Color image forming apparatus having shiftable transfer conveyor belt and attraction assisting roller

• US 5,765,082 A
• Filed: 11/19/1996
• Issued: 06/09/1998
• Est. Priority Date: 11/20/1995
• Status: Expired due to Term

• Current Assignee: Casio Computer Company Limited, Casio Electronic Technology Company Limited (Casio Computer Company Limited)
• Original Assignee: Casio Computer Company Limited
• Inventors: Hagiwara, Kazuyoshi, Abe, Tetsuya, Numazu, Toshihiko
• Primary Examiner(s): BEATTY, ROBERT B
• Application Number:
  US08/751,814
• Time in Patent Office: 567 Days
• Field of Search: 399/299, 399/303, 399/312, 399/317, 399/316
• US Class Current: 399/299
• CPC Class Codes: G03G 15/01 for producing multicoloured copies colour correction in photography G03C; colour correction in printing plate production
• CPC Class Codes: G03G 15/0131 for transferring a pattern to a second base
• CPC Class Codes: G03G 15/0194 primary transfer to the final recording medium G03G15/0184 takes precedence
• CPC Class Codes: G03G 2215/0103 Plural electrographic recording members
• CPC Class Codes: G03G 2215/0119 Linear arrangement adjacent plural transfer points
• CPC Class Codes: G03G 2215/0141 the linear arrangement being horizontal

Abstract

An image forming apparatus includes a plurality of image carriers arranged side by side along the outer surface of a conveying portion of a transfer belt. The transfer belt is stretched between a first upstream roller and a second downstream roller. An image forming medium is conveyed on the belt so as to have multiple color images transferred thereto. The transfer belt has a swing lever so as to move the belt between a horizontal full color position and an inclined monochrome position. A stationary support roller which is arranged within the transfer belt and at a position nearer to the second downstream roller maintains a position of the image forming medium constant even when a monochrome image is being transferred. In addition, an electrostatic attraction roller located outside the transfer belt is arranged at a specific angle relative to the first roller to assist in the attraction of the image forming medium to the transfer belt.

Claims

1. An image forming apparatus for forming an image on an image recording medium supplied from an image recording medium supply unit, said apparatus comprising:

first and second rollers arranged separate from each other, at least one of the first and second rollers being supplied with a rotation force;

a conveyor belt stretched between the first and second rollers for attracting the image recording medium supplied from the image recording medium supply unit onto an outer surface of a conveying portion of the conveyor belt between the first and second rollers, said conveyor belt being circulated by the first and second rollers to convey the image recording medium from one of the first and second rollers toward the other of the first and second rollers, such that;

(i) the first roller is positioned at an upstream end of the outer surface of the conveying portion of the conveyor belt in a moving direction of the outer surface of the conveying portion of the conveyor belt, (ii) the second roller is positioned at a downstream end of the outer surface of the conveying portion of the conveyor belt in the moving direction, and (iii) the image recording medium is introduced onto the outer surface of the conveying portion of the conveyor belt at the upstream end thereof;

plurality of image carriers arranged side by side along the outer surface of the conveying portion of the conveyor belt, at least one of the image carriers being in contact with the image recording medium on the outer surface of the conveying portion of the conveyor belt;

a plurality of toner image forming devices for forming toner images of respective predetermined different colors on the image carriers;

a plurality of image transfer devices arranged in a space encircled by the conveyor belt such that the plurality of transfer devices are opposite to the plurality of image carriers with the conveying portion of the conveyor belt being interposed therebetween, wherein at least one of the image transfer devices which is opposite to the at least one of the image carriers which is in contact with the image recording medium is applied with an image transfer bias to transfer a given toner image from the at least one of the image carriers to the image recording medium; and

an attraction assisting roller arranged to press the conveyor belt on the first roller so that the conveyor belt, together with the image recording medium supplied to the upstream end of the outer surface of the conveying portion of the conveyor belt, is pinched by the attraction assisting roller and the first roller, so that the image recording medium is assisted to be attracted onto the outer surface of the conveying portion of the conveyor belt, wherein the attraction assisting roller has a positional relationship with respect to the first roller and the outer surface of the conveying portion of the conveyor belt such that a line passing a rotation center of the attraction assisting roller and a rotation center of the first roller intersects at an angle of less than 90°

with a line extending along a direction in which the outer surface of the conveying portion of the conveyor belt extends from a conveyor belt pinch point at which the attraction assisting roller and the first roller pinch the conveyor belt.

2. An image forming apparatus according to claim 1, further comprising an attraction bias application mechanism for applying an attraction bias on the attraction assisting roller.

3. An image forming apparatus according to claim 2, wherein the attraction bias application mechanism applies to the attraction assisting roller a voltage of a same polarity as a predetermined polarity of the image transfer bias.

4. An image forming apparatus according to claim 3, wherein the at least one of the image carriers which is in contact with the image recording medium on the outer surface of the conveying portion of the conveyor belt is located nearer to the second roller than the other image carriers, and wherein the image forming apparatus further comprises:

a belt moving mechanism for moving the conveyor belt between a mono-color image transfer position wherein the conveyor belt is in contact with the image carrier nearer to the second roller and a full-color image transfer position wherein the conveyor belt is in contact with all of the image carriers, wherein the belt moving mechanism maintains a position of the image recording medium constant relative to the image carrier nearer to the second roller when the image recording medium on the outer surface of the conveying portion of the conveyor belt arrives at the image carrier nearer to the second roller and while the conveyor belt is in the mono-color image transfer position and the full-color image transfer position; and

a belt movement controller for controlling an operation of the belt moving mechanism to selectively move the conveyor belt between the mono-color image transfer position and the full-color image transfer position, wherein a range of the movement of the conveyor belt between the mono-color image transfer position and the full-color image transfer position is so set that the positional relationship of the attraction assisting roller with respect to the first roller and the outer surface of the conveying portion of the conveyor belt is maintained while the conveyor belt is in the mono-color image transfer position and the full-color image transfer position.

5. An image forming apparatus according to claim 4, wherein the attraction bias application device applies the attraction bias to the attraction assisting roller when the belt moving mechanism moves the conveyor belt to the mono-color image transfer position.

6. An image forming apparatus according to claim 4, wherein the one of the toner image forming devices corresponding to the image carrier nearer to the second roller forms a black toner image, and the other toner image forming devices corresponding to the other image carriers form color toner images other than black.

7. An image forming apparatus according to claim 2, wherein the at least one of the image carriers which is in contact with the image recording medium on the outer surface of the conveying portion of the conveyor belt is located nearer to the second roller than the other image carriers, and wherein the image forming apparatus further comprises:

a belt moving mechanism for moving the conveyor belt between a mono-color image transfer position wherein the conveyor belt is in contact with the image carrier nearer to the second roller and a full-color image transfer position wherein the conveyor belt is in contact with all of the image carriers, wherein the belt moving mechanism maintains a position of the image recording medium constant relative to the image carrier nearer to the second roller when the image recording medium on the outer surface of the conveying portion of the conveyor belt arrives at the image carrier nearer to the second roller and while the conveyor belt is in the mono-color image transfer position and the full-color image transfer position; and

a belt movement controller for controlling an operation of the belt moving mechanism to selectively move the conveyor belt between the mono-color image transfer position and the full-color image transfer position, wherein a range of the movement of the conveyor belt between the mono-color image transfer position and the full-color image transfer position is so set that the positional relationship of the attraction assisting roller with respect to the first roller and the outer surface of the conveying portion of the conveyor belt is maintained while the conveyor belt is in the mono-color image transfer position and the full-color image transfer position.

8. An image forming apparatus according to claim 7, wherein the one of the toner image forming devices corresponding to the image carrier nearer to the second roller forms a black toner image, and the other toner image forming devices corresponding to the other image carriers form color toner images other than black.

9. An image forming apparatus according to claim 1, wherein the at least one of the image carriers which is in contact with the image recording medium on the outer surface of the conveying portion of the conveyor belt is located nearer to the second roller than the other image carriers, and wherein the image forming apparatus further comprises:

a belt moving mechanism for moving the conveyor belt between a mono-color image transfer position wherein the conveyor belt is in contact with the image carrier nearer to the second roller and a full-color image transfer position wherein the conveyor belt is in contact with all of the image carriers, wherein the belt moving mechanism maintains a position of the image recording medium constant relative to the image carrier nearer to the second roller when the image recording medium on the outer surface of the conveying portion of the conveyor belt arrives at the image carrier nearer to the second roller and while the conveyor belt is in the mono-color image transfer position and the full-color image transfer position; and

a belt movement controller for controlling an operation of the belt moving mechanism to selectively move the conveyor belt between the mono-color image transfer position and the full-color image transfer position, wherein a range of the movement of the conveyor belt between the mono-color image transfer position and the full-color image transfer position is so set that the positional relationship of the attraction assisting roller with respect to the first roller and the outer surface of the conveying portion of the conveyor belt is maintained while the conveyor belt is in the mono-color image transfer position and the full-color image transfer position.

10. An image forming apparatus according to claim 9, wherein the one of the toner image forming devices corresponding to the image carrier nearer to the second roller forms a black toner image, and the other toner image forming devices corresponding to the other image carriers form color toner images other than black.

11. An image forming apparatus for forming an image on an image recording medium supplied from an image recording medium supply unit, comprising:

first and second rollers arranged separate from each other, at least one of the first and second rollers being supplied with a rotation force;

a conveyor belt stretched between the first and second rollers for attracting the image recording medium supplied from the image recording medium supply unit onto an outer surface of a conveying portion of the conveyor belt between the first and second rollers, said conveyor belt being circulated by the first and second rollers to convey the image recording medium from one of the first and second rollers toward the other of the first and second rollers, such that;

(i) the first roller is positioned at an upstream end of the outer surface of the conveying portion of the conveyor belt in a moving direction of the outer surface of the conveying portion of the conveyor belt, (ii) the second roller is positioned at a downstream end of the outer surface of the conveying portion of the conveyor belt in the moving direction, and (iii) the image recording medium is introduced onto the outer surface of the conveying portion of the conveyor belt at the upstream end thereof;

a plurality of image carriers arranged side by side along the outer surface of the conveying portion of the conveyor belt, wherein at least one of the image carriers, including the one of the image carriers located nearer to the second roller than the other image carriers, is in contact with the image recording medium on the outer surface of the conveying portion of the conveyor belt;

a plurality of toner image forming devices for forming toner images of respective predetermined different colors on the image carriers;

a plurality of image transfer devices arranged in a space encircled by the conveyor belt such that the plurality of transfer devices are opposite to the plurality of image carriers with the conveying portion of the conveyor belt being interposed therebetween, wherein at least one of the image transfer devices which is opposite to the at least one of the image carriers which is in contact with the image recording medium transfers a given toner image from the at least one of the image carriers to the image recording medium;

a belt moving mechanism for moving the conveyor belt between a mono-color image transfer position wherein the conveyor belt is in contact with the image carrier nearer to the second roller and a full-color image transfer position wherein the conveyor belt is in contact with all of the image carriers, wherein the belt moving mechanism includes;

(i) a stationary support roller which is arranged in the space encircled by the conveyor belt between the image transfer device opposite to the image carrier nearer to the second roller and the image transfer device opposite to the one of the image carriers next nearer to the second roller, said stationary support roller always contacting an inner surface of the conveying portion of the conveyor belt to maintain a position of the image recording medium constant relative to the image carrier nearer to the second roller when the image recording medium on the outer surface of the conveying portion of the conveyor belt arrives at the image carrier nearer to the second roller and while the conveyor belt is in the mono-color image transfer position and the full-color image transfer position, and (ii) a swing member which is swingable on a rotational axis of the stationary support roller to move the conveyor belt selectively to one or both of the mono-color image transfer position and the full-color image transfer position; and

a belt movement controller for controlling the swing movement of the swing member.

12. An image forming apparatus according to claim 11, wherein the swing member includes a movable support roller arranged in the space encircled by the conveyor belt between the first roller and the one of the image transfer devices which is located nearer to the first roller, said movable support roller being moved to intersect the inner surface of the conveying portion of the conveyor belt by the swing movement of the swing member, whereby the movable support roller moves the conveyor belt between the mono-color image transfer position and the full-color image transfer position.

13. An image forming apparatus according to claim 11, wherein the swing member supports the image transfer devices other than the image transfer device nearer to the second roller so as to move the other image transfer devices by the swing movement of the swing member.

14. An image forming apparatus according to claim 11, further comprising a roller support mechanism for supporting the first and second rollers to fix the first and second rollers to the apparatus and to fix a positional relationship between the first roller and the image recording medium supply unit.

15. An image forming apparatus according to claim 11, wherein the one of the toner image forming devices corresponding to the image carrier nearer to the second roller forms a black toner image, and the other toner image forming devices corresponding to the other image carriers form color toner images other than black.

16. An image forming apparatus for forming an image on an image recording medium supplied from an image recording medium supply unit, comprising:

first and second rollers arranged separate from each other, at least one of the first and second rollers being supplied with a rotation force;

a conveyor belt stretched between the first and second rollers for attracting the image recording medium supplied from the image recording medium supply unit onto an outer surface of a conveying portion of the conveyor belt between the first and second rollers, said conveyor belt being circulated by the first and second rollers to convey the image recording medium from one of the first and second rollers toward the other of the first and second rollers, such that;

(i) the first roller is positioned at an upstream end of the outer surface of the conveying portion of the conveyor belt in a moving direction of the outer surface of the conveying portion of the conveyor belt, (ii) the second roller is positioned at a downstream end of the outer surface of the conveying portion of the conveyor belt in the moving direction, and (iii) the image recording medium is introduced onto the outer surface of the conveying portion of the conveyor belt at the upstream end thereof;

a plurality of image carriers arranged side by side along the outer surface of the conveying portion of the conveyor belt, wherein at least one of the image carriers, including the one of the image carriers located nearer to the second roller than the other image carriers, is in contact with the image recording medium on the outer surface of the conveying portion of the conveyor belt;

a plurality of toner image forming devices for forming toner images of respective predetermined different colors on the image carriers;

a plurality of image transfer devices arranged in a space encircled by the conveyor belt such that the plurality of transfer devices are opposite to the plurality of image carriers with the conveying portion of the conveyor belt being interposed therebetween, wherein at least one of the image transfer devices which is opposite to the at least one of the image carriers which is in contact with the image recording medium transfers a given toner image from the at least one of the image carriers to the image recording medium;

a roller support mechanism for supporting the first and second rollers to fix the first and second rollers to the apparatus and to fix a positional relationship between the first roller and the image recording medium supply unit;

a belt moving mechanism for moving the conveyor belt between a mono-color image transfer position wherein the conveyor belt is in contact with the image carrier nearer to the second roller and a full-color image transfer position wherein the conveyor belt is in contact with all of the image carriers, wherein the belt moving mechanism maintains a position of the image recording medium constant relative to the image carrier nearer to the second roller when the image recording medium on the outer surface of the conveying portion of the conveyor belt arrives at the image carrier nearer to the second roller and while the conveyor belt is in the mono-color image transfer position and the full-color image transfer position; and

a belt movement controller for controlling an operation of the belt moving mechanism to selectively move the conveyor belt between the mono-color image transfer position and the full-color image transfer position.

17. An image forming apparatus according to claim 16, further comprising:

a stationary support roller which is arranged in the space encircled by the conveyor belt between the image transfer device opposite to the image carrier nearer to the second roller and the image transfer device opposite to the one of the image carriers next nearer to the second roller, said stationary support roller always contacting an inner surface of the conveying portion of the conveyor belt to maintain a position of the image recording medium constant relative to the image carrier nearer to the second roller when the image recording medium on the outer surface of the conveying portion of the conveyor belt arrives at the image carrier nearer to the second roller and while the conveyor belt is in the mono-color image transfer position and the full-color image transfer position; and

a swing member which is swingable on a rotational axis of the stationary support roller to move the conveyor belt selectively to one or both of the mono-color image transfer position and the full-color image transfer position.