Method and apparatus for controlling the registration of sheets

Device for controlling the circumferential register in a digital multi-color printing machine for printing sheets during a printing process, in particular in an electrophotographically operating printing machine, comprising color printing units producing for each sheet, at least one register mark per color printing unit of the multi-color printing machine, assigned to said sheet and defined with respect to its position, relative to one of the color marks itself, said color marks being applied to a support for said sheets and a monitoring and control arrangement for detecting register marks, for determining at least relatively the positions of said register marks and for controlling the color printing units based on the determination of the position of the register marks of a sheet, the circumferential register of at least one sheet being controlled, said sheet following the sheet associated with said determined register marks downstream of the printing process

• wherein
• for recto-printing and verso-printing both sides of sheets, the monitoring and control arrangement is set up in such a manner that, during at least one of the detection of register marks, during the at least relative determination of the positions of these register marks and during the control of the color printing units, a distinction or differentiation based on the register mark positions can be made in order to assign the respective register mark to a recto printing side or a verso printing side of a sheet, so that, in order to control the color printing units based on the register mark positions for recto printing, only the positions of register marks assigned to a recto printing side and, for verso printing, only the positions of register marks assigned to a verso printing side can be used and taken into consideration.