KR101094925B1 - image forming apparatus for duplex printing - Google Patents

Abstract

A double-sided print image forming apparatus capable of double-sided printing at a high speed is provided. The duplex printing image forming apparatus includes a conveying unit having a conveying roller for conveying paper along a printing path; An image forming unit for forming an image on the paper; A discharge unit including a discharge roller and a discharge back-up roller for discharging the paper on which the image is formed along the discharge path; And a duplex printing unit having a back feed roller which transfers a sheet of paper having an image formed on one side through a conveying path. The duplex printing unit includes a sheet and a sheet which enters the conveying path from the discharge path during duplex printing. It characterized in that it comprises a gap for separating the discharge roller and the discharge medium backup roller from each other so that the paper entering the discharge path in the path cross each other. According to the present invention, by providing a clearance portion that allows the paper entering the transport path in the delivery path and the paper entering the delivery path in the printing path to cross each other, the timing and the paper is picked up the next sheet when duplex printing It is possible to set the timing of entering the printing path in the same manner as in the one-side printing, and as a result, it is possible to improve the printing speed in the two-sided printing to almost the same level as in the one-sided printing on the basis of the number of printing surfaces.

Duplex printing, output roller, backup roller, play, separation, speed, improvement,

Description

Image forming apparatus for duplex printing

1 is a conceptual diagram of a conventional double-sided printing image forming apparatus.

2A to 2C are schematic views illustrating the operation of the image forming apparatus shown in Fig. 1;

FIG. 3 is a view illustrating a problem that occurs when the second paper is picked up and the timing at which the first paper enters the printing path in the conveyance path in the same manner as in the single-sided printing when duplex printing of the image forming apparatus shown in FIG. Conceptual diagram.

4 is a schematic view of a duplex laser printer according to the present invention;

5A and 5B are partial side views illustrating the operation of the play portion of the duplex printing unit of the laser printer shown in FIG. 4;

FIG. 6 is a schematic diagram illustrating a clutch of a transfer delay portion of a duplex printing unit of the laser printer shown in FIG. 4; FIG.

7A to 7H are conceptual views illustrating the operation of the image forming apparatus shown in FIG.

Fig. 8 is a partial side view illustrating a modification of the operation portion of the play portion of the duplex printing unit of the duplex laser printer according to the present invention.

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

100: laser printer 106: transfer unit

130: image forming unit 132: photosensitive member

144: discharge sensor 150: discharge unit

166: transfer roller 163: discharge roller

164: badge backup roller 165: play part

168: operating part 169: solenoid

178: operating lever 170, 190: reverse feed roller

196: transfer delay unit 199: clutch

The present invention relates to an image forming apparatus such as a laser printer, a copying machine, and the like, and more particularly, to a double-sided printing image forming apparatus capable of double-sided printing at a high speed.

In general, a double-sided printing image forming apparatus 1 such as a double-sided printing laser printer, a double-sided printing copier, or the like, has a printing path A for forming a toner image on the paper P, one side or both sides, as shown in FIG. A conveyance path (B) for discharging the finished paper (P), and a printing side of the finished paper (P) for reverse side printing to reverse the printing surface (P), and transfer it to the printing path (A) again. It is configured to have a path (C).

In the printing path A, the pickup roller 7, the first and second transfer rollers 23 and 28, the photosensitive member 32, the transfer roller 66, the heating roller 41, and the pressure roller 42 are usually It is arranged at a predetermined position in the paper feed direction. The pickup roller 7 picks up the paper P loaded in the paper cassette and transfers it to the first and second feed rollers 23 and 28, and the first and second feed rollers 23 and 28 are pick-up rollers ( The paper P conveyed by 7) is transferred to the transfer nip between the photosensitive member 32 and the transfer roller 66. The photosensitive member 32 forms a toner image by a laser scanning unit (LSU) (not shown) and a developer, and the transfer roller 66 passes through the transfer nip between the photosensitive member 32 and the paper P. A toner image formed on the photosensitive member 32 is transferred to the paper P by applying a predetermined transfer voltage and pressure thereto. The heating roller 41 and the pressure roller 42 fix the toner image transferred to the paper P on the paper P with heat and pressure.

In the discharge path B, a discharge roller 63 and a discharge backup roller 64 for discharging the paper P to the outside are disposed.

The conveying direction switching guide 54 prints the printing path upstream of the paper conveying direction B so as to guide the paper P, which is conveyed by the reverse rotation of the discharge roller 63, to the conveying path C during duplex printing. It is arrange | positioned between (A) and a conveyance path | route (C).

In the conveyance path C, the 1st and 2nd reverse conveyance rollers 70 and 90 which convey the sheet | seat P through the conveyance path C are arrange | positioned.

The printing operation of the conventional double-sided printing image forming apparatus 1 configured as described above will be described with reference to FIGS. 2A to 2C.

First, the first paper P1 positioned at the top of the paper P loaded in the paper feed cassette is picked up by the pickup roller 7 and then the first and second feed rollers 23, along the printing path A. 28 is transferred to the transfer nip between the photosensitive member 32 and the transfer roller 66.

On one surface of the first paper P1 moved to the transfer nip, for example, the upper surface, the toner image formed on the photosensitive member 32 is transferred by a transfer voltage and pressure applied by the transfer roller 66 in the transfer nip.

The toner image transferred to the upper surface of the first paper P1 is fixed to the upper surface of the first paper P by the heating roller 41 and the pressure roller 42.

The first paper P1 on which the toner image is fixed enters the discharge path B by the heating roller 41 and the pressure roller 42 and is transferred to the discharge medium not shown by the discharge roller 63. At this time, as shown in Figure 2a, the front end portion of the first paper (P1) pushes the discharge sensor 44 located downstream of the paper transport direction of the heating roller 41, whereby the discharge sensor 44 is turned on It is detected that the first paper P1 passes.

At this time, when the single-sided printing mode is performed, the first paper P1 is discharged to the discharge bin by the discharge roller 63. Also, when there is more data to be printed on the next paper, that is, the second paper P2, The second paper P2 of the paper feed cassette is picked up by the pickup roller 7 according to the 'on' signal of the discharge sensor 44 and moved to the transfer nip via the first and second feed rollers 23 and 28. After the image forming process as described above, it is discharged to the discharge medium by the discharge roller 63.

However, when the duplex printing mode is performed, as shown in FIG. 2B, the discharge roller 63 has a predetermined time after the rear end of the first paper P1 is turned 'off' through the discharge sensor 44. Until the rear end of the first paper P1 reaches the paper conveying direction downstream of the conveying direction switching guide 54 and extends toward the conveying path C by the stiffness of the paper itself. The paper P1 is moved in the discharge direction and then driven to reverse rotation. As a result, the first paper P1 enters the conveying path C without being discharged into the discharge bin.

In addition, when the rear end of the first paper P1 'offs' the output sensor 44, and there is more data to be printed on the next paper, that is, the second paper P, the second paper P2 of the paper feed cassette. ) Is picked up by the pick-up roller 7 and moved to the transfer nip via the first and second feed rollers 23 and 28 as in the method described above.

As shown in FIG. 2C, when the first paper P1 completely enters the transport path C, the leading end of the second paper P2 is near the nip between the discharge roller 63 and the discharge backup roller 64. Will approach.

Thereafter, the first paper P1 is guided back to the printing path A by the first and second reverse feed rollers 70 and 90, that is, the lower surface is printed through the image forming process as described above. The discharge roller is discharged to the discharge bin by the discharge roller 63.

In addition, the second paper P2 is moved in the discharge direction until a predetermined time elapses after the rear end passes through the discharge sensor 44 and then enters the conveyance path C by reverse rotation of the discharge roller 63. Then, after the conveying process and the image forming process as described above is discharged to the discharge medium by the discharge roller 63.

However, in the conventional double-sided printing image forming apparatus 1 which operates as described above, the timing at which the second paper P2 is picked up during the single-sided printing is as shown in FIG. 2A. On the other hand, the timing at which the second paper P2 is picked up during the duplex printing is set at the point of time 'on' by the front end of the sheet), as shown in FIG. 2B. The timing at which the end of the second paper P2 enters the printing path A, which is set to the point of 'off' by the end, is conveyed corresponding to the timing at which the second paper P2 is picked up, as shown in Fig. 2C. It is set at intervals. Therefore, the printing speed in duplex printing, especially in the case of duplex printing of a plurality of sheets, is significantly slower than in the case of single-sided printing.

In order to solve the problem of lowering the printing speed when printing on both sides, various attempts have been made until recently. One of them is the image forming on both sides so that the second paper P2 can be picked up when the discharge sensor is 'on' by the leading end of the first paper P1 which has completed image formation on both sides. It is a method for providing a separate discharge path for discharging only the first paper (P). However, in the double-sided printing image forming apparatus (not shown) using this method, when the first paper P1 having completed image formation is discharged on both sides, the second paper P2 is picked up as in the case of single-sided printing. When the first sheet of paper (P1) having completed image formation on one side is transferred to the discharge path, the sheet sensor is still turned on by the rear end of the first sheet of paper (P1) having completed image formation on one surface. When the second paper P2 is picked up and the second paper P2 enters the printing path A, the transfer corresponds to the timing at which the second paper P2 is picked up from the rear end of the first paper P1. It is entered at intervals. Therefore, although the printing speed at the time of double-sided printing is improved compared to the conventional double-sided printing image forming apparatus 1 shown in Fig. 1, there is still a problem that is slower than the printing speed at the time of single side printing.

Therefore, in order to increase the printing speed at the time of duplex printing to the level at the time of single-sided printing, the timing at which the second paper P2 is picked up and the timing at which the second paper P2 enters the printing path A at the time of double-sided printing are compared with the one-sided printing. It is most certain to set the same time and feed interval. In this case, however, as shown in FIG. 3, the tip of the second paper P2 is discharged as the first paper P1 enters the conveyance path C by the reverse rotation of the discharge roller 63. The nip between the 63 and the medium backup roller 64 is reached, and as a result, the first and second papers P1 and P2 collide with each other to generate jams.

Therefore, the timing at which the second paper P2 is picked up and the timing at which the paper enters the printing path A at the same time as in the single-sided printing so as to increase the printing speed in the two-sided printing to the level at the one-sided printing and While setting the feed interval, there is a need for the development of a new double-sided printing image forming apparatus in which the first and second papers P1 and P2 do not collide with each other to generate jams.

The present invention has been made to solve the above problems, an object of the present invention is to provide a double-sided printing image forming apparatus that can increase the printing speed when printing on both sides to approximately the same level as the one-sided printing on the basis of the number of printing surface There is.

In order to achieve the above object, a double-sided printing image forming apparatus according to an embodiment of the present invention comprises: a conveying unit having at least one conveying roller for conveying paper along a printing path; An image forming unit for forming an image on the paper; A discharge unit including a discharge roller and a discharge back-up roller for discharging the paper on which the image is formed along the discharge path; And a double-sided printing unit having at least one reverse feed roller for transferring the paper having an image formed on one side thereof through the transfer path, wherein the double-sided printing unit enters the transfer path from the discharge path when printing on both sides. It characterized in that it comprises a clearance for separating the discharge roller and the discharge back-up roller from each other so that the paper and the paper entering the discharge path in the printing path to cross each other.

The clearance portion may include an elastic support portion for elastically supporting the discharge medium backup roller in a first position in contact with the discharge roller, and an operation portion for moving the discharge medium backup roller to a second position spaced apart from the discharge roller.

The elastic support portion is composed of an elastic spring for elastically supporting the discharge medium backup roller, the operation portion, the operating lever is rotatably supported, the operation lever for moving one of the shaft of the discharge roller and the discharge medium backup roller in contact with the discharge medium backup roller, And a solenoid which rotates the operation lever to move one of the shafts of the moving roller and the medium backup roller to move the medium backup roller to the second position.

The reverse feed roller of the double-sided printing unit is preferably driven faster than the feed roller of the transfer unit. To this end, the duplex printing unit has a conveying delay unit for delaying the conveyance of the sheet so that the sheet which is quickly moved by the reverse conveying roller in the conveying path may enter the printing path which is conveyed slowly by the conveying roller.

The transfer delay unit includes at least one first sensor installed in the printing path, at least one second sensor installed in the transport path, and a clutch to block power transmission to the reverse feed roller according to the operation of the first and second sensors. .

Hereinafter, a double-sided printing image forming apparatus according to the present invention will be described with reference to the accompanying drawings.

4 schematically illustrates a duplex printing image forming apparatus according to the present invention.

The image forming apparatus according to the present invention is a laser printer 100 for printing and outputting data input from an external device such as a PC.

Referring to FIG. 4, the laser printer 100 of the present invention includes a paper feed cassette 111, a transfer unit 106, an image forming unit 130, a discharge unit 150, and a duplex printing unit 180. .

The paper feeding cassette 111 is installed under the frame 110 of the main body, and supports the paper P to be elastically lifted and lowered through the paper pressing plate 113 supported by the elastic spring 112.

In the upper part of the paper cassette 111, a transport unit 106 is provided for sequentially picking up and transporting the sheets P stacked on the paper cassette 111 one by one.

The transfer unit 106 is provided with a pickup roller 107 for picking up the paper P loaded in the paper feed cassette 111. The paper P picked up by the pickup roller 107 is registered by the transfer roller 123 and the transfer backup roller 124 along the transfer guide 122 constituting the printing path A. It is transferred to the nip between the backup rollers 129.

The register sensor 125 is arranged upstream of the register roller 128 in the paper feed direction. The register sensor 125 includes a sensing unit having a light emitting unit for emitting light and a light receiving unit for receiving light emitted from the light emitting unit, and a sensing lever which protrudes through the printing path A and is disposed between the light emitting unit and the light receiving unit. It can be configured as an optical sensor. Since the configuration of the optical sensor is generally the same as that known in the art, further detailed description is omitted.

The register roller 128 is aligned by the nip between the register roller 128 and the register backup roller 129 after the register sensor 125 is 'on' by the leading end of the paper P. It is driven to convey the paper P after a predetermined time delay until

The image forming unit 130 is detachably installed on a frame (not shown) of the main body above the transfer unit 106.

The image forming unit 130 includes a drum-shaped photosensitive member 132 that forms an electrostatic latent image by a laser beam emitted from the LSU 176 in accordance with an image signal.

The LSU 176 emits a laser beam corresponding to the data to be printed from the internal laser diode to the photosensitive member 132 when the feed sensor 126 is 'on' by the leading end of the paper P. FIG. The feed sensor 126 is disposed downstream of the paper feed direction of the register roller 128, and may be configured as an optical sensor like the register sensor 125.

Around the photosensitive member 132, a charging roller 149 for charging the photosensitive member 132, a developing roller 147 for attaching toner to an electrostatic latent image formed on the photosensitive member 132, and developing the toner image, and printing the toner image (P) ), A cleaning blade 148 for cleaning the toner residue remaining on the surface of the photosensitive member 132 after transfer, and a waste toner container 146 for storing the toner residue.

Under the photosensitive member 132, a transfer roller 166 for transferring the toner image formed on the photosensitive member 132 to paper P is provided. The transfer roller 166 is arranged to apply a predetermined pressure to the photosensitive member 132, and a predetermined transfer bias voltage is applied.

Downstream of the paper conveying direction of the photosensitive member 132, a heating roller 141 and a pressure roller 142 are provided as a fixing unit 140 for fixing and fixing the toner image transferred to the paper P.

Downward in the paper transport direction of the heating roller 141, a discharge sensor for detecting the timing of reverse rotation operation of the delivery roller 163 of the delivery unit 150 described later for duplex printing and the timing of picking up the paper P ( 144 is disposed. The discharge sensor 144 may be configured as an optical sensor like the register sensor 125 and the transfer sensor 126.

Downstream of the paper conveyance direction of the discharge sensor 144, a static electricity removing brush 155 for removing static electricity of the paper P is disposed. The static electricity removing brush 155 is formed by the static electricity when the paper P crosses between the gaps generated between the discharge roller 163 and the discharge backup backup roller 164 by the play portion 165 as described below. P) does not stick to each other.

The discharge unit 150 is for discharging the paper P on which the toner image has been fixed by the fixing unit 140 to the external discharge table 167, and is transported downstream of the paper feeding direction of the fixing unit 140. A discharge roller 163 and a discharge medium backup roller 164 disposed along the 122 are provided. The discharge roller 163 discharges the paper P conveyed by the fixing roller 141 to the discharge table 167 along the discharge path B.

The duplex printing unit 180 is for printing on the back surface of the paper P, for example, on the bottom surface thereof, and includes a reverse feed guide 162, a transfer direction switching guide 154, and first and second reverse feed rollers ( 170, 190, and a clearance 165.

The reverse feed guide 162 constitutes a conveying path C for reentering the paper P having an image formed on one side, that is, the upper surface, into the developing unit 130.

The transfer direction switching guide 154 guides the paper P to move to the transport path C for double-sided printing, and the printing path upstream of the discharge path B of the discharge roller 163 of the discharge unit 150. It is arrange | positioned at the point where (A) and the conveyance path | route C meet. The conveying direction switching guide 154 is connected to a solenoid not shown when the paper P, which has been printed on the upper surface, is conveyed back by the discharge roller 163 whose driving direction is switched by a known direction changing device not shown. 4 is moved from the solid line position (FIG. 5A) to the dotted line position (FIG. 5B). Since the operation and configuration of the transfer direction switching guide 154 is the same as that known in the art, further description thereof will be omitted.

The first conveyance sensor 175 is disposed downstream of the first conveyance roller 170 in the paper conveying direction. The first conveying sensor 175 detects whether the paper P, which has completed image formation on the upper surface, has reached the nip between the first reverse feed roller 170 and the first reverse feed backup roller 171 to be described later. Provided for determining timing of operating solenoid 169 of 165. The first transport sensor 175 may be configured as an optical sensor like the discharge sensor 144.

Further, a second conveyance sensor 195 is disposed downstream of the paper conveying direction of the second reverse conveyance roller 190. The second conveyance sensor 195 may operate the clutch P 199 (FIG. 6) of the transfer delay unit 196, which will be described later, whether or not the paper P having completed image formation on the upper surface may enter the printing path A. FIG. Is provided for detecting timing. That is, when the second conveyance sensor 195 is 'on' by the paper P, the control unit (not shown) moves to the printing path A according to the operation of the register sensor 125 and / or the conveying sensor 126. It is determined whether there is paper P entering, and if there is paper P entering the printing path A, the first and second reverse feeds until the paper P completely enters the printing path A. The driving of the rollers 170 and 190 is stopped. In addition, when there is no paper P entering the printing path A, the control unit 'off' the clutch 199 to drive the second reverse feed driven faster than the register roller 128 by the reverse feed drive motor 197. Power transmission to the roller 190 is blocked, thereby allowing the paper P to enter the printing path A without generating jams.

The first and second reverse feed rollers 170 and 190 are arranged at regular intervals along the reverse feed guide 162 to move the paper P through the conveying path C. The first and second reverse feed rollers 170 and 190 are transfer rollers 123 and registers of the transfer unit 106 so as to transfer the paper P conveyed along the conveying path C to the printing path A quickly. It is driven at a higher speed than the feed roller 123, the register roller 128 and the like by a drive motor for driving the roller 128 and the like and a separate back feed drive motor 197.

Therefore, it is necessary to allow the paper P, which is rapidly moved by the second reverse feed roller 190 in the transport path C, to enter the printing path A, which is slowly transported by the register roller 129. .

To this end, the duplex printing unit 180 includes a transfer delay unit 196.

The transfer delay unit 196 includes a second transfer sensor 195 installed downstream of the second reverse feed roller 190 in the paper transfer direction, a register sensor 125 provided upstream of the easy transfer direction of the register roller 128, and the first transfer sensor 195. The clutch 199 cuts off the power transmitted from the reverse feed drive motor 197 to the second reverse feed roller 190 according to the operation of the second conveyance sensor 195 and the register sensor 125.

As shown in FIG. 6, the clutch 199 is an electronic clutch that can be obtained commercially as a single product, and the first reverse feed roller gear 190a coaxially formed with the second reverse feed roller 190 and the reverse feed drive motor. It is provided in the gear train 201 which connects between the drive gears 198 of 197.

The clutch 199 has the front end portion of the paper P after the second conveyance sensor 195 and the register sensor 125 are sequentially operated by the front end portion of the paper P, and then the register roller 128 and the register backup roller 129. After a predetermined time to engage the nip between the) elapses, it operates to 'off'. Therefore, the paper P which quickly enters the printing path A from the conveying path C by the second reverse feed roller 190 is formed between the register roller 128 and the register backup roller 129 without jamming. It may enter the nip of and may be conveyed by the register roller 128.

As shown in FIGS. 5A and 5B, the clearance part 165 separates the medium backup roller 164 from the medium roller 163 to form a constant gap between the medium roller 163 and the medium backup roller 164. To form, it is composed of an elastic support 166, and the operation unit 168.

The elastic support 166 is for elastically supporting the medium backup roller 164 at a contact position in contact with the medium roller 163, as shown in FIG. 5A, and the shaft 164a of the medium backup roller 164. It is composed of an elastic spring that elastically supports both ends of the fixing frame (111a).

The operation unit 168 is to move the discharge backup roller 164 from the discharge roller 163 to a spaced position in contact with the limiting roller 161, the moving roller 177, the operation lever 178, and It consists of a solenoid 169. The moving roller 177 is rotatably supported by the first end 178a of the operating lever 178. The operation lever 178 is supported to be rotatable on the rotation shaft 179 of the fixed frame 111a at the center. The solenoid 169 includes a plunger 169a that protrudes by an electromagnetic force of an inner coil (not shown) and pushes the second end 178b of the operating lever 178 when it is 'on'. As shown in FIG. 5B, when the plunger 169a pushes the second end 178b of the actuating lever 178, the actuating lever 178 is in one direction, for example clockwise, with respect to the rotation axis 179. And thereby the moving roller 177 moves the discharge backup roller 164 to a spaced position against the elastic force of the elastic support 166.

As such, when the solenoid 169 is 'on', the discharge backup roller 164 is spaced apart from each other by the operation lever 178 and the moving roller 177. As a result, a constant gap is formed between the medium roller 163 and the medium backup roller 164. This gap is formed by the first reverse feed roller 170 entering the conveying path C by the first reverse feed roller 170, for example, a paper having an image formed on the upper surface when printing on both sides. After the image is formed on the upper surface or both the upper surface and both sides, the paper discharged by the heating roller 141, for example, the second paper P2 or the first paper P1 enters the transport path C. The paper P1 or the second paper P2 can be discharged through the discharge roller 163 and the discharge backup roller 164 without generating jams. Therefore, the timing at which the second paper P2 is picked up for double-sided printing is the same time as the timing for picking up the second paper P for single-sided printing, for example, the discharge sensor 144 is at the leading end of the first paper P1. The timing at which the second paper P2 enters the printing path A at the timing at which the second paper P2 is picked up from the rear end of the first paper P1. It is possible to set to have a corresponding tooth spacing, so that the printing speed in duplex printing can be improved to almost the same level as in single-sided printing on the basis of the number of printed surfaces.

Optionally, the actuating portion 168 'may be configured not to include the moving roller 177 to simplify the configuration, as shown in FIG. In this case, the first end 178a 'of the actuating lever 178' has a C-shaped projection spaced at a predetermined interval by the width of the discharge backup roller 164 to contact both ends of the shaft 164a of the discharge backup roller 164. It is formed in the form.

The operation of the double-sided printing laser printer 100 according to the present invention configured as described above will be described with reference to FIGS. 4 to 7H.

First, the first paper P1 located at the top of the paper P loaded in the paper cassette 111 is picked up by the pickup roller 107 and then along the transfer guide 122 by the feed roller 123. It is conveyed toward the register roller 128.

At this time, the register sensor 125 installed in front of the register roller 128 is 'on' by the front end of the first paper (P1). As the register sensor 125 is 'on', the register roller 128 has a predetermined time until the tip of the first paper P1 is aligned by the nip between the register roller 128 and the register backup roller 129. After being delayed and driven, the first paper P1 is conveyed toward the image forming unit 130 by the register roller 128.

While the first paper P1 is conveyed toward the image forming unit 130, the photosensitive member 132 has an electrostatic latent image by the laser beam emitted from the LSU 176 operating according to the 'on' signal of the transfer sensor 126. Is formed, and the electrostatic latent image formed on the photosensitive member 32 is developed by the developing roller 147 to be attached to the toner to form a visible toner image.

The toner image formed on the photosensitive member 132 is transferred to the transfer nip between the photosensitive member 132 of the image forming unit 130 and the transfer roller 166 along the transfer guide 122. The transfer roller 166 is transferred onto one surface of the first paper P1, for example, the upper surface, and the toner image transferred to the upper surface of the first paper P is a heating roller constituting the fixing unit 140 ( 141 and the pressure roller 142 is fixed to the upper surface of the first paper (P1).

After the toner image is transferred from the photosensitive member 132 to the upper surface of the first paper P1, the toner residue remaining on the surface of the photosensitive member 132 according to the transfer efficiency is removed by the cleaning blade 148, thereby cleaning the cleaning blade 148. It is stored in the waste toner container 146 located below.

Thereafter, as shown in FIG. 7A, the first paper P1 pushes the discharge sensor 144 located downstream of the heating roller 141 in the paper transport direction, and thus the discharge sensor 144 is 'on'. .

At this time, when the printer 100 performs the single-sided printing mode, the first paper P1 is discharged to the discharge tray 167 by the discharge roller 163, and when there is more data to be printed on the next sheet. , The second paper P2 located at the top of the paper feed cassette 111 is picked up by the pickup roller 107 according to the 'on' signal of the discharge sensor 144, and thus the feed roller 123 and the register roller 128 After moving to the transfer nip through the image forming process as described above is discharged to the discharge stage 167 by the discharge roller 163.

However, when the duplex printing mode is performed, the discharge roller 163 has the rear end of the first paper P1 passing through the discharge sensor 144 to 'off' the discharge sensor 144 as shown in FIG. 7B. After a predetermined time has elapsed, that is, until the rear end portion of the first paper P1 reaches the paper conveying direction downstream of the conveying direction switching guide 154 and is extended to the conveying path C by the paper itself. The first paper P1 is moved in the discharge direction. In addition, when there is more data to be printed on the next sheet, the second paper P2 of the paper feed cassette 111 is picked up when the output sensor 144 is 'on' by the leading end of the first paper P1. 107 is picked up and transferred to the transfer nip via the transfer roller 123 and the register roller 128.

Thereafter, when the rear end of the first paper P1 reaches the paper conveying direction downstream of the conveying direction switching guide 154, the discharge roller 163 is driven to rotate in reverse by a known direction changing device. As a result, the first paper P1 enters the transport path C without being discharged to the discharge stage 167.

While the first paper P1 enters the conveying path C, the second paper P2 is transferred to the heat roller 141 and the pressure roller 142 after the toner image is transferred to the upper surface of the transfer nip. The toner image is fixed by this.

Thereafter, as shown in FIG. 7C, the front end portion of the first paper P1 passes through the nip between the first reverse feed roller 170 and the first reverse feed backup roller 171 to allow the first double-sided sensor 175 to be used. When passing through the first two-sided sensor 175 reaches a position to 'on', the solenoid 169 is 'on'.

As the solenoid 169 is 'on', as shown in FIG. 5B, the actuating lever 178 is rotated clockwise about the rotation shaft 179 by the plunger 169a through the moving roller 177. The medium backup roller 164 is moved to a spaced position spaced apart from the medium roller 163. As a result, a predetermined gap is generated between the medium backup roller 164 and the backup roller 163.

Accordingly, the first paper P1 is conveyed along the conveying path C by the conveying force of the first reverse feed roller 170 which is driven rapidly, while the second paper has passed through the transfer nip and the fixing unit 140. P1 is transferred in the discharge direction through the gap between the discharge backup roller 164 and the backup roller 163 by the transfer force of the heating roller 141. At this time, the discharge roller 163 is driven to rotate forward by the direction switching device.

Thereafter, when the rear end of the first paper P1 passes through the first double-sided sensor 175 and the first double-sided sensor 175 is 'off', the solenoid 169 is 'off'.

As the solenoid 169 is 'off', the discharge backup roller 164 rotates the operation lever 178 counterclockwise by the elastic restoring force of the elastic spring of the elastic support 166, and the discharge roller 163 It returns to the contact position which touched.

At this time, the second paper (P2) is located at a position where the rear end is not out of the nip between the heating roller 141 and the pressure roller 142, and is transported in the discharge direction by the heating roller 141 and the discharge roller 163. do.

Thereafter, when the first paper P1 passes through the second double-sided sensor 195 by the second reverse feed roller 190 which is rapidly driven, the second double-sided sensor 195 is turned on, and the control unit (not shown) It is determined whether the first paper P1 or other paper is in the printing path A by determining whether the restoring sensor 125 and the transfer sensor 126 are on, and the paper is in the printing path A. If it is determined that there is no, the second reverse feed roller 190 is continuously driven to enter the first paper P1 into the printing path A.

As shown in FIG. 7D, when the front end portion of the first paper P1 enters the printing path A and passes through the register sensor 125 to turn on the register sensor 125, the controller may control the first paper. The electronic clutch 199 is stopped so that the driving of the second reverse feed roller 190 is stopped after a predetermined time when the distal end portion of P1 engages the nip between the register roller 128 and the register backup roller 129. Operate to 'off'. Therefore, the first paper P1 rapidly entering the printing path A from the conveying path C by the second reverse feed roller 190 enters the printing path A without jamming.

In this way, the first paper P1 entering the printing path A is moved toward the image forming unit 130 and the fixing unit 140 by the register roller 128, and is formed through the image forming process as described above. That is, an image is printed on the lower surface, and then transferred to the discharge roller 163 side, that is, to the discharge path B side.

On the other hand, the second paper P2 has a discharge roller when the rear end reaches the paper conveying direction downstream of the conveying direction switching guide 154, similarly to the conveying operation of the first paper P1 described with reference to FIGS. 7B and 7C. Entering into the transport path (C) by the reverse rotation of 163, as shown in Figure 7e, the front end portion 'on' the first two-sided sensor 175, and then discharged by the operation of the play portion 165. When the backup roller 164 is spaced apart from the discharge roller 163, the conveying path C is driven by the first reverse feed roller 170 which is driven rapidly in the gap between the discharge roller 163 and the discharge backup roller 164. Are conveyed accordingly.

At this time, even if the first paper P1 which completes image formation on both sides and is discharged toward the discharge path B reaches the nip between the discharge roller 163 and the discharge backup roller 164, the second paper P2 is separated by the gap. It is discharged along the discharge path (B) by the heating roller 141 without hitting the).

Thereafter, the rear end portion of the second paper P2 passes through the first two-sided sensor 175 to 'off' the first two-sided sensor 175, and then the discharge backup roller 164 is operated by the play part 165. Upon contact with the discharge roller 163, the first paper P1 is discharged to the discharge tray 167 by the discharge roller 163.

As shown in FIG. 7F, while the first paper P1 is discharged to the discharge tray 167 along the discharge path B, the second paper P2 is formed of the first paper described with reference to FIG. 7D ( In the same manner as in the print path entry operation of P1), the print path A is entered.

 Thereafter, the first paper P1 is completely discharged to the discharge tray 167 by the discharge roller 163, and the second paper P2 entering the printing path A is formed by the register roller 128. Moving toward the unit 130 and the fixing unit 140, an image is printed on the bottom surface through the image forming process as described above.

Subsequently, as shown in FIG. 7G, when the leading end of the second paper P2 passes through the discharge sensor 144 and turns on the discharge sensor 144, the control unit further has data to be duplex printed on the next sheet. Determine if there is. If it is determined that there is data to be printed, the third paper P3 of the paper feed cassette 111 is picked up by the pickup roller 107 and transferred to the transfer nip through the transfer roller 123 and the register roller 128. Transferred.

As shown in FIG. 7H, after the second paper P2 is discharged to the discharge stage 167, the third paper P3 passes through the image forming process, and then the tip thereof passes through the discharge sensor 144. When the sensor 144 is turned on, the controller determines whether there is more data to be duplexed on the next sheet again. If it is determined that there is data to be printed, the fourth paper P4 of the paper feed cassette 111 is picked up by the pickup roller 107 and transferred to the transfer nip through the transfer roller 123 and the register roller 128. Transferred.

Thereafter, the printing operation of the third and fourth papers P3 and P4 has data to be printed in the same manner as the printing operation of the first and second papers P1 and P2 described above with reference to FIGS. 7A to 7H. It is performed repeatedly when disappeared.

As described above, the double-sided printing image forming apparatus according to the present invention has a clearance for allowing the paper entering the transport path in the delivery path and the paper entering the delivery path in the printing path to cross-move each other, thereby, It is possible to set the timing at which the next paper is picked up and the timing at which the paper enters the printing path in the same way as in single-sided printing. As a result, the printing speed in double-sided printing is almost the same as that in single-sided printing based on the number of printed pages. You can improve to the same level.

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 embodiments, and any person having ordinary skill in the art to which the present invention pertains without departing from the spirit and spirit of the present invention claimed in the claims may make various modifications and variations. Implementation will be possible.

Claims (5)

A conveying unit having at least one conveying roller for conveying paper along a printing path; An image forming unit for forming an image on the paper; A discharge unit including a discharge roller and a discharge back-up roller for discharging the paper on which the image is formed along the discharge path; And And a duplex printing unit having at least one reverse feed roller for conveying a sheet of paper having an image formed on one surface through a conveying path. The double-sided printing unit has a clearance for separating the discharge roller and the discharge backup roller from each other so that the paper entering the transport path from the discharge path and the paper entering the discharge path from the printing path can cross each other. Duplex printing image forming apparatus comprising a. The method of claim 1, wherein the play portion, An elastic support for elastically supporting the discharge medium backup roller at a first position in contact with the discharge roller; And And an operation unit for moving the discharge backup roller to a second position spaced apart from the discharge roller. 3. The method of claim 2, The elastic support portion includes an elastic spring for elastically supporting the discharge medium backup roller; The actuating unit is rotatably supported and moves one of the moving lever in contact with the medium backup roller and the axis of the medium backup roller, and one of the axes of the moving roller and the medium backup roller. And a solenoid which rotates the operation lever to move the discharge backup roller to a second position. The method of claim 1. The reverse feed roller of the duplex printing unit is driven faster than the feed roller of the transfer unit; The conveying path is connected to the printing path so that the paper entering the conveying path from the discharge path may enter the printing path when duplex printing: The double-sided printing unit is installed in the printing path, the conveying path, and a power transmission path for transmitting a driving force to the reverse conveying roller, and the paper which is quickly conveyed by the reverse conveying roller in the conveying path is fed to the conveying roller. And a transfer delay unit for controlling power transfer to the reverse feed roller to delay the transfer of the paper and enter the printing path when entering the printing path which is slowly transferred by the printing path. Device. The method of claim 4, wherein the transfer delay unit, At least one first sensor installed in the printing path; At least one second sensor installed in the transport path; And And a clutch for blocking power transmission to the reverse feed roller in accordance with the operation of the first and second sensors.

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