JPH08106186A - Paper transport device for image forming apparatus - Google Patents

Abstract

(57) [Summary] [Purpose] Control is performed so that paper conveyance problems due to changes in the relationship between the registration roller linear velocity and the grip roller linear velocity do not occur. [Structure] When the number of passed sheets of paper P reaches a predetermined number of passed sheets, a time for determining a slack amount (registration sensor 3
The time period from the detection of the paper P in 3 until the driving of the grip roller pair 21 is stopped) is gradually increased, and the slack of the paper P between the registration roller pair 22 and the grip roller pair 21 is changed with time. Manage.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a copying machine, a printer,
The present invention relates to a sheet conveying device of an image forming apparatus such as a facsimile, a printing machine, and an electronic blackboard.

[0002]

2. Description of the Related Art FIG. 5 is a sectional view showing a laser printer, which is an example of an image forming apparatus, and schematically shows the entire structure of its internal mechanism. In the figure, 10 is the main body of the apparatus, in which the upper structure 10a is replaced with the lower structure 10b.
It is attached by a hinge 11 so as to be openable and closable, and a belt-shaped photosensitive member 12 is provided at the substantially center inside. Around the photoconductor 12, a charging device 13, a developing device 14, a transfer device 15, and a cleaning device 16 are arranged in the order of the driving direction of the photoconductor 12 shown by the arrow in FIG. An optical writer 17 is arranged in the main body, and a paper feed cassette 18 is arranged in the lower part of the main body of the apparatus.

The operation of such a laser printer will be described. The cassette paper P sent out in the direction of arrow A from the paper feed cassette 18 by the paper feed roller 20 of the paper feed device 19 is paired with the registration roller pair 2 by the grip roller pair 21.
2 and conveys it to the lower side of the photoconductor 12 at a proper timing. The photoconductor 12 operates counterclockwise as indicated by the arrow in the figure, and at that time, the surface of the photoconductor 12 is uniformly charged by the charger 13. An electrostatic latent image is formed on the photoconductor 12 by irradiating the laser beam L from the optical writing device 17, and the latent image is visualized by toner when passing through the developing device 14.
The visible image is transferred by the transfer device 15 onto the upper surface of the sheet P conveyed to the lower side of the photoconductor 12. The sheet P on which the image is transferred is guided by the conveyance guide 23 and is conveyed between the heating roller 25 and the pressure roller 26 of the fixing device 24 to fix the visible image. Then, the paper P that has exited the fixing device 24 is further conveyed by the paper ejection rollers 27, and is ejected in the direction of arrow B through the paper ejection switching claw 28. On the other hand, after the visible image is transferred, the photoconductor 12 is cleaned by a cleaning device 16 to remove the residual toner, and then the static eliminator 2 is removed.
Remove electricity at 9.

FIG. 1 is a partially enlarged view of the vicinity of the registration roller pair 22. The leading edge of the paper P sent by the grip roller pair 21 is the filler 33 of the registration sensor 33.
When a is tilted down, it strikes the nip of the registration roller pair 22 and the skew is corrected (state P2 in FIG. 1). After a lapse of a predetermined time t1 after the sheet is detected by the registration sensor 33, the driving of the grip roller pair 21 is stopped and the sheet P is stopped between the registration roller pair 22 and the grip roller 21 with a certain amount of slack (FIG. 1). State of P1). afterwards,
The registration roller pair 22 and the grip roller pair 21 are simultaneously driven to convey the paper P.

At this time, the linear velocity between the registration roller pair 22 and the grip roller pair 21 is slightly higher than the linear velocity of the registration roller pair 22, the linear velocity of the grip roller pair 21 is the same, or If it is slightly slower, paper P
It is necessary that slack remains between the registration roller pair 22 and the grip roller pair 21 when the trailing edge passes through the grip roller pair 21.

However, when the linear velocity of the grip roller is faster than the linear velocity of the registration roller, the state of P3 in FIG. 1 is reached, and the waist of the sheet P is broken, and the sheet P hitting the nip between the pair of registration rollers 22. The edges of the can be partially or totally separated. Further, when the grip roller linear velocity is too slower than the registration roller linear velocity, the sheet P is stretched between the registration roller pair 22 and the load fluctuation on the sheet that affects the conveyance accuracy of the registration roller pair 22. Occurs, and problems such as jitter on the image and changes in the image length occur.

In order to prevent such a problem from occurring, as shown in the graph of FIG. 6, initially, the grip roller linear velocity (dotted line) is slightly higher than the registration roller linear velocity (solid line in the diagram). Even if it is set, while a large amount of paper is being passed, the outer diameter of the grip roller pair 21 that bears the load of the paper feed unit is worn and the linear velocity decreases, and the grip speed is higher than the linear velocity of the registration rollers. If the linear velocity of the roller is too slow, a problem may occur.

In view of the above-mentioned problems, the technique disclosed in Japanese Utility Model Laid-Open No. 2-119448 makes the linear velocity of the intermediate roller higher than the linear velocity of the registration roller to absorb the deflection of the sheet between the rollers. A rocking guide plate is provided.
However, this technique is liable to generate noise when the swing guide plate moves, easily break the paper when the thin paper is conveyed due to the weak stiffness of the paper, and costly due to the swing structure of the guide plate. There are problems that the assemblability is deteriorated, and further, the amount of deflection before registration is changed due to wear of the intermediate roller, and stable feeding performance cannot be obtained.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a sheet conveying device for an image forming apparatus which solves the above conventional problems with a simple structure.

[0010]

In order to achieve the above object, a sheet conveying device of an image forming apparatus according to the present invention has a registration roller for adjusting a writing position of a sheet and correcting skew, and a registration roller. Grip roller located upstream of the registration roller to absorb the load of the paper feeding unit so as to maintain the accuracy of the paper conveyance by the registration roller, and a registration sensor for detecting that the leading edge of the paper reaches the registration roller. In the image forming apparatus having the above-mentioned configuration, the time when the driving of the grip roller is stopped and the paper is slackened after the arrival of the leading edge of the paper by the registration sensor is changed is changed for each predetermined number of passed sheets. .

In the sheet conveying device of the image forming apparatus according to the present invention, a slack detecting sensor for detecting the amount of slack of the sheet is arranged between the registration roller and the grip roller, and the arrival of the sheet is detected by the registration sensor. It is also possible to adopt a configuration in which the time for slackening the paper is changed according to the time until the detection output of the slack detection sensor is generated later.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. It should be noted that, in the following, the portions common to the conventional ones will be denoted by the same reference numerals, and overlapping description will be omitted.

A first embodiment of a sheet conveying device of an image forming apparatus according to the present invention will be described with reference to FIGS. 1 and 2. This embodiment has the same apparatus configuration as that of FIG. 1 already described, and as shown in the graph of FIG. 2, the number of sheets of paper P passed is a predetermined number of sheets (n1, n2). When it reaches, the control is performed to gradually increase the time t1 for determining the amount of slack, that is, the time from when the registration sensor 33 detects the paper P to when the driving of the grip roller pair 21 is stopped. Thus, the registration roller pair 22 and the grip roller pair 21 are prevented from causing the above-described problems when the grip roller linear speed is too fast or the grip roller linear speed is too slower than the registration roller linear speed. The slack of the paper P in between is managed with time.

FIG. 3 and FIG. 4 show a second embodiment of the sheet conveying device of the image forming apparatus according to the present invention. As shown, in this embodiment, the registration roller pair 22 and the grip roller pair 2
A slack detecting sensor 32 for detecting the amount of slack of the paper P is provided between the sheets 1. The sag detecting sensor 32 includes a registration roller pair 22 and a grip roller pair 21.
It is composed of a rotatable lever 32a positioned on the upper side of the sheet P between them and a sensor main body 32b holding the lever 32a. In this embodiment, the grip roller linear velocity decreases with time and the registration roller pair 22 and When the amount of slack of the paper P between the grip roller pair 21 decreases, the registration sensor 3
Slack detection sensor 3 after detecting the arrival of the paper P at 3
Since the time t2 until the detection output at 2 is generated becomes shorter, when it is determined that the time t2 becomes smaller than a predetermined value, the time t1 for determining the amount of slack is controlled to be longer and the registration roller pair 22 and The slack of the paper P between the grip roller pair 21 is managed over time.

[0015]

According to the paper conveying apparatus of the image forming apparatus of the present invention, the grip speed is expected to decrease due to wear of the grip roller, and the grip is detected after the registration sensor detects the arrival of the paper every time a certain number of sheets are passed. Since the amount of paper slack is controlled by changing the time until the roller drive is stopped, paper skew and wrinkles occur due to excessive slack of the paper between the registration roller and the grip roller, and the image when the paper is stretched is displayed. There is an effect that it is possible to prevent the jitter and the change of the image length at a low cost.

In the sheet conveying device of the image forming apparatus according to the present invention, a slack detecting sensor for detecting the amount of slack of the sheet is provided between the registration roller and the grip roller, and when it is judged that the slack is small, the registration sensor is detected. The length of time from when the arrival of paper is detected until the driving of the grip roller is stopped is lengthened.Therefore, the paper becomes too slack between the registration roller and the grip roller, paper skew or wrinkles occur, and the paper is stretched. There is an effect that the amount of slack of the paper can be managed so as to always prevent the jitter on the image and the change in the image length.

[Brief description of drawings]

FIG. 1 is a partially enlarged view near a registration roller for showing a first embodiment of a sheet conveying device of an image forming apparatus according to the present invention.

FIG. 2 is a diagram showing a relationship between the number of passed sheets and the time from when the registration sensor detects arrival of the sheet to when the driving of the grip roller is stopped in the embodiment of FIG.

FIG. 3 is a partially enlarged view of the vicinity of the registration rollers for showing the second embodiment of the sheet conveying device of the image forming apparatus according to the present invention.

FIG. 4 is a diagram showing a relationship between a paper arrival detection of a registration sensor and a detection result of a slack detection sensor of the embodiment of FIG.

FIG. 5 is a cross-sectional view showing a laser printer as an example of an image forming apparatus.

FIG. 6 is a diagram showing a relationship between a linear velocity of a registration roller, a linear velocity of a grip roller, and the number of passed sheets.

[Explanation of Codes] 21 Grip Roller Pair 22 Registration Roller Pair 32 Slack Detection Sensor 32a Lever 32b Sensor Main Body 33 Registration Sensor 33a Filler P Paper

Claims (2)

[Claims] 1. A registration roller that adjusts a writing position of a sheet and corrects a skew, and a sheet feeding unit that is located on the upstream side of the registration roller so as to maintain the precision of conveying the sheet by the registration roller. In the image forming apparatus having a grip roller that absorbs the load of the sheet and a registration sensor that detects that the leading edge of the paper has reached the registration roller, the grip roller is driven from the detection of the leading edge of the paper by the registration sensor. A sheet conveying device of an image forming apparatus, characterized in that the time for stopping and slackening the sheet is changed for each predetermined number of sheets passed. 2. A registration roller that adjusts the writing position of the paper and corrects skewing, and a paper feed unit that is located upstream of the registration roller so as to maintain the accuracy of carrying the paper by the registration rollers. In an image forming apparatus having a grip roller that absorbs the load of the sheet and a registration sensor that detects that the leading edge of the sheet has reached the registration roller, the slack of the sheet between the registration roller and the grip roller. An image formation characterized by arranging a slack detection sensor for detecting the amount, and changing the time for slackening the paper according to the time until the detection output of the slack detection sensor occurs after the arrival of the paper by the registration sensor is detected. Paper transport device of the device.