JP2000191207A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an imager capable of suitably reversing sheets without degrading productivity and high-speed increase and carriage at a reversing part. SOLUTION: A plurality of reversing passes 51, 52 are provided at a sheet reversing part 50 for reversing sheets and the sheets to be carried to the sheet reversing part 50 via a carrier device 14 are sorted into the plurality of reversing passes 51, 52 in sequence with a sorting means 15. Positively/reversibly rotatable drawing and discharging means 16, 17 are provided on the respective reversing passes 51, 52 for discharging the sorted sheets, after drawn into the reversing passes 51, 52, toward a discharge passage or a re-carriage passage. A control means controls the sorting means 15 and the drawing and discharging means 16, 17 to sort the sheets in sequence into the plurality of reversing passes 51, 52 and discharge the sorted sheets sorted in sequence toward the discharge passage and the re-carriage passage.

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 having a structure in which a sheet is inverted before being discharged or re-conveyed to an image forming section, and more particularly to an apparatus which conveys a sheet at a sheet interval of 0 or a very narrow interval. About.

[0002]

2. Description of the Related Art A conventional image forming apparatus such as a copying machine or a printer is provided with a reversing sheet discharging function for stacking sheets on which images have been formed on a sheet discharging tray with an image forming surface facing down. Many have come to be seen. Further, after the sheet on which the image is formed on one side is reversed by the sheet reversing unit, the image forming unit is provided with an automatic double-sided recording function in which the image is formed on the back side by re-conveying the sheet from the re-conveying path to the image forming unit. Many devices have also been seen.

In these image forming apparatuses, a sheet on which an image has been formed is discharged to a discharge tray provided on the upper surface of the main body of the image forming apparatus to perform a reverse discharge (hereinafter, referred to as a top discharge). In other words, the image forming apparatus includes means for reversing a sheet in a reversing path in the image forming apparatus main body (partly in an option mounted outside the main body).
Most of these image forming apparatuses are roughly classified into two types: one for reversing a recording sheet at one location, and one for reversal discharge, automatic double-sided printing, and the like.

On the other hand, in order to obtain maximum productivity at a predetermined process speed, an image forming apparatus having a transport system in which the distance between sheets is made as small as possible (hereinafter referred to as a transport system between small sheets). Devices are becoming more common. Note that the ultimate is an image forming apparatus having a conveyance system with no sheet-to-sheet spacing and no sheet-to-sheet spacing.

In an image forming apparatus having a transport system between small paper sheets, a sheet reversing unit is used to correct a delay of a recording sheet in a reversing unit except for a unit having a top surface discharging function. The transport (reversal) speed of the recording sheet at the reversing unit is extremely increased as compared with the transport speed at the image forming unit of the image forming apparatus, or the reversal of the recording sheet is performed after the productivity is reduced. Only in modes that require
The countermeasures are taken by, for example, widening the space between sheets that can be easily inverted.

[0006]

However, it is extremely difficult for a conventional image forming apparatus having such a configuration to cope with a mode in which sheet reversal is continuously performed without reducing productivity. Certainly, when considering only the reverse paper ejection, it is possible to handle it by performing the above-described top paper ejection.However, there is an image forming apparatus equipped with an automatic duplex that requires continuous sheet inversion during continuous recording, It is assumed that a variety of applications are installed in high-speed machines, etc., especially in applications that cannot support top-side paper ejection, or in image forming units such as copiers of the conventional type. For those with a reader at the top and impossible to eject the top surface, it is impossible to say that it is impossible to respond to the mode in which the recording sheet is reversed continuously without reducing the productivity with the conventional reversing configuration. Absent.

Here, taking the reversing unit shown in FIG. 7 as an example,
The conditions required for performing the reverse discharge will be specifically described. In FIG. 1, 1 is a fixing roller, 2 is an inner discharge roller, 3 is a reversing roller, 4 is an outer discharging roller, and 6 is a reversing flapper. Further, P is a stop position of the rear end of the sheet drawn by the reversing roller (hereinafter, referred to as a reversing stop position), l ₁ is the distance from the reversal stopping position P to the reversing roller 3, and l ₂ is the distance This is the distance to the reversal stop position P.

The recording sheet on which an image has been formed by the image forming unit passes through the fixing roller 1, the inner discharge roller 2, and the reversing flapper 6 switched to the reversing unit, and then the rear end is reversed by the reversing roller 3. The reversing roller 3 is stopped until the stop position P is reached.
It stops at this reversal stop position P.

Next, after a lapse of a certain period of time, the reversing roller 3 rotates in the reverse direction, whereby the recording sheet is conveyed, for example, in the direction of the paper discharge port of the image forming apparatus, and is externally discharged by the external paper discharging roller 4 to the outside of the image forming apparatus main body. The paper is discharged to the provided paper discharge tray in an inverted state.

By the way, the conveying speed of the recording sheet at the inverting portions in the same V ₁ the conveying speed of the image forming unit, the recording sheet of the time during reversal stop T (N th escapes the reversing rollers 3, N + 1 sheet of the recording sheet includes a time required for switching the forward and reverse reversing roller 3 when it enters the reversing roller 3.) as when the length of the conveying direction in a continuous recording mode of the recording sheet S ₁ , distance L ₁ of the recording sheet required to perform the reverse discharge is expressed as follows.

L ₁ = V ₁ × [(S ₁ −l ₁ ) / V ₁ + (S ₁ −l ₁ ) / V ₁ + T] (S ₁ > l ₁ + l ₂ ) = 2S ₁ −2l ₁ + T × V ₁ (S ₁ > l ₁ + l ₂ ) However, the interval between the recording sheets obtained by this equation is an equation representing a minimum required sheet interval, and is a distance from the reversing roller 3 to the branch point S in FIG. In the area of R, the rear end portion of the Nth recording sheet in the conveyance direction and the front end portion of the (N + 1) th recording sheet in the conveyance direction are rubbed. When the rubbing is not performed, the distance: (R−
l ₁ ) × 2 recording sheet movements are added, but the calculation formula is omitted.

On the other hand, in the reversing section, a commonly used means is to use a recording sheet in the image forming section immediately after the recording sheet comes out of an area restricted by the conveying speed of the recording sheet for image formation. There is a printer that performs conveyance and reversal at a speed higher than the conveyance speed of the recording sheet and corresponds to a relatively narrow recording sheet interval.

In this case, the interval between the recording sheets will be described by taking an example of a reversing unit having the same configuration as that shown in FIG. 1. When the trailing edge of the recording sheet passes through the inner discharge roller 2, the conveying speed of the image forming unit ( Assuming that the sheet is transported at a speed of (X × V ₁ ) X times the process speed) V ₁ , the minimum sheet interval L
₂ is expressed as follows.

L ₂ = V ₁ × [(S ₁ −l ₁ −l ₂ ) / V ₁ + l ₂ / (X × V ₁ ) + (S ₁ −l ₁ ) / (X × V ₁ ) + T] ( S ₁ > l ₁ + l ₂ ) = (1 + 1 / X) × (S ₁ −l ₁ ) − (1-1 / X) × l ₂ + T × V ₁ (S ₁ > l ₁ + l ₂ ) Since the formula is also a formula expressing the minimum necessary paper interval, the rear end of the N-th recording sheet in the direction of conveyance in the area of the distance R from the reversing roller 3 to the branch point S in FIG. And the N + 1-th recording sheet in the transport direction. Also, when the rubbing is not performed, the distance: (R-l ₁ ), similarly to the equation.
The recording sheet movement of × 2 is added, but the calculation formula is omitted. In this case, l ₂ is the recording sheet matches the carrying distance to the carry out once stopped from being conveyed accelerated.

However, even in this equation, it is impossible to make the paper interval 0 even if X → ∞. If the paper interval is set to 0 in this configuration, it is necessary to increase the speed of the inner discharge roller 2 not from the trailing edge of the recording sheet but from the upstream side. If the speed is further increased from the upstream side, for example, a speed difference from the fixing roller 1 may occur, and the fixing may not be performed well.

Accordingly, the present invention has been made in view of such a situation, and without reducing productivity.
Another object of the present invention is to provide an image forming apparatus capable of suitably reversing a sheet without performing an extremely high-speed conveyance in a reversing unit.

[0017]

According to the present invention, an image is formed by reversing a sheet in a sheet reversing section and then discharging the sheet from a discharge path or re-conveying the sheet from a re-conveying path to an image forming section. In the image forming apparatus, a conveying unit provided on the upstream side of the sheet reversing unit and conveying the sheet to the sheet reversing unit, and the sheet conveyed to the sheet reversing unit and conveyed to the sheet reversing unit are provided. A plurality of reversing paths for reversing, a distributing means for sequentially distributing the sheets to the plurality of reversing paths, and a sheet provided for each of the reversing paths, and after the sheets distributed by the distributing means are drawn into the reversing path. Forward / reverse reversible pull-in / discharge means for discharging the sheet toward the discharge path or the re-conveying path; and sequentially distributing the sheet to the plurality of reversing paths. Is characterized in further comprising control means for controlling said distributing means and said inlet discharging means so as to direct the discharge passage or re-conveying path in the order in which distributes over bets, the.

The present invention further comprises a detecting means for detecting a sheet conveyed from the conveying means to the sheet reversing section, and the control means comprises a sorting means and a drawing-in / discharging means based on a detection signal from the detecting means. Is controlled.

Further, the present invention is characterized in that the control means controls the transport means to increase the sheet transport speed based on a detection signal from the detection means.

Further, the present invention is characterized in that the control means controls the sorting means to change the sorting direction of the next sheet before the sorted sheet passes through the sorting means. is there.

The present invention is characterized in that the distributing means has a flapper member for directly distributing the sheet, and a sheet guide member interlocked with the distributing operation of the flapper member.

Further, the present invention is characterized in that the interval between the sheets conveyed from the conveying means is zero or extremely narrow.

Further, as in the present invention, a plurality of reversing paths are provided in a sheet reversing section for reversing a sheet on which an image is formed on one side, and a plurality of sheets conveyed to the sheet reversing section by a conveying device are distributed by a plurality of means. Assign to the reverse path sequentially. Further, the sorted sheets are drawn into the reversing path by a reversible drawing / discharging means provided in each reversing path, and then discharged toward a discharge path or a re-conveying path. Further, the control means controls the sorting means and the drawing-in / discharging means so as to sort the sheets sequentially into a plurality of reversing paths and to discharge the reversing sheets toward the discharge path or the re-conveying path in the order in which the sheets are sorted.

[0024]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a diagram showing a schematic configuration of an image forming apparatus according to an embodiment of the present invention. In FIG. 1, reference numeral 5 denotes a paper discharge tray, 7 denotes a manual feed tray, 8 denotes a paper feed cassette, and 9 denotes a paper feed cassette.
Denotes a conveyor belt, 10 denotes an image forming section provided with four electrophotographic photosensitive drums 10a, 10b, 10c and 10d serving as image forming means, and 11 denotes a fixing device.

In the image forming apparatus having such a configuration, the recording sheets P are selectively fed from the manual feed tray 7 or the paper feed cassette 8, and the recording sheets P are stacked on the transport belt 9 (practical use). The upper side adsorbs the recording sheet on the conveyor belt), and the four electrophotographic photosensitive drums 10a, 10a, 1 according to an electric signal of image information transmitted from a reader scanner, a personal computer, or the like (not shown).
The toner images formed on the surfaces of Ob, 10c, and 10d are sequentially transferred to the recording sheet P conveyed on the conveyor belt 9.

Thereafter, the toner image is permanently fixed on the recording sheet P by the fixing device 11, so that a monochrome or full-color image is formed. The recording sheet P on which an image has been formed in this manner is discharged and stacked on the discharge tray 5 via the discharge path 12.

Incidentally, in FIG.
1 is a reversing unit that is provided between the recording sheet P and the discharge passage 12 and inverts the recording sheet P. When an image is formed on both sides of the recording sheet P, the reversing unit 50 reverses the recording sheet P. When the sheet is conveyed to the image forming unit 10 via the double-sided path 53 which is a re-conveying path, and the sheet is reversed, the recording sheet is reversed by the reversing unit 50,
It discharges to the top.

Although the detailed description of this image forming apparatus is omitted, in order to make the best use of the process speed, specifically, to make the best use of a certain process speed, the paper interval is set to 0 ( The recording sheet P can be transported in a state where there is no space between the preceding sheet and the succeeding sheet, and an image can be formed in that state.

In this image forming apparatus, as shown in FIG. 3, the reversing unit 50 inverts the recording sheet P so that reversal discharge and automatic double-sided recording can be performed in a state where the sheet interval is zero. Inverting paths 51 and 52 are provided in parallel at two upper and lower locations as a space for drawing a recording sheet.

On the other hand, FIG. 2 is an enlarged view of the reversing section 50. In FIG. 2, reference numeral 14 denotes a first internal discharge roller which is a conveying device for conveying a sheet to the reversing section 50, and reference numeral 15 denotes a sheet guide to be described later. A reversing flapper, which is a flapper member constituting a distributing means together with the members, 16 is an upper reversing roller provided in an upper reversing path (hereinafter, referred to as an upper reversing path) 51, and 17 is a lower path (hereinafter, referred to as a lower reversing path). 52
The lower reversing roller 19 is provided with a sheet sensor as a detecting means for detecting the leading end of the recording sheet.

The upper reversing roller 16 and the lower reversing roller 17 serving as the drawing-in / discharging means are driven independently of each other, whereby the upper reversing path 51 and the lower reversing path 52 are independently driven. The recording sheet can be turned over.

The recording sheet P is alternately reversed by the upper and lower reversing paths 51 and 52 which can independently reverse the recording sheet.
Even if the paper interval of the sheet is zero, each of the reversing paths 51, 5
In (2), a paper interval corresponding to the size of the recording sheet (length in the transport direction) can be temporarily provided. Thus, the recording sheet P can be reversed without performing the extremely increased conveyance in the reversing unit 50.

The recording sheet P alternately reversed in each of the reversing paths 51 and 52 then travels toward the second inner discharge roller 18 while being guided by the rear end face of the flapper 15 in the transport direction. 2, the paper is alternately fed to the paper discharge tray 5 or the double-sided path 52 by the paper discharge rollers 18 inside.

In the present embodiment, as described above, after the recording sheet P is drawn into the reversing paths 51 and 52 so as to correspond to a relatively narrow sheet interval, each reversing roller 51 The speeds of 16 and 17 are increased. Then, the ratio X of the speed increasing can be calculated by the formula, and the L ₂ and S ₁ to calculate the same value. Further, in the case where the sheet interval is 0, compared to the reversing unit having only one reversing space as shown in FIG.
The recording sheet can be reversed at a reasonable speed increase.

Here, the formula is modified to obtain the rate X of the speed increase of the reversing system as follows.

S ₁ = (1 + 1 / X) × (S ₁ −l ₁ ) − (1-1 / X) × l ₂ + T × V ₁ (S ₁ > l ₁ + l ₂ ) ⇔X = (S ₁ − l ₁ + l ₂ ) / (l ₁ + l ₂ -TV ₁ ) (S ₁ > l ₁ + l ₂ ) As can be seen from this equation, the size of the recording sheet (length in the conveying direction), the roller position, the reversal position, Since the rate X of the speed increase is determined by the path length, when it is used in determining the actual configuration of the image forming apparatus, each is set based on the corresponding material (size) under more severe conditions, and the configuration is You just have to decide.

On the other hand, in order to operate this inversion system,
The reversing flapper 15 needs to perform an operation of alternately distributing recording sheets continuously conveyed at a sheet interval of 0 to upper and lower reversing paths 51 and 52.

Here, there are the following three methods for controlling the inversion flapper 15.

First, as a relatively simple method, it is assumed that in the continuous recording mode, the leading edge of the first recording sheet is detected by the sheet sensor 19, and thereafter the image formation of the recording sheet is performed at a fixed timing. There is a method 1 in which the recording sheet is alternately distributed to the upper and lower reversing paths by operating the reversing flapper 15 up and down at a certain timing according to the set recording sheet size.

Further, since the image formation is accurately performed on each recording sheet in the image forming section 10, a method 2 for determining the operation timing of the reversal flapper 15 from the timing of writing the image (image signal) is provided. is there.

After the trailing edge of the recording sheet comes off, the first
When the speed of the internal discharge roller 14 is increased, the first internal discharge roller 1
Utilizing a gap formed between the front sheet 4 and the branch point S (top position of the inverted flapper) of the upside-down paths 51 and 52, the rear end of the preceding sheet and the front end of the succeeding sheet are detected each time within that interval. There is a third method of controlling the inversion flapper 15 according to the signal.

Here, which method is to be selected is not particularly limited as long as it is possible to select a method which is optimal for the specifications of the image forming apparatus, particularly, for the process speed and the like. In the present embodiment, method 3 is selected as described later.

On the other hand, the reversal flapper 1 is driven by a sheet interval of 0 or a slight sheet interval caused by speed increase after passing through the image forming section.
In this embodiment, since it is difficult to perform the control of switching the recording sheet P, the recording sheet P switches the reversing flapper 15 while passing the branch point S, and the next recording sheet is switched to a reversing path different from the previous recording sheet. I send it to.

For this reason, the configuration of the reversing flapper 15 is such that even if the reversing flapper 15 is switched in a state where the recording sheet does not pass through the branch point S of the upside-down reversing paths 51 and 52, the conveyance of the recording sheet P is not affected. That is, even when the reversing flapper 15 is switched while the recording sheet is passing near the reversing flapper, the sheet can be conveyed without being jammed.

In this embodiment, as shown in FIG. 3, the recording sheet can be conveyed without being jammed even when the reversing flapper 15 is switched while the recording sheet is passing. First and second flappers 20a and 20 which are sheet guide members capable of retracting a small amount.
b is provided.

Here, the first and second flapper 20
Reference numerals a and 20b are used to more reliably guide the recording sheet from the first inner discharge roller 14 to each of the reversing paths 51 and 52. As shown in the drawing, the tip of the reversing flapper 15 is at the upper position. In other words, when the recording sheet is
When the sheet is conveyed to the first flapper 15, the tip of the reversing flapper 15 contacts the upper first flapper 20 a and the first flapper 2
0a is slightly retracted. This allows
The entrance to the lower inversion path 52 is widened, and the recording sheet can be guided to the lower inversion path 52 more reliably.

The first flapper 20a is always pushed toward the reversing flapper 15 by a spring (not shown), and the spring force at this time is such that the tip of the reversing flapper 15 is as shown in FIG. When the recording sheet reaches the state shown in FIG. 3 before passing through the reversing flapper 15 in order to convey the next recording sheet to the lower reversing path 52, the recording sheet is moved to the reversing flapper 15 and the first flapper 20a. And so that the recording sheet can be conveyed even when the recording sheet is sandwiched between them.

Then, with this configuration,
Even if the reversing flapper 15 is switched in a state where the recording sheet does not pass through the branch point S of the upside-down paths 51 and 52, the conveyance of the recording sheet can be prevented. The configuration in which the first flapper 20a is brought into contact with the reversing flapper 15 is not limited to the configuration using a spring. For example, even if the first flapper 20a is brought into contact with the reversing flapper 15 by its own weight,
There is no problem as long as the recording sheet can be conveyed while sandwiching it.

On the other hand, when the tip of the reversing flapper 15 is at the lower position, that is, when the recording sheet is conveyed to the upper reversing path 51, the tip of the reversing flapper 15 is moved to the lower second flapper 20b as shown in FIG. In this state, the second flapper 20b retracts a little in this state.

As a result, the entrance to the upper reversing path 51 is widened, and the recording sheet can be guided to the upper reversing path 51 more reliably. Note that the second flapper 20b also
Similarly to the first flapper 20a, the recording sheet can be transported even when the recording sheet is sandwiched together with the reversing flapper 15.

Next, in the continuous mode of the image forming apparatus in which the sheet interval is 0 or the sheet interval is extremely narrow, the reversal operation of a series of recording sheets will be described with reference to the flowchart shown in FIG. I do.

Here, the control of the inversion operation is performed by the method 3 described above. FIG. 6 is a block diagram of a control device that is a control unit that controls the operation of the image forming apparatus including the control of the inversion operation.
Reference numeral 60 denotes a control device, and 61 denotes a solenoid for operating the reversing flapper 15. When the solenoid is ON, the reversing flapper 15 is in an upper position (see FIG. 3) for feeding the recording sheet to the lower reversing path 52, and when the solenoid is OFF.
At times, it is set so as to be in a state of a lower position where the recording sheet is fed to the upper reversing path 51 (see FIG. 4).

First, when the sheet sensor 19 detects the leading edge of the Nth recording sheet on which the image formation is completed (S-
1) The control device 60 turns on the solenoid 61 until the leading edge of the recording sheet reaches the branch point S (see FIG. 2) of the upside down paths 51 and 52 (S-2). Similarly, by the time the leading edge of the recording sheet reaches the lower reversing roller 17, the lower reversing roller 17 has the same transport speed as the image forming unit in the normal rotation direction (the direction in which the recording sheet is drawn into the lower reversing path 52). (S-3).

Next, as shown in FIG. 2, the distance from the first inner discharge roller 14 to the sheet sensor 19 is l ₃ , the size of the recording sheet (the length in the transport direction) is S ₁ , and when the conveyance speed of the recording sheet (process speed) in the V _1, after detecting the leading edge of the sheet sensor 19 is a recording sheet, the _{[(S 1 -l 3) /} V 1] below the time after the inversion roller 17 records to accelerated the sheet conveying speed in the X × V ₁ (S-
4). The operation up to this point is performed by detecting the leading edge of the Nth recording sheet.

Next, a gap formed between the Nth recording sheet and the (N + 1) th sheet by the accelerated conveyance, that is, in the sheet interval, the N
When the rear end of the recording sheet is detected by the sheet sensor 19 (S-5), the lower reversing roller 17 is stopped after [(l ₂ −l ₃ ) / (X × V ₁ )] hours (S-6). ), The conveyance of the recording sheet is temporarily stopped.

Next, after a lapse of T time in this state (here, the switching time of the forward / reverse rotation required to pull out the recording sheet from the lower reversing roller 17 and pull in the next fed recording sheet is excluded). Then, the lower reversing roller 17 is rotated in the reverse direction (the direction of feeding from the lower reversing section 52 to the second inner discharge roller 18) (S-7), and the recording sheet is moved from the reversing section 50 to the discharge tray 5 or the two-sided path 53. Send to Up to this point is performed by detecting the trailing edge of the recording sheet.

Next, when the sheet sensor 19 detects the leading edge of the (N + 1) th recording sheet between the sheets formed by the accelerated transport of the Nth recording sheet (S-8), the leading edge of the recording sheet rises. Before the solenoid 6 reaches the reversing roller 16,
1 is turned off (S-9). Similarly, N +
By the time the leading edge of the first recording sheet reaches the upper reversing roller 16, the upper reversing roller 16 is rotated in the normal direction (the direction in which the recording sheet is drawn into the upper reversing path 51).
0 (S-1).
0).

As shown in FIG. 2, the distance from the first inner discharge roller 14 to the sheet sensor 19 is l ₃ , the size of the recording sheet (the length in the conveying direction) is S ₁ , and the recording in the image forming section 10 is performed. when the conveying speed of the sheet (process speed) in the V _1, after detecting the leading edge of the sheet sensor 19 recording sheet _{[(S 1 -l 3) /} V 1] the conveying speed of time after a recording sheet (X × V ₁ ) (S-l ₁ ). The operation performed so far is performed by detecting the leading edge of the (N + 1) th recording sheet.

Next, as described above, the rear end of the (N + 1) th recording sheet is detected by the sheet sensor 19 (S-1).
2) After [(l ₂ −l ₃ ) / (X × V ₁ )] hours, the upper reversing roller 16 is stopped (S-13), and the conveyance of the recording sheet is temporarily stopped.

In this state, after a lapse of T time (here, the switching time of the forward / reverse rotation required to pull out the recording sheet from the lower reversing roller 17 and pull in the next fed recording sheet is excluded). The roller 16 is rotated in the reverse direction (the direction from the upper reversing section 51 to the second inner discharge roller 18) (S-14), and the recording sheet is fed from the reversing section 50 to the discharge tray 5 or the two-sided path 53. Up to this point is performed by detecting the trailing edge of the recording sheet.

Then, the upper and lower inversion paths 5
The recording sheets that have been sorted and inverted into the sheets 1 and 52 are discharged onto the discharge tray 5 through the discharge path 12 or conveyed to the image forming unit 10 through the double-sided path 53. In the continuous recording mode, the above-described series of operations is repeated by the set number.

As described above, the reversing section 50 is provided with the upper and lower reversing paths 51 and 52, and the recording sheets are sequentially sorted to the reversing paths 51 and 52, and then discharged toward the discharge path 12 or the two-sided path 53. Thus, the recording sheet P can be reversed without performing the extremely increased conveyance in the reversing unit 50.

The settings of the upper reversing path 51 and the lower reversing path 52, specifically, the lengths of the reversing paths 51 and 52, the positions of the reversing rollers 16 and 17, the transport speed at the time of increasing the speed, and the like are the same. More preferred. The reason is, for example, upside down path 5
If the transport speed at the time of speed increase is different between 1 and 52, the drive corresponding to a plurality of transport speeds is performed in a portion after the second inner discharge roller where the recording sheets distributed to the upside-down reversing paths 51 and 52 are rejoined. This is because a system is required.

Since the sequence such as the operation of the inversion flapper 15 becomes complicated, it is more advantageous to make the configuration of the upside-down inversion path the same as much as possible (preferably a mirror image relationship is more preferable). It is also advantageous for merging after inversion.

[0066]

As described above, according to the present invention, a plurality of reversing paths are provided in the sheet reversing section, the sheets are sequentially distributed to these reversing paths, and then the discharge path or re-conveyance is performed in the order in which the reversing sheets are distributed. By discharging the sheet toward the passage, even if the sheet interval is 0 or extremely narrow, the sheet can be appropriately turned over without lowering the productivity and without performing extremely high-speed conveyance at the reversing section. Can be.

[Brief description of the drawings]

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

FIG. 2 is an enlarged view of a reversing unit of the image forming apparatus.

FIG. 3 is an enlarged view of a main part of the reversing unit.

FIG. 4 is a diagram illustrating a state in which a recording sheet is distributed to an upper reversing pass of the reversing unit.

FIG. 5 is a flowchart showing a sheet reversing operation of the reversing unit.

FIG. 6 is a control block diagram of the image forming apparatus.

FIG. 7 is a diagram illustrating a configuration of a reversing unit in a conventional image forming apparatus.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 fixing roller 5 paper discharge tray 10 image forming unit 12 discharge path 14 first inner paper discharge roller 15 reversing flapper 16 upper reversing roller 17 lower reversing roller 18 second inner paper discharging roller 19 sheet sensor 20a first reversing flapper 20b second Reversing flapper 50 Reversing part 51 Upper reversing path 52 Lower reversing path 53 Double-sided path 60 Control device 61 Solenoid

Claims (6)

[Claims] 1. An image forming apparatus in which a sheet is reversed by a sheet reversing section and then discharged from a discharge path or re-conveyed from a re-conveying path to an image forming section to form an image. Conveying means provided on the upstream side of the reversing section for conveying the sheet to the sheet reversing section; and a plurality of reversing paths provided in the sheet reversing section for reversing the sheet conveyed to the sheet reversing section. And a allocating means for sequentially allocating the sheet to the plurality of reversing paths; and providing the sheets allocated to the reversing paths and distributed by the allocating means to the reversing path.
Forward and reverse reversible pull-in / discharge means for discharging toward the discharge passage or the re-conveying passage; and sequentially distributing the sheet to the plurality of reversing paths; and An image forming apparatus comprising: a control unit that controls the distribution unit and the drawing-in / discharging unit so as to be directed. 2. A detecting means for detecting a sheet conveyed from the conveying means to a sheet reversing unit, wherein the control means controls the sorting means and the drawing-in / discharging means based on a detection signal from the detecting means. The image forming apparatus according to claim 1, wherein: 3. The image forming apparatus according to claim 2, wherein the control unit controls the transport unit to increase a sheet transport speed based on a detection signal from the detection unit. 4. The control device according to claim 1, wherein the control unit controls the distribution unit to change a distribution direction of a next sheet before the allocated sheet passes through the distribution unit. Image forming device. 5. The image forming apparatus according to claim 1, wherein the sorting unit includes a flapper member for directly sorting the sheet, and a sheet guide member interlocking with the sorting operation of the flapper member. 6. The image forming apparatus according to claim 1, wherein an interval between the sheets conveyed from the conveying unit is 0 or an extremely small interval.