JP3511279B2 - Double-sided image forming device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention 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 improvement of 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 photoconductor is transferred onto a first surface of a sheet and fixed, and then the sheet is reversed and re-fed. Then
Then, a method of transferring and fixing the second image formed on the photoconductor to the second surface of the paper is common. However, in this method, since the image forming unit is passed twice, the productivity per sheet is slower than half that at the time of single-sided recording, and the sheet is curled at the time of the first fixing. There are various problems such as a defective transfer at the time of the second transfer, a wrinkle of the paper at the time of fixing, a paper jam easily occurring, a noise when the paper is inverted and re-fed, and the like.

As a double-sided image forming apparatus that solves the above problems, for example, two image forming units are arranged to face each other and a toner image is simultaneously transferred to both sides of the paper by one sheet feeding (for example, Japanese Patent Laid-Open No. 63-63057). Publication, Japanese Patent Laid-Open No. 2-2
No. 59670), or a type in which two image forming units are arranged in parallel and toner images are sequentially transferred to both sides of the paper by one sheet feeding (for example, JP-A-5-150573). ing.

[0004]

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

As a means for solving such a technical problem, there has already been provided a device in which two image forming units are arranged in parallel and each image forming unit can form an image on only one side when the one-side print mode is selected. It has been proposed (for example, JP-A-8-248695). However, in this type of type, when the single-sided print mode is selected, the image forming operation by each image forming unit is performed by completely different sheet carrying paths (sheet feeding-fixing-discharging). Each section must be provided with its own dedicated paper carrying path, and there is a technical problem that the entire apparatus becomes complicated and large, and the cost is significantly increased. Further, as another prior art, as a sheet conveying path for two image forming sections arranged in parallel, a dedicated conveying path for single-sided printing is provided, and the image forming section on one side is stopped at the time of single-sided printing to extend the life. A target has also been proposed (for example, Japanese Patent Laid-Open No. 60-3667), but there is a technical problem that productivity in single-sided printing does not increase and the apparatus becomes complicated.

The present invention has been made to solve the above-mentioned technical problem, and provides a double-sided image forming apparatus having a simple structure and high productivity even when the single-sided image forming mode is selected. Is.

[0007]

That is , the first aspect of the present invention
1A, the first and second images are formed on both sides of the recording material conveyance path 6 as shown in FIG. 1A.
It has two image forming units 1 and 2 placed on it , and when two-sided image forming mode is selected, the two image forming units 1 and 2 form images on both sides of one recording material 3 and a plurality of recording materials are formed. A double-sided image forming apparatus for forming an image on only one side of the recording material 3 by using two image forming sections together and selectively using each recording material when the single-sided image forming mode is selected. At least a part of the recording material conveyance path 6 from the recording material 3 supplied from the recording medium 3 to the fixing means 5 is image-formed by the image forming units 1 and 2 when the single-sided image forming mode is selected. Is provided with a common recording material conveying path 7 through which both of

In such a technical means, the double-sided image forming apparatus according to the present application broadly includes a copying apparatus, a printer and the like which adopt an electrophotographic system, an electrostatic recording system and the like. , 2 may be those in which the image carriers carrying images are arranged opposite to each other, or the image carriers may be arranged in parallel. The image carrier may be in the form of an image forming carrier such as a photoconductor or a dielectric, or may be arranged opposite to the image forming carrier and the image forming carrier. Further, the image forming carrier may be provided with an intermediate transfer member on which each image is temporarily transferred by the primary transfer means.
Note that these points are the same even in the mode of FIG. 1B described later.

Further, in such an aspect, the common recording material conveying path 7 is provided with the recording material 3 supplied from the recording material supplying means 4.
Is acceptable as long as it is at least a part of the recording material conveying path 6 up to the fixing means 5, but from the viewpoint of downsizing the apparatus configuration, the recording material 3 supplied from the recording material supply means 4 is It is preferable that all the recording material conveying paths 6 up to the fixing unit 5 are the common recording material conveying paths 7.

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

A second aspect of the present invention is shown in FIG.
And the first and second images are formed respectively and
It has two image forming units 1 and 2 arranged on both sides of the recording material conveying path 6, and when two-sided image forming mode is selected, images are formed on both sides of one recording material 3 by the two image forming units 1 and 2. A double-sided image forming apparatus that forms an image on only one side of the recording material 3 by each of the image forming units 1 and 2 when the single-sided image forming mode is selected. In at least a part of the recording material conveying path 6 from the recording material 3 supplied to the fixing means 5 to the fixing means 5, two recording materials 3 on which images are formed by the image forming units 1 and 2 are superposed and conveyed. Recording material conveyance control means 8
It is characterized by having.

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

Further, the recording material feeding control means 8 may be one that superposes and feeds the two recording materials 3 sent from the recording material feeding means 4, but it is easy to control the overlapping arrangement of the recording materials 3. Considering this, it is preferable that the recording materials 3 are fed one by one from the two recording material supply means 4 and are superposed on each other. In this mode, one of the simplest control methods is to feed the recording material 3 one by one from the two recording material supply means 4 in synchronization with the image forming timing of each of the image forming units 1 and 2. It is preferable that the recording material 3 is naturally arranged so as to be superposed.

Further, from the viewpoint of more accurately controlling the position of the overlapping arrangement of the recording materials 3, the recording material conveyance control means 8 serves as the recording material conveyance path 6 to temporarily correct the positioning of the recording materials 3. There is provided a positioning correction means, and the start timing of sending the recording material 3 from the two recording material supply means 4 is controlled so that the two recording materials 3 reach the positioning correction means substantially at the same time. preferable. In this aspect, 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 conveyance control unit 8 is the recording material conveyance path 6. The recording material 3 has two positioning correction means for temporarily positioning the recording material 3 therein, and each positioning correction means individually determines the timing of entry of the recording material 3 into the transfer position of each image forming unit 1, 2. A controlled mode is preferred.

Furthermore, the polymerization state of the two recording materials 3 is not limited to the state in which both recording materials 3 are completely polymerized and arranged, and includes the mode in which at least a part thereof is polymerized and arranged. At this time, when priority is given to the productivity improvement in the single-sided image forming mode, it is preferable that the two recording materials 3 are completely overlapped, but the common fixing unit 5 fixes them at the same time. From the viewpoint of further improving the peeling performance of the recording material 3 at the fixing portion, the recording material conveyance control means 8 shifts the two recording materials 3 by a certain amount at least before entering the fixing position. It is preferable to carry out polymerization conveyance in the state.

Further, in a mode in which the recording material 3 is superposed and conveyed, the recording material 3 usually formed in each of the image forming sections 1 and 2 is used.
Since the image bearing surfaces of No. 2 are reversed, it is necessary to properly correct the arrangement state of each recording material 3 on which one-sided image is formed at the time of discharging. Under such a request, the recording material conveyance control unit 8 causes the recording material 3 that has passed through the fixing unit 5 to discharge.
It is preferable that the two recording materials 3 superposed and arranged are separated and only one of them is reversed and discharged. At this time,
From the viewpoint of ensuring the separation operation of the two recording materials 3, at least the two recording materials 3 are displaced by a certain amount before the two recording materials 3 superposed at the discharge portion are separated. It is preferable to carry out polymerization and conveyance.

Further, the recording material conveyance control means 8 has 2
From the viewpoint of eliminating a mistake in selecting the size of one sheet of recording material 3 and improving the workability thereof, when selecting the single-sided image forming mode, two recording material supply means 4 of the specified recording material size are selected. The delivery control of the recording material 3 may be performed. Further, from the viewpoint of simplifying the instruction operation of superposing and conveying the recording materials 3, the recording material conveying control means 8 may superpose and convey the recording materials 3 under the condition that only the single-sided image forming mode is selected. However, in the single-sided image forming mode, if there is a request to perform high-quality image formation on one sheet of recording material 3, the recording material conveyance control unit 8 sets the single-sided image forming mode . , Normal mode
A single-sided high-speed image formation mode is provided in addition to the
Only under the condition that the image forming mode is selected , the recording material 3
Alternatively , the single- sided image formation may be performed on one recording material 3 under the condition that the single-sided high-speed image formation mode is not selected.

Furthermore, since the mode in which the recording material 3 is superposed and conveyed is thicker than the mode in which only one recording material 3 is conveyed, the same transfer conditions and the same transfer conditions as those in which only one recording material 3 is conveyed are used. There is a concern that good image formation may not be performed under the fixing conditions. From the viewpoint of effectively avoiding such a concern, the recording material conveyance control unit 8 has two image forming units 1 and 2 under the condition that two recording materials 3 are simultaneously transferred on one side.
2, the transfer conditions of the common transfer unit may be changed, or the set temperature of the common fixing unit 5 may be 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-mentioned technical means will be described. First, in the invention of FIG. 1A, a common recording material conveyance path 7 is provided in at least 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. It is provided. The recording material 3 on which images are formed by the respective image forming units 1 and 2 passes through the common recording material conveying path 7 when the single-sided image forming mode is selected.
Therefore, it is not necessary to provide a recording material conveying path dedicated to the single-sided image forming mode for each of the image forming sections 1 and 2, the layout of the recording material conveying path 6 is simplified, and each of the image forming sections 1 and 2 is simplified. The length of the recording material conveying path toward the recording medium is not set unnecessarily long.

Next, the invention of FIG. 1B will be described. In the recording material conveyance control means 8, the recording material 3 supplied from the recording material supply means 4 reaches the fixing means 5 when the single-sided image forming mode is selected. In at least a part of the recording material conveying path 6 up to, the two recording materials 3 on which images are formed by the image forming units 1 and 2 are superposed and conveyed. Therefore, if the two recording materials 3 are superposed and conveyed to the transfer portion and the fixing portion of each image forming portion 1, 2, the first and second recording materials formed in each image forming portion 1, 2 will be described. The image is transferred or fixed on one side of each of the two recording materials 3.
The production amount in the single-sided image forming mode is approximately doubled as compared with the mode in which the recording materials 3 are conveyed in parallel. Moreover, since the number of recording material conveying paths 6 required for superposing and conveying two recording materials 3 is one, the layout of the recording material conveying paths 6 is simplified accordingly.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described below in detail based on the embodiments shown in the accompanying drawings. First Embodiment FIG. 2 shows a schematic configuration of a first embodiment (a printer in this embodiment) of a double-sided image forming apparatus to which the present invention is applied.
In the figure, this double-sided image forming apparatus is shown in FIG.
The first image forming unit 20a that forms the first image on the surface, and the second image forming unit 20b that forms the second image on the second surface of the paper P
A fixing device 50 for fixing the image on the paper P that has passed through the image forming units 20a and 20b, and the image forming units 20a and 2
0b and the fixing device 50, and a paper conveyance system 60 that conveys the paper P.

In the present embodiment, each image forming section 20.
Reference numerals a and 20b denote photosensitive drums 21a and 21b, and a charging roll 22 that charges 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 and 23b, and developing devices 24a and 2 that visualize the electrostatic latent images written on the photosensitive drums 21a and 21b with toner.
4b, the intermediate transfer belts 25a and 25b arranged in contact with the photosensitive drums 21a and 21b, and the photosensitive drums 21a and 2b.
Primary transfer rolls 26a and 26b for primarily transferring the toner images T1 and T2 (for example, normal images in the present embodiment) on the intermediate transfer belts 25a and 25b, and the photosensitive drums 21a and 2b.
Cleaners 27a, 27b for removing the residual toner on 1b
It has and. A pair of polarity reversal corotrons 28 and 29 are arranged opposite to each other on the downstream side of the primary transfer position of the intermediate transfer belt 25b of the second image forming unit 20b with the intermediate transfer belt 25b interposed therebetween.

Further, in the present embodiment, each of the intermediate transfer belts 25a and 25b is stretched around an appropriate number of holding rolls (one of which is a driving roll and the other of which is a driven roll), and the photosensitive drums 21a and 21b. It is designed to rotate in synchronization with. Reference numerals 30a and 30b are belt cleaners that remove 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, or 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. -It is formed so that it may become cm, and the thickness is set to 0.08 mm, for example.

Further, the holding rolls arranged corresponding to the regions where the intermediate transfer belts 25a and 25b come into contact with or come close to each other are configured as the secondary transfer rolls 40a and 40b. The secondary transfer rolls 40a and 40b can be transferred by using conductive ones, but when transferring to a small size paper, if the first and second intermediate transfer belts 25a and 25b come into direct contact, An excessive current flows between the transfer rolls 40a and 40b, a sufficient transfer electric field cannot be formed, and a transfer failure occurs, or the intermediate transfer belts 25a and 25b.
Since it is easily damaged, it is preferable to use at least a conductive roll coated with a semi-conductive or insulating material as a roll for applying a bias.

In the present embodiment, the secondary transfer roll 40
For both a and 40b, a secondary transfer roll 40 is used which is a metal shaft coated with EPDM rubber in which carbon black is dispersed and whose volume resistivity is 10 ⁶ Ω · cm.
The transfer bias 41 was applied to the shaft of a, and the shaft of the secondary transfer roll 40b was grounded. Incidentally, as the coating material, polyurethane rubber or silicone rubber in which conductive particles (carbon black, aluminum or the like) or an ion conductive agent (LiClO ₄ or the like) are dispersed may be used.
The volume resistivity is preferably 10 ⁵ to 10 ⁹ Ω · cm.

Furthermore, in the present embodiment, the toner T
1, T2 uses negatively charged toner, and the primary transfer roll 26a,
26b is a direct current +10 μA, and polarity reversal corotrons 28 and 29 are an alternating voltage 8 kVp-p / 600.
Direct current voltages of +1 kV and -1 kV were superimposed on Hz, and a direct current voltage of -2 kV was applied to the secondary transfer roll 40a.

In addition, the first and second photosensitive drums 21a, 21
b outer diameter and first and second intermediate transfer belts 25a, 25b
Have the same circumference. As a result, the images are formed on the photosensitive drums 21a and 21b at the same timing, so that the images on both the front and back sides or the image on the one side of the two sheets P can be accurately aligned. Further, the distance from the secondary transfer position to the fixing device 50 is shorter than the minimum sheet length, and the rotation speed of the fixing roll is the same as or slightly slower than the speed of the intermediate transfer belts 25a and 25b. Furthermore, in the fixing device 50, the upper and lower fixing rolls have the same shape so that the fixing nip has a linear shape, and heaters are arranged inside thereof.

Further, in the present embodiment, the paper transport system 60 has three paper trays 61 to 63 for accommodating the paper P of a predetermined size, for example.
The sheet P is stored by the feed rolls 64 provided in each of the three sheets.
Are sent out one by one. In this example, it is assumed that the paper trays 61 and 63 contain paper P of the same size. The paper transport system 60 is connected to each of the paper trays 61 to 63 and extends in a substantially vertical direction, and a paper vertical transport path 65 that is connected to the paper vertical transport path 65 to extend in a substantially horizontal direction and both images. Forming part 20a,
20b secondary transfer position (secondary transfer rolls 40a, 40b
And a paper horizontal conveyance path 66 that passes through the position of the fixing device 50, and the end of the paper horizontal conveyance path 66 is arranged at a position facing the discharge tray 67.

Further, for example, three paired conveying rolls 68 are arranged at predetermined intervals in the paper vertical conveying path 65, while the paper horizontal conveying path 66 has the paper vertical conveying path 6 in the horizontal direction.
In order from the 5 side, a pair of transport rolls 69, a pair of registration rolls for registration (hereinafter abbreviated as registration rolls) 70 for position adjustment, and a fixing device 50 on the front side of the secondary transfer positions of both image forming units 20a and 20b. A pair of conveying rolls 71 is provided on the rear side of the sheet, and an inverter unit 72 for reversing the sheet is provided on the front side of the discharge tray 67. In the present embodiment, as shown in FIG. 2, the basic configuration of the inverter unit 72 includes a mountain-shaped inversion bypass transport path 73 that bypasses the paper horizontal transport path 66 and has a bypass transport path. 7
The pair of transport rollers 74 and 75 are arranged on the sheet horizontal transport path 66 located on the inlet side and the exit side of the sheet 3, and the pair of reversing rolls 76 are disposed on the top of the bypass transport path 73. A switching gate 77 for switching the transport path is provided on the entrance side of the bypass transport path 73. The detailed configuration and operation of the inverter unit 72 will be described later.

Furthermore, FIG. 12 shows an image forming process control apparatus used in this embodiment. In the figure, the image forming process control device 110 includes a CPU 111 and a ROM 11.
2, RAM 113 and input / output interface 114,
The microcomputer system 115 includes, for example, a paper size switch (the switch is abbreviated as SW in FIG. 12, the same applies hereinafter) 101, a double-sided print mode switch 102, and a single-sided print mode switch 1.
03, signals from the print start switch 104, the print job counter 105, and the like are taken into 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 sections 20a and 20b, the secondary transfer section setting voltage 121, the fixing section setting temperature 122, and the first to third sheets are output through the output interface 115. The trays 61 to 63, the register roll 70, the inverter unit 72, etc. are controlled.

Next, an image forming process of the double-sided image forming apparatus according to this embodiment will be described. First, the double-sided print mode will be described. Paper size switch 1 now
When the print start switch 104 is operated after selecting 01 and the double-sided print mode switch 102,
The double-sided printing operation is started in accordance with the flowchart of 3. That is, a normal toner image T is formed on the surface of each photosensitive drum 21a, 21b by a well-known electrophotographic process.
1, T2 is formed. Then, the first toner image T1 formed on the first photosensitive drum 21a is transferred to the primary transfer roll 26a.
Thus, the image is transferred onto the first intermediate transfer belt 25a which 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 21a
The second toner image T2 formed on b is transferred onto the second intermediate transfer belt 25b by the primary transfer roll 26b, and a voltage is applied to the pair of polarity reversal corotrons 28 and 29 provided with the second intermediate transfer belt 25b interposed therebetween. Is applied to invert the polarity of the second toner image T2.

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 registration roll 70 forms the sheet P. P is temporarily stopped in the state of forming a loop, and then the paper P is transferred to the secondary transfer roll 40 at the timing of the image writing position on the paper P.
The intermediate transfer belts 25a and 25b are conveyed between a and 40b.
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. By applying a negative bias voltage 41 to the secondary transfer roll 40a, 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 repulsive force of the same polarity. Is transferred onto the paper P from the intermediate transfer belt 25a. On the other hand, the toner image T2 on the second intermediate transfer belt 25b whose polarity is reversed to the positive polarity by the polarity reversing corotrons 28 and 29 cancels the negative charge 43 on the back surface of the intermediate transfer belt 25b by grounding the secondary transfer roll 40b. Then, it is transferred onto the paper P by the suction force of the secondary transfer roll 40a. In this way, both surfaces can be transferred simultaneously.

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

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

Here, as shown in FIG. 4, the feeding timing of the papers P1 and P2 from the two paper trays 61 and 63 is, as shown in FIG. 4, the paper feeding path from the respective feeding positions of the two paper trays 61 and 63 to the registration roll 70. Of the paper P2 from the paper tray 63 for the transport time t corresponding to the difference L in the length of
It is only necessary to set the feeding start timing of the sheet tray earlier than the sheet tray 61. Then, the two sheets of paper P1 and P2 are
As shown in FIG. 5, the tip ends are aligned with each other so as to overlap each other, and the transfer rolls 68 and 69 reach the registration roll 70 at substantially the same time.

Further, as shown in FIG. 14, the print image of the odd page is processed by the first image forming section 20a, and the print image of the even page is processed by the second image forming section 20b. To be done. Therefore, 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. 21b to 2nd
After the primary transfer to the intermediate transfer belt 25b, the polarities are reversed by the polarity reversing corotrons 28 and 29. In this case, the orientation of the first toner image T1 is vertically inverted with respect to the orientation of the second toner image T2 in consideration of the reversal of the sheet P1 in the inverter unit 72 described later. If one sheet of paper P1 is supplied from one sheet of paper tray 61, the first print image of the processing target
It is processed 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 the two sheets P1 and P2 are overlapped with each other to form a loop having substantially the same shape, and then the secondary transfer roll is timed at the image writing position on the sheets. Two sheets of paper P1 and P2 are conveyed between 40a and 40b in an overlapping state, and the toner image T1 on the intermediate transfer belt 25a is on one side (intermediate side) of the paper P1 as shown in FIG. The toner image T2 on the intermediate transfer belt 25b is transferred onto one surface of the paper P2 (the surface facing the intermediate transfer belt 25b) on the transfer belt 25a.

In particular, in the present embodiment, when the secondary transfer is performed on two sheets of paper P1 and P2 at the time of one-sided printing, the apparent thickness of the sheet is thicker than 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 portion by a single-sided printing operation signal (single-sided printing mode selection signal), specifically, The optimum image is secured by changing the voltage applied to the secondary transfer roll 40a. In the present embodiment, for example, a normal transfer voltage for one sheet is −2 kV.
In the case of the DC voltage of, the transfer voltage for the two sheets may be set to around -3 kV.

After that, the papers P1 and P2 on which the toner images T1 and T2 are transferred on one side are directly conveyed to the fixing device 50, and the toner images T1 and T2 on the papers P1 and P2 are fixed to the fixing device 50.
Then two sheets are fixed at the same time. In particular, in the present embodiment, when fixing is performed on two sheets of paper P1 and P2 at the time of single-sided printing, the apparent thickness of the sheet is thicker than that of normal fixing on one sheet. Therefore, in order to obtain the optimum fixing performance, as shown in FIG. 16, the optimum fixing performance is ensured by changing the temperature setting of the fixing unit according to the operation signal for single-sided printing. In the present embodiment, for example, when the normal fixing temperature setting for one sheet is 160 degrees, the fixing temperature setting for two sheets may be set to about 180 degrees.

When performing fixing on two sheets at the time of single-sided printing, as a modified form for obtaining optimum fixing performance, instead of changing the set temperature of the fixing unit, as shown in FIG. The process speed of the entire apparatus may be changed (set to a process speed slower than usual), or the process speed of the entire apparatus may be changed in addition to changing the set temperature of the fixing unit.

Thereafter, the fixed papers P1 and P2 pass through the transport roll 71 and are inverted and discharged by the inverter section 72 only so that the image writing surfaces of the papers P1 and P2 are in the same direction. The sheets P1 and P2 are aligned and discharged onto the discharge tray 67. Here, based on FIGS. 6 to 11,
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 the one roll 741 and the transport roll 75 of the transport rolls 74 are set to the same speed as the paper transport speed. The other roll 742 has a structure in which the speed can be changed in two stages of a normal mode at the same speed as the one roll 741 or a high speed mode higher than that of the roll 741 by a driving device (not shown). Further, the reversing roll 76 is one roll 7 of the transport roll 74.
It is set to the same value as the high speed of 42 and is configured to be able to rotate in the forward and reverse directions by a driving device (not shown). Furthermore,
A paper position sensor 78 for detecting the leading end positions of the papers P1 and P2 is installed behind the transfer roll 74 and in front of the switching gate 77, and the switching gate 77 switches based on a detection signal from the paper position sensor 78. It is supposed to be selected. Furthermore, a switching gate 79 is arranged at the branch portion of the bypass conveyance path 73, and a sheet position sensor 80 for detecting the trailing edge position of the sheet P1 is installed in front of the reversing roll 76 of the bypass conveyance path 73. The switching gate 79 is switched and selected based on the detection signal from the paper position sensor 80.

In FIG. 6, the fixed sheets P1 and P2 pass through the transport roll 71 and then the transport roll 7 of the inverter section 72.
Pass 4. At this time, the switching position of the switching gate 7 is determined by the signal that the sheet position sensor 78 detects the leading edges of the sheets P1 and P2.
7 is moved downward (solid line in the figure) by a solenoid (not shown), and at the same time, one roll 7 of the transport rolls 74 is moved.
42 is rotated at high speed. Then, as shown in FIG.
Among the overlapping sheets P1 and P2, the sheet P1 on the conveying roll 742 side leads to the switching gate 77 in a state where the sheet P1 advances toward the reversing roll 76 side through the bypass conveying path 73.

Further, as shown in FIG. 8, the switching gate 77 returns to the original position before the leading edge of the paper P2 reaches the switching gate 77, and the paper P2 directly goes to the transport roll 75 side. Further, as shown in FIG. 9, the paper P1 is conveyed by the reversing roll 76, and the paper position sensor 80 causes the paper P1 to move.
When the passage of the rear end is detected, the rotation of the reversing roll 76 is stopped at an appropriate timing by the signal, the switching gate 79 is moved to the position shown in FIG. Close up. After that, 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 carried by the carrying roll 75 in a state of being overlapped with the paper P2. At this time, although there is a difference in conveyance speed between the conveyance roll 75 and the reversing roll 76, as shown in FIG. 10, a space 81 for ensuring the loop formation of the sheet P1 is provided in the exit side passage portion of the bypass conveyance passage 73. Therefore, no trouble occurs. After that, as shown in FIG. 11, the two sheets of paper P1 and P2 are
Is discharged onto the discharge tray 67 with the image writing surface in the same direction. At this time, even if the two sheets of paper P1 and P2 are ejected in a misaligned state, they are aligned on the ejection tray 67, and no trouble occurs.

As described above, in the present embodiment, the productivity at the time of single-sided printing can be doubled without complicating the apparatus structure as compared with the mode of carrying one sheet at a time in parallel. . Further, in the present embodiment, as shown in FIG. 13, since the automatic sequence for selecting and operating the two paper trays 61 and 63 of the designated size by the operation signal for single-sided printing is used, the operator can change the size of the paper by the operator. It is possible to prevent selection mistakes.

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

Second Embodiment The basic configuration of the double-sided image forming apparatus according to the present embodiment is substantially the same as that of the first embodiment, but unlike the first embodiment,
As shown in FIG. 18, in addition to the normal mode, a single-sided high-speed print mode is provided in the single-sided print mode, and the single-sided high-speed print mode switch 106 (shown by a phantom line in FIG. 12) is operated to operate the single-sided high-speed print mode. Is selected, two single-sided high-speed printing operations are started after selecting two paper trays of the specified size, and when the single-sided high-speed print mode switch 106 is not operated, single-sided normal printing is performed after selecting one paper tray of the specified size. The operation is started. According to the present embodiment, in the single-sided print mode, it is possible to selectively use the high-speed mode in which two sheets of paper are superposed and conveyed and the normal mode in which one sheet of paper is conveyed one by one according to the application (for example, required image quality). 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 the double-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 that of the first embodiment. The same components as those in the first embodiment are designated by the same reference numerals as those in the first embodiment, and the 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, for example, three paper trays 1.
The second sheet conveying path 142 that branches into 32 to 134 and the two sheet conveying paths 141 and 142 are merged, and both image forming units 20 are connected.
a, 20b secondary transfer positions, and a third paper transport path 143 that extends to the discharge tray 67 after passing through the position of the fixing device 50. The first and second paper transport paths 141, 142 are provided at predetermined intervals. And a registration roll 70a, 70b for aligning the sheets are provided near the exit end of each sheet conveyance path 141, 142. Further, in the third sheet conveyance path 143, Conveying rolls 69 and 71 and an inverter unit 72 are arranged in this order from the upstream side in the sheet conveying direction. In this embodiment, for example, the paper sizes of the paper trays 131 and 132 are the same.

Next, the image forming process of the double-sided image forming apparatus according to this 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 the registration roll 70a or 70b by the conveyance roll 144, and the registration roll 70a or 70b
The paper is temporarily stopped in a loop, and then the paper is conveyed between the secondary transfer rolls 40a and 40b at the timing of the image writing position on the paper, and the toner images on the intermediate transfer belts 25a and 25b are transferred. T1 and T2 are transferred onto the sheet P at the same time, and the fixing device 50 fixes both sides at the same time.

Next, the single-sided print mode will be described. When the single-sided print mode is selected in the same manner as in the first embodiment, the paper P is fed from the two paper trays (131 and 132 in this example) by the operation signal of the single-sided print.
1, P2 is sent out. The paper P1 delivered from the paper tray 131 is conveyed to the secondary transfer portion at the timing of image writing on the toner image T1 by the registration roll 70a. The paper P2 delivered from the paper tray 132 is conveyed to the secondary transfer portion at the timing of the image writing on the toner image T2 by the registration roll 70b. The two sheets P1 and P2 are conveyed between the secondary transfer rolls 40a and 40b in an overlapped state, and the toner image T1 on the intermediate transfer belt 25a is the sheet P1 due to the above-described image forming configuration.
The toner images T2 on the intermediate transfer belt 25ba are transferred onto the paper P2. After that, single-sided printing is achieved with high production in the same process as described above.

In the present embodiment, the registration rollers 70a and 70b are provided for the respective sheets P1 and P2, so that the image writing positions can be individually adjusted to the image forming units 20a and 20b with high accuracy. As compared with the first embodiment, the accuracy of the image writing position on the sheets P1 and P2 becomes better.

The registration roll 70 is provided for each of the sheets P1 and P2.
a and 70b are provided, the image forming units 20a and 20b
By arbitrarily shifting the transfer positions of the toner images T1 and T2 of b, the two sheets of paper P1 and P2 are overlapped with a certain amount of shift and can be conveyed to the secondary transfer portion. In this way, the papers P1 and P2 are fed by a fixed amount (for example, g = 10 mm).
When the sheet P1 and P2 are shifted, the sheets P1 and P2 pass through the nip region n of the fixing device 50 in a state where the leading ends of the sheets P1 and P2 are displaced. At this time, for example, by providing a hardness difference between the fixing rolls 501 and 502, the peelability with respect to the previously displaced sheet P2 is prioritized.
The sheet P1 which is displaced rearward with respect to the sheet P2 is pulled by the peeling operation of the sheet P2 and smoothly peeled off. Therefore, 2
In a mode in which the leading ends of the two sheets of paper P1 and P2 are shifted and conveyed to the fixing unit, the peeling performance of the paper is reduced as compared with a mode in which the leading ends of the two sheets of paper P1 and P2 pass through the fixing unit at the same time. It becomes possible to prevent.

21. Fourth Embodiment FIG. 21 shows a double-sided image forming apparatus according to a fourth embodiment of the present invention. In the figure, this 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. The second image forming unit 20b is provided with separate transfer units (corotrons in this example) 151 and 152, respectively. Then, in the present embodiment, each image forming unit 20
Reference numerals a and 20b denote electrophotographic devices (not shown) arranged around the photosensitive drums 21a and 20b, in addition to the transfer sections 151 and 152, and a static eliminator for peeling a sheet near the transfer sections 151 and 152. (Corotron in this example) 153 is provided.

The sheet conveying system 60 used in this embodiment is, for example, a first sheet conveying path 141 that branches into two sheet trays 131 to 132 and passes through the transfer section 151 of the first image forming section 20a. For example, the second paper transport path 142 leading to one paper tray 133 and the both paper transport paths 141, 142 are merged, passed through the transfer section 152 of the second image forming section 20b, and the position of the fixing device 50 and discharged. Tray 67
A third sheet conveying path 143 extending to the first and second sheet conveying paths 141 and 142, and conveying rollers 144 are arranged at predetermined intervals.
Registration rollers 70a and 70b for aligning sheets are arranged near the exit end of the sheet 142, and further, the third sheet conveying path 14 is provided.
3 includes a transport roll 7 in order from the upstream side of the sheet transport direction.
1 and the inverter section 72 are arranged. In this embodiment, for example, the paper trays 131 and 132 have the same paper size, and the reference numeral 154 is a paper transport belt.

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

Next, the single-sided print mode will be described. When the single-sided print mode is selected in the same manner as in the first embodiment, the paper P from the two paper trays (131 and 132 in this example) is output by a single-sided print operation signal.
1, P2 is sent out. The timing of this delivery is
The paper tray 132 located far from the two paper trays 131 and 132 for the transport time corresponding to the difference in the length of the paper transport path from the delivery position to the registration roll 70a.
The delivery start timing of is set early. In this state, the two sheets P1 and P2 reach the registration roll 70a by the transport roll 144 at substantially the same time, with their leading end positions being substantially at each other.

Then, in the registration roll 70a, the sheets P1 and P2 are temporarily stopped while forming a loop of substantially the same shape, and then the transfer section 151 of the first image forming section 20a is adjusted at the timing of the image writing position on the sheet. The sheet P1 is transferred to one side of the sheet P1, and then the transfer section 152 of the second image forming section 20b transfers to one side of the sheet P2, and the fixing section 50 fixes two sheets at the same time and passes through the inverter section 72 described above. After that, the two sheets P1 and P2 are discharged to the discharge tray 67. With the above configuration, the productivity for single-sided printing is
The configuration can be doubled without complicating the configuration, as compared with a mode in which the sheets are conveyed one by one in parallel.

Another operation example of the single-sided print mode in this embodiment will be described. In this operation example, it is assumed that the paper sizes of the paper trays 131 and 133 are the same. That is, the papers P1 and P2 are sent out from the two paper trays 131 and 133, respectively, by the operation signal for single-sided printing. Paper P1 sent from the paper tray 131
In the registration roll 70a, after temporarily stopping in a looped state, the transfer unit 151 of the first image forming unit 20a transfers the image onto one side of the paper P1 at the timing of the image writing position on the paper, and then , Toward the transfer unit 152 of the second image forming unit 20b. On the other hand, the paper tray 13
The sheet P2 sent from the sheet 3 is temporarily stopped in the loop state in the registration roll 70b, and then heads to the transfer section 152 of the second image forming section 20b at the timing of the image writing position on the sheet. Second image forming unit 2
The two sheets P1 and P2 merge before the transfer section 152 of 0b, and the sheet P2 is transferred to the transfer section 152 in an overlapping state.
After being transferred onto one side of the sheet, two sheets are simultaneously fixed by the fixing device 50, and after passing through the above-mentioned inverter section 72, the two sheets are discharged to the discharge tray 67. In this operation example, the respective sheets P1 and P2 need only be sent out at the timing of the respective image writing positions, and the two sheets P1 and P2 do not have to be reliably overlapped. Even in this operation example,
Compared with a mode in which the sheets are conveyed one by one in parallel, the print productivity for one side of the double-sided image forming apparatus can be significantly increased without complicating the configuration.

Fifth Embodiment FIG. 22 shows a fifth embodiment in which the present invention is applied to a color double-sided 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, but unlike the first embodiment, a first YMCK toner image is formed.
Photosensitive drum group 21a (specifically, 21aY, 21aM,
21aC, 21aK), the second photosensitive drum group 21b (specifically 21bY, 21bM, 21bC, 21bK) and their corresponding primary transfer rolls 26a (specifically 26a.
Y, 26aM, 26aC, 26aK, 26bY, 26bM, 2
6bC, 26bK). The sheet conveying system 60 and other components similar to those in the first embodiment are designated by the same reference numerals as those in the first embodiment, and the detailed description thereof is omitted here.

In this embodiment, the toners T1 and T2 are negatively charged toners, and the primary transfer rolls 26aY to 26a are used.
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 and a grid voltage of +500 V are applied to the polarity reversal 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, the image forming process of the double-sided image forming apparatus according to this embodiment will be described. First, the double-sided print mode will be described. Image first photosensitive drum group 2
From 1aY, 21aM, 21aC, and 21aK, the first toner images T1 are continuously transferred in the order of YMCK onto the first intermediate transfer belt 25a by the primary transfer rolls 26aY, 26aM, 26aC, and 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
6bY, 26bM, 26bC, and 26bK are sequentially transferred onto the second intermediate transfer belt 25b, and then a voltage is applied to the polarity reversing corotron 28 provided facing the tension roll 33 that is grounded, so that the second toner image T2 is formed. Invert the polarity. The sheet P is conveyed from one of the sheet trays 61 to 63 at the same timing, and the intermediate transfer belts 25a, 2
After the toner images T1 and T2 on 5b are transferred onto the paper P at the same time, the fixing device 50 fixes the both surfaces at the same time.

As described above, the photosensitive drum groups 21a, 21
b, the YMCK toner images are transferred onto the intermediate transfer belts 25a and 25b in an overlapping manner, and the intermediate transfer belts 25a and 25b are transferred.
The paper is conveyed between b and the images on the intermediate transfer belts 25a and 25b are simultaneously transferred to both surfaces of the paper by the electric field between the secondary transfer rolls 40a and 40b, and the fixing device 50 is directly used.
A two-sided color image can be obtained by horizontally transporting the image onto the sheet and fixing it on both sides simultaneously.

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 individual sheet trays 61 and 63, respectively, and stacking two sheets to obtain a single-sided print, it is possible to greatly improve the productivity in single-sided printing.

In the present embodiment, as a color double-sided image forming apparatus, a so-called tandem type in which each of the image forming sections 20a and 20b is provided with a plurality of photosensitive drums 21a and 21b, a developing device (not shown), etc., is shown. 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 applied to a 4-cycle type color double-sided image forming apparatus. In the figure,
Although the basic configuration of the color double-sided image forming apparatus is substantially the same as that of the first embodiment, the photosensitive drum 21 is different from the first embodiment.
Around the a and 21b, rotary developing devices 34a and 34b for full color (yellow (Y), magenta (M), cyan (C), black (K) in this embodiment) are mounted, and secondary A contact / separation mechanism (not shown) for disposing the intermediate transfer belts 25a, 25b in the cycle before the secondary transfer and for arranging the transfer rollers 40a, 40b in the pre-secondary transfer, and for arranging them in proximity or contact at the time of the secondary transfer. Is provided.

According to this modification, in the double-sided print mode, the photosensitive drums 21a and 21b are rotated a plurality of times and the Y
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 transferred onto the intermediate transfer belts 25a and 25b, and then, between the intermediate transfer belts 25a and 25b. The paper is conveyed and the intermediate transfer belt 25
The images on a and 25b are simultaneously transferred to both sides of the paper by the electric field between the secondary transfer rolls 40a and 40b, and are conveyed horizontally to the fixing device 50 as they are for simultaneous fixing on both sides. On the other hand, when the single-sided print mode is carried out in this modification, the sheets P1 and P2 are respectively fed out from the two sheet trays 61 and 63 in the same manner as the operation shown in the first embodiment, and two sheets are superposed on each other to form a single-sided print. Obtaining a print can greatly improve the productivity in single-sided printing.

[0067]

As described above, according to the first aspect of the present invention, in the double-sided image forming apparatus, at least a part of the recording material conveying path is selected when the single-sided image forming mode is selected.
Since the common recording material conveying path through which the recording material image- formed in each image forming section passes is provided, the recording material conveying path dedicated to the single-sided image forming mode is individually provided for each image forming section. Since it is not necessary to provide it, the layout of the recording material conveying path can be simplified by that much, and it is not necessary to set the recording material conveying path length toward each image forming unit unnecessarily long. Further, in the present invention, a plurality of recording materials
When using the single-sided image forming mode, use both image forming units together.
In addition, only one side of the recording material can be used by selectively using each recording material.
Since two images are formed,
It is possible to form a single-sided image that is effectively used. 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 invention, at least a part of the recording material conveying path conveys two recording materials in a superposed manner when the single-sided image forming mode is selected, and each recording material is conveyed in each image forming section. Since the image is formed on one side of the sheet, it is possible to perform one-side transfer on each of the two recording materials that are superposed and arranged at the transfer section of each image forming section, or to fix each side on the fixing section. The recording material conveying path can be shared for the two recording materials that are superposed, and it is not necessary to separately provide a recording material conveying path dedicated to the single-sided image forming mode. It is possible to simplify the layout and shorten the recording material conveyance path length. Therefore, in the double-sided image forming apparatus, the productivity in the single-sided image forming mode can be significantly improved as compared with the mode in which the recording materials are conveyed in parallel one by one without complicating the apparatus.

[Brief description of drawings]

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 showing an outline of the double-sided image forming apparatus according to the first embodiment.

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

FIG. 4 is an explanatory diagram showing a state of feeding a sheet from a sheet feeding device in a single-sided print mode.

FIG. 5 is an explanatory diagram showing the operation of the secondary transfer portion in the single-sided print mode.

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

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

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

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

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

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

FIG. 12 is a block diagram showing 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 showing the processing contents of a single-sided print mode.

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

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

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

FIG. 18 is a flowchart showing print mode selection processing in the double-sided image forming apparatus according to the second embodiment.

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

20 (a) and 20 (b) are explanatory diagrams showing the behavior when the sheet used in the third embodiment enters the fixing unit in a superposed state.

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

FIG. 22 is an explanatory diagram showing 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 forming part, 2 ... 2nd image forming 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 section, 20b ... Second image forming section, 40a, 40b ... Secondary transfer roll, 50 ... Fixing device,
61 to 63 ... Paper tray, 65 ... Paper vertical transport path, 66
... Paper horizontal transport path, 70, 70a, 70b ... Registration roll (registration roll), 72 ... Inverter section,
110 ... Image forming process control device, 131-134 ... Paper tray, 141-143 ... Paper transport path

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Kenichi Sanshin               Fujize, 2274 Hongo, Ebina City, Kanagawa Prefecture               Within Rocks Co., Ltd. (72) Inventor Mitsuo Yamamoto               Fujize, 2274 Hongo, Ebina City, Kanagawa Prefecture               Within Rocks Co., Ltd. (72) Inventor Ken Mizomi               Fujize, 2274 Hongo, Ebina City, Kanagawa Prefecture               Within Rocks Co., Ltd. (72) Inventor Yoshiya Manashi               Fujize, 2274 Hongo, Ebina City, Kanagawa Prefecture               Within Rocks Co., Ltd.                (56) References JP-A-57-157259 (JP, A)                 Actual Kaihei 2-53043 (JP, U)

Claims (20)

(57) [Claims] 1. A first image and a second image are formed respectively and
It has two image forming units arranged on both sides of the recording material conveying path, and when two-sided image forming mode is selected, the two image forming units form images on both sides of one recording material and record a plurality of sheets. When the single-sided image forming mode for the material is selected, the two image forming sections are used together and selectively used for each recording material.
A double-sided image forming apparatus for forming an image on only one side of a recording material, wherein a single-sided image forming mode is selected in at least a part of the recording material conveying path from the recording material supply means to the fixing means. A double-sided image forming apparatus, characterized in that a common recording material conveying path through which recording materials image-formed by respective image forming sections pass together is provided. 2. The double-sided image forming apparatus according to claim 1, further comprising a common transfer unit which is shared by respective image forming sections and which transfers an image onto one side of a recording material when the one-sided image forming mode is selected. A double-sided image forming apparatus characterized by the above. 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 section when the single-sided image forming mode is selected. A double-sided image forming apparatus characterized in that 4. The double-sided image forming apparatus according to claim 1, wherein all of the recording material conveying paths from the recording material supplying means to the fixing means are common recording material conveying paths. Double-sided image forming apparatus. 5. The first and second images are formed respectively and
It has two image forming units arranged on both sides of the recording material conveying path, and when two-sided image forming mode is selected, the two image forming units form images on both sides of one recording material, and one-sided image forming mode. A double-sided image forming apparatus that forms an image on only one side of a recording material by each image forming unit at the time of selection, and when the one-sided image forming mode is selected, the recording material supplied from the recording material supply unit reaches the fixing unit. A double-sided image forming apparatus comprising a recording material conveyance control means for superposing and conveying two recording materials on which images are formed by respective image forming units, in at least a part of the recording material conveyance path. 6. The double-sided image forming apparatus according to claim 5, wherein the recording material conveyance control means superposes and conveys the recording material to at least the transfer position. 7. The double-sided image forming apparatus according to claim 5, wherein the recording material conveyance control means superposes and conveys the recording material to at least the fixing position. 8. The double-sided image forming apparatus according to claim 5, wherein the recording material feeding control means feeds one recording material from each of the two recording material supply means and superimposes two recording materials. Double-sided image forming apparatus. 9. The double-sided image forming apparatus according to claim 5, wherein the recording material conveyance control means feeds the recording material one by one from the two recording material supply means at a timing of image formation of each image forming section. A double-sided image forming apparatus characterized by the above. 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 positioning 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 supplying means are controlled so that the two recording materials arrive at the same time. 11. The double-sided image forming apparatus according to claim 5, wherein the recording material conveyance control means has two positioning correction means for temporarily positioning-correcting the recording material in the recording material conveyance path. A double-sided image forming apparatus, wherein the correction means individually controls the timing of the recording material entering the transfer position of each image forming portion. 12. The double-sided image forming apparatus according to claim 5, wherein the recording material conveyance control means conveys and superposes the two recording materials in a state where they are displaced by a certain amount before entering the fixing position. A double-sided image forming apparatus characterized by: 13. The double-sided image forming apparatus according to claim 5, wherein the recording material conveyance control means separates two recording materials superposed from each other at a discharging portion of the recording material which has passed through the fixing means. A double-sided image forming apparatus characterized in that it is only reversed and discharged. 14. The double-sided image forming apparatus according to claim 13, wherein the recording material conveyance control means shifts the two recording materials by a certain amount before separating the two recording materials superposed at the discharge portion. A double-sided image forming apparatus, wherein the double-sided image forming apparatus is for superposing and conveying in a state. 15. The double-sided image forming apparatus according to claim 5, wherein the recording material conveyance control means selects the single-sided image forming mode.
A two- sided image forming apparatus, wherein two recording material supply means of a specified recording material size are selected to control the delivery of the recording material. 16. The double-sided image forming apparatus according to claim 5, wherein the recording material conveyance control means superposes and conveys the recording material under the condition that only the 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 is set to a single-sided image forming mode .
In addition to the normal mode, a single-sided high-speed image forming mode is provided
A double-sided image forming apparatus characterized in that a recording material is superposed and conveyed only under the condition that a high speed image forming mode is selected . 18. The double-sided image forming apparatus according to claim 5, wherein the recording material conveyance control means transfers the recording material to one side of the two recording materials at the same time, and the transfer condition of the common transfer means in the two image forming portions. A double-sided image forming apparatus, characterized in that. 19. The double-sided image forming apparatus according to claim 5, wherein the recording material conveyance control means changes the set temperature of the common fixing means under the condition that two recording materials are simultaneously fixed on one side. Double-sided image forming apparatus. 20. The double-sided image forming apparatus according to claim 5, wherein the recording material conveyance control means changes the process speed of the common fixing means under the condition that two recording materials are simultaneously fixed on one side. Double-sided image forming apparatus.