Device and method for printing on one or both sides of a plurality of flat objects

An apparatus for printing on one or both sides of flat objects, said apparatus comprising:

• a loop-shaped conveying path for the flat objects, said conveying path being configured to convey the objects individually along a first section of the conveying path, and to convey a stack of the objects along a second section of the conveying path;
• an infeed conveyor for the objects, said infeed conveyor being configured to individually feed the objects to be printed upstream to a printer in the first section of the conveying path;
• a printer arranged along the first section of the conveying path and being configured to print the objects fed individually to the printer by the first section of the conveying path;
• a first discharge conveyor for the objects, said first discharge conveyor being configured and controlled to discharge the objects to be printed on both sides downstream to the printer from the first section of the conveying path toward the second section thereof one by one;
• a first collector for said objects, said first collector being arranged downstream to said first discharge conveyor at said second section of said conveying path and being configured to collect objects discharged from said first discharge conveyor in a stack;
• a stack conveyor for conveying the stack of the objects from the first collector along the second section of the conveying path;
• and
• a second collector for the objects, said second collector being arranged at the second section of the conveying path and being configured to receive part or all of the stack conveyed by the stack conveyor along the second section of the conveying path and to introduce the objects individually upstream of the printer into the first section of the conveying path, wherein the first collector is configured to deliver part or all of the stack to the stack conveyor until a predetermined height of the stack is reached, and wherein the number of objects received by the stack conveyor in the stack is at least two of the flat objects.