Sheet stacker and image forming apparatus incorporating same

A sheet stacker comprising:

• a tray configured to store a stack of sheets;
• a conveyor above the tray, the conveyor configured to convey a sheet in a conveyance direction;
• a leading end guide above the tray and downstream from the conveyor in the conveyance direction, the leading end guide configured to guide the sheet from the conveyor to the tray;
• and
• an air exhaust configured to exhaust air above an upper surface of the stack of sheets on the tray to an upstream from the tray in the conveyance direction,
• wherein the leading end guide is configured to:
• hold a leading end of the sheet conveyed by the conveyor at a holding position;
• and
• release the leading end of the sheet at a release position downstream from the holding position in the conveyance direction, and
• wherein the air exhaust has an opening opened toward the upper surface of the stack of sheets, the opening being larger than a thickness of the sheet in a vertical direction and larger than a maximum width of the sheet in a width direction of the sheet, the width direction of the sheet being perpendicular to the conveyance direction.