Sheet stacking apparatus and sheet stacking method

A sheet stacking method for positioning each of a plurality of sheets sequentially thrown in from a conveying device at a predetermined stacking position and stacking the sheets in layers using a sheet stacking apparatus, which includes a stacking platform having a stacking surface on which the sheet thrown in from the conveying device is placed and a plurality of the sheets are stacked, a front member which is provided at the conveying device side of the stacking platform with an air blowing device for forming an airflow in the sheet conveying direction under the sheet thrown in from the conveying device, a back member which is provided at a back side of the stacking platform, to come in contact with a front end of the sheet thrown in from the conveying device, and receive the sheet to be stacked on the stacking platform, and a pair of side members provided facing each other outside the stacking platform in a width direction of the stacking platform, wherein the pair of side members is provided with a pair of lower side members which is provided with an approximately same distance therebetween as the sheet width and limits a movement in the sheet width direction, a pair of upper side members which is provided above the pair of lower side members, each of which is provided with a movable section movable in the sheet width direction, and on which tapered surfaces are formed facing each other in a generally V shape, and a control device which controls a distance between the pair of upper side members by driving the movable sections of the pair of upper side members,

• the method comprising stacking sheets in the layers on the stacking surface of the stacking platform by repeating:
• a first step of controlling the distance between the pair of upper side members so that, immediately after a sheet is thrown in from the conveying device, the distance between the lower ends of the pair of tapered surfaces is narrower than the sheet width, and placing the thrown-in sheet between the pair of tapered surfaces;
• a second step of controlling the distance between the pair of upper side members so as to be gradually extended as the sheet advances in a direction toward the back member by the inertia of the thrown-in sheet and the airflow from the air blowing device, and allowing a center portion of the sheet placed between the pair of tapered surfaces to be bent downward by its own weight;
• and
• a third step of controlling the distance between the lower ends of the pair of tapered surfaces so that the distance becomes wider than the sheet width when the sheet advances immediately before being in contact with the back member, and dropping the sheet.