JP2002221832A - Image forming apparatus and paper carrying method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus and a paper carrying method for dispensing with change of the number of circularly carried sheets by making the rotating and driving timing of a 2nd paper feeding means same even in the case of forming images on both sides of several kinds of different size paper. SOLUTION: This image forming apparatus has a 1st paper feeding means, the 2nd paper feeding means receiving the paper from the 1st paper feeding means and carrying it to an image forming part, the image forming part for forming the image by transferring a toner image to the paper from the 2nd paper feeding means and then fixing it on the paper, and a circularly carrying means reversing and carrying the paper on the 1st side of which the image is formed and circularly carrying it to the 2nd paper feeding means again. The image forming apparatus is provided with a control means controlling so that paper carrying speed by the circularly carrying means may be changed when the paper size is different and the number of circulating sheets is the same.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as an electrophotographic copying machine or a printer for circulating and conveying a sheet, and a sheet conveying method.

[0002]

2. Description of the Related Art In order to form an image on both sides of a sheet of paper such as plain paper, a circulating conveyance means (hereinafter, also referred to as ADU) for reversing and conveying the sheet on which an image is formed on one side is provided. 2. Description of the Related Art An image forming apparatus is known.

In image formation, for example, five sheets of paper are continuously fed from a paper feed tray, and a toner image formed on a photosensitive drum is continuously printed on a first surface (front surface) of the paper. In order to circulate the paper after the transfer and the fixing process, the ADU is inverted by the ADU, the conveyance is continued without substantially stopping the paper, and the paper is circulated and conveyed again to the transfer area. A method of temporarily stacking a plurality of sheets on an intermediate tray so that another toner image formed thereon is transferred to the second surface (back surface) of the sheet and discharged to a sheet discharge tray after the fixing process. There is no known so-called non-stack circulating transfer system.

Image formation on the sixth through tenth sheets is processed as a second group, and image formation on the next five more sheets is processed as a third group.

In the case of using such a non-stack circulating conveyance system, the above-described five sheets are circulated in a circulating conveyance path (registration roller generally referred to as a second paper supply means). (Inversion area-registration roller)
Substantially, it is always in a transport state.

[0006]

FIG. 5 is a schematic view showing the structure of an image forming apparatus according to the present invention, which is used here to explain the problems of the conventional structure.

In the figure, 31 is a photosensitive drum, 56 is a registration roller as a second paper feeding means, 57 is a pre-transfer roller,
35 is a transfer pole as a transfer means for performing a transfer area,
Reference numeral 38 denotes a fixing device that forms a fixing area, 61 denotes a fixing discharge roller, 62 denotes a switching unit that switches a conveyance path, and 600 and 6.
Reference numerals 10 and 620 denote transport rollers, which constitute a reverse discharge / refeed section for reverse discharge and circulating transport.

800, 810, 820, 830, 84
Reference numerals 0 and 850 denote transport rollers constituting the circulating transport unit 8 for performing the reverse and transport of the sheet, and the transport roller 800 is hereinafter referred to as an ADU reverse roller as the reverse unit of the present invention.

Reference numeral 55 denotes a transport roller provided at the junction of the transport path between the paper fed through the ADU 8 and the paper fed from the paper feed tray 400, for example.

The above-described circulating transport path corresponds to a loop indicated by a thick arrow. The process of forming a two-sided image using the ADU 8 will be described focusing on the movement of the sheet. For example, the first sheet feeding unit continuously outputs the sheet from the sheet feeding tray 400 at predetermined time intervals according to the execution of the image forming process. The five sheets fed to the registration rollers 56 sequentially reach the registration rollers 56 via the conveyance rollers 55, and are detected by detection means (not shown).
The sheet is fed again by the rotation of the registration roller 56, and enters the transfer area in a state of being superimposed on the toner image area formed on the photosensitive drum 31.

The sheet on which the toner image has been transferred to the first surface by the action of the transfer pole 35 in the transfer area is separated from the photosensitive drum 31 and conveyed to a fixing device 38.

The sheet having the toner image fixed by the heating and pressurizing action in the fixing device 38 is sent downward along a conveyance path switched by a fixing discharge roller 61 and a switching means 62. , Transport roller 60
After being sequentially moved in the transport path formed to the upper right by 0 to 620, it reaches the ADU reversing roller 800.

At the timing when the rear end of the ADU reversing roller 800 is nipped in the traveling direction, the rotation of the ADU reversing roller 800 is controlled in the reverse direction, so that the sheet is turned upside down, and the rear end is used as the front end. A transport path formed in the ADU 8 while being transported in the opposite direction to the above, ie,
After being horizontally transported rightward in the figure by the transport rollers 810 to 850, it is guided upward, and eventually reaches the registration roller 56 via the transport roller 55, and then reaches the second surface through the same process as described above. A toner image is formed.

Thereafter, after the fixing process by the fixing device 38, the sheet is discharged,
Are sequentially discharged to the paper discharge tray 64 via the.

By the way, in such an image forming apparatus, for example, the number of image forming sheets obtained per unit time is set based on a predetermined sheet size (particularly, the length of a specific sheet in the conveying direction). In fact, various efforts have been made to achieve this.

As one of the problems, there is a problem of the operation timing of the registration roller. For example, it is conceivable to devise such that the registration roller can be operated at a constant interval on a sheet of a reference size.

For example, a sheet of a reference size arrives at the registration roller 56, and a process of forming a toner image on the photosensitive drum 31 is started in synchronization with the feeding by the registration roller 56, and the transfer is performed. Pole 35
The distance from the exposure section to the transfer electrode and the distance from the registration roller to the transfer electrode are set to be the same so that the toner image area and the paper overlap in the transfer area having the photoconductor drum 31, the registration roller 56, A configuration is conceivable in which the linear velocity of the pre-transfer roller 57 is set to be the same, and the registration roller is always operated at a constant interval by appropriately selecting the circulation path length.

However, there is no problem in control if one sheet of paper is used, but there is a problem in a case where a plurality of sheets of different sizes are targeted and the number of circulations is the same.

FIG. 6A schematically shows a deviation of the paper interval when the same number of sheets are circulated using a sheet of a reference size and a sheet of a size other than the reference size.

For example, if the reference size is a letter size (216
mm × 279 mm, and the registration roller portion (second
The paper interval (the interval between the trailing edge of the preceding paper and the leading edge of the succeeding paper) in the paper feeding unit) is substantially constant.

In other words, by controlling the registration roller to rotate at predetermined time intervals, an image is formed on the first surface (shown as side 1 in the figure) of the paper at the predetermined paper interval. The last fifth sheet (the sheet on which the image is to be formed on the first side) and the first sheet after the sheet is turned over and circulated and conveyed (shown as side 2 in the figure,
Various conditions, such as the length of a paper circulating conveyance path, are set so that the paper interval with the first transfer paper on which an image is formed on the second surface is also constant. High productivity per hit has been achieved.

However, as shown in FIG. 6B, the size is smaller than the letter size which is the reference size.
For example, when a sheet of A4 size (210 mm × 297 mm, short side in the transport direction) is selected, the paper interval between sheets fed for image formation on the first side, and the image on the second side The interval between the sheets re-fed for formation is the same as that in FIG. 6A, since the time interval for the rotational driving of the registration rollers is the same as that in FIG. 6A. The distance between the trailing edge of the fifth sheet on which the image is formed on the first side and the leading end of the first sheet on which the image is formed on the second side is fixed at a slightly wider sheet interval because of the smaller size. Becomes narrower.

This is due to the fact that the reversal time of the paper in the ADU is shortened by the small size.

To cope with such a problem, at this time, for example, it is necessary to start an image forming process on the photosensitive drum and to accelerate the rotational drive timing of the registration roller. In this case, the control becomes complicated, and the productivity per unit time cannot be improved.

On the other hand, it is not preferable to change the rotational drive of the registration roller for each sheet size because the load on the control system increases.

Also, a size larger than the standard size paper, for example, wide paper (228.6 mm × 279 mm)
FIG. 6 shows a case in which a sheet whose short side is the transport direction is selected.
As shown in FIG. 6C, a phenomenon opposite to the case of FIG. 6B occurs.

That is, the reverse time of the sheet becomes longer by an amount corresponding to the large size, and therefore, the fifth sheet on which an image is formed on the first side and the first sheet on which the image is formed on the second side are separated. Paper interval becomes wide.

To cope with such a problem, control similar to that described above and necessary only at this time is inevitable, and the same problem remains.

As another problem different from the above, in the process of feeding paper at predetermined time intervals from the paper feed tray to the registration rollers, a paper feed delay may occur for some reason. In the case where the paper cannot be detected within a predetermined time in the second paper feed unit, the apparatus is appropriately stopped on the assumption that a trouble has occurred, and as a result, productivity has been reduced.

The present invention has been made in view of the above problems, and its main purpose is to provide a simple configuration, and even if images are formed on both sides of a plurality of types of paper having different sizes, the number of circulating conveyance sheets is the second. An object of the present invention is to provide an image forming apparatus and a sheet conveying method which do not need to be changed by making the rotational driving timings of sheet feeding units the same.

It is another object of the present invention to provide an image forming apparatus and a method of transporting sheets that can increase productivity per unit time even if there is a delay in sheet feeding from a sheet feeding tray.

[0032]

The object of the present invention can be achieved by the following constitution.

(1) First paper feeding means for feeding paper one sheet at a time, second paper feeding means for receiving paper from the first paper feeding means and conveying the paper to the image forming section, An image forming unit for forming an image by transferring and fixing a toner image to a sheet from a paper unit, and forming an image on a second surface of the sheet on which an image is formed on the first surface by the image forming unit for,
Circulating transport means for reversing and transporting the paper on which the image is formed on the first surface and circulating and transporting the paper again to the second paper feeding means; After sequentially forming an image, the sheet is reversed and conveyed by the circulating conveyance means and circulated and conveyed to the second paper supply means,
In an image forming apparatus for sequentially forming an image on a second side of a sheet on which an image is formed on the first side, if the size of the sheet is different and the number of circulated sheets is the same, An image forming apparatus, comprising: a control unit for controlling so as to change the conveying speed of the image forming apparatus.

(2) The image forming apparatus according to (1), wherein the change of the transport speed is a change of a reverse transport speed by a reversing unit constituting the circulating transport unit.

(3) A first paper feeding means for feeding paper one by one, a second paper feeding means for receiving the paper from the first paper feeding means and conveying the paper to the image forming section, An image forming unit for forming an image by transferring and fixing a toner image to a sheet from a paper unit, and forming an image on a second surface of the sheet on which an image is formed on the first surface by the image forming unit for,
Circulating transport means for reversing and transporting the paper on which the image is formed on the first surface and circulating and transporting the paper again to the second paper feeding means; After sequentially forming an image, the sheet is reversed and conveyed by the circulating conveyance means and circulated and conveyed to the second paper supply means,
In a method of conveying a sheet in an image forming apparatus for sequentially forming an image on a second side of a sheet on which an image is formed on the first side, when the size of the sheet is different and the number of circulating sheets is the same, The circulating time required from the time when the paper is started to be transported from the second paper feeding unit to the image forming unit to the time when the paper is reversed by the circulating transportation means and circulated and reaches the second paper feeding unit is constant. Controlling the transport of the paper by the circulating transport means.

(4) The method of conveying a sheet according to the above (3), wherein the control of the sheet conveying is a change of a sheet conveying speed.

(5) The method of conveying a sheet according to (3), wherein the change of the conveying speed of the sheet is a change of the conveying speed in a reversing means constituting the circulating conveying means.

(6) A first paper feeding means for feeding paper one by one, a second paper feeding means for receiving paper from the first paper feeding means and conveying the paper to an image forming section, An image forming unit for forming an image by transferring and fixing a toner image to a sheet from a paper unit, and forming an image on a second surface of the sheet on which an image is formed on the first surface by the image forming unit for,
Circulating transport means for reversing and transporting the paper on which the image is formed on the first surface and circulating and transporting the paper again to the second paper feeding means; After sequentially forming an image, the sheet is reversed and conveyed by the circulating conveyance means and circulated and conveyed to the second paper supply means,
In an image forming apparatus that sequentially forms an image on a second side of a sheet having an image formed on the first side, if a paper feed delay occurs during continuous paper feeding from a paper feed tray, the preceding paper An image forming apparatus, comprising: control means for controlling the conveyance of a sheet so that the conveyance speed is reduced or temporarily stopped.

(7) The permissible time of the paper feed delay can be set, and the control means inhibits the paper feed from the paper feed tray when the paper feed delay time is longer than the permissible time. The image forming apparatus according to the above (6), wherein the control is performed so as to perform

(8) When the control of the deceleration or the pause is being executed on the preceding paper, the control means interrupts the control of the deceleration or the pause, and sets the normal transport speed. The image forming apparatus according to (7), wherein control is performed such that conveyance of the preceding sheet is restarted.

[0041]

FIG. 1 is a schematic diagram showing the structure of an image forming apparatus according to the present invention.

In the copying machine as the image forming apparatus of the present embodiment, an automatic document feeder 1 is provided at the top of the copying machine main body, and an image reading device 2, an image forming unit 3, a paper storage unit is provided in the copying machine main body. 4, paper feeding unit 5, reversing paper ejection / re-feeding unit 6,
And an ADU 8 as the circulation inversion means described above.

The reversing sheet discharging / re-feeding unit 6 and the ADU 8 have been described above, and therefore the description of the configuration will be omitted except when necessary.

The automatic document feeder 1 feeds a document one sheet at a time, transports the document to an image reading position, and discharges the document after image reading to a predetermined place.

The automatic document feeder 1 includes a document placing table 11 on which a document is placed, a document separating means 12 for separating the document placed on the document placing table 11, and a document separated by the document separating means 12. A document conveying means 13 including a plurality of rollers for conveying, a document discharging means 14 for discharging a document conveyed by the document conveying means 13, a document discharge table on which a document discharged by the document discharging means 14 is placed. 15 and document reversing means 16 comprising a pair of rollers for reversing the front and back of the document when reading images on both sides of the document.

In view of the processing process, a plurality of documents (not shown) placed on the document table 11 are
The originals are separated one by one by the original separating unit 12 and conveyed toward the image reading position by the original conveying unit 13.

The original reading position is set at the original conveying means 1.
3, the image reading device 2
The image of the original is read through the slit 21 constituting.

The document from which the image has been read is discharged onto a document discharge table 15 by the document discharge means 14.

When reading images on both sides of a document, the document once read on one side is guided to the document reversing means 16, and the reverse of the roller with the rear end of the document applied to the rollers is performed. By reversing the front and back of the original by the rotation control and conveying the original again by the original conveying means 13, an image on another surface can be read at the original reading position.

These steps are repeated for the number of originals placed on the original placing table 11. Further, the automatic document feeder 1 is configured to be foldable, and by raising the automatic document feeder 1 to open the platen glass 22, a document is directly placed on the platen glass 22. It is configured so that it can be copied.

The image reading device 2 is a means for reading an image on a document and obtaining image data. The slit 21, a lamp 231 serving as a light source for irradiating the document, and a light source for reflecting light reflected from the document. A first mirror unit 23 formed by integrating the first mirror 232 with the first mirror 23;
A second mirror unit 24 that integrates a second mirror 241 and a third mirror 242 that reflect light from the second mirror 241;
An imaging lens 25 that forms an image of the reflected light from the second mirror unit 24 on an image sensor (hereinafter, referred to as a CCD) 26 described below, and a light image formed by the imaging lens 25 is photoelectrically converted. Linear CCD for obtaining image information
26.

The image information is subjected to appropriate image processing and then temporarily stored in a memory (not shown).

In the embodiment in which the image reading device 2 reads the document fed by the automatic document feeder 1, the first mirror unit 23 and the second mirror unit 2
4 is fixed at a position as shown.

On the other hand, in a mode of reading an image of an original placed directly on the platen glass 22, the first mirror unit 23 and the second mirror unit 24 are moved along the platen glass while maintaining the optical path length. This is done by causing

The image forming section 3 finally forms an image on a sheet based on the image data obtained by the image reading device 2.

The image forming section 3 in the embodiment is
A photosensitive drum 31 having a photoconductive photosensitive layer on its surface, and a charger 32 for uniformly charging the surface of the photosensitive drum 31;
A laser writing system 33, which is operated based on image data after image processing and is an exposure unit for exposing the photosensitive drum 31 to form a latent image by exposing the photosensitive drum 31, forms a latent image formed on the photosensitive drum 31. Developing device 3 that reversely develops an image to form a toner image
4. a transfer pole 35 for transferring the toner image onto a sheet of paper;
A static eliminator 36 that promotes separation by discharging electricity by performing corona discharge, a cleaning unit 37 for cleaning the photosensitive drum 31 after the transfer process is completed, and a heating roller type fixing for fixing a toner image on the paper It has a device 38, and the above-mentioned inverted sheet discharging / re-feeding unit 6 and ADU8.

In the image formation according to the above configuration, the photosensitive drum 31 rotating in the direction of the arrow is sequentially charged by an appropriate driving means by a charger 32, and an electrostatic latent image is formed by dot exposure by a laser writing system 33. The transfer pole 3 is formed on a sheet fed synchronously by the start of rotation of a registration roller 56 as a second sheet feeding means so as to be superimposed on the toner image area by the developing unit 34 and then superimposed on the toner image area.
The transfer is performed through the action of No. 5.

Thereafter, the sheet on which the toner image has been transferred is separated from the surface of the photosensitive drum 31 by the static eliminator 36, and the toner image is fixed on the sheet by the heating and pressing action of the fixing device 38.

On the other hand, the photosensitive drum 3 passing through the transfer area
1 further continues to rotate, the residual toner is removed by the cleaning means 37, and preparation for the next image formation is made.

In the embodiment, the static eliminator 3
Between the fixing device 6 and the fixing device 38, a transport belt 39 for transporting the paper separated by the neutralizer 36 is provided.

The paper storage unit 4 integrally includes storage units 405, 415, and 425, which are storage containers for storing sheets in a stacked state, and paper supply units 51, 52, and 53 as first paper supply means. Paper feed trays 400, 410, 420
Are arranged in the up-down direction, and sheets of different sizes are stored in the sheet feeding tray.

For example, paper (letter size) defined as a reference size is stored in the paper feed tray 400, A4 size paper is stored in 410, and wide size paper is stored in 420. (The short side extends along the transport direction).

The paper stored in these paper feed trays is not limited to the plain paper described above, but may be recycled paper, OHP sheets, or the like.

The paper feed units 51, 52, and 53 have a paper feed roller 50 having a substantially fixed position when the paper feed tray is pushed into a predetermined position in the apparatus and loading is completed.
5, 535, 555, and separation rollers 506, 536, 556 for preventing layering.

The paper feed section 5 is a transport means for transporting the paper from each of the paper feed trays to the image forming section 3, and has a pair of transport rollers R1, R2, R3, R4, R5, R6.
have.

PS is a photo sensor, and the paper feed tray 400
The paper supplied by the paper supply roller 500 from the conveyance roller pair R1 provided downstream of the separation roller 506
, And is provided at a position immediately before the conveying roller pair R1.

More specifically, output information from the photosensor PS indicating whether or not the sheet has arrived at the conveying roller pair R1 within a predetermined time from the start of sheet feeding is used as information for controlling sheet conveyance thereafter. This is used, and will be described later.

The photosensor PS as described above is provided for the paper feed trays 410 and 420 in the same manner.

It is preferable that the transport roller pairs R1 to R3 are provided integrally with the paper feed units 51 to 53 as pre-registration rollers.

The reversing sheet discharging / re-feeding section 6 is an area for re-feeding the sheet after image formation in accordance with the reversing sheet discharging or duplex copying process. A switching unit 62 is provided for switching the transport path between the case where the sheet is discharged outside the apparatus, the case where the sheet is reversed and the sheet is discharged after being turned over, and the case where the sheet is re-fed to form an image on the back surface of the sheet.

When the paper on which an image is formed is to be discharged as it is, that is, with the final image surface facing upward, the switching means 62 is positioned at the position shown by the dashed line in FIG. When the sheet is turned over and discharged, the switching unit 62 is positioned at the position shown by the solid line in the figure, and the sheet conveyed by the fixing discharge roller 61 is once conveyed to the ADU 8 side, and the sheet is switched. 6
2, the sheet is reversed and conveyed by the conveying roller 600, and is discharged to the discharge tray 64 outside the apparatus by passing the switching means 62 on the left side.

Further, when an image is formed on the back side of a sheet,
The switching means 62 is positioned at the position shown by the solid line in the figure,
The sheet conveyed by the fixing discharge roller 61 is conveyed to the ADU reversing roller 800 by the respective conveying rollers of the reversing sheet discharging / re-feeding unit 6 driven by the sheet discharging motor, and the roller performs switchback to be turned on and off. After the reversal, the sheet is circulated and transported to the registration roller 56.

In the above configuration, the reverse transport roller 8
Reference numeral 00 denotes an ADU reversing motor, which is rotationally driven in the normal and reverse directions.
Are rotationally driven by a registration motor.

Further, as described above, continuous image formation can be performed by using the non-stack circulating conveyance system with five sheets as one set.

For example, when an A4 size sheet shorter in the transport direction than the reference size is selected and used,
The conveyance speed of the sheet in the ADU 8 is controlled and changed so as to be slow, and the operation of the registration roller 56 for the first sheet after the reversal is performed at the same time interval as when the sheet of the reference size is used. It is configured to operate.

In other words, when the size of the paper is different and the number of circulating sheets is the same, when the paper is started to be conveyed from the second paper supply means to the image forming section, the paper is reversed by the circulating conveyance means. And then circulate and transport the second
The transport of the sheet by the circulating transport unit is controlled so that the circulating time required to reach the paper feeding unit is constant.

Change of paper transport speed in the ADU;
That is, to reduce the transport speed, the ADU reversing roller 80
This can be achieved by controlling the number of rotations of the drive motor 0 to be small.

On the other hand, when a wide-size sheet having a length in the transport direction longer than the reference size is selected and used, on the contrary, control is performed so that the transport speed of the sheet in the ADU is increased. The operation of the registration roller 56 with respect to the first sheet can be performed at the same time interval as when a sheet of the reference size is used.

In other words, when the size of the paper is different and the number of circulating sheets is the same, when the conveyance of the sheet from the second paper supply unit to the image forming unit is started, the paper is reversed by the circulating conveyance unit. And then circulate and transport the second
The transport of the sheet by the circulating transport unit is controlled so that the circulating time required to reach the paper feeding unit is constant.

The speed at which the paper is conveyed in the ADU can be increased by controlling the rotation speed of the ADU reversing motor for driving the ADU reversing roller 800 to be large.

FIG. 7 is a block diagram related to the control of the present invention. In FIG. 7, a CPU is an arithmetic processing device as control means of the present invention.

The CPU receives signals from the paper size detection sensor, photosensor PS, and operation display unit of each paper feed tray.

Further, a sheet feeding motor, a registration motor, an AD
The drive of the U reversing motor, the transport motor, the paper discharge motor and the switching means 62 is controlled to control the transport of the paper by each roller.

FIG. 2 is a flowchart showing a program related to the control. In this flowchart, the reference size of the paper is letter size,
The number of circulating sheets of A4 size, letter size, and wide size is the same.

When the image formation is started, the size of the paper to be selected and fed is read from the size data buffer in step 1 and it is determined in step 2 whether or not the sheet is, for example, A4 size. The number of rotations of the ADU reversing motor, which is the driving source of the reversing roller, is reduced (the motor control clock is made slower).

If N (No) in step 2, it is determined in step 4 whether or not it is a wide paper size. If Y, the rotation speed of the ADU reverse motor is increased in step 5 (the motor control clock is made faster).

If N in step 4, the feed paper is a standard-size paper (letter-size paper) and the ADU
The reversing motor has a normal (reference) rotation speed.

In other words, when the size of the paper is different and the number of circulating sheets is the same, when the conveyance of the paper from the second paper supply means to the image forming section is started, the circulating conveyance means reversely conveys the paper. At least, the transport of the paper by the circulating transport unit is controlled so that the circulating time required to reach the second paper feeding unit after being circulated and transported is constant.

As will be understood from the above description, the control means for changing the paper transport speed in the ADU is the arithmetic processing unit CPU.

Regarding the change of the transport speed of the paper in the ADU, it is preferable to control the rotation speed of the ADU reversing roller 800 so as to change only the transport speed. Depending on the case, it is also possible to achieve other parts in the circulating conveyance path instead of in the ADU, that is, in the present embodiment, the conveyance forming the reverse discharge / refeed unit 6. It can be achieved by controlling the rollers. Further, the present invention is not limited to the above-described configuration such as the configuration of the circulating transport path, the arrangement of the ADU rollers or the addition of a motor, so that the degree of freedom in design is wide.

FIGS. 3A and 3B are diagrams schematically showing the paper interval after the problem in the case where the paper of the reference size and the paper of a size other than the reference size are used is improved. FIG. a)
Similarly, FIG. 6B shows the paper interval when image formation is performed on the first and second surfaces of the reference size paper. FIG. 6B corresponds to FIG. 6B, and FIG. 6 (c).

In other words, (a) to (c) of FIG.
Can be said to be a diagram showing that the time interval of the operation of the registration rollers can be made constant irrespective of the sheet size, so that the control is simple and that high productivity per unit time is maintained.

FIG. 4 is a flowchart of the sheet feeding control including a case where a sheet feeding delay occurs during continuous sheet feeding from the sheet feeding tray.

Referring to FIG. 1, at the start of the image forming process, for example, the sheet feeding roller 505
Is started (step 10), and the paper feed tray 400
The first sheet inside is fed.

Next, it is determined whether or not a paper feed delay has occurred based on the information detected by the photosensor PS accompanying the paper feed operation (step 11).

The paper feed delay is an allowable time that can be set for each paper size, in other words, whether the paper has arrived from the paper feed tray to the transport means R1 within a predetermined set time set for each size. Substantially, the determination is made based on whether the photosensor PS has detected the image.

If the determination as to whether or not the paper feed delay has occurred is YES (hereinafter, referred to as Y), the paper feed operation for the same paper (the same paper feed paper) is repeated (retry). It is determined whether or not it has been repeated three or more times (step 12). If no (No: hereinafter, expressed as N),
It is determined whether an image is being formed on the preceding paper (preceding paper) (step 13).

In the following, the case of the first sheet and the case of
The second and fifth sheets will be described separately.

In the case where the first sheet is currently fed, a feed delay has occurred in the first sheet having no preceding sheet. The motors other than the feeding motor to be turned off are turned off (step 14), and the process returns to step 10.

If the sheet is not detected by the photosensor PS even if the sheet feeding operation is repeated three times or more, a jam flag is set so as to stop the sheet as a paper jam (jam) (step 15). Since there is no preceding sheet, the sheet feeding motor is turned off in step 27, the apparatus is stopped, and the jam display is displayed on the operation display unit.

On the other hand, if it is determined in step 11 that there is no sheet feeding delay and N is determined, the process proceeds from step 11 to step 17 and step 19, where the second sheet feeding by the registration roller 56 is started, and image formation on the side 1 of the sheet is performed. And circulating transport in the ADU 8 is performed.

Further, it is determined whether or not additional paper cannot be fed under the paper feeding conditions determined from the circulation path length and the paper size (step 21).

At present, it is N since it is the first sheet, and therefore, the flow returns to step S10. This cycle is performed for the five sheets, which can be said to be the number of sheets to be processed as described above. If Y is determined in step 21, the first sheet after being inverted by the ADU 8 is transferred to the second sheet feeding unit (register roller). (Synonymous with the position 56).
Paper feeding is started (step 23), and the second side of the paper is
That is, the image formation on the side 2 (step 24) and the subsequent conveyance of the paper toward the paper discharge tray 64 are confirmed (step 25), and when the image formation of the set number of copies and the paper discharge are completed (step 26), Is stopped.

If the image formation and the discharge of the set number of copies have not been completed, the process returns to step 10 and the above operation is repeated.

Next, for example, in the case where any one of the second to fifth sheets is currently being fed, if it is determined in step 11 that a paper feed delay has occurred, the preceding sheet Therefore, if N in step 12, it is determined in step 13 whether an image is being formed on the preceding sheet. If Y is in the course of image formation, monitoring is performed until the end of image formation. Is temporarily stopped, and the motors other than the sheet feeding motor are turned off (Step 14), and Step 10
Return to

If the same sheet is fed three times, and the sheet is not detected by the photosensor PS within a predetermined period of time, the sheet feeding motor is turned off.
The flow proceeds from step 12 to step 15, where a jam flag is set to stop the apparatus after discharging the preceding sheet to the discharge tray, and it is determined whether or not there is a preceding sheet (step 16).

If there is a preceding sheet, Y is obtained in step 16, so the process proceeds to step 17, where it is determined whether or not the conveyance of the preceding sheet is stopped. After the respective transport motors that were turned off in step 14 are turned on in order to start the transport of the preceding sheet at the normal transport speed, and after image formation has been performed on all preceding sheets to step 26, , The device is stopped in step 27.

As described above, the normal conveyance is resumed for the paper fed before the occurrence of the paper feed delay, and the image formation is performed so that the image formation of the preceding paper without any problem is continued. Thus, a decrease in productivity per unit time can be prevented as much as possible.

In the present embodiment, the control of the preceding sheet when the sheet feeding delay occurs is temporarily stopped in the present embodiment, but may be performed at a reduced speed in a mode that does not hinder image formation.

Although the paper used in the present embodiment has been described as letter size, A4 size, and wide paper, the present invention is not limited to this, including the size and the transport direction.

Specifically, when the non-stack circulating transport system is used, the productivity as described above is possible depending on the relationship between the circulating path length and the size of the paper in the transport direction.
It can also be applied to more than one type of transfer paper.

[0112]

According to the present invention, the second paper supply means can be operated at predetermined time intervals for a plurality of papers having different sizes in the transport direction, so that the control is simple and the productivity per unit time can be reduced. Can be higher.

Further, even if a paper feed delay occurs, the image forming process is restarted for the preceding paper, so that high productivity can be maintained.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating a configuration of an image forming apparatus according to the present invention.

FIG. 2 is a program flowchart related to control.

FIG. 3 is a diagram schematically illustrating a paper interval after a problem in a case where a sheet of a reference size and a sheet of a size other than the reference size are used is improved.

FIG. 4 is a sheet feeding control flowchart including a case where a sheet feeding delay occurs during continuous sheet feeding from a sheet feeding tray.

FIG. 5 is a diagram for explaining a problem of a conventional configuration.

FIG. 6 is a diagram schematically illustrating a deviation of a paper interval between a sheet of a reference size and a sheet of a size other than the reference size.

FIG. 7 is a block diagram related to control.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 automatic document feeder 2 image reading device 3 image forming unit 4 paper head unit 5 paper feeding unit 6 reversing discharge / refeeding unit 8 ADU (circulating transport unit) 56 registration roller (second paper feed unit) PS photo Sensor

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) G03G 21/14 G03G 21/00 372 3F100 F term (reference) 2H027 DA20 DC04 DC10 DC19 DE07 ED16 EE03 EE05 EF09 2H028 BA06 BA09 BA16 BB04 2H072 AA05 AA09 AA13 AA14 AA16 AA24 AA29 AA32 AB07 BA03 BA12 CA01 CA02 CB01 CB09 FA01 JA02 3F049 AA10 DA12 EA10 EA28 EA29 LA07 LB03 3F053 BA03 LA07 LB03 3F100 AA02 BA17 CA03 CA15 DA04 EA04

Claims (8)

[Claims] A first sheet feeding means for feeding sheets one by one;
A second paper supply unit that receives the paper from the first paper supply unit and conveys the paper to the image forming unit; a toner image is transferred onto the paper from the second paper supply unit and then fixed to form an image; An image forming unit for forming an image on the second surface of the sheet on which the image is formed on the first surface by the image forming unit, inverting and conveying the sheet on which the image is formed on the first surface, A circulating transport unit for circulating and transporting the paper to the second paper feeding unit again. After the image forming unit sequentially forms an image on the first surface of a predetermined number of sheets, the circulating transport unit reversely transports the image. An image forming apparatus that circulates and conveys the paper to the second paper supply unit and sequentially forms an image on the second surface of the paper on which the image is formed on the first surface, wherein the size of the paper is different and the number of circulated sheets is the same In the case of, the paper is An image forming apparatus comprising a control unit for controlling a conveyance speed to be changed. 2. The image forming apparatus according to claim 1, wherein the change of the transport speed is a change of a reverse transport speed by a reversing unit constituting the circulating transport unit. 3. A first sheet feeding means for feeding sheets one by one,
A second paper supply unit that receives the paper from the first paper supply unit and conveys the paper to the image forming unit; a toner image is transferred onto the paper from the second paper supply unit and then fixed to form an image; An image forming unit for forming an image on the second surface of the sheet on which the image is formed on the first surface by the image forming unit, inverting and conveying the sheet on which the image is formed on the first surface, A circulating transport unit for circulating and transporting the paper to the second paper feeding unit again. After the image forming unit sequentially forms an image on the first surface of a predetermined number of sheets, the circulating transport unit reversely transports the image. A method of transporting paper in an image forming apparatus that circulates and transports the paper to the second paper supply unit and sequentially forms an image on the second surface of the paper on which the image is formed on the first surface, wherein: If the number of circulations is the same, (2) It is assumed that the circulation time required from the time when the paper is started to be transported from the paper feeding unit to the image forming unit to the time when the paper is reversely transported by the circulating transportation unit and circulated and reaches the second paper feeding unit is constant. A method of transporting a sheet, comprising controlling the transport of the sheet by the circulating transport means. 4. The sheet conveying method according to claim 3, wherein the control of the sheet conveying is a change of a sheet conveying speed. 5. The sheet conveying method according to claim 3, wherein the change of the sheet conveying speed is a change of a conveying speed in a reversing unit constituting the circulating conveying unit. 6. A first sheet feeding means for feeding sheets one by one,
A second paper supply unit that receives the paper from the first paper supply unit and conveys the paper to the image forming unit; a toner image is transferred onto the paper from the second paper supply unit and then fixed to form an image; An image forming unit for forming an image on the second surface of the sheet on which the image is formed on the first surface by the image forming unit, inverting and conveying the sheet on which the image is formed on the first surface, A circulating transport unit for circulating and transporting the paper to the second paper feeding unit again. After the image forming unit sequentially forms an image on the first surface of a predetermined number of sheets, the circulating transport unit reversely transports the image. An image forming apparatus that circulates and conveys the sheet having the image formed on the first side to the second side, and sequentially forms an image on the second side of the sheet having the image formed on the first side; If a delay occurs, reduce the transport speed of the preceding paper or An image forming apparatus, comprising: a control unit for controlling conveyance of a sheet so as to stop the printing operation. 7. An allowable time of a paper feed delay can be set,
7. The image forming apparatus according to claim 6, wherein the control unit controls to prohibit paper feeding from a paper feeding tray when the paper feeding delay time is equal to or longer than the permissible time. apparatus. 8. When the control of the deceleration or the pause is already being performed on the preceding paper, the control means interrupts the control of the deceleration or the pause, and stops at the normal transport speed. The image forming apparatus according to claim 7, wherein control is performed such that conveyance of a preceding sheet is restarted.