JPH04454A - Image forming device - Google Patents

Abstract

PURPOSE:To surely carry a transfer paper without causing deviation by forming a charge pattern on a carrying belt consisting of a dielectric and attracting and holding the transfer paper. CONSTITUTION:The carrying belt 2 consisting of dielectric endless belt is shifted in a direction (a) by driving and rotating a conductive roller 4. Next, an AC voltage is impressed on an electrode 3 provided to be opposed to the grounded roller 4 and in contact with the belt 2 for instance, from a power source 5, so that alternating induction charge is induced to form the charge pattern at a specified pitch. Continuously, the transfer paper 1 is supplied at a point P being a position where the belt 2 is separated from the roller 4 and attracted and carried by non-uniform electric field formed on the belt 2 so as to transfer a toner image on a photosensitive drum 6. The ununiform alternating voltage is impressed by the electrode 3.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an image forming apparatus such as a color copying machine, a color printer, and a color facsimile.

[Conventional technology]

A color copying machine that uses an electrophotographic process, in which toner images of different colors sequentially formed on one photoreceptor are aligned and transferred onto the same transfer paper (sheet), and then fixed to obtain a color copy. It has been known.

In this case, in addition to the method of wrapping the transfer paper around the transfer drum that is in contact with the photoreceptor drum and rotating the transfer drum, and transferring the toner images onto the transfer paper in an overlapping manner, the transfer paper is transported back and forth horizontally multiple times to form the toner image. A method of superimposing transfer is also known, but in this method, an unfixed toner image is placed on the transfer paper, so it cannot be conveyed while being held between a pair of conveyance rollers.

In addition, not only color copying machines but also monochrome (black and white, etc.) copying machines have the risk of the heat from the fixing device degrading the photoconductor, so the transfer position along the photoconductor and the fixing device are quite far apart. , the transfer paper carrying the unfixed toner image must be conveyed between them. As a means for conveying a transfer paper carrying an unfixed toner image as described above, a device that uses an endless conveyor belt and conveys the transfer paper in close contact with the conveyor belt is widely used.

Mechanisms for bringing the transfer paper into close contact with the conveyor belt include (1) air suction method, (2) grip method, (3) electric double layer method, (41 < L-shaped electrode ring-embedded type, etc.) It has been known.

Method (1) uses a fan to create a negative pressure inside the belt and holds the sheet by suction force. This method requires an air pump and an air passage to suck air, making the device bulky. There is a drawback.

In the method (2), a gripper is provided on the belt, and the leading edge of the fed sheet is gripped by the gripper to hold and convey the sheet. This method requires operating time for the gripper, making it difficult to convey the sheet continuously at high speed, and has the problem that conveyance jams may occur due to gripping errors in the gripper.

Method (3) is a method often adopted for transfer belts in electrostatic recording devices, in which an electric double layer is formed on the layer containing the belt and sheet by corona charging, etc., and the sheet is held by electrostatic attraction. It is used for transportation. When transfer conveyance is performed using this method, the sheet is held and conveyed by the belt due to the electric double layer formed by the first corona charge, but once the sheet is separated from the belt, the holding force is lost and the electric charge on the conveyor belt is remains, so the conveyor belt must be charged again after static electricity is removed for the second sheet, which is not practical.

The method (4) is a method used in pen plotters and the like, but it is expensive and difficult to form into an endless belt. In addition, the transfer belt of an electrostatic recording device has
Since there is a buried electrode, there are negative effects such as a decrease in transfer efficiency and uneven transfer.

All of the above methods have problems, so
To deal with this, Japanese Patent Laid-Open No. 5528016 proposes a method in which a charge pattern is created on a conveyor belt and the sheet is held and conveyed by electrostatic attraction.

Further, JP-A-62-1) 6958 discloses a color copying device equipped with a transfer device using a transfer drum, and JP-A-62-145261, JP-A 63-1)
Japanese Patent No. 965 discloses a method of sequentially transferring images of a plurality of colors using a plurality of photosensitive drums as the transfer paper advances.

Further, the transfer paper is held in a transfer paper conveying means that moves in the same direction as the moving direction of the image carrier on which the image is formed, and the transfer paper is brought into contact with the image carrier in the transfer section and is moved forward while the image is imaged. A color image forming apparatus is already known in which an image of each color is superimposed on a transfer paper by repeating the step of moving the transfer paper conveyance means back for the number of developers to be used after transferring the image. For example, there is a device described in Japanese Patent Application Laid-Open No. 62-1) 8366. The apparatus described in this publication reciprocates a transfer paper held by a transfer paper conveyance means to sequentially transfer images in a transfer section of an image carrier. When the transfer paper held by the transfer paper conveying means moves forward to transfer the image, the leading end in the advancing direction separates from the conveying means, and
When the roller is moving back and waiting for the next image transfer, the rear end is separated from the conveying means.

[Problem to be solved by the invention]

The conventional method shown in Japanese Patent Application Laid-Open No. 55-28016 is as follows:
No consideration was given to the feeding position of the sheet relative to the conveyor belt, and although a charge pattern was formed on the surface of the conveyor belt, there was a problem in that a large conveying force could not be obtained.

Further, in the technique disclosed in the above-mentioned Japanese Patent Application Laid-open No. 62-1) 6958, positioning can be easily achieved since, in terms of the principle of positioning, two rotations of the photoreceptor make one rotation of the transfer drum. However, since the leading edge of the paper is clamped, there are problems in that not only is it impossible to transfer an image to the leading edge, but also it is difficult to transfer images to thick paper such as postcards.

Furthermore, JP-A-62-145261, JP-A-63
-1) In the technology disclosed in Publication No. 965, since there are multiple photoreceptors (it is difficult to make the diameters of the photoreceptors the same), a mechanism such as transferring during a whole number of rotations of the photoreceptor is required. , there is a problem that the configuration becomes complicated.

On the other hand, in the apparatus described in Japanese Patent Application Laid-open No. 62-1) 8366, a portion of the transfer paper is temporarily separated from the transfer paper conveying means before and after the image transfer process. This is advantageous in making the transport means small and downsizing the image forming apparatus. However, when a plurality of images are superimposed and transferred, the conveying means and the transfer paper become misaligned, causing color shift in the transferred images and degrading copy quality.

In order to prevent the transfer paper from shifting, it is possible to increase the holding power of the transfer paper by applying an electric charge to the part of the transfer belt that is separated from the transfer paper, but it is difficult to transfer the next image. When transferring, the potential of the belt surface in the previously separated area may differ from the surface potential of other areas, or as the transfer process for each color goes through, it is necessary to apply a gradually larger current. There is a problem that differences in efficiency occur, resulting in density unevenness in the final image.

The first object of the present invention is to reliably transport objects such as sheets with a simple structure without causing any misalignment, based on a system in which a charge pattern is formed on a transport belt made of a dielectric material. An object of the present invention is to provide an image forming apparatus equipped with a small-sized and reliable dielectric conveying device that can perform the following steps.

A second object of the present invention is to provide an image forming apparatus that employs a switchback (reciprocating) transfer method and can obtain good image quality without color shift.

A third object of the present invention is to provide an image forming apparatus that can obtain images without density unevenness.

[Means to solve the problem]

The first purpose is to provide an endless conveyor belt made of dielectric material, a plurality of rollers that span this conveyor belt,
Among these rollers, a grounded conductive roller and a charge pattern forming electrode are opposed to each other across the conveyor belt, and form an alternating charge pattern on the surface of the conveyor belt, and the rotating conveyor belt is separated from the conductive roller. This is achieved by a first means provided with a feeding means made of a dielectric material and provided near a position where the conveyed object is sent out.

Furthermore, in the first means, this can also be achieved by setting the voltage applied to the charge pattern forming electrode to be an alternating current voltage.

Furthermore, in the first means, this can also be achieved by applying a non-uniform alternating voltage to the voltage applied to the charge pattern forming electrode.

The second purpose is to provide an image carrier on which a developed image is formed, and a dielectric belt that transports the transfer paper in order to reciprocate and transfer the developed image multiple times in one layer. ,
In an image forming apparatus that has an electrode that forms an unequal electric field charge pattern on a dielectric belt and conveys a transfer paper by electrostatic adsorption, when the transfer paper is re-adsorbed, the transfer paper is brought into contact with the electrode from above the electrode opposite to the electrode. This is achieved by the second means of inserting it.

The third purpose is to hold a transfer paper on a transfer paper conveying means that moves in the same direction as the moving direction of the image carrier on which the image is formed, and to bring the transfer paper into contact with the image carrier in a transfer section. In an image forming apparatus that overlays an image for each color on a transfer paper by repeating the process of moving the transfer paper transport means backward after transferring an image while moving the transfer paper forward, when the transfer paper is moved back after the transfer process is completed, This is achieved by a third means that includes a charge density pattern forming means for forming an alternating charge density pattern on the surface of the transfer paper transport means that is remote from the transfer paper.

[Effect]

According to the first means, an alternating current or irregular alternating voltage is applied to the charge pattern forming electrode, a corresponding charge pattern is formed on the conveyor belt, and the conveyed object made of a dielectric material is attracted. . A feeding device including registration rollers, conveyance rollers, etc. feeds the object to be conveyed to a position where the conductive roller and the conveyance belt are separated from each other, that is, to a position where the conveyance belts that feed in opposite directions start running parallel to each other or very close to the position.

According to the second means, when the transfer paper is returned, the transfer paper is inserted in contact with the electrodes opposite to the electrodes that form the unequal electric field charge pattern on the dielectric belt, so that the transfer paper is attracted with sufficient adsorption force. This enables high-quality image transfer without misregistration of the transfer paper, that is, with no color misregistration.

Furthermore, according to the third means, when the transfer paper on which the image has been transferred is moved back, an alternating current voltage is applied to the surface of the transfer paper conveying means that is away from the transfer paper to form a charge density pattern. This increases the adsorption force between the transfer paper and the transfer paper conveying means.

〔Example〕

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

FIG. 1 is a block diagram of a dielectric conveying device according to an embodiment of the present invention, and FIGS. 2 and 3 are perspective views centering on the conveying belt portion of the same device.

In FIG. 1, 1 is a sheet, 2 is a conveyor belt consisting of an endless dielectric belt, 3 is a plate-shaped charge pattern forming electrode (hereinafter simply referred to as an electrode), 4 is a grounded conductive roller, and 5 is an electrode. 3, a power supply that applies voltage to 6;
7 is a photosensitive drum that contacts the conveyor belt 2 at the transfer position;
A transfer charger faces the photosensitive drum 6 with the conveyor belt 2 in between, and a registration roller 8 sends out the sheet 1 toward the conveyor belt 2.

The conveyor belt 2 is stretched between a conductive roller 4 and another roller (not shown), and is rotated and transferred in the direction of arrow a by rotationally driving the conductive roller 4 in a counterclockwise direction.

The electrode 3 is provided so that its tip is in contact with the conveyor belt 2 at a position facing the conductive roller 4, and forms a charge pattern on the surface of the conveyor belt 2 as described later.
The grounded conductive roller 4 serves as a counter electrode at that time.

It goes without saying that the position where the sheet 1 is fed by the registration roller 8 is downstream of the contact position of the electrode 3 with respect to the moving direction of the conveyor belt 2.
is supplied to a position P away from the conductive roller 4. Therefore, the registration roller 8 is
It is arranged so that it is supplied to the point.

The sheet 1 held by the conveyor belt 2 is transferred to the photoreceptor drum 6 at the transfer position! At this time, the transfer charger 7
The toner image is transferred onto the sheet 1 when the toner receives the electrostatic attraction force.

FIG. 2 is a perspective view of the conveying device showing the charging state of the conveying belt 2 when an AC voltage of AHz is applied to the electrode 3 from the power source 5.

The conveyor belt 2 is supplied with an A
Alternating induced charges are induced by the alternating voltage at z and the grounded conductive roller 4.

Here, the conveyor belt 2 moves at a constant speed of mm/s in the direction of arrow a.
If the conveyor belt 2 moves at a speed of
A charge pattern is formed in which charge densities -ρ and +ρ are alternately arranged at a pitch of V/Amm. Similar charge patterns are also formed on the back surface of the conveyor belt 2 with a phase shift of 180°.

Due to the charge pattern formed in this way, an unequal electric field is formed near the surface of the conveyor belt 2, and the dielectric sheet 1 is electrostatically attracted to the conveyor belt 2 by this electric field, and is held without shifting. It is carried on the conveyor belt 2 and conveyed.

Here, the sheet 1 is supplied onto the conveyor belt 2 by the above-mentioned P
By conveying the sheet l in contact with the point, that is, the position where the drive roller 4 and the conveyor belt 2 are separated, a large electrostatic attraction force can be obtained.

To explain the specific effect using an experimental example, a frequency of 500
While applying an AC voltage with a peak voltage of 3 KV to the electrode 3, the conveyor belt 2 was driven at a linear speed of 500 mm/S, and the A3
(Vertical) size plain paper is fed to the conveyor belt 2, and when the contact length with the conveyor belt reaches 100 mm, attach a spring gauge to the rear end of the sheet 1 as shown in Fig. 4 to increase the holding force. As a result of measuring the tensile strength, a tensile yield strength of 2 kgf or more was measured.

On the other hand, when the charging side is charged to the same polarity as the applied voltage in corona charging to form an electric double layer, or as shown in FIG. In the arrangement position of the registration rollers 8 such that the sheet 1 is supplied to the point P' on the downstream side, the sheet 1-
The holding force of the conveyor belt 2 against the belt 1 is significantly reduced.

FIG. 3 shows a charge pattern formed on the conveyor belt 2 by the power supply 5 that outputs a non-uniform alternating voltage. A charge pattern is formed in which the pitch of the charged portion and the (+) charge is uneven depending on the location, and the same pattern with the opposite polarity as the front surface is formed on the back surface. However, in this case as well, the same sheet holding and conveying ability as in the embodiment shown in FIG. 2 can be obtained.

Note that the electrode 3 is not limited to a blade-like one, but may also be a small-diameter metal roller. Further, the applied voltage may be an AC voltage with a DC component superimposed thereon.

Furthermore, the conveyance device of the present invention is capable of holding and conveying not only a thin sheet such as a transfer paper but also any dielectric member that has a large plane and can be supported on this plane.

Next, a second embodiment will be described.

FIG. 6 is a block diagram of one embodiment of the present invention, and FIG. 7 is a block diagram showing the operating state of the same embodiment.
C) Belt (image carrier), 12 is a PC drive roller, 13
is a PC driven roller, 14 is a charger, 15 is an optical writing unit, 16 is a developing roller (Y: yellow), 17 is a developing unit (Y) with built-in developing roller (Y) 16, 18 is a developing roller (M: magenta), 19 is the developing roller (M)
Developing unit I-(M) with built-in 18, 20 with developing roller (C Nijian), 21 with developing roller (C) 20 with built-in developing unit (C), 22 with developing roller (BK Niblack), 23 with developing roller A developing unit (BK) with a built-in developing roller (BK) 22, 24 is a transfer paper, 25 is a paper feed roller, 26 is a registration roller, 27 is a transfer paper conveyance belt (derivative belt), 28 is a transfer drive roller, 29 is a Transfer driven roller, 30 is a contact/separation switching roller, 31 is a transfer device, 3
2a and 32b are electrode rollers having the transfer driving roller 28 and the transfer driven roller 29 as opposing electrodes, respectively; 33a;
33b is an AC power supply for the electrode rollers 32a and 32b, 34 is a counter electrode plate, 35 is a transfer heat cleaner, and 35a is a transfer
・Rollers provided on the root cleaner 35, 36 is a path switching member, 37 is a paper leading edge guide plate, 38 is a paper trailing edge guide plate, 39 is a PC heating cleaner, 40 is a PC heating 1
), 41 is a fixing unit, 42 is a paper discharge tray, 43 is a transfer sheet for return, and 44 is a transfer sheet for forward.

FIG. 8 is an explanatory diagram of the drive control system of this embodiment, with 46
is a PC drive motor, 47 is an encoder for the PC drive unit 46, 48 is a one-rotation sensor, 49 is a drive motor for the transfer belt 27, 50 is an encoder for the drive motor 49, 51 is a main board, 52 is a PC Servo control board, 5
3 is a transfer servo control board.

Next, the operation of the above embodiment will be explained with reference to the timing chart of FIG.

When the print switch is turned on (a in FIG. 9), the PC drive roller 12 rotates clockwise by the PC drive motor 46, and the photoconductor belt 1) rotates in the direction of the arrow in FIG. 6 at a linear speed of v2. Rotate. At the same time, the transfer paper conveyance belt 27 (
The drive motor 49 of the transfer belt (hereinafter abbreviated as the transfer belt) first starts normal rotation (see the g and h signals and the speed diagram of j in Fig. 9), and then rotates in the direction of the left arrow at a linear speed of V. move. In addition,
■Ah■.

It is controlled and driven to rotate under the following conditions.

Now, photoreceptor belt 1) (hereinafter abbreviated as PC belt)
The static electricity is removed by the static eliminator 40, and the entire surface is uniformly charged by the charger 14, and the process is performed so that the following conditions are satisfied.

(2) The static eliminator 40 irradiates light or applies static eliminating corona to the surface of the PC belt 1) from which toner has been previously removed by the PC belt cleaner 39.
The surface potential of the C-belt 1) is set to approximately OV.

■, In the case of negative-positive process, the toner is PC belt 1
) The entire surface of the PC helmet 1) must be uniformly charged by the charger 14 since it adheres to uncharged areas on the surface.

(2) The charger 14 performs uniform charging by corona discharge, but the discharge generates a slight 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 1) and impair the clarity of the image.

Therefore, the influence of ozone is eliminated by blowing air from behind the charger 14 using a fan (not shown) or by suctioning it.

By the way, a one-rotation sensor 48 for detecting rotation is installed on the shaft of the PC drive roller 12, and a detection pulse is output every time the PC drive roller I2 makes one rotation (d in Fig. 9). .

In the example shown in FIG. 9, the semiconductor laser (hereinafter abbreviated as LD) of the optical writing unit 15 is controlled and started to be driven at the timing of the third pulse of this one-rotation detection sensor 48. However, other types of lasers or L
Other optical writing units such as an ED array or an LCD array may be used), and first, optical writing is started based on seven image data to form an electrostatic latent image.

This image data is read by a color image reading device (not shown), for example, as Blue, Green, and R.
ED's three color separated lights are read, and based on the intensity level of each color light, image calculation processing is performed to determine Y, M,
This is image data written in each color of C and BK.

Apart from this, other color image processing systems (e.g. color facsimiles, word processors).

It may also be image data output from a personal computer (such as a personal computer). The connection interface for this purpose may be individually supported.

By the way, the developing unit 17.1 that visualizes the electrostatic latent image
9, 21.23 are usually developing rollers 16.1B, 20
．． 22 is in a position where it does not touch the surface of the PC helmet 1).

Then, the developing unit of the corresponding color is pressed to the left in FIG.
) is set at a position where each developing roller 16.18, 20.22 comes into contact with the surface by a predetermined amount.

At the same time, in order to make only the corresponding developing unit have a developing function, driving of the developing roller and the parts contributing to development is started (m-, p in FIG. 9).

Now, first, seven latent images have been formed, so the developing unit (Y) 17 is applied to that surface at the right time.
is brought into contact with the surface of the PC belt 1) and driven (m in FIG. 9), and seven images are visualized.

The next step is the transfer process, in which the transfer belt 27 is moved to the transfer section (PC
The vertical position of the contact/separation switching roller 30 is switched so that it contacts and separates from the surface of the PC belt 1) at point T) of the drive roller 12.

First, when the printing operation starts, the transfer belt 27 is driven in the direction of the left arrow as described above, and then the contact/separation switching roller 30 is pressed to the upper position to move the transfer belt 27 to the PC.
Contact the belt 1).

(t in Figure 9).

Then, at a predetermined timing, the transfer paper 24 is transferred to the paper feed roller 2.
The paper is fed at step 5, and then conveyed by registration rollers 26 at a timing that matches the position of the image formed on the surface of the PC belt 1).

The conveyed transfer paper 24 is inserted along the transfer belt 27.

Note that the charge on the transfer belt 27 is uniformly removed over the entire surface. Further, at this time, a cleaning process is also being performed by the transfer belt cleaner 35.

Now, when the leading edge of the seven visualized images reaches point T8, which is a predetermined distance from the transfer position point T, the transfer drive motor forward rotation start signal SI (h in FIG. 9) is sent to the transfer servo control board of the drive motor 49. 53. However, at the time of S3, it is already rotating in the normal direction, and continues to rotate in the normal direction (j in FIG. 9).

The timing at S2 is substantially when the leading edge of the transfer paper 24 reaches the point R7, that is, the position Il in the front direction of the transfer position T, and also at the point 7 of the PC belt 1).
This is the point in time when the leading edge of the image reaches the WT8 point l, which is in front of the T point.

In the example shown in FIG.
The number of pulses P of the encoder 47 of the drive motor 46. This is the point at which the robot has rotated a considerable amount (d, e, f, h in Figure 9). During this time, PC HELT 1) has moved by the distance from point E (image writing position) to point T5.

After time t1 has elapsed from point 81, the leading edge of the 7th image and the leading edge of the transfer paper 24 both move the distance 1) and reach the transfer position T, and thereafter, the 7th image is transferred by the transfer device 31. be exposed.

At this time, the number of pulses of the encoder 47 at time t is Pl
, the number of pulses of the encoder 50 of the drive motor 49 is P T
+ (e, k in Figure 9). Here both encoders 4
With a resolution of 7.50, if the belt movement dimensions per pulse are the same, then P I = P
If T + and the ratio of both is α, then P, and P T
I becomes a value corresponding to the coefficient α. In this example, P
+ ” This will be explained below as a condition for P T +.

Now, as the seventh image transfer process progresses, the leading edge of the transfer paper 24 separates from the transfer belt 27, passes over the solid line position of the path switching member 36 relative to the transfer paper 24, and advances in the direction of the paper leading edge guide plate 37.

Then, seven more image transfer steps proceed, and when the trailing edge of the transfer paper 24 passes the point T by a distance of 12, that is, S
When the transfer paper 24 has moved a distance of C1+ + lP (transfer paper size) + 12 from time 9 (time 1.+12, at this time, the transfer paper 24 is at the position indicated by the dashed-dotted line 44), the transfer drive is started. The drive motor 49 is activated by the motor reverse signal.
(i, j in Figure 9).

Prior to this reverse rotation, the contact/separation switching roller 30 is lowered to the lower position to separate the transfer belt 27 from the PC belt surface. The reverse rotation causes the transfer belt 27 and the transfer paper 24 to quickly return in the direction of the right arrow at a speed of VR (>VF). During the reverse rotation, the transfer paper 24 and the transfer belt 27 on which the transfer paper 24 is mounted, with the transfer drive roller 28 as a counter electrode,
During the reverse rotation, an AC voltage is applied by the power source 33 between the electrode rollers 32a for forming a charge pattern to form a charge pattern (W in FIG. 9). As a result, the suction force is obtained for the portion of the leading end of the transfer paper 24 that is spaced apart from the transfer belt 27. At this time, during the short return time of t3, 1. +12
The position is controlled to the right by a distance equal to the distance moved to the left by , and the position is returned to the original position.

During this return, the rear end of the transfer paper 24 is separated from the transfer belt 27 and advances toward the paper rear end guide plate 38.

Then, the transfer paper 24 accurately returns a predetermined distance, stops at the one-dot chain line state position of the stop position 43 (paper leading edge position is at point R7), and waits for transfer of the second color M image (time t4). )do.

On the other hand, in PC HELT 1), the second color M image is already being formed even 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 from the start of Y image writing.
The process starts when the PC drive roller 12 has made an integral number of rotations, in the case of FIG. 9 of this embodiment, when it has made four rotations.

Then, the developing unit (Y) 17 is contacted and driven only for the 7th image area, and before the second color M image area reaches the developing unit (Y) 17, the developing unit (Y) 17 is connected to the PC.
It separates from the surface of the belt 1) and the drive is stopped.

Instead, the developing unit (M) 18 develops the PC health 1 after passing the 7 image areas and before the leading edge of the M image area arrives.
-1) is contacted and driven (n in Fig. 9), 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 T3 point, that is, as in the case of the 7 images of the first color, from the M image data writing start timing, the PC drive roller 12 is rotated 4 times and the encoder 47 of the PC drive motor 46 is pulsed. Number P. At the point when the transfer drive motor has rotated by a certain amount, the transfer drive motor forward rotation start signal S is sent.
2 is input to the transfer servo control board 53. At the same time or with a slight delay, the contact/separation switching roller 30 starts pressing in the upward position direction and is brought into contact with the transfer paper 24 at least until the leading edge reaches the T point. Also, at the timing of the start of normal rotation, the transfer driven roller 29 is used as a counter electrode, and an AC current is applied between the electrode roller 32b for creating a charge pattern during operation.
A voltage is applied by a voltage source 133b to form a charge pattern (X in FIG. 9). As a result, the suction force is obtained at the rear end of the transfer paper 24 at a portion spaced apart from the transfer belt 27.

Furthermore, at the start of printing, an AC voltage is applied to the electricity a33b in the same manner as described above in order to eliminate static electricity from the transfer belt 27 (the ninth
(X in the diagram).

Now, at time t from the timing of S2, PC HELP 1-1
), the number of pulses of the encoder 47 of the PC drive motor 46 is equal to the surface movement distance l of the P1 PC belt 1), as in the case of the previous seven images.

Therefore, the transfer paper 24 also rises from a speed of 0 to VF (=VF) during this period of Ll, and during this period, the distance from the first color S to the time t1 Nii l
In this case, position control is also performed so that the two match.

As a result, 1. So the tip of the transfer paper 24 is 1! ,
This means that the seven images of the first color and the M image of the second color are aligned on the transfer paper.

Thereafter, the same steps as those described above are repeated.

Namely, M image transfer, transfer paper quick return, and C
Proceed to image data writing, C development, C image transfer, transfer paper quick return, BK image data including sound, BK development, and BKK image transfer.

Next, referring to FIG. 7, the process after BKK image transfer will be explained.

In the BKK image transfer process, the paper path switching member 36 moves to one point #Jf! The transfer paper, which has been switched to the position and is undergoing the transfer process, moves toward the fixing device 41 and even after the transfer of the rear end of the transfer paper 24 is completed, the drive motor 49 continues to rotate in the normal direction and transports the transfer paper 24 to the left. , and the fixed color print is carried out to the paper output tray 42 (j, u, v in Fig. 9).
).

When performing a repeat operation as in the case of FIG. 9, after recording the sound of the BK image data on the first sheet, proceed to write the Y image data on the second sheet as shown in FIG. The operation control of the transfer belt 27 is also carried out in the same manner as from the beginning of the first sheet.

Note that the PC belt 1) has residual toner removed by a PC belt cleaner 39, residual charge is further removed by a static eliminator 40, and then moves toward the charger 14.

Finally, after the last color print is delivered to the paper ejection tray 42 and the PC belt 1) and transfer belt 27 are cleaned, the operation is stopped and the system returns to its initial state.

In the above explanation, the order of image formation is Y, M, CBK,
Furthermore, although the arrangement of the developing units 17, 1, 9, and 2123 has been described as Y, M, C, and BK from the top, the arrangement is not limited to this.

In addition, although the electrostatic latent image formation for each color has been explained using a method in which digital image processing of each color image data is optically written using an LD, etc., an analog optical image of a normal electrophotographic copying machine is placed at the E point position at a predetermined timing. Similar color recording can be performed by controlling the position and forming 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 twice in succession. The operation of each part is controlled so that this process is completed in , or three times.

In addition, in the case of single-color recording, the developing units 17, 19, 21, and 23 of that color are contacted and driven, and the transfer belt 27 remains in contact with the PC belt 1) until a predetermined number of sheets are completed. Further, the paper path switching member 36 is held at a position where it guides the transfer paper toward the fixing device 41 and performs a recording operation.

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

Furthermore, the operation timings of the transfer belt 27 and the transfer paper 24 will be explained in detail.

At the transfer paper position 44 where seven images have been transferred, a portion of the transfer paper 24 on the transfer belt 27 is attracted to the transfer belt 27 by the transfer current of the transfer device 31. However, the portion of the transfer paper 24 that is away from the transfer belt 27 has no suction force.

Here, the transfer drive roller 28 rotates in the reverse direction, and the transfer belt 27 moves in the direction of the arrow vR force. AC type m at that timing
33a is applied to the transfer drive roller 28 as a counter electrode via the electrode roller 32a. This forms a slit-shaped charge pattern on the transfer belt 27 and generates an unequal electric field. This unequal electric field can re-adsorb the portion of the transfer paper 24 that has lost its adsorption force and is away from the transfer belt 27.

In this re-adsorption, as shown in FIG. 6, a charge pattern is formed using the transfer drive roller 28 as a counter electrode. If it is not moved, the attraction force due to the unequal electric field will not be generated. FIG. 10 shows a configuration in which a suction force can be obtained, and FIG. 1) shows a configuration in which no suction force is generated.

Next, when transferring the M image, that is, the transfer belt 27 moves in the V direction, the transfer paper 24 is at the stop position 43, and the transfer paper 2
When the rear end portion of the transfer roller 4 is separated from the transfer driven roller 29 and the next transfer starts, an AC voltage from the AC power source 33b is applied to the transfer driven roller 29 as a counter electrode via the electrode roller 32b.

As a result, the transfer paper 24 is re-adsorbed in the same manner as on the driving side.

In the above embodiment, when a slit-shaped charge pattern is formed on the transfer belt 27 when the transfer belt returns in overlapping transfer and an uneven electric field is generated, the leading edge of the transfer paper 24 that has separated from the transfer belt 27 will be removed when the transfer belt returns. The electric potential of the portion where the transfer belt meets again and the rear end portion of the transfer paper 24 remaining on the transfer belt 27 without being peeled off is made uniform, and the attraction force between the transfer paper 24 and the transfer belt 27 is maintained. The rear end also maintains the suction force after the second color in the same way as when returning.

Furthermore, in general, in overlapping transfer, at the time of first transfer (first color)
It is necessary to make the transfer current for the second transfer (second color) larger than the transfer current for applying an electric field equivalent to that for 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, according to this embodiment, the second, third, and fourth colors can be transferred using the same transfer current as the second color using the electrode rollers 32a, 32b and the AC power supplies 33a, 33b.

Note that FIG. 1O and FIG. 1) are explanatory diagrams of main parts showing the adsorption state of this embodiment.

Next, a third embodiment will be described.

FIG. 12 is a configuration diagram of the color image forming apparatus according to this embodiment. The difference from the color image forming apparatus shown in FIG. The two points are that the electrode roller 32 and the AC power source 33 are integrated.

After the forward movement of the transfer paper PA having the length IP, its leading end is connected to the paper leading edge guide plate 37, and its intermediate part is connected to the path switching member 3.
6, transfer the length “a” of the rear end to the transfer belt 27.
be placed above. The transfer paper PB that has moved backward is positioned with its leading end on the transfer belt 27 and its rear end on the paper leading edge guide plate 37.

The timing of forming the charge density pattern on the transfer belt 27 will be explained in detail.

At the position where the transfer of the first color (yellow image) has been completed and the backward movement has been completed, only the length raJ of the transfer paper PA rests on the transfer belt 27, and is attracted by the attraction force of the transfer corona of the transfer device 31. ing. Therefore, the IA'P-aJ portion of the transfer paper separated from the transfer belt 27 has no suction force.

Even when the transfer belt 27 starts to move back and the transfer paper that has been separated until now joins the transfer belt 27, the suction force in this part is weak, and the transfer paper is moved back to the standby position (PB) where the back movement has ended.
In this case, since there is no adsorption force between the transfer paper PB and the transfer belt 27, the transfer paper shifts with respect to the transfer belt 27,
Accurate overlapping transfer cannot be expected.

Therefore, when the transfer drive roller 28 is reversely rotated and the transfer belt 27 is moved back at the speed VR, the AC voltage from the AC power source 33 is applied to the electrode roller 32 with the transfer drive roller 28 as a counter electrode. Apply via. As a result, a positive and negative charge density pattern is formed on the surface of the transfer belt 27 at a portion corresponding to "pP-aJ" of the transfer paper PA, and an unequal electric field is generated. Therefore, when the transfer belt 27 moves back at a rapid speed,
The transfer paper is held without shifting its holding position.

In the illustrated embodiment, the electrode that applies charge to the transfer belt 27 has a roller shape, but it may also have a blade shape.

[Effects of the Invention] As described above, according to the invention according to claims 1 to 3, an alternating ÷←← charge pattern is formed on the surface of the conveyor belt, thereby holding the sheet, and thereby increasing the speed of the conveyor belt. During rotation, the conveyed object is supplied close to the position away from the conductive roller, which improves reliability and ensures that the conveyed object is electrostatically attracted to the conveyor belt and conveyed. can. Furthermore, since the charge pattern does not increase the amount of charge on the conveyed object itself, there is no influence from the charging of the dielectric conveyed object.

Further, according to the fourth aspect of the invention, even when the transfer paper is reciprocated, the transfer paper can be sufficiently held by the electrodes forming the unequal electric field charge pattern and the counter electrode. It is possible to provide a color recording device that performs high-quality image transfer without color shift.

Furthermore, according to the fifth aspect of the invention, alternating charge density patterns are formed on the surface of the transfer paper conveying means (transfer belt) that is away from the transfer paper when the transfer process is completed, so that the transfer paper and the transfer belt The relative position between the two will not shift. Therefore, there is no shift in the transfer position of the images, and good overlapping images can be obtained.

Furthermore, since the surface potential of the transfer belt does not increase significantly during each transfer process, there is no need to increase the transfer current multiple times, and there is no image disturbance.

By forming the charge density pattern that attracts the transfer paper to the transfer paper conveyance means as described above, the effective length of the transfer belt can be shortened, and the image forming apparatus itself can be downsized.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a dielectric conveying device according to an embodiment of the present invention, Figs. 2 and 3 are perspective views of the same device, centering on the conveying belt section, and Fig. 4 shows the suction force of the conveying belt. FIG. 5 is an explanatory diagram showing an example of an inappropriate sheet feeding position. FIG. 6 is a configuration diagram of an image forming apparatus according to a second embodiment of the present invention. FIG. 7 is a diagram showing an example of an inappropriate sheet feeding position. Fig. 8 is an explanatory diagram of the drive control system of the embodiment;
The figure is a timing chart of the same example, Fig. 10, Fig. 1)
The figure is an explanatory view of the main parts showing the suction state of the same embodiment, and FIG. 12 is a configuration diagram of an image forming apparatus according to the third embodiment. ■... Sheet, 2... Conveyance belt, 3... Charge pattern forming electrode, 4... Conductive roller, 8... Registration roller, 1)... Image carrier, 24... transfer paper,
27... Dielectric belt, 28.29... Counter electrode,
322.3 Figure Figure Figure Figure

Claims (5)

[Claims] (1) An endless conveyor belt made of a dielectric material, a plurality of rollers that span this conveyor belt, and a grounded conductive roller among these rollers that faces each other across the conveyor belt, and is placed on the surface of the conveyor belt. A charge pattern forming electrode that forms an alternating charge pattern, and a feeding means made of a dielectric material that is provided near a position where the rotating conveyor belt separates from the conductive roller and feeds out the conveyed object. Features of the image forming device. (2) The image forming apparatus according to claim 1, wherein the voltage applied to the charge pattern forming electrode is an alternating current voltage. (3) The image forming apparatus according to claim 1, wherein the voltage applied to the charge pattern forming electrode is a non-uniform alternating voltage. (4) an image carrier on whose surface a developed image is formed;
It has a dielectric belt that transports the transfer paper in order to reciprocate and transfer the visualized image multiple times, and electrodes that form an unequal electric field charge pattern on the dielectric belt. An image forming apparatus that performs electrostatic adsorption, comprising means for inserting the transfer paper in contact with it from above an electrode opposite to the electrode when the transfer paper is re-adsorbed. (5) A transfer paper is held by a transfer paper conveying means that moves in the same direction as the moving direction of the image carrier on which the image is formed, and while the transfer paper is moved forward in contact with the image carrier in the transfer section. In an image forming apparatus that overlays an image for each color on a transfer paper by repeating the process of moving the transfer paper transport means backward after transferring an image, when the transfer paper is moved back after the transfer process is completed, the transfer paper An image forming apparatus comprising a charge density pattern forming means for forming an alternating charge density pattern on a surface of a transfer paper conveying means that is separated from the transfer paper conveying means.