Method and device for managing ink quality in an inkjet printer

Method of operating an inkjet printer that comprises a fluid circuit, a print head connected to the fluid circuit through an umbilical, the method comprising:

• calibrating the inkjet printer according to:
• measuring with a pressure sensor at a reference point in the fluid circuit or the print head, an ink pressure at a temperature T and at a nominal jet velocity;
• correcting data representative of a theoretical characteristic reference curve that relates the pressure in the fluid circuit or the print head, the ink density, the ink viscosity, the operating temperature, and said nominal velocity of the ink jet generated by the print head, as a function of the difference between the measured ink pressure and a pressure resulting from said characteristic reference curve for said temperature T and said nominal jet velocity;
• forming an actual characteristic reference curve based on the corrected data, thereby accounting for variations or changes in geometric or mechanical parameters of said fluid circuit and
• forming an inkjet based on the actual characteristic reference curve, wherein the formed inkjet has a velocity equal to or close to said nominal velocity, and a pressure controlled to be equal to or close to the pressure at said reference point according to the actual characteristic reference curve,
• measuring a parameter representative of the viscosity of the ink used in the ink circuit at a temperature T, during formation of the ink jet;
• and
• adding a quantity of solvent into the ink when the viscosity is higher than a given reference value,
• in which a quantity representative of the viscosity of the ink used in the ink circuit is a pressure of said ink, a quantity of solvent being added into the ink when the measured pressure of said ink is higher than a given reference value, and
• in which the quantity of solvent to be added depends on the dilution coefficient (Cd) of the ink.