Medium stacker and image forming system incorporating the medium stacker

A medium stacker comprising:

• a stacking portion having a stacking face to stack a sheet medium on which an image is formed;
• a rotary portion configured to hold a leading end of the sheet medium in a sheet conveyance direction, reverse the sheet medium on the stacking face of the stacking portion, and convey the sheet medium;
• a medium holder configured to hold the sheet medium when the sheet medium is conveyed by the rotary portion;
• a medium mover configured to move the sheet medium to a predetermined position in a direction orthogonal to the sheet conveyance direction of the sheet medium while the sheet medium is held by the rotary portion;
• and
• circuitry configured to control the rotary portion and the medium mover;
• wherein the medium mover is configured to move the medium holder together with the sheet medium in a same direction as a direction of movement of the sheet medium.

A medium stacker comprising:

• a stacking portion having a stacking face to stack a sheet medium on which an image is formed;
• a rotary portion configured to hold a leading end of the sheet medium in a sheet conveyance direction, reverse the sheet medium on the stacking face of the stacking portion, and convey the sheet medium;
• a medium holder configured to hold the sheet medium when the sheet medium is conveyed by the rotary portion,
• the medium holder includes:
• a first holder configured to hold the leading end of the sheet medium in the sheet conveyance direction, on an outer circumferential surface of the rotary portion;
• and
• a second holder configured to hold a portion of the sheet medium other than the leading end of the sheet medium, on the rotary portion when the sheet medium is conveyed by the rotary portion;
• and
• circuitry configured to control the rotary portion;
• wherein the second holder includes a rotary member configured to rotate to convey the sheet medium, and
• wherein a rotational speed of the rotary member is configured to be controlled by the circuitry.