised, it starts contacting the sheet from a shallow angle, and therefore the sheet surface is separated without being damaged. The operation can start. Also,
When the lifting member descends, it makes a deep angle with respect to the conveyance guide surface, so that the tip of the lifting member quickly descends below the conveyance guide surface.

(7) According to the invention described in each of the tenth to sixteenth aspects, it is possible to provide the sheet rear end portion spacing means having various configurations with a simple configuration other than the above and having a high reliability. ..

(8) According to the seventeenth aspect of the invention, when the noise generated by the rear end spacing means or the frequent shift noise generated by the timing roller drive part has an adverse effect under the use environment, Since the person can arbitrarily quit the sheet-less sheet-feeding mode and select the normal sheet-feeding mode, a comfortable operation can be performed according to the operation mode suited to the use environment.

(9) According to the invention of claim 18,
When high-speed continuous image formation cannot be performed in the sheet-less sheet feed mode due to delays in image formation preparation, noise is generated by the trailing edge separating unit and the timing roller drive unit is automatically changed to the normal sheet feed mode. Frequent shifting noise can be reduced and comfortable driving can be performed.

(10) According to the nineteenth aspect of the present invention, when it is necessary to switch the transport path, the normal paper feed mode is automatically selected, and the conventional transport path switching means facilitates switching of the transport path. Switching can be done.

(11) According to the invention as set forth in claims 20 and 21, even if the feeding start command for the succeeding sheet is slightly delayed due to a delay in image forming preparation or the like, the conveying speed and speed of the succeeding sheet and By changing the period selected for the specific speed, the time required for feeding is shortened, and the sheet-less sheet feeding mode can be maintained.

(12) According to the invention as set forth in claim 22, when the jam occurs, it is controlled so as to lower the rear end separating means which may be an obstacle of the conveying path, and the rear end separating means during the jam processing. The operability is improved because it is not damaged or the jam is hard to handle due to the hand.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a configuration of a sheet feeding device according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram for sequentially explaining a sheet feeding operation of the apparatus.

FIG. 3 is a timing chart thereof.

FIG. 4 is a control block diagram of an image forming apparatus including the sheet feeding apparatus.

5A to 5C are explanatory diagrams sequentially showing another sheet feeding operation by the sheet feeding apparatus shown in FIG.

FIG. 6 is a timing chart thereof.

FIG. 7 is a cross-sectional view showing in detail the configuration of the sheet rear end portion separating means shown in FIG.

FIG. 8 is a cross-sectional view showing another configuration of the sheet rear end spacing means.

FIG. 9 is an explanatory diagram explaining its operation.

FIG. 10 is a cross-sectional view showing still another configuration of the sheet rear end spacing means.

FIG. 11 is an explanatory diagram explaining its operation.

FIG. 12 is a cross-sectional view showing several examples of friction reducing means at the tip of the pushing member.

FIG. 13 is a cross-sectional view showing still another configuration of the sheet rear end portion separating means.

FIG. 14 is an explanatory diagram explaining its operation.

FIG. 15 is a cross-sectional view showing still another configuration of the sheet rear end portion separating means.

FIG. 16 is an explanatory diagram explaining its operation.

FIG. 17 is a cross-sectional view showing still another configuration of the sheet rear end portion separating means.

FIG. 18 is an explanatory diagram explaining its operation.

FIG. 19 is a time chart of each part in the normal feeding mode in the case of having a sheet-less feeding mode in which sheets are continuously fed with a minimum sheet interval and a normal feeding mode in which sheets are continuously fed at normal intervals. Is.

FIG. 20 is an example of a time chart of each part in the case where the feeding mode is automatically selected according to the interval between the trailing sheet feeding start command and the running sheet feeding operation.

FIG. 21 is a flowchart of the feeding mode selection in that case.

FIG. 22 is a cross-sectional view showing an example of an image forming apparatus having a plurality of selectable sheet conveyance paths.

FIG. 23 is a flowchart of sheet feeding mode selection accompanying the switching of the conveyance path of the image forming apparatus.

FIG. 24 is an explanatory diagram illustrating a control for reducing the sheet interval to the interval in the sheet-less mode when the instruction to start the feeding of the succeeding sheet is delayed with respect to the feeding operation of the preceding sheet. Is.

FIG. 25 is an explanatory diagram illustrating one of the control methods.

FIG. 26 is an explanatory diagram illustrating another one of the control methods.

FIG. 27 is a flowchart of the operation of the trailing edge separating means when a jam is detected during operation of the sheet trailing edge separating means.

FIG. 28 is a cross-sectional view showing an example of the configuration of a sheet feeding device of a conventional image forming apparatus.

[Explanation of symbols]

 1 Pickup Roller 2 Separation Claw 3 Registration Sensor 4 Timing Roller Pair 5 Timing Sensor 6 Pushing Member (Sheet Rear End Separation Means) 7 Crank 8 Transport Roller 9 Transfer Separation Charger 10 Photoconductor 11 Transport Guide Surface 11a Sliding Guide 11b Abbreviated circular cross-section groove 15 Host computer 16 Controller 17 Main body controller 28 Operation panel 29 Antireflection sheet 30 Paper feed unit 31, 32, 33 Fork gate 60 Solenoid 61 Spring 62 Push-up member 63 Sliding guide 70 Push-in member 71 Roller 72 4 Fluoroethylene resin coating 73 4 Fluoroethylene resin tape 80 Charging pole 81 Charging case 82 Static erasing brush 90 Intake fan 91 Suction box 92 Opening 100 Air nozzle 101 Fan

Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location G03G 15/00 102 110 110 7369-2H

Claims (22)

[Claims] 1. A sheet feeding device for continuously feeding cut sheets at a predetermined interval, a sheet detecting means for detecting an edge of a sheet conveyed on a feeding path, and a trailing edge of a preceding sheet. A trailing edge separating means that is spaced apart from the sheet detecting means outside the detectable area of the sheet detecting means in a direction intersecting the sheet conveying surface, while separating the trailing edge of the preceding sheet by the separating means. The leading edge of the trailing sheet is positioned by the sheet detecting means, and then the trailing edge of the preceding sheet is released from the sheet detecting means, and the trailing edge of the leading sheet and the leading edge of the trailing sheet are released. A sheet feeding device, which is controlled so as to maintain a constant interval between the sheet and the sheet. 2. The sheet feeding apparatus according to claim 1, wherein, when the leading edge of the succeeding sheet is positioned, the conveying speed of the succeeding sheet is set higher than a predetermined conveying speed of the preceding sheet. 3. A sheet is fed in advance with the trailing edge of the preceding sheet and the leading edge of the trailing sheet overlapped with each other, and the trailing edge of the preceding sheet is trailed at the timing before the leading edge of the trailing sheet reaches the sheet detecting means. 2. The end sheet separating means separates the sheet from the sheet detecting means, the leading edge of the succeeding sheet is positioned while the trailing edge of the preceding sheet is separated, and the sheet is conveyed at a predetermined interval. The sheet feeding device described. 4. The trailing sheet leading edge positioning is performed by the sheet detecting means detecting the trailing sheet leading edge and then conveying the trailing sheet at a slow speed in a counter feeding direction, and the sheet detecting means detecting the trailing sheet. The sheet feeding apparatus according to claim 1, wherein the sheet feeding apparatus is performed by stopping the conveyance at a position where the sheet is lost. 5. A timing roller having a controllable conveyance speed is provided upstream of the sheet detecting means, and the trailing sheet leading edge positioning operation is performed by the timing roller and the registration operation is also performed by the roller. The sheet feeding device according to claim 4. 6. The sheet detecting means is a reflection type optical sensor, and a direction of a straight line connecting a light emitting portion and a light receiving portion thereof is made to substantially coincide with a sheet conveying direction. The sheet feeding device described. 7. An optical axis direction of a light emitting portion or a light receiving portion of the reflection type optical sensor is provided so as to be substantially parallel to a direction in which a rear end portion of a sheet lifted by the rear end portion separating means extends. The sheet feeding device according to claim 6. 8. The rear end separating means comprises a crank arranged below the sheet conveying path, and a push-up member which is connected to the crank and reciprocates to push up the sheet from the lower surface side. The sheet feeding device according to claim 1, wherein: 9. The center of rotation of the crank is located downstream of the leading end side of the pushing-up member in the sheet conveying direction, and the rotation direction of the crank is opposite to the sheet conveying direction on the side close to the sheet conveying path. The sheet feeding device according to claim 8, wherein 10. The rear end separating means is composed of a solenoid disposed below the sheet conveying path and a push-up member which is connected to the solenoid and reciprocates to push up the sheet from the lower surface side. The sheet feeding device according to claim 1, wherein: 11. The sheet feeding apparatus according to claim 10, wherein an approach direction of the pushing-up member with respect to the sheet is inclined to an upstream side in a sheet conveying direction. 12. The rear end separating means is provided with a cut-out circular groove extending in a direction perpendicular to the sheet conveying direction on an upper surface of a guide member provided below the sheet conveying path, and a sheet from the upper surface of the sheet. The sheet feeding apparatus according to claim 1, further comprising a pressing member having a lower end portion having an arcuate cross section that is pressed and pushed into the groove. 13. The sheet feeding apparatus according to claim 8, wherein the surface of the pushing-up member or the pushing member which is in sliding contact with the sheet is provided with a friction reducing means. . 14. The sheet feeding apparatus according to claim 1, wherein the trailing edge portion separating means is an electrostatic attraction means provided on the upper side of the sheet conveying path. 15. The sheet according to claim 1, wherein the rear end portion separating means is provided on an upper side of the sheet conveying path, and comprises a suction means for sucking the sheet by a negative pressure generated by an intake fan. Feeding device. 16. The sheet feeding apparatus according to claim 1, wherein the trailing edge portion separating means is an air nozzle provided below the sheet conveying path and blowing air upward. 17. A sheet-less feeding mode in which the trailing edge separating means is operated to continuously feed sheets while keeping the sheet spacing to a minimum, and a relatively wide sheet without operating the trailing edge separating means. 2. The sheet feeding apparatus according to claim 1, wherein a normal feeding mode of continuously feeding sheets at intervals can be arbitrarily selected. 18. The normal feeding mode is automatically selected when the instruction to start feeding the trailing sheet is sent after a lapse of a certain time or more with respect to the feeding operation of the preceding sheet. The sheet feeding apparatus according to claim 17, wherein the sheet feeding apparatus is a sheet feeding apparatus. 19. A plurality of sheet discharge paths or sheet feed paths that can be selectively switched, and a preceding sheet and a succeeding sheet are designated to be conveyed through the same sheet discharge path or the same sheet feed path. 18. The sheet feeding apparatus according to claim 17, wherein the normal feeding mode is automatically selected when not in operation. 20. A timing roller having a controllable conveyance speed is provided upstream of the sheet detecting means, and the timing roller is provided in accordance with a timing at which a succeeding sheet feeding start command is sent with respect to a preceding sheet feeding operation. 2. The sheet feeding device according to claim 1, wherein the conveying speed of the succeeding sheet is changed by the timing roller. 21. A timing roller capable of selecting a conveying speed stepwise is provided upstream of the sheet detecting means, and at a timing when a succeeding sheet feeding start command is sent with respect to a preceding sheet feeding operation. The sheet feeding device according to claim 1, wherein the period in which the conveying speed of the succeeding sheet is selected to a specific speed is changed by the timing roller. 22. Even when the conveyance operation is interrupted when a jam is detected while the rear end separating means is in operation, the rear end separating means remains inoperative until the rear end separating means becomes inoperative. The sheet feeding apparatus according to claim 1, wherein the sheet feeding apparatus is controlled to continue the operation of.