Patent ID: 8339660

Claim:
A tandem continuous paper printer comprising: a first printer engine that, apart from performing printing of print data that comprises a print job, performs printing of a tandem check mark on paper at a page interval called “a check page interval S”, said check page interval S comprising a random interval; a second printer engine comprising a sensor that detects whether said tandem check mark at the check page interval S exists when a printing of respective pages by the second printer engine is performed, the check page interval S being generated in units of pages; and a printer controller which provides image data to said first and second printer engines, said random interval being generated by said printer controller, wherein tandem printing is performed by using the second printer engine on paper that has been printed on by the first printer engine, wherein the second printer engine continues with the printing of the print data if the tandem check mark is recognized by the sensor, wherein the printing of the print data is stopped if the tandem check mark is not recognized by sensor, and wherein the tandem check mark is given for a plurality of pages defined by the check page interval S.