JPH09212009A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device which maintains satisfactory image-quality free from transfer omission regardlessly of conditions of a recording material and environmental conditions. SOLUTION: An Hi-side high voltage power source 100 and an Lo-side high voltage power source 101 are connected to an attraction electrifier 5C inside a transfer sheet 55S and opposite an attraction roller 5G with the transfer sheet 55S of a transfer drum 5 between them, so that they can be switched with a switching means 102. In the beginning part of an attracting operation, the front end of the recording paper P is strongly attracted to the transfer sheet 55S by the application of an attracting bias to the electrifier 5C from the Hi-side high voltage power source 100. In the latter part of the attracting- operation, the latter half of the recording paper P, which follows the front end, is weakly attracted by the application of an attracting bias to the electrifier 5C from the Lo-side high voltage power source 102.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a printer or a facsimile copying machine using an electrophotographic system, and more particularly to a multiple image forming apparatus.

[0002]

2. Description of the Related Art An apparatus for performing recording by an electrophotographic method or the like while conveying a recording medium such as a recording paper, for example, an electrophotographic image forming apparatus is generally known as having a structure as shown in FIG.

The image forming apparatus shown in FIG. 12 is roughly divided into an image input section 90R and an image output section 90P.
The image input unit 90R is a device for inputting image information to be recorded, performing various kinds of processing to obtain an image signal, and then sending the image signal to the image output unit 90P.

The image output section 90P is an image forming section 91 such as a photoconductor for forming a recorded image according to an image signal.
A plurality of paper feed units 92A, 92B and 92C for stacking the recording paper P and sending it one by one, and the recording paper sent from the paper feed unit to the registration roller 9
6, the registration roller pre-conveying section 97A including the registration roller pre-conveying roller (hereinafter, referred to as pre-registration conveying roller) 97A, and the recording sheet sent from the registration roller 96 on the surface thereof by the action of the suction section 99. A transfer drum 93 that conveys an image onto a recording sheet while conveying it while holding the image, a fixing unit 94 that fixes the image recorded on the recording sheet, and all operations of devices in the apparatus including these. And a control unit 95 for controlling

Next, the recording operation will be described in detail step by step. When the operation of the apparatus is started, first, the paper feeding unit 92
One recording sheet P as a recording material is fed from any one of A, 92B, and 92C, and then is fed to the registration roller 96 by the pre-registration transport roller 97A. At this time, the registration roller 96 has stopped. The pre-registration transport roller 97A continues the transport of the recording paper for a short period of time after the leading edge of the recording paper hits the stopped registration roller 96, and performs a predetermined loop on the recording paper (hereinafter referred to as a pre-registration loop). To form. After that, the registration roller 9
6 and the pre-registration transport roller 97A rotate to feed the looped recording paper P onto the transfer drum 93 and form an image at a predetermined position on the recording paper.

The image input section 90R starts its operation with the image formation start signal as a reference, sequentially inputs image information and converts it into an image signal for recording, and at the same time, the image forming section 91 of the image output section 90P receives the image information. Output. In the image forming section 91, a toner image is formed on the photosensitive drum 93 by processes such as latent image formation and development corresponding to the image signal.

The recording paper P sent out onto the transfer drum 93
By the action of the suction roller 99A of the suction unit 99,
While being electrostatically adsorbed and held on the carrier medium 100 made of a thin dielectric film or the like forming the outer peripheral surface of the transfer drum 93, the image forming unit 91 is rotated as the transfer drum 93 rotates.
The image is transferred to the image transfer area T opposite to. While the recording paper P conveyed to the image transfer area T passes therethrough,
The toner image formed by the image forming unit 91 is transferred onto the surface of the recording paper P, and the image is recorded.

The recording paper P on which an image has been recorded is conveyed to the fixing unit 94 side as the transfer drum 93 rotates, where it is separated from the transfer drum 93 and sent to the fixing unit 94. Then, the fixing unit 94 applies heat and / or pressure to the recording paper P to fix the toner image on the recording paper P, and then the recording paper P goes out of the image forming apparatus through the paper discharge unit. Is discharged.

Next, the general structure of the suction portion 99 will be described in detail with reference to FIG. The recording paper P sent out from the registration roller 96 is guided between the pair of opposed suction guides 99R and 99L, and is transferred to the transfer drum 9
3 reaches the adsorption position. Both guides 99R and 99L are
In order to allow the leading edge of the recording paper P to smoothly enter the suction position without fluttering, it is preferable that the distance between them be as narrow as possible. At the suction position, the suction roller 99A is arranged outside the transport medium 100.
A is grounded. A suction charger 99B, which is a corona charger, is provided inside the transport medium 100 so as to face the suction roller 99A.

In synchronism with the timing when the recording paper P enters the suction position, a high voltage is applied to the suction charger 99B to generate corona and the suction roller 99A is brought into contact with the conveying medium 100. As a result, electric charges are generated in the recording paper P and the conveyance medium 100 sandwiched between the conveyance medium 100 and the suction roller 99A, and the recording paper P is electrostatically adsorbed to the conveyance medium 100.

[0011]

However, when the recording paper P enters the suction position, the widthwise central portion of the recording paper P comes before the both ends, and the conveying medium 100 and the suction roller 99A.
There is a behavior in which it reaches the nip portion formed by and adsorption starts, and thereafter both ends enter the nip portion and adsorption at both ends starts.

In such a case, the recording paper P is shown in FIG.
As shown in (a), the central portion in the width direction is attracted to the transport medium 100 in a state of being convex in the traveling direction, and as the adsorption progresses, the excess portion of the recording paper P is wrinkled to the central portion as a wrinkle, and recording is performed. At the trailing edge of the paper P, as shown in FIG. 14B, the central portion bulges upward with respect to the surface of the recording paper and rises from the transport medium 100. This is because the recording paper P has a strong suction force to the transport medium 100, and the excess portion of the recording paper P is not corrected at the trailing end portion. As a result, there is a problem that the transfer omission occurs at the trailing edge of the recording paper P.

The phenomenon of swelling of the recording paper P is particularly caused when the recording paper is highly moistened under a high humidity condition or in a "wavy" state in which the circumference of the recording paper is stretched compared to the central portion in the double-sided copy mode. Is remarkable. When there is a wave,
In many cases, even if the front ends enter the central portion and both end portions, the transfer omission occurs.

SUMMARY OF THE INVENTION In view of the above problems, an object of the present invention is to provide an image forming apparatus which always maintains good image quality without causing transfer defects regardless of the conditions of recording materials and environmental conditions.

[0015]

The above object is achieved by an image forming apparatus according to the present invention. In summary, the present invention relates to a recording material carrier that carries and conveys an adsorbed recording material, an image forming unit that forms an image on the recording material carried by the recording material carrier, and the recording material carrier. In an image forming apparatus having an adsorbing means for adsorbing a recording material on a body, an adsorbing force for adsorbing the recording material on the recording material carrying member is changed in a conveying direction of the recording material or is orthogonal to a conveying direction of the recording material. The image forming apparatus is characterized by changing the direction. According to the present invention, the change of the suction force can be performed according to the size, thickness, material of the recording material, the use environment, or the single-sided or double-sided copy mode.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of an image forming apparatus according to the present invention will be described below in more detail with reference to the drawings.

FIG. 1 is a sectional view showing the construction of an embodiment of the image forming apparatus of the present invention. The image forming apparatus has a digital color image reader unit in the upper part and a printer unit in the lower part.

In the reader section, the original 30 is placed on the original table glass 31 and is exposed and scanned by the exposure lamp 32. Then, the reflected light image from the original 30 is condensed by the lens 33 on the full-color sensor 34 to obtain a color-separated image signal. This signal passes through an amplifier circuit (not shown), undergoes various processing in a video processing unit (not shown), and is then sent to the printer unit.

The printer section has the following configuration. A photosensitive drum 1 as an image bearing member is rotatably supported at its center, and is rotationally driven in the arrow direction by a motor (not shown). A pre-exposure lamp 11, a primary charger 2, an exposure optical system 3 such as a laser, a potential sensor 12, a developing device 4, a light quantity detecting means 13 on the drum, which faces the outer peripheral surface of the photosensitive drum 1 along the rotation direction thereof. A transfer drum 5 as a recording material carrier and a cleaning device 6 are sequentially arranged.

The pre-exposure lamp 11 and the primary charger 2 provide the surface of the photosensitive drum 1 with a uniform charge amount. Then, the optical system 3 exposes the light beam E, such as a laser beam, which is modulated according to the recorded image signal, onto the photosensitive drum 1 via the polygon mirror 3A, the lens 3B, etc., and the surface of the photosensitive drum 1 is exposed. A latent image is formed.

The electrostatic latent image formed on the photosensitive drum 1 is developed by the developing device 4 and visualized as a toner image. The developing device 4 includes yellow, cyan, magenta,
Four developing devices 4Y, 4C, 4M, and 4K, which respectively contain black developer (toner), are arranged side by side, and these four developing devices 4Y, 4C, 4M, and 4K respectively include eccentric cams 24Y. , 24C, 24M, 24K operation,
It is configured to be movable so as to selectively come close to the photosensitive drum 1.

A transfer drum 5 is installed on the left side of the photosensitive drum 1 in the figure, and an area where the transfer drum 5 and the photosensitive drum 1 face each other is such that the toner image formed on the photosensitive drum 1 is recorded on a recording paper. It is an image transfer area for transfer. The portion where the cleaning device 6 is installed on the downstream side of the image transfer area is a cleaning portion of the photosensitive drum 1, and the toner left on the photosensitive drum 1 without being transferred to the recording paper is scraped off by the cleaning device 6. Then, the surface of the photosensitive drum 1 is cleaned.

The image forming apparatus has upper, middle, and lower three-stage cassette paper feeding devices (paper feeding units) and one manual paper feeding device. Of these, the middle-stage paper feeding unit 40 will be described (the upper and lower tiers are substantially the same as the middle tier, and the description thereof will be omitted). The paper feeding unit 40 includes a cassette 41 for storing the recording paper P as a recording material. A pickup roller 42 for feeding the recording papers P one by one from the cassette 41, and feed rollers 43A, 43B, and conveyance rollers for conveying the recording papers P fed from the pickup roller 42 to the transfer / conveyance unit 50. 45
It is composed of A, 45B, 45C and a paper guide rail.
The manual paper feeding device includes a manual paper feeding tray 41T, a paper feeding roller 42M, and a separation pad (not shown).

The transfer / transport unit 50 is roughly divided into a transfer section 50A and the transfer drum 5. The transport unit 50A will be described with reference to FIG. 2. The transport unit 50A includes guides 48A, 48B, 48C, 48D, and 48E for guiding the recording paper P inherited from the paper feeding unit 40, and transport rollers 46A and 46B. , 46C, pre-registration transport rollers (pre-registration roller transport rollers) 47A, 47B, and registration rollers as recording material supply means for feeding the recording paper P to the transfer drum 5 at the image forming timing of the image forming section. The pair 44 and suction guides 48F and 48G as guide means for guiding the recording paper P at the time of feeding it out.

The conveying rollers 46A, 46B and 46C have a curling function. In order to change the traveling direction of the recording paper P by bending the recording paper P into a curved shape indicated by R in the figure at the guides 48B and 48D, the guides 48B and 48D have a curved shape and sway in the arrow direction. It is movably supported (hereinafter referred to as swing guides 48B and 48D). This is to secure a space for a loop of the recording paper P that occurs when the leading end of the recording paper P is temporarily stopped by the registration roller 44.

A mechanism for releasing the pressure contact is added to the registration roller 44. FIG. 3 shows the configuration. The registration roller 44, as shown in FIG.
It is composed of a pair of metal roller 44A and rubber roller 44B, which are pressed against each other by a spring (not shown). Both ends of the rubber roller 44B are held via bearings in the elongated holes of the side plate 44C (the side plate on the front side is not shown) so as to be separated from the metal roller 44A.

Further, the release cam 44D is the camshaft 44.
The gear 44F is fixed to the shaft E and has one end of the shaft 44E for transmitting the drive from the apparatus main body to the shaft 44E.
The spring clutch 44G is fixed, and the cam 44D can be selectively rotated by 180 ° and stopped by the cooperation of both and the plunger (not shown). Due to the rotation of the cam 44D, one end of the swing arm 44J is pushed and swings about the arm center shaft 44H. The other end of the arm 44J has a rubber roller 44B.
It is located near both ends.

The swing arm 44J is moved by the above swing.
It contacts the rubber roller 44B and displaces it against the pressure contact spring, and operates to separate the rubber roller 44B from the metal roller 44A. That is, as shown in FIG. 3A, both rollers 44 are aligned with the phase in which the cam 44D is stopped.
A and 44B are in pressure contact with each other, and as shown in FIG. 3 (b), they are separated from each other.

As shown in FIG. 4, the transfer drum 5 is formed by winding a transfer sheet 55S in a cylindrical shape around a frame 55F in which annular members 55A at both ends are connected by a connecting member 55B. As the material of the transfer sheet 55S, for example, a dielectric film such as polyethylene terephthalate (PET) or polyvinylidene fluoride (PVdF) is used.

The recording paper P sent from the registration roller 44
As shown in FIG. 1, the suction roller 5G is supported at a position where it rushes into the transfer drum 5 so as to be separable from and in contact with the front surface of the transfer sheet 55S. A backup member for facing the pressing force of the suction roller 5G and a suction charger 5C are arranged at the opposite positions.

In the image transfer area where the photosensitive drum 1 and the transfer drum 5 face each other, a transfer charger 5B is arranged on the back surface side of the transfer sheet 55S. On the downstream side, the recording paper P
A separating member for separating the electric charge, specifically, the charger 5 for static elimination
H, a separation claw 8A, a transfer sheet pushing-up roller 8B, and the like are arranged, and subsequently, the transfer sheet charge eliminating charger 5
D and 5E are arranged with the transfer sheet 55S interposed therebetween.
Further, on the downstream side of the transfer sheet 55S, there are provided a brush roller 14 for cleaning toner, paper dust and the like adhering to the surface (recording paper holding surface) of the transfer sheet 55S, and a corona discharger or a brush type static eliminator 15. . Furthermore, the oil used in the fixing unit 9 during double-sided recording is the recording paper P.
The oil removing roller 1 for cleaning the transfer sheet 55S may be attached to the surface of the transfer sheet 55S.
6 and a backup brush 17 are provided.

The transfer drum 5 is configured so as to be capable of being brought into contact with and separated from the photosensitive drum 1, and is separated from the photosensitive drum 1 except during a normal image forming operation. This is to prevent the transfer drum 5 and the photosensitive drum 1 from contacting each other for a long time, and to prevent the recording paper P or the like from contacting the photosensitive drum 1 and damaging the surface during the jam processing. Is. The transfer drum 5 and the photosensitive drum 1 each have a gear flange at one end thereof, and when the both drums contact each other, the gears mesh with each other and the rotation of the photosensitive drum 1 is transmitted to the transfer drum 5 side. Further, in this apparatus, the transfer / conveyance unit 50 is configured to be pulled out from the main body to the front side by the sliders 62A and 62B. This is to make jam processing or maintenance more reliable and easy.

The fixing unit 9 has a fixing roller 9A internally provided with a heat source such as a halogen heater, a pressure roller 9B which is pressed against the fixing roller (this roller 9B may also have a heat source). Fixing and pressure roller pair 9A,
Transport belt 9C for guiding the recording paper P to the nip portion of 9B
And an ejection guide 9D, a paper ejection roller 9E for ejecting the recording paper P ejected from the roller pairs 9A and 9B to the outside of the apparatus, and the like.

This apparatus has a mechanism for automatically recording images on both sides of the recording paper P. To describe it, there is a transport path switching guide 19 immediately downstream of the fixing unit 9 so that either the paper path discharged to the outside of the apparatus after fixing or the paper path for double-sided recording is automatically set. It is supposed to be selected. The double-sided recording paper path includes a conveyance vertical path 20, a reverse path 21A, a reverse roller 21B, an intermediate tray 22 and the like.
The recording paper P, which has been once guided to, is retreated by the reverse rotation of the reversing roller 21B and is retracted in the direction opposite to the direction in which the trailing end of the recording paper P is fed, and is stored in the intermediate tray 22. After that, the sheet is again fed from the intermediate tray 22 to the transfer drum 5, and an image is formed on the other surface of the recording sheet P in the same manner as described above. In the guide portion 23 above the intermediate tray 22, a plurality of guides are selectively moved up and down according to the size of the recording paper to be stored. It is possible to store and load by aligning with the top of the.

The control unit comprises a control board and a motor drive board for controlling the operation of the mechanism in each unit.

Next, a description will be added according to the operation of the image forming apparatus. The case where the recording sheet P is fed from the sheet feeding unit 40 in the middle stage is taken as an example.

When the image forming operation start signal is issued, first, the cam 71 makes a half rotation, and accordingly the transfer drum 5 swings and moves to the operating position, and the gears of the flanges of the transfer drum 5 and the photosensitive drum 1 are brought into contact with each other. Mesh with each other, and the transfer drum 5 rotates in synchronization with the photosensitive drum 1. At the same time, the pickup roller 42 feeds the recording paper P from the cassette 41 one by one. The recording paper P sent out is fed by the paper feed rollers 43A and 43B and the conveyance rollers 45B and 45C.
The paper is guided between the paper feed guides and conveyed to the conveyance unit 50A.

In the transport section 50A, first, the recording paper P
When the recording paper P passes through the curling rollers 46A, 46B, and 46C, a predetermined amount of curling is applied to the recording paper P in the winding direction around the transfer drum 5. After that, the pre-registration conveyance rollers 47A, 47B and the paper guides 48A, 48B, 48
By the action of C, 48D, and 48E, the recording paper P is conveyed to the registration roller 44 while changing the conveying direction. At this time, the registration rollers 44 are stopped, the leading edge of the recording paper P abuts on the nip portion of the registration rollers 44, and the driving of the transport rollers 47A and 47B is stopped after a certain time period. Then, a loop indicated by R in FIG. 2 is generated in the recording paper P in the meantime, but the space required for the loop is automatically expanded by the swing guides 48B and 48D being spread by the waist (rigidity) of the recording paper P. Formed.

In this image forming apparatus, the loop amount before registration (loop amount before registration rollers) is set to 8 mm. The pre-registration loop amount represents the amount by which the recording paper P is further fed after the leading edge of the recording paper P hits the registration roller 44. Taking a pre-registration loop amount of 8 mm
It is necessary to ensure the paper feeding stability from the lower sheet feeding unit where the timing of arrival of the recording paper P to the registration roller 44 portion may vary most. After that, the registration roller 44 and the pre-registration transport rollers 47A and 47B start to rotate after a predetermined time with reference to the timing when the image forming unit starts image formation. The timing of this rotation is set so that the recording paper P and the toner image on the photosensitive drum 1 coincide exactly in the image transfer area.

When the recording paper P rushes into the transfer drum 5 and comes into contact with the transfer sheet 55S, the recording paper P is statically placed on the transfer sheet film 55S by corona discharge from the adsorption charger 5C and contact with the adsorption roller 5G. Electro-adsorbed. The suction roller 5G is normally separated from the transfer drum 5 to reduce the load, and is brought into pressure contact with the transfer drum 5 only when the recording paper P is thrust. The transfer drum 5 rotates in synchronization with the photosensitive drum 1, and the recording paper P is conveyed to the image transfer area while being held on it.

Therefore, after the toner image formed on the photosensitive drum 1 is transferred to the surface thereof by the transfer charger 5B, the recording paper P is conveyed to the separating section. Since the toner image of one color is transferred by one transfer, the recording paper P is separated in the case of a monochromatic image, but the separation operation is not performed in the case of forming a multicolor image, and the recording paper P is separated. On recording paper P
While being held, it makes one round and is conveyed again to the transfer area. Then, the next toner image is further transferred onto the recording paper P so as to be superimposed on the previous toner image. By repeating this process by the required number of toner images, that is, four times, a full-color image in which toner images of four colors are laminated on the recording paper P is formed. The brush roller 14 and the like are supported so as to be separable from and in contact with the surface of the transfer drum 5, and are separated from each other at least during this multiple transfer process.

When the transfer of the four colors is completed, the attracting force between the recording paper P and the transfer sheet 55S is reduced by the action of the discharging charger 5H in the separating portion, and the separating claw 8A that follows is removed.
The recording paper P is separated from the transfer drum 5 by such operations.

The recording paper P separated from the transfer drum 5 is
Transported to the fixing unit 9 by the transport belt 9C,
The nip portion between the fixing roller 9A and the pressure roller 9B is accurately guided on the entrance guide 9D. And the fixing roller 9A
By the heat and the pressure of the pressure roller 9B, the toner images of four colors are fixed on the paper surface of the recording paper P, and the single-sided full-color image formation is completed. After that, the recording paper P is ejected from the paper ejection roller 9
It is transported by E and discharged outside the apparatus. Finally, the transfer drum 5 is separated from the photosensitive drum 1 (retracted position),
The device stops.

At the time of double-sided recording, the operation of the switching guide 19 guides the single-sided full-color recording paper P, which has been fixed as described above, to the conveying vertical path 20 and then is reversed by the reversing roller 21B via the reversing path 21A to record. The paper P is stored in the intermediate tray 22. And the required number of recording sheets P
After the sheets are stacked, the single-sided full-color recording paper P is sent out from the intermediate tray 22 one by one by the pickup roller 25,
The sheet is conveyed to the conveying section 50A by the sheet feeding rollers 26A and 26B. After that, a full-color image is formed on the other surface of the recording paper P by going through the same process as described above, and the double-sided full-color image formation is completed after fixing. Finally, the switching guide 19 is not operated, and the recording paper P on which the double-sided full-color image is formed is ejected out of the apparatus.

The recording sheet P is transferred onto the transfer sheet 55 of the transfer drum 5.
The operation of adsorbing on S will be described in detail with reference to FIG. According to the present embodiment, the adsorption charger 5C has the structure shown in FIG.
As shown in (a), it is switchably connected to the Hi-side high-voltage power supply 100 and the Lo-side high-voltage power supply 101 via the switching means 102, and the suction bias applied to the suction charger 5C is switched to switch the transfer sheet 55S. It is possible to change the suction force of the recording paper P to the sheet.

For the transfer drum 5 on which the recording paper P rotates,
When it enters at the suction nip portion (suction position) Q, Hi
The side high-voltage power supply 100 is turned on, the switching means 102 is connected to the Hi-side high-voltage power supply 100, and the attraction bias from the Hi-side high-voltage power supply 100 is applied to the attraction charger 5C. As a result, corona discharge occurs and the recording paper P
Also, electric charges are injected into the transfer sheet 55S, and the leading end of the recording sheet P is electrostatically adsorbed on the surface of the transfer sheet 55S. However, since a high adsorption bias from the Hi-side high-voltage power supply 100 is applied, strong adsorption is achieved. Adsorbed by force. This is because in the initial suction operation, the leading edge of the recording paper P is sucked with a relatively strong suction force, is firmly gripped by the transfer sheet 55S, and the recording paper P is affected by the upstream transport registration roller 44 and pre-registration roller 47. This is to prevent the sheet from moving from the transfer sheet 55S and to prevent the sheet from peeling off toward the photosensitive drum 1 side during the transfer operation at the subsequent transfer position T. A suitable adsorption bias for initial adsorption is approximately 7 KV and 15 to 20 mA.

Next, when the recording paper P is adsorbed onto the transfer sheet 55S from the tip portion and the tip portion is fed by a predetermined amount h1 from the position of the adsorption nip portion Q, the Lo side high voltage power source 10
1 is turned on, the switching means 102 is switched to the Lo-side high-voltage power supply 101, and the registration roller 44
Are separated. As a result, the latter half of the recording paper P following the leading edge is electrostatically adsorbed on the surface of the transfer sheet 55S. In the latter half of the adsorption operation, a relatively low adsorption bias from the Lo-side high-voltage power supply 100 is obtained. Is applied, it is adsorbed with a relatively weak adsorption force.

The front end of the recording paper P has already been transferred to the transfer sheet 55S.
Since it is firmly fixed on the upper part of the recording paper P, there is no concern that the recording paper P will peel off from the transfer sheet 55S even if the latter half of the recording paper P is weakly adsorbed. The wrinkles accumulated from the leading end of the recording paper P can be offset from the transfer sheet 55S and stretched.
Therefore, it is possible to prevent the central portion of the rear end portion of the recording paper P from bulging upward with respect to the surface of the recording paper and floating from the transfer sheet 55S, and the transfer omission of the recording paper P can be eliminated. The suction bias for the latter half of the suction is 6 at about 3 KV.
About 9 mA is suitable.

FIG. 6 shows a model diagram of the distribution of the suction force of the recording paper P on the transfer sheet 55S. Leading edge h1 of recording paper P
The suction force is large in the area of, and the rear end portion after that is small.
As described above, in this embodiment, since the suction force at the trailing end of the recording paper P is made small, it is possible to correct the rising in the latter half of the recording paper P and eliminate the transfer omission.

In the above, an example has been described in which two high voltage power supplies 100 and 102 on the Hi side and the Lo side are provided and switched.
With the output of the high-voltage power supply being variable, the voltage of the suction bias is lowered as the recording paper P supplied to the transfer drum 5 is conveyed, and as shown in FIG. 7, from the leading end of the recording paper P to the latter half thereof. The distribution may be such that the suction force gradually decreases in a curve.

The change in the suction force of the recording paper P in the conveying direction depends on the size and thickness of the recording paper P, the material, the environment around the apparatus,
Depending on the one-sided / two-sided image forming mode, it is possible to determine whether or not this is necessary, and then perform the operation.

A block diagram of the above control is shown in FIG.
On the input side of the suction control means 110 for controlling suction, the temperature and humidity information of the apparatus atmosphere from the temperature and humidity sensor 111, the size information of the recording paper P from the size detection means 112, and the mode input means of the apparatus main body operation unit. The image formation mode information from 113 and the paper type information of the recording paper P from the paper type input means 114 of the apparatus main body operation unit are input. Suction control means 1
At the output side of 10, the adsorption Hi-side high-voltage power supply 100, the adsorption Lo-side high-voltage power supply 101, and the switching means 102.
Is connected.

Based on the above input information, the suction control means 110 determines whether or not to change the suction force according to the table of Table 1. In Table 1, the mark ◯ indicates the execution of the control for changing the suction force, and the mark x indicates that the recording recording paper P is sucked onto the transfer sheet 55S by a constant suction force as usual.

[0054]

[Table 1]

The transfer omission caused by the recording paper P floating up from the transfer sheet 55S is more likely to occur in a high humidity environment in which the amount of water in the air is large and the paper tends to absorb moisture. The double-sided mode, in which the suction operation is performed in a state where image formation is performed and waviness occurs, is more likely to occur.

As for the type of paper, plain paper (6
4g / m ² paper to 80g / m ² paper is most likely to cause transfer omission, and then thick paper (105g / m ^{2 to} 158g / m)
² paper), then OHP paper. By size of paper, large size (A3, B4, 1
1 x 17 etc.) is a small size (A4, B5, LTR)
More likely to occur.

That is, when the image is formed under the conditions of large size of plain paper, double-sided mode, and high humidity, transfer omission is most likely to occur, and small size of OHP paper, single-sided mode, low humidity to normal environment. Image formation is most unlikely to occur under certain conditions.

According to Table 1, the attraction force control according to the present invention is executed for the place where the occurrence frequency is high in each image forming mode, and the attraction is performed normally in the unnecessary mode. As a result, the recording paper P is optimally adsorbed.

In the above description, the suction force of the recording paper P to the transfer sheet 55S is changed in the recording paper conveyance direction, but it may be changed in the direction orthogonal to the recording paper conveyance direction.

Another embodiment of the present invention will be described. FIG. 9 is a sectional view showing a suction portion around a transfer drum in another embodiment of the present invention.

As shown in FIG. 9, in the present embodiment, the transfer sheet 55S is cylindrically wound around the transfer drum ring 55A before and after the transfer drum 5, and the transfer sheet 55S is attracted to the inner side (back side) of the transfer sheet 55S. A brush 5C is provided.
The suction brush 5C is connected to the suction high-voltage power supply 120, and the tip of the brush portion is in contact with the back surface of the transfer sheet 55S.

A suction roller 5G is provided on the opposite side of the transfer sheet 55S sandwiching the recording paper P. Suction roller 5
G is both end members 501, 503 and the central member 50 between them.
It is divided into two parts, and the insulating members 504 and 50 are provided between the end members 501 and 503 and the central member 502, respectively.
It is divided by five. The both end members 501, 503 and the central member 502 are respectively provided with switching means 506, 50.
It is grounded via 8, 507.

During the suction operation, when the recording paper P is in the position shown in FIG. 5 (a), the switching means 506, 50
By turning on all 7, 508 and dropping the respective members 501 to 503 of the suction roller 5G to the ground, by applying the suction bias from the high voltage power source 120 to the suction charger 5C, the leading end portion of the recording paper P and Electric charges are injected into the entire width direction of the transfer sheet 55S, and the entire width direction of the leading end portion of the recording paper P is adsorbed.

Then, as shown in FIG. 5B, when the recording paper P advances from the position of the nip portion Q by a predetermined amount h1, the switching means 506 and 507 are turned off and the suction roller 5G.
Only the central member 502 of this is dropped to the ground, and the high voltage power source 1
The suction bias from 20 is also applied to the suction charger 5C by lowering the voltage by the width of the grounded portion of the suction roller 5G. As a result, the latter half of the recording paper P after the leading end is adsorbed only in the central portion, so that the wrinkles of the recording paper P accumulated by the conveyance are extended from the central portion in the width direction to both ends, and the latter half of the recording paper P is absorbed. There is no uplift in the central part of. Therefore, it is possible to prevent the occurrence of transfer omission.

FIG. 10 shows a model diagram of the suction force distribution in the above suction operation.

In the above, the suction roller 5G is integrally formed by the members 501, 502 and 503 which are divided into three parts in the longitudinal direction and the insulating members 504 and 505 therebetween, but the suction roller is divided into a plurality in the longitudinal direction. Independent split rollers, each split roller is independently swingably supported, all the split rollers are brought into contact with the transfer sheet 55S in the initial suction operation, and in the latter suction operation,
The split rollers at both ends may be separated from each other, and only the split rollers at the center may be brought into contact with each other.

As shown in FIG. 11, the suction brush 5C has two end brushes 511 divided into three parts in the longitudinal direction.
513 and the central brush 512, and the high voltage power supplies 517, 5 are connected to the brushes 511, 513, 512, respectively.
19, 518 as switching means 514, 516, 51
Connect via 5. Then, the three brushes 511 to 512 suck the front end of the recording paper P at the time of initial suction, and only the central brush 512 sucks only the central portion of the recording paper P after the front end at the time of the latter half suction. May be.

Also in this embodiment, since the suction force distribution similar to that of FIG. 10 is obtained, the same effect is achieved.

In the above, the case where the suction force is changed in the conveyance direction of the recording paper P and the case where it is changed in the direction orthogonal to the conveyance direction have been described. You may give it a force change.

[0070]

As described above, according to the image forming apparatus of the present invention, the adsorbing force for adsorbing the recording material to the recording material carrier that carries and conveys the recording material is set in the recording material conveying direction or Since the recording material is changed in the orthogonal direction, it is possible to extend the recording material without excessively restraining it on the recording material carrier without accumulating wrinkles and to prevent the recording material from floating. Therefore, the recording material can be satisfactorily transferred, and a high-quality image without transfer defects can be obtained. Further, the execution of the change in the suction force of the recording material is determined according to the size, the thickness, the material of the recording material, the usage environment, the single-sided copy mode, and the double-sided copy mode.

[Brief description of drawings]

FIG. 1 is a sectional view showing the configuration of an embodiment of an image forming apparatus of the present invention.

FIG. 2 is an explanatory diagram illustrating a configuration of a transport unit of the image forming apparatus in FIG.

3 is a perspective view showing a registration roller releasing mechanism of the image forming apparatus of FIG.

4 is a perspective view showing a transfer drum of the image forming apparatus of FIG.

5 is an explanatory diagram showing the operation of a suction unit of the image forming apparatus of FIG.

FIG. 6 is a model diagram showing the distribution of the suction force of the recording paper by the suction operation of the suction section of FIG.

FIG. 7 is a model diagram showing another example of the suction force distribution of recording paper.

FIG. 8 is a control block diagram for performing the suction operation of FIG.

FIG. 9 is a front view showing a suction unit according to another embodiment of the present invention.

FIG. 10 is a model diagram showing the distribution of the suction force of the recording paper by the suction operation of the suction unit of FIG.

FIG. 11 is a front view showing another example of the suction unit according to the present invention.

FIG. 12 is a sectional view showing a configuration of a conventional image forming apparatus.

13 is an explanatory diagram showing a configuration of a suction unit in the image forming apparatus in FIG.

14 is a plan view showing a suction state of the recording paper by the suction portion of FIG.

[Explanation of symbols]

 1 Photosensitive Drum 5 Transfer Drum 5C Adsorption Charging Device 5G Adsorption Roller 44, 44A, 44B Registration Roller 47, 48 Pre-Registration Conveying Roller 48A to 48E Paper Guide 48F to 48K Adsorption Guide 50 Transfer Conveying Unit 55S Transfer Sheet P Recording Paper Q Adsorption Position T Transfer unit 100 Hi-side high-voltage power supply 101 Lo-side high-voltage power supply 102 Switching means

Claims (8)

[Claims] 1. A recording material carrier for carrying and conveying the adsorbed recording material, an image forming means for forming an image on the recording material carried by the recording material carrier, and recording on the recording material carrier. An image forming apparatus having an adsorbing means for adsorbing a material, wherein an adsorbing force for adsorbing the recording material on the recording material carrier is changed in a conveying direction of the recording material. 2. The image forming apparatus according to claim 1, wherein the attraction force for attracting the recording material is larger at the front end portion than at the rear end portion in the conveyance direction of the recording material. 3. A recording material carrier that carries and conveys the adsorbed recording material, image forming means for forming an image on the recording material carried by the recording material carrier, and recording on the recording material carrier. An image forming apparatus having an adsorbing means for adsorbing a material, wherein an adsorbing force for adsorbing the recording material on the recording material carrier is changed in a direction orthogonal to a conveying direction of the recording material. 4. The image forming apparatus according to claim 3, wherein the attraction force for attracting the recording material is larger at the central portion than at both ends in the direction orthogonal to the recording material conveying direction. 5. The image forming apparatus according to claim 1, 2, 3, or 4, wherein the change of the suction force is performed according to the size of the recording material. 6. The image forming apparatus according to claim 1, 2, 3, or 4, wherein the change of the suction force is performed according to the thickness or material of the recording material. 7. The image forming apparatus according to claim 1, wherein the change of the suction force is performed in accordance with a use environment. 8. The change of the suction force is performed according to a single-sided mode in which an image is formed on one side of a recording sheet and a double-sided mode in which an image is formed on both sides of the recording sheet.
Or the image forming apparatus of 4.