JP2010091677A - Image forming device - Google Patents

Abstract

A high-productivity image forming apparatus that suppresses poor sheet separation after passing through a fixing unit and has stable sheet transportability.
An image forming apparatus includes a fixing device that pressurizes and heats an image on a sheet, and includes a conveyance unit that continuously conveys a trailing edge of a preceding sheet and a leading edge of a following sheet. The overlapping portion between the preceding sheet and the succeeding sheet is overlapped so that the upper and lower relationships are reversed between the leading edge of the first surface and the leading edge of the second surface. Thereby, the separation failure of the sheet after passing through the fixing unit is suppressed, and stable sheet transportability is obtained.
[Selection] Figure 1

Description

  The present invention relates to an image forming apparatus such as a copying machine, a facsimile, or a printer that forms an image on a sheet using an electrophotographic system.

  In general, an electrophotographic image forming apparatus uses a method in which a toner image formed by an image forming unit is electrostatically transferred onto a sheet, and the toner image is melted and fixed by a fixing device. A sheet as a recording material continuously conveyed toward the image forming unit is conveyed while maintaining a predetermined interval (between sheets).

  In recent years, there has been an increasing demand for high productivity of image forming apparatuses. In order to meet such a demand, the sheet conveyance speed is increased and the number of sheets passed per unit time is increased.

  Therefore, in order to increase the number of sheets passed per unit time while reducing the sheet interval between successive sheets and suppressing the sheet conveyance speed as much as possible, the non-image part (margin part) of the preceding sheet and the succeeding sheet is overlapped. A conveying method for conveying has been proposed.

  That is, Japanese Patent Application Laid-Open No. H10-228688 discloses a technique in which the time for passing through the image forming unit is minimized by stacking sheets, and the image forming operation is shortened to achieve high productivity.

  Also, Patent Document 2 discloses a method of conveying a sheet while reliably switching the overlapping direction of the leading and trailing edges of the sheet according to the discharge unit during double-sided recording and forming a stable overlapping amount and overlapping state. Yes.

  Japanese Patent Application Laid-Open No. 2004-228620 has a conveyance process in which the trailing edge of the preceding sheet and the leading edge of the succeeding sheet are overlapped, and the positional relationship of the overlapping portion of the sheet between the electrophotographic photosensitive drum and the fixing unit. Inversion means for inverting is provided. And what implement | achieves the stable conveyance in a fixing part is disclosed.

JP 2001-324844 JP 2002-160849 A JP 2003-98775 A

  However, even if a conveyance method that conveys sheets in a stacked manner is used, it is necessary to increase the sheet conveyance speed in order to meet the demand for high productivity, and the toner image is heated by the fixing device. Time is shortened.

  For this reason, there is a problem that poor conveyance or separation due to catching of a sheet by a conveyance auxiliary means (separation claw or separation guide) after fixing due to poor toner melting state or unstable discharge behavior is likely to occur. is there.

  The technical problem of the present invention has been made in view of the circumstances as described above, and the purpose thereof is to suppress poor sheet separation when passing through the fixing unit, and to provide a highly productive image having stable sheet transportability. It is to provide a forming apparatus.

  In order to achieve the above object, a typical configuration according to the present invention includes a conveyance unit that continuously conveys a trailing edge of a preceding sheet and a leading edge of a following sheet, and a toner image on the sheet. In an image forming apparatus having a pressure heating fixing device, the overlapping portion of the preceding sheet and the succeeding sheet is overlapped so that the top and bottom relations are reversed between the leading edge of the first surface and the leading edge of the second surface. It is characterized by.

  According to the present invention, it is possible to obtain a highly productive image forming apparatus capable of suppressing sheet separation failure after passing through the fixing unit and stably transporting the sheet.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic longitudinal sectional view of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a block diagram of the image forming apparatus of FIG.

  In the image forming apparatus shown in FIG. 1, the surface of the photosensitive drum 1 as an image forming unit is uniformly charged by the charging device 2, and then the laser beam is scanned by the exposure unit 3. As a result, an electrostatic latent image is formed on the surface of the photosensitive drum 1, and the electrostatic latent image is visualized by the developing means 4 to form a toner image.

  The toner image formed on the photosensitive drum 1 is transferred to the sheet fed by the transfer unit 5, and the toner remaining on the photosensitive drum 1 is removed by the cleaning device 6.

  A plurality of feeding devices 7 capable of storing a plurality of types of sheets of different sizes and different directions are detachably attached to the lower part of the image forming apparatus. One sheet is fed by a feeding roller 8 and a separation claw (not shown). Separately fed.

  The fed sheet is conveyed to the registration roller pair 10 by the conveyance roller 9 to correct skewing and is conveyed in synchronization with the toner image on the photosensitive drum 1. Then, after the toner image is transferred from the photosensitive drum 1 by the transfer unit 5, the sheet is conveyed to the fixing device 12 by the conveying belt 11, and the toner image is permanently fixed on the sheet by being heated under pressure. .

  The image forming apparatus is provided with a face-down discharge unit that discharges with the recording surface facing up, and a side-up part of the image forming apparatus with a face-up discharge unit that discharges with the recording surface facing down, and a photosensitive drum A refeed means is provided between 1 and the feeding device 7.

  The sheet on which the image is fixed by the fixing device 12 is selectively guided by switching the switching member 13. The sheet after passing through the fixing device 12 is conveyed at a higher speed than the conveying speed at the time of fixing at a desired timing described later.

  When the sheet is discharged from the face-down discharge unit, the sheet is guided to the upward reversing path 15 by the switching member 13 and discharged to the face-down discharge tray 18 by the first reversing roller 16 and the second reversing roller 17 that also serves as the discharging roller. Is done.

  When the sheet is discharged from the face-up discharge unit, the sheet is guided by the switching member 13 to a discharge roller 19 provided on the side of the image forming apparatus, and discharged and stacked on the face-up discharge tray 20.

  On the other hand, when recording an image on the second side of the sheet on which the image is recorded on the first side, that is, when recording on both sides, the sheet is first guided to the reverse path 15 by the switching member 13, and the first reverse roller 16 and the second reverse The roller 17 holds and conveys the sheet.

  Then, when the trailing edge of the sheet passes through the return prevention member 14 in the vicinity of the switching member 13, the conveyance direction of the first reverse roller 16 and the second reverse roller 17 is reversed, and the sheet is guided to the double-sided conveyance path 21 of the refeed means. . Here, the return preventing member 14 blocks the vicinity of the switching member 13 so that the sheet does not return to the fixing device 12.

  In the double-sided conveyance path 21, a plurality of double-sided conveyance rollers 22 are provided, and the sheet is again fed to the registration roller pair 10. By reversing the sheet conveyance direction by the reversing path 15 in this way, the re-fed sheet can be reversed with respect to the surface of the photosensitive drum 1, and an image can be formed on both sides. Yes.

  A feeding conveyance path L1 extending from the feeding device 7 of the feeding means to the photosensitive drum 1 and a refeeding conveyance path L2 extending from the double-sided conveyance path 21 of the refeeding means to the photosensitive drum 1 are registered rollers. It merges on the upstream side of Pair 10. A guide recess 23 described later is provided at the junction.

  Further, a sensor 24 for detecting the sheet is disposed in the feeding conveyance path L1, and a sensor 25 for detecting the sheet is also disposed in the refeed conveyance path L2.

  In the image forming apparatus, as shown in FIG. 2, an input image 41 is input to a controller 42 which is a central control unit. The controller 42 receives an image forming unit 43, a paper transport unit 44, Control the paper feed unit 45.

  Next, a re-feeding operation at the time of sheet double-side recording will be described. First, as shown in FIG. 3, a plurality of sheets S1 and S2 on which images of the first surface are recorded are sequentially accumulated in the duplex conveyance path 21 and the reversal path 15.

  The preceding sheet S1 that has entered the double-sided conveyance path 21 stops at the re-feed standby position P advanced by a predetermined distance A after the leading edge is detected by the sensor 25 of the re-feed conveyance path L2, and waits for re-feeding. . The succeeding sheet S2 waits with a predetermined interval between sheets.

  From this state, the recording on the first side and the recording on the second side are alternately performed, and the trailing edge of the preceding sheet overlaps the leading edge of the following sheet at the junction of the feeding conveyance path L1 and the refeed conveyance path L2. It will be.

  Hereinafter, sheet stacking control in double-sided recording will be described. In this embodiment, the stacking order is changed by controlling the angle of the registration roller pair 10, the refeed start timing of the refeed sheet, and the refeed speed.

(In the case of image formation on the first side and only one side)
FIGS. 4 and 5 are diagrams for explaining the case where the second-side recording sheet precedes. The same control is performed during image formation on only one side.

  In FIG. 4, the sheet F <b> 2 is stopped at the feeding standby position Q that has been advanced by a predetermined distance B after the leading edge of the sheet F <b> 2 is detected by the sensor 24 in the feeding conveyance path L <b> 1. Then, as shown in FIG. 5, the preceding sheet S1 is conveyed at the speed V and the trailing end passes through the sensor 25. At the same time, the registration roller pair 10 is nip line (tangent to the roller at the nip portion) by a drive mechanism (not shown). Is tilted so that the rear end of the preceding sheet S1 overlaps the succeeding sheet F2.

  Thereafter, the subsequent sheet F2 starts to be conveyed at a speed V2 that is faster than the speed V, and is returned to the speed V after a predetermined time, thereby forming an overlap amount Y. Thereafter, the sheet S1 and the sheet F2 are conveyed at the speed V in synchronization with the overlap amount Y maintained.

  Next, the behavior of the sheet after being fixed in the overlapped state will be described with reference to FIG. A fixing roller 30 includes a heat source (not shown), and is controlled at a constant temperature by a temperature detection element (not shown) and a temperature control unit.

  A pressure roller 31 is pressed against the fixing member, and the nip portion is formed by pressing the fixing roller 30 with a pressure of 100 N to 1000 N.

  Reference numeral 32 denotes an upper separation claw close to the fixing roller, which guides the sheet discharged in the winding direction toward the fixing roller 30 side. The upper separation claw is disposed in non-contact with the fixing roller, but may be in contact therewith.

  When the upper separation claw comes into contact, the discharge behavior is stable, but if the conveyance speed is fast, the sheet is not rigid such as thin paper or high humidity, or if the sheet tip collides with the separation claw tip, the separation failure Will occur.

  In addition, the contact separation claw may cause scratches on the surface of the fixing roller, or scratches caused by rubbing the image surface with the separation claw.

  On the other hand, since there is no fear of such scratches in the non-contact type separation claw, in the normal state, the leading end of the sheet is guided by the non-contact type separation claw, and good sheet conveyance is possible.

  If the sheet is not rigid such as when the conveyance speed is high or the sheet is thin or humid, a solid image (a state where a toner image is present on the entire surface of the sheet) may be formed at the leading edge of the sheet. In this case, due to the affinity between the toner and the fixing roller, the leading end of the sheet is easily caught in the gap between the leading end of the separation claw and the surface of the fixing roller, which may cause separation failure.

  Reference numeral 33 denotes a lower separation claw close to the pressure roller, which is a lower separation claw close to the pressure roller, and guides the sheet discharged in the winding direction toward the pressure roller 31.

  As with the upper separation claw 32, the lower separation claw 33 may be either a non-contact type or a contact type. The advantages and disadvantages of each are almost the same.

  At the time of forming the first side and one side, since the sheet has not been fixed even once, it must be fixed in a high humidity environment or in a state where the sheet has no rigidity such as thin paper. In addition, when the amount of toner loaded is large, such as a solid image (an image in which the toner image is transferred without a gap), the viscosity of the toner increases and it is difficult to separate from the fixing roller. If such conditions overlap, a separation failure is likely to occur between the upper separation claw 32 and the fixing roller.

  In this embodiment, since the trailing edge of the preceding sheet S1 overlaps the leading edge of the succeeding sheet F2, the leading edge of the sheet F2 to be discharged to the fixing roller side is guided by the upper separation claw 32. Therefore, a stable discharge behavior with no separation failure can be obtained.

  That is, since the separation failure of the sheet after passing through the fixing device 12 is suppressed, the sheet is stably conveyed while maintaining high productivity of image formation.

(In the case of forming both sides on the second side)
7 and 8 are diagrams illustrating a case where the second sheet is stacked on the preceding sheet. As shown in FIG. 7, the sheet F1 going to the first-side recording is conveyed at a constant speed V, and the standby is performed when the rear end of the sheet F1 comes to the junction M of the feeding conveyance path L1 and the refeed conveyance path L2. The refeeding of the sheet S1 toward the second-side recording that has been performed is started.

  Here, the succeeding sheet S1 is conveyed at a speed V2 faster than the speed V, and catches up and begins to overlap when the rear end of the preceding sheet F1 passes the guide recess 23.

  Here, as shown in FIG. 8, the registration roller pair 10 arranged on the downstream side of the joining portion can tilt the nip line (the tangent line of the roller in the nip portion) by a driving mechanism (not shown). By tilting the nip tangent of the registration roller pair 10 toward the guide recess 23 with respect to the transport direction, the trailing edge of the preceding sheet F1 enters the guide recess 23 due to its elasticity.

  As a result, the leading edge of the succeeding sheet S1 can surely overlap the upper side of the trailing edge of the preceding sheet F1. Thereafter, when the overlap amount reaches a predetermined X, the speed of the succeeding sheet S1 is reduced from V2 to V. Thereafter, the preceding sheet F1 and the succeeding sheet S1 are synchronized in a state where the overlap amount X is maintained. It is conveyed at a speed V.

  Next, the behavior of the sheet after being fixed in the overlapping state will be described with reference to FIG. At the time of forming the second side, the sheet once fixed is reversely switched back, and after the image is formed again, it passes through the fixing unit again. Winding around is difficult to occur.

  On the other hand, if there is a solid image on the first surface, the fixed toner contracts during the cooling process, and the sheet curls (referred to as toner curl). At this time, since the image surface contracts, the curled state is formed in which the image surface side is curved into the concave portion.

  When the curled sheet passes through the fixing unit after being reversed by the switchback, the toner surface faces downward, so that the curled sheet has a concavely curled shape.

  In the present embodiment, as shown in FIG. 9, since the trailing edge of the preceding sheet F1 overlaps the leading edge of the succeeding sheet S1, the leading edge of the sheet S1 to be discharged downward is the lower separation claw. Guided by 33, a stable discharge behavior with no separation failure is obtained.

  When the first side has a small amount of applied toner on both sides, the above-mentioned toner curl is less likely to occur, so that the separation failure in the lower separation claw direction is less likely to occur than when the first side is a solid image.

  Therefore, when the image ratio of the first surface of the rear end of the first sheet (the front end portion of the second sheet) is low, it is not necessary to superimpose the succeeding sheet S1 on the leading end of the preceding sheet.

  On the other hand, when the leading edge of the second surface is a solid image, separation failure is less likely to occur compared to the first surface, but separation failure may occur when the recording sheet is not rigid. .

  Therefore, it is more effective that the separation failure is less likely to occur if the method of overlapping the leading edge of the second surface is determined based on the image information of the trailing edge of the first sheet (the leading edge of the second sheet).

  The control in this case will be described using the flowchart of FIG.

  First, image formation is started on the preceding sheet, and the succeeding sheet is waiting at the standby position (step 1).

  If the succeeding sheet is the first face (step 2), the fixing member is likely to cause a separation failure with the upper separation claw, so that the preceding sheet F1 is facing up and the succeeding sheet S1 is facing down. The registration roller pair 10 is controlled so as to overlap (step 3).

  When the succeeding sheet is the second side, the image ratio of the rear end of the first side (the back side of the front end of the second side) on which the first image has been formed is counted by the video counter of the controller (step 4).

  If it is equal to or greater than the predetermined value, a separation failure is likely to occur at the lower separation claw 33 due to curling, so the registration roller pair 10 is controlled so that the succeeding sheet S1 is superimposed on the preceding sheet F1 ( Step 5). If it is less than the predetermined value, the same control as in step 3 may be performed.

  Thus, in the present embodiment, the overlapping portion of the preceding sheet and the succeeding sheet that are continuously conveyed is overlapped so that the top and bottom relations are reversed between the leading edge of the first surface and the leading edge of the second surface, The relationship between the top and bottom at the leading edge of the first surface and the leading edge of the second surface is determined by the image ratio of the first surface.

  As a result, poor separation of the sheet when passing through the fixing unit is suppressed, and a highly productive image forming apparatus having stable sheet transportability is obtained.

1 is a schematic longitudinal sectional view of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a block diagram of the image forming apparatus illustrated in FIG. 1. FIG. 2 is an explanatory diagram of a refeed operation of the image forming apparatus illustrated in FIG. 1. It is a figure which shows the time at the time of single side | surface and the overlap preparation of the 1st surface of both surfaces. It is a figure which shows immediately after the superimposition at the time of single side | surface and both surfaces 1st surface. It is sectional drawing at the time of the fixing at the time of the single side | surface and both surfaces 1st surface. It is a figure which shows the time of the overlap preparation of the 2nd surface of both surfaces. It is a figure which shows immediately after the superimposition of both surfaces 2nd. It is sectional drawing just after fixation of the 2nd surface of both surfaces. It is a flowchart which shows control.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photosensitive drum 2 Charging device 3 Exposure means 4 Developing means 5 Transfer means 6 Cleaning device 7 Feeding device 8 Feeding roller 9 Conveying roller
10 Registration roller pair
11 Conveyor belt
12 Fixing device
13 Switching member
14 Return prevention member
15 Reverse road
16 First reversing roller
17 Second reversing roller
18 Face-down output tray
19 Discharge roller
20 Face-up output tray
21 Double-sided conveyance path
22 Double-sided transport roller
23 Guide recess
24, 26 sensors
30 Fixing roller
31 Pressure roller
32 upper separation nails
33 Lower separation claw L1 Feed conveyance path L2 Refeed conveyance path S1, S2, F1, F2 Sheet

Claims (2)

In an image forming apparatus comprising: a conveying unit that continuously conveys a trailing end of a preceding sheet and a leading end of a succeeding sheet; and a fixing device that pressurizes and heats a toner image on the sheet.
An image forming apparatus, wherein an overlapping portion between a preceding sheet and a succeeding sheet is overlapped so that an upper and lower relationship is reversed between a leading edge of a first surface and a leading edge of a second surface. The image forming apparatus according to claim 1, wherein the relationship between the top and bottom at the leading edge of the first surface and the leading edge of the second surface is determined by an image ratio of the first surface.

Images