JPH08334987A - Image forming device - Google Patents

Abstract

PURPOSE: To provide an image forming device capable of stably obtaining a high-quality image by preventing irregularities in the image on a transfer material caused by the friction between the transfer material guiding member of a separation charger and the transfer material. CONSTITUTION: This image forming device is provided with the separation charger 9 whose transfer material carrying path side is opened and which is constituted by arranging a ladder state guiding member (transfer material guiding member) 10 at the opened part, and the transfer material P is separated by the charger 9 after the transfer material P is allowed to abut on a transferable toner image formed on the surface of a photoreceptor drum(image carrier) 1 and the toner image is electrostatically transferred on the transfer material P. The device is provided with means (an arm 72, a solenoid 74 and a spring 76) for weakening the contact of the transfer material P with the guiding member 10 on the way where the transfer material P passes on the charger 9. The strong friction between the guiding member 10 and the transfer material P is prevented. The irregularities in the image on the transfer material P accompanying friction between them are prevented, and the high-quality image is stably obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention develops an electrostatic latent image formed on an image carrier as a toner image and transfers the toner onto a transfer material sent to the image carrier at a predetermined timing. The present invention relates to an image forming apparatus that transfers an image to form an image.

[0002]

2. Description of the Related Art A sheet-like transfer material such as paper is brought into contact with a transferable toner image electrostatically formed on a surface of an image carrier by charged toner, and corona discharge is applied to the back surface of the transfer material so as to have a polarity opposite to that of the toner. Transfer the toner image to the transfer material by applying an electric charge, and then perform a DC corona discharge with the same polarity as the toner or an AC corona discharge with the effective value with the same polarity as the toner on the back surface of the transfer material to transfer the charge during transfer. 2. Description of the Related Art An image forming apparatus that neutralizes and removes electricity and separates a transfer material from an image carrier is well known.

When a toner image is transferred to a transfer material, the transfer material is guided to the surface of the image carrier by a flat plate-shaped recording material guide member (hereinafter referred to as a guide member) provided so as to face each other and transferred. A corona discharge having a polarity opposite to that of the toner is applied from the back surface of the transfer material by the charger.

Further, in the separation charger for separating the transfer material from the image carrier, the side facing the image carrier is open, and the transfer material passes between the separation charger and the image carrier. To do. Therefore, there is a possibility that the transfer material reaching the position of the separation charger enters the separation charger to cause a wire breakage or a jam, and therefore the ladder-shaped transfer material usually made of a dielectric material is provided on the open side of the separation charger. The guide member is provided to prevent the transfer material from entering the separating charger.

However, if the above measures are taken, the toner on the transfer material may scatter at the contact portion between the guide member and the transfer material, resulting in image distortion. In order to prevent this, it has been proposed to specify the material of the guide member (see Japanese Patent Laid-Open No. 62-240986).

On the other hand, a method has been proposed in which suction at the separating portion is strengthened only at the tip portion in order to improve the separability of the transfer material and prevent contamination (see Japanese Patent Laid-Open No. 2-2468).

[0007]

However, conventionally,
When an image is formed on a transfer material that has been left in a low-humidity environment for a long time through a transfer material or a fixing device once, and then a dry transfer material is passed through the image forming device for a long time, the ladder of the transfer material and the separation charger The guide member is charged up due to friction with the linear guide member, which may cause image distortion in the latter half of the transfer material. In particular, in the case of a halftone image or a photographic image, image distortion is easily noticeable and appears as vertical white stripes or black stripes.

The present invention has been made in view of the above problems, and an object of the present invention is to prevent image disturbance on a transfer material due to rubbing between the transfer material guide member of the separation charging device and the transfer material, and to achieve high quality. An object of the present invention is to provide an image forming apparatus that can stably obtain various images.

[0009]

In order to achieve the above-mentioned object, the invention according to claim 1 has a separation charger in which the transfer material conveying path side is open and a transfer material guide member is arranged in the open portion. An image in which a transfer material is brought into contact with a transferable toner image formed on the surface of an image carrier, the toner image is electrostatically transferred to the transfer material, and then the transfer material is separated by the separation charger. The forming apparatus is characterized in that means for weakening the contact between the transfer material and the transfer material guide member is provided while the transfer material is passing over the separation charger.

According to a second aspect of the invention, in the first aspect of the invention, the means for weakening the contact between the transfer material and the transfer material guide member is a means for moving the transfer material guide member away from the image carrier. Is characterized by.

According to a third aspect of the present invention, in the first aspect of the invention, the means for weakening the contact between the transfer material and the transfer material guide member is means for moving the conveyor belt up and down. .

According to a fourth aspect of the present invention, in the first aspect of the present invention, the means for weakening the contact between the transfer material and the transfer material guide member is configured to change the suction from the separation charger to change the circumference of the conveyor belt. It is characterized in that the speed is made slower than that of the image carrier.

[0013]

According to the present invention, strong rubbing between the transfer material and the transfer material guiding member is prevented, and image disturbance on the transfer material due to the rubbing of both is prevented, and a high quality image is stably obtained. be able to.

[0014]

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

<First Embodiment> FIGS. 1 and 2 are sectional views of the essential parts of an image forming apparatus according to the first embodiment of the present invention, in which 1 is a photosensitive drum which is an image carrier, and 2 is a photosensitive drum. Photosensitive drum 1
A potential sensor 3 for detecting the surface potential of the photosensitive drum 1, a developing device 3 for developing an electrostatic latent image formed on the photosensitive drum 1 by an electrostatic latent image forming means (not shown), A pre-transfer charger 5 for performing tribo control of the developed toner, registration rollers 5 and 7 for feeding the transfer material P to the transfer position by aligning the front end of the transfer material P with the developed toner image front end in good timing. Is an upper transfer guide and a lower transfer guide that accurately guide the transfer material P that has left the registration roller 5 to the transfer position. Further, 8 is a transfer charging device for transferring the toner image on the photosensitive drum 1 onto the transfer material P, 9 is a separation charging device for discharging the transfer material P and separating it from the photosensitive drum 1, 10 is A ladder-shaped guide member for smoothly guiding the transfer material P without being caught on the separation charger 9.
Reference numeral 11 is a conveyor belt for feeding the transfer material P to a fixing device (not shown).

By the way, one end of the guide member 10 is rotatably supported about a rotary shaft 71, and the other end is connected to one end of an L-shaped arm 72. And
An intermediate portion of the arm 72 is rotatably supported by a shaft 73, and the other end of the arm 72 is connected to a solenoid 74. In addition, a stopper 72a is provided on the bent portion of the arm 72.
Is projected, and the stopper 72a is an L-shaped sheet metal 75.
The rotation of the arm 72 is restricted by engaging with the concave groove 75a. The arm 72 is urged downward by the spring 76 (in the direction in which the guide member 10 is lowered as shown in FIG. 2).

When the solenoid 74 is turned on, the arm 72 rotates about the shaft 73 in the arrow direction (clockwise direction) as shown in FIG. 1, and the stopper 72a of the arm 72 is L-shaped. When the arm 72 is stopped at the time when the arm 72 is engaged with the groove 75a of the sheet metal 75, the ladder-shaped guide member 10 is raised above the conveyor belt 11.

Further, in the state shown in FIG. 1, the solenoid 7
When the switch 4 is turned off, the arm 72 rotates in the direction of the arrow (counterclockwise) about the shaft 73 by the urging force of the spring 76 as shown in FIG. It will be in the state of falling.

As described above, the position of the ladder-shaped guide member 10 is controlled by turning on / off the solenoid 74, and when the solenoid 74 is on, the guide member 10 goes up and off.
The guide member 10 is lowered in this state. The timing chart is shown in FIG.

In FIG. 3, the tip of the transfer material P is o,
The times of passing through p, q, s, and u (see FIGS. 1 and 2) are to, tp, tq, ts, and tu, respectively. The solenoid 74 is turned on when the registration roller 5 is turned on, and is turned off at a time tu, which is a little time after the leading edge of the transfer material P is placed on the conveyor belt 11.

By the way, ON / OFF of the solenoid 74
The operation may be performed so that the leading end of the transfer material P does not hit the conveyor belt 11 after passing through the rear end s of the guide member 10, and the ON operation can be performed for a shorter time. The solenoid 74 is turned on immediately before the tip of the transfer material P reaches s,
The solenoid 74 may be turned off immediately after the front end of the transfer material P is placed on the conveyor belt 11.

However, in order to prevent image shift, etc.,
Before the tip of the transfer material P touches the guide member 10, the solenoid 74 is turned on at least before the time tq so that the friction between the transfer belt 11 and the transfer material P is sufficiently ensured. It is desirable to turn off the solenoid 74 from the state where the transfer material P does not shift even if it moves (then, the solenoid 74 turns off from about the time tu).

Thus, as in the present embodiment, the guide member 10 is raised only when the front end of the transfer material P passes, and the guide member 10 is lowered in other cases, so that the latter half of the transfer material P is Strong rubbing with the guide member 10 can be prevented, image disturbance on the transfer material P can be prevented, and a high-quality image can be stably obtained.

<Second Embodiment> Next, a second embodiment of the present invention will be described with reference to FIGS. Incidentally, FIG. 4 is a sectional view of the main part of the image forming apparatus according to the second embodiment of the present invention, and FIG. 5 is a timing chart for controlling the vertical movement of the conveyor belt, which is shown in FIG. 1 and FIG. The same elements are denoted by the same reference numerals, and description thereof will be omitted below.

In the first embodiment, the guide member 10 was moved up and down, but in the present embodiment, the carrying ladder-like guide member 10 is used.
Is fixed and the conveyor belt 11 is moved up and down.

The conveyor belt 11 is wound around a belt drive roller 21 and a tension roller 22, and is rotationally driven by the belt drive roller 21 which rotates in the direction of the arrow in the figure.

A stepping motor 23 capable of forward and reverse rotation is installed below the tension roller 22, and an output shaft 24 of the stepping motor 23 constitutes a screw shaft.

On the other hand, the tension roller 22 is supported by a nut-shaped support 25, and the output shaft 24 of the stepping motor 23 is screwed onto the support 25.

When the stepping motor 23 is driven to rotate the output shaft 24 in the forward and reverse directions, the support column 25 screwed onto the output shaft 24 and the tension roller 2 supported by the support column 25 are supported.
2 moves up and down, whereby the conveyor belt 11 is moved up and down between the position shown by the chain line and the position shown by the solid line in FIG.

Regarding the height relationship between the guide member 10 and the conveyor belt 11, usually, the conveyor belt 11 is at the solid line position in FIG. 4, and the guide member 10 is at a position higher than the conveyor belt 11. The reason is that the front end of the transfer material is the conveyor belt 1.
This is because it does not hit 1.

Then, when the leading edge of the transfer material passes through the guide member 10 and the conveyor belt 11 is raised upward as shown by the broken line in FIG. 4, the transfer material is supported by the conveyor belt 11.
This does not rub strongly against the guide member 10, and as in the first embodiment, image disturbance on the transfer material can be prevented and a high quality image can be stably obtained.

FIG. 5 shows a timing chart for moving the conveyor belt 11 up and down.

As shown in FIG. 5, when the leading edge of the transfer material reaches the rear end s of the ladder-shaped guide member 10 (time ts), the stepping motor 23 is driven, and the height of the conveyor belt 1 is transferred from time tu. The leading edge of the material is gradually raised up to a time tu when it reaches the position of u of the conveyor belt 11. Then, when the trailing edge of the transfer material reaches s (time ts), it is gradually lowered. This is repeated every time one transfer material passes.

As in the first embodiment, the control timing described above may be controlled so that the leading edge of the transfer material does not hit the conveyor belt 11.
It is sufficient to lower the conveyor belt 11 only when it comes into the vehicle 1. However, if the height of the conveyor belt 11 is changed too rapidly, image defects such as transfer deviation are likely to occur, and therefore the height of the conveyor belt 11 needs to be gradually changed.

<Third Embodiment> Next, a third embodiment of the present invention will be described with reference to FIGS. 6 and 7. 6 is a cross-sectional view of the essential parts of the image forming apparatus according to the third embodiment of the present invention, and FIG. 7 is a timing chart for controlling the ON / OFF of the suction fan and the peripheral speed of the conveyor belt. In FIG. The same elements as those shown in FIGS. 1 and 2 are denoted by the same reference numerals, and description thereof will be omitted below.

In this embodiment, the height of the conveyor belt 11 is fixed and its peripheral speed is controlled.

As shown in FIG. 6, the separation charger 9 and the conveyor belt 11 are connected by a suction duct 13.
The suction duct 13 is provided with a suction fan 12 and a suction valve 14. By the opening / closing operation of the suction valve 14, the suction by the separation charger 9 is turned ON / OFF.

On the other hand, the conveyor belt 11 is driven by the drive roller 15, but the drive roller 15 is driven by the speed variable motor 16, so that the peripheral speed of the conveyor belt 11 can be controlled arbitrarily.

Here, the suction timing of the separation charger 9 and the peripheral speed of the conveyor belt 11 will be described.

The suction of the separation charger 9 is usually 5 m above the wire.
The wind speed is about 2 m / sec to 0.7 m / sec when the separation charger 9 is sucked, which is detected by measuring the measurement by the wind speed at a position of about m. still,
As described above, the suction of the separation charger 9 is ON / OFF controlled by the suction valve 14.

The suction by the separation charger 9 is carried out in order to prevent separation failure and retransfer of the tip of the transfer material P. This is very effective because the tip of the transfer material P is the first separation on the transfer charger 8 side. This is when it is on the charger 9. Then, the transfer material P
The transfer material P has already been separated by the time when the tip of the transfer material P has reached the rear end edge point 10a of the guide member 10 of the separation charger 9, and retransfer separation failure does not occur even if suction is turned off.

FIG. 7 shows the ON / OFF timing of the suction valve 14.

The suction valve 14 is turned on from the time point (time tp) when the tip of the transfer material P reaches the point p where it comes into contact with the photosensitive drum 1,
It is turned off when the front end of the transfer material P reaches the rear end s of the guide member 10 (time ts). Further, the control of the current value of the separation charger 9 is also weakened in the latter half of the transfer material P. The separation differential current is turned on shortly before the registration roller 5 is turned on, and -100 μA flows. Then, when the registration roller 5 is turned on, a normal separation current of −200 μA is supplied, and the current value is gradually reduced when the leading edge of the transfer material P reaches s (time ts).

On the other hand, the peripheral speed of the conveyor belt 11 is set slightly slower (about 0.5%) than the photosensitive drum 1, and a slight loop is formed in the latter half of the transfer material P (this state is shown in FIG. 6 is shown by a broken line, and the solid line shows the state of the transfer material P when sucking).

As described above, the suction of the separation charger 9 is turned off midway and the peripheral speed of the conveyor belt 11 is slightly reduced to form a loop on the transfer material P, and the transfer material P and the ladder-shaped guide member 10 are formed. Since it was prevented from rubbing strongly,
Image disturbance on the transfer material P can be prevented, and a high-quality image can be stably obtained.

Further, by weakening the separation current of the separation charger 9 in the latter half of the transfer material P, the disadvantage of retransfer in the latter half of the transfer material P caused by the loop generation of the transfer material P does not occur, and the above object is achieved. can do.

If the speed of the transfer material P sent by the photosensitive drum 1 or the registration roller 5 and the peripheral speed of the conveyor belt 11 are too different, if the transfer material P is long, especially at the rear end portion of the transfer material P. The loop can become too large. In order to prevent such a situation from occurring, control may be performed in which the peripheral speed of the conveyor belt 11 is reduced for a certain period of time. FIG. 7 shows an example of the timing for lowering the peripheral speed of the conveyor belt 11. In FIG. 7, vp is the peripheral speed of the photosensitive drum 1, and the conveyor belt 11 is controlled to slow down the rotation of the motor 16 so that it is fed at a speed of 95% of vp for a fixed time Δt.

[0048]

As is apparent from the above description, according to the present invention, the image carrier is provided with the separation charger which is open on the transfer material conveying path side and has the transfer material guide member arranged in the open portion. In an image forming apparatus, a transfer material is brought into contact with a transferable toner image formed on the surface, the toner image is electrostatically transferred to the transfer material, and then the transfer material is separated by the separation charger. Since the means for weakening the contact between the transfer material and the transfer material guide member is provided while the transfer material is passing over the separation charger, the transfer material guide member of the separation charger and the transfer material are rubbed against each other. It is possible to prevent image distortion on the transfer material due to, and to stably obtain a high-quality image.

[Brief description of drawings]

FIG. 1 is a sectional view of an essential part of an image forming apparatus according to a first embodiment of the present invention.

FIG. 2 is a sectional view of an essential part of the image forming apparatus according to the first embodiment of the present invention.

FIG. 3 is a timing chart for controlling ON / OFF of a solenoid in the image forming apparatus according to the first exemplary embodiment of the present invention.

FIG. 4 is a sectional view of a main part of an image forming apparatus according to a second embodiment of the present invention.

FIG. 5 is a timing chart for controlling the vertical movement of the conveyor belt in the image forming apparatus according to the second embodiment of the present invention.

FIG. 6 is a sectional view of a main part of an image forming apparatus according to a third embodiment of the present invention.

FIG. 7 is a timing chart for controlling ON / OFF of the suction fan and the peripheral speed of the conveyor belt in the image forming apparatus according to the third exemplary embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Image carrier (photosensitive drum) 9 Separation charger 10 Ladder guide member (transfer material guide member) 11 Conveyor belt 14 Suction valve 16 Motor 23 Stepping motor 74 Solenoid P Transfer material

Claims (4)

[Claims] 1. A transfer material transport path side is opened, and a separation charging device is provided which has a transfer material guide member in the open portion, and the transfer material is brought into contact with a transferable toner image formed on the surface of an image carrier. ,
In an image forming apparatus in which the toner image is electrostatically transferred to a transfer material and then the transfer material is separated by the separation charging device, the transfer material is in the process of passing on the separation charging device. An image forming apparatus comprising means for weakening the contact between the transfer material and the transfer material guide member. 2. The image forming apparatus according to claim 1, wherein the means for weakening the contact between the transfer material and the transfer material guide member is means for moving the transfer material guide member away from the image carrier. 3. The image forming apparatus according to claim 1, wherein the means for weakening the contact between the transfer material and the transfer material guide member is means for vertically moving the conveyor belt. 4. The means for weakening the contact between the transfer material and the transfer material guide member changes the suction from the separation charger,
The image forming apparatus according to claim 1, wherein the image forming apparatus is a unit that makes the peripheral speed of the conveyor belt slower than that of the image carrier.