JP2008139396A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of preventing toner adhesion between paper sheets continuously ejected on a paper output tray and capable of correcting or eliminating the curling of the paper sheet subjected to the fixing. <P>SOLUTION: The image forming apparatus includes: a pair of conveying rollers 52 and a pair of paper ejection rollers 54 above a fixing device 37; and a second paper conveyance path 53 extending between these pairs of rollers. The second paper conveyance path 53 is formed as a curving conveyance path which curves in the direction opposite to the curling direction of the paper sheet passing through the fixing device 37. A cooling air passage 74 is formed sideways near the fixing nip area 39 of the fixing device 37 and the pair of conveying rollers 52. A shield member 76 is provided for intercepting the flow of cooling air from the cooling air passage 74 to the pair of conveying rollers 52. In addition, blowing of cooling air from the cooling air passage 74 to the paper conveyance path 53 takes place near the pair of paper ejection rollers 54. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an electrophotographic image forming apparatus such as, for example, a copying machine, a printer, a facsimile, or a complex machine of these.

  Conventionally, for example, in Patent Document 1 below, immediately after a sheet passes through a fixing nip portion of a roller-pair type fixing device, air is blown to the toner image fixing surface of the sheet by a cooling fan to cool the sheet and the fixed toner image. Thus, there is disclosed a fixing device that prevents the toner on the lower surface of the paper from adhering to the back surface of the paper that is sequentially stacked and accommodated on the paper discharge tray. When toner adhesion as described above occurs, the toner may be peeled off from the surface of the paper when the adhered papers are separated, and image defects may occur.

  In general, paper that has passed through a fixing device that melts and fixes a toner image adhering to the paper by heat and pressure is curled due to factors such as water content of the paper, fixing temperature, and curvature of the fixing nip. It is known to occur easily.

Japanese Patent Laid-Open No. 5-150677

  However, when the paper is cooled immediately after passing through the fixing device as in the fixing device disclosed in Patent Document 1, the curled state generated on the paper is fixed. If a large number of the curled sheets are continuously discharged onto the discharge tray, the sheets cannot be stacked in a well-aligned state and the stacking capacity is deteriorated or the curling is not performed. If it is large, the paper may be rounded and not stacked in the discharge order, but scattered on the paper discharge tray.

  Therefore, in order to solve the above problems, the present invention prevents toner adhesion between sheets continuously discharged onto a discharge tray, and can correct or eliminate curling of sheets after fixing. It is an object to provide a forming apparatus.

In order to solve the above-described problem, the first invention of the present application is a first conveying unit that conveys a sheet immediately after passing through the fixing nip portion of the fixing device, and the first conveying unit extends along the sheet conveying direction. A paper transport path, a second transport section provided in the paper transport path for transporting the paper downstream of the first transport section in the paper transport direction, the first transport section, and the first transport section An image forming apparatus including a cooling air flow path for blowing cooling air to the paper conveyance path between the second conveyance unit,
The sheet conveyance path between the first conveyance section and the second conveyance section is formed as a curved conveyance path that curves in a direction opposite to the curl direction of the sheet generated by passing through the fixing device. An air flow path is formed in the vicinity of the side of the fixing nip portion and the first transport portion of the fixing device, and a shielding member that blocks the flow of cooling air from the cooling air flow passage to the first transport portion side. And cooling air is blown out from the cooling air flow path to the sheet conveying path in the vicinity of the second conveying unit.

  According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the shielding member is configured integrally with a conveyance guide that forms the sheet conveyance path.

  According to a third aspect of the present invention, in the image forming apparatus according to the first aspect, the sheet conveying speed of the first conveying unit is set faster than the sheet conveying speed of the fixing device. .

  According to a fourth aspect of the present invention, in the image forming apparatus of the first aspect, the sheet conveying speed of the second conveying unit is set faster than the sheet conveying speed of the first conveying unit. Features.

  According to a fifth invention of the present application, in the first invention, the fixing device is of an induction heating type including a core unit that generates magnetic flux, and the cooling air flow path is along an outer surface of the core unit. The cooling air is provided to flow.

  According to a sixth aspect of the present invention, in the image forming apparatus according to the first aspect, the cooling air flow path forms a heat transfer prevention space between a toner container and the fixing device. And

  In the image forming apparatus according to the present invention, the paper curled by passing through the fixing device is transported through a curved transport path that curves in the direction opposite to the curling direction, whereby the curl can be corrected or eliminated. .

  Further, since a shielding member for preventing cooling air from flowing from the cooling air passage passing through the vicinity of the side of the fixing nip portion of the fixing device to the first conveying portion side is provided, the first conveying portion, the fixing nip portion, And the inside of the paper conveyance path between them can be prevented from being cooled by the cooling air, and as a result, the curled state is fixed by cooling the paper immediately after passing through the fixing device. It can be avoided.

  Further, since the cooling air is blown out from the cooling air flow path to the sheet conveying path in the vicinity of the second conveying unit, the sheet in the sheet conveying path immediately before the second conveying unit and the second conveying unit are arranged. And can be cooled moderately. As a result, the paper is cooled after curling is corrected by passing through the curved conveyance path, so that the curl correction state of the paper is fixed (that is, after being restored to the original flat state) on the discharge tray. The toner image on the paper is completely solidified by this cooling, and toner adhesion occurs between the paper even when the paper is continuously discharged and stacked on the paper discharge tray. Nor.

  Furthermore, since the sheet is cooled to a temperature equal to or lower than the melting temperature of the wax contained in the toner immediately before the second conveyance unit, the toner wax does not adhere when passing through the second conveyance unit, and the second The transport unit is also cooled to the toner wax melting temperature or lower, so that even if the toner wax adheres to the second transport unit, the adhered toner wax re-adheres to, for example, an OHP sheet that passes through the second transport unit. No wax marks are left on the OHP sheet discharged onto the paper discharge tray.

  Therefore, according to the image forming apparatus of the present invention, it is possible to prevent adhesion of toner between sheets continuously discharged onto the sheet discharge tray and to correct or eliminate curling of the sheet after fixing.

Embodiments of the present invention will be described below with reference to the accompanying drawings.
FIG. 1 schematically shows the overall configuration of an image forming apparatus 10 according to the first embodiment of the present invention. The image forming apparatus 10 includes an intermediate transfer belt 12 in the approximate center inside the apparatus. The intermediate transfer belt 12 in the form of an endless sheet is supported around each of the four rotatable rollers disposed on the inner side, and for example, the roller 14 is rotationally driven by a motor (not shown). As a result, it rotates in the direction of arrow A.

  Below the lower portion of the intermediate transfer belt 12 that extends in the horizontal direction, yellow (Y), magenta (M), cyan (C), and black (K) toners are sequentially arranged from the upstream side in the rotation direction of the intermediate transfer belt 21. The four imaging units 22Y, 22M, 22C, and 22K respectively corresponding to are arranged side by side in the horizontal direction. The black imaging unit 22K is configured to be larger than the other imaging units 22Y, 22M, and 22C in order to provide high durability performance with respect to frequent monochrome printing. An exposure device 23 is disposed below each of the imaging units 22Y, 22M, 22C, and 22K.

  The imaging units 22Y, 22M, 22C, and 22K are respectively a drum-shaped photoreceptor 24, a charger 26 that uniformly charges the surface of the photoreceptor 24, and the surface of the uniformly charged photoreceptor 24 from the exposure device 23. A developing device 28 that develops an electrostatic latent image formed by irradiation of lasers L (Y), L (M), L (C), and L (K) with toner to form a toner image. Yes. The photosensitive members 24 of the imaging units 22Y, 22M, 22C, and 22K are in contact with the intermediate transfer belt 24, respectively. Corresponding to each of the imaging units 22Y, 22M, 22C, and 22K, four primary transfer rollers 30 are rotatably provided so as to sandwich the intermediate transfer belt 12 with the photoreceptor 24.

  Above the intermediate transfer belt 12, four toner containers 32 respectively corresponding to the four color toners are arranged side by side. The toners of the respective colors are supplied from the toner containers 32 to the developing units 28 of the corresponding imaging units 22Y, 22M, 22C, and 22K through supply paths (not shown) according to the remaining amount of toner in the developing unit 28. It has become.

  A secondary transfer roller 34 is pressed against a portion of the intermediate transfer belt 12 supported by the roller 14, and a contact portion between the intermediate transfer belt 12 and the secondary transfer roller 34 becomes a secondary transfer nip portion 36. ing. Also, above the secondary transfer roller 34, a roller-pair type comprising a fixing roller 37a heated above the melting temperature of the toner and a pressure roller 37b pressed against the fixing roller 37a in a casing 37c. A fixing device 37 is disposed, and a contact portion between the fixing roller 37 a and the pressure roller 37 b is a fixing nip portion 39.

  The heating method of the fixing roller 37a may be a heater heating type or an induction heating type. Further, for example, a belt-type fixing device other than the roller pair type may be used.

  A cleaning device 38 is disposed in contact with the portion of the intermediate transfer belt supported by the roller 16 so that the toner remaining on the intermediate transfer belt 12 after the secondary transfer of the toner image is collected. Yes.

  A paper feeding unit 40 is provided at the lower part of the image forming apparatus 10. The sheets (not shown) stacked and accommodated in the sheet feeding unit 40 are sent out from the sheet feeding unit 40 one by one from the uppermost one by the rotation of the sheet feeding roller 42.

  From the paper supply unit 40, a paper transport path 44 extends upward. The sheet conveyance path 44 is arranged in order along the sheet conveyance direction, with each nip portion of the conveyance roller pairs 46 and 48, the nip portion between the timing roller pair 50, the secondary transfer nip portion 36, and the fixing nip portion of the fixing device 37. 39.

  Further, the sheet conveyance path 53 is provided on the upper surface of the image forming apparatus 10 from the nip portion of the conveyance roller pair (first conveyance unit) 52 that conveys the sheet immediately after passing through the fixing nip portion 39 of the fixing device 37. A paper discharge roller pair (second transport unit) 54 for discharging paper onto the paper discharge tray 11 is connected. The sheet conveyance speed of the conveyance roller pair 52 can be set faster than the sheet conveyance speed of the fixing device 37, and the sheet conveyance speed of the paper discharge roller pair 54 is set faster than the sheet conveyance speed of the conveyance roller pair 52. It is configured to be able to. Hereinafter, the first sheet conveyance path 51 is distinguished from the fixing nip portion 39 to the conveyance roller pair 52, and the second sheet conveyance path 53 is distinguished from the conveyance roller pair 52 to the paper discharge roller pair 54.

  The second paper conveyance path 53 is formed as a curved conveyance path that is curved in a direction opposite to the curl direction of the paper generated by passing through the fixing nip portion 39 of the fixing device 37 by the conveyance guides provided on both sides thereof. ing. Here, the curl direction of the sheet is a curl direction in which the sheet is curved so that when the sheet passes through the fixing nip portion 39 of the fixing device 37, the sheet is convex toward the fixing roller 37a and concave toward the pressure roller 37b. Assumes. In the present embodiment, the discharge roller pair 54 is the second transfer unit of the present invention, but the second transfer unit may be another transfer unit (roller pair or belt) other than the discharge roller pair. .

  A flat partition wall 70 is provided between the black toner container 32K and the fixing device 37 so as to cover the upper side of the intermediate transfer belt 12. The partition wall 70 extends along the side surface of the casing 37c of the fixing device 37. A flat partition wall 72 is erected. A cooling air flow path 74 is formed between the partition walls 70 and 72 and the inner wall surface of the apparatus main body. The cooling air flow path 74 is provided in the vicinity of the side of the fixing nip portion 39 and the conveyance roller pair 52 of the fixing device 37. The cooling air flowing through the cooling air flow path 74 flows from the lower side to the upper side as indicated by arrows in FIG. 1, and is near the paper discharge roller pair 54 and the paper than the curved portion of the second paper transport path 53. It is blown out downstream in the conveying direction.

  The cooling air flow path 74 also functions as a heat transfer prevention space for preventing heat transfer from the fixing device 37 to the black toner container 32K. Can be prevented.

  As shown in FIG. 2, at the rear of the black toner container 32K (the rear side in the direction perpendicular to the paper surface of FIG. 1), a fan 77 that draws air from the outside of the apparatus and the fan 77 is connected and blown out from the fan 77. And a duct 78 for blowing out the air to the cooling air flow path 74. The cooling air blown out from the duct 78 to the cooling air flow path 74 is changed in direction by fins and front walls (not shown) and flows along the partition walls 70 and 72.

  Further, a shielding member 76 for preventing the flow of cooling air from the rising portion of the cooling air flow path 74 toward the conveyance roller pair 52 side is a conveyance guide 53a that forms the second conveyance path 53 with the casing 37c of the fixing device 37. It is arranged between. The shielding member 76 may be provided integrally with the conveyance guide 53a. Alternatively, the shielding member 76 may be configured as a part of the flat conveyance guide 53a by bending, or the partition wall 72 itself may be configured as a shielding member by extending the partition wall 72 upward. Also good.

  From the second conveyance path 53, a sheet reversing path 60 is branched above the conveyance roller pair 52. The sheet reversing path 60 extends downward from the branch position, and joins the sheet conveying path 44 below the timing roller pair 50 via the nip portions of the conveying roller pairs 62, 64, 66, and 68. Yes. The paper reversing path 60 is used for duplex printing. That is, the sheet with the toner image fixed on the surface is switched back by the discharge roller pair 54 after a part of the sheet is sent to the outside of the image forming apparatus to be switched back and introduced into the sheet reversing path 60. . Thereafter, the sheet is conveyed downward along the sheet reversing path 60 by the conveying roller pairs 62, 64, 66, and 68, and is again sent to the secondary transfer nip portion 36 via the sheet conveying path 44 and the timing roller pair 50, As a result, the toner image is transferred to the back side of the sheet.

  The guides on both sides forming each paper transport path 44, 51, 53 and paper reversing path 60 may be configured in any way as long as they fulfill the function of guiding the transported paper, for example, metal or resin It may be composed of a single flat plate made of metal, a plurality of rod-like members or strip-like members made of, for example, metal or resin, which are arranged in parallel with each other and are elongated in the paper conveyance direction.

Next, an image forming operation of the image forming apparatus 10 having the above configuration will be described.
For example, when a print signal and image data are received from an external device such as a personal computer, an image forming operation is started. In the case of a color image, the image data is divided into data for each color by a control unit (not shown) and then input to the exposure device 23.

  In each of the imaging units 22Y, 22M, 22C, and 22K, the surface of the photosensitive member 24 that is rotationally driven in the clockwise direction in FIG. 1 is uniformly charged by the charger 26, and then the exposure device 23 responds to each color image data. An electrostatic latent image is formed by exposure to lasers L (Y), L (M), L (C), and L (K). Thereafter, the electrostatic latent image is developed by the developing device 28 to become a toner image. The toner images formed on the photosensitive member 24 in each of the imaging units 22Y, 22M, 22C, and 22K are sequentially transferred onto the intermediate transfer belt 12 by the electrostatic adsorption action of the primary transfer roller 30 to which the primary transfer bias is applied. Primary transfer is performed in the superimposed state.

  When the image data is a monochrome image, only the black imaging unit 22K operates to form a toner image, which is primarily transferred onto the intermediate transfer belt 12.

  The sheet fed from the sheet feeding unit 40 to the sheet conveyance path 44 by the sheet feeding roller 42 is in a standby state with its leading end nipped by the timing roller pair 50, and transferred 4 onto the intermediate transfer belt 12. The color toner image is introduced into the secondary transfer unit 36 by the timing roller pair 50 in synchronization with the arrival of the color toner image at the secondary transfer unit 36 according to the rotation of the intermediate transfer belt 12. At this time, since the secondary transfer bias is applied to the secondary transfer roller 34, the four-color toner images on the intermediate transfer belt 12 are secondarily transferred collectively onto the sheet by the electrostatic adsorption action.

  When the paper on which the toner image is transferred passes through the fixing nip portion 39 of the fixing device 37, the toner image is melted and fixed by the action of heat and pressure. At this time, the paper that has passed through the fixing device 37 is curled with a convex shape on the fixing roller 37a side and a concave shape on the pressure roller 37b side. Thereafter, the sheet is conveyed to the second sheet conveying path 53 through the first sheet conveying path 51 to the conveying roller pair 52. At this time, the sheet conveying speed of the conveying roller pair 52 is higher than the sheet conveying speed of the fixing device 37. Is set slightly faster, the sheet is pulled so as to be stretched in the first sheet conveyance path 51. By passing the sheet through the fixing nip portion 39 while applying a pulling force to a sheet in a high temperature state (for example, 80 ° C.), the sheet curl state is corrected.

  Thereafter, the sheet is conveyed through the second sheet conveyance path 53 by the conveyance roller pair 52 and the discharge roller pair 54. At this time, the second sheet conveyance path 53 is curved and curved in a direction opposite to the curl direction of the sheet. Since it is formed as a path, the curl correcting action acts on the sheet conveyed along the curved conveyance path. In FIG. 1, the curved conveyance path is formed so as to protrude to the opposite side of the conveyance roller pair 52 with respect to the nip line of the nip portion of the discharge roller pair 54. This further increases the curl correction effect. In view of this effect, the curved conveyance path may be formed so as to protrude to the opposite side of the discharge roller pair 54 with respect to the nip line of the nip portion of the conveyance roller pair 52. Here, the “nip line” is a linear extension of a line formed at the nip portion (roller pressure contact portion) when the nip portion is viewed from the axial direction of the roller pair as shown in FIG.

  In addition, since the paper conveyance speed of the paper discharge roller pair 54 is set slightly faster than the paper conveyance speed of the conveyance roller pair 52, the sheet nipped by both the roller pairs 52 and 54 has a lower part of the curved conveyance path. A pulling force acts so as to be pressed against the conveyance guide 53a, and this also corrects or eliminates the curl of the sheet. Further, in the second paper transport path 53 in the vicinity of the pair of paper discharge rollers 54, the cooling air from the cooling air passage 74 is blown onto the paper and cooled, so that the paper is in a state where the curl has been corrected or eliminated (ie, The paper is fixed in the original flat state and is discharged straight onto the paper discharge tray 11 from the paper discharge roller pair 54 in a state of extending straight.

  As described above, in the image forming apparatus 10 of the present embodiment, the paper that has been curled due to the passage of the fixing device 37 is transported through the curved transport path 53 that curves in the direction opposite to the curl direction. Further, by applying a pulling force by the conveying roller pair 52 and the paper discharge roller pair 54, the curl of the paper can be corrected or eliminated.

  Further, since a shielding member 76 is provided to prevent the cooling air from flowing from the cooling air passage 74 passing through the vicinity of the fixing nip portion 39 of the fixing device 37 to the conveying roller pair 52 side. It is possible to prevent the ambient temperature of the one sheet conveyance path 51 and the inside of the fixing device 37 from being cooled by the cooling air, and as a result, the sheet is cooled immediately after passing through the fixing device 37 and curled. It can be avoided that the state is fixed.

  Further, since the cooling air is blown out from the cooling air flow path 74 to the second paper conveyance path 53 in the vicinity of the paper discharge roller pair 54, the second paper conveyance path 53 immediately before the paper discharge roller pair 54 is configured. The sheet and the paper discharge roller pair 54 can be appropriately cooled (for example, 40 ° C.). As a result, the paper is cooled after curling is corrected by passing through the curved conveyance path 53, so that the paper discharge tray is fixed after the curled correction state of the paper is fixed (that is, after the original flat state is restored). 11, and the toner image on the paper is completely solidified by this cooling, so that even if the paper is continuously discharged and stacked on the paper discharge tray 11, the toner adhesion between the papers is achieved. It does not occur.

  Furthermore, the toner wax adheres to the rollers when passing through the paper discharge roller pair 54 by cooling the sheet to a temperature equal to or lower than the melting temperature of the wax contained in the toner (for example, 74 ° C.) immediately before the paper discharge roller pair 54. In addition, since the discharge roller pair 54 is also cooled to the toner wax melting temperature or lower, even if the toner wax adheres to the discharge roller pair 54, the adhering toner wax is not discharged. For example, it does not reattach to the OHP sheet passing through the pair 54, and a wax trace such as a roller trace is not attached to the OHP sheet discharged onto the paper discharge tray 11. In this respect, the flow of the cooling air may be adjusted so that the temperature of each pair of conveyance rollers that conveys the sheet after fixing and the sheet passing therethrough are equal.

  Therefore, according to the image forming apparatus 10 of the present embodiment, it is possible to prevent toner adhesion between sheets continuously discharged onto the sheet discharge tray 11 and to correct or eliminate curling of the sheet after fixing.

  Next, the image forming apparatus according to the second embodiment will be described with reference to FIGS. 3 and 4. In the image forming apparatus according to the second embodiment, the cooling air flow path 74 is provided on the side surface of the casing 37 c of the fixing device 37. The difference is that the opening extends upward from the formed opening through the inside of the fixing device 37.

  The fixing device 37 in this case is of an induction heating type and includes a magnetic flux generating coil unit 80 that generates a magnetic flux for heating the fixing roller 37a of the fixing device 37 by electromagnetic induction, as shown in FIG. Yes. The cooling air flow path 74 that has entered the inside from the side surface of the fixing device 37 extends along the outer surface of the magnetic flux generating coil unit 80 and is formed so as to come out from the upper portion of the fixing device 37. As a result, the magnetic flux generating coil unit 80 that rises in temperature due to the heat generated by the coil can be cooled, and as a result, a reduction in induction heating efficiency can be prevented.

  In the image forming apparatus according to the first and second embodiments, the paper discharge roller pair 54 switches back the single-side printed paper and sends it to the paper reversing path 60 during double-sided printing. There is a switchback path that branches from the second paper transport path 53 and extends to a pair of switchback rollers disposed near the upper side of the paper discharge roller pair 54, and the second paper transport path 53 and the switchback path are branched. The present invention may be applied to an image forming apparatus provided with a switching guide that is rotated at a position within a predetermined angle range.

  Note that the present invention is not limited to a tandem type image forming apparatus, and may be applied to other types (for example, a 4-cycle type) image forming apparatus.

1 is an overall configuration diagram of an image forming apparatus according to a first embodiment. The perspective view which shows a cooling air flow path with a fan and a duct. FIG. 6 is a main part configuration diagram of an image forming apparatus according to a second embodiment. FIG. 4 is a partially enlarged view of the vicinity of the fixing device in FIG. 3.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Image forming apparatus 37 ... Fixing device 39 ... Fixing nip part 44 ... Paper conveyance path 51 ... 1st paper conveyance path 52 ... Conveying roller pair (1st conveyance part)
53. Second paper transport path 53a. Transport guide 54. Paper discharge roller pair (second transport unit)
60 ... sheet reversing path 74 ... cooling air flow path 76 ... shielding member 77 ... fan 78 ... duct 80 ... magnetic flux generating coil unit

Claims (6)

A first conveying unit that conveys a sheet immediately after passing through a fixing nip portion of the fixing device; a sheet conveying path extending from the first conveying unit along a sheet conveying direction; and the sheet with respect to the first conveying unit Cooling air is supplied to the second conveyance unit provided in the sheet conveyance path for conveying the sheet on the downstream side in the conveyance direction, and the sheet conveyance path between the first conveyance unit and the second conveyance unit. An image forming apparatus having a cooling air flow path for blowing out,
The sheet conveyance path between the first conveyance section and the second conveyance section is formed as a curved conveyance path that curves in a direction opposite to the curl direction of the sheet generated by passing through the fixing device. An air flow path is formed in the vicinity of the side of the fixing nip portion and the first transport portion of the fixing device, and a shielding member that blocks the flow of cooling air from the cooling air flow passage to the first transport portion side. The image forming apparatus is characterized in that the cooling air is blown out from the cooling air flow path to the sheet conveying path in the vicinity of the second conveying unit.   The image forming apparatus according to claim 1, wherein the shielding member is configured integrally with a conveyance guide that forms the sheet conveyance path.   The image forming apparatus according to claim 1, wherein a sheet conveyance speed of the first conveyance unit is set to be higher than a sheet conveyance speed of the fixing device.   The image forming apparatus according to claim 1, wherein a sheet conveyance speed of the second conveyance unit is set to be higher than a sheet conveyance speed of the first conveyance unit.   The fixing device is of an induction heating type including a magnetic flux generating core unit that generates magnetic flux, and the cooling air flow path is provided so that cooling air flows along an outer surface of the magnetic flux generating core unit. The image forming apparatus according to claim 1, wherein:   The image forming apparatus according to claim 1, wherein the cooling air flow path forms a heat transfer prevention space between a toner container and the fixing device.

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