Method and apparatus for producing duplex prints and image forming system using the same Number:6,801,742 from the United States Patent and Trademark Office (PTO) owispatent An image forming apparatus of the present invention includes a plurality of image carriers arranged along a first intermediate image transfer belt. Toner images of different colors formed on the image carriers are sequentially transferred to the first intermediate image transfer belt one above the other to complete a first image. The first image is transferred to a second image transfer belt and then transferred to one side of a sheet. At the same time, a second image completed on the first image transfer belt is directly transferred to the other side of the same sheet. First and second control means are respectively disposed in the loop of the first intermediate image transfer body and the loop of the second intermediate image transfer body. The apparatus of the present invention can form color images on both sides of the recording medium rapidly in accurate register.<H producing, apparatus, Method, and, appa, 6801742.html, Patent, pto, 6801742

Title: Method and apparatus for producing duplex prints and image forming system using the same

Abstract: An image forming apparatus of the present invention includes a plurality of image carriers arranged along a first intermediate image transfer belt. Toner images of different colors formed on the image carriers are sequentially transferred to the first intermediate image transfer belt one above the other to complete a first image. The first image is transferred to a second image transfer belt and then transferred to one side of a sheet. At the same time, a second image completed on the first image transfer belt is directly transferred to the other side of the same sheet. First and second control means are respectively disposed in the loop of the first intermediate image transfer body and the loop of the second intermediate image transfer body. The apparatus of the present invention can form color images on both sides of the recording medium rapidly in accurate register.

Patent Number: 6,801,742 Issued on 10/05/2004 to Mochimaru, et al.

Inventors: Mochimaru; Hideaki (Kanagawa, JP), Omata; Yasukuni (Kanagawa, JP), Sohmiya; Norimasa (Saitama, JP), Kaneko; Chiemi (Ibaraki, JP), Kouno; Yuzo (Chiba, JP)
Assignee: Ricoh Company, Ltd. (Tokyo, JP)

Appl. No.: 10/252,104

Filed: September 23, 2002

Foreign Application Priority Data


Sep 21, 2001 [JP]			2001-290284
Sep 25, 2001 [JP]			2001-290420
Jan 28, 2002 [JP]			2002-019287
Aug 22, 2002 [JP]			2002-241953
Aug 27, 2002 [JP]			2002-246463

Current U.S. Class: 399/309 ; 399/124; 399/301; 399/302; 399/66; 399/92; 399/94; 399/98

Field of Search: 399/309,302,308,120-125,107,110,111,301,66,92,94,364,374,98

References Cited [Referenced By]

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Foreign Patent Documents


32 17 461	Nov., 1983	DE
1 202 131	May., 2002	EP
1 215 544	Jun., 2002	EP
1 237 056	Sep., 2002	EP
59-111653	Jun., 1984	JP
8-160703	Jun., 1996	JP
9-258518	Oct., 1997	JP
2000-081742	Mar., 2000	JP
2001-075376	Mar., 2001	JP
2002-040720	Feb., 2002	JP

Primary Examiner: Chen; Sophia S.
Attorney, Agent or Firm: Oblon, Spivak, McClelland, Maier & Neustadt, P.C.

Claims

What is claimed is:

1. An image forming method comprising the steps of electrostatically transferring toner images of different colors each being formed on a particular one of a plurality of image carriers to a first intermediate image transfer body one above the other to thereby form a first composite image; electrostatically transferring the first composite image to a second intermediate image transfer body; electrostatically transferring the first composite image from said second intermediate image transfer body to one side of a recording medium; electrostatically transferring to the other side of the recording medium a second composite image formed on said first intermediate image transfer body by transferring toner images of different colors formed on said plurality of image carriers one above the other; and fixing the first composite image and the second composite image of the recording medium at the same time.

2. The method as claimed in claim 1, further comprising fixing the first composite image and the second composite image at the same time by using first heating means and second heating means respectively positioned outside and inside of said second intermediate image transfer body.

3. An image forming apparatus comprising: a plurality of image carriers on each of which a toner image of a particular color is formed; a first intermediate image transfer body to which toner images of different colors formed on said plurality of image carriers are transferred one above the other to thereby form a first composite image; a second intermediate image transfer body to which the first composite image is transferred; first image transferring means for electrostatically transferring the toner images from said plurality of image carriers to said first intermediate image transfer body; second image transferring means for electrostatically transferring the first composite image from said first intermediate image transfer body to said second intermediate image transfer body; third image transferring means for transferring the first composite image from said second image transfer body to one side of a recording medium; fourth image transferring means for transferring to the other side of the recording medium a second composite image formed on said first intermediate image transfer body by transferring toner images of different colors respectively formed on said plurality of image carriers; and fixing means for fixing the first composite image and the second composite image of the recording medium.

4. The apparatus as claimed in claim 3, wherein said second image transferring means bifunctions as said fourth image transferring means.

5. The apparatus as claimed in claim 3, wherein said third image transferring means faces, but does not contact, a surface of said second intermediate image transfer body.

6. The apparatus as claimed in claim 3, wherein said first intermediate image transfer body and said second intermediate image transfer body each comprise an endless belt passed over a plurality of support members and driven to move.

7. The apparatus as claimed in claim 3, wherein said second intermediate image transfer body comprises an endless belt passed over a plurality of support members and driven to move, and said second image transferring means and said fourth image transferring means are disposed in a loop of the endless belt.

8. The apparatus as claimed in claim 3, wherein said first intermediate image transfer body comprises an endless belt passed over a plurality of support members and driven to move, and said second image transferring means and said fourth image transferring means are disposed in a loop of the endless belt.

9. The apparatus as claimed in claim 3, wherein said first intermediate image transfer body comprises an endless belt passed over a plurality of support members and driven to move, said first intermediate image transfer body has a height smaller than a width in a horizontal direction, and a path for conveying the recording medium and said first intermediate image transfer body are positioned relative to each other such that said recording medium passes one end of said first intermediate image transfer body in the horizontal direction.

10. The apparatus as claimed in claim 3, wherein said first intermediate image transfer body comprises an endless belt passed over a plurality of support members and driven to move, said first intermediate image transfer body has a height smaller than a width in a horizontal direction, said second intermediate image transfer body is positioned below said first intermediate image transfer body, and a path for conveying the recording medium, said first intermediate image transfer body and said second intermediate image transfer body are positioned relative to each other such that said recording medium passes a nip between said first intermediate image transfer body and said second intermediate image transfer body in a substantially horizontal direction.

11. The apparatus as claimed in claim 10, further comprising a manual sheet feeding section, wherein a path for conveying the recording medium substantially linearly extends from said manual sheet feeding section to a tray to which the recording medium passed through said fixing means is driven out.

12. The apparatus as claimed in claim 3, wherein said first intermediate image transfer body comprises an endless belt passed over a plurality of support members and driven to move, and said plurality of image carriers are arranged side by side along either one of an upper run and a lower run of said first intermediate image transfer body.

13. The apparatus as claimed in claim 3, further comprising a tray positioned above said first intermediate image transfer body for stacking the recording medium passed through said fixing means, wherein said tray is inclined such that a downstream portion in a direction in which the recording medium is discharged to said tray is higher in level than an upstream portion, and said first intermediate image transfer body comprises an endless belt passed over a plurality of support members and has an upper run substantially parallel to said tray.

14. The apparatus as claimed in claim 3, wherein a path for conveying the recording medium extends such that said recording medium is conveyed from below an image transfer position where the image is to be transferred to said recording medium, and said fixing means is positioned above said image transfer position.

15. The apparatus as claimed in claim 3, further comprising a recording medium feeding device for feeding the recording medium toward an image transfer position where the image is to be transferred to said recording medium is positioned in a range below said image transfer position, wherein said second image transfer body comprises an endless belt passed over a plurality of support members and driven to rotate, and said fixing means has a fixing portion facing a surface portion of said second intermediate image transfer body that supports the recording medium moving toward said fixing means via a nip between said first intermediate image transfer body and said second intermediate image transfer body or substantially an extension of said surface.

16. The apparatus as claimed in claim 3, further comprising registering means for conveying the recording medium to an image transfer position where the image is to be transferred at a preselected timing, wherein a portion of said second intermediate image transfer body below the image transfer position is set back from a vertical line passing through said image transfer position away from said registering means so as not to interfere with said registering means.

17. The apparatus as claimed in claim 3, further comprising registering means for conveying the recording medium to an image transfer position where the image is to be transferred at a preselected timing, at least one of a portion of said first intermediate image transfer body and a portion of said second intermediate image transfer body upstream of the image transfer position in a direction of recording medium conveyance is set back from a horizontal line passing through said image transfer position away from said registering means so as not to interfere with said registering means.

18. The apparatus as claimed in claim 3, wherein said second intermediate image transfer body comprises an endless belt passed over a plurality of support members and driven to move, and said fixing means comprises heating means disposed in a loop of the endless belt.

19. The apparatus as claimed in claim 18, further comprising cooling means configured to cool said second intermediate image transfer body at a position downstream of said fixing means in a direction in which said second intermediate image transfer body moves, but upstream of an image transfer position where the image is to be transferred to the recording medium.

20. The apparatus as claimed in claim 3, wherein said second intermediate image transfer body comprises an endless belt comprising a heat-resistant base coated whose surface is covered with a parting layer.

21. The apparatus as claimed in claim 20, further comprising cooling means configured to cool said second intermediate image transfer body at a position downstream of said fixing means in a direction in which said second intermediate image transfer body moves, but upstream of an image transfer position where the image is to be transferred to the recording medium.

22. The apparatus as claimed in claim 3, further comprising a housing made up of a stationary housing and a movable housing openable relative to said stationary housing at a boundary defined by a path for conveying the recording medium, wherein said fixing means comprises first heating means and second heating means between which the recording medium passes, said first heating means and second heating means are respectively mounted on said stationary housing and said movable housing such that when said movable housing is opened, said first heating means and said second heating means are moved away from each other, and said first intermediate image transfer body and said second intermediate image transfer body are respectively mounted on said stationary housing and said movable housing such that when said movable housing is opened, said first intermediate image transfer body and said second intermediate image transfer body are moved away from each other.

23. The apparatus as claimed in claim 22, wherein said third image transferring means is mounted on said stationary housing such that when said movable housing is opened, said third image transferring means is exposed to an outside of said housing.

24. The apparatus as claimed in claim 22, wherein when said movable housing is opened, at least one of said first intermediate image transfer body and said second intermediate image transfer body is removable from said housing.

25. The apparatus as claimed in claim 3, further comprising a housing made up of a stationary housing and a movable housing openable relative to said stationary housing at a boundary defined by a path for conveying the recording medium, wherein said first intermediate image transfer body and said second intermediate image transfer body are respectively mounted on said movable housing and said stationary housing such that when said movable housing is opened, said first intermediate image transfer body and said second intermediate image transfer body are moved away from each other.

26. The apparatus as claimed in claim 25, wherein said third image transferring means is mounted on said movable housing such that when said movable housing is opened, said third image transferring means is exposed to an outside of said housing.

27. The apparatus as claimed in claim 25, wherein when said movable housing is opened, at least one of said first intermediate image transfer body and said second intermediate image transfer body is removable from said housing.

28. The apparatus as claimed in claim 3, wherein said first intermediate image transfer body and said second intermediate image transfer body each comprise an endless belt passed over a plurality of support members and driven to move, said first intermediate image transfer body has a height smaller than a width in a horizontal direction, said second intermediate image transfer body has a height greater than a width in the horizontal direction, and a path for conveying the recording medium and said first intermediate image transfer body are positioned relative to each other such that said recording medium passes one end of said first intermediate image transfer body in the vertical direction, said apparatus further comprising: registering means for conveying the recording medium toward an image transfer position where the image is to be transferred to said recording medium at a preselected timing, said registering means being positioned in a range between said image transfer position and a bottom of said second intermediate image transfer body in a direction of height; and a first recording medium feeding device and a second recording medium feeding device configured to feed the recording medium each, wherein said first recording medium feeding device is positioned below said first intermediate image transfer body, said second recording medium feeding device is positioned such that a leading edge of the recording medium fed therefrom lies in a range below said second intermediate image transfer body, and said second recording medium feeding device protrudes to an outside of a housing of said apparatus.

29. The apparatus as claimed in claim 28, further comprising an exposing device positioned below said first intermediate image transfer body for exposing said plurality of image carriers to thereby form latent images on said plurality of image carriers.

30. The apparatus as claimed in claim 28, wherein said housing comprises a stationary housing and a movable housing openable relative to said stationary housing, and assuming that a path extending from said first recording medium feeding device to said registering means is a first path, and that a path extending from said second recording medium feeding means to said first path is a second path, then said movable housing is positioned relative to said first path and said second path such that when said movable housing is opened, said first path and said second path both are uncovered.

31. The apparatus as claimed in claim 30, wherein said registering means comprises a registration roller pair made up of a first roller and a second roller that are respectively mounted on said stationary housing and said movable housing, said apparatus further comprising: first impurity removing means and second impurity removing means for respectively cleaning a surface of said first roller and a surface of said second roller; and a first impurity storing member and a second impurity storing member for respectively storing impurities collected by said first impurity removing means and said second impurity removing means, wherein said first impurity storing member and said second impurity storing member are positioned at opposite sides of said first path, and said first impurity removing means and said first impurity storing member are mounted on said stationary housing while said second impurity removing means and said second impurity storing member are mounted on said movable housing.

32. The apparatus as claimed in claim 30, further comprising: a cleaning unit for cleaning a surface of said second intermediate image transfer body; and a waste toner storing member for storing toner, which is left on said second intermediate image transfer body after image transfer, collected by said cleaning unit, wherein said waste toner storing member and said cleaning unit are mounted on said movable housing with said waste toner storing member adjoining said second impurity storing member.

33. The apparatus as claimed in claim 32, wherein when said movable housing is opened, at least one of said waste toner storing member and said second impurity storing member is removable from said movable housing.

34. The apparatus as claimed in claim 32, wherein said waste toner storing member and said second impurity storing member are constructed integrally with each other.

35. The apparatus as claimed in claim 32, wherein said first impurity storing member, said second impurity storing member and said waste toner storing member serve as guides for guiding the recording medium being conveyed.

36. The apparatus as claimed in claim 30, wherein said second path has a radius of curvature of 40 mm or above.

37. The apparatus as claimed in claim 28, wherein said first roller and said second roller of said registration roller pair contact the recording medium over an entire width of said recording medium.

38. The apparatus as claimed in claim 3, further comprising an outlet roller pair for conveying the recording medium coming out of said fixing means to a tray, wherein a path extending from said fixing means to said outlet roller pair has a radius of curvature of 40 mm or above.

39. The apparatus as claimed in claim 3, further comprising: a plurality of toner containers respectively storing toner of different colors to be replenished to a plurality of developing units; and a space for accommodating said plurality of toner containers at a position below a tray on which the recording medium passed through said fixing means is to be stacked, but above said first intermediate image transfer body; wherein said tray is openable to allow said plurality of toner containers stored in said space to be replaced.

40. The apparatus as claimed in claim 39, further comprising protecting means for protecting the toner stored in said plurality of toner containers from heat.

41. The apparatus as claimed in claim 40, wherein said protecting means comprises a heat insulating member intervening between said space and said fixing means.

42. The apparatus as claimed in claim 40, wherein said protecting means bifunctions as heat insulating means intervening between a cleaning unit, which cleans a surface of said first intermediate image transfer body after transfer of the first image and the second image, and said fixing means.

43. The apparatus as claimed in claim 40, wherein said protecting means comprises means for causing air to flow between said space and said fixing means.

44. The apparatus as claimed in claim 40, wherein said protecting means comprises a cover surrounding at least one of said plurality of toner containers.

45. The apparatus as claimed in claim 3, further comprising: a plurality of toner containers respectively storing toner of different colors to be replenished to a plurality of developing units; a space for accommodating said plurality of toner containers at a position below a tray on which the recording medium passed through said fixing means is to be stacked, but above said first intermediate image transfer body; and a door positioned below a tray on which the recording medium passed through said fixing means is to be stacked, and openable to allow said plurality of toner containers stored in said space to be replaced.

46. The apparatus as claimed in claim 45, further comprising protecting means for protecting the toner stored in said plurality of toner containers from heat.

47. The apparatus as claimed in claim 46, wherein said protecting means comprises a heat insulating member intervening between said space and said fixing means.

48. The apparatus as claimed in claim 46, wherein said protecting means bifinctions as heat insulating means intervening between a cleaning unit, which cleans a surface of said first intermediate image transfer body after transfer of the first image and the second image, and said fixing means.

49. The apparatus as claimed in claim 46, wherein said protecting means comprises means for causing air to flow between said space and said fixing means.

50. The apparatus as claimed in claim 46, wherein said protecting means comprises a cover surrounding at least one of said plurality of toner containers.

51. The apparatus as claimed in claim 3, further comprising a reading unit for reading a document, said reading unit being positioned above a tray on which the recording medium passed through said fixing means is to be stacked.

52. The apparatus as claimed in claim 51, wherein said reading unit comprises first reading means and second reading means for respectively reading images printed on both sides of the document while said document is in conveyance.

53. The apparatus as claimed in claim 3, wherein said apparatus is selectively operable in a mode in which the first image and the second image are transferred to opposite sides of the recording medium or a mode in which a composite toner image formed on said first intermediate image transfer body is directly transferred to the recording medium and said recording medium carrying only said composite toner image is passed through said fixing means.

54. The apparatus as claimed in claim 3, further comprising a tray on which the recording medium passed through said fixing means is to be stacked, wherein said tray, said first intermediate image transfer body and said second intermediate image transfer body are positioned relative to each other such that said recording medium is stacked on said tray with the image transferred from said first intermediate image transfer body facing downward.

55. The apparatus as claimed in claim 3, further comprising a first tray and a second tray to which the recording medium passed through said fixing means is selectively stacked, wherein said first tray, said second tray, said first intermediate image transfer body and said second intermediate image transfer body are positioned relative to each other such that the image transferred from said first intermediate image transfer body to the recording medium faces downward when said recording medium is stacked on said first tray or faces upward when said recording medium is stacked on said second tray, and switching means is provided for steering the recording medium to either one of said first tray and said second tray.

56. The apparatus as claimed in claim 3, wherein said apparatus is selectively operable in a mode in which the first image and the second image are transferred to opposite sides of the recording medium or a mode in which a composite toner image formed on said first intermediate image transfer body is transferred to said recording medium by way of said second intermediate image transfer body and said recording medium carrying only said composite toner image is passed through said fixing means.

57. The apparatus as claimed in claim 3, wherein said apparatus is operable in a mode in which the toner image is transferred from any one of said plurality of image carriers to said first intermediate image transfer body and then transferred from said first intermediate image transfer body to the recording medium.

58. The apparatus as claimed in claim 3, wherein said first intermediate image transfer body has a higher volume resistance than said second intermediate image transfer body.

59. The apparatus as claimed in claim 3, wherein said first intermediate image transfer body has a higher surface resistivity than said second intermediate image transfer body.

60. An image forming system comprising: an image forming apparatus; and a host connected to said image forming apparatus; said image forming apparatus comprising: a plurality of image carriers on each of which a toner image of a particular color is formed; a first intermediate image transfer body to which toner images of different colors formed on said plurality of image carriers are transferred one above the other to thereby form a first composite image; a second intermediate image transfer body to which the first composite image is transferred; first image transferring means for electrostatically transferring the toner images from said plurality of image carriers to said first intermediate image transfer body; second image transferring means for electrostatically transferring the first composite image from said first intermediate image transfer body to said second intermediate image transfer body; third image transferring means for transferring the first composite image from said second image transfer body to one side of a recording medium; fourth image transferring means for transferring to the other side of the recording medium a second composite image formed on said first intermediate image transfer body by transferring toner images of different colors respectively formed on said plurality of image carriers; and fixing means for fixing the first composite image and the second composite image of the recording medium.

61. An image forming apparatus comprising: a plurality of image carriers; a first intermediate image transfer body; a second intermediate image transfer body; and control means for controlling an image forming process; wherein a composite toner image formed on said first intermediate image transfer body by transferring toner images of different color from said plurality of image carriers is transferred to said second intermediate image transfer body and then from said second intermediate image transfer body to one side of a recording medium while a next composite toner image is transferred from said first intermediate image transfer body to the other side of said recording medium, and said control means adjoins at least one of said first intermediate image transfer body and said second intermediate image transfer body.

62. The apparatus as claimed in claim 61, wherein said second intermediate image transfer body comprises a 50 .mu.m to 500 .mu.m thick base formed of polyimide or polyamideimide and a 1.5 mm to 3 mm thick rib formed of rubber and provided on said rib for preventing said second intermediate image transfer body from skewing.

63. The apparatus as claimed in claim 61, further comprising: a host capable of setting and controlling the image forming process.

64. An image forming apparatus comprising: a plurality of image carriers; a first intermediate image transfer body; a second intermediate image transfer body; a plurality of image forming means each for forming a toner image of a particular color on a particular one of said plurality of image carriers; first control means adjoining said first intermediate image transfer body for controlling an image forming process; and second control means adjoining said second intermediate image transfer body for controlling the image forming process, wherein a composite toner image formed on said first intermediate image transfer body by transferring toner images of different color from said plurality of image carriers is transferred to said second intermediate image transfer body and then from said second intermediate image transfer body to one side of a recording medium while a next composite toner image is transferred from said first intermediate image transfer body to the other side of said recording medium.

65. The apparatus as claimed in claim 64, wherein said first intermediate image transfer body and said second intermediate image transfer body each comprise an endless belt, and said first control means and said second control means are respectively disposed in a loop of said first intermediate image transfer body and a loop of said second intermediate image transfer body.

66. The apparatus as claimed in claim 65, wherein said first control means and said second control means each comprise a timing mark positioned on an inner surface of the belt and sensing means for sensing said timing mark.

67. The apparatus as claimed in claim 66, wherein said timing mark comprises a mark printed on the inner surface of the belt.

68. The apparatus as claimed in claim 66, wherein said timing mark is formed on a rib provided on an inner surface of the belt.

69. The apparatus as claimed in claim 66, wherein said timing mark comprises a recess formed in a rib provided on an edge of an inner surface of the belt for preventing said belt from skewing.

70. The apparatus as claimed in claim 66, wherein said timing mark is formed on a rib provided on an edge of an inner surface of the belt for preventing said belt from skewing and is visible from a side of said belt.

71. The apparatus as claimed in claim 66, wherein said sensing means comprises non-contact type sensing means located at a side of the belt.

72. The apparatus as claimed in claim 66, wherein said plurality of image carriers are arranged side by side along said first intermediate image transfer body, toner images formed on said plurality of image carriers by said plurality of image forming means are transferred to said first intermediate image transfer body one above the other to form a composite toner image, and formation of images on said plurality of image carriers is controlled on the basis of an output of said sensing means of said first control means representative of said timing mark.

73. The apparatus as claimed in claim 66, wherein a timing for transferring the toner images from said plurality of image carriers to said first intermediate image transfer body is controlled on the basis of an output of said sensing means of said first control means representative of said timing mark.

74. The apparatus as claimed in claim 66, wherein a timing for transferring the composite toner image from said first intermediate image transfer body to said second intermediate image transfer body is controlled on the basis of an output of said sensing means of said first control means representative of said timing mark.

75. The apparatus as claimed in claim 66, wherein conveyance of the recording medium is controlled on the basis of an output of said sensing means of said first control means and an output of said sensing means of said second control means representative of said timing mark.

76. The apparatus as claimed in claim 64, wherein said second intermediate image transfer body comprises a 50 .mu.m to 500 .mu.m thick base formed of polyimide or polyamideimide and a 1.5 mm to 3 mm thick rib formed of rubber and provided on said rib for preventing said second intermediate image transfer body from skewing.

77. The apparatus as claimed in claim 64, further comprising: a host capable of setting and controlling the image forming process.

78. An image forming apparatus comprising: a plurality of image carriers; a first intermediate image transfer body; a second intermediate image transfer body comprising an endless belt; a plurality of image forming means each for forming a toner image of a particular color on a particular one of said plurality of image carriers; a timing mark provided on said second intermediate image transfer body; and sensing means adjoining said second intermediate image transfer body for sensing said timing mark, wherein a composite toner image formed on said first intermediate image transfer body by transferring toner images of different color from said plurality of image carriers is transferred to said second intermediate image transfer body and then from said second intermediate image transfer body to one side of a recording medium while a next composite toner image is transferred from said first intermediate image transfer body to the other side of said recording medium, and a movement of said second intermediate image transfer body is stopped after an image forming process on the basis of an output of said sensing means representative of said timing mark.

79. The apparatus as claimed in claim 78, further comprising stop data storing means for storing a last stop position of said second intermediate image transfer body, wherein said second intermediate image transfer body is so controlled on the basis of said last stop position as not to stop at a position coincident with said last stop position.

80. The apparatus as claimed in claim 79, wherein to stop said second intermediate image transfer belt, a motor is controlled on the basis of a period of time counted by a counter since a time when said sensing means has sensed said timing mark.

81. The apparatus as claimed in claim 78, wherein said second intermediate image transfer body is driven by a stepping motor.

82. The apparatus as claimed in claim 78, wherein a stop of said second intermediate image transfer body is controlled in a particular manner in each of a simplex print mode and a duplex print mode.

83. The apparatus as claimed in claim 78, wherein image transferring means for transferring the composite toner image from said second intermediate image transfer body to the one side of the recording medium does not contact the recording medium.

84. The apparatus as claimed in claim 78, wherein said second intermediate image transfer body comprises a 50 .mu.m to 500 .mu.m thick base formed of polyimide or polyamideimide and a 1.5 mm to 3 mm thick rib formed of rubber and provided on said rib for preventing said second intermediate image transfer body from skewing.

85. The apparatus as claimed in claim 78, further comprising: a host capable of setting and controlling the image forming process.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of forming images on both sides of a single sheet or recording medium, an apparatus for practicing the method, and an image forming system using the apparatus.

2. Description of the Background Art

Various image forming apparatuses including electrophotographic copiers, facsimile apparatuses, printers and multiplex machines having at least two of their functions are extensively used today. For example, an image forming apparatus of the type capable of producing a duplex print carrying images on both sides thereof is known in the art. This type of apparatus transfers toner images of different colors formed on image carriers to one side of a sheet one above the other, fixes the resulting composite image, and then switches back, the sheet to thereby turn it. Subsequently, the apparatus again feeds the same sheet to the image carriers so as to transfer the next toner images of different colors from the image carriers to the other side of the sheet and then fixes the resulting composite image.

A problem with the image forming apparatus of the type described is that it has to switch back the sheet carrying the image on one side thereof and again feed it to the image carriers, resulting in a long image forming time and therefore low productivity. Another problem is that the sheet carrying the image only on one side thereof is apt to curl due to fixation, making conveyance unreliable.

Japanese Patent Laid-Open Publication No. 8-160703, for example, discloses an image forming apparatus capable of producing a duplex, color print with a single photoconductive element and two intermediate image transfer belts. This image forming apparatus includes a plurality of developing units each storing toner of particular color arranged around the photoconductive element. Toner images of different colors are sequentially formed on the photoconductive element while being sequentially transferred to a first intermediate image transfer belt one above the other, completing a full-color image. Subsequently, the full-color image is transferred from the first intermediate image transfer belt to a second intermediate image transfer belt. Thereafter, another full-color image is formed on the first intermediate image transfer belt in exactly the same manner as the previous full-color image. The two-full-color images are respectively transferred from the second and first belts to both sides of a sheet.

Japanese Patent Laid-Open Publication No. 9-258518 teaches a color image forming apparatus with a duplex print capability and also including a single photoconductive element and two intermediate image transfer belts. A plurality of developing units each storing toner of particular color are arranged around the photoconductive element. Exposure and development are repeated color by color to thereby form a full-color image on the photoconductive element. The full-color image is transferred from the photoconductive element to a first image transfer body and therefrom to a toner image acceptor or second intermediate image transfer body. Subsequently, another full-color image is transferred from the photoconductive element to the first intermediate image transfer body. The two full-color images are respectively transferred to opposite sides of a sheet from the toner image acceptor and first intermediate image transfer body.

However, the apparatus of Laid-Open Publication No. 8-160730 has the following problem left unsolved. In the full-color print mode, a toner image of one color is formed on the photoconductive element and transferred to the first intermediate image transfer body for a single rotation of the element, so that a single full-color image to be transferred to one side of a sheet is completed by four rotations of the element in total. Such a procedure is time-consuming and lower in productivity.

On the other hand, the apparatus of Laid-Open Publication No. 9-258518 uses four exposing units and four chargers for forming a full-color image on the photoconductive element and then transferring it to the intermediate image transfer body, reducing the image forming time. However, the exposing units are arranged within the photoconductive element, which is transparent for light. The photoconductive element therefore must be provided with a particular characteristic and a particular configuration and cannot be made compact. Further, a wasteful space exists around the intermediate image transfer body, increasing the overall size of the apparatus. In addition, charging and development repeated in the vicinity of a position where toner exists make it difficult to insure a stable image forming process.

Although the apparatuses of Laid-Open Publications stated above have some problems left unsolved, they solve to some extent the problem that the switchback of a sheet and the curl of a sheet ascribable to fixation obstruct reliable sheet conveyance. Neither one of them, however, gives consideration to the accurate register of images transferred to opposite sides of a sheet.

Moreover, assume that an intermediate image transfer belt or image carrier, which is passed over rollers, is brought to a stop at the same position every time image formation ends. Then, the belt is apt to curl complementarily to the circumference of each roller. The curl appears in the form of a projection on the belt and obstructs the close contact of an image carried on the belt and a sheet in the event of transfer, thereby rendering the image blurred or otherwise defective on the sheet. This is particularly true with a duplex print type image forming apparatus using non-contact type image transferring means.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a method and an apparatus capable of forming color images on both sides of a sheet in a short period of time, and an image forming system using the same.

It is another object of the present invention to provide a method and an apparatus capable of forming images on both sides of a sheet in accurate register, and an image forming system using the same.

It is a further object of the present invention to provide a method and an apparatus capable of insuring close contact of an intermediate image transfer belt and a sheet by obviating a curl to thereby obviate defective images, and an image forming system using the same. In accordance with the present invention, an image forming method begins with a step of electrostatically transferring toner images of different colors formed on a plurality of image carriers to a first intermediate image transfer body one above the other to thereby form a first composite image. The first composite image is electrostatically transferred from the first intermediate image transfer body to a second intermediate image transfer body and therefrom to one side of a sheet. A second composite image formed on the first intermediate image transfer body in exactly the same manner as the first image is electrostatically transferred from the first intermediate image transfer body to the other side of the same sheet. The first and second composite images are fixed on the recording medium at the same time.

Also, in accordance with the present invention, an image forming apparatus includes a plurality of image carriers on each of which a toner image of particular color is formed. Toner images of different colors formed on the image carriers are transferred to a first intermediate image transfer body one above the other to thereby form a first composite image. The first composite image is transferred from the first intermediate image transfer body to a second intermediate image transfer body. A first image transferring device electrostatically transfers the toner images from each image carrier to the first intermediate image transfer body. A second image transferring device electrostatically transferring the first composite image from the first intermediate image transfer body to the second intermediate image transfer body. A third image transferring device transfers the first composite image from the second image transfer body to one side of a sheet. A fourth image transferring device transfers to the other side of the recording medium a second composite image formed on the first intermediate image transfer body in exactly the same manner as the first composite. A fixing unit fixes the first and second composite images of the sheet at the same time.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description taken with the accompanying drawings in which:

FIG. 1 is a vertical section showing a first embodiment of the image forming apparatus in accordance with the present invention;

FIG. 2 is a view showing a first intermediate image transfer body included in the illustrative embodiment;

FIG. 3 is a fragmentary section showing a movable housing included in the illustrative embodiment in an open position;

FIG. 4 is a vertical section showing a second embodiment of the present invention;

FIG. 5 is a fragmentary section showing a movable housing included in the second embodiment in an open position;

FIG. 6 is a vertical section showing a third embodiment of the present invention;

FIG. 7 is a vertical section showing a fourth embodiment of the present invention;

FIG. 8 is a view showing a first and a second intermediate image transfer body included in the fourth embodiment;

FIG. 9 is a section showing a movable housing included in the fourth embodiment in an open position;

FIG. 10 is an isometric view showing a specific image forming system available with the present invention;

FIG. 11 is a view similar to FIG. 10, showing another specific image forming system;

FIG. 12 is an isometric view showing a specific configuration of the image forming apparatus of the present invention additionally including a scanner;

FIG. 13 is a perspective view of a stand included in the configuration of FIG. 12;

FIG. 14 is a section of the apparatus shown in FIG. 12;

FIG. 15 is a view showing an image sensor included in the scanner;

FIG. 16 is a vertical section showing a fifth embodiment of the present invention;

FIG. 17 shows an image transfer roller included in the fifth embodiment and playing the role of second and fourth image transferring means;

FIG. 18 shows a support roller included in the fifth embodiment and playing the role of the second and fourth image transferring means;

FIG. 19 shows a first intermediate image transfer body included in the fifth embodiment;

FIG. 20 is a section showing a movable housing included in the fifth embodiment in an open position;

FIG. 21 is a section showing a sixth embodiment of the present invention;

FIGS. 22A and 22B show timing marks particular to the sixth embodiment;

FIG. 23 shows a second intermediate image transfer body included in the sixth embodiment;

FIG. 24 is a view for describing a curl to appear on the second intermediate image transfer body;

FIG. 25 is a view demonstrating how the curl of FIG. 24 degrades image quality;

FIG. 26 is a timing chart representative of a control procedure to be executed by the sixth embodiment in the duplex print mode;

FIG. 27 is a timing chart representative of a control procedure to be executed in the simplex print mode;

FIGS. 28A and 28B show another specific configuration of the timing mark;

FIGS. 29A through 29D show other specific configurations of the timing mark;

FIG. 30 is a schematic block diagram showing a specific control system of the present invention;

FIG. 31 illustrates an endless belt having a heat resistant base covered with a parting layer; and

FIG. 32 illustrates a registration roller contacting an image recording medium.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1 of the drawings, a first embodiment of the image forming apparatus in accordance with the present invention is shown and implemented as a printer by way of example. As shown, the printer includes a housing 1 in which a plurality of (four in the illustrative embodiment) photoconductive drums 2Y (yellow), 2M (magenta), 2C (cyan) and 2BK (black) are arranged side by side. The drums 2Y through 2BK are a specific form of image carriers. A toner image of particular color is to be formed on each of the drums 2Y through 2BK. While the colors of toner images to be formed on the drums 2Y through 2BK are open to choice, a yellow, a magenta, a cyan and a black toner image are assumed to be formed on the drums 2Y through 2BK, respectively.

The drums 2Y through 2BK each may be replaced with an image carrier implemented as an endless photoconductive belt passed over a plurality of rollers. The drums 2Y through 2BK each may be made up of a hollow, cylindrical aluminum core having a diameter of 30 mm to 100 mm and a photoconductive, organic semiconductor layer formed on the core.

The drums 2Y through 2BK are held in contact with a first intermediate image transfer body 3, which is implemented as an endless belt in the illustrative embodiment. The intermediate image transfer body (first belt hereinafter) 3 is pa