JPH04177273A - Overlapped transfer transporting device - Google Patents

Abstract

PURPOSE:To prevent disturbance of transfer from being generated without having any relation with a size of a transfer sheet by a method wherein after a belt is reciprocated and a transfer is completed, a reciprocating end at a position where the belt is changed over from its forward movement to its returning movement is variably controlled in response to a size of the transfer sheet. CONSTITUTION:When an overlapped image is formed, a latent image is carried on a photo-sensitive belt 1, the latent image is visualized as a toner image and this is transported toward a transfer part which is a belt part just above a transfer corona 21. In turn, a transfer sheet S fed onto a transfer belt 17 in compliance with a timing of the transportation is moved leftwardly (forward move) together with the belt. After the belt is moved forward and the transfer is completed, a going end part which is a position where the belt is changed over from a forward movement to a returning state is variably controlled in response to a size of the transfer sheet in order to transfer a subsequent overlapped image to the transfer sheet after completion of the transfer. That is, when a transfer sheet of small size is applied, a rear end position of the transfer sheet S(34) when the transfer sheet reaches the end of the returning movement is changed to a point Fs' rather than a point Fe. With such an arrangement, occurrence of disturbance of transfer in the transfer sheet is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an overlapping transfer conveyance device applied to image forming apparatuses such as color copying machines, color facsimiles, and color printers.

(Prior Art) (1) An image forming apparatus which obtains a desired overlapping image by sequentially overlapping a plurality of toner images formed on a latent image carrier onto the same transfer paper is disclosed in Japanese Unexamined Patent Publication No. 58-198062 and It is disclosed in Japanese Patent Application Laid-open No. 118366/1983. In this technology, when the transfer paper held by the transfer paper conveying means is particularly large in size, when the image is transferred forward, the leading edge in the traveling direction separates from the belt and extends forward, allowing the next image to be transferred. When the belt moves back and is on standby, the rear end separates from the belt and extends rearward.

■Also. Although it is not publicly known, the transfer paper is held on the belt by the adsorption force generated by the unequal electric field charge pattern formed in advance on the reciprocating dielectric belt by the electric field charge pattern forming means, while the latent image carrier is held on the belt. A position where the leading edge of the transfer paper separates from the belt when the belt moves forward, and is used in an image forming apparatus that obtains a desired overlapping image by sequentially overlapping and transferring multiple toner images that are sequentially formed on the same transfer paper. An overlapping transfer conveying device has been proposed in which the electric field charge pattern forming means is disposed at a first position nearby and at a second position near a position where the trailing edge of the transfer sheet separates from the belt during backward movement. ing.

This unequal electric field charge pattern is formed, for example, as a charge density pattern arranged at a constant pitch on the belt by an AC voltage applied from an electrode roller serving as an electric field charge pattern forming means that rotates in pressure contact with the belt. . Due to the electric field density pattern formed in this way,
An unequal electric field is formed near the surface of the belt, and this electric field causes a force component in the direction perpendicular to the paper surface to act on the transfer paper.
It is attracted to the belt and held without shifting, and is transported integrally with the belt.

(Problem to be Solved by the Invention) In the technique (2) above, the end of the transfer paper comes off the belt before and after the image transfer process. This is suitable for shortening the belt and downsizing the entire image forming apparatus, but there is a risk that the paper will not be held securely against the belt, and in the case of color copying, it will cause color misalignment and This may cause a drop in quality.

On the other hand, in the technique (2) above, the adsorption of carbon on the transfer paper to the belt is strengthened by the action of the unequal electric field, so the problem in the technique (2) is resolved. However, depending on the size of the transfer paper, there may be an area on the belt within the area of the transfer paper where the unequal electric field charge pattern is not formed. Then.

In this region, the image transfer conditions are different from those in the region where the unequal electric field charge pattern is formed, resulting in image unevenness.

SUMMARY OF THE INVENTION An object of the present invention is to provide an overlapping transfer conveying device that does not cause uneven transfer due to the above reasons, regardless of the size of the transfer paper used in the image forming apparatus. .

(Means for Solving the Problem) In order to achieve the above object, in the present invention, in the technique proposed in item (2) above, after the belt is moved forward to complete the transfer, the next layer of transfer paper after the transfer has been completed is In order to transfer the image, the forward movement end, which is the position at which the belt is switched from forward movement to backward movement, is variably controlled according to the size of the transfer paper.

In this case, when the length of the formation area of the unequal electric field charge pattern after the portion corresponding to the leading edge of the transfer paper formed on the belt during the backward movement of the belt is Lac, the electric field charge pattern arranged at the second position It is effective to determine the forward end so that the LaC is larger than the circumferential length of the belt from the forming means to the portion corresponding to the tip of the transfer paper, regardless of the size of the transfer paper.

(Function) The formation area of the unequal electric field charge pattern formed by the first electric field charge pattern when the belt moves back is formed in a size such that it can reach at least the second electric field charge pattern forming means when the belt moves back. Thus, by determining and controlling the forward end of the belt, an unequal electric field lightning pattern is continuously formed on the belt.

(Example) In FIG. 2, reference numeral 1 indicates a photoreceptor belt as a latent image carrier, which is supported by a driving roller 2 at one end and a driven roller (not shown) at the other end. It is designed to be rotated.

A transfer belt 17 made of a dielectric material is disposed perpendicular to the photoreceptor belt 1 and close to and opposite the drive roller 2 . This belt 17 is supported by a driving roller 18 and a driven roller 19, and the driving roller 2 is located approximately at the center in the longitudinal direction, and a transfer corona is located on the back side of the belt 17 at a position facing the roller. 21 are arranged.

When forming a superimposed image, a latent image is carried on the photoreceptor belt 1, which is then visualized as a toner image and sent toward a transfer section, which is a portion of the belt directly above the transfer corona 21.

Meanwhile, at the same timing, the transfer paper S fed onto the transfer belt 17 is moved to the left (forward movement) together with the belt.

When the leading edge of the paper reaches the transfer section, the photoreceptor belt 1
The upper toner image also reaches the transfer section and is transferred onto the transfer paper by the action of the transfer corona 21.

In this transfer process, the transfer paper S is sent to a position where its rear end is removed from the transfer section, that is, to a position shown as point Fs in FIG. 2. The transfer paper in this state is labeled S (34)
This position is referred to as the forward end of the belt 17. At this forward end, the belt 17 immediately moves backwards to the right (backwards) together with the transfer belt 17, and reaches the RT point where the leading edge of the transfer paper S has come off the transfer section, in preparation for the next overlapping transfer. The direction of belt movement can be switched. Belt 17 at this position
This is called the reciprocating end.

Then, the process proceeds in synchronization with the arrival of the toner images for overlapping transfer formed on the photoreceptor belt 1 to the transfer section, and overlapping images are formed in the same manner as described above.

After repeating these steps a required number of times, the transfer paper S moves further to the left and is discharged from the transfer belt 17 in order to proceed to the fixing process.

By the way, as mentioned above and as shown in FIG. 2, if the size of the transfer paper is larger than the transfer belt 17 to a certain extent, the direction of movement of the belt changes at the end of the forward stroke and at the end of the backward stroke. Sometimes, the edge of the transfer paper slips off the belt, making the support on the belt unstable.
A positional deviation occurs from the original position.

In order to avoid this, an electric field charge pattern forming means is provided as a means for obtaining paper adsorption force.

This electric field charge pattern forming means is an electrode roller 22.2.
2' and AC power sources 23 and 23' connected thereto. The electrode roller 22 is movably in contact with the drive roller 18 at a first position near the position where the leading edge of the transfer paper separates from the belt when the belt moves forward, that is, at a position diagonally below the left of the drive roller 18, and similarly. The electrode roller 22' is movably in contact with the driven roller 19 at a second position near the position where the trailing edge of the transfer sheet separates from the belt when the belt moves back, that is, at a position diagonally below and to the right of the driven roller 19. .

When the transfer belt 17 moves forward, an AC voltage is applied from the AC power source 23' to the electrode roller 22' with the driven roller 19 as the opposing electrode, and when the belt moves backward, the electrode roller 22' with the driven roller 19 as the opposing electrode is applied. By applying an alternating current voltage to the rollers 22 from an alternating current power supply 23, a striped unequal electric field charge pattern is formed on each belt as these electrode rollers rotate.

In this way, in the combination of forward movement (normal rotation) and backward movement (reverse rotation) of the transfer belt 17, an unequal electric field charge pattern is formed over the entire belt area that contacts the transfer paper. The paper adsorption effect caused by the charge pattern prevents the transfer paper from shifting.

On the other hand, if the electrode roller 2
If there is a region where 2, 22' does not contact the belt, no charge pattern is formed in that region.

The formed area and image transfer conditions will be different, resulting in image unevenness.

Taking this point into consideration and referring to FIG. 2 again, when the transfer process is completed and the transfer belt 17 reaches the forward end, the distance corresponds to I ACl from the leading edge of the transfer paper S (34). area of the transfer belt, that is, "distance from the leading edge of the transfer paper to the top of the drive roller = distance 1 from the rear edge of the transfer paper to the top of the drive roller" minus "the distance from the total length of the transfer paper 121" to "the distance from the top of the drive roller The distance J1!(1
, )'' passes through the electrode roller 22 during the backward motion. Therefore, when the transfer belt 17 moves back from the forward movement end, an unequal electric field charge pattern is formed in the area of the transfer belt corresponding to the distance I Act.

Here, the position of the leading edge of the transfer paper 5 (33) when it reaches the backward movement end is defined as the RT point. Then, the distance from the leading edge of the transfer paper to the top of the driven roller 111tl,' plus the distance (IF+')J for the circumference of the driven roller from the top of the r driven roller to the contact point of the electrode roller with the roller l,″+l,
The region corresponding to l 1 is not the region to which the electrode roller 22' is passed during forward movement and a voltage is applied. That is, when the transfer belt 17 moves forward from the backward movement end, the distance is 1. '+1.
An unequal electric field charge pattern is formed after the area of the transfer belt corresponding to '.

Therefore, l,' +1. As long as the relationship ``<Lcx'' holds, an unequal electric field charge pattern is formed seamlessly on the transfer belt corresponding to the transfer paper, and when the size of the transfer paper is large to some extent as shown in FIG. ,l'
There is no problem because the conditions for <lAc engineering are met.

However, as shown in Fig. 1, when the transfer paper size is small, with a total length of 1.2 (where l, , < 1.2), the transfer paper S (34) at the forward end is Assuming that the trailing edge position is the same Fs point as in the case of large-sized transfer paper in FIG. 2, 1. '+lR'>1Ac2', and a region is created where no charge pattern is formed due to the difference between the left and right sides of the inequality sign.

Therefore, in this example, after the belt is moved forward and the transfer is completed, the next overlapping image is transferred to the transfer paper after the transfer is completed, so the forward movement end is the position where the belt is switched from the forward movement to the backward movement. was decided to be variably controlled according to the size of the transfer paper.

In other words, when using small-sized transfer paper, the rear end position of the transfer paper S (34) when it reaches the backward movement end is as shown in FIG.
The point is changed to point Fs', which is to the left of the point.

As a result, the distance I AC2 becomes the distance I AC of a small value.
2', IF' + L'<Lcz', and a seamless charge pattern is formed.

Such control of the leading edge position of the transfer paper is performed by the configuration of the block diagram shown in the third factor. In the figure, information 100 for detecting the size of one sheet of transfer paper to be used is input to a main board 41 including a central processing unit (CPU), and based on this information, control information is output to a servo control board 43, The belt drive motor 39 is controlled.

Here, "one paper size detection" is performed as follows. There are five sensors (
A photo interrupter) is provided. On the other hand, the sensor corresponding portion of the paper cassette is provided with a shielding plate designed to shield the sensor according to the size of the paper stored in the paper cassette. Therefore, paper size detection information is obtained according to the paper size detection code as shown in FIG. 4 depending on the shielding state of the sensor by the shielding plate.

In FIG. 4, black circles indicate that the sensor is not shielded, and white circles indicate that the sensor is shielded.

In this way, the belt is controlled to move backward until the formation region of the unequal electric field charge pattern formed during the forward movement reaches at least the second electric field charge pattern forming means, thereby forming the unequal electric field lightning pattern. As a result of being seamlessly formed on the belt, it is possible to obtain a good image without transfer unevenness on all transfer papers to which it is applied.

Next, a color recording apparatus will be explained as an example of an image forming apparatus suitable for carrying out the present invention.6 Note that in the following explanation, the same functions as in FIGS. It is indicated by the symbol. Further, the symbol Y means yellow, M means magenta, C means cyan, and Bk means black.

First, when the print switch is turned on (a in FIG. 6(1)), the photoreceptor belt 1 is rotated clockwise by the PC drive motor 36 for driving the photoreceptor belt 2.
As shown in FIGS. 5 and 7, it rotates in the direction of the arrow at a linear velocity of vP.

At the same time, the transfer drive motor 39 for driving the transfer belt 17 first rotates in the normal direction (g, h in FIG. 6 (1)).
(see the signal and the speed diagram of j), and then start the
As shown in the figure, it rotates in the direction of the left arrow at a linear velocity of VF.

Note that each motor is controlled and driven so that these speeds rotate under the condition of VP=VF.

Now, the photoreceptor belt 1 has a static eliminator 30 for the photoreceptor belt.
Static electricity is removed with ! The entire surface is uniformly charged by the electric appliance 4, and the processing is performed to satisfy the following conditions.

1. The static eliminator 30 irradiates light M (or applies a static eliminating corona) onto the surface of the photoreceptor belt 1 from which toner has been removed by the cleaner 29 in advance, and removes the toner from the surface of the photoreceptor belt 1.
The surface potential of is set to approximately Ov.

2. 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 photoreceptor belt 1 must be uniformly charged by a charger.

3. The charger performs uniform charging by corona discharge, but
A slight amount of ozone is generated by discharge. Although this ozone decomposes in a short time when the discharge is stopped, it may have an adverse effect on the surface of the photoreceptor belt 1 and impair the sharpness of the image. Therefore, the influence of ozone is eliminated by blowing air from behind the charger using a fan or the like (not shown) or by sucking air.

By the way, a one-rotation sensor is installed on the shaft of the drive roller 2, and a detection pulse is output every time the drive roller 2 makes one rotation (d in FIG. 6(1)).

In the example of FIG. 6 (1), at the timing of the third pulse of this one-rotation detection sensor, the semiconductor laser (hereinafter abbreviated as LD) of the optical writing unit 5 is used. type of laser or LED array,
An optical writing unit (in addition to an LCD array, etc.) may be controlled and driven, and first, optical writing based on seven image data is started to form an electrostatic latent image (d in the figure).

This image data and other image data following this are read by a color image reading device (not shown).

The three-color separated lights of blue, green, and red are read, and image calculation processing is performed based on the intensity level of each color light to write image data of each color of Y, M, C, and Bk. This is what I did.

Apart from this, other color image processing systems (e.g.
The image data may be output from a color facsimile, a personal computer, etc., and the connection interface for this may be individually supported.

By the way, the developing device for visualizing the electrostatic latent image 7.9.11.
13 is normally located at a position where the developing roller 6, 8, 10° 12 does not come into contact with the surface of the photoreceptor belt 1. 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 of the corresponding color, in the example of FIG. 5, the developing roller 6 is pressed to the left. The photoreceptor is then set at a position where it is in a predetermined contact state with the surface of the photoreceptor.

At the same time, in order to provide only that developing device with a developing function, driving of the developing roller and the parts contributing to development is started (m=p in FIG. 6(2)).

Now, since seven latent images have already been formed as described above, the developing roller 6 of the Y developing device is brought into contact with the photoreceptor surface at the appropriate timing and is driven (as shown in FIG. 6 (2)). m] and visualize the 7 images.

The next step is the transfer process, and the roller for switching between contact and separation is moved so that the transfer belt 17 contacts and separates from the surface of the photoreceptor belt 1 at the transfer portion (point T where the drive roller 2 faces the transfer belt 17). 20 vertical positions are switched.

When the transfer operation starts in this way, the transfer belt 17 is driven in the direction of the left arrow as described above, and then the roller 20
is pressed to the upper position to bring the transfer belt 17 into contact with the photoreceptor belt 1 (t in FIG. 6(2)).

Then, at a predetermined timing, the transfer paper 14 is transferred to the transfer roller 1.
The paper is fed at step 5, and then conveyed by registration rollers 16 at the appropriate timing to match the position of the image formed on photoreceptor belt 1.

The conveyed transfer paper S is inserted along the transfer belt 17. It should be noted that static electricity removal from the transfer belt is performed uniformly over the entire surface. Further, at this time, a cleaning process is also being performed by the transfer belt cleaner 25.

Now, when the leading edge of the 7 visualized images reaches 16 points at a predetermined distance from the transfer position point T, the transfer drive motor forward rotation start signal S (h in Fig. 6 (1)) is applied to the transfer drive motor. The information is input to the servo control board 43. However, at the time of the transfer drive motor normal rotation start signal S, it is already rotating in the normal direction, and continues to rotate in the normal direction (j in FIG. 6(1)).

The timing of the transfer drive motor normal rotation start signal S□ is substantially at the time when the leading edge of the transfer paper reaches the RT point, that is, the position 11 in the front direction of the transfer position T point.

This is also the time when the leading edge of the seven images on the photoreceptor belt 1 reaches the point Ts, which is a position 11 in front of the point T.

In the example shown in FIG. 6 (1), this is the point at which the drive roller 2 has rotated four times and further rotated by the number of encoder pulses PO of the PC drive motor 36 from the Y image data writing start timing (see FIG. 6). (1) d, e, f, h).

During this time, the photoreceptor belt 1 is moved to point E (image writing position).
It has moved the distance from to point Ts.

Time t from the time of transfer drive motor normal rotation start signal S,
After the process, the leading edge of the 7 images and the leading edge of the transfer paper both move a distance of 1 □ and reach the transfer position T, and thereafter the 7 images are transferred by the transfer corona 21.

At this time, PC at time t1, the number of pulses of the dynamic motor encoder 37 is Pl, and the number of pulses of the transfer drive motor encoder 40 is PT (e, k in FIG. 6(1)). Here, as the resolution of both encoders, if the belt movement dimension per pulse is the same, then P□=PT
, and if the ratio between the two is α, Pl and PT have values corresponding to the coefficient α.

In this example, the condition will be described below as P,=PTi.

Now, as the seventh image transfer process progresses, the leading edge of the transfer paper separates from the transfer belt 17, passes over the solid line position of the path switching member 26, and advances toward the paper leading edge guide plate 27.

Then, seven more image transfer steps proceed, and the trailing edge of the transfer paper becomes
From the time when the transfer paper passes the point T by a distance of 12, that is, from the time when the transfer drive motor forward rotation start signal S1 is received, the transfer paper moves to lz+t.
When the transfer paper has moved a distance of p (transfer paper size) + 1 □ (time t + tz) (at this time, the transfer paper is 1 shown as S (34)
The transfer drive motor is rotated in the reverse direction by the transfer drive motor reversal signal (at the ly position shown in Figure 6 (1)).
J).

Prior to this reverse rotation, the roller 20 is lowered to the lower position to separate the transfer belt 17 from the belt surface.

Due to reverse rotation, the transfer belt and transfer paper move in the direction of the right arrow.
Make a quick return at a speed of (>VF).

During reverse rotation, the transfer paper and the transfer belt 17 carrying the transfer paper are
An AC power source 23 is connected between the drive roller 18 as a counter electrode and the electrode roller 22 for creating a reversed dark charge pattern.
A voltage is applied and a charge pattern is created (Figure 6 (
2) w).

As a result, a suction force is obtained at the leading end of the transfer paper S and at a portion spaced apart from the transfer belt 17.

At this time, in a short period of time t3, the position is controlled to the right and returned by a distance equal to the distance moved leftward in t□+t2.

During this return, the trailing edge of the transfer paper separates from the transfer belt 17 and advances toward the paper trailing edge guide plate 28, and then accurately returns a predetermined distance so that the transfer paper S (33
) at the dashed-dotted line state position (the paper leading edge position is at point R7) and waits for transfer of the second color M image (time t4).

On the other hand, on the photoreceptor belt 1, the second color M image has already been formed during the transfer of the first color seven images. That is, the formation of an electrostatic latent image by optical writing by controlling and driving the LD based on the M image data starts at the point when the drive roller 2 makes an integer number of rotations (4 in FIG. 6 (1)) from the start of Y image writing.
It starts at the point when it rotates).

Then, in the developing device, the developing roller 6 of the Y developing device 7 contacts and is driven only in the 7th image area, and before the second color M image area arrives, the developing roller 6 is separated from the photoreceptor belt 1 and the driving is stopped. will be stopped.

Instead, the developing roller 8 comes into contact with the photoreceptor belt 1 and is activated (n in FIG. 6(2)) after the image area passes but before the leading edge of the M image area reaches the M image area. Only the image area is visualized into a 1M image.

Next, when the leading edge of the M image reaches the Ts point, that is, as in the case of the 7 images of the first color, from the start timing of writing the M image data, four rotations of the drive roller 2 and a pulse of the encoder 37 with a PC drive motor are generated. When the transfer drive motor has rotated by an amount equivalent to several Po, a transfer drive motor normal rotation start signal S2 is inputted to the transfer servo control circuit 43.

At the same time or with a slight delay, the contact/separation switching roller 20 starts pressing in the upward position direction and is brought into contact with the transfer paper until at least the leading edge of the transfer paper reaches the T point.

Further, at the timing of the start of forward rotation, an AC voltage 23' is applied between the electrode rollers 22' for creating a charge pattern during reverse rotation, using the photoreceptor belt 19 as a counter electrode, to form a charge pattern (FIG. 6 (2)). X). As a result, an adhesion force is obtained for the rear end of the photoreceptor belt 14 at a distance from the photoreceptor belt 17, and at the start of printing, the AC voltage 23' is applied in order to eliminate static electricity from the photoreceptor belt 17. is applied (X in FIG. 6(2)).

Now, at time t from the timing of the transfer drive motor forward rotation start signal s2, the photoreceptor belt 1 becomes like the case of the previous 7 images, the number of pulses of the encoder 37 becomes P□, and the PC belt surface movement distance becomes 1□. ing.

Therefore, during this time t□, the transfer paper S is also started up from the state of speed O to VF= (VP), and during this time, the distance at time t1 from the first color transfer drive motor forward rotation start signal S1 is 11, position control is also performed in this case so that the two coincide.

As a result, here as well, the leading edge of the transfer paper reaches the distance JI at time t.
This means that the 7 images of the first color and the M image of the second color are aligned on the transfer paper.

Thereafter, repeat the same steps as above. That is, the process proceeds to M 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 path switching member 26
The position is switched to the dot-dashed line, and the transfer paper during the transfer process advances toward the fixing device 31. Even when the trailing edge of the transfer paper has been transferred, the transfer drive motor 39 continues to rotate normally and moves the transfer paper to the left. The transported and fixed color prints are delivered to the tray 32 (J v u in FIGS. 6 (1) and (2)
rV).

When performing a repeat operation as in the case of No. 6@, after writing the Bk image data on the first sheet, proceed to write the Y image data on the second sheet as shown in the same figure. The operation control is also the same as from the beginning of the first sheet.

Note that the photoreceptor belt 1 has residual toner removed by a cleaner 29 , residual charge is further removed by a static eliminator 30 , and the photoreceptor belt 1 moves toward the charger 4 .

Finally, after the last color print is delivered to the tray 32 and the photoreceptor belt 1 and transfer belt 17 are cleaned, the operation is stopped and the initial state is restored.

In the above explanation, the order of forming one image is Y, M, C.

Although it has been set as Bk, it is not limited to this.

Furthermore, although the electrostatic latent image formation for each color has been explained using a method in which digitally processed color image data is used for optical writing using an LD, etc., an analog optical image of a normal electrophotographic copying machine is placed at a predetermined position at point E. Similar color recording can also be performed by controlling the timing and position of the image to form an image.

Up to this point, we have explained four-color overlapping recording of Y, M, C, and Bk, but in the case of these two-color or three-color overlapping recording, image formation and transfer of the necessary colors must be performed consecutively. The operation of each part is controlled so that this process is completed in two or three times.

In the case of single-color recording, the developing device for that color is brought into contact and driven until a predetermined number of sheets are completed, the transfer belt 17 remains in contact with the photoreceptor belt 1, and the path switching member 26 is kept in contact with the photoreceptor belt 1. , in the direction of the fixing device 31, is held at a position that guides the transfer paper and performs a recording operation.

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

The developing colors are not limited to the above four colors, and blue, green, red, and other desired colors may be used in combination as required.

The above is the explanation based on the embodiment shown in FIG.

Further, each timing of the transfer belt 17 and the transfer paper S will be explained in detail.

At the position of the transfer paper S (34) where seven images have been transferred, a portion of the transfer paper S on the transfer belt 17 is attracted to the transfer belt 17 by the transfer current of the transfer corona 21. However, the portion of the transfer paper S that is away from the transfer belt 17 has no suction force.

Here, the drive roller 18 rotates in the opposite direction, and the transfer belt moves in the direction of the arrow VR force. At that timing, the AC voltage from the AC power supply 23 is applied to the drive roller 1 via the electrode roller 22.
8 is applied as a counter electrode.

As a result, a slit-shaped charge pattern is formed on the transfer belt 17, and an unequal electric field is generated.

This unequal electric field is caused by the transfer paper S which has lost its adsorption force.
It functions to re-adsorb the portion of the transfer belt 17 that has separated from the transfer belt 17.

In this re-adsorption, as shown in FIG.
A charge pattern is formed by using the transfer paper as a counter electrode, but unless the transfer belt 17 is moved while the transfer paper is in contact with the circumferential portion of the drive roller 18, the attraction force due to the unequal electric field will not be generated.

Next, when transferring the M image, that is, the transfer belt moves in the VF force direction, the transfer paper 5 (33) is at the position shown in the figure, the trailing edge of the transfer paper leaves the driven roller 19, and the next transfer starts. At this time, an AC voltage from the AC power source 23' is applied via the electrode roller 22' to the driven roller 19 as a counter electrode. As a result, the photoreceptor belt 14 is re-adsorbed in the same manner as on the drive side.

In this way, in overlapping transfer, when a slit-shaped charge pattern is formed on the transfer belt 17 when the transfer belt returns, and an uneven electric field is generated, the leading edge of the transfer paper S (34) separated from the transfer belt 17 Equalize the potential of the part that meets the transfer belt again at the time of return and the rear end part of the transfer paper S that remains on the transfer belt without peeling off, and
The adsorption force of the transfer belt 17 is maintained. The rear end is also 2
The same effect can be obtained by maintaining the adsorption force after the ogle and when returning.

Generally, in overlapping transfer, it is necessary to increase the transfer current during the second transfer (second color) by the transfer current during the first transfer (first color) to apply an electric field equivalent to that during the first transfer. This is because the potentials of the transfer paper and the transfer belt increase to some extent during the first transfer.

In this manner, in the transfer of four colors, a considerably large current (actually about 1 mA) must be applied to the fourth color. However, in this example, the electrode rollers 22, 22' and the AC power source 23
．． 23' allows the second, third, and fourth colors to be transferred with the same transfer current as the second color.

When carrying out the present invention, in FIG. 6(1), when a small-sized transfer paper is used, the time point at which the transfer drive motor reverse rotation start signal h is generated is shifted to the right.

(Effects of the Invention) According to the present invention, it is possible to provide an overlapping transfer conveying device that does not cause transfer unevenness due to displacement of transfer sheets on all transfer sheets applied to an image forming apparatus.

[Brief explanation of the drawing]

1 and 2 are diagrams explaining the main parts of the overlapping transfer conveyance device according to the present invention, FIG. 3 is a block diagram suitable for implementing the present invention, and FIG. 4 is a diagram explaining the paper size detection code, FIG. 5 is an overall configuration diagram of a color recording device as an example of an image forming device to which the overlapping transfer conveyance device according to the present invention is applied, and FIG. 6 is a timing chart explaining the basic operation of the same device. FIG. 7 is a drive control diagram. It is a block diagram. 17... Transfer belt, 22.22'... Electrode roller, S, S (33), S (34)... Transfer paper. , Iku), Deputy
People Toru Kabayama (Ishi (and 1 other person) Kata 4 Koku)

Claims (1)

[Claims] 1. While holding the transfer paper on the belt by the adsorption force generated by the unequal electric field charge pattern formed in advance by the electric field charge pattern forming means on the reciprocating dielectric belt, It is used in an image forming apparatus that obtains a desired overlapping image by sequentially overlapping and transferring a plurality of toner images formed on an image carrier onto the same transfer paper, and when the belt moves forward, the leading edge of the transfer paper moves away from the belt. An overlapping transfer transfer device in which the electric field charge pattern forming means is disposed at a first position near the separating position and at a second position near the position where the trailing edge of the transfer sheet separates from the belt during backward movement. After the belt moves forward and transfer is completed, the forward movement end is the position where the belt is switched from forward movement to backward movement in order to transfer the next overlapping image to the transfer paper after this transfer is completed. An overlapping transfer conveyance device characterized by variable control according to the size of transfer paper. 2. In claim 1, when the length of the formation region of the unequal electric field charge pattern after the portion corresponding to the leading edge of the transfer paper formed on the belt when the belt moves is Lac, The forward movement end is determined such that the Lac is larger than the belt circumference from the electric field charge pattern forming means to the portion corresponding to the leading edge of the transfer paper, regardless of the size of the transfer paper. Overlap transfer conveyance device.