Patent ID: 9126425
Filing Date: 2015-09-08
Classification: B41J

Abstract:
1. A duplex printing system, comprising: first and second print engines to respectively print on a first side of a web and a second side of the web; a controller to: control the first print engine to print recto pages and associated recto checkmarks; control the second print engine to print verso pages and associated verso checkmarks; and modify a length of successive printed recto and verso checkmarks in accordance with a respective recto checkmark length sequence and verso checkmark length sequence; a recto checkmark sequence calculator to determine a sequence position in the recto checkmark length sequence of a printed recto checkmark; a verso checkmark sequence calculator to determine a sequence position in the verso checkmark length sequence of a printed verso checkmark; and a checkmark sequence verifier to determine print errors based on the determined recto and verso checkmark sequence positions, wherein the recto checkmark length sequence is based on a first continuously varying periodic function, and wherein the verso checkmark length sequence is based on a second continuously varying periodic function.