JP4469321B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile machine, or a plotter, and more particularly to an image forming apparatus having a mechanism for accurately performing a transfer position alignment of a recording medium and a toner image.

In multicolor image forming apparatuses such as full-color printers and spot color printers, a plurality of photosensitive drums are arranged along the traveling direction of an intermediate transfer belt composed of an endless belt, and electrostatic latent images formed on the respective photosensitive drums are arranged. There is a tandem system in which toners of different colors are adsorbed to form a toner image and sequentially transferred onto a transfer belt.
In such an image forming apparatus, normally, the sheets stacked on the sheet feeding device are fed out one by one, and the fed-out sheets are conveyed toward the toner image transfer position. As a method of aligning the position of the toner image with the sheet, the sheet is temporarily stopped by the pair of registration rollers before the transfer position, and the pair of registration rollers is driven in time with the toner image conveyed on the transfer belt. A method of feeding a sheet to a transfer position is generally known.

In addition, the sheet may be conveyed obliquely from the sheet feeding device. In this case, the sheet is formed by abutting the leading end of the sheet against the nip of the stopped pair of registration rollers and then pushing the sheet further. A method of correcting the leading edge of the sheet at the nip position of the registration roller pair by the bending of the sheet is often used.
As another method, as shown in Patent Document 1, gate means for positioning in the direction perpendicular to the paper conveyance direction is provided on the conveyance path, and the paper position is corrected by abutting the leading edge of the paper against the gate means. A method has been proposed.

However, in the method in which the leading edge of the paper is brought into contact with the nip of the registration roller pair, the leading edge of the paper bites into the nip of the registration roller pair when the leading edge of the paper is curled or when the paper conveyance path in front of the registration roller is not a straight line. It is difficult to break the paper jam and the leading edge. Further, when a thick sheet reaches the registration roller pair in an oblique state, the correction by the above-described method cannot be performed, and there is a problem that the thick sheet bites into the nip of the registration roller pair in an oblique state.
In the configuration of Patent Document 1, the sheet is stopped by the gate unit. However, since the registration roller pair is disposed immediately after the gate unit, the sheet is not removed after the gate unit is opened, such as when the leading end of the sheet is curled. The leading edge is difficult to bite into the nip of the registration roller pair, so that the paper jam or leading edge breaks, or the leading edge of the paper bends when the paper hits the gate means. There was a problem in biting into.

In order to solve this problem, in Patent Document 2, a gate unit is disposed on the downstream side of the registration roller pair, and the leading end of the sheet is abutted against the gate unit in a state where the registration roller pair is separated, and then positioning is performed. There has been proposed a system in which after a pair of registration rollers are brought into contact with each other and a sheet is sandwiched, the gate means is opened and conveyed to an image transfer portion by a registration roller pair at a predetermined timing.
According to this method, the leading edge of the sheet after positioning by the gate means is sandwiched by the pair of registration rollers, so that it can be conveyed to the image transfer site without causing a shift after positioning.

Japanese Patent No. 2893540 JP 2002-265097 A Japanese Patent Laid-Open No. 11-30884 JP 2003-252485 A JP 2003-206051 A

However, in the method described in Patent Document 2, since the sheet is conveyed to the image transfer site using the registration roller pair as the final conveyance unit after the gate unit is opened, the separation operation of the registration roller pair with respect to the next sheet and the gate unit The closing operation has to be performed after the conveyance of the registration roller pair is completed, that is, after the trailing edge of the sheet has passed through the registration roller pair.
In other words, the paper feeding speed cannot cope with the high speed image forming operation, which hinders the high speed image forming apparatus.

  The main object of the present invention is to provide an image forming apparatus capable of improving the paper feeding speed while accurately performing transfer position alignment with a toner image, and capable of coping with high speed.

In order to achieve the above object, according to the first aspect of the present invention, there is provided a gate means capable of opening and closing a recording medium conveyance path and capable of positioning by abutting the leading end of the recording medium at a closed position, and recording of the gate means. A registration roller pair that is provided in the vicinity of the upstream side in the medium conveyance direction, and that can be contacted / separated, and positioning is performed by the gate means in a state in which the registration roller pair is separated; In an image forming apparatus in which the gate unit is opened and the recording medium is conveyed to the image transfer site downstream of the gate unit in the recording medium conveyance direction at a predetermined timing by the pair of registration rollers, between the gate unit and the image transfer site. disposed, and a recording medium timing rollers can be conveyed to the image transfer position, the recording medium conveying direction upstream of the resist roller pair And a pair of conveying rollers that are capable of conveying the recording medium toward the registration roller pair and that can contact and separate, and after the positioning, the registration roller pair is brought into contact, and then the conveyance roller pair is separated from the registration roller pair. After the registration roller pair is conveyed, the registration roller pair is separated at the arrival timing of the recording medium with respect to the timing roller pair , and after the registration roller pair is separated, the rear end of the recording medium passes through the conveyance roller pair. The conveying roller pair is brought into contact, and the gate means is closed after the rear end of the recording medium passes through the gate means .

  According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the registration roller pair is positioned upstream of the registration roller pair in the recording medium conveyance direction, and includes a recording medium detection unit that detects the recording medium. Based on the detection information by the means, the recording medium is brought into contact with the gate means, and the recording medium is stopped while the recording medium is bent.

According to a third aspect of the present invention, in the image forming apparatus according to the second aspect , the amount of deflection of the recording medium depends on the type of the recording medium, the thickness of the recording medium, the width of the recording medium, or the length of the recording medium. It can be changed .

According to a fourth aspect of the present invention, in the image forming apparatus according to the second aspect , when the recording medium is abutted against the gate means, the speed of the pair of conveying rollers is reduced before the recording medium abuts against the gate means. It is characterized by that.

According to a fifth aspect of the present invention, in the image forming apparatus according to the fourth aspect , the conveyance speed of the recording medium when the recording medium is abutted against the gate means is defined as the type of the recording medium, the thickness of the recording medium, and the recording medium. characterized in that the length of the width or the recording medium of the medium is therefore changeable.

  According to the present invention, it is possible to improve the paper feed speed while accurately aligning the transfer position with the toner image, and it is possible to cope with a higher speed.

Hereinafter, a first embodiment of the present invention will be described with reference to FIGS.
First, an outline of a four-color full-color image forming apparatus as an “image forming apparatus using a paper positioning mechanism” in the present embodiment will be described with reference to FIG. The image forming apparatus includes four image forming units 1 a, 1 b, 1 c, and 1 d arranged along the traveling direction of the transfer belt 10.
The image forming unit 1a includes a photosensitive drum 2a as an image carrier, a drum charger 3a, an exposure device 4a, a developing device 5a, a transfer device 6a, a cleaning device 7a, and the like. The image forming units 1b to 1d are configured similarly to 1a.
The image forming units 1a to 1d form images having different colors, for example, 1a is yellow, 1b is magenta, 1c is cyan, and 1d is black.
Upon receiving an image forming operation start instruction signal from a controller (not shown), the photosensitive drum 2a starts rotating in the direction of arrow B and continues rotating until the image forming operation ends. When the photosensitive drum 2a starts rotating, a high voltage is applied to the charger 3a, and negative charges are uniformly charged on the surface of the photosensitive drum 2a.

Then, when the character data or graphic data converted into a dot image is sent from the controller (not shown) to the image forming apparatus as an on / off signal of the exposure device 4a, a laser beam is emitted from the exposure device 4a to the surface of the photosensitive drum 2a. A portion irradiated with light and a portion not irradiated are formed. When the portion where the charge is reduced on the photosensitive drum 2a reaches the position facing the developing device 5a by the irradiation of the laser beam from the exposure device 4a, the portion where the charge is reduced on the photosensitive drum 2a is charged with a negative charge. The attracted toner is attracted to form a toner image.
When the toner image formed on the photosensitive drum 2a reaches the transfer device 6a as the primary transfer means, the toner image is rotated in the direction of arrow A by the action of a high voltage applied to the transfer device 6a. Transferred onto the belt 10. Note that the toner remaining without being transferred onto the photosensitive drum 2a even after passing through the transfer position (image transfer portion) is cleaned by the cleaning 7a and is prepared for the next image forming operation.

An image forming operation is performed in the same manner in the image forming unit 1b following the image forming unit 1a, and the toner image formed on the photosensitive drum 2b is applied on the transfer belt 10 by the action of a high voltage applied to the transfer device 6b. Transcribed.
At this time, the timing at which the image formed by the image forming unit 1a and transferred onto the transfer belt 10 reaches the transfer device 6b and the toner image formed on the photosensitive drum 2b are transferred to the transfer belt 10. The toner images formed by the image forming unit 1a and the image forming unit 1b are overlapped on the transfer belt 10 by matching the timing.
Similarly, a full color image is formed on the transfer belt 10 by superimposing the toner images formed by the image forming units 1 c and 1 d on the transfer belt 10.

At the same time when the full-color image reaches the paper transfer unit 9 as the secondary transfer unit, the paper 8 as the recording medium conveyed in the direction of arrow C from the paper feed unit (not shown) of the image forming apparatus is transferred to the paper transfer unit 9. The full color image on the transfer belt 10 is transferred to the paper 8 by the action of the high voltage applied to the paper transfer device 9. When the paper 8 is conveyed to the fixing device 11, the toner image on the paper 8 is melted and fixed on the paper 8.
On the other hand, after the full-color image has passed through the paper transfer unit 9, toner that is not transferred adheres to the transfer belt 10, and the toner is cleaned by the belt cleaning mechanism 12.

Hereinafter, a paper positioning mechanism in front of the paper transfer unit 9 (upstream in the paper conveyance direction) will be described in detail.
FIG. 1 is a schematic configuration diagram showing a paper positioning mechanism. As shown in FIG. 1, the paper positioning mechanism of the present embodiment includes a gate means 13 for positioning the leading edge of the paper by abutting the conveyed paper, and upstream of the gate means 13 in the paper conveyance direction (hereinafter simply “ Registration roller pair 14 arranged in the vicinity of the upstream), conveyance roller pair 15 arranged upstream of the registration roller pair 14, and paper detection for detecting the paper arranged upstream of the gate means 13. Means 16, and a timing roller pair 17 disposed between the gate means 13 and the image transfer part on the downstream side (hereinafter simply referred to as “downstream”) in the sheet conveyance direction.
The registration roller pair 14, the conveyance roller pair 15, and the timing roller pair 17 are provided so as to be able to contact and separate (separate, contact, or press contact) by driving means (not shown).

Next, the sheet positioning operation will be described with reference to FIG.
The sheet 8 fed out from the sheet feeding unit is conveyed in the direction of arrow C at a specified speed V1 toward the gate means 13 by the conveying roller pair 15 and the like. At this time, before the sheet 8 reaches the registration roller pair 14, the registration roller pair 14 is separated and the gate means 13 is closed. (FIG. 3A).
Further, since the leading edge of the conveyed paper 8 hits the gate means 13 and the rear end side of the paper 8 is sent to the downstream side by the conveying roller pair 15 from the abutted state (overfeed), the paper 8 is bent. (FIG. 3B).
Here, the speed at which the paper 8 strikes the gate means 13 and the amount of flexure of the paper will be described with reference to FIG. 4. The paper 8 conveyed at the speed V1 from the paper feed unit is gated at the speed V1. Then, when the paper detection means 16 detects the leading edge of the paper and T11 elapses, a stop process of a drive means (not shown) which is a drive source of the conveying roller pair 15 is executed.

Since the paper 8 is pushed by the conveying roller pair 15 for T12 after the leading edge of the paper 8 hits the gate means 13, the paper 8 is bent by T12. At this time, the amount of deflection of the paper 8 can be adjusted by adjusting T11. However, the amount of deflection of the paper 8 is determined in advance according to conditions such as the paper type, paper thickness, paper width, and paper length. And vary according to the value.
More specifically, the controller memory stores in advance a data table of the relationship between the condition such as the type of paper and the like that has been obtained in advance by experiments and the excessive feed, and the paper condition is set by an operation panel (not shown), or When it is automatically detected by a detection means (not shown) or condition information is input by a PC (not shown), a numerical value for overfeed corresponding to the condition is extracted from the data table and set.

Due to the excessive feeding in the state of being abutted against the gate means 13, the front end of the paper 8 is corrected for the oblique shift. In this state, the registration roller pair 14 closes in the direction of arrow E and presses the paper, whereby the leading edge of the paper 8 is positioned at the position of the gate means 13 (FIG. 3C).
Subsequently, the gate means 13 is opened in the direction of the arrow F so as to be retracted from the transport path, and the transport roller pair 15 is separated in the direction of the arrow G, so that the paper 8 returns to a straight state (FIG. 3D). . That is, the positional deviation on the upstream side of the registration roller pair 14 is also corrected.

From this state, the registration roller pair 14 has a predetermined timing, that is, the front end in the belt rotation direction of the toner image on the transfer belt 10 and the front end in the conveyance direction of the paper 8 in time with the toner image carried on the transfer belt 10. The paper 8 is conveyed at a specified speed in the direction of arrow C at the timing when the predetermined position of the part coincides (FIG. 3E).
When the leading edge of the paper 8 reaches the nip of the timing roller pair 17 and is ready to be conveyed by the timing roller pair 17, the registration roller pair 14 is separated in the direction of arrow I to obtain the next paper positioning state. When the trailing edge of the paper 8 passes through the transport roller pair 15, the transport roller pair 15 is pressed in the direction of the arrow H to prepare for the next paper transport (FIG. 3 (f)).
The arrival timing of the leading edge of the sheet 8 with respect to the timing roller pair 17 is managed by the number of rotations, time, and the like after the registration roller pair 14 starts to rotate. This management value is preferably determined in advance according to conditions such as paper type, paper thickness, paper width, paper length, and the like, and is preferably varied according to the values.
When the trailing edge of the paper 8 passes through the gate means 13, the gate means 13 closes in the direction of the arrow J so as to block the paper transport path, and waits for the arrival of the next paper (following paper) (FIG. 3 (g)).

As shown in FIG. 4, the time required for transporting the paper 8 to the image transfer site with only the registration roller pair 14, that is, waiting for the rear end of the paper 8 to pass through the registration roller pair 14 (conventional method), is longer. Can have Y margin.
For this reason, the closing operation of the gate unit 13 can be performed at a timing immediately after the trailing edge of the sheet passes through the gate unit 13, and the distance between sheets can be shortened.
In FIG. 4, “ON” indicates a contact or closing operation, and “OFF” indicates a separation or opening operation.

By repeating the operations described above, positioning of the sheet conveyed in an oblique state can be accurately performed under various conditions.
In this embodiment, the separation / pressure contact of the conveying roller pair 15 has been described. However, depending on the length of the sheet 8 being conveyed, when the leading end of the sheet 8 stops at the position of the gate means 13, the rear end is the conveying roller pair. 15, the roller pair 18 may be placed on the upstream side of the roller 15. In this case, the roller pair 18 is also separated and pressed in the same manner as the conveying roller pair 15.

A second embodiment will be described with reference to FIG. In addition, the same part as the said embodiment is shown with the same code | symbol, and unless it was especially required, the description on the structure and function which were already demonstrated is abbreviate | omitted, and only the principal part is demonstrated.
When T21 elapses after the sheet 8 conveyed at the speed of V1 from the sheet feeding unit reaches the sheet detection unit 16, the driving unit decelerating process of the conveyance roller pair 15 is started, and the sheet 8 hits the gate unit 13. Until the speed of the conveying roller pair 15 is reduced to V2 (V1> V2).
By doing so, the paper 8 strikes the gate means 13 at a speed of V2 that is slower than V1. When T22 has passed since the sheet 8 arrived at the sheet detecting means 16, the driving means for stopping the driving roller pair 15 is stopped. As a result, the sheet 8 stops in a state in which the deflection for the time T23 from when the sheet 8 hits the gate means 13 until the conveyance roller pair 15 stops is formed. This amount of deflection can be adjusted by T22.

As with the first embodiment, the amount of deflection of the paper 8 and the speed V2 when the paper 8 is brought into contact with the gate means 13 are optimized in advance according to conditions such as the paper type, paper thickness, paper width, paper length, and the like. A value is determined, and is varied according to the value.
By repeating the operation described above, the paper 8 conveyed in an oblique state is accurately positioned, and damage to the front end of the paper due to the paper 8 hitting the gate means 13 is prevented. Even under certain conditions, it is surely implemented.

It is a principal part front view of the positioning mechanism part in the 1st Embodiment of this invention. 1 is a schematic diagram of an image forming apparatus. FIGS. 5A and 5B are diagrams illustrating a flow of positioning operation, in which FIG. 5A is a diagram illustrating a state before the leading end of the sheet hits the gate unit, and FIG. ) Is a diagram showing a state in which the registration roller pair is closed and the leading end of the paper is sandwiched, (d) is a diagram showing a state in which the gate means is opened, and (e) is a diagram showing a state in which conveyance is started by the registration roller pair, (F) is a diagram showing a state in which the leading edge of the paper reaches the timing roller pair and the registration roller pair is separated, and (g) is a diagram showing a state in which the gate means is closed and the next paper is ready for positioning. . It is a timing chart. It is a timing chart in a 2nd embodiment.

Explanation of symbols

8 Paper as recording medium 13 Gate means 14 Registration roller pair 15 Conveying roller pair 17 Timing roller pair

Claims (5)

A gate means capable of opening and closing a recording medium conveyance path and positioning the recording medium by abutting the leading edge of the recording medium at a closed position; Positioning with the gate means in a state in which the registration roller pair is separated, and after the positioning, the registration roller pair is brought into contact and the gate means is opened, and the recording medium is opened at a predetermined timing by the registration roller pair. In the image forming apparatus for transporting the image transfer portion downstream of the gate means in the recording medium transport direction,
A timing roller pair disposed between the gate means and the image transfer site and capable of transporting the recording medium to the image transfer site, and positioned upstream of the registration roller pair in the recording medium transport direction. A pair of conveying rollers that can be conveyed toward the roller pair and that can be moved toward and away from the roller pair;
After the positioning, the registration roller pair is brought into contact, and then the conveyance roller pair is separated and conveyed by the registration roller pair,
The registration roller pair is separated at the arrival timing of the recording medium with respect to the timing roller pair ,
After separating the registration roller pair, the rear end of the recording medium passes through the transport roller pair and then the transport roller pair is brought into contact, and the rear end of the recording medium passes through the gate means and then the gate means is closed. An image forming apparatus. The image forming apparatus according to claim 1.
The registration roller pair is positioned upstream of the recording medium conveyance direction, and includes a recording medium detection unit that detects the recording medium. Based on the detection information by the recording medium detection unit, the recording medium is abutted against the gate unit. An image forming apparatus characterized in that the recording medium is stopped in a state where the tape is bent. The image forming apparatus according to claim 2 .
An image forming apparatus , wherein the amount of bending of the recording medium can be changed according to the type of the recording medium, the thickness of the recording medium, the width of the recording medium, or the length of the recording medium . The image forming apparatus according to claim 2 .
An image forming apparatus characterized in that, when a recording medium is abutted against the gate means, the speed of the conveying roller pair is reduced before the recording medium abuts against the gate means . The image forming apparatus according to claim 4 .
The conveying speed of the recording medium when abutting the recording medium to said gate means, the type of the recording medium, the thickness of the recording medium, characterized in that the length of the width or the recording medium of the recording medium thus can be changed Image forming apparatus.

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