Sheet ejection device, sheet post-processing device including the same and image forming system

A sheet ejection device comprising:

• an ejection roller pair which ejects a sheet from an ejection port in a predetermined ejection direction;
• a stacking tray which is arranged on a downstream side of the ejection roller pair in the ejection direction and on which the sheet ejected by the ejection roller pair is stacked;
• a protrusion member which protrudes above the stacking tray from the ejection port and is supported to be able to reciprocate between a protrusion position where a tip end of the sheet ejected by the ejection roller pair is brought into contact with an upper surface to be guided in the ejection direction and a retraction position where the protrusion member is retracted from above the stacking tray;
• and
• a movement mechanism which moves the protrusion member in a predetermined movement direction between the protrusion position and the retraction position,
• wherein the movement mechanism includes:
• a rotation shaft which extends in a width direction orthogonal to the ejection direction and is rotatably supported;
• a holding member which is coupled to the rotation shaft and holds the protrusion member movably along the movement direction;
• and
• a rack and pinion mechanism which includes:
• a pinion gear supported by the rotation shaft;
• and
• a rack gear including a large number of gear teeth which are formed on a surface of the protrusion member opposite the pinion gear and are aligned along the movement direction of the protrusion member,
• in at least a part of the rack gear in the movement direction, a narrow width region is provided which is formed by cutting out a part of the gear teeth in the axial direction and which includes a narrow width gear and a cutout portion,
• in the narrow width region, the pinion gear is slidable between a meshing position where the pinion gear meshes with the narrow width gear and a release position where the pinion gear is opposite the cutout portion such that the meshing with the narrow width gear is released and
• in a state where the pinion gear has slid to the release position, the protrusion member can be relatively moved with respect to the pinion gear in the movement direction.