JPH03184061A - Both side image forming device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a double-sided image forming apparatus such as a color copying device, a color printer, a color facsimile, etc. [Prior art] Double-sided image forming apparatuses that form images on both sides of a material are known.

The transfer belt that transports the transfer material to the transfer position where the visible image on the photoreceptor is transferred is formed to be able to move back and forth, and the transfer material after the surface image is formed is reversely transported so that the trailing edge becomes the leading edge by the reverse movement of the transfer belt. However, a double-sided image forming apparatus that inverts and guides the transfer material to a transfer position on a photoreceptor is known, for example, from Japanese Patent Laid-Open No. 59-166 and Japanese Patent Laid-Open No. 54-24639.

In this conventional device, the transfer material is reversed and guided to the transfer position after the image is formed on the surface and before fixing.As a result, the image on the transfer material is rubbed by rollers and guide members on the way as it is transported unfixed. This poses a problem in that not only the image deteriorates, but also the guide members, rollers, etc. become stained. Furthermore, since the front and rear edges of the transfer material are reversed, it is necessary to provide a device for reversing the double-sided document and guiding it to the exposure position so that the front and rear edges of the images on the back and front surfaces are not reversed. In this case, in the case of single-sided originals, it is necessary for the operator to rearrange the front and rear edges of every other original and feed the original. Or without reversing the original,
Scanning and exposure of the back side of the document must be performed in the opposite direction, which poses problems in that it takes time and effort for the operator to operate and the timing control becomes complicated.

[Problem to be solved by the invention]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned conventional problems and provide a double-sided image forming apparatus that has a simple structure and is capable of forming color double-sided images.

[Means to solve the problem]

The present invention solves the above problem by forming a latent image by optically writing on the photoreceptor with a writing means, making the latent image visible by development, and exposing the transfer material to be transferred back and forth by a reciprocating transfer belt. In an image forming apparatus capable of superimposing and transferring images of bodies, a guide plate extending along a transfer belt, a fixing path branching from the guide plate and extending to a fixing device, and switching between the guide plate and the fixing path are performed. a fixing switching claw, an ejection path extending from the exit of the fixing device, a reversing path formed as a curved path branching from the ejection path and connected to an end of the guide plate opposite to the transfer belt side, and the ejection path. The problem was solved by a double-sided image forming apparatus characterized by being provided with a reversal switching claw for switching between the path and the reversal path.

Furthermore, the present invention solves the above-mentioned problems by having a storage means for storing image data for at least one page of a document, an adsorption means for adsorbing a transfer material to the transfer belt, and forming an image on the back side by using the storage means. This problem was solved by a double-sided image forming apparatus that is characterized in that it sequentially performs printing from the trailing edge line to the leading edge line of an image on one page.

[Effect]

According to the present invention, by reciprocating the reciprocating transfer belt over the guide plate and the conveying path of the transfer belt, the transfer material is transferred with color separated images on the photoreceptor in an overlapping manner, thereby forming a color image. The transfer material after the color image has been formed is branched from the guide plate by switching the fixing switching claw, is conveyed to the fixing device, and is fixed. In the case of single-sided image formation, it is ejected from the fixing device through the ejection path, but in the case of double-sided image formation, the transfer material with the image fixed on the front side is guided to the reversal path by switching the reversal switching claw, and then guided onto the guide plate. and further guided onto a conveyor belt. At this time, the transfer material is fed onto the conveyor belt in the opposite direction to that during image formation on the front surface, so the position of the leading edge of the transfer material is reversed. In other words, when forming an image on the back side, the trailing edge of the transfer material is at the leading edge position when forming an image on the front side.

When forming an image on the back side, a latent image is sequentially formed on the photoreceptor from the rear edge line of the image of one page to the front edge using a storage means that stores image data for at least one page, and an image based on the latent image is formed. When the image is transferred to a transfer material using the above method, the front and rear edges of the images on the front and back sides are reversed.

〔Example〕

The details of the present invention will be explained based on embodiments shown in the drawings.

A copying machine as an example of an image forming apparatus using the present invention can have a tank bottom as shown in FIG.

In FIG. 1, an image of a document on a contact glass page is read by a known reading device 2, for example, a reading device 2.
The optical signal read by the image sensor 3 is changed into an electrical signal and sent to the optical writing unit 5 in the printer part 4 as a writing signal.

The printer part 4 is provided with a photoreceptor belt 8 that is wound around a driving roller 6 and a driven roller 7.
Along the travel path, a corona charger 9, a writing position 10 by the writing unit 5, a developing device 11, and a transfer corona charger 12 are installed.
, a cleaning device 13, and a static eliminator 14 are arranged in this order.

The developing device 11 includes a developing device, for example, a yellow developing device 11a and a magenta developing device 11, each of which develops a latent image of a separated color image of a color image using separated color toner.
b. Cyan developer 11c and black developer l if necessary.
Has an id. A developing roller 15 for applying toner to the photoreceptor belt 8 is provided in each of the developing units 11a to lid.

A transfer material, for example, a transfer paper 17 is called out from a paper feed device, for example, a cassette 7) 16 by a paper feed roller 18, and is fed by registration rollers 19 in synchronization with the image on the photoreceptor belt 8.

Transfer belt 2 as a transfer paper conveying means for conveying the transfer paper
0 is wound around the transfer belt driving roller 21 and the transfer belt driven roller 22, and the transfer belt 20 comes into contact with the photoreceptor belt 8 at the transfer position T by the transfer corona charger 12 by switching movement of the contact/separation switching roller 23. It is formed so as to be able to switch between a contact position where it moves and a non-contact position where it leaves.

The transfer paper 17 fed by the registration rollers 19 is placed on the transfer belt 20, and is attracted to the transfer belt 20 by being charged by a charge applying means 24 as an attraction means.

In the illustrated example, the transfer paper 17 is conveyed by the transfer belt 20 along a substantially horizontal conveyance roller, and the photoreceptor belt 8 is arranged to extend substantially vertically; however, the shape is not limited to this. do not have.

The transfer belt 20 that conveys the transfer paper 17 is configured to be neutralized by a static eliminating corona discharger 25 on the return side opposite to the conveying side, and to be able to clean the transfer belt 20 by a transfer belt cleaning device 26.

a conveyance path by a transfer belt 20 as a transfer paper conveyance means;
Alternatively, a fixing path 27 is formed as a branch path upward from an extension of the transport path. A fixing device 2 is installed in the middle of the fixing path 27.
8 is formed. On the other hand, an extension of the conveyance path by the transfer belt 20 is provided by a guide plate 2 for guiding the paper leading edge, which also serves as a discharge path.
Formed as 9. The fixing path 27 and the guide plate 29 are formed so as to be selectively selected by a fixing switching claw 30.

The guide plate 29 can be used as an unfixed discharge path for discharging the transferred paper without being fixed. When the transferred paper is conveyed to the fixing path 27 which is selected by the fixing switching claw 30, the fixing device 2
8, and after fixing, the paper can be discharged to a paper tray 31.

When the transfer paper that is attracted to the transfer belt 20 and conveyed is discharged after the transfer is completed, the transfer paper 17 and the transfer belt 20 are neutralized by the separation charger 32, the electrostatic attraction force is removed, and the transfer paper is discharged. It can be separated from the belt 20.

A transfer paper trailing edge guide 33 is formed on the side of the transfer belt 20 opposite to the discharge path on the side where the transfer paper 17 is sucked and conveyed, that is, on the extension toward the entrance side, and is formed below the paper feeder 16 in the illustrated example. .

The machine frame 3 of the printer at the transfer paper trailing edge guide 33
An opening 34 is formed at 5 as a paper refeed port.

FIG. 1 shows an example of a copying device for forming a single-sided guide.
In this apparatus, parts related to the fixing device 2B and the guide plate 29 are constructed as shown in FIG. 2 in the double-sided image forming apparatus according to the present invention.

In FIG. 2, a reversing conveyance unit 36 is formed to be attachable to a printer frame 35. As shown in FIG. Reversing conveyance unit 36
has a casing 37 that can be fixed to a machine frame 35, and within the casing 37 are provided a discharge passage 3B and a reversing passage 39 branching from the discharge passage 38.

In order to attach the reversing transport unit 36, an opening 40 communicating with the exit of the fixing device I28 is formed in the machine frame 35, and when the reversing transport unit 36 is fixed, the discharge path 38 is formed to be connected to the opening 40. Ru.

In this case, the free end 41 of the curved reversing path 39 opens at a position facing the machine frame 35 and can be connected to the guide plate 29 .

At a branch position between the discharge path 38 and the reversal path 39, a reversal switching pawl 42 is supported by a support shaft 42a so as to be able to switch and swing, and is switched by the operation of a solenoid or the like.

The discharge path 38 is provided with a discharge roller 43, and the reversing roller 39 is provided with feed rollers 44, 45.

When the casing 37 is equipped with a zero reversing conveyance unit 36 in which a tray 31' for accommodating the transfer material discharged from the discharge path 36 is attached, the paper discharge tray 31 provided in the machine frame 35 is removed.

When the reversing conveyance unit 36 is attached to the machine frame 35, the discharge roller 43 and the feed rollers 44, 45 can be configured to be driven and connected to the drive system of the fixing solenoid 28, for example, gears, or they can be built into the casing 37. It is also possible to adopt a structure in which it is driven by a motor or the like.

A connector may be provided to which a power source, signal line, etc. can be connected to and removed from the main control board 46 of the image forming apparatus in accordance with the attachment and detachment of the casing 37 to the machine frame 35.

When the reversing transport unit 36 is attached, it can be used as a double-sided copying machine, and when the reversing transport unit 36 is removed, it can be used as a single-sided copying machine as shown in FIG. Therefore, by simply preparing the copying machine and reversing conveyance unit 36 shown in FIG. 1, it is possible to meet both the demand for single-sided copying machines and the demand for double-sided copying machines.

The operation of this device will be explained.

When the print switch is turned on, the drive roller 6 is rotated clockwise in the figure by the photoreceptor motor controlled based on a signal from the main control board 46, and the photoreceptor belt 8 is rotated.
rotates in the direction of the arrow at a linear velocity of vP.

At the same time, the transfer belt drive roller 21 is driven by the transfer drive motor and starts normal rotation, and the transfer belt 20
also rotates in the direction of the left arrow at a linear velocity of vF. In addition, V, -V,
It is controlled and driven to rotate under the following conditions.

The photoreceptor belt 8 (hereinafter abbreviated as PC belt) is neutralized by a static eliminator 14 and uniformly charged over the entire surface by a charger 9, and is processed so as to satisfy the following conditions.

That is, the static eliminator 14 removes toner from the surface of the PC belt 8 by the cleaning device 13 in advance.
The surface potential of the PC belt is brought to approximately Ov by irradiating light or applying a charge-eliminating corona. In the case of a negative/positive process, since toner adheres to uncharged areas on the surface of the photoreceptor, the entire surface of the PC belt 8 must be uniformly charged by the charger 9. performs uniform charging by corona discharge, but the discharge generates a small amount of ozone. Although this ozone decomposes in a short time when the discharge is stopped, it may have an adverse effect on the surface of the PC belt and impair the clarity of the image. Therefore, air is sent from behind the charger 9 using a fan or the like (not shown), or
Inhale to eliminate the effects of ozone.

An encoder is fixed to the shaft of the drive roller 6, and a rotation detection sensor is installed on the encoder so that one detection pulse is output for each rotation of the drive roller 6.

At the timing of, for example, the third pulse of this rotation detection sensor, the semiconductor laser (hereinafter abbreviated as LD) of the optical writing unit is controlled and started to be driven. (Other optical writing units such as an LED array or an LCD array may also be used). First, optical writing is started based on yellow (Y) image data to form an electrostatic latent image.

This image data is captured by the color image reading device installed at the top of Figure 1! ! 2, for example, reads the three color separated lights of blue, green, and red, and performs image calculation processing based on the intensity level of each separated color light to produce yellow (Y), magenta (M), and cyan ( C), black (Bk
) is written image data for each color.

Apart from this, image data output from other color image processing systems, such as color facsimiles, word processors, personal computers, etc., may also be used.
The connection interface for this purpose may be individually supported.

The developing device 11 that visualizes the electrostatic latent image on the PC belt 8 is normally located at a position where the developing roller 15 does not come into contact with the surface of the PC belt 8. Then, only from just before the latent image surface of the corresponding color reaches the position of the developing roller of each color to just after passing through, the developing device (11a to 11d) of the corresponding color is pressed to the left in FIG. Then, the developing roller 15 is set at a position where it comes into contact with the photoreceptor surface by a predetermined amount.

At the same time, in order to provide only that developing device with a developing function, the developing roller and the parts contributing to development are started to be driven.

First, since seven latent images have been formed, the Y developing device 11a is brought into contact with and driven on the surface of the photoreceptor after tying with respect to that surface, and the seven images are visualized.

The next step is the transfer process, and the transfer belt 20 is moved in such a way that it comes into contact with and separates from the PCC bottom surface at the transfer position (the position of the drive roller 6).
The vertical position of the separation switching roller 23 is switched.

When the printing operation starts, the transfer belt 20
is driven in the direction of the left arrow, and then presses the transfer belt contact/separation switching roller 23 to the upper position to bring the transfer belt 20 into contact with the PC belt 8.

Then, at a predetermined timing, the transfer paper 17 is transferred to the paper feed roller 1.
The paper is fed by the PC belt 8, and then transported through the holes by the registration rollers 19 at a timing that matches the position of the image formed on the surface of the PC belt 8.

The perforated transfer paper 17 is applied with a voltage of a predetermined polarity by the charge applying means 24, and is attracted to the transfer belt 20 charged with a desired charge density pattern, and is transported so that the paper position does not shift during transfer. be done. This charge applying means 24
is formed by an electrode plate or an electrode roller in contact with the transfer belt 20, and a voltage is applied by a power source 20a, for example, an AC power source (or a DC power source), and charges are applied to the transfer belt 20 in a striped or checkered pattern. Note that the transfer belt 20 is uniformly neutralized by a static eliminating corona discharger 25 prior to the transfer process of the first color. At this time, a cleaning process is also performed by the transfer belt cleaning device 26.

When the leading edge of the visualized Yiii image reaches a position T3 point a predetermined distance from the transfer position T, a normal rotation start signal S1 of the transfer drive motor 36 is inputted to the control drive circuit of the transfer drive motor.

However, at the time point 51, it is already rotating in the normal direction, and continues to rotate in the normal direction.

The S1 timing is essentially when the leading edge of the transfer paper 17 is at the R7 point,
That is, this is the point in time when the transfer position T reaches the position i in the near direction, and also the point in time when both seven image leading ends of the PC belt reach the position T in the near direction it of the transfer value itT.

This is the point at which the drive roller 6 has rotated four times and further rotated by the number of pulses P6 of the photoreceptor drive motor encoder provided in the photoreceptor drive motor from the Y image data writing start timing. During this time, the PC belt has moved by a distance from the image writing position 10 to the position T8.

After time t1 has passed from point 31, both the leading edge of the YN image and the leading edge of the transfer paper are I! Move the page distance to transfer position T
After that, the transfer corona charger 12 reaches Y+i! N image transfer is performed.

Time at this time 1. The number of pulses of the photoreceptor drive motor encoder becomes P11, and the number of pulses of the transfer drive motor encoder becomes P□.

Here, as the resolution of both encoders, if the belt movement dimension per pulse is the same, then P
, =P, , and if the ratio of the two is α, Pl and pt+ have values corresponding to the coefficient α.

In this example, the condition will be explained below as Pl=Pl.

As the Y image transfer process progresses, the leading edge of the transfer paper separates from the transfer belt 20, passes over the fixing switching claw 30 shown by the solid line in the figure, and advances toward the paper leading edge guide plate 29.

Then, the Y image transfer process further progresses, and the transfer paper size becomes 1. The rear edge of the transfer paper moves from the transfer position T to the distance j! 8, that is, from the point 81, the transfer paper becomes 1+ +I
! p+i! When the transfer paper is moved a distance of t and is at the position indicated by the two-dot chain line in the figure as indicated by 17' (time t++t
t), by a reversal signal to the transfer drive motor 36;
Rotate the same motor in the opposite direction.

Prior to this reverse rotation, the transfer belt contact/separation switching roller 23 is lowered to the lower position to separate the transfer belt 20 from the PC belt surface.

By the reverse rotation of the transfer drive motor 36, the transfer belt 20
The transfer paper 17' is then fink-returned in the direction of the right arrow at a speed Vt (>VF).

At this time, due to the short return time of time t, time +
The position is controlled to the right by a distance equal to the distance moved to the left during time t, and the position is returned to the right.

During this return, the trailing edge of the transfer paper separates from the transfer belt and advances toward the paper trailing edge guide plate 33, and returns exactly a predetermined distance to the position indicated by the dashed-dotted line 17'' ( The paper stops at the position where the leading edge of the paper is at position R7) and waits for the second color M image transfer (time ta).
do.

On the other hand, on the PC belt 8, the second color M image is already being formed during the transfer of the first color seven images. That is,
Formation of an electrostatic latent image by optical writing by controlling and driving the LD based on the M image data starts when the photoreceptor driving roller 6 has rotated an integral number of times, for example, when the photoconductor driving roller 6 has rotated four times, from the start of Y image writing. There is.

Then, the developing HII uses the Y developing unit 11b only for the 7 image areas.
is contacted and driven, and before the second color M image area arrives, the Y developing device 11a is separated from the PC belt surface and the driving is stopped. In this case, instead, the M developing unit 11b is operated by the PC after seven image areas have passed and before the leading edge of the M image area has arrived.
It is brought into contact with and driven by the belt surface, and only the M image latent image area is visualized into an M image.

Next, when the leading edge of the M image reaches the position Ts, that is, the same as in the case of the 7 images of the first color, the drive roller 21 rotates four times and the photoreceptor drive motor encoder pulses several times from the M image data writing start timing. . At the point when the transfer drive motor has moved by a corresponding number of rotations, the transfer drive motor inputs a normal rotation start signal S2 to the control drive circuit.

At the same time or with a slight delay, the transfer paper belt contact/separation switching roller 23 starts pressing operation in the upward position direction and is brought into contact with the transfer paper belt until at least the leading edge of the transfer paper reaches the transfer position T.

At time t1 from the timing of St, the number of pulses of the photoreceptor drive motor encoder of the PC belt 8 becomes P, and the PC belt surface movement distance #11, as in the case of the seven images described above.

Therefore, for the transfer paper, it takes 1. During this period, the speed is raised from the state of 0 to VF (=VP), and during this period the speed is increased to 1
In this case again, P + "'
Position control is also performed so that P□ and both coincide.

This means that the leading edge of the transfer paper has moved 11 times in time L1, and the seven images of the first color and the M image of the second color are aligned on the transfer paper.

After that, repeat the same steps as above. That is, the process proceeds to M image transfer, transfer paper quick return, C image data writing, C development, CWi image transfer, transfer paper quick return, Bk image data writing, Bk development, and Bk image transfer.

Next, the process after Bk image transfer will be explained.

In the Bk image transfer process, the fixing switching claw 30 switches to the position indicated by the dashed-dotted line, and the transfer paper during the transfer process is discharged from its leading edge by the paper separation charger 32 in the direction of the transfer path 27, that is, the fixing device 28. Even if the trailing edge of the transfer paper has finished transferring, the transfer drive motor continues to rotate normally and transports the transfer paper to the left, and the fixed color print is as shown in Figure 1. directly to tray 31, the second
In the figure, the reversal switching claw 42 is switched to the solid line position and discharged! 153B and is discharged to the paper discharge tray 31'.

At this time, the transfer belt 20 is uniformly charge-eliminated by applying a charge-eliminating corona from the timing when the rear end of the first image area passes the charge-eliminating corona discharger 25 .

When performing the next image forming repeat operation, select 1.
After writing the Bk image data for the second image, continue to write the Y image data for the second image.
As the image data is written, the operations of the transfer paper and transfer belt are controlled in the same manner as from the beginning of the first sheet.

Note that the PC belt 8 has residual toner removed by the post-transfer cleaning device 13, and further, the residual ¥1 charge is removed by the static eliminator l4, and the PC belt 8 moves toward the charger 9.

Further, in the case of monochrome recording, the developing device of that color is contacted and driven until a predetermined number of sheets are completed, the transfer belt 20 remains in contact with the PC belt 8, and the fixing switching claw 30 is It is held at a position that guides the transfer paper in the direction of the fixing device 28 and performs a recording operation.

Therefore, in repeat recording, the print creation speed is 4/3 times faster when printing with 3 colors, twice as fast when printing with 2 colors, and 4 times faster when printing with a single color than when printing with 4 colors.

The developing color is not limited to the above four colors, and blue, green, red, and other colors may be used in combination as necessary.

The above is an explanation of the operation of normal monochrome to four-color single-sided image formation. Next, the operation of double-sided image formation will be explained.

To explain the operation of forming a color image using four colors, the operation from forming a four-color image on the front surface to fixing it by the fixing device 28 is the same as the above operation, so the explanation will be omitted.

The double-sided copying mode is set on the operation display board 47, and when copying on one side of the front side is completed in the same manner as described above, and when an image is to be formed on the back side, the reversal switching claw 42 is moved by a chain line in response to a signal from the main control board 46. It is switched to the position shown,
The transfer paper is sent to the guide Fi, 29 through the reversing path 39. Simultaneously or at the same time as the switching of the reversing switching claw 42, the fixing switching claw 3o is switched to the position shown by the solid line by a signal from the main control board 46, so that the transfer paper moving on the guide plate 29 is placed above the transfer bell 20. sent to.

When the leading edge of the transfer paper is detected by the paper detection sensor 48 provided on the fixing switching claw 30, a signal is sent through the main control board 46 to reverse the transfer drive roller 21, and in synchronization with this, the back side charge applying means 49 as a suction means The AC piezoelectric 111150 is turned on to form a charge on the transfer belt in a predetermined pattern similar to the charge applying means 24, and the transfer sheet is held by suction and conveyed until the rear end reaches the R7 point and then stopped.

The back side charge applying means 49 can also be used as a charge applying means to the transfer belt during return during single-sided image formation, or the back side charge applying means 49 can be omitted and the charge applying means 24 can apply the charge. . The paper detection sensor 48 can also be a sensor used for jam detection, slip detection, etc. during single-sided image formation.

Based on the output of the paper detection sensor 48, writing of image data for forming an image on the back side is started, and in the case of a color image, writing of seven images is started first. In this case, since it was reversed in the reversing path 39, the leading end and the trailing end are reversed on the front and back surfaces. Therefore, when writing to the back side, image data is stored in a memory that stores one page, and is written sequentially from the rear end line of the image data.

This allows the front and back edges of the front and back images to match.

The subsequent image forming process can be carried out in exactly the same manner as in the case of single-sided copying, except that writing is performed from the trailing edge line of one page. When all image formation on the back side is completed, the reversal switching claw 42 is switched to the solid line position, and the fixed transfer paper is discharged to the tray 31' through the discharge path 38.

〔effect〕

According to the present invention, when forming an image on the back side, the transfer paper after fixing is reversed and conveyed onto the contact glass by a reversible transfer belt, so that the image is rubbed with a simple structure.

It is now possible to form images on the screen without any trouble. Therefore, deterioration of image quality and contamination of parts were prevented.

According to the present invention, when writing on the back side, by writing from the trailing edge line of one page's worth of image data using the memory that stores the image data, it is possible to eliminate the mismatch between the front and rear edges caused by reversing the transfer paper, and moreover, it is possible to eliminate the mismatch between the front and rear edges due to the reversal of the transfer paper. This is possible with a compact device that does not require any parts.

According to the present invention, the reversing conveyance unit can be easily removed from the machine frame of the image forming apparatus, and it has become possible to easily switch from a single-sided image forming apparatus to a double-sided image forming apparatus, and also has a built-in device specifically for duplexing. Since this is not necessary, the device becomes more compact and costs can be reduced.

[Brief explanation of drawings]

FIG. 1 is an overall schematic diagram of an image forming apparatus using the present invention;
FIG. 2 is a sectional view of a portion related to the reversing conveyance unit according to the present invention. 5... Writing means 8... Photoreceptor 11... Original device 20... Transfer belt 27... Fixing path
29... Guide plate 30... Fixing switching claw 31.31
'... Tray 36... Reversing conveyance unit 39... Reversing path 42... Reversing switching claw 24.4
7...Adsorption means

Claims (2)

[Claims] (1) Form a latent image by optically writing on the photoreceptor using a writing means, make the latent image visible by development, and make the image on the photoreceptor visible on the transfer material that is transported back and forth by a reciprocating transfer belt. An image forming apparatus capable of overlapping transfer includes a guide plate extending along a transfer belt, a fixing path branching from the guide plate and extending to a fixing device, and a fixing switching claw for switching between the guide plate and the fixing path. an ejection path extending from the exit of the fixing device; a reversing path formed as a curved path branching from the ejection path and connecting to an end of the guide plate opposite to the transfer belt side; and the ejection path and the reversing path. A double-sided image forming apparatus characterized by being provided with a reversal switching claw for switching between the two sides. (2) It has a storage means for storing image data for at least one page of the original, and has an adsorption means for adsorbing the transfer material to the transfer belt, and the image formation on the back side is performed by the storage means.
2. The double-sided image forming apparatus according to claim 1, wherein the double-sided image forming apparatus performs the image forming process sequentially from the trailing edge line to the leading edge line of the image on the page.