JPS63112325A - Both surface image forming device - Google Patents

Abstract

PURPOSE:To prevent the deterioration of the quality of a both surface image by allowing the driving-out roller of the both surface unit of a both surface image forming device to contact the opposite surface to the first image surface of the lowest paper sheet stacked onto a stacker means and to turn in the paper feeding direction. CONSTITUTION:The latent image of an image written into a photosensitive material drum 3 by the laser writing-in device 2 of a laser printer 1 is changed to a toner image by a prescribed electrostatic photograph process, and the paper sheets having the latent image are sent out one by one from a paper feeding tray 4, and the latent image is printed onto one side surface of a paper sheet supplied from a resist roller 5, by the action of a printing charge 6. The paper sheet onto which the toner image is printed is fixation-processed by a fixing device 7, and sent into a reversal unit 10. When the both surface image formation is carried out, said paper sheet is discharged into a both surface unit 20. As for the driving-out roller 25 of the both surface unit 20, the shaft position is fixed at the lower position in the vicinity of the front edge of a stacker 21, and the undersurface of the lowest paper sheet discharged onto the stacker 21, i.e., the surface on the opposite side to the first image formation surface contacts the peripheral surface of the roller 25, and its turned in the paper feeding direction.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a double-sided image forming apparatus that is capable of performing double-sided image formation using an image forming unit such as a copying machine or a printer.

A device that performs double-sided image formation using an image forming unit that forms an image on one side of paper, such as a copying machine or a printer, uses an image forming unit that forms an image on one side of the paper from the image forming unit. A reversing unit that can switch between a means for receiving ejected paper and ejecting it as it is to the outside of the machine and a means for reversing it face-to-face and ejecting it outside the machine; There is known a structure in which a double-sided unit is used to restore the stacked sheets and feed the stacked sheets one by one to the image forming unit in order to form an image on the back side.

FIG. 3 is a diagram showing an example, in which a laser printer 1 is used as the image forming unit.

The latent image of the image written on the photoreceptor drum 3 by the laser writing device 2 is made into a toner image by a predetermined electrostatic photographic process. The image is transferred onto one side of the paper fed by the transfer charger 6. The paper onto which the toner image has been transferred is fixed by a fixing device 7 and then sent to a reversing unit 10. Inside the reversing unit 10,
So-called three-roller type reversing roller 11 and reversing guide 1
2 is provided, and either the paper is ejected to the sorter or output tray 13 outside the machine without being reversed or it is ejected, or the paper is reversed upward from the reversing guide 12 and output to the reversing output tray 14. It is possible to select whether to advance the paper to the duplex unit 20 provided at the bottom of the printer main body 1 and the reversing unit 10. When performing one-sided image formation, the path for discharging the paper to the duplex unit 20 is selected. Ru.

A stacker 21 is provided in the duplex unit 20 to temporarily stack ejected sheets, and the ejection port can be switched according to the paper size so that the leading edge of the paper is aligned with the leading edge of the stacker 21 regardless of the paper size. A paper refeed conveyance path 22 and a guide plate 23 are provided. When a predetermined number of sheets are stacked, a pick-up roller 24 comes into pressure contact near the leading end of the stacked sheet bundle, and the sheets are fed one by one to the registration rollers 5 of the printer main body 1 in response to a back image forming signal.

The paper on which the back side printing has been completed is discharged from the reversing unit 10 to a sorter or tray 13 or a reversing paper output tray 14.

Conventionally, in a double-sided image forming apparatus with this configuration, 1 normal double-sided unit 2
The 0 pick-up roller 24 presses against the top sheet of the stack of sheets on the stacker 21 during refeeding, and refeeds the sheets one by one from the top.

When using this device to record pages 1 to 8 on both sides of four sheets of paper, for example, write 1, 3, 5, 7; 8, 6° and 4.2 pages in the laser writing device of printer 1. The image information signals are inputted in the order of
, 3, 5.7 pages are transferred, reversed in the reversing unit 10, and placed on the stacker 21 in the duplex unit 20.
Pages 1.3 and 5.7 are stacked in order from the bottom with the printed side facing up. Next, the pick-up roller 24 comes into pressure contact with the top surface of the stack of sheets, and at a predetermined timing, the sheets are re-fed from the top to the printer 1 along the path indicated by the broken line, and images of pages 8, 6, and 4.2 are printed on the back side, respectively. 1 When the pages are reversed through the reversing unit 10 and discharged onto a tray outside the machine, the pages are stacked in the same order. At this time, if the paper is ejected straight to the paper output tray or sorter without being turned over, the pages will not be in the same order6. Now, as mentioned above, the duplex unit's feed roller 24 has conventionally been in pressure contact with the top surface of the stacked paper bundles. Paper was re-fed sequentially from the top, which caused the following problems.

(b) As the calling roller rubs the top surface of the paper, which is the first image forming surface, the image becomes dirty, toner adheres to the surface of the roller, and the friction coefficient decreases over time.

Paper refeeding becomes less reliable.

(b) When there are many pages to be recorded continuously, the time from fixation on the front side to image formation on the back side varies greatly depending on the page (
For example, in the above example, pages 7 to 8 are the shortest and pages 1 to 2 are the longest).As a result, the degree of expansion and contraction of the paper due to fixing heat varies, and the reliability of the re-imaged image may vary. Varies depending on the page.

(c) Until the last page of the paper on which the image was formed on the front side is completely overlapped with the upper east of the paper on the stacker of the duplex unit, the calling roller cannot be pressed onto it. This means that the processing time becomes longer.

-W-Description The present invention solves the above-mentioned drawbacks of the conventional double-sided image forming apparatus having the above-mentioned configuration.The quality of double-sided images does not deteriorate, the conveyance during back-side image formation is reliable, and the processing time for one double-sided image is reduced. The purpose of the present invention is to provide a double-sided image forming device with no waste.

In order to achieve the above-mentioned object, the present invention provides a double-sided image forming apparatus having the above-mentioned configuration, in which the calling roller of the duplex unit is located on the side opposite to the first image surface of the lowest sheet of paper stacked on the stacking means. It is characterized by contacting the surface and rotating in the paper feeding direction.

Embodiments of the present invention will be described in detail below based on the drawings.

FIG. 1 is a diagram showing an embodiment in which the present invention is applied to the double-sided image forming apparatus previously explained in FIG. 3. Therefore, the same members are given the same reference numerals and their explanations will be omitted.

This embodiment differs from the conventional apparatus shown in FIG. 3 only in the position of the calling roller of the duplex unit 20. In this embodiment, the pick-up roller 25 is provided near the front end of the stacker 21 at a lower position with its axis fixed, and is located on the lower surface of the lowest sheet of paper discharged onto the stacker 21, that is, on the opposite side of the first image forming surface. The surface contacts the circumferential surface of the calling roller 25.

Therefore, the image surface is not smeared by the calling roller 25, and toner does not adhere to the calling roller and the coefficient of friction decreases over time, thereby preventing the reliability of paper refeeding from being impaired.

In addition, once surface imaging is completed, the lowest sheet of paper on the stacker can be re-fed to the printer 1 without waiting for the last sheet to be stacked, reducing wasted processing time. disappears.

Furthermore, since the time from the time of fixing the front surface to the time of image formation on the back surface is the same for all sheets of paper, there is no difference in the reliability of each page based on the difference in the amount of thermal expansion and contraction.

Note that when performing double-sided image formation with the double-sided image forming apparatus according to the present invention, the input order of image information signals to the writing device is different from the conventional one. When recording, input in the order of 1, 3° 5.7: 2, 4, 6.8, and as shown in Figure 2, first feed four sheets of paper from the paper feed cassette as shown by solid lines, and then 1.3, 5.7
The pages are imaged, reversed by the reversing unit 10, and stacked on the stacker of the duplex unit 20. Next, the paper is fed into the printer main body 1 one by one from the bottom of the paper stack along the path shown by the broken line, images of pages 2, 4, 6.8 are created, and the paper is fed straight to the sorter or output tray 13 without turning over. By discharging the paper sheets, a bundle of prints with the same page order can be obtained.

Effects As described above, according to the present invention, it is possible to prevent stains on the image surface caused by the feed roller of a single-sided unit and a decrease in conveyance reliability due to toner adhering to the feed roller, and also to reduce the image forming processing time. Waste and deterioration of reliability due to thermal expansion and contraction can be eliminated.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing the schematic configuration of an embodiment of the present invention, and FIG.
The figure is an explanatory diagram showing the procedure for forming images with the same page order using the device, FIG. 3 is a cross-sectional view showing the schematic configuration of an example of a conventional double-sided image forming device, and FIG. FIG. 3 is an explanatory diagram showing a procedure for forming uniform images.

Claims (1)

[Claims] An image forming unit has an image forming section that creates an image on one side of the paper fed from the paper feed means, a means for receiving the paper ejected from the image forming unit and ejecting it out of the machine as it is, and an inverted machine. a reversing unit having a switchable means for discharging the sheets to the outside; a stacking means for receiving and stacking the sheets reversed and discharged from the reversing unit in the order in which they are received;
In a double-sided image forming apparatus comprising a duplex unit that picks up sheets stacked on a stacking means by a calling roller and feeds the sheets one by one to the image forming section of the image forming unit, the calling roller of the duplex unit is stacked on the stacking means. What is claimed is: 1. A double-sided image forming device, wherein the double-sided image forming device contacts the surface opposite to the first image surface of the lowest sheet of paper, and rotates in the paper feeding direction.