JP4429243B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus that includes a recording medium stacking unit that can stack a plurality of recording media and can automatically supply the recording medium.

Conventionally, when supplying recording paper in an image forming apparatus, air is blown by a device that stops conveyance of the recording paper when double feeding (double feeding) of the recording paper is detected, or by a so-called air knife when double feeding is detected. There is known a method of separating the recording paper that has been double-fed in (see Patent Document 1).
JP 2002-370840 A

  However, when the double-fed recording paper is detected and the conveyance of the recording paper is stopped, the recording paper whose conveyance has been stopped stays inside the apparatus, causing jamming and forcing the user to useless work. Depending on where the recording paper stops, there is a risk of damaging components such as the photoreceptor.

  Also, in the method of separating the recording paper using an air knife when double feeding is detected, if the recording paper that has been double fed is not held by the transport roller, the recording paper is unpositioned by blowing air. In addition to stabilization, skew occurs in the recording paper, and if the skew increases, problems such as jamming occur in the recording paper separated in the conveyance path.

  The present invention has been made in view of the above-described conventional problems, and eliminates a jam caused by the supplied recording medium staying in the apparatus due to the multiple feeding of the recording medium, An object of the present invention is to provide an image forming apparatus capable of realizing a stable supply of a recording medium.

The configuration of the image forming apparatus according to the present invention for solving the above-described problems is as follows.
The image forming apparatus according to claim 1, a recording medium stacking unit capable of stacking a plurality of recording media, and a recording medium transport unit configured to transport the recording medium supplied one by one from the recording medium stacking unit to the image forming unit. And
Double feed detection means for detecting whether or not the next transported recording medium P2 is double fed to the recording medium P1 which has been normally fed without being double fed from the recording medium stacking unit, and the double fed recording In an image forming apparatus comprising a recording medium suction means for sucking the medium P2, and capable of automatically supplying a recording medium from the recording medium stacking unit,
The recording medium suction means sucks the double-fed recording medium P2, stops transport of the recording medium P2 in the sucked state, and enables the recording medium P2 to move. When it is conveyed to a position that can be detected by the double feed detection means, the rear end of the recording medium is disposed at a position where it can be sucked,
The recording medium conveying unit is provided with a conveying roller for conveying the recording medium toward the image forming unit on the downstream side of the double feed detecting unit,
When the double feed of the recording medium P2 is detected by the double feed detection means, the recording medium suction means sucks the trailing end of the double-fed recording medium P2 and stops its conveyance, and the recording medium conveyance The means conveys the normally supplied recording medium P1 toward the image forming unit by the conveying roller, thereby separating the normally supplied recording medium P1 from the double-fed recording medium P2. It is what.

According to a second aspect of the present invention, in addition to the configuration described in the first aspect, the recording medium suction unit includes a conveyance belt that can be driven along a recording medium conveyance direction, and a drive that drives the conveyance belt. It has a roller and a suction device which is disposed on the opposite side of the conveying belt to the recording medium conveying side and sucks the recording medium toward the conveying belt .

According to a third aspect of the present invention, in addition to the configuration described in the first or second aspect , the recording medium suction unit sucks the double-fed recording medium P2 , and then the double-fed recording medium. P2 is displaced in the direction opposite to the conveyance direction of the recording medium P1 to be supplied.

According to a fourth aspect of the present invention, in addition to the configuration described in the first or second aspect , the recording medium conveying unit performs recording when the double-fed detection unit detects the double-fed recording medium. It is characterized in that the speed of conveying the medium is reduced.

In addition to the configuration described in claim 2, the image forming apparatus described in claim 5 is configured so that the recording medium transporting unit is configured so that the double-recorded recording medium P2 is separated from the previously supplied recording medium P1. The separated recording medium P2 is conveyed by driving the conveying belt of the recording medium suction means to adjust the position of the leading end on the upstream side in the conveying direction.

In addition to the configuration described in claim 5 , the image forming apparatus described in claim 6 is configured such that the recording medium transporting unit separates the normally supplied recording medium P1 from the multi-fed recording medium P2. The recording medium suction means transports the double-recorded recording medium P2 to the transport roller, and temporarily stops the transport after the transport .

  In the present invention, the position adjustment in the conveyance of the recording medium includes the leading edge adjustment and positioning adjustment of the recording medium using a PS roller or the like.

  According to a seventh aspect of the present invention, in addition to the configuration described in any one of the first to sixth aspects, the double-feed detection unit is configured to detect the overlap of the recording medium double-fed by ultrasonic waves. It is characterized by detecting the feeding amount.

According to the first aspect of the invention, when the double feeding of the recording medium P2 is detected by the double feeding detecting means, the recording medium suction means sucks the rear end of the double fed recording medium P2. The conveyance is stopped, and the recording medium conveying unit conveys the normally supplied recording medium P1 toward the image forming unit by the conveying roller, thereby double-feeding the normally supplied recording medium P1. By separating the recording medium P2 from the recording medium P2 , even if the recording medium is double-fed, the double-fed recording medium P2 can be surely separated, and the supplied recording medium can be used without stopping the apparatus. It is possible to eliminate a jam caused by staying inside the recording medium and to supply a stable recording medium.
Further, the configuration of the recording medium suction means is configured to suck the rear end of the multi-feed recording medium P2, so that the rear of the multi-feed recording medium P2 is carried by the transport of the supplied recording medium. The multi-fed recording medium can be separated without curling the end side.

  Moreover, according to invention of Claims 2-7, in addition to the said common effect obtained by the invention of Claim 1, the following effect can be acquired.

According to the third aspect of the present invention, the configuration of the recording medium suction means is opposite to the transport direction of the recording medium supplied with the double fed recording medium after the double fed recording medium is sucked. By displacing in the direction, it is possible to reliably separate the recording medium that has been double-fed from the recording medium that is supplied.

According to the invention described in claim 4 , the configuration of the recording medium transporting unit is configured to reduce the speed of transporting the recording medium when the recording medium fed by the double feeding detecting unit is detected. Thus, since the double-fed recording medium can be reliably sucked by the suction means, the double-fed recording medium and the supplied recording medium can be reliably separated.

According to the fifth aspect of the present invention, the configuration of the recording medium transporting unit is configured to adjust the position of the leading end portion on the upstream side in the transport direction of the recording medium P1 supplied after the multi-feed recording medium is separated. Since this is done, it is possible to stably adjust the position of the supplied recording medium P1 without being affected by the recording medium that has been double fed.

  According to the seventh aspect of the invention, the configuration of the double feed detecting means is configured to detect the double feed amount of the double-feeded recording medium, so that the double-feed recording medium is sucked. Since it is possible to easily estimate the time to perform, it is possible to prevent the recording medium from being skewed and output the image without reducing the image forming speed.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
1 and 2 show an example of an embodiment of the present invention. FIG. 1 is an explanatory diagram showing the overall configuration of the image forming apparatus according to the embodiment of the present invention. FIG. 2 shows the main body of the image forming apparatus. FIG.

  The image forming apparatus 1A according to the present embodiment uses a predetermined sheet-like recording sheet (hereinafter, referred to as a sheet) that serves as a recording medium by electrophotographic processing of image data read by a scanner or the like or image data transmitted from the outside. )) Is output and formed as a monochrome image, and a paper feed tray (recording medium stacking unit) 8 capable of stacking a plurality of sheets P, and a sheet P supplied from the paper feed tray 8 to the image forming unit 14. A sheet conveying section (recording medium conveying means) 59 for conveying is provided, and the sheet P can be automatically supplied from the sheet feeding tray 8.

  First, the overall configuration of the image forming apparatus 1A according to the present embodiment will be described with reference to the drawings.

  As shown in FIGS. 1 and 2, the image forming apparatus 1 </ b> A mainly includes an exposure unit 1, a developing device 2, a photosensitive drum 3, a charger 4, a charge eliminating device 41, a cleaner unit 5, a fixing unit 6, and a sheet conveyance path. 7, an apparatus main body 1A1 including a paper feed tray 8, a paper discharge tray 9, a transfer mechanism (transfer means) 10, and the like, and an automatic document processing apparatus 1A2.

  A document placing table 21 made of transparent glass on which a document is placed is provided on the upper surface of the apparatus main body 1A1. Above the document placing table 21, the automatic document processing device 1A2 is swingably opened upward. On the other hand, a scanner unit 22 serving as a document reading unit that reads image information of a document is disposed below the document placing table 21.

  Below the scanner unit 22, an exposure unit 1, a developing device 2, a photosensitive drum 3, a charger 4, a charge eliminating device 41, a cleaner unit 5, a fixing unit 6, a paper transport path 7, a paper discharge tray 9, and a transfer mechanism. 10 is disposed, and a paper feed tray 8 in which the paper P is stored is disposed below.

  The exposure unit 1 performs exposure by irradiating the surface of the photosensitive drum 3 uniformly charged by the charger 4 with laser light according to image data (image information for printing) output from an image processing unit (not shown). Thus, it has a function of writing and forming an electrostatic latent image corresponding to image data on the surface of the photosensitive drum 3.

  The exposure unit 1 is disposed immediately below the scanner unit 22 and above the photosensitive drum 3, and employs laser scanning units (LSU) 13 a and 13 b including a laser irradiation unit 11 and a reflection mirror 12. In the present embodiment, in order to perform high-speed printing processing, a technique of using a plurality of laser beams to reduce the irradiation timing is adopted, and a two-beam technique is adopted.

  In this embodiment, the laser scanning units (LSU) 13a and 13b are used for the exposure unit 1, but a light emitting element arranged in an array, for example, an EL or LED writing head may be used. .

  As shown in FIG. 2, the photosensitive drum 3 has a cylindrical shape, is disposed below the exposure unit 1, and is rotated in a predetermined direction (the direction of arrow A in the figure) by a driving unit and a control unit (not shown). Is controlled. Along the outer peripheral surface of the photosensitive drum 3, the sheet peeling claw 31, the cleaner unit 5, the charger 4 as an electric field generating unit, and the development head toward the downstream side in the rotational direction of the photosensitive drum with reference to the position after completion of image transfer. The device 2 and the static eliminator 41 are arranged in this order.

  The sheet peeling claw 31 is disposed so as to be able to contact and separate from the outer peripheral surface of the photosensitive drum 3 by a solenoid 32. The sheet peeling claw 31 is stuck to the surface of the photosensitive drum 3 when the unfixed toner image on the photosensitive drum 3 is transferred to the sheet P in a state of being in contact with the outer peripheral surface of the photosensitive drum 3. The sheet P is peeled off.

  Note that a driving motor or the like may be employed as the driving means for the sheet peeling claw 31 instead of the solenoid 32, and other driving means may be selected.

  The developing device 2 visualizes the electrostatic latent image formed on the photosensitive drum 3 with black toner, and is downstream of the charger 4 in the rotating direction of the photosensitive drum (the direction of arrow A in the figure). It is arranged substantially horizontally (right side in the figure) on the side of the photosensitive drum 3. A registration roller 15 is disposed below the developing unit 2 on the upstream side in the recording medium conveyance direction.

  The registration roller 15 aligns the front end of the paper P supplied from the paper feed tray 8 and the toner image on the photoconductive drum 3 and conveys it between the photoconductive drum 3 and the transfer belt 103 (not shown). The operation is controlled by the drive means and the control means.

The charger 4 is a charging unit for uniformly charging the surface of the photosensitive drum 3 to a predetermined potential, and is disposed above the photosensitive drum 3 and in the vicinity of the outer peripheral surface thereof.
In the present embodiment, the charger type charger 4 is used, but a contact type roller type or a brush type may be used.

  The static eliminator 41 is a pre-transfer static eliminator for reducing the surface potential of the photosensitive drum 3 in order to facilitate the transfer of the toner image formed on the surface of the photosensitive drum 3 to the paper P. It is arranged downstream of the developing device 2 in the drum rotating direction and close to the outer peripheral surface below the photosensitive drum 3.

  In the present embodiment, the static eliminator 41 is configured using a static elimination electrode. However, a static elimination lamp may be used in place of the static elimination electrode, or other static elimination may be used.

  The cleaner unit 5 removes and collects toner remaining on the surface of the photosensitive drum 3 after development and image transfer. The cleaner unit 5 is located at a position substantially opposite to the developing device 2 with the photosensitive drum 3 interposed therebetween. The drum 3 is disposed substantially horizontally (left side in the drawing) on the side.

As described above, the electrostatic image visualized on the photosensitive drum 3 is applied from the transfer mechanism 10 onto the paper P on which the electric field having the opposite polarity to the electric charge of the electrostatic image is conveyed. Transferred onto P.
For example, when the electrostatic image has a charge of (−) polarity, the applied polarity of the transfer mechanism 10 is (+) polarity.

  As shown in FIG. 2, the transfer mechanism 10 is bridged by a driving roller 101, a driven roller 102, and other rollers, and has a predetermined resistance value (in this embodiment, a range of 1 × 10 9 to 1 × 10 13 Ω · cm). A transfer belt unit having a transfer belt 103 is disposed, and is arranged below the photosensitive drum 3 so that the surface of the transfer belt 103 is in contact with a part of the outer peripheral surface of the photosensitive drum 3. . The transfer belt 103 conveys the paper P while pressing it against the photosensitive drum 3.

  An elastic conductive roller 105 capable of applying a transfer electric field with a conductivity different from that of the driving roller 101 and the driven roller 102 is disposed at the contact portion 104 between the photosensitive drum 3 and the transfer belt 103.

  The elastic conductive roller 105 is made of a soft material such as elastic rubber or foamable resin. Since the elastic conductive roller 105 has elasticity, the photosensitive drum 3 and the transfer belt 103 are not in line contact but in surface contact having a predetermined width (referred to as a transfer nip), so that the sheet P to be conveyed is conveyed. The transfer efficiency can be improved.

  Further, on the downstream side of the transfer area of the transfer belt 103 in the sheet conveyance direction, a discharge roller 106 for discharging the electric field applied to the sheet P to be transferred in the transfer area and smoothly transferring to the next process is transferred. It is arranged on the back side of the belt 103.

  In addition, the transfer mechanism 10 is provided with a cleaning unit 107 that removes dirt from the residual toner on the transfer belt 103 and a plurality of charge removal mechanisms 108 that perform charge removal on the transfer belt 103. As a technique for performing static elimination used in the static elimination mechanism 108, there is a technique of grounding through an apparatus, or a technique of positively applying a polarity opposite to the polarity of the transfer electric field.

  The electrostatic image (unfixed toner) transferred onto the paper P by the transfer mechanism 10 is conveyed to the fixing unit 6 and is pressurized and heated to melt the unfixed toner and be fixed on the paper P. .

  As shown in FIG. 2, the fixing unit 6 includes a heating roller 6a and a pressure roller 6b. The heating roller 6a is rotated while the paper P is sandwiched between the heating roller 6a and the pressure roller 6b, and heated. By passing between the roller 6a and the pressure roller 6b, the toner image transferred onto the paper P is melted and fixed.

  A conveyance roller 16 that conveys the paper P is provided downstream of the fixing unit 6 in the paper conveyance direction.

  The heating roller 6a is provided with a sheet peeling claw 611, a roller surface temperature detecting member (thermistor) 612, and a roller surface cleaning member 613 on the outer peripheral portion, and the heating roller surface is set to a predetermined temperature (fixing set temperature) on the inner peripheral portion. : Approximately 160 to 200 ° C.).

  The pressure roller 6b is provided with a pressure member 621 that allows the pressure roller 6b to come into pressure contact with the heating roller 6a at a predetermined pressure amount at both ends of the roller. Further, the pressure roller 6b is heated on the outer periphery of the pressure roller 6b. Similarly to the outer periphery of the roller 6a, a sheet peeling claw 622 and a roller surface cleaning member 623 are arranged.

  As shown in FIG. 2, the fixing unit 6 is configured to remove unfixed toner on the conveyed paper P at a pressure contact portion (called a so-called fixing nip portion) 600 between the heating roller 6a and the pressure roller 6b. The unfixed toner is fixed on the paper P by the application of the heat applied by the heat roller 6a to melt and the throwing action on the paper P by the pressure contact force between the heating roller 6a and the pressure roller 6b.

  The paper feed tray 8 is used for accumulating a plurality of sheets (paper sheets) on which image information is output (printed). The exposure unit 1, the developing device 2, the photosensitive drum 3, the charger 4, and the charge eliminating device. The image forming unit 14 is configured below the image forming unit 14 including the apparatus 41, the cleaner unit 5, the fixing unit 6, and the like. A paper pickup roller 8a is disposed on the upper side of the paper discharge side of the paper feed tray 8 (see FIG. 3).

  The sheet pickup roller 8a picks up the sheets P stacked and stored in the sheet feed tray 8 one by one from the uppermost layer, and moves toward the downstream side (for convenience, the flow-out side (cassette side) of the sheet P is upstream and discharged). The paper side is the downstream side.) The paper is conveyed to the registration roller (also referred to as “idle roller”) 15 side on the paper conveyance path 7.

  In the image forming apparatus 1A according to the present embodiment, in order to perform high-speed printing processing, a plurality of paper supply units capable of storing 500 to 1500 sheets of standard size sheets P in each tray are provided below the image forming unit 14. A paper tray 8 is disposed, and on the other hand, a large-capacity paper feed cassette 81 capable of storing a large amount of a plurality of paper types is disposed on the side of the apparatus, and an irregular type is mainly disposed above the large-capacity paper feed cassette 81. A manual feed tray 82 corresponding to size printing or the like is provided.

  The paper discharge tray 9 is disposed on the side of the apparatus opposite to the manual feed tray 82. Further, instead of the paper discharge tray 9, a post-processing device (device for performing stapling, punching, etc.) of paper discharge, a multi-stage paper discharge tray, and the like can be arranged as options.

  The paper transport path 7 is configured between the above-described photosensitive drum 3 and the paper feed tray 8, and transports the paper P1 supplied from the paper feed tray 8 to the transfer mechanism 10 one by one. A sheet on which the toner image is transferred from the photosensitive drum 3 is conveyed to the fixing unit 6, and after the unfixed toner image is fixed on the sheet in the fixing unit 6, a sheet conveyance path formed according to the designated processing mode. In addition, the sheet is conveyed by a branching claw.

Here, the sheet conveyance path 7 will be described in detail with reference to the drawings.
FIG. 3 is an explanatory diagram showing the configuration of the sheet conveyance path of the image forming apparatus according to the present embodiment, and FIG. 4 is a portion showing the configuration of the branched sheet conveyance path constituting the sheet conveyance path and the branching claw for communicating them. FIG.

  As shown in FIGS. 3 and 4, the sheet conveyance path 7 mainly includes the first sheet conveyance path 7 a 1 from the sheet feed tray 8 to the registration rollers 15, and the fixing unit 6 from the registration rollers 15 via the transfer mechanism 10. The second paper transport path 7a2 that passes through and reaches the downstream transport roller 16, the third paper transport path 7a3 that reaches the paper discharge roller 17 for discharging the paper from the transport roller 16 to the paper discharge tray 9, and the transport roller 16 The fourth paper transport path 7a4 for reversing the paper P from the first paper, the fifth paper transport path 7a5 communicating with the fourth paper transport path 7a4 and the reverse transport roller 18 for transporting the paper P to the registration roller 15 again, the paper discharge roller A sixth paper transport path 7a6 that reverses from 17 and transports the paper P, a seventh paper transport path 7a7 that communicates with the sixth paper transport path and avoids the fifth paper transport path 7a5, and a seventh paper transport path 7a7 Communicate with switch It is composed of the eighth sheet conveying path 7a8 leading to Kkurora 19.

  A plurality of sheets P are arranged in the sheet transport path 7 according to the processing mode. In the present embodiment, as shown in FIG. 3, eight sheets P of (1) to (8) (indicated by the circled numbers in the figure) are arranged in the sheet transport path 7. The number of sheets P allowed in the sheet conveyance path can be changed in any way depending on the configuration of the sheet conveyance path.

  Further, in the paper transport path 7, a plurality of branching claws for selecting the paper transport path according to the selected processing mode and changing the transport path of the paper P are provided at the branch points of the paper transport path. .

  As shown in FIG. 4, in the vicinity of the downstream side of the transport roller 16, a branch claw 20a that communicates with the third paper transport path 7a3 or the fourth paper transport path 7a4 is provided so as to be able to swing and displace. The branch claw 20a is operated by a solenoid (not shown).

  On the downstream side of the fourth paper transport path 7a4, a branch claw 20b that connects the fourth paper transport path 7a4 and the fifth paper transport path 7a5 or the fifth paper transport path 7a5 and the sixth paper transport path 7a6 swings. Displaceable. The branch claw 20b is operated by a spring member (not shown) and the elastic force of the paper P.

  On the downstream side of the sixth paper conveyance path 7a6, a branch claw 20c communicating with the fifth paper conveyance path 7a5 or the seventh paper conveyance path 7a7 is provided so as to be able to swing and displace. The branch claw 20c is operated by a solenoid (not shown).

  On the downstream side of the seventh paper transport path 7a7, a branch claw 20d that connects the seventh paper transport path 7a7 and the eighth paper transport path 7a8 or the fifth paper transport path 7a5 and the eighth paper transport path 7a8 is rocked. It is provided so that it can be displaced dynamically. The branch claw 20d is operated by a solenoid (not shown).

  On the upstream side of the fifth paper transport path 7a5, a branch claw 20e is provided for smoothly connecting the fourth paper transport path 7a4 and the eighth paper transport path 7a8 and the fifth paper transport path 7a5.

  With the paper conveyance path 7 configured as described above, the branch claws 20a to 20d are operated according to the requested processing mode, and the conveyance path of the paper P corresponding to the processing mode can be selected.

  Next, a sheet conveyance process corresponding to the processing mode of the image forming apparatus 1A will be described with reference to the drawings.

As shown in FIG. 3, the paper P that matches the print request is selected from the plurality of paper feed trays 8 and is transported to the registration rollers 15 by the transport rollers in the paper transport path 7.
The paper P that has reached the registration roller 15 and has stopped once is conveyed to the transfer mechanism 10 by the rotation of the registration roller again at the timing when the leading edge of the paper P and the image information on the photosensitive drum 3 coincide with each other. After an unfixed toner image (image information) is transferred from the photosensitive drum 3 to the top, the toner image is fixed on the paper P by the fixing unit 6 and is discharged to the paper discharge tray 9.

  In the conveyance path in the sheet conveyance path 7, the sheet discharge tray from the fixing unit 6 onward is processed by the processing mode (copier mode, printer mode, FAX mode) of the image forming apparatus 1 </ b> A and the printing processing method (single-sided printing, duplex printing). The transport method up to 9 is different.

  Normally, in the copier mode, since the user performs an operation in the vicinity of the image forming apparatus 1A, a method called “face-up discharge” in which the printing surface is discharged with its upper side is often used.

  On the other hand, in each mode such as printer, FAX, etc., the “face-down discharge” method for aligning the page order of the discharged paper P because the user is not in the vicinity of the image forming apparatus 1A is often used.

  Accordingly, in the image forming apparatus 1A, the sheet P meeting the above purpose is discharged through the plurality of transport paths and the plurality of branch claws until the sheet P that has passed through the fixing unit 6 is discharged to the sheet discharge tray 9. Is supposed to do.

(Face-up discharge with single-sided printing)
In the image forming apparatus 1A, in the case of the single-sided printing of the paper P and the face-up discharge method, the branch claw 20a is not shown in FIG. The third paper transport path 7a3 is opened by a solenoid or the like, and the fourth paper transport path 7a4 is shielded.

  The leading end of the transported paper P is navigated to the branching claw 20a, passes through the third paper transport path 7a3, and is discharged to the paper discharge tray 9 through the paper discharge roller 17.

(Face-down discharge with single-sided printing)
In the image forming apparatus 1A, in the case of the single-sided printing of the paper P and the face-down discharge method, the branching claw 20a has a claw position switching unit (not shown) immediately before the paper P that has passed the fixing unit 6 passes the transport roller 16. (Solenoid or the like) opens the fourth paper transport path 7a4 and shields the third paper transport path 7a3.

  Further, the branching claw 20c opens the fifth paper conveyance path 7a5 and shields the seventh paper conveyance path 7a7 by a claw position switching means (not shown).

  The transported paper P is navigated to the branch claw 20a by the leading end of the paper P and passes through the fourth paper transport path 7a4, and the branch claw 20b is moved by the waist (material strength) of the front end of the paper P and the transport force. Then, after the fifth paper transport path 7a5 is opened, it is navigated to the branch claw 20c and guided to the fifth paper transport path 7a5.

When the trailing edge of the paper P reaches the position of the branching claw 20e, the conveyance of the paper P is temporarily stopped.
The branch claw 20c opens the sixth paper conveyance path 7a6 and shields the seventh paper conveyance path 7a7 by a claw position switching means (not shown).

  At this time, the branching claw 20b is naturally displaced by an elastic member (spring or the like) disposed on a branching claw holding shaft (not shown) so as to shield the fourth paper conveyance path 7a4.

  Thereafter, the reverse conveyance roller 18 rotates in the reverse direction to re-convey the paper P, and the conveyed paper P passes through the sixth paper conveyance path 7a6 from the rear end side where it stays at the position of the branching claw 20e. The paper is discharged to the paper discharge tray 9 through the paper discharge roller 17.

(Discharge using the double-sided printing method)
When double-sided printing is performed in the image forming apparatus 1A, the first claw printing (front surface printing) of the paper P is finished, and immediately before the paper P that has passed the fixing unit 6 passes the transport roller 16, the branch claw 20a is The claw position switching means (not shown) (solenoid or the like) opens the fourth paper conveyance path 7a4 and shields the third paper conveyance path 7a3.

  Further, the branching claw 20c opens the seventh paper conveyance path 7a7 and shields the fifth paper conveyance path 7a5 by a claw position switching means (not shown). Further, the branch claw 20d opens the sixth paper transport path 7a6 by a claw position switching means (not shown).

  The sheet P to be conveyed is navigated by the branch claw 20a at the leading end thereof, passes through the fourth sheet conveyance path 7a4, and the branch claw 20b is moved by the waist (material strength) and the conveyance force at the front end of the sheet P. After the movement, it is navigated to the branching claw 20c and guided to the seventh paper transport path 7a7 and the sixth paper transport path 7a6.

  When the trailing edge of the sheet P reaches the sixth sheet conveyance path 7a6, the conveyance of the sheet P is temporarily stopped (completion of the first surface switchback). Thereafter, when the branching claw 20d shields the seventh paper conveyance path 7a7 by a claw position switching means (not shown) and the conveyance path to the branching claw 20e is opened, the switchback roller 19 rotates reversely, so Transport is performed.

  The transported paper P passes through the fifth paper transport path 7a5 from the rear end side where it stays at the position of the sixth paper transport path 7a6 via the branching claw 20e, and in the printing process (transfer process in the transfer mechanism). It is conveyed to the registration roller 15 arranged immediately before.

  Thereafter, the second side printing (back side printing) of the paper P is completed, and the paper P that has passed through the fixing unit 6 is subjected to the same processing as described above (single-sided printing and face-up discharge), and the paper discharge tray 9 To be discharged.

Next, the configuration of the paper transport unit 59 according to the present embodiment will be described with reference to the drawings.
FIG. 5 is a schematic diagram illustrating a configuration of a sheet conveying unit included in the image forming apparatus according to the present embodiment, FIG. 6 is an explanatory diagram illustrating a state where sheets are double-fed in the sheet conveying unit, and FIG. FIG. 8 is a plan view showing a configuration of a paper suction unit that constitutes the paper transport unit.

  The paper transport unit 59 is configured to transport the paper P from the paper feed tray 8 to the image forming unit 14 via the paper transport path 7 in accordance with the processing mode of the image forming apparatus 1A.

  As shown in FIG. 5, the paper transport unit 59 detects whether or not the paper P is double-fed from the paper feed tray 8 on the paper transport path 591 from the paper feed tray 8 to the paper transport path 7. A feed detection sensor (double feed detection means) 592 and a paper suction unit (recording medium suction means) 593 for sucking the double fed paper P2 are provided.

  The double feed detection sensor 592 is provided on the upstream side in the paper transport direction with respect to the paper suction unit 593 on the paper transport path 591. The double feed detection sensor 592 and the sheet suction unit 593 are arranged at a predetermined interval.

  Specifically, the positional relationship between the double feed detection sensor 592 and the paper suction unit 593 is such that, for example, when the A4 size paper P is used, the vicinity of the leading edge of the paper can be detected by the double feed detection sensor 592. When conveyed, the vicinity of the rear end of the sheet is disposed so as to face the sheet suction unit 593.

  With this configuration, as shown in FIG. 6, when it is detected that the paper P fed by the double feed detection sensor 592 has been double fed, one of the rear end portions of the double fed paper P2 is detected. The part can be sucked by the sheet suction part 593. In the figure, reference numeral P1 indicates a sheet fed by the pickup roller 8a, and P2 indicates a sheet that is double-fed.

  In the present embodiment, as the double feed detection sensor 592, an ultrasonic double feed detection sensor that detects whether one or a plurality of sheets are conveyed by ultrasonic waves is used.

  Specifically, as shown in FIG. 7, the double feed detection sensor 592 includes a transmission unit 592a and a reception unit 592b, and a transmission circuit 592a1 for transmitting ultrasonic waves to the reception unit 592a side and the ultrasonic waves thereof. Is provided with a resonance circuit 592b1 for resonating the received ultrasonic waves, and an amplification circuit 592b2 for amplifying the ultrasonic waves. The amplification circuit 592b2 is provided on the receiving unit 592b side. The analog signal is converted into a digital signal by the A / D circuit 592b3, and arithmetic processing is performed by the CPU 54 based on the digital signal to determine whether or not the fed paper P1 is a single sheet (whether it has been double-fed). Has been.

  Specifically, by using an OMRON ultrasonic double feed detection sensor (MA200DA-1), it becomes possible to accurately and easily recognize the double feed amount of the double fed paper P2, and the double feed is performed. It is possible to easily estimate the time for sucking the sheet P2. As a result, it is possible to output the paper without preventing the skew of the paper and reducing the image forming speed.

  As shown in FIGS. 6 and 7, the paper suction unit 593 mainly winds the plurality of transport belts 593a that can be driven along the paper transport direction and the plurality of transport belts 593a, and also transports the transport belt 593a. And a suction device 593c that is disposed on the back side of the transport belt 593a (on the side opposite to the side on which the paper is disposed) for suction.

  The conveying belt 593a has a plurality of through holes 593a1 formed on the conveying surface. By sucking air through the through holes 593a1 from the back side of the conveying belt 593a by the suction device 593c, the sheet on the sheet conveying path 591 side is removed. It is designed to suck.

Next, a control system of the image forming apparatus 1A according to the present embodiment will be described with reference to the drawings.
FIG. 9 is a block diagram showing the configuration of the electric control unit of the image forming apparatus according to the present embodiment.
As shown in FIG. 9, the image forming apparatus 1 </ b> A according to the present embodiment stores image reading processing, image processing, image forming processing, paper P conveyance processing, and the like in a ROM (Read Only Memory) 55 in advance. A central processing unit (CPU) 54 executes processing using temporary storage means such as a RAM (Random access Memory) 56 according to a program.
Note that storage means such as an HDD (hard disk drive) can be used in place of the ROM 55 and the RAM 56.

  In the image forming apparatus 1A, document image information (document image data) read by the scanner unit 22 or document image information transmitted from each terminal device connected to a communication network (not shown) is transmitted via the communication processing unit 58. Are input to the image processing unit 57.

  The image processing unit 57 processes the document image information stored in the storage unit such as the RAM 56 into a print image suitable for printing (image formation on paper) by the above program.

The image information for printing is input to the image forming unit 14.
Image forming unit 14, paper conveyance unit (various detection / control of paper in the paper conveyance path 7) 59, fixing unit 6, paper discharge processing unit (various detection / control of paper in the paper discharge roller 17) .) 60 is interlocked with each drive control unit 62.

The sheet conveyed by the sheet conveying unit 59 is subjected to a printing process (image information printing process in the image forming unit 14), and then a fixing process (fixing unit 6) for the printed sheet. The paper is discharged to the paper discharge tray 9.
Note that detection signals from a pre-registration detection switch 596, a fixing detection switch (not shown), a paper discharge detection switch, and the like are input to the paper transport unit 59.

  The pre-registration detection switch 596 is a switch that detects whether or not a sheet has reached the registration roller 15. The fixing detection switch is a switch that detects whether or not a sheet has reached the fixing unit 6. The paper discharge detection switch is a switch that detects whether or not the paper is discharged.

  Further, the conveyance state of the paper P conveyed by the paper conveyance unit 59 is detected by the double feed detection sensor 592, and when the paper P is double fed, the conveyance of the paper P is temporarily stopped by the paper suction unit 593. Has been.

  In the present embodiment, based on a signal output from the double feed detection sensor 592 and a program stored in the ROM 55, a paper double feed determination function (function for determining whether or not a paper has been double-feeded) provided in the CPU 54. When it is determined that the paper P has been double-fed, the suction device 593c is operated to suck the double-fed paper P2, and the driving roller 593b is stopped to temporarily carry the paper P2 by the conveyance belt 593a. To stop.

The image forming apparatus 1 </ b> A is provided with an operating condition setting unit 77.
The operation condition setting unit 77 is configured to perform image formation or conveyance conditions of the image forming apparatus 1A according to an image formation request set by the user using the operation switches 76 or an image formation condition such as the type of recording medium (paper) The operation conditions are set.

  The image forming apparatus 1 </ b> A is a driving actuator such as a reading unit (scanner unit 22), a sheet conveying unit 59, an image forming unit 14, a fixing unit 6, and a paper discharge processing unit 60 according to the set operating conditions. Operations of a certain document reading drive unit 64, paper transport drive unit 66, print processing drive unit 68, fixing drive unit 70, and paper discharge drive unit 72, that is, operations synchronized in accordance with commands of the CPU 54 based on a program stored in the ROM 55. The control is performed by the drive control unit 62.

The document reading drive unit 64 is a drive actuator for the scanner unit 22.
The paper transport drive unit 66 is a motor for driving the paper transport unit 59, specifically, the paper pickup roller 8 a and the registration roller 15 on the paper transport path 7 described above.
The print processing drive unit 68 is a drive motor for the photosensitive drum 3.
The fixing driving unit 70 is a driving motor for the heating roller 6 a and the pressure roller 6 b of the fixing unit 6.

The paper discharge drive unit 72 is a drive motor such as a paper discharge roller 17.
The drive motors of these drive units can be appropriately configured through a power transmission mechanism using the same or different motors as drive sources.

  Further, the image forming apparatus 1A includes, as an optional configuration 74, a post-processing device (stapling, punching, a multi-stage paper discharge tray, a shifter, etc.), an automatic document reading device (automatic document processing device 1A2, etc.), a large capacity paper feed cassette 81, etc. can be arranged, and the optional configuration 74 has the control unit 74a in each optional configuration 74 separately from the control unit of the image forming apparatus 1A, and adjusts the timing with the communication processing unit 58. Is configured to synchronize.

  The recording medium detection unit 78 detects that the leading edge of the paper reaches the fixing unit 6 or the carry-out unit.

  Specifically, the recording medium detection unit 78 includes a conveyance time measuring unit 79a that measures the conveyance time of the sheet after the sheet is sent out from the registration roller 15 that introduces the sheet at the entrance of the sheet conveyance path 7, and the registration roller. A conveyance timing detection unit 79b for detecting the conveyance timing of the paper in the paper conveyance path 7 based on the distance from the fixing unit 6 to be controlled and the paper discharge roller 17 and the conveyance speed of the paper.

  In the present embodiment, the recording medium detection unit 78 is based on the conveyance timing of the recording medium detected by the conveyance timing detection unit 79b when the sheet reaches (enters) the fixing unit 6 and the discharge roller 17 respectively. I try to detect it.

Next, sheet feeding and conveyance in the image forming apparatus 1A according to the present embodiment will be described in detail based on a flowchart.
FIG. 10 is a flowchart showing a sheet feeding and conveying process of the image forming apparatus according to the present embodiment.

Sheet feeding and conveyance (sheet feeding operation) in the image forming apparatus 1A are performed as follows based on the flowchart shown in FIG.
First, when image output is instructed by the operation switches 76 of the image forming apparatus 1A or an external device, sheet conveyance (sheet feeding operation) is started (step S1).

  In the conveyance of the sheet, the sheet P1 fed from the sheet feeding tray 8 by the sheet pickup roller 8a is taken out one by one. The paper taken out from the paper feed tray 8 is conveyed along a paper conveyance path 591.

  When the conveyed paper passes through the double feed detection sensor 592, based on the signal output from the double feed detection sensor 592, whether or not the paper P is double fed by the paper double feed determination function 594 provided in the CPU 54 is determined. It is detected (step S2). If it is determined by the paper double feed determination function 594 that the paper is not double-fed, the next paper P is fed (step S3).

  On the other hand, when it is determined in step S2 that the conveyed paper P has been double-fed, when the conveyed paper reaches the conveyance roller 595 on the downstream side in the paper conveyance direction of the double-feed detection sensor 592 (step S4). Then, the sheet P2 double-fed by the suction device 593c is sucked, and the conveyance belt 593a is stopped to temporarily stop the conveyance of the sheet (sheet double-feed prevention process) (step S5). At this time, the rear end portion of the double fed paper P2 is sucked.

  When the predetermined paper P1 is transferred to the image transfer process and the double feed is released (step S6), the paper P2 whose conveyance is temporarily stopped is sucked by the suction device 593c. Then, it is conveyed again by the conveying belt 593a (step S7).

  When the leading edge of the conveyed paper P2 reaches the conveyance roller 595 (step S8), the conveyance of the paper P2 by the conveyance roller 595 and the paper suction unit 593 is stopped. That is, the sheet P2 is in a standby state (step S9).

  When conveyance of the next sheet is instructed (step S10) and the requested sheet size is the same size as the sheet P2 waiting (held) in step S9 (step S11), the conveyance roller 595 is driven. Then, the sheet P2 is conveyed and the process proceeds to the next step (step of transferring the image onto the sheet) (step S12).

  When there is an instruction to feed the next sheet (step S13), the process proceeds to circled code 2, and the process returns to step S1 to start the sheet feeding operation again.

  On the other hand, if the requested paper size is different from the standby (held) paper size in step S11, the paper is transported by driving the transport rollers 595 (step S14), and the image forming unit The image passes through without being transferred to the outside of the apparatus and is discharged (discharged) (step S15).

  Then, the paper feed tray of the designated paper size is selected (step S16), the process proceeds to circled code 2, and the process returns to step S1 to start the next paper feed operation again.

  With the above configuration, according to the present embodiment, when the paper P1 is fed from the paper feed tray 8, even when the paper P2 is double fed, the apparatus is not stopped to prevent jamming. Thus, the paper P2 that has been double fed reliably can be separated and waited, and the paper P2 can be supplied in accordance with the next paper feed timing. As a result, it is possible to eliminate jamming due to the paper P2 supplied by double feeding staying in the apparatus, and to realize stable paper supply.

In addition, according to the present embodiment, since the rear end portion of the multi-feed paper P2 is sucked by the paper suction portion 593, the multi-feed is performed along with the conveyance of the normally supplied paper P1. It is possible to reliably separate the supplied paper P1 and the double-fed paper P2 without curling the rear end portion of the paper P2.

  Further, since the multi-feed paper P2 is transported along with the paper P1 to be fed, it is transported in a state where it is overlapped with the paper P1 to be fed or in a state where the supplied paper P1 precedes. When the fed paper P1 is transported in a preceding state by sucking the trailing edge of the multi-feed paper P2 by the paper suction unit 593 as in this embodiment, Since only the rear end portion of the double-fed paper P2 can be sucked, only the double-fed paper P2 can be reliably held and separated from the supplied paper P1.

  In the present embodiment, the conveyance belt 593a of the paper suction unit 593 is stopped when the double-feed paper P2 is detected. However, the present invention does not limit the configuration of the paper suction unit 593. For example, after the double-feed paper P2 is sucked, the double-feed paper P2 may be moved by a predetermined amount in the direction opposite to the transport direction of the supplied paper P1. With this configuration, it is possible to reliably separate the paper P2 that has been multi-fed and the paper P1 that is being supplied.

  In the present embodiment, the sheet conveyance speed is not limited. However, as a modification, for example, when the sheet P2 double-detected by the double-feed detection sensor 592 is detected, the sheet conveyance speed is decreased. You may do it. With this configuration, the double-feed paper P2 can be reliably sucked by the paper suction unit 593, so that the double-feed paper P2 and the supplied paper P1 can be reliably separated. .

  In addition, the present invention is not limited to the configuration of the transport roller that transports the paper. As a modification of the present embodiment, for example, the paper P1 supplied after the multi-feed paper P2 is separated is used. The registration roller 15 may be used to adjust the position of the leading end on the upstream side in the transport direction. With this configuration, it is possible to stably adjust the position of the supplied paper P1 without being affected by the multi-feed paper P2.

  Furthermore, in this embodiment, the double feed detection sensor 592 and the paper suction unit 593 perform the paper double feed prevention process immediately after the paper is fed from the paper feed tray 8. It is not limited to the installation position of the feed detection sensor 592 and the paper suction unit 593, and a double feed detection sensor and a paper suction unit may be provided as appropriate according to the configuration and length of the paper transport path. Various configurations can be developed.

  In the present embodiment, the image forming apparatus 1A has been described as an example. However, the present invention can be expanded to various apparatuses without being limited to the image forming apparatus as long as it has a configuration for conveying paper. It is.

1 is an explanatory diagram showing an overall configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a partial detail view showing a configuration of an apparatus main body of the image forming apparatus. FIG. 4 is an explanatory diagram illustrating a configuration of a sheet conveyance path of the image forming apparatus. FIG. 4 is a partial detail view illustrating a configuration of a branched paper conveyance path that constitutes the paper conveyance path and a branching claw that connects the branched paper conveyance paths. FIG. 2 is a schematic diagram illustrating a configuration of a sheet conveying unit that constitutes the image forming apparatus. FIG. 6 is an explanatory diagram illustrating a state in which sheets are multi-fed in the sheet conveying unit. FIG. 3 is a block diagram illustrating a configuration of a double feed detection sensor that constitutes the paper transport unit. FIG. 4 is a plan view showing a configuration of a paper suction unit that constitutes the paper transport unit. 2 is a block diagram illustrating a configuration of an electric control unit of the image forming apparatus. FIG. 4 is a flowchart illustrating a sheet feeding and conveying process of the image forming apparatus.

Explanation of symbols

1A image forming apparatus 7 paper transport path 8 paper feed tray (recording medium stacking unit)
8a Paper pickup roller 14 Image forming unit 15 Registration roller 54 CPU
59 Paper transport section (recording medium transport means)
591 Paper transport path 592 Double feed detection sensor (double feed detection means)
592a Reception unit 592a1 Transmission circuit 592a2 Amplification circuit 592b Reception unit 592b1 Resonance circuit 592b2 Amplification circuit 592b3 A / D circuit 593 Paper suction unit (recording medium suction unit)
593a Conveying belt 593a1 Through hole 593b Drive roller 593c Suction device 594 Paper double feed determination function P Paper P1 Paper fed P2 Paper fed double

Claims (7)

A recording medium stacking unit capable of stacking a plurality of recording media, and a recording medium transporting unit for transporting the recording medium supplied one by one from the recording medium stacking unit to the image forming unit,
Double feed detection means for detecting whether or not the next transported recording medium P2 is double fed to the recording medium P1 which has been normally fed without being double fed from the recording medium stacking unit, and the double fed recording In an image forming apparatus comprising a recording medium suction means for sucking the medium P2, and capable of automatically supplying a recording medium from the recording medium stacking unit,
The recording medium suction means sucks the double-fed recording medium P2, stops transport of the recording medium P2 in the sucked state, and enables the recording medium P2 to move. When it is conveyed to a position that can be detected by the double feed detection means, the rear end of the recording medium is disposed at a position where it can be sucked,
The recording medium conveying unit is provided with a conveying roller for conveying the recording medium toward the image forming unit on the downstream side of the double feed detecting unit,
When the double feed of the recording medium P2 is detected by the double feed detection means, the recording medium suction means sucks the trailing end of the double-fed recording medium P2 and stops its conveyance, and the recording medium conveyance The means conveys the normally supplied recording medium P1 toward the image forming unit by the conveying roller, thereby separating the normally supplied recording medium P1 from the double-fed recording medium P2. An image forming apparatus. The recording medium suction unit is disposed on a side opposite to the recording medium conveying side of the conveying belt, a conveying belt that can be driven along the recording medium conveying direction, a driving roller that drives the conveying belt, and conveys the recording medium. The image forming apparatus according to claim 1, further comprising a suction device that suctions the belt . The recording medium suction means, after sucking the recording medium P2 that are multi-fed, claims, characterized in that to displace in a direction opposite to the conveying direction of the recording medium P1 to be supplied to the double feed printing media P2 Item 3. The image forming apparatus according to Item 1 or 2 . 3. The image forming apparatus according to claim 1, wherein the recording medium conveying unit reduces the speed at which the recording medium is conveyed when the double-detected recording medium is detected by the multi-feed detecting unit. 3. The recording medium transporting unit according to claim 2, wherein the recording medium transporting unit adjusts the position of the leading end on the upstream side in the transporting direction after the double-fed recording medium P <b> 2 is separated from the previously supplied recording medium P <b> 1. Image forming apparatus. The recording medium conveying means separates the normally supplied recording medium P1 from the double-fed recording medium P2, and then the recording medium suction means conveys the double-fed recording medium P2 to the conveying roller. The image forming apparatus according to claim 1 , wherein the conveyance is temporarily stopped after the conveyance . The image forming apparatus according to claim 1, wherein the double feed detecting unit detects a double feed amount of a recording medium double-fed by an ultrasonic wave.

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