This invention provides a stacker for use in forming stacks of cut sheets received from an upstream utilization device (e.g. a printer, cutter, etc.) that allows for positive driving of sheets into a stack using a stacking unit that includes a series of grippers that are adapted to grip and release a leading edge of each sheet at the appropriate time. In this manner, each sheet is gripped as it arrives from the upstream operation and is passed downstream into the stack, being released so as to properly decelerate at the stack's backstop. The grippers are mounted on a continuous belt between a pair of opposing drive sprockets. An edge sensor located upstream of the stacking unit triggers motion of the belts. The grippers are actuated by a mechanical cam arrangement to selectively grip and release at predetermined positions as the belt is driven.

An image forming apparatus includes a display unit, an image forming unit, a detecting unit to detect whether a sheet is on the tray, a moving unit to cause the tray to ascend and to descend to a lower limit position per a tray sheet amount, and a determination unit to determine that tray descent is interrupted at a position located higher than the lower limit position. At the lower limit position, a screen prompting tray sheet removal is displayed. When the tray descent is interrupted, a screen is displayed to include a tray sheet removal prompt and a notice that an obstacle presents under the tray, an image forming process is stopped, and then the tray is caused to ascend when the sheets are not on the tray and then the image forming process is resumed, even if the obstacle presents under the tray.

An image forming apparatus includes a display unit, an image forming unit, a detecting unit to detect whether a sheet is on the tray, a moving unit to cause the tray to ascend and to descend to a lower limit position per a tray sheet amount, and a determination unit to determine that tray descent is interrupted at a position located higher than the lower limit position. At the lower limit position, a screen prompting tray sheet removal is displayed. When the tray descent is interrupted, a screen is displayed to include a tray sheet removal prompt and a notice that an obstacle presents under the tray, an image forming process is stopped, and then the tray is caused to ascend when the sheets are not on the tray and then the image forming process is resumed, even if the obstacle presents under the tray.

A sheet processing apparatus capable of properly stacking sheets by detecting abnormality of a sheet stacking state during a sheet stacking operation to thereby prevent stack overflow. In the sheet processing apparatus, a conveyed sheet is stacked on a stacking tray. A sheet presence sensor detects a sheet on a sheet stacking surface of the stacking tray. A sheet height reduction sensor detects sheets within a predetermined distance downward from the uppermost surface of sheets stacked on the stacking tray. When the sheet presence sensor detects no sheet, and the sheet height reduction sensor detects a sheet during an operation for discharging a plurality of sheets onto the stacking tray, it is determined that an abnormal stacking state has occurred, and conveyance of a sheet is stopped.

A sheet processing apparatus capable of properly stacking sheets by detecting abnormality of a sheet stacking state during a sheet stacking operation to thereby prevent stack overflow. In the sheet processing apparatus, a conveyed sheet is stacked on a stacking tray. A sheet presence sensor detects a sheet on a sheet stacking surface of the stacking tray. A sheet height reduction sensor detects sheets within a predetermined distance downward from the uppermost surface of sheets stacked on the stacking tray. When the sheet presence sensor detects no sheet, and the sheet height reduction sensor detects a sheet during an operation for discharging a plurality of sheets onto the stacking tray, it is determined that an abnormal stacking state has occurred, and conveyance of a sheet is stopped.

The present invention is to provide a sheet stacking device for stacking sheets on which an image is formed, in which an initial operation time at the time the device is turned on is shortened, and, at the same time, the initial operation is simplified. This configuration enables reduction in operation noise and a prompt start at the time when the device is started.

The present invention is to provide a sheet stacking device for stacking sheets on which an image is formed, in which an initial operation time at the time the device is turned on is shortened, and, at the same time, the initial operation is simplified. This configuration enables reduction in operation noise and a prompt start at the time when the device is started.

Even when descending of a sheet stacking unit is interrupted by an obstacle, sheet stacking operation is resumed in a range in which the sheet stacking unit is movable.

Even when descending of a sheet stacking unit is interrupted by an obstacle, sheet stacking operation is resumed in a range in which the sheet stacking unit is movable.

A storage module (1) comprises a storage zone (3) for storing flat articles (2) by accumulation in a stack and on edge, a main conveyor (9) that extends transversely to the storage zone, a stacking function for transferring an article from the main conveyor to the storage zone and for stacking it at the back of the stack of articles in the storage zone, and an unstacking function for extracting an article from the stack of articles and for transferring it to the main conveyor. The unstacking function comprises an unstacking plate (7) having a perforated belt and controlled suction and disposed between the main conveyor and the storage zone, said unstacking plate having a first segment parallel to the stack of articles and a second segment that is adjacent to the first segment and that extends slantwise relative to the first segment, said controlled suction being disposed in the slantwise second segment of the unstacking plate.