Motion control for sheets in a duplex loop of a printing apparatus

The present invention relates to controlling the motion of sheets moving through a printing apparatus, where the apparatus is capable of "duplexing," or printing on both sides of a sheet. In a printing apparatus capable of producing duplex, or two-sided, prints, print sheets which have received a first-side image move to an inverter and a duplex loop which re-feeds the sheet to receive the second-side image. The sheets move through the duplex loop at different speed than through the main path where images are placed. A control system controls the time in which a change in speed of a sheet in the duplex loop is initiated. The control system takes into account a desired amount of buckle experienced by the sheet, which is useful in de-skewing the sheet before receiving an image.