JPH0836283A - Image forming device - Google Patents

Abstract

(57) [Summary] (Correction) [Structure] Photoreceptor (image carrier) 8, transfer charger (transfer means) 10, fixing device (fixing means) 20, transfer portion of the transfer charger 10. In the image forming apparatus including the registration roller pair 17 installed on the upstream side of the
The transfer charger 10 has a length L in the transport direction of the transfer material.
Of the transfer material from the transfer position to the fixing device 20 is L ₁ , and from the registration roller pair 17 to the fixing device 20.
The transfer charger 10, the fixing device 20, and the registration roller pair 17 are arranged so that L ₁ > L or L ₂ <L, where L ₂ is the transport distance of the transfer material up to. [Effect] When L ₁ > L, the rear end of the transfer material has passed through the transfer charger 10 when the transfer material has entered the fixing device 20, and when L ₂ <L, the rear end of the transfer material is Since it is held by the pair of registration rollers 17, the transfer material fixing device 20
It is possible to prevent the image from being disturbed at the transfer portion due to the impact at the time of rushing in.

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 an electrophotographic copying apparatus or an electrophotographic printer which utilizes an electrostatic transfer process, and more particularly to an image forming apparatus having a transfer / separation device.

[0002]

2. Description of the Related Art A conventional image forming apparatus electrostatically forms a transferable toner image on the surface of a rotating image carrier, and a transfer material that runs synchronously is brought into close contact with the toner image position of the image carrier. At the same time, the back surface of the transfer material is charged with a polarity opposite to that of the toner, and the toner image on the image carrier is transferred to the transfer material side.

In such an image forming apparatus, in order to convey the transfer material carrying the toner image to the fixing portion, it is necessary to separate the transfer material after transfer from the image carrier.

By the way, various types of separating means for separating the transfer material from the image bearing member have been proposed in the past. For example, a separating charger is arranged on the downstream side in the traveling direction of the transfer material, and AC discharge is performed. Alternatively, there is one in which a discharge having a DC discharge of the same polarity as the toner is applied to the transfer material. This separation means
By removing the charge of the transfer material, the attraction of the transfer material to the image carrier is removed, whereby the elasticity of the transfer material itself or its own weight is used to separate the transfer material from the image carrier. It is configured as described above and has already been widely put into practical use.

FIG. 3 is a sectional view of a main part of a copying machine provided with such a separating means and a drum-shaped image carrier (photoconductor). The operation of the copying machine will be outlined below with reference to FIG. To do.

The surface photoconductive layer of the photoconductor 8 which rotates in the direction of the arrow a in the figure is uniformly charged by the primary charger 13 and then receives the original light image to form an electrostatic latent image on the photoconductor surface. This electrostatic latent image reaches the position of the developing device 9 as the photoconductor 8 rotates, is visualized as a toner image by being supplied with toner there, and further advances to a transfer portion including the transfer charger 10. Leading to.

On the other hand, the transfer material P guided along the path 34 comes into contact with the photoconductor 8 at the transfer portion, and at this position, the transfer charger 10 imparts a charge having a characteristic opposite to that of the toner to the back surface, As a result, the toner image carried on the photoconductor 8 is attracted and transferred by the electrostatic attraction force.
After that, when the charge of the transfer material P is erased by the separation charging device 11 arranged on the downstream side of the transfer charging device 10, the adsorption action of the transfer material P on the photoconductor 8 is lost, and the transfer material P is lost.
The elasticity of itself, and in the case of the configuration shown in the figure, the transfer material P
The transfer material P is separated from the photoconductor 8 by its own weight and moves to the next step along the conveying means 18. In addition, the transfer described above
The separation process is excellent for all types of image forming apparatus.

[0008]

However, in recent years,
Since the image forming apparatus has been downsized, the following problems have occurred.

That is, as shown in FIG. 4, when the transfer material P enters the fixing device 20, the rear end of the transfer material P does not pass over the transfer charger 10, so the transfer process is completed. If not happened. Therefore, when the transfer material P plunges into the fixing device 20, the shock may cause the transfer material P to vibrate, resulting in a minute image shake in the transfer process, which may adversely affect image formation. In particular, when the transfer material P is a thick letter, or when the rigidity of the paper which is the transfer material P is high in a low temperature and low humidity environment, the adverse effect is great.

As measures against the above problems, several kinds of proposals as shown in FIG. 5 have been made. As an example thereof, the transfer path from the transfer means 18 to the fixing device 20 is bent into a dogleg shape and the transfer material P is bent (that is, the transfer material P
There is something that prevents the vibration from being transmitted to the transfer part.

The above method is certainly effective, but if the portion E in the drawing of the conveying path has to be arranged in a position lower than the conventional one, and there is a space in the lower direction, Although it is applicable, when a double-sided multiplex transport path 19 is provided below the transporting means 18 as shown in FIG. 4, there is no space in terms of space and the apparatus must be upsized. . This conflicts with the recent miniaturization of devices.

As another example, the pressure roller 42 is shown in FIG.
To a position indicated by a dotted line in FIG.
There is a type in which the vector direction of the shock when it rushes in is directed in the direction of arrow A so that the vibration is not transmitted to the transfer portion. This method is also effective, but the pressure roller 4
Since the position 2 is moved in the direction of the dotted line in FIG. 5, the curl of the transfer material P (particularly in the downward direction) becomes large, and the rear end of the transfer material bounces. Then, in order to solve these problems, a major change in the device is required.

Further, as another example, there is proposed a device in which a suction fan 35 is provided in the conveying means 18 to increase the suction force between the transfer material P and the conveying belt 18a so that the vibration is not transmitted to the transfer portion. .

However, in the above method, an increase in cost for adding the suction fan 35 itself and its driving means is unavoidable, and cannot be said to be the best means for carrying out.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a transfer portion at the transfer portion due to an impact at the time when the transfer material is rushed into the fixing means without a major modification of the apparatus. An object of the present invention is to provide an image forming apparatus capable of preventing image distortion.

[0016]

In order to achieve the above object, the invention according to claim 1 provides an image carrier and a transfer means for transferring an unfixed developer image formed on the image carrier to a transfer material. An image formation including a fixing unit for fixing the unfixed developer image transferred to the transfer material by the transfer unit, and a roller pair installed upstream of the transfer unit of the transfer unit in the transport direction. In the apparatus, the length of the transfer material in the transport direction is L, the transport distance of the transfer material from the transfer position of the transfer unit to the fixing device is L ₁ , and the transfer material from the roller pair to the fixing device is transported. The transfer means, the fixing means, and the roller pair are arranged so that L ₁ > L or L ₂ <L when the distance is L ₂ .

According to a second aspect of the invention, in the first aspect of the invention, the roller pair is the first roller pair located upstream of the transfer portion of the transfer means in the transport direction. And

Further, the invention according to claim 3 is characterized in that, in the invention according to claim 2, the roller pair is a registration roller pair.

[0019]

According to the present invention, when the length L of the transfer material in the transport direction is short, the relationship with the transport distance L ₁ of the transfer material is L _1.
> L, and when the transfer material rushes into the fixing means, the trailing edge of the transfer material has passed through the transfer means, so that minute image shake does not occur in the transfer step.

On the other hand, when the length L of the transfer material in the transport direction is long, the relationship with the transport distance L ₂ of the transfer material is L ₂ <L, and when the transfer material enters the fixing means, the transfer material Since the rear end is held by the roller pair, it is possible to prevent the image from being disturbed at the transfer portion due to the impact when the transfer material enters the fixing unit.

Further, according to the present invention, the above effects can be obtained without major modification of the device.

[0022]

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

FIG. 1 is a sectional view of a conveying section of a copying apparatus which is an image forming apparatus according to the present invention, and FIG. 2 is a sectional view of the copying apparatus.

The copying apparatus 1 according to the present embodiment is constructed so as to be able to perform multiplex copying or double-sided copying on the same transfer material P, which is a copying unit (as shown in FIG. 2). It has a copying machine main body 3 having an image forming section 2 built therein.

The apparatus main body 3 is provided with a document placing table 4, a light source 5, a lens system 6, upper and lower two-stage cassettes 7a and 7b, and the like, and a drum-shaped photosensitive body 8 and the like are provided in a substantially central portion thereof. The copying section 2 constituted by is arranged.

Further, in the vicinity of the periphery of the photoconductor 8, two developing devices 9a and 9a containing toners of different colors are contained.
b is provided so that it can be set / reset by moving in the direction of the arrow so that it can be copied in a desired color, and further on the downstream side in the rotational direction of the photoconductor 8, a transfer charger 10, a separation charger 11, a cleaner 12 and a primary charger. Chargers 13 are provided respectively.

On the other hand, paper feed rollers 14a and 14b are provided in the vicinity of the cassettes 7a and 7b, and one of the paper feed rollers 14a and 14b sends out one by one from the cassette 7a or 7b. The transfer material P is
Transport roller pair 15a or 15b, path 16a or 16b
And is guided to the registration roller pair 17. Further, the transfer material P, which is subjected to multiple copying or double-sided copying, is guided to the registration roller pair 17 via a sheet conveying path 19 provided under the apparatus main body 3.

On the other hand, on the downstream side of the separation charging device 11 (downstream side in the transport direction of the transfer material P), a transport device 18 having a transport belt 18a is arranged, and on the downstream side of this transport device 18, a fixing device is provided. 20 are provided. The fixing device 20
Includes a fixing roller 41 and a pressure roller 42 that rotate in contact with each other.

Further, a paper discharge portion including a first discharge roller pair 21 and a second discharge roller pair 22 is provided on the downstream side of the fixing device 20, and the fixing portion is provided in the paper discharge portion. The transfer material P ejected from the apparatus 20 is ejected from the first ejection roller pair 21 through the second ejection roller pair 22 to a tray or the like outside the apparatus.

A flapper 23 and an auxiliary flapper 24 are arranged between the first discharge roller pair 21 and the second discharge roller pair 22, and normally, the first discharge roller pair 21 discharges. The transferred transfer material P is conveyed along the upper side of the flapper 23 at the solid line position. Then, the auxiliary flapper 24 is vibrated by the conveying force of the transfer material P, and the detection arm 25 operates the optical sensor 26 based on the vibration to detect the passage of the transfer material P, and the second discharge roller pair that normally rotates. The transfer material P is discharged outside the machine by 22.

On the other hand, during double-sided copying, the transfer material P is partially discharged outside the apparatus by the forward rotation of the second discharge roller pair 22 as in the normal state, up to the middle. When the rear end of P leaves the auxiliary flapper 24, the second discharge roller pair 22 is reversely driven by the operation of the detection arm 25 and the optical sensor 26, and the transfer material P is thereby driven by the auxiliary flapper 24 and the flapper 23. It is guided by the left side portion and introduced into the path 27. Therefore, during double-sided copying, the second discharge roller pair 22, the detection arm 25,
The transfer material P is re-fed by the optical sensor 26 and the path 27.

Further, in the case of multiple copying, the flapper 23 is switched to the position shown by the dotted line in FIG.
The transfer material P discharged from No. 1 is directly introduced into the path 27 by the guiding action of the right side portion of the flapper 23. Therefore,
At the time of multiple copying, the transfer material P is re-fed by the first discharge roller pair 21, the flapper 23 and the path 27.
Then, the transfer material P introduced into the path 27 is conveyed by the conveying roller pair 28 and conveying roller pairs 29, 30 constituting the conveying means.
And the registration roller pair 17 via the sheet conveying path 19.
Will be guided to. The sheet conveying path 19 includes a pair of registration rollers 31 configured to be movable in the axial direction in order to align one lateral end of the transfer material P with a reference position.

By the way, a transfer material presence / absence detecting means 32 is disposed in close proximity to the registration roller pair 17, and the transfer material presence / absence detecting means 32 is a limiter such as a micro switch, and is usually shown by a solid line. It is located in the transfer material conveyance path, and when the transfer material P passes through it, the detection arm operates to generate a signal.

Further, in the vicinity of the registration roller pair 17,
An optical sensor 33 for detecting the thickness of the transfer material is installed, and the optical sensor 33 includes a light emitting portion 33a in which a large number of light emitting elements are arranged in parallel and a light receiving portion 33b in which a large number of light receiving elements are arranged. Has been done.

As a method of feeding the transfer material, the cassette 7 is used.
In addition to feeding from a and 7b, by rotating the manual feed tray 50 in the direction of arrow B in FIG. 2, the tray 50 is also fed under the upper feed roller 14a to feed the paper, so-called manual feed. Is also possible.

When the transfer material fed from the cassette 7a or 7b passes through the detecting means 32, the time until the leading edge of the transfer material enters the fixing device 20 and the trailing edge of the transfer material are detected. The time to complete the transfer process is known.

Here, the schematic structure of the conveying section of the copying apparatus 1 will be described with reference to FIG.

The conveyance distance of the transfer material P from the transfer position by the transfer charger 10 to the center position of the fixing roller 41 and the pressure roller 42 of the fixing device 20 is L ₁ , and the registration roller pair 17
The transfer distance of the transfer material P from the center position of the fixing roller 41 to the center position of the fixing roller 41 is L ₂ . The transfer material fed from the cassettes 7a and 7b has various standard sizes such as A3, A4, B4 and B5.

When the length of the transfer material P loaded in the cassettes 7a and 7b in the transport direction is L, the transfer charger 10 is set so that L ₁ > L or L ₂ <L. A pair of registration rollers 17 and a fixing device 20 are arranged. Therefore, when the length L of the transfer material P fed from the cassettes 7a and 7b in the conveyance direction is short, the transfer distance L of the transfer material P is L.
Is L _1> L next relationship between _1, the transfer material P is fixing device 20
When the transfer material P enters the transfer charger 10, the rear end of the transfer material P is transferred to the transfer charger 10.
Since it passes through the top, minute image shake does not occur in the transfer process.

On the other hand, when the length L of the transfer material P fed from the cassettes 7a and 7b in the transport direction is long, the relationship with the transport distance L ₂ of the transfer material P is L ₂ <L, and the transfer material P is Since the rear end of the transfer material P is held by the registration roller pair 17 when the transfer material P enters the fixing device 20, it is possible to prevent the image from being disturbed in the transfer portion due to the impact when the transfer material P enters the fixing device 20. You can

According to the present embodiment, the above effects can be obtained without major modification of the device.

[0042]

As is apparent from the above description, according to the present invention, an image carrier, transfer means for transferring an unfixed developer image formed on the image carrier to a transfer material, and the transfer means. In the image forming apparatus including a fixing unit that fixes the unfixed developer image transferred to the transfer material by the transfer unit, and a roller pair installed on the upstream side in the transport direction with respect to the transfer unit of the transfer unit, The length of the transfer material in the transport direction is L, the transport distance of the transfer material from the transfer position of the transfer unit to the fixing device is L ₁ , and the transport distance of the transfer material from the roller pair to the fixing device is L ₂ In this case, since the transfer means, the fixing means and the roller pair are arranged so that L ₁ > L or L ₂ <L, it is possible to prevent the transfer material from entering the fixing means without major modification of the apparatus. Prevents image distortion at the transfer area due to impact The effect of being able to be obtained is obtained.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a configuration of a conveying section of a copying apparatus which is an image forming apparatus according to the present invention.

FIG. 2 is a cross-sectional view of a copying machine that is an image forming apparatus according to the present invention.

FIG. 3 is a cross-sectional view showing a configuration of a carrying section of a conventional copying apparatus.

FIG. 4 is a sectional view of a conventional copying apparatus.

FIG. 5 is a cross-sectional view showing a configuration around a transfer material conveying path of a conventional copying apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Copier (image forming apparatus) 8 Photoconductor (image carrier) 10 Transfer charger (transfer means) 17 Registration roller pair (roller pair) 20 Fixing device (fixing means) P Transfer material

Claims (3)

[Claims] 1. An image carrier, transfer means for transferring the unfixed developer image formed on the image carrier to a transfer material, and the unfixed developer image transferred to the transfer material by the transfer means is fixed. In an image forming apparatus including a fixing unit configured to cause the transfer unit and a roller pair installed on the upstream side in the transport direction with respect to the transfer unit of the transfer unit, a length of the transfer material in the transport direction is L,
When the transport distance of the transfer material from the transfer position of the transfer unit to the fixing device is L ₁ and the transport distance of the transfer material from the roller pair to the fixing device is L ₂ , L ₁ > L or L ₂ An image forming apparatus in which the transfer unit, the fixing unit, and the roller pair are arranged so that <L. 2. The image forming apparatus according to claim 1, wherein the roller pair is the first roller pair located upstream of the transfer portion of the transfer unit in the transport direction. 3. The image forming apparatus according to claim 2, wherein the roller pair is a registration roller pair.