Patent ID: 7296793

Claim:
A sheet processing apparatus aligning and stacking a sheet or sheet bundle comprising: stacking portion on which the sheet or sheet bundle is stacked; conveying portion which conveys the sheet or sheet bundle toward the stacking portion; sheet rear end aligning unit which aligns a rear end of the sheet or sheet bundle upon pressing toward the stacking portion, the rear end of the sheet or sheet bundle conveyed by the conveying portion; and controlling portion which controls acceleration of the sheet rear end aligning unit by determining at least one feature of the sheet or sheet bundle being pressed, wherein the controlling portion controls the acceleration of the sheet rear end aligning unit so that acceleration of the sheet or sheet bundle by pressing of the sheet rear end aligning unit satisfies a relation: α≦−μ 1 ′g and α≦−μ 2 ′g where acceleration of the sheet or sheet bundle by pressing of the sheet rear end aligning unit at a time that the sheet rear end aligning unit presses the rear end of the sheet or sheet bundle to align the rear end, is denoted as α, where gravitational acceleration is denoted as g, where coefficient of kinetic friction between the sheet or sheet bundle pressed by the sheet rear end aligning unit and the stacking portion is denoted as μ 1 ′, and where coefficient of kinetic friction between the sheet or sheet bundle pressed by the sheet rear end aligning unit and the sheet or sheet bundle already stacked on the stacking portion is denoted as μ 2 ′.