Image forming system

Abstract

An image recording apparatus for recording an image on a sheet by a main scanning with a laser beam and a sub-scanning of the sheet, the image recording apparatus having: a pair of upstream rollers, arranged upstream of an exposing position of the laser beam; a pair of downstream rollers, wherein the sub-scanning is conducted by nipping and conveying the sheet with the pairs of upstream rollers and downstream rollers; wherein the pair of downstream rollers includes: a first roller driven by a drive section; a second roller, having a total weight of 300 g or less, wherein a gap amount of a nip between the first and the second rollers is set smaller than a thickness of the sheet; and a roller holding section for holding both ends of the second roller so as to be capable of driven rotation.

Description

BACKGROUND OF THE INVENTION [0001] The present invention relates to an image recording apparatus for recording an image wherein a sheet-like object to be scanned is conveyed while being sandwiched between a pair of rollers. [0002] Patent Document 1 discloses a method for recording an image on the whole surface of a sheet as a recording medium by conveying it with two sets of nip rollers. It is well known that an image defect (irregularities across the sheet feed direction) tends to be produced by the flapping of the sheet or irregular rotation of the drive system, when the leading edge of the sheet enters the second nip roller located downstream and the tailing edge of the sheet gets out of the upstream first nip roller, according to this method. To solve the problem caused when the tailing edge of the sheet gets out of the upstream first nip roller, it is a common practice to release the first nip roller before the sheet gets out of the roll, as described in the Patent Document 2. ...

AI Technical Summary

Benefits of technology

[0012] In view of the prior art problems described above, it is an object of the present invention to provide an image recording apparatus capable of avoiding an adverse effect caused by the entry of foreign substances on the roller pair to convey the sheet-like object for sub-scanning transportation, whereby a high-quality image is achieved.

[0021] According to the aforementioned image recording apparatus, in the aforementioned downstream roller pairs to convey the recording medium for sub-scanning, the second roller has a smaller weight and / or lower starting torque than that of the prior art, and such holding means as a bearing is configured so as to be driven. Accordingly, when a sheet-like object to be scanned has entered the nip gap, the second roller is easily driven and the nip gap expands rapidly according to the thickness. This arrangement reduces the irregularities when the leading edge of the sheet-like object to be scanned has been fed by the upstream roller pair. At the same time, this arrangement eliminates the need of preliminary rotation of the second roller. This makes it possible to eliminate the use of the prior art runner having a poor resistance to incoming foreign substances, and to avoid a bad effect of the incoming foreign substances upon the downstream roller, whereby a high-quality image can be obtained.

[0024] In this case, it is preferred that control be provided to increase the nip pressure a predetermined time after the leading edge of the sheet-like object to be scanned has entered the downstream roller. This increases the nip pressure of the downstream roller pair a predetermined time after the leading edge of the sheet-like object to be scanned has entered the downstream roller. This arrangement reduces the irregularities at the time of entry of the sheet-like object, and improves the conveying performance after the entry.

[0026] The image recording apparatus of the present invention eliminates an adverse effect of the entry of foreign substances such as dust and dirt, upon the downstream roller for conveying the sheet-like object for sub-scanning, whereby a high-quality image is provided.

Problems solved by technology

It is well known that an image defect (irregularities across the sheet feed direction) tends to be produced by the flapping of the sheet or irregular rotation of the drive system, when the leading edge of the sheet enters the second nip roller located downstream and the tailing edge of the sheet gets out of the upstream first nip roller, according to this method.

However, when the detached roller contacts the sheet, irregularities still tend to occur.

However, this method involves a complicated mechanism for rotating and rocking the roller (concurrent revolving and rotating).

And because of using heavy weight and large inertia rollers, this method is not sufficient from the point of reducing the irregularities at the time of contact.

Thus, the conveyance force of the nip roller will lose to an increased resistance of conveyance by the guide, with the result that a slip will occur during conveyance.

There is concern about the possibility of such problems.

Further, if foreign substances such as dust and dirt have deposited on the structural portion (hitting runner portion) for this preliminary rotation, the hitting runner will become loose by the thickness of foreign substances.

This will result in irregularities appearing in the image.

This will result in unstable conveyance.

There is concern about the possibility of such problems.

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