JP2000095410A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To surely attactingly carry a record material to a transcription drum by once stopping drive of a curling means when the extreme end of the record material reaches the curling means. SOLUTION: For effectively stopping when the extreme end PO part of a record material passes through a curling means 14, a hard roller 14a is provided with a movement detecting sensor 15 as an extreme end detecting means. Namely when the record material P passes through the hard roller 14a, because the hard roller 14a moves by thickness portion of the record material, the movement detecting sensor 15 detects the movement, and hence drive of the hard rollers 14a, 14b and an elastic roller 14c is stopped. By constituting the device in this way, when the record material extreme end PO reaches the curling means 14, it can be stopped. Further, by fitting strong curl onto the record material extreme end PO, the curl quantity of the whole record material P can be reduced into the degree of a half of the maximum, carry after a transcription process is smoothened, and the favorable attracting carry can be realized.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image forming apparatus such as a copying machine and a laser beam printer for electrostatically forming an image on a recording material such as recording paper or a resin sheet.

[0002]

2. Description of the Related Art Conventionally, in an image forming apparatus such as a copying machine or a laser beam printer, an image carrier such as a photosensitive drum and a recording material carrier (transfer drum, transfer belt, etc.) for carrying a recording material such as paper. Are known. Particularly, in the case of a four-color full-color image forming apparatus, a color image is formed by forming a toner image of each color on an image carrier, sequentially transferring the toner images onto a recording material carried on a transfer drum, and superimposing the toner images. There are cases.

However, if the recording material is thick or has high rigidity, it may be difficult to make the recording material attract the transfer drum. Therefore, a curling unit 50 as shown in FIG. 5 may be conventionally provided on the upstream side of the transfer drum. The curling means 50 includes two hard rollers disposed on one side of the transport path.
It comprises 50a, 50b and one elastic roller 50c arranged on the other. When the recording material P passes through the curling means 50, the elastic roller 50c is turned into a hard roller 50a,
By applying the pressure to 50b, the recording material P can be curled in the direction along the transfer drum.

[0004] By attaching such a curl to the recording material P, the suction conveyance to the transfer drum becomes advantageous, and the recording material P
Even when the transfer drum is thick or has high rigidity, it is possible to perform suction transfer by the transfer drum. When the pressing force of the elastic roller 50c is increased, a larger curl can be applied to the recording material P, and stable suction conveyance can be performed even on a thicker and more rigid recording material P.

[0005]

However, if the recording material is excessively curled, the recording material is separated from the transfer drum and transported to the fixing device even if the recording material can be attracted and transported to the transfer drum. In such a case, there is a possibility that an adverse effect such as an image failure may occur, or a conveyance failure may occur. Such adverse effects are more likely to occur as the recording material is thicker or has higher rigidity.

In the case where the image is formed on both sides by re-feeding, the curl along the transfer drum when forming the image on the first side is reduced when the image on the second side is formed. The curl is in the direction warped with respect to the transfer drum. Therefore, if too strong a curl is formed during the image formation on the first side, there is a problem in that the suction transfer to the transfer drum is not successful during the image formation on the second side, and the transfer cannot be performed.

In order to solve these problems, a method has been proposed in which the pressing force of the curling means is made variable. However, this requires a complicated mechanism, and it is difficult to properly adjust the curl amount.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an image forming apparatus which has a simple structure and ensures that a recording material is conveyed to a transfer drum by suction.

[0009]

In order to solve the above-mentioned problems, the main components of an image forming apparatus according to the present invention include an image carrier for carrying a latent image, and a toner image formed by developing the latent image. An image having a developing means for carrying out the recording, a transfer drum for carrying the recording material and transferring the toner image onto the recording material, and a curling means arranged upstream of the transfer drum in the transport direction to curl the recording material In the forming apparatus, when the leading end of the recording material reaches the curling unit, the driving of the curling unit is temporarily stopped.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An example of an image forming apparatus according to the present invention will be described with reference to the drawings. 1 is an overall configuration diagram of an image forming apparatus according to the present embodiment, FIG. 2 is an enlarged configuration diagram of a transfer drum, FIG. 3 is a diagram illustrating a curling unit, and FIG. 4 is another configuration of a curling unit. FIG.

(Overall Configuration) The image forming apparatus 1 shown in FIG. 1 is an electrophotographic full-color image forming apparatus. The image forming apparatus 1 includes a photosensitive drum 2 serving as an image carrier, a charger 3 serving as a charging unit for charging the photosensitive drum 2 around the photosensitive drum 2, an optical device 4 serving as a latent image forming unit, and a toner image of each color. Developing device 5y and magenta developing device 5 for developing
m, a cyan developing device 5c, a black developing device 5k, a transfer drum 6 and a transfer charging brush 6b as transfer means for carrying and conveying a recording material and transferring a toner image onto the recording material P.
An image forming unit including a cleaning device 7 for cleaning the photosensitive drum 2 is provided.

When forming an image, first, the photosensitive drum 2
Is uniformly charged by the charger 3, and the optical device 4 irradiates light onto the original according to image information of the first color, for example, yellow, of the original sent from the reading unit 8 to form a latent image. The latent image on the photosensitive drum 2 is developed by the yellow developing device 5y, and is visualized as a first color toner image.

On the other hand, the recording material P is stacked on a feeding cassette 9, is separated and fed one by one, is conveyed to the transfer drum 6, and rotates a plurality of times while being carried on the transfer drum 6 as shown in FIG. I do. The residual toner on the surface of the recording material P is removed by the thickness of the surface of the transfer drum, and the recording material P is again provided for the next image formation. This process is repeated for each of the remaining colors (magenta, cyan,
Black) to form a full-color image on the recording material P.

The recording material P which has completed the transfer process is separated
Transfer drum 6 by the separation charger 10a and the separator 10b.
And discharged to the discharge tray 13 via the fixing device 12,
Be loaded. The transfer drum 6 from which the recording material P carried on the surface has run out is removed by the transfer cleaner 11 to remove unnecessary toner attached to the surface, and is used for carrying the next recording material P.

The fixing device 12 has a fixing roller 12b containing a heater 12a and a pressing roller 12c pressed against the fixing roller 12b.
The recording material P is heated and pressurized while being nipped and conveyed at the nip portion of both rollers, so that the toner image on the recording material P is melted and fixed to the recording material P and fixed.

(Transfer Drum) The transfer drum 6 will be described in detail with reference to FIG. In FIG. 2, the transfer drum 6
A transfer sheet 6a, which is a recording material bearing member that electrostatically attracts the recording material and rotates in the direction of arrow C, is replaced on the outer peripheral surface of the recording sheet. Both ends of the transfer sheet 6a are attached to a connecting member (not shown) of the transfer drum 6. In this embodiment, the transfer sheet 6a has a thickness of 150 μm and a volume resistivity of 10 μm.
A PC (polycarbonate) film of ¹⁵ ΩCm or more is used.

At the time of image formation, first, the inner static eliminator 6c,
By operating the outer static eliminator 6d, the transfer sheet 6a is electrically initialized, and the recording material P is fed from the direction of arrow B by a conveying means (not shown). Here, the electrically installed suction roller 6e is brought into close contact with the transfer sheet 6a by a driving source (not shown), and the suction charging brush 6
By f, a current (charge) is injected from the back surface of the transfer sheet 6a (the surface opposite to the surface carrying the transfer material). This induces (induces) a current (charge) in a direction opposite to that of the attraction / charging brush 6f. As a result, the recording material and the transfer sheet are polarized, and the recording material is electrostatically attracted to the transfer sheet. Note that the suction roller 6e operates to immediately separate from the transfer drum after the suction operation of the recording material P onto the transfer drum 6 is completed.

Next, a current (charge) having the same polarity as that of the attraction charging brush 6f is injected into the transfer charging brush 6b, and the toner image formed on the photosensitive drum 2 is transferred onto the recording material P.
In this embodiment, an organic OP is used for the photosensitive drum.
A photosensitive drum having a C photosensitive member on its surface is employed. The photosensitive drum employs a so-called reversal developing method in which the photosensitive drum is initially charged to the same polarity as the toner and developed in a portion where the charge amount is reduced by laser exposure. When performing multiple transfer, this transfer operation is repeated a desired number of times, and then a roller 6 for separation.
g, separated from the transfer drum 6 by the separation charger 10a. When a series of adsorption, transfer, and separation operations are completed, the inner static eliminator 6c and the outer static eliminator 6d operate again, and the transfer sheet 6a
Is electrically initialized.

(Curling means) A curling means for curling the recording material P in advance along the transfer drum in order to carry the sheet on the transfer drum 6 smoothly.
14 are provided. As shown in FIG. 3, the curling means 14 includes hard rollers 14a and 14b formed of a rigid material such as metal or resin, and an elastic roller 14c formed of an elastic material such as rubber. ing. Two hard rollers 14 are provided on one side of the conveying path of the recording material P.
a and 14b, and an elastic roller 14c is provided on the other side of the conveyance path.
And pressed against both the two hard rollers. Therefore, when the recording material P is passed through the curling means 14 in the direction of the arrow A, the recording material P
A curl in the direction along 14c can be provided. Further, these rollers are provided with a clutch (not shown) so that the rotation operation can be arbitrarily turned ON / OFF.

Here, according to the study by the inventors, the recording material P
Is peeled off from the transfer drum 6 from the leading edge P0 of the recording material, and it is known that if the suction property is sufficiently secured, the suction conveyance is basically achieved. That is, if a sufficient amount of curl can be added to the leading end P0 of the recording material, a certain amount of curl may be added to other portions of the recording material P.

It can also be seen that the curl amount of the recording material P also depends on the speed at which the recording material P passes through the curling means. The slower the recording material P is, the stronger the curl shape becomes. Was. By using this, the driving is temporarily stopped when the leading end P0 of the recording material passes through the curling means 14, so that a large curl amount can be applied only to the leading end P0 of the recording material.

In this embodiment, in order to effectively stop the leading end P0 of the recording material when the leading end P0 passes through the curling unit 14, the hard roller 14a is provided with a movement detecting sensor 15 as leading end detecting means. That is, when the recording material P passes through the hard roller 14a, the hard roller 14a moves by the thickness of the recording material. Therefore, the movement is detected by the movement detection sensor 15, whereby the hard rollers 14a, 14b and the elastic roller 14c are detected. Was stopped. With such a configuration, it is ensured that the leading end P0 of the recording material is
Can be stopped when it reaches.

As shown in FIG. 4, a mechanical lever 16a is provided upstream of the curling means 14 in the conveying direction as a tip detecting means.
A means for detecting the leading edge P0 of the recording material, such as a light transmission type sensor 16 having a function of calculating the time required for the leading edge P0 of the recording material to reach the curling means 14 from there, and stopping the curling means 14 May be. In this case, it is preferable that the light transmission type sensor 16 is closer to the curling means 14 because the accuracy is higher.However, at least there is no other conveying means such as a pair of rollers between the curling means 14 and the light transmission type sensor 16. Is desirable. This is because the arrival time of the recording material P to the curling means 14 is slightly changed due to the presence of another conveying means.
This is because, at the moment when the leading edge P0 of the recording material enters the curling unit 14, the curling unit 14 may not be stopped properly.

Since the strong curl is applied only to the leading end P0 of the recording material, the curl amount of the entire recording material P can be reduced to about half at the maximum, and the conveyance after the transfer process can be smoothly performed. It has become possible to realize good suction conveyance. Also, in the case where the image is formed on both sides by re-feeding, the curl amount applied to the entire recording material P may be small. It is easy to re-curl along.

[Other Embodiments] As described above, the present invention has a very simple structure in which the driving of the curl applying means 14 is temporarily stopped. Therefore, the curl amount can be adjusted only by controlling the stop time. It is also possible to easily control that the curling of the leading end of the recording material is not performed.
Therefore, it is possible to perform control such that the present invention is applied to the recording material P that is difficult to be attracted and conveyed to the transfer drum 6, and that the present invention is not applied to the recording material P that is difficult to be separated from the transfer drum 6. it can.

For example, the present invention is applied to a paper having a large thickness or a paper having a high rigidity because the paper has a strong stiffness and easily peels off from the transfer drum unless a stronger curl is applied. On the other hand, thin paper,
The paper having low rigidity has a weak stiffness and does not require a very strong curl. If the curl amount is too large, it is difficult to peel off the transfer drum 6 after the completion of the transfer process. Therefore, such a case can be dealt with by applying a weak curl to the entire recording material without applying the present invention.

Similarly, whether or not to carry out the present invention may be controlled depending on the environment at the time of image formation. That is, in a low humidity environment, the paper dries and the stiffness becomes stronger, and the present invention is implemented. In a high humidity environment, the paper absorbs moisture and the stiffness is weakened. It can be configured.

In the case where an image is formed on both sides, if a large curl is applied to the first side, it becomes difficult to carry by suction during the image formation on the second side. By carrying out the present invention only at the time of forming an image on the second side without carrying out the present invention, it is possible to preferably carry out suction and conveyance.

As described above, the curling means is controlled in accordance with the physical properties such as the thickness and rigidity of the recording material, the environment such as humidity, and the operating conditions such as the first and second sides of the double-sided image formation. This makes it possible to improve the transportability of the recording material in various cases.

[0030]

As described above, in the image forming apparatus according to the present invention, the driving of the curling means is temporarily stopped to form a strong curl only at the leading end of the recording material, so that the curling means can be added. The recording material can be effectively attracted to the transfer drum and conveyed without changing the pressure with a very simple configuration.

In addition, since the curl amount is adjusted by controlling the stop time, the above-described structure can be easily controlled according to the physical properties such as the thickness of the recording material and the operating environment. Further, the conveyance in the image forming apparatus can be stabilized.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of an image forming apparatus according to an embodiment.

FIG. 2 is an enlarged configuration diagram of a transfer drum.

FIG. 3 is a diagram illustrating curling means.

FIG. 4 is a diagram illustrating another configuration of the curling means.

FIG. 5 is a diagram illustrating a curling unit according to a conventional example.

[Explanation of symbols]

 P: Recording material P0: Recording material tip 1 ... Image forming device 2 ... Photosensitive drum 3 ... Charger 4 ... Optical device 5c ... Cyan developing device 5k ... Black developing device 5m ... Magenta developing device 5y ... Yellow developing device 6 ... Transfer drum 6a ... transfer sheet 6b ... transfer charging brush 6c ... inner static eliminator 6d ... outer static eliminator 6e ... suction roller 6f ... suction charging brush 6g ... roller 7 ... cleaning device 8 ... reading unit 9 ... feeding cassette 10 ... separating means 10a ... Separation charger 10b Separation unit 11 Transfer cleaner 12 Fixing unit 12a Heater 12b Fixing roller 12c Pressure roller 13 Discharge tray 14 Curling means 14a Hard roller 14b Hard roller 14c Elastic roller 15 Movement detection sensor 16: Light transmission type sensor 16a: Mechanical lever

Claims (6)

[Claims] An image carrier that carries a latent image; a developing unit that develops the latent image to form a toner image; a transfer drum that carries a recording material and transfers the toner image to the recording material; An image forming apparatus having a curling unit disposed on the upstream side in the transfer direction of the transfer drum and curling the recording material, wherein when the leading end of the recording material reaches the curling unit,
An image forming apparatus, wherein driving of the curling unit is temporarily stopped. 2. An image according to claim 1, further comprising a leading end detecting unit for detecting a leading end of said recording material, between said curling unit and a recording material conveying unit on the upstream side in the conveying direction. Forming equipment. 3. An operation of temporarily stopping the driving of the curling unit is performed according to a physical property value of a recording material during image formation, an environment during image formation that affects the physical property value of the recording material, or an operating condition of the apparatus. The image forming apparatus according to claim 1, wherein the control is performed in accordance with the image forming apparatus. 4. The image forming apparatus according to claim 3, wherein the physical property value of the recording material is a thickness or rigidity of the recording material. 5. The image forming apparatus according to claim 3, wherein the environment at the time of image formation is humidity around the image forming apparatus. 6. The image forming apparatus according to claim 3, wherein the operating condition of the image forming apparatus is that the recording material is reversed and re-fed to perform image recording on both sides.