Method of automatically controlling print quality in digital printing

A method of automatically controlling digital printing of a document print job on media sheets comprising:

• (a) providing a print engine;
• (b) disposing a first sensor at a first location external to the print engine for measuring an image printed on a media sheet by the engine;
• (c) disposing a second sensor at a location upstream in the print process of the first sensor for measuring an image on a surface internal to the print engine of one of a photoreceptor drum, a photoreceptor belt, an intermediate drum, an intermediate belt, and an imaging drum;
• (d) while printing measuring an image on the surface internal to the print engine with the second sensor;
• (e) printing the measured image on a media sheet;
• (f) subsequently measuring the printed image on the media sheet with the first sensor;
• (g) automatically periodically determining a performance metric of the image printed on the media sheet and, if acceptable, saving the measurement of the corresponding image measured on the surface internal to the print engine from the second sensor as a reference, and if not acceptable, automatically calculating and applying a control signal and repeating steps (d)-(f);
• (h) executing the print job and automatically periodically measuring an image on the surface internal to the print engine at the upstream location using the second sensor and comparing with the saved reference;
• and,
• (i) automatically repeating steps (d)-(g) if the comparison in step (h) is not within an acceptable range;
• and, continuing the print job if the comparison of step (h) is within an acceptable range.