JPH1124330A - Both side image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a both-side image forming device provided with high productivity even at the time of selecting the one side image forming mode, with a simple constitution. SOLUTION: This device is provided with a recording material transporting common path 7 for allowing either recording material 3 provided with the respective image formed by the image forming sections 1 and 2 to pass there through, at the time of selecting the one side image forming mode at least, on a section of the recording material transporting path 6 for leading the recording material 3 being fed from recording material feeding means 4 to fixing means 5. Moreover, the device is provided with recording material transportcontrolling means 8 capable of making two sheets of recording material 3 that the image is formed thereon by respectively image forming section 1 and 2 stack-transported at least, on the one section of the recording material transporting path 6 for leading the recording material 3 being fed from the recording material feeding means 4 to the fixing means 5, at the time of selecting the one side image forming mode.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an electrophotographic copying machine,
The present invention relates to an image forming apparatus such as a printer, and more particularly to an improvement in a double-sided image forming apparatus capable of forming a double-sided image.

[0002]

2. Description of the Related Art In a conventional image forming apparatus capable of forming a double-sided image, a first image formed on a photoreceptor is transferred and fixed on a first surface of a sheet, and then the sheet is turned over and re-fed. And
Subsequently, a method of transferring and fixing the second image formed on the photoconductor on the second surface of the sheet is generally used. However, in this method, since the image forming unit passes the paper twice, the productivity per sheet becomes slower than half of that for single-sided recording, and the paper curls during the first fixing. There are various problems such as poor transfer at the second transfer and fixing, paper wrinkling, the occurrence of jams in the conveyance path, and noise when the paper is reversed and re-fed.

As a double-sided image forming apparatus which solves the above-mentioned problem, for example, a type in which two image forming sections are arranged to face each other and a toner image is simultaneously transferred to both sides of a sheet by one sheet feed (for example, JP-A-63-63057) Gazette, Japanese Patent Laid-Open No.
Japanese Patent Application Laid-Open No. HEI 5-150573), and a type in which two image forming units are arranged in parallel and toner images are sequentially transferred to both sides of a sheet by a single sheet feed (for example, JP-A-5-150573) have already been proposed. ing.

[0004]

However, in this type of double-sided image forming apparatus, the following technical problems have been found. That is, although the productivity in double-sided printing increases, the productivity in single-sided printing does not change. Therefore, there is a technical problem that the advantage of the apparatus cannot be utilized when the single-sided printing is frequently used.

[0005] As means for solving such technical problems, there is already an apparatus in which two image forming units are arranged in parallel, and when the single-sided print mode is selected, each image forming unit can form an image on only one side. It has been proposed (for example, Japanese Patent Application Laid-Open No. 8-248895). However, in this type, when the one-sided print mode is selected, the image forming operation by each image forming unit is performed by completely different paper transport paths (paper sending-fixing-discharging). Each section has to provide a dedicated paper transport path, and there has been a technical problem that the entire apparatus becomes complicated and large, and the cost is greatly increased. Further, as another prior art, a dedicated conveyance path for one-sided printing is provided as a paper conveyance path for two image forming units arranged in parallel, and one side of the image forming unit is stopped during one-sided printing to extend the life. Although a target has been proposed (for example, Japanese Patent Application Laid-Open No. 60-3667), there has been a technical problem that productivity in single-sided printing does not increase and the apparatus becomes complicated.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described technical problem, and provides a double-sided image forming apparatus having a simple configuration and high productivity even when a single-sided image forming mode is selected. It is.

[0007]

That is, the first aspect of the present invention is as follows.
1A, as shown in FIG. 1A, has two image forming units 1 and 2 on which a first image and a second image are formed, respectively. , 2 to form an image on both sides of one recording material 3, and each image forming section 1, 2 at the time of selecting the single-sided image forming mode.
A double-sided image forming apparatus for forming an image on only one side of a recording material 3, wherein at least a part of a recording material transport path 6 from a recording material supply unit 4 to a fixing unit 5 includes: When the one-sided image forming mode is selected, a common recording material transport path 7 through which the recording material 3 on which images are formed by the respective image forming units 1 and 2 pass is provided.

In such technical means, the double-sided image forming apparatus according to the present invention widely includes a copying apparatus, a printer, and the like employing an electrophotographic system, an electrostatic recording system, or the like. , 2 may be those in which image carriers for carrying images are arranged facing each other, or those in which the image carriers are arranged in parallel. The image carrier may be an image forming carrier such as a photoreceptor or a dielectric, or may be disposed opposite to the image forming carrier and the image forming carrier. Further, an embodiment may be provided which includes an intermediate transfer body on which each image on the image forming carrier is temporarily transferred by the primary transfer unit.
Note that these points are the same in the embodiment of FIG. 1B described later.

In such an embodiment, the common recording material conveyance path 7 is provided with the recording material 3 supplied from the recording material supply means 4.
May be at least part of the recording material transport path 6 leading to the fixing means 5, but from the viewpoint of making the apparatus configuration compact, the recording material 3 supplied from the recording material supplying means 4 It is preferable that the entire recording material transport path 6 leading to the fixing unit 5 is the common recording material transport path 7.

Further, from the viewpoint of further simplifying the apparatus configuration, for example, taking a transfer unit as an example, when the one-sided image forming mode is selected, the recording material 3 is shared by the image forming units 1 and 2. It is preferable to provide a common transfer unit for transferring an image to one side of the recording medium. In the case of a fixing unit, for example, the recording material formed by each of the image forming units 1 and 2 when the one-sided image forming mode is selected. It is preferable to provide a common fixing unit 5 for fixing an image on one side of the fixing unit 3.

A second embodiment of the present invention is shown in FIG.
The first and second images are respectively formed as shown in FIG.
It has two image forming units 1 and 2 and forms images on both sides of one recording material 3 by the two image forming units 1 and 2 when the double-sided image forming mode is selected, and also forms each image when the single-sided image forming mode is selected. A two-sided image forming apparatus for forming an image on only one side of the recording material 3 by the units 1 and 2, wherein the recording material 3 supplied from the recording material supply unit 4 reaches the fixing unit 5 when the one-sided image forming mode is selected. A recording material conveyance control unit 8 for superimposing and conveying two recording materials 3 on which images are formed by the respective image forming units 1 and 2 in at least a part of the recording material conveyance path 6. Things.

In such technical means, the design of the recording material conveyance control means 8 may be appropriately changed as long as the recording material 3 is superposed and conveyed in at least a part of the recording material conveyance path 6. From the viewpoint of simplification of the configuration and improvement in productivity of single-sided image formation, a mode in which the recording material 3 is superposed and conveyed at least to the transfer position and a common transfer unit can be used, or at least the fixing position It is preferable that the recording material 3 is superimposed and conveyed, and a common fixing unit can be used. It is preferable that the recording material 3 is superimposed and conveyed over substantially the entire area of the recording material conveying path 6 as much as possible.

The recording material transport control means 8 may be any device that superimposes and transports the two recording materials 3 sent from the recording material supply means 4. In consideration of this, it is preferable that the recording material 3 is sent out from the two recording material supply means 4 one by one, and two recording materials are superposed. In this embodiment, one of the simplest control methods is to send out the recording material 3 one by one from the two recording material supply means 4 in accordance with the image forming timing of each of the image forming units 1 and 2, and It is preferable that the recording material 3 is naturally superposed and arranged.

Further, from the viewpoint of more accurately controlling the overlapping arrangement of the recording material 3, the recording material transport control means 8 temporarily corrects the position of the recording material 3 in the recording material transport path 6. In this embodiment, the start timing of sending the recording material 3 from the two recording material supply units 4 is controlled so that the two recording materials 3 reach the positioning correction unit substantially simultaneously. preferable. In this embodiment, from the viewpoint of more accurately controlling the positional accuracy between the transfer positions of the image forming units 1 and 2 and the recording material 3, the recording material transport control unit 8 includes the recording material transport path 6. There are two positioning correction means for temporarily correcting the position of the recording material 3 therein, and each positioning correction means individually controls the timing of entry of the recording material 3 into the transfer position of each of the image forming units 1 and 2. A mode of controlling is preferable.

Furthermore, the state of superposition of the two recording materials 3 is not limited to the mode in which both are completely superposed, but includes the mode in which at least a part is superposed. At this time, if priority is given to improving the productivity in the one-sided image forming mode, it is preferable that the two recording materials 3 are completely overlapped and arranged. From the viewpoint of further improving the peeling performance of the recording material 3 in the fixing unit, the recording material conveyance control unit 8 shifts at least two recording materials 3 by a certain amount before entering the fixing position. It is preferable to carry out polymerization conveyance in a state.

In a mode in which the recording material 3 is conveyed in a superposed manner, the recording material 3 usually formed in each of the image forming sections 1 and 2 is used.
Since the image carrying surface of the recording material 3 is turned upside down, it is necessary to properly correct the arrangement state of each recording material 3 on which a single-sided image is formed at the time of discharge. Under such a request, the recording material conveyance control unit 8 controls the discharge unit of the recording material 3 that has passed the fixing unit 5 to
It is preferable that the two recording materials 3 arranged in an overlapped manner are separated, and only one of the recording materials 3 is inverted and discharged. At this time,
From the viewpoint of ensuring the separating operation of the two recording materials 3, at least the two recording materials 3 are shifted by a certain amount before the two recording materials 3 overlapped and arranged at the discharge unit. It is preferable to carry out polymerization conveyance.

Further, the recording material conveyance control means 8 includes 2
From the viewpoint of eliminating mistakes in the selection of the size of the recording material 3 and improving the workability, when the single-sided image forming mode is selected, two types of recording material supply means 4 of the designated recording material size are selected. The delivery control of the recording material 3 may be performed. Further, from the viewpoint of simplifying the operation of instructing the stacking and conveyance of the recording material 3, the recording material conveyance control unit 8 is configured to stack and convey the recording material 3 under the condition that only the one-sided image forming mode is selected. However, if there is a request to form, for example, a high-quality image on one recording material 3 in the single-sided image forming mode, the recording material transport control unit 8 may control the single-sided image forming mode and the single-sided image forming mode. Only under the condition that the two-sheet feed mode is selected at the same time, the recording material 3 is superposed and conveyed, and under the condition that the two-sheet feed mode is not selected, one-sided image formation is performed on one recording material 3. You may.

Furthermore, the mode in which the recording material 3 is superimposed and conveyed is thicker than the mode in which only one recording material 3 is conveyed. There is a concern that good image formation may not be performed under fixing conditions. From the viewpoint of effectively avoiding such a concern, the recording material conveyance control means 8 includes two image forming units 1 and 2 under the condition that two recording materials 3 are simultaneously transferred on one side.
2, the transfer condition of the common transfer unit is changed, or the set temperature of the common fixing unit 5 is changed under the condition that two recording materials 3 are simultaneously fixed on one side, or It is preferable to change the process speed of the common fixing unit 5 under the condition that two recording materials 3 are simultaneously fixed on one side.

Next, the operation of the above technical means will be described. First, in the invention of FIG. 1A, a common recording material conveyance path 7 is provided at least in a part of the recording material conveyance path 6 until the recording material 3 supplied from the recording material supply means 4 reaches the fixing means 5. Is provided. When the one-sided image forming mode is selected, the recording material 3 on which images are formed by the image forming units 1 and 2 passes through the common recording material conveyance path 7 together.
Therefore, it is not necessary to provide a recording material transport path dedicated to the single-sided image forming mode for each of the image forming units 1 and 2, and the layout of the recording material transport path 6 is simplified, and each of the image forming units 1 and 2 is not required. The length of the recording material conveying path toward the printer is not set unnecessarily long.

Next, the invention of FIG. 1B will be described. When the one-sided image forming mode is selected, the recording material transport control means 8 causes the recording material 3 supplied from the recording material supply means 4 to reach the fixing means 5. In at least a part of the recording material transport path 6, the two recording materials 3 on which images are formed by the respective image forming units 1 and 2 are superimposed and transported. Therefore, if two recording materials 3 are superposed and conveyed to the transfer unit and the fixing unit of each of the image forming units 1 and 2, the first and second recording materials formed by the image forming units 1 and 2 are The image is transferred to one side of the two recording materials 3 or is fixed to one side thereof.
The production amount in the one-sided image forming mode is increased about twice as compared with the mode in which the recording materials 3 are conveyed in parallel. Further, since only one recording material transport path 6 is required when the two recording materials 3 are stacked and transported, the layout of the recording material transport path 6 is simplified accordingly.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail based on an embodiment shown in the accompanying drawings. First Embodiment FIG. 2 shows a schematic configuration of a first embodiment (a printer in the present embodiment) of a two-sided image forming apparatus to which the present invention is applied.
In FIG. 1, the two-sided image forming apparatus is configured to
A first image forming unit 20a that forms a first image on the surface of the sheet P, and a second image forming unit 20b that forms a second image on the second surface of the sheet P
A fixing unit 50 for fixing an image on the sheet P passing through both image forming units 20a and 20b;
0b and a paper transport system 60 for transporting the paper P to the fixing device 50.

In this embodiment, each image forming unit 20
Reference numerals a and 20b denote photosensitive drums 21a and 21b and a charging roll 22 for charging the surfaces of the photosensitive drums 21a and 21b.
a, 22b and an exposure device 23 for writing electrostatic latent images for the first and second images on the charged photosensitive drums 21a, 21b.
a, 23b and developing units 24a, 2 for visualizing the electrostatic latent images written on the photosensitive drums 21a, 21b with toner.
4b, intermediate transfer belts 25a and 25b arranged in contact with photosensitive drums 21a and 21b, and photosensitive drums 21a and 2b.
Primary transfer rolls 26a and 26b for primarily transferring toner images T1 and T2 (for example, normal images in this embodiment) on the intermediate transfer belts 25a and 25b, and the photosensitive drums 21a and 2b
Cleaners 27a and 27b for removing the residual toner on
And A pair of polarity-reversing corotrons 28 and 29 are disposed on the downstream side of the primary transfer position of the intermediate transfer belt 25b of the second image forming unit 20b so as to face each other with the intermediate transfer belt 25b interposed therebetween.

In the present embodiment, each of the intermediate transfer belts 25a and 25b is wound around an appropriate number of holding rolls (one is a driving roll and the other is a driven roll), and the photosensitive drums 21a and 21b It is designed to rotate in synchronization with. Reference numerals 30a and 30b denote belt cleaners for removing residual toner on the intermediate transfer belts 25a and 25b. Then, the intermediate transfer belts 25a and 25b
Is a resin such as polyimide, acrylic, vinyl chloride, polyester, polycarbonate, polyethylene terephthalate (PET) or various rubbers containing an appropriate amount of an antistatic agent such as carbon black, and having a volume resistivity of 10 ⁹ to 10 ¹⁴ Ω. Cm, and its thickness is set to, for example, 0.08 mm.

Further, holding rolls arranged corresponding to areas where the respective intermediate transfer belts 25a and 25b are in contact with or close to each other are configured as secondary transfer rolls 40a and 40b. Although the transfer can be performed by using a conductive material for both the secondary transfer rolls 40a and 40b, the secondary transfer rolls 40a and 40b can be transferred to a small-sized sheet when the first and second intermediate transfer belts 25a and 25b are in direct contact with each other. An excessive current flows between the transfer rolls 40a and 40b, so that a sufficient transfer electric field cannot be formed and transfer failure occurs, or the intermediate transfer belts 25a and 25b
It is preferable to use at least a conductive roll coated with a semi-conductive or insulating material as a roll to apply a bias because the roll is easily damaged.

In this embodiment, the secondary transfer roll 40
For both a and b, a metal shaft coated with EPDM rubber dispersed with carbon black and having a volume resistivity of 10 ⁶ Ω · cm is used.
The transfer bias 41 was applied to the shaft a, and the shaft of the secondary transfer roll 40b was grounded. In addition, as the coating material, a material obtained by dispersing conductive particles (such as carbon black or aluminum) or an ion conductive agent (such as LiClO ₄ ) in polyurethane rubber or silicon rubber can be used.
The volume resistivity is preferably set to 10 ⁵ to 10 ⁹ Ω · cm.

Further, in the present embodiment, the toner T
1 and T2 use negatively charged toner, and the primary transfer rolls 26a,
A DC current of +10 μA is applied to each of the electrodes 26b, and an AC voltage of 8 kVp-p / 600 is applied to the polarity inversion corotrons 28 and 29.
Hz, DC voltages of +1 kV and -1 kV were superimposed on each other, and a DC voltage of -2 kV was applied to the secondary transfer roll 40a.

The first and second photosensitive drums 21a, 21a
b and the first and second intermediate transfer belts 25a and 25b
Have the same circumference. Thus, by forming images on the photosensitive drums 21a and 21b at the same timing, the positions of the images on both the front and back surfaces or the images on one surface of the two sheets of paper P are accurately aligned. Further, the distance from the secondary transfer position to the fixing device 50 was shorter than the minimum sheet length, and the rotation speed of the fixing roll was equal to or slightly lower than the speed of the intermediate transfer belts 25a and 25b. Further, the fixing device 50 has the same shape of the upper and lower fixing rolls so that the fixing nip is linear, and the heaters are arranged inside thereof.

In this embodiment, the paper transport system 60 has, for example, three paper trays 61 to 63 containing paper P of a predetermined size.
The paper P is stored by the feed rolls 64 provided in
Are sent out one by one. In this example, it is assumed that paper sheets P of the same size are stored in the paper trays 61 and 63. The paper transport system 60 is branched and connected to each of the paper trays 61 to 63 and extends substantially in the vertical direction. The paper transport system 60 is communicatively connected to the paper vertical transport path 65 and extends in the substantially horizontal direction. Forming part 20a,
20b secondary transfer position (secondary transfer rolls 40a, 40b
Nip section), and a paper horizontal transport path 66 passing through the fixing device 50 position, and the end of the paper horizontal transport path 66 is disposed at a position facing the discharge tray 67.

Further, for example, three pairs of transport rollers 68 are arranged at predetermined intervals in the paper vertical transport path 65, while the paper vertical transport path 6 is disposed in the paper horizontal transport path 66.
In order from the fifth side, a paired transport roll 69, a paired registration roll (hereinafter abbreviated as a registration roll) 70 for positioning in front of the secondary transfer position of the image forming units 20a and 20b, and a fixing device 50 A pair of transport rollers 71 are provided on the rear side, and an inverter section 72 for sheet reversal is provided on the front side of the discharge tray 67, respectively. In the present embodiment, as shown in FIG. 2, the basic configuration of the inverter section 72 includes a mountain-shaped reversing bypass transport path 73 that bypasses the sheet horizontal transport path 66. 7
A pair of transport rolls 74 and 75 are disposed on the paper horizontal transport path 66 located on the entrance side and the exit side of the sheet 3, and a pair of reverse rolls 76 are disposed on the top of the bypass transport path 73. On the entrance side of the bypass conveyance path 73, a switching gate 77 for switching the conveyance path is provided. The detailed configuration and operation of the inverter unit 72 will be described later.

FIG. 12 shows an image forming process control apparatus used in the present embodiment. In the figure, an image forming process control device 110 includes a CPU 111, a ROM 11
2, RAM 113 and input / output interface 114,
For example, a paper size switch (in FIG. 12, the switch is abbreviated to SW, the same applies hereinafter) 101, a double-sided print mode switch 102, a single-sided print mode switch 1
03, signals from the print start switch 104, the print job counter 105, and the like are input to the CPU 111 via the input interface 114. CPU
111 executes an image forming process program (see FIG. 13 to FIG. 17) pre-installed in the ROM 112,
A control signal corresponding to the double-sided print mode or the single-sided print mode is generated, and the image forming units 20a and 20b, the secondary transfer unit set voltage 121, the fixing unit set temperature 122, the first to third sheets are output via the output interface 115. The trays 61 to 63, the registration roll 70, the inverter 72, and the like are controlled.

Next, an image forming process of the double-sided image forming apparatus according to the present embodiment will be described. First, the duplex print mode will be described. Now, paper size switch 1
01, when the print start switch 104 is operated after selecting the double-sided print mode switch 102, FIG.
The double-sided printing operation is started according to the flowchart of FIG. That is, a normal toner image T is formed on the surface of each of the photosensitive drums 21a and 21b by a known electrophotographic process.
1. Form T2. Then, the first toner image T1 formed on the first photosensitive drum 21a is transferred to the primary transfer roll 26a.
As a result, the image is transferred onto the first intermediate transfer belt 25a that moves at substantially the same speed as the first photosensitive drum 21a. Similarly, at the same timing as on the first photosensitive drum 21a, the second photosensitive drum 21
The second toner image T2 formed on the second intermediate transfer belt 25b is transferred onto the second intermediate transfer belt 25b by the primary transfer roll 26b, and a voltage is applied to a pair of polarity reversing corotrons 28 and 29 provided with the second intermediate transfer belt 25b interposed therebetween. Is applied, the polarity of the second toner image T2 is inverted.

When one sheet P of a predetermined size is sent out from one of the sheet trays 61 to 63, the sheet P is conveyed to the registration roll 70 by the conveyance rolls 68 and 69, and the sheet P is fed by the registration roll 70. P temporarily stops in a state where a loop is formed, and then transfers the sheet P to the secondary transfer roll 40 in accordance with the timing of the image writing position on the sheet P.
a, 40b, and transferred to the intermediate transfer belts 25a, 25b.
The upper toner images T1 and T2 are simultaneously transferred onto the paper P.

Here, the principle of the secondary transfer will be described in detail mainly with reference to FIG. The negative toner image T1 on the first intermediate transfer belt 25a cancels the positive charge 42 on the back surface of the intermediate transfer belt 25a and applies the same repulsive force by applying a negative bias voltage 41 to the secondary transfer roll 40a. Is transferred onto the sheet P from the intermediate transfer belt 25a. On the other hand, the negative charge 43 on the back surface of the intermediate transfer belt 25b is canceled by grounding the secondary transfer roll 40b of the toner image T2 on the second intermediate transfer belt 25b whose polarity has been inverted to the positive polarity by the polarity inversion corotrons 28 and 29. Then, the toner image is transferred onto the sheet P by the suction force of the secondary transfer roll 40a. In this way, transfer can be performed on both sides simultaneously.

Thereafter, the toner images T1 and T2 on the sheet P are simultaneously fixed on both sides by the fixing device 50. Then, the paper P is transported by the transport roll 71 and the transport rolls 74 and 7 of the inverter unit 72.
5 discharges to the discharge tray 67. The sheet P may be discharged after being inverted by the inverter unit 72. With the above operation, a double-sided image is formed on the sheet P.

Next, the one-sided print mode will be described. When the print start switch 104 is operated after selecting the paper size switch 101 and the single-sided print mode switch 103, two paper trays of the designated size (for example, 61 and 63 in this example) are selected according to the flowchart of FIG. , A one-sided printing operation is started. At this time, as shown in FIG. 14, for example, based on the count value from the print job counter 105, if there are two pages of remaining print jobs, two paper trays 61,
The sheets P1 and P2 are sent out from the sheet 63, and if the remaining print job is only for one page, one sheet P1 is sent out from one sheet tray 61, for example.

Here, the timing of feeding the sheets P1 and P2 from the two sheet trays 61 and 63 is, as shown in FIG. 4, the sheet feeding path from the sending position of each of the two sheet trays 61 and 63 to the registration roll 70. Paper P2 from the paper tray 63 for a transport time t corresponding to the length difference L
May be set earlier than the paper tray 61. Then, the two sheets P1 and P2 are as shown in FIG.
As shown in (2), they are superposed and arranged in a state where their leading ends are substantially aligned with each other, and reach the registration roll 70 almost simultaneously by the transport rolls 68 and 69.

As shown in FIG. 14, a print image of an odd page is processed by a first image forming unit 20a, and a print image of an even page is processed by a second image forming unit 20b. Is done. For this reason, the first toner image T1 of the odd-numbered page is primarily transferred from the first photosensitive drum 21a to the first intermediate transfer belt 25a, and the second toner image T2 of the even-numbered page is transferred to the second photosensitive drum 25a. 2nd from 21b
After the primary transfer to the intermediate transfer belt 25b, the polarity is reversed by the polarity reversing corotrons 28 and 29. In this case, the direction of the first toner image T1 is upside down with respect to the direction of the second toner image T2 in consideration of the reversal of the sheet P1 in the inverter unit 72 described later. When one sheet of paper P1 is supplied from one sheet tray 61, the first print target image is processed.
The processing is performed by the image forming unit 20a.

Further, in the registration roll 70, the two sheets P1 and P2 are temporarily stopped in a state where they are overlapped to form a loop of substantially the same shape, and then the secondary transfer roll is adjusted by adjusting the timing of the image writing position on the sheet. The sheets P1 and P2 are conveyed in a state of being overlapped between the sheets 40a and 40b, and the toner image T1 on the intermediate transfer belt 25a is formed on one side (intermediate) of the sheet P1 as shown in FIG. The toner image T2 on the intermediate transfer belt 25b is transferred onto one surface (the surface facing the intermediate transfer belt 25b) of the sheet P2 on the transfer belt 25a (the surface facing the transfer belt 25b).

In particular, in the present embodiment, when the secondary transfer is performed on two sheets P1 and P2 at the time of one-sided printing, the apparent thickness of the sheet is larger than that of the normal transfer on one sheet. Become. Therefore, in order to obtain the optimum transfer efficiency at the time of single-sided printing, as shown in FIG. 15, a process for increasing the voltage setting of the secondary transfer unit by a single-sided printing operation signal (single-sided print mode selection signal) as compared with a normal process. The optimal image is secured by changing the voltage applied to the secondary transfer roll 40a. In the present embodiment, for example, the transfer voltage for one normal sheet is -2 kV.
In this case, the transfer voltage for the two sheets may be set to about -3 kV.

Thereafter, the sheets P1, P2 having the toner images T1, T2 transferred to one side thereof are respectively conveyed to the fixing device 50 as they are, and the toner images T1, T2 on the respective sheets P1, P2 are transferred to the fixing device 50.
Are fixed simultaneously. In particular, in the present embodiment, when fixing is performed on two sheets P1 and P2 at the time of one-sided printing, the apparent thickness of the sheet is larger than that of the normal fixing on one sheet. Therefore, in order to obtain the optimum fixing performance, as shown in FIG. 16, the temperature setting of the fixing unit is changed by the operation signal of the single-sided printing, so that the optimum fixing performance is ensured. In the present embodiment, for example, when the setting of the fixing temperature for one normal sheet is 160 degrees, the setting of the fixing temperature for two sheets may be set to about 180 degrees.

When fixing is performed on two sheets at the time of one-sided printing, as a modification for obtaining the optimum fixing performance, instead of changing the set temperature of the fixing section, as shown in FIG. The process speed of the entire apparatus may be changed (set to a process speed lower than usual), or the process speed of the entire apparatus may be changed in addition to the change of the set temperature of the fixing unit.

After that, the fixed sheets P1 and P2 pass through the transport roll 71 and are inverted and discharged by the inverter 72 only the sheet P1 so that the image writing surfaces of the sheets P1 and P2 are in the same direction. The sheets P1 and P2 are aligned and discharged on a discharge tray 67. Here, based on FIGS.
The details of the inverter unit 72 will be described. In the present embodiment, the basic configuration of the inverter unit 72 is as described above, and one of the rolls 741 and the transport roll 75 of the transport rolls 74 are set at the same speed as the paper transport speed. The other roll 742 has a configuration in which a drive device (not shown) can change the speed in two stages: a normal mode at the same speed as the one of the rolls 741 or a high-speed mode at a higher speed than the roll 741. The reversing roll 76 is one of the rolls 7 of the transport roll 74.
It is set to the same value as the high-speed speed of 42, and can be rotated in the normal and reverse directions by a driving device (not shown). Furthermore,
A paper position sensor 78 for detecting the leading end positions of the sheets P1 and P2 is provided behind the transport roller 74 and before the switching gate 77. The switching gate 77 switches based on a detection signal from the paper position sensor 78. Is to be selected. Further, a switching gate 79 is provided at a branch portion of the bypass conveyance path 73, and a sheet position sensor 80 for detecting the rear end position of the sheet P1 is provided on the bypass conveyance path 73 in front of the reversing roll 76. The switching gate 79 is switched and selected based on the detection signal from the sheet position sensor 80.

In FIG. 6, the fixed sheets P1 and P2 pass through the transport rolls 71 and are transported by the transport rolls 7 of the inverter section 72.
Pass 4 At this time, the switch gate 7 receives a signal indicating that the leading ends of the sheets P1 and P2 have been detected by the sheet position sensor 78.
7 is moved downward (solid line in the figure) by a solenoid (not shown), and at the same time, one roll 7
42 is rotated at high speed. Then, as shown in FIG.
Of the overlapped sheets P1, P2, the sheet P1 on the side of the transport roll 742 reaches the switching gate 77 in a state in which the sheet P1 advances, and the sheet P1 travels toward the reversing roll 76 through the bypass transport path 73.

As shown in FIG. 8, before the leading edge of the sheet P2 reaches the switching gate 77, the switching gate 77 returns to the original position, and the sheet P2 moves toward the transport roll 75 as it is. Further, as shown in FIG. 9, the sheet P1 is transported by the reversing roll 76, and the sheet position sensor 80 detects the sheet P1.
When the passage of the trailing end is detected, the rotation of the reversing roll 76 is stopped at an appropriate timing according to the signal, the switching gate 79 is moved to the position shown in FIG. Close up. Thereafter, when the reversing roll 76 is rotated in the reverse direction, the sheet P1 advances toward the transport roll 75 through the exit side passage of the bypass transport path 73.

Thereafter, as shown in FIG. 10, the paper P1 is transported by the transport roll 75 in a state of overlapping with the paper P2. At this time, there is a difference in the transport speed between the transport roll 75 and the reversing roll 76, but as shown in FIG. 10, a space 81 for securing the loop formation of the paper P1 is provided in the exit side passage portion of the bypass transport path 73. Therefore, no problem occurs. Then, as shown in FIG. 11, two sheets P1, P2
Are discharged to the discharge tray 67 with the image writing surface in the same direction. At this time, even if the two sheets P1 and P2 are discharged in a shifted state, they are aligned on the discharge tray 67, so that no problem occurs.

As described above, in the present embodiment, the productivity at the time of single-sided printing can be improved twice as much as the mode of carrying one sheet at a time without complicating the apparatus configuration. . Further, in the present embodiment, as shown in FIG. 13, an automatic sequence for selecting and operating two paper trays 61 and 63 of a designated size in accordance with an operation signal for one-sided printing is performed. It is possible to prevent selection errors.

In the present embodiment, the transfer device 26
Although bias rolls are used for a, 26b, 40a, and 40b, corotrons may be used. Further, in this embodiment, the polarity of the toner image T2 is inverted on the second intermediate transfer belt 25b by using the toner having the same charging polarity, but may be inverted on the photosensitive drum 21b. Different toners may be used. Further, in this embodiment, a transfer bias is applied to one of the secondary transfer rolls 40a and the other secondary transfer roll 40b is grounded. However, transfer biases having different polarities are applied to both the secondary transfer rolls 40a and 40b. It may be applied. Such design modification items can be appropriately adopted in the following embodiments.

Embodiment 2 The basic structure of a double-sided image forming apparatus according to the present embodiment is substantially the same as that of Embodiment 1, but is different from Embodiment 1.
As shown in FIG. 18, a simplex high-speed print mode is provided in addition to the normal mode in the simplex print mode. For example, by operating a simplex high-speed print mode switch 106 (indicated by a virtual line in FIG. 12), the simplex high-speed print mode is set. , Select two paper trays of the specified size, start single-sided high-speed printing operation, and if the single-sided high-speed print mode switch 106 is not operated, select one of the specified size paper trays and then perform single-sided normal printing. The operation is started. According to the present embodiment, in the single-sided print mode, the high-speed mode in which two sheets of paper are superimposed and conveyed and the normal mode in which one sheet of paper is conveyed one by one can be selectively used according to the application (for example, required image quality or the like). It is possible.

Third Embodiment FIG. 19 shows an outline of a third embodiment of a double-sided image forming apparatus to which the present invention is applied. In the figure, the basic configuration of a two-sided image forming apparatus according to the present embodiment is substantially the same as that of the first embodiment, but the paper transport system 60 is different from the first embodiment. Note that components similar to those of the first embodiment are denoted by the same reference numerals as those of the first embodiment, and detailed description thereof is omitted here. That is, the paper transport system 60 used in the present embodiment includes, for example, a first paper transport path 141 leading to one paper tray 131 and three paper trays 1, for example.
The second sheet conveying path 142 branches into the two sheet conveying paths 141 and 142, and the two image forming sections 20.
a and 20b, and a third paper transport path 143 extending to the discharge tray 67 through the fixing device 50 position. The first and second paper transport paths 141 and 142 are provided at predetermined intervals. In addition to the arrangement of the transport rolls 144, the registration rollers 70a and 70b for aligning the paper are disposed near the exit ends of the respective paper transport paths 141 and 142, and the third paper transport path 143 The transport rolls 69 and 71 and the inverter unit 72 are arranged in this order from the upstream side in the transport direction of the paper. In the present embodiment, for example, the sheet sizes of the sheet trays 131 and 132 are the same.

Next, an image forming process of the double-sided image forming apparatus according to the present embodiment will be described. First, in the double-sided print mode, when one sheet of a predetermined size is sent out from any of the sheet trays 131 to 134,
The sheet is conveyed to a registration roll 70a or 70b by a conveyance roll 144, and the registration roll 70a or 70b
After the paper is temporarily stopped in a loop, the paper is conveyed between the secondary transfer rolls 40a and 40b in accordance with the timing of the image writing position on the paper, and the toner image on the intermediate transfer belts 25a and 25b is transferred. T1 and T2 are simultaneously transferred onto the sheet P and are fixed simultaneously on both sides by the fixing device 50.

Next, the one-sided print mode will be described. When the single-sided printing mode is selected in the same manner as in the first embodiment, the sheet P is supplied from two paper trays (131 and 132 in this example) in response to an operation signal for single-sided printing.
1, P2 is sent out. The sheet P1 sent out from the sheet tray 131 is conveyed to the secondary transfer unit by the registration roller 70a at the timing of image writing on the toner image T1. The sheet P2 sent from the sheet tray 132 is conveyed to the secondary transfer unit by the registration roller 70b at the timing of writing the image on the toner image T2. The sheets P1 and P2 are conveyed between the secondary transfer rolls 40a and 40b in a state where the sheets P1 and P2 overlap each other.
Above, the toner images T2 on the intermediate transfer belt 25ba are respectively transferred onto the sheet P2. Thereafter, single-sided printing is achieved with high production in the same steps as those described above.

In this embodiment, since the registration rolls 70a and 70b are provided for each of the sheets P1 and P2, the image writing position can be individually adjusted with high precision for each of the image forming units 20a and 20b. As a result, the accuracy of the image writing position on the sheets P1 and P2 is improved as compared with the first embodiment.

The registration roll 70 is provided for each of the sheets P1 and P2.
a, 70b, the image forming units 20a, 20
By arbitrarily shifting the transfer positions of the toner images T1 and T2 of b, the two sheets P1 and P2 overlap with a certain amount of shift and can be transported to the secondary transfer unit. In this way, a certain amount of paper P1, P2 (for example, g = 10 mm
When the sheet P1 is shifted, the sheets P1 and P2 pass through the nip area n of the fixing device 50 in a state where the leading ends of the sheets P1 and P2 are shifted, as shown in FIGS. At this time, if a difference in hardness is provided between the fixing rolls 501 and 502, for example, the removability of the sheet P2 shifted earlier is prioritized.
The sheet P1 shifted backward with respect to the sheet P2 is pulled by the sheet P2 peeling operation and is smoothly peeled. Therefore, 2
In the mode in which the leading ends of the two sheets P1 and P2 are shifted to be conveyed to the fixing unit, compared with the case where the leading ends of the two sheets P1 and P2 pass through the fixing unit at the same time, the deterioration of the sheet peeling performance is reduced. Can be prevented.

Fourth Embodiment FIG. 21 shows a four-sided image forming apparatus according to a fourth embodiment of the present invention. In the figure, the present embodiment differs from the first to third embodiments in that a first image forming unit 20a and a second image forming unit 20b are arranged in parallel, and the first image forming unit 20a The second image forming section 20b is provided with separate transfer sections (corotrons in this example) 151 and 152, respectively. In the present embodiment, each image forming unit 20
Reference numerals a and 20b denote an electrophotographic device (not shown) provided around the photosensitive drums 21a and 20b in addition to the transfer units 151 and 152. Near the transfer units 151 and 152, a static eliminator for removing a sheet is provided. (Corotron in this example) 153 is provided.

The paper transport system 60 used in the present embodiment is, for example, a first paper transport path 141 that branches into two paper trays 131 to 132 and passes through the transfer unit 151 of the first image forming unit 20a. For example, the second paper transport path 142 leading to one paper tray 133 and the two paper transport paths 141 and 142 join together, and are discharged through the transfer unit 152 and the fixing unit 50 of the second image forming unit 20b. Tray 67
And a third paper transport path 143 extending to the first and second paper transport paths 141 and 142. The first and second paper transport paths 141 and 142 are provided with transport rolls 144 at predetermined intervals.
In the vicinity of the exit end of the sheet 142, registration rollers 70a and 70b for sheet alignment are provided.
3 includes transport rolls 7 in order from the upstream side in the paper transport direction.
1 and an inverter unit 72 are provided. In the present embodiment, for example, the paper sizes of the paper trays 131 and 132 are the same, and reference numeral 154 is a paper transport belt.

Next, an image forming process of the double-sided image forming apparatus according to the present embodiment will be described. First, in the double-sided print mode, one sheet is fed from one of the sheet trays 131 to 132, and the front surface is transferred by the transfer unit 151 of the first image forming unit 20a by a well-known electrophotographic process. 2 Transfer part 1 of image forming part 20b
The transfer of the back surface is performed at 52, and the sheet fixed by the fixing unit 50 is discharged to a discharge tray 67. With the above configuration and operation, a two-sided image is formed on a sheet.

Next, the one-sided print mode will be described. When the single-sided print mode is selected in the same manner as in the first embodiment, the sheet P is supplied from two paper trays (131 and 132 in this example) in response to an operation signal for single-sided printing.
1, P2 is sent out. The timing of this sending is
The paper tray 132 located far away by the transport time corresponding to the difference in the length of the paper transport path from the feed position of each of the two paper trays 131 and 132 to the registration roll 70a.
Is set earlier. In this state, the two papers P1 and P2 arrive at the registration roll 70a at the same time by the transport roll 144 with the leading end positions of the two papers being substantially the same.

Then, on the registration roll 70a, the sheets P1 and P2 are temporarily stopped in a state of forming a loop having substantially the same shape, and then the transfer section 151 of the first image forming section 20a is adjusted to the timing of the image writing position on the sheet. Is transferred to one side of the sheet P1, and then transferred to one side of the sheet P2 by the transfer unit 152 of the second image forming unit 20b, and two sheets are fixed at the same time by the fixing unit 50 and passed through the inverter unit 72 described above. Thereafter, the two sheets P1 and P2 are discharged to the discharge tray 67. With the above configuration, the productivity during single-sided printing is
Compared with a mode of transporting one sheet at a time in parallel, the configuration can be improved twice without complicating the configuration.

Another operation example of the single-sided print mode according to the present embodiment will be described. In this operation example, it is assumed that the sheet sizes of the sheet trays 131 and 133 are the same. That is, the sheets P1 and P2 are sent out from the two sheet trays 131 and 133, respectively, by the operation signal of the single-sided printing. Paper P1 sent from paper tray 131
In the register roll 70a, after temporarily stopping in a state where a loop is formed, the transfer is performed on one side of the sheet P1 by the transfer unit 151 of the first image forming unit 20a by adjusting the timing of the image writing position on the sheet, To the transfer unit 152 of the second image forming unit 20b. On the other hand, the paper tray 13
The sheet P2 sent out from No. 3 temporarily stops in a state in which a loop is formed on the registration roll 70b, and then goes to the transfer unit 152 of the second image forming unit 20b with the timing of the image writing position on the sheet adjusted. Second image forming unit 2
0b, the two sheets P1 and P2 merge before the transfer section 152, and the sheets P2 and P2 in the transfer section 152 in an overlapping state.
Are transferred to one side of the sheet, and two sheets are fixed at the same time by the fixing device 50. After passing through the above-described inverter section 72, the two sheets are discharged to the discharge tray 67. In this operation example, the sheets P1 and P2 only need to be sent at the timing of each image writing position, and the two sheets P1 and P2 do not need to be surely overlapped. Even in this operation example,
Compared to a mode in which the sheets are conveyed one by one in parallel, the print productivity on one side of the double-sided image forming apparatus can be greatly increased without complicating the configuration at all.

Fifth Embodiment FIG. 22 shows a fifth embodiment in which the present invention is applied to a color duplex image forming apparatus. In the figure, the basic configuration of the double-sided image forming apparatus is substantially the same as that of the first embodiment.
Photosensitive drum group 21a (specifically, 21aY, 21aM,
21aC, 21aK), the second photosensitive drum group 21b (specifically, 21bY, 21bM, 21bC, 21bK), and the corresponding primary transfer roll 26a (specifically, 26a
Y, 26aM, 26aC, 26aK, 26bY, 26bM, 2
6bC, 26bK). Note that the same components as those in the first embodiment are denoted by the same reference numerals as those in the first embodiment, and detailed description thereof is omitted here.

In this embodiment, the toners T1 and T2 use negatively-charged toner, and the primary transfer rolls 26aY to 26a
A DC current of +10 μA is applied to each of K, 26bY to 26bK for each transfer of YMCK, a DC current of +300 μA, a grid voltage of +500 V is applied to the polarity inversion corotron 28, and a DC voltage of −2 kV is applied to the contact roll 48 in contact with the secondary transfer roll 40a. did. The secondary transfer roll 40b was grounded.

Next, an image forming process of the double-sided image forming apparatus according to the present embodiment will be described. First, the two-sided print mode will be described.
From 1aY, 21aM, 21aC, 21aK, the first toner image T1 is successively transferred onto the first intermediate transfer belt 25a in the order of YMCK by primary transfer rolls 26aY, 26aM, 26aC, 26aK. Similarly, the second toner image T2 (YMCK) formed on the second photosensitive drum group 21bY, 21bM, 21bC, 21bK is transferred to the primary transfer roll 2
After the images are sequentially transferred onto the second intermediate transfer belt 25b by 6bY, 26bM, 26bC, and 26bK, a voltage is applied to the polarity reversal corotron 28 provided opposite the grounded tension roll 33 to form the second toner image T2. Reverse polarity. The sheet P is conveyed from any one of the sheet trays 61 to 63 at the same timing, and the intermediate transfer belts 25a, 25
After the toner images T1 and T2 on 5b are simultaneously transferred onto the sheet P, both sides are fixed simultaneously by the fixing device 50.

As described above, the photosensitive drum groups 21a, 21a
b, the YMCK toner images are transferred onto the intermediate transfer belts 25a and 25b in a superimposed manner, respectively.
b, the images on the intermediate transfer belts 25a and 25b are simultaneously transferred to both sides of the paper by the electric field between the secondary transfer rolls 40a and 40b, respectively, and the fixing device 50
, And fixed simultaneously on both sides to obtain a two-sided color image.

On the other hand, when the single-sided print mode is executed with the above configuration, the same operation as in the first embodiment is performed.
By sending out the sheets P1 and P2 from the sheet trays 61 and 63, respectively, and superimposing the two sheets to obtain one-sided prints, the productivity in one-sided printing can be greatly improved.

In this embodiment, as a color double-sided image forming apparatus, a so-called tandem type image forming unit in which a plurality of photosensitive drums 21a and 21b, a developing unit (not shown) and the like are arranged in parallel is used as each image forming unit 20a and 20b. However, the present invention is not limited to this, and a four-cycle type or the like may be appropriately applied. FIG. 23 shows an example in which the present invention is applied to a 4-cycle type color duplex image forming apparatus. In the figure,
The basic configuration of the color double-sided image forming apparatus is substantially the same as that of the first embodiment, but is different from the first embodiment.
a, 21b are mounted with rotary developing units 34a, 34b for full color (in this embodiment, yellow (Y), magenta (M), cyan (C), black (K)). A contact / separation mechanism (not shown) is provided between the transfer rolls 40a and 40b so that the intermediate transfer belts 25a and 25b are separated from each other in a cycle before the secondary transfer, and are close to or in contact with each other during the secondary transfer. Is provided.

According to this modification, in the double-sided printing mode, the photosensitive drums 21a and 21b are rotated a plurality of times to
The first toner image T1 and the second toner image T2 of the MCK are sequentially formed, and the respective color component toner images T1 and T2 are sequentially superimposed and transferred onto the intermediate transfer belts 25a and 25b, and then between the intermediate transfer belts 25a and 25b. The sheet is conveyed, and the intermediate transfer belt 25
The images on a and 25b are simultaneously transferred to both sides of the sheet by the electric field between the secondary transfer rolls 40a and 40b, respectively, and are horizontally transported to the fixing device 50 as they are to simultaneously fix both sides. On the other hand, when the single-sided print mode is executed in this modified embodiment, the sheets P1 and P2 are respectively sent out from the two sheet trays 61 and 63 in the same manner as in the operation shown in the first embodiment, and two sheets are superimposed on each other. By obtaining a print, productivity during single-sided printing can be significantly improved.

[0067]

As described above, according to the first aspect of the present invention, at least a part of the recording material conveying path is formed by each image forming section when the one-sided image forming mode is selected. Is provided with a common recording material conveyance path through which both pass, so that it is not necessary to individually provide a recording material conveyance path dedicated to the single-sided image forming mode for each image forming unit. Layout can be simplified,
In addition, it is not necessary to unnecessarily set the length of the image forming section toward each image forming section. Therefore, in the double-sided image forming apparatus, the productivity in the single-sided image forming mode can be improved without complicating the apparatus.

According to the fifth aspect of the present invention, when at least one part of the recording material conveying path is selected, when the one-sided image forming mode is selected, two recording materials are superposed and conveyed. In addition to the above, an image is formed on one side of the recording material, so that it is possible to perform one-side transfer on the two recording materials superposed and arranged on the transfer unit of each image forming unit, and to fix one side on the fixing unit. In addition, the recording material transport path can be shared for the two recording materials that are superposed and arranged, and there is no need to separately provide a recording material transport path dedicated to the single-sided image forming mode. Can be simplified and the length of the recording material conveying path can be shortened. Therefore, in the double-sided image forming apparatus, the productivity in the single-sided image forming mode can be greatly improved as compared with a mode in which the recording materials are conveyed one by one without complicating the apparatus.

[Brief description of the drawings]

FIGS. 1A and 1B are explanatory views showing an outline of a double-sided image forming apparatus according to the present invention.

FIG. 2 is an explanatory diagram illustrating an outline of a double-sided image forming apparatus according to the first embodiment;

FIG. 3 is an explanatory diagram illustrating an operation of a secondary transfer unit in a double-sided print mode.

FIG. 4 is an explanatory diagram illustrating a state in which a sheet is fed from a sheet feeding device in a single-sided print mode.

FIG. 5 is an explanatory diagram illustrating an operation of a secondary transfer unit in a single-sided print mode.

FIG. 6 is an explanatory diagram illustrating an inverter unit in a single-sided print mode.

FIG. 7 is an explanatory diagram illustrating an operation process of the inverter unit in the single-sided print mode.

FIG. 8 is an explanatory diagram illustrating an operation process of the inverter unit in the single-sided print mode.

FIG. 9 is an explanatory diagram illustrating an operation process of the inverter unit in the single-sided print mode.

FIG. 10 is an explanatory diagram illustrating an operation process of the inverter unit in the single-sided print mode.

FIG. 11 is an explanatory diagram illustrating an operation process of the inverter unit in the single-sided print mode.

FIG. 12 is a block diagram illustrating an image forming process control system used in the first embodiment.

FIG. 13 is a flowchart illustrating a print mode selection process.

FIG. 14 is a flowchart illustrating processing in a single-sided print mode.

FIG. 15 is a flowchart illustrating a transfer condition setting process of a transfer unit.

FIG. 16 is a flowchart illustrating a fixing condition setting process of a fixing unit.

FIG. 17 is a flowchart illustrating a process speed setting process.

FIG. 18 is a flowchart illustrating print mode selection processing in the duplex image forming apparatus according to the second embodiment.

FIG. 19 is an explanatory diagram showing an outline of a two-sided image forming apparatus according to a third embodiment.

FIGS. 20A and 20B are explanatory diagrams illustrating a behavior when a sheet used in the third embodiment enters a fixing unit in a superposed state.

FIG. 21 is an explanatory diagram illustrating an outline of a two-sided image forming apparatus according to a fourth embodiment.

FIG. 22 is an explanatory diagram illustrating an outline of a double-sided image forming apparatus according to a fifth embodiment.

FIG. 23 is an explanatory diagram showing a modification of the double-sided image forming apparatus according to the fifth embodiment.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... 1st image formation part, 2 ... 2nd image formation part, 3 ... Recording material, 4 ... Recording material supply means, 5 ... Fixing means, 6 ... Recording material conveyance path, 7 ... Common recording material conveyance path, 8 ... Recording material conveyance control means, 20a: first image forming unit, 20b: second image forming unit, 40a, 40b: secondary transfer roll, 50: fixing unit,
61 to 63: paper tray, 65: paper vertical conveyance path, 66
… Paper horizontal conveyance path, 70, 70a, 70b… registration roll (registration roll), 72… inverter section,
110: image forming process controller, 131 to 134: paper tray, 141 to 143: paper transport path

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Mitsuo Yamamoto 2274 Hongo, Fuji Xerox Co., Ltd. Inventor Yoshiya Mashimo 2274 Hongo, Ebina City, Kanagawa Prefecture Inside Fuji Xerox Co., Ltd.

Claims (20)

[Claims] 1. A method according to claim 1, wherein a first image and a second image are respectively formed.
One image forming unit, and two when the double-sided image forming mode is selected.
A double-sided image forming apparatus for forming an image on both sides of one recording material by one image forming unit and forming an image on only one side of the recording material by each image forming unit when a single-sided image forming mode is selected, comprising: At least a portion of the recording material transport path from the supply unit to the fixing unit through which the recording material supplied from the supply unit passes the recording material to be image-formed by each image forming unit when the single-sided image forming mode is selected. A double-sided image forming apparatus comprising a recording material conveying path. 2. The double-sided image forming apparatus according to claim 1, further comprising: a common transfer unit that is shared by each image forming unit and transfers an image to one side of a recording material when a single-sided image forming mode is selected. A double-sided image forming apparatus characterized by the above-mentioned. 3. The double-sided image forming apparatus according to claim 1, further comprising a common fixing unit for fixing an image on one side of a recording material formed by each image forming unit when a single-sided image forming mode is selected. A double-sided image forming apparatus. 4. The double-sided image forming apparatus according to claim 1, wherein the entire recording material transport path from the recording material supplied from the recording material supply means to the fixing means is a common recording material transport path. Image forming apparatus. 5. A method in which a first image and a second image are formed, respectively.
One image forming unit, and two when the double-sided image forming mode is selected.
A two-sided image forming apparatus for forming an image on both sides of one recording material by one image forming unit and forming an image on only one side of the recording material by each image forming unit when a single-sided image forming mode is selected, comprising: When the forming mode is selected, two recording materials, on which images are formed by the respective image forming units, are superimposed and conveyed in at least a part of the recording material conveying path from the recording material supply unit to the fixing unit. A double-sided image forming apparatus, comprising a recording material conveyance control means. 6. The double-sided image forming apparatus according to claim 5, wherein the recording material conveyance control means superimposes and conveys the recording material to at least a transfer position. 7. The double-sided image forming apparatus according to claim 5, wherein the recording material conveyance control means superimposes and conveys the recording material to at least a fixing position. 8. The double-sided image forming apparatus according to claim 5, wherein the recording material transport control means sends out the recording material one by one from two recording material supply means and superimposes two sheets. Image forming apparatus. 9. The double-sided image forming apparatus according to claim 5, wherein the recording material conveyance control unit sends out the recording material one by one from the two recording material supply units in accordance with the image forming timing of each image forming unit. A double-sided image forming apparatus characterized by the above-mentioned. 10. The double-sided image forming apparatus according to claim 5, wherein the recording material conveyance control means has a positioning correction means for temporarily correcting the position of the recording material in the recording material conveyance path. The two-sided image forming apparatus is characterized in that the start timings of sending the recording materials from the two recording material supply units are controlled so that the two recording materials arrive at substantially the same time. 11. The double-sided image forming apparatus according to claim 5, wherein the recording material conveyance control means includes two positioning correction means for temporarily correcting the position of the recording material in the recording material conveyance path. A double-sided image forming apparatus, wherein a timing at which a recording material enters a transfer position of each image forming unit is individually controlled by a correction unit. 12. The double-sided image forming apparatus according to claim 5, wherein the recording material conveyance control means superimposes and conveys at least two recording materials in a state shifted by a predetermined amount before entering at least a fixing position. A two-sided image forming apparatus. 13. The double-sided image forming apparatus according to claim 5, wherein the recording material conveyance control means separates the two recording materials arranged one on the other at a discharge portion of the recording material having passed through the fixing means. A two-sided image forming apparatus characterized in that only the sheet is inverted and discharged. 14. The double-sided image forming apparatus according to claim 13, wherein the recording material transport control means shifts the two recording materials by a predetermined amount at least before separating the two recording materials superposed and arranged at the discharge unit. A double-sided image forming apparatus characterized in that it is superposed and conveyed in a state. 15. The double-sided image forming apparatus according to claim 5, wherein the recording material conveyance control unit is configured to:
A two-sided image forming apparatus, wherein two kinds of recording material supply means of a designated recording material size are selected to perform recording material sending control. 16. A double-sided image forming apparatus according to claim 5, wherein the recording material conveyance control means superimposes and conveys the recording material under a condition that only a single-sided image forming mode is selected. Forming equipment. 17. The double-sided image forming apparatus according to claim 5, wherein the recording material conveyance control means superimposes and conveys the recording material only under a condition that a single-sided image forming mode and a two-sheet feeding mode are simultaneously selected. A duplex image forming apparatus. 18. The double-sided image forming apparatus according to claim 5, wherein the recording material conveyance control unit is configured to transfer two recording materials simultaneously on one side of the recording medium by a transfer condition of a common transfer unit in the two image forming units. And a double-sided image forming apparatus. 19. The double-sided image forming apparatus according to claim 5, wherein the recording material conveyance control unit changes a set temperature of the common fixing unit under a condition that two recording materials are fixed on one side simultaneously. Image forming apparatus. 20. The double-sided image forming apparatus according to claim 5, wherein the recording material conveyance control unit changes a process speed of a common fixing unit under a condition that two recording materials are simultaneously fixed on one side. Image forming apparatus.