Sheet postprocessing apparatus and image forming system

1. A sheet postprocessing apparatus comprising:

a processing tray on which sheets are stacked and arranged;

a vertical registration member for registering a front edge side and a rear edge side in a transport direction of the sheets stacked and arranged on the processing tray; and

a sheet pressing member for pressing the sheets stacked on the processing tray from above,

the vertical registration member increasing a rate of increase in transport force generated for the sheets by the vertical registration member, in conjunction with a rate of increase in transport resistance generated for the sheets by the sheet pressing member with an increase in number of the sheets stacked on the processing tray,

wherein the vertical registration member includes a rotating shaft, two or more flexible paddles provided radially with respect to the rotating shaft and rotating with the rotating shaft, and a same number of projecting portions provided radially with respect to the rotating shaft, each of the projecting portions is downstream from a respective one of the paddles with respect to a direction of rotation of the rotating shaft, and rotating with the rotating shaft,

a distance from an edge of the each of the paddles to the center of the rotating shaft is longer than a distance from an edge of the each of the projecting portions to the center of the rotating shaft,

the each of the projecting portions is disposed relative to the each of the paddles so as to create a space in which the each of the paddles is deflected toward the each of the projecting portions,

distances from the edges of the projecting portions to the center of the rotating shaft are all equal.

2. The sheet postprocessing apparatus according to claim 1 , wherein

the projecting portion is rigid.

3. The sheet postprocessing apparatus according to claim 1 , wherein

at least the edge of the projecting portion is formed of an elastic member.

4. An image forming system comprising:

an image forming apparatus; and

a sheet postprocessing apparatus for performing postprocessing on a sheet on which an image has been formed by the image forming apparatus,

the sheet postprocessing apparatus being the sheet postprocessing apparatus according to claim 1 .

5. A sheet postprocessing apparatus comprising:

a processing tray on which sheets are stacked and arranged;

a vertical registration member for registering a front edge side and a rear edge side in a transport direction of the sheets stacked and arranged on the processing tray; and

a sheet pressing member for pressing the sheets stacked on the processing tray from above,

the vertical registration member increasing a rate of increase in transport force generated for the sheets by the vertical registration member, in conjunction with a rate of increase in transport resistance generated for the sheets by the sheet pressing member with an increase in number of the sheets stacked on the processing tray,

wherein the vertical registration member includes a rotating shaft, a flexible paddle provided radially with respect to the rotating shaft and rotating with the rotating shaft, and a projecting portion provided radially with respect to the rotating shaft, downstream from the paddle with respect to a direction of rotation of the rotating shaft, and rotating with the rotating shaft,

a distance from an edge of the paddle to the center of the rotating shaft is longer than a distance from an edge of the projecting portion to the center of the rotating shaft,

the projecting portion is disposed relative to the paddle so as to create a space in which the paddle is deflected toward the projecting portion, and

at least the edge of the projecting portion is formed of an elastic member.