Sheet curl correction apparatus and image forming apparatus

An image forming apparatus comprising:

• an image forming unit for forming an image on a sheet;
• a fixing part for thermally fixing the image to the sheet;
• and
• a sheet curl correction apparatus for correcting curl in the sheet on which the image is fixed;
• wherein the sheet curl correction apparatus comprises:
• a first roller rotating about a first rotation shaft and formed resiliently deformable;
• a second roller rotating about a second rotation shaft that is parallel to the first rotation shaft and formed from a harder material than the first roller;
• a supporting member that supports the first roller and the second roller;
• a first actuator that rotates the supporting member about a third rotation shaft;
• a first gear connected to an end of the second roller on a side closer to the first actuator;
• a second gear that engages with the first gear;
• a third gear that rotates coaxially with the second gear;
• an input gear that engages with the third gear;
• and
• a second actuator that transmits a rotational force to the input gear;
• wherein the second roller is brought into pressure contact with the first roller to bite thereinto such that a curved nip through which the sheet passes is formed between the first roller and the second roller,
• wherein the third rotation shaft extends parallel to an axial direction of the first rotation shaft in a first plane that includes a leading edge and a trailing edge of the nip, and
• wherein the first actuator causes the supporting member to rotate between a first position at which the sheet moving towards the nip is received from the leading edge of the nip and a second position at which the sheet moving towards the nip is received from the trailing edge of the nip.

A sheet curl correction apparatus that corrects curl in a sheet by passing the sheet between a first roller and a second roller, the apparatus comprising:

• a curl correction unit comprising the first roller and the second roller, and a supporting member that rotatably supports the first roller and the second roller, and is rotatable about a third rotation shaft that is parallel to a first rotation shaft of the first roller and a second rotation shaft of the second roller, the curl correction unit causing a direction of curl correction through the first roller and the second roller to switch accompanying rotation of the supporting member to;
• a first actuator that drives the supporting member to rotate;
• and
• a second actuator that drives at least one of the first roller and the second roller to rotate;
• wherein the first actuator and the second actuator are disposed on a fixing member on the sheet curl correction apparatus main portion that rotatably supports the curl correction unit, and are disposed on one end of the first rotation shaft of the first roller and the second rotation shaft of the second roller in the curl correction unit;
• and
• wherein the first actuator and the second actuator each comprise a single drive motor that is switchable between a positive rotation direction and a reverse rotation direction.

An image forming apparatus that comprises an image forming unit for forming an image based on image data processed per page, the image forming apparatus printing an image formed in the image forming unit per page on one surface of a sheet of paper and another image per page on another surface of the same sheet of paper and discharging the sheet of paper, the image forming apparatus comprising:

• a curl correction apparatus for correcting a curl produced in the sheet of paper on which the images are formed by the image forming unit, the curl correction apparatus configured to be switchable between a first condition in which curl is corrected by curving the sheet of paper towards the one surface of the sheet of paper and a second condition in which curl is corrected by curving the sheet of paper towards the other surface of the sheet of paper;
• a calculation unit for calculating a coverage rate for the one surface of the sheet of paper and a coverage rate for the other surface of the sheet of paper based on the image data prior to the image forming unit forming an image;
• a determination unit for determining whether to switch the curl correction apparatus to the first condition or to the second condition based on the coverage rate calculated by the calculation unit prior to the image forming unit forming an image;
• and
• a switching unit for switching the curl correction apparatus between the first condition and the second condition based on a result of determination determined by the determination unit prior to the image forming unit forming an image.