KR20030091587A - Image forming apparatus for duplex printing having a paper-mooring and reversal part - Google Patents

Abstract

PURPOSE: A two-sided printing image forming apparatus having a paper mooring/inverting unit is provided to improve two-sided printing speed to a level corresponding to single-sided printing speed. CONSTITUTION: A two-sided printing image forming apparatus includes a paper stack unit(110), a pick-up/transfer unit(106) for picking up and transferring papers(115) stacked in the paper stack unit, a developing unit(130) for forming a toner image on paper, a fixing unit(140) for fixing the toner image, a paper discharging unit(150), and a two-sided printing unit(160) having a paper return path(B) for returning paper one side of which has been printed to the developing unit and a transfer part(180) for transferring paper through the paper return path. The two-sided printing unit includes a paper transfer direction switch(143) and a paper mooring/inverting part(170). The paper transfer direction switch guides a paper transfer direction to move paper to the paper return path in case of two-sided printing. The paper mooring/inverting part temporarily moors paper one side of which has been printed and, simultaneously, inverts the printed face of the paper while the next paper is being printed.

Description

Image forming apparatus for duplex printing having a paper-mooring and reversal part}

The present invention relates to an image forming apparatus such as a laser printer, a copier, and more particularly, a paper that can improve the printing speed when printing on both sides to a printing speed level when printing on both sides by installing a media middle mooring / reversing portion in the duplex printing path. A double-sided printable image forming apparatus having an intermediate pending / inverting portion.

In general, a double-sided printing image forming apparatus, for example, a double-sided printing laser printer 1, is provided on the paper feed cassette 10 and the paper feed cassette 10 on which the paper 15 is loaded, as shown in FIG. A paper feed guide 22 that is provided to form a paper feed path for guiding the paper 15 picked up by the first pick-up roller 20, the first pick-up roller 20 for picking up the paper 15, and the paper feed. A developing unit 30 for forming a toner image on one surface of the paper conveyed through the guide 22, and a fixing unit 40 for fixing the toner image formed on one surface of the paper 15 passing through the developing unit 30; , 41), a feed roller 50 for conveying the paper 15 passing through the fixing units 40, 41, a discharge roller 60 disposed above the feed roller 50 to discharge the paper 15, In order to print the back side of the paper in the duplex printing mode, the paper transport guide 22 sends the paper 15 discharged through the output roller 60. A paper backfeed guide 62 for forming a paper conveyance path for reentry, and first and second backfeed rollers 70 and 90 for backfeeding the paper through the paper backfeed guide 62; .

The developing unit 30 receives an optical signal such as a laser beam from a laser scanning unit (LSU) 36 according to an image signal, and a photosensitive drum 32 for forming an electrostatic latent image, and a photosensitive for forming an electrostatic latent image. A developing roller (not shown) for attaching toner to the drum 32 and developing the toner image is provided.

At the lower side of the photosensitive drum 32 of the developing unit 30, a transfer roller 34 for transferring the toner image formed on the photosensitive drum 32 to the paper 15 is provided.

The fixing units 40 and 41 consist of a heating roller 41 and a fixing roller 40 for fixing the toner image formed on the paper 15 to the paper with heat and pressure.

In addition, between the paper feed guide 22 where the output roller 60 is located and the paper backward feed guide 62, a paper inversion is formed by a vertical arm that guides the paper 15 to the paper backward feed guide 62 in the duplex printing mode. The guide 42 is hingedly elastically fixed. The paper reversing guide 42 is provided with a paper sensor (not shown) for detecting the passage of paper.

For manual feeding, the laser printer 1 is loaded on the multipurpose feeder 27, a paper sensor (not shown) for detecting the presence of paper in the multipurpose feeder 27, and the manual feeder 27. And a second pickup roller 25 for picking up the sheet of paper 15 and transferring the sheet of paper 15 to the developing unit 30 through the sheet conveying guide 22.

Looking at the two-sided printing process of the laser printer 1 configured as described above, first, the paper 15 loaded in the paper feed cassette 10 or the multipurpose feeder 27 is prepared according to the operation of the paper sensor for manual feeding. After being picked up by the first or second pick-up rollers 20, 25, it is moved to the developing unit 30 along the paper feed guide 22.

While the paper 15 is being transferred to the developing unit 30, an electrostatic latent image is formed in the photosensitive drum 32 of the developing unit 30 by the laser beam emitted from the LSU 36 in accordance with an image signal. The electrostatic latent image developed at 32 is attached to a toner by a developing roller and developed into a toner image in the form of a visible image.

The toner image formed on the photosensitive drum 32 is one surface of the paper 15 by the transfer roller 34 when the paper 15 is transferred to the developing unit 30 along the paper transfer guide 22. For example, the toner image transferred onto the upper surface and transferred to the upper surface of the paper 15 is fixed to the upper surface of the paper 15 by the heating roller 41 and the fixing roller 40 constituting the fixing unit.

The paper 15 passing through the heating roller 41 and the fixing roller 40 enters the discharge roller 60 by the feed roller 50. At this time, the paper 15 pushes the paper reversing guide 42 to the position shown by the solid line at the position shown by the dotted line in FIG. 1 by the rotational force of the feed roller 50. 15) will detect the passage.

At this time, when the printer performs the single-sided printing mode, the paper 15 is discharged to the paper discharge stage 59 through the discharge roller 60.

However, when the duplex printing mode is performed, the discharge roller 60 has a separate forward / reverse drive control unit according to a signal of the paper detection sensor generated after the rear end of the paper 15 passes through the paper reversal guide 42. It is driven to reverse rotation by (not shown). As a result, the paper 15 enters the paper backfeed guide 62 without being discharged out of the machine. At this time, the paper reversing guide 42 is elastically returned to the position shown by the dotted line in FIG. 1, so that the paper 15 is guided by the paper reversing guide 42 to the paper reverse feed guide 62. It can be easily entered.

The paper 15 arriving at the paper backfeed guide 62 is conveyed to the alignment roller 80 by the first backfeed roller 70. Since the alignment roller 80 is installed to be turned about 5 degrees, the leading end of the paper 15 is pushed and aligned by the alignment roller 80.

The paper 15 aligned by the alignment roller 80 is passed through the second reverse feed roller 90 to the paper feed guide 22 again, and the other side of the paper 15, i.e., the lower surface, is as described above. After the printing process is discharged to the external paper discharge bin (59).

However, in the conventional laser printer 1, when printing on both sides, one sheet of paper finishes printing on one side and the other side, and then prints on the next sheet. There was a problem falling significantly.

The present invention has been made in order to solve the above problems, an object of the present invention is to provide a print position after printing the back side of each sheet of paper on both sides when printing on both sides of two or more sheets by installing a median mooring / inverting section in the duplex printing path. The present invention provides a double-sided printable image forming apparatus having a paper intermediate mooring / reversing portion capable of shortening the time to be transferred to the double-sided printing speed to a level of single-sided printing speed.

Another object of the present invention is that the driving unit for the duplex printing is driven in the same direction as the rotational direction of the other driving unit, which can be simply driven by the existing drive motor without the need for a separate additional motor or complicated power transmission structure A double-sided printable image forming apparatus having a mooring / inverting portion is provided.

1 is a cross-sectional view of a conventional laser printer capable of double-sided printing.

Figure 2 is a schematic diagram of a double-sided printable laser printer with a media middle mooring / reversing portion in accordance with a preferred embodiment of the present invention.

* Description of the symbols for the main parts of the drawings *

1: laser printer 20, 25, 107, 125: pickup roller

27, 127: bypass tray 30, 130: developing unit

32, 132: photosensitive drum 59, 159: paper output tray

143: paper feed direction switching unit 144: paper detection sensor

145: paper feed direction switching lever 160: duplex printing unit

170: paper intermediate pending / reversing section 171: paper intermediate loading zone

172: pickup portion 180: transfer portion

In order to achieve the above object, the present invention provides a paper loading unit detachably installed in the frame of the main body; A pickup / transfer unit for picking up and transferring paper loaded in the paper stacking unit; A developing unit for forming a toner image on the paper; A fixing unit for heating and pressing a toner image formed on a sheet to fix the toner image into a visible image; A discharge unit for discharging the paper on which the fixing of the visible image is completed through the fixing unit; And a duplex printing unit having a paper conveyance path for reentering the printed paper on one surface into a developing unit to form an image on the back side of the paper, and a transfer unit for moving the paper through the paper conveyance path. In the forming apparatus, a duplex printing unit is provided between the fixing unit and the delivery unit, and a paper conveying direction switching section for guiding the paper conveying direction so that the paper moves to the paper conveying path during duplex printing, and one side of the paper where the subsequent paper is picked up. The present invention provides a double-sided printable image forming apparatus including a paper intermediate mooring / reversing portion which temporarily holds a sheet on which printing on one side is first printed while the printing is in progress, and reverses the printing surface of the sheet.

In the preferred embodiment, the paper intermediate mooring / reversing portion discharges the paper conveyed through the paper conveying path by the paper conveying direction switching part out of the paper conveying path, thereby temporarily stacking the paper and inverting the printing surface of the paper. And a pick-up section for picking up the paper stacked on the paper stacking path and entering the paper transporting path.

The pick-up unit is composed of a paper detection sensor for detecting the paper loading status of the paper intermediate stack, and a pickup roller capable of picking up the paper moored in the paper intermediate stack and transferring it to the paper conveying path. At this time, the paper intermediate mooring / reversing unit can be used as the manual feeding unit.

Further, it is preferable that the pickup roller and the transfer portion of the pickup portion are driven by the same motor as the motor driving the pickup / transfer unit so as to be driven at least in the same driving direction of the pickup / transfer unit.

Optionally, the paper intermediate mooring / reversing part is a reverse roller for discharging the paper conveyed through the paper conveying path by the paper conveying direction switching part out of the paper conveying path, and a paper sensor disposed upstream of the paper conveying path with respect to the reverse roller. When the rear end of the paper is sensed by the paper sensor, the reverse roller reversely rotates to reverse the printing surface of the paper, and the reverse roller forward / reverse drive control member controls the sheet to enter the paper conveying path again, and the reverse roller. It may be composed of a reverse guide member for guiding the paper entering the paper conveyance path during the reverse rotation of the.

Hereinafter, with reference to the accompanying drawings will be described in detail a double-sided printable image forming apparatus having a paper intermediate mooring / reversing portion according to a preferred embodiment of the present invention.

Referring to Fig. 2, a laser printer constituting an image forming apparatus having a paper intermediate mooring / reversing portion according to the present invention is schematically illustrated.

This laser printer picks up and feeds the paper feed cassette 110 which is detachably installed in the frame (not shown) of the main body 101, and the paper 115 loaded in the paper cassette 110, and transports it. ), A developing unit 130 for forming a toner image on the paper 115, a fixing unit 140 and a fixing unit 140 for fixing the toner image formed on the paper 115 by heat and compression to fix it as a visible image. The paper delivery unit 150 for discharging the paper 115 on which the visible image has been fixed is discharged, and the paper 115 which has been printed on one surface through the fixing unit 140 to print an image on the back surface of the paper 115. It includes a duplex printing unit 160 to re-enter the developing unit 130.

The paper feed cassette 110 is installed at the lower portion of the main body 110, and supports the paper to elastically lift and lower the paper through the paper pressing plate 112 supported by the elastic spring 111.

A pickup / transfer unit 106 is provided above the paper cassette 110 to sequentially pick up and transport the sheets 115 stacked on the paper cassette 110 one by one. The pickup / transfer unit 106 is a first paper sensor (not shown) that detects whether paper is loaded in the paper cassette 110, and a first pickup roller that picks up paper 115 loaded in the paper cassette 110. 107, and a feed roller 124 / backup rollers 126, 127, 128 for conveying the picked paper 115 to the developing unit 130.

In order to manually feed the paper 115, the pickup / transfer unit 106 is a paper tray 127, a manual feed tray that is folded to protrude forward of the main body 101 or to be stored in the front wall of the main body 101. A second paper sensor (not shown) that detects the paper stacking condition of 127 and a second pickup roller which picks up the paper 115 loaded on the bypass tray 127 and feeds it toward the feed roller 124 ( 125). In this way, the multipurpose feeder 127, the second sheet sensor and the second pickup roller 125 constitute a manual feeder.

The developing unit 130 is installed above the pick-up / transfer unit 106 detachably from a frame (not shown) of the main body 101, and is electrostatic latent image by a laser beam emitted from the LSU 136 in accordance with an image signal. A developing roller (not shown) for charging the photosensitive drum 132, a charging roller (not shown) for forming the photosensitive drum 132, and developing a toner image by attaching toner to an electrostatic latent formed on the photosensitive drum 132; Not).

The fixing unit 140 for pressing and fixing the toner image includes a heating roller 141 and a fixing roller 142.

The discharge unit 150 includes a plurality of discharge rollers 155 and a backup roller 156 that are installed to correspond to each other. The discharge unit 150 includes a paper 115 on which the toner image has been fixed by the fixing unit 140. It serves as a badge (159).

The double-sided printing unit 160 is a paper conveying path (B), the fixing unit 140 and the discharge unit for re-entering the paper 115, which has been printed on one side to the developing unit 130 to proceed printing on the back of the paper 115 Installed between the units 150, the paper conveying direction switching unit 143 for guiding the paper conveying direction so that the paper 115 moves in the paper conveying path B during duplex printing, and the subsequent paper 115 is picked up on one side. During printing, the paper intermediate mooring / reversing unit 170 for temporarily mooring the paper 115 on which one-side printing is first completed and inverting the printing surface of the paper 115, and the paper 115 through the paper conveying path. It includes a transfer unit 180 to move through (B).

The paper conveying direction switching unit 143 is a paper conveying path B downstream of the paper conveying path A of the fixing unit 140 to guide the paper 115 to move to the paper conveying path B for duplex printing. ) Is placed at the point where it meets.

The paper feed direction switching unit 143 moves the paper 115 according to the paper detection signal of the third paper detection sensor 144 and the third paper detection sensor 144 for detecting the leading end of the paper 115. Is composed of a paper conveying direction switching lever 145 for switching the paper conveying path B side.

The third sheet sensor 144 has a form of a rotation lever supported by a rotation shaft connected to a limit switch or a solenoid to rotate by contact with the sheet 115. As the third paper sensor 144 rotates in contact with the paper 115, the third paper sensor 144 detects the front end of the paper 115 and transmits a paper detection signal to the controller, thereby controlling the paper feed direction switching lever 145. By rotating, the paper 115 serves as a sensor for guiding the paper conveying path B.

The paper intermediate mooring / reversing unit 170 is configured to first print on one side while the subsequent paper 115 is picked up and print on one side, and then to the paper conveying path B by the paper transfer direction switching unit 143. The paper intermediate stacking stand which protrudes toward the back of the main body 101 so as to discharge the conveyed paper 115 out of the paper conveying path B to temporarily hold the paper 115 and reverse the printing surface of the paper 115. 171, and a pick-up unit 172 for picking up the paper 115 stacked on the paper intermediate stacking stand 171 and transporting the paper 115 in the paper conveying path B. FIG.

The paper intermediate stack 171 protrudes from the main body 101 only when printing on both sides, and is folded in a normal manner so that it is folded and stored in the back wall of the main body 101. The pickup unit 172 picks up a fourth paper sensor (not shown) for detecting the presence or absence of the paper intermediate stack 171, and the paper 115 held by the paper intermediate stack 171. It consists of a pick-up roller that can be transported in the conveying path (B).

Pick-up rollers of the pick-up unit 172 are driving parts of the laser printer, for example, the first pick-up roller 107, the transfer roller 124, the transfer roller 134, the fixing roller 142, the discharge roller 155 It is driven in the same direction as the driving direction of the back, for example, counterclockwise. Therefore, the paper intermediate mooring / reversing unit 170 can be simply driven by the driving force of the existing driving motor without requiring a separate driving motor or a complex power transmission structure.

In addition, since the paper intermediate mooring / reversing unit 170 is the same as the configuration of the manual feeding unit 127 and 125 installed in front of the main body 101, the paper feeding unit 127 and 125 installed in the front side may be omitted and used as the manual feeding unit. It may be.

In this case, the control unit detects the paper loading status of the paper intermediate loading zone 171 through the fourth paper detection sensor of the pickup unit 172 at the beginning of printing, and if the paper 115 is detected, the pickup unit 172. Through the paper feed.

In addition, the paper intermediate mooring / reversing unit 170 optionally has a disadvantage in that the configuration is complicated, but the paper conveying the paper 115 transferred to the paper conveying path B by the paper conveying direction switching unit 143 is conveyed. When the rear end of the paper is detected by a reversing roller (not shown) for discharging out of the path B, a paper sensor (not shown) disposed upstream of the paper conveying path B with respect to the reversing roller, and a container sensor Reverse roller forward / reverse drive control member (not shown) for controlling the paper to enter the paper conveying path B while reversely rotating the reverse roller to reverse the printing surface of the paper, and during reverse rotation of the reverse roller. It may be constituted by a paper inversion guide member (not shown) provided to be rotatable to guide the paper from entering the paper conveyance path B. FIG.

The forward and reverse rotation driving control members for driving the reverse roller in the forward and reverse directions in duplex printing are generally known. In general, a gear train for driving the reverse roller in the forward direction (not shown) and a gear train for driving in the reverse direction Power transmission gear unit (not shown) having a (not shown), swing gear train (not shown) for switching engagement between the forward drive gear train and the reverse drive gear train, and the swing gear train It consists of a solenoid portion (not shown).

The paper reversing guide member is formed to have a shape that can be plurally arranged at equal intervals on a common rotating shaft provided in the width direction of the paper to guide the leading end of the paper in a desired conveying direction.

The transfer unit 180 of the duplex printing unit 160 is picked up by the pick-up unit 172 of the paper intermediate mooring / reversing unit 170 and enters the paper 115 entering the paper conveying path B. And first and second conveying rollers 181 and 182 for conveying to the conveying roller 124 of 106. Like the pickup rollers of the pickup unit 172, the first and second conveying rollers 181 and 182 may also be driven in the same direction as the driving direction of the other driving units, that is, counterclockwise, so as not to be driven by a separate driving motor or a power transmission unit. Driven to rotate.

As described above, the laser printer of the present invention includes a paper intermediate mooring / reversing unit for temporarily mooring and inverting the paper 115 that has completed one side printing while the subsequent paper 115 is picked up and printing on one side. 170), printing of the paper can be continuously performed without time interruption due to the reversal and transfer of the paper during duplex printing.

In addition, since the driving parts for double-sided printing, such as the pickup rollers of the pickup unit 172 and the first and second transfer rollers 181 and 182, rotate in the same direction as the rollers of the other drive units, a separate motor or power transmission unit It can be simply driven by a conventional drive motor without the need.

The operation of the double-sided printable laser printer having the paper intermediate mooring / reversing portion according to the preferred embodiment of the present invention configured as described above will be described in detail with reference to FIG. 2.

First, assuming that the printing paper 115 is automatically fed, the first pickup roller of the pickup / transfer unit 106 with the paper cassette 110 loaded with the paper 115 mounted on the main body 101. 107 is rotationally driven in close contact with the sheet 115 according to the command of the controller. Accordingly, one sheet of paper, that is, the first sheet 115, is picked up by the first pickup roller 107 and is transferred between the transfer roller 124 and the backup rollers 126, 128, and 129.

The first sheet 115 conveyed between the conveying roller 124 and the backup rollers 126, 128, 129 is conveyed toward the developing unit 130 by the rotational driving force of the conveying roller 124.

While the first paper 115 is conveyed toward the developing unit 130, the LSU 136 irradiates a laser beam to the surface of the photosensitive drum 132 charged by corona discharge or the like according to an image signal to cause an electrostatic latent image. The latent electrostatic image formed on the photosensitive drum 132 is attached to the toner particles by a developing roller which rotates to face the photosensitive drum 132 and is developed into a visible toner image.

After that, when the first sheet 115 is continuously conveyed by the feed roller 124 to pass through the lower portion of the photosensitive drum 132, the toner image formed on the photosensitive drum 132 is transferred to the photosensitive drum 132 and the transfer roller ( 134 is transferred to one surface of the first sheet 115 by a high voltage having a polarity opposite to that of the toner applied to the transfer roller 134.

After the toner image is transferred, when the first sheet 115 arrives at the fixing unit 140, the toner image transferred to one surface of the first sheet 115 is heated by the heating roller 141 and the fixing roller 142. It is fixed to the printed image by pressing.

As such, the first paper 115 having a desired image printed on one surface thereof is continuously conveyed by the rotational force of the heating roller 141, the fixing roller 142, and the like, while pushing the third paper sensor 144. Accordingly, the third paper sensor 144 fixed to the rotation shaft connected to the limit switch or the solenoid rotates in contact with the first paper 115 and transmits the paper detection signal to the controller.

At this time, when the laser printer is performing the single-sided printing mode, the control unit drives the discharge roller 155 of the discharge unit 150 to discharge the first sheet 115 to the external sheet discharge unit 159.

However, in the case of performing the duplex printing mode, for example, when duplex printing a plurality of sheets 115, the control unit rotates the sheet feed direction switching lever 145 so that the first sheet 115 returns the sheet conveyance path. You will be guided to enter (B).

The first sheet 115 entering the sheet conveying path B is discharged and loaded onto the sheet stacking unit 171 so that the printing surface is reversed by driving forces such as the heating roller 141 and the fixing roller 142.

While the first paper 115 is loaded on the paper intermediate stack 171, the control unit picks up the next paper, that is, the second paper 115 through the first pickup roller 107 with a paper margin, and transfers the feed roller ( 124).

Then, the first sheet 115 discharged to the sheet stacking unit 171 is picked up by the pick-up unit 172 and transferred through the first and second conveying rollers 181 and 182, and the pick-up roller 107 The second paper 115 picked up by the printing roller proceeds to one side of the paper as described above through the developing unit 130 and the fixing unit 140 by the feed roller 124.

When the second paper 115 moves the third paper sensor 144 while moving after completing the one-side printing, the control unit rotates the paper feed direction switching lever 145 so that the second paper 115 conveys the paper. Guide to enter the path (B). At this time, the first sheet 115 enters the sheet conveying path A by the conveying roller 124.

Thereafter, the second paper 115 is loaded on the paper intermediate stack 171, and the first paper 115 is printed on the back surface of the paper through the developing unit 130 and the fixing unit 140. When the paper is transferred to the delivery unit 150 without moving to the paper conveyance path B under the control of the control unit according to the operation of the paper sensor 144, the control unit again papers the next sheet, that is, the third sheet 115. The margin is picked up by the first pick-up roller 107 and then conveyed toward the feed roller 124.

Then, the second paper 115 loaded on the paper intermediate stack 171 is picked up by the pickup section 172 and transported by the first and second conveying rollers 181 and 182, and the first paper ( 115 is discharged to the paper stack 159, the third sheet 115 is printed on one surface of the paper through the developing unit 130 and the fixing unit 140.

Then, the third sheet 115 enters the sheet conveying path B through the sheet conveying direction switching lever 145 and is loaded on the sheet stacking unit 171, and the second sheet 115 is conveyed to the conveying roller 124. After passing through the shape unit 130 and the fixing unit 140 through the printing on the back side of the paper through the control of the control unit according to the operation of the paper sensor 144 does not move to the paper transport path (B) When it is conveyed to the discharge unit 150 without, the control unit again picks up the fourth paper 115 through the first pickup roller 107 with the paper margin and transfers it toward the feed roller 124.

These operations are repeated for the next sheets 115, and the printing ends when duplex printing of the final sheet 115 is finished.

As described above, the double-sided printable laser printer having the paper intermediate mooring / reversing part according to the present invention has a paper intermediate mooring / reversing part in the duplex printing path so that the back side of each sheet of paper is double-sided when printing on both sides of two or more sheets of paper. By shortening the time to be transferred to the printing position after printing, it is possible to obtain the effect of improving the duplex printing speed to the single-sided printing speed level.

In addition, in the double-sided printable laser printer of the present invention, the rollers used in the paper intermediate mooring / reversing portion, the conveying portion, etc. constituting the double-sided printing unit are driven in the same direction as other feed rollers, so that a separate drive motor or complex power transmission It can be simply driven by a conventional drive motor without requiring a structure.

In the above, specific preferred embodiments of the present invention have been illustrated and described. However, the present invention is not limited to the above-described embodiment, and various modifications and variations can be made by those skilled in the art without departing from the gist of the present invention as claimed in the claims. It will be possible.

Claims (6)

A paper loading unit detachably installed on a frame of the main body; A pickup / transfer unit for picking up and transferring the paper loaded in the paper loading unit; A developing unit for forming a toner image on the paper; A fixing unit for heating and pressing a toner image formed on a sheet to fix the toner image into a visible image; A discharge unit for discharging the paper on which the fixing of the visible image is completed through the fixing unit; And a duplex printing unit including a paper conveying path for re-entering the printed paper on one surface to the developing unit to form an image on the back side of the paper, and a conveying unit for moving the paper through the paper conveying path. In a possible image forming apparatus, The duplex printing unit is installed between the fixing unit and the output unit, the paper transfer direction switching unit for guiding the paper transfer direction so that the paper moves to the paper transport path when duplex printing, and the subsequent paper is picked up to print on one side. And a paper intermediary mooring / reversing unit for temporarily mooring the paper on which one-side printing is first completed while in progress and inverting the printing surface of the paper. According to claim 1, wherein the paper intermediate mooring / inversion unit, An intermediate sheet disposed with respect to the paper conveying path so that the paper conveyed through the paper conveying path by the paper conveying direction switching unit is discharged out of the paper conveying path to temporarily load the paper and to reverse the printing surface of the paper; Loading table; And And a pick-up unit for picking up the paper stacked on the paper stacking unit and transporting the paper to the paper conveying path. The method of claim 2, wherein the pickup unit, A paper sensor for detecting paper stacking status of the paper stacking unit; And And a pickup roller capable of picking up the paper moored on the paper intermediate stack and transferring the paper to the paper conveyance path. 4. The image forming apparatus as claimed in claim 3, wherein the paper intermediate mooring / reversing unit is used as a manual feeding unit. The method of claim 4, wherein the pickup roller and the transfer unit of the pickup portion is driven by the same motor as the motor for driving the pickup / transfer unit to be driven at least in the same driving direction of the pickup / transfer unit. A double-sided printable image forming apparatus having a paper intermediate pending / reversing section. According to claim 1, wherein the paper intermediate mooring / inversion unit, A reverse roller for discharging the paper conveyed through the paper conveying path by the paper conveying direction switching unit out of the paper conveying path; A sheet sensor disposed upstream of the sheet conveying path with respect to the inversion roller; A reverse roller forward / reverse rotation drive control member which controls to enter the paper back into the paper conveying path while reversely rotating the reverse roller to reverse the printing surface of the paper when the rear end of the paper is detected by the container sensor; And And a guide member for guiding the paper from entering the paper conveyance path during the reverse rotation of the reversing roller.