Image forming apparatus

An image forming apparatus comprising:

• a main body unit that includes a print device configured to execute a print process to form an image on a sheet, the main body unit configured to discharge the sheet with the image formed thereon in a predetermined main conveyance direction;
• a plurality of coupled units that are coupled with each other and are coupled with the main body unit at downstream of the main body unit in the main conveyance direction;
• a control device configured to control devices that are included in the main body unit and the plurality of coupled units;
• and
• an operation device configured to receive a user operation, wherein
• each of the plurality of coupled units includes:
• a housing having a main opening and a door that is configured to open and close the main opening;
• a sheet stack carriage including a carriage portion and a stack tray on which sheets can be stacked, the carriage portion configured to be stored into and drawn out from the housing via the main opening;
• a lift mechanism configured to move up and down the stack tray of the sheet stack carriage stored in the housing;
• and
• a sheet conveyance device configured to change from one of a stack conveyance state and a relay conveyance state to the other, wherein in the stack conveyance state, the sheet conveyance device conveys the sheet discharged from the main body unit or another coupled unit that is coupled therewith at upstream in the main conveyance direction, to a stack conveyance path that is toward onto the stack tray, and in the relay conveyance state, the sheet conveyance device conveys the sheet to a relay conveyance path that is toward another coupled unit that is coupled therewith at downstream in the main conveyance direction, wherein
• the control device executes a specified number stack control in which the sheet conveyance device of a target unit is held in the stack conveyance state and the sheet conveyance device of another coupled unit that is present upstream of the target unit in the main conveyance direction, is held in the relay conveyance state until a predetermined specified number of sheets are stacked on the stack tray of the target unit that is selected from the plurality of coupled units,
• the control device further executes an interruption stack control when the operation device receives a predetermined interruption operation during execution of the specified number stack control,
• the interruption stack control includes:
• either a first conveyance change control or a second conveyance change control;
• and a retraction control, wherein
• in the first conveyance change control, the sheet conveyance device of the target unit is changed to the relay conveyance state, and the sheet conveyance device of another coupled unit that is present downstream of the target unit in the main conveyance direction is changed to the stack conveyance state,
• in the second conveyance change control, the sheet conveyance device of another coupled unit that is present upstream of the target unit in the main conveyance direction is changed to the stack conveyance state,
• in the retraction control, the lift mechanism of the target unit is caused to execute a mount operation by which the stack tray is moved down to a mount position on the carriage portion, and
• in the interruption stack control, the control device causes the print device to execute an interruption print process to form, on a sheet, a number that indicates a number of sheets stacked on the stack tray of the target unit, and executes either the first conveyance change control or the second conveyance change control and the retraction control when the sheet with the number printed thereon has been conveyed to the stack tray of the target unit.