Image forming apparatus

Abstract

The image forming apparatus of the present invention includes a first and a second main conveyance path, a first and a second processing unit, a transfer unit, and a fixing unit. The first and second main conveyance paths come together after having branched apart between a paper supply unit and a paper delivery unit. A recording medium is selectively conveyed along either one of the first and second main conveyance path. Image formation is performed by a method of electrophotography by, alternatively, either the first or second processing unit. Between the first and second main conveyance paths where they are branched apart, the transfer unit generates a transfer electric field between itself and one or the other of the first and second processing unit. The fixing unit controls the temperature of a first or a second fixing roller, which are disposed in the first and second main conveyance path after they have come together, alternatively.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic figure showing the structure of an image forming apparatus according to an embodiment of the present invention;

FIG. 2A is a figure showing the initial state of a three way gate of the image forming apparatus;

FIG. 2B is a figure showing the state of the three way gate of this image forming apparatus when a sheet of paper is being conveyed in the direction of a second paper discharge conveyance path;

FIG. 2C is a figure showing the state of the three way gate of this image forming apparatus when a sheet of paper is being conveyed in the direction of a first paper discharge conveyance path;

FIG. 2D is a figure showing the state of the three way gate of this image forming apparatus when a sheet of paper is being conveyed in the direction of the second paper discharge conveyance path;

FIG. 3A is a figure showing the state of this image forming apparatus during double sided image formation, when a sheet of paper is being conveyed in the direction of the first paper discharge conveyance path;

FIG. 3B is a figure showing the state of this image forming apparatus during double sided image formation, when this sheet of paper is being switch back conveyed towards the second paper discharge conveyance path;

FIG. 3C is a figure showing the state of this image forming apparatus during double sided image formation, when this sheet of paper is being conveyed towards an auxiliary conveyance path;

FIG. 3D is a figure showing the state of this image forming apparatus during double sided image formation, when this sheet of paper is being conveyed towards a processing unit for a second time;

FIG. 4 is a figure showing the detailed structure of a transfer unit of the image forming apparatus;

FIG. 5 is a figure showing the operation of the embodiment of the image forming apparatus of the present invention during color image formation;

FIG. 6 is a figure showing the operation of the embodiment of the image forming apparatus of the present invention during monochrome image formation;

FIG. 7 is a front sectional view of a fixing unit, which is a fixing device;

FIG. 8 is a side view of the fixing unit;

FIG. 9 is a block diagram of a control unit of the image forming apparatus;

FIG. 10 is a flow chart showing the sequence of processing by the control unit, during both color and monochrome image formation;

FIG. 11 is a flow chart showing the details of surface temperature control during the processing sequence by the control unit;

FIG. 12 is a figure showing a situation during color image formation by the fixing unit;

FIG. 13 is a figure showing a situation during monochrome image formation by the fixing unit;

FIG. 14 is a figure showing the operation of an image forming apparatus according to another embodiment of the present invention, during color image formation;

FIG. 15 is a figure showing the operation of this image forming apparatus according to this other embodiment of the present invention, during monochrome image formation; and

FIG. 16 is a flow chart showing the sequence of processing by this image forming apparatus according to this other embodiment of the present invention, during both color and monochrome image formation.

Claims

1. An image forming apparatus, comprising: a paper supply unit which supplies recording medium;a paper delivery unit which stores the recording medium for which image formation processing has been completed;a conveyance path, along which the recording medium is conveyed from the paper supply unit to the paper delivery unit;first and second processing units comprising respective first and second image carrying members, upon which toner images are formed by developing image data;a transfer unit which transcribes a toner image from the first or second image carrying member, to the recording medium which is being conveyed upon the conveyance path; anda fixing unit which fixes the toner image upon the recording medium in the conveyance path, between the transfer unit and the paper delivery unit;wherein the conveyance path includes first and second main conveyance paths which branch apart between the paper supply unit and the transfer unit, and come together between the transfer unit and the fixing unit;the image forming apparatus further comprising a conveyance direction changeover member, provided upon the conveyance path, which selectively conveys paper supplied from the paper supply unit to either one of the first and second main conveyance path, according to the image data; andwherein: the first and second processing units are arranged so that the first and second image carrying members approach one another upon the first and second main conveyance paths respectively; andthe transfer unit selectively generates a transfer electric field between itself and the first or second image carrying member, according to the image data.

2. The image forming apparatus described in claim 1, wherein the first and second processing units differ in image formation processing speed,the image forming apparatus further comprising a control unit which controls the conveyance speed of the recording medium along the first and second main conveyance paths so as to accord with the image formation processing speeds.

3. The image forming apparatus described in claim 1, further comprising a conveyance direction change member which changes the conveyance direction of the recording medium from the first and second main conveyance paths to the fixing unit.

4. The image forming apparatus described in claim 1, wherein: the conveyance path comprises a conveyance belt, which is an endless belt included in the first and second main conveyance paths, and which is extended over and driven by a plurality of rollers so as to shift along a loop shaped shift path; andthe transfer unit is disposed on the inside of the shift path.

5. The image forming apparatus described in claim 4, wherein the transfer unit comprises first and second transfer devices which are disposed so as to approach the first and second image carrying members, respectively.

6. The image forming apparatus described in claim 5, further comprising a high voltage power supply which applies a common transfer voltage to the first and second transfer devices.

7. The image forming apparatus described in claim 4, wherein the plurality of rollers comprise: a first roller which is disposed in the conveyance path where the first and second main conveyance paths branch apart, and which is grounded; anda second roller which is disposed in the conveyance path where the first and second main conveyance paths come together, and which is set to an electrically floating state.

8. The image forming apparatus described in claim 4, further comprising a drive source which drives one or another of the plurality of rollers in such a manner that the direction of rotation of the plurality of rollers is selectively inverted according to the image data.

9. The image forming apparatus described in claim 5, wherein the transfer unit comprises: a support member which supports the first and second transfer devices; anda shift member which shifts the support member, so that the endless belt is pressed into contact with a one of the first and the second image carrying member upon which a toner image is formed, with a pressing contact force adapted to create a transfer region capable of transcribing the toner image onto the recording medium.

10. The image forming apparatus described in claim 9, wherein the shift member shifts the support member so as to hold that one of the first and second image carrying member upon which no toner image is formed at a predetermined distance away from the endless belt.

11. The image forming apparatus described in claim 10, wherein the predetermined distance is a distance at which toner which remains upon the one of the first and second image carrying member upon which no toner image is formed is not transcribed to the endless belt by the electric field which the first or second transfer device creates.

12. The image forming apparatus described in claim 10, wherein the predetermined distance is a distance at which electric charge originating in the electric field is not imparted to the one of the first and second image carrying member upon which no toner image is formed.

13. The image forming apparatus described in claim 1, wherein: the first processing unit forms the toner image with toners of a plurality of colors by image formation processing according to a method of electrophotography; andthe second processing unit forms the toner image with toner of a single color by image formation processing according to a method of electrophotography.

14. The image forming apparatus described in claim 1, wherein the fixing unit comprises: first and second fixing rollers, past which the recording medium passes, one of which principally performs heat processing upon the recording medium by application of heat thereto, and one of which principally performs pressurization processing upon the recording medium by pressurizing it, alternatively;first and second heaters which respectively heat up the first and second fixing rollers; anda drive changeover unit which drives the first or second heater, alternatively, according to whether a toner image formed by the first processing unit or a toner image formed by the second processing unit has been transcribed to the recording medium.

15. The image forming apparatus described in claim 14, further comprising first and second cleaning members which respectively clean the surfaces of the first and second fixing rollers.

16. The image forming apparatus described in claim 14, having a symmetrical structure on opposite sides of the conveyance path.

17. The image forming apparatus described in claim 14, wherein the consumption of electrical power by the first and second heaters during the image formation is less than or equal to the rated electrical power of the image forming apparatus.

18. The image forming apparatus described in claim 14, wherein the first and second processing units differ in image formation processing speed, and further comprising a control unit which controls the conveyance speed of the recording medium by the first and second fixing rollers, so as to accord with the image formation processing speeds.

19. The image forming apparatus described in claim 14, wherein: the first processing unit creates the toner image in a plurality of colors by image formation processing according to a method of electrophotography; andthe second processing unit creates the toner image in a single color by image formation processing according to a method of electrophotography.

20. The image forming apparatus described in claim 19, further comprising an application member which applies a release agent to the surface of that one of the first and second fixing rollers which performs heating processing during image formation based upon color image data.