Patent Document ID: 20150375537
Application ID: 14750720
Patent Flag: 0

Claim One:
1. A method for accurately controlling a medium displacement in an inkjet printer by determining a relation between an actuation signal and a medium displacement, the actuation signal causing a rotation of a roller by actuating a drive motor that is coupled to the roller by a slip free transmission such that the rotation speed of the drive motor is higher than the rotation speed of the roller that passes its surface movement to a medium pinched onto its surface, the method comprising the steps of: a) establishing a set of calibration actuation signals each corresponding to a nominal calibration step; b) printing a first reference mark on the medium; c) selecting a calibration actuation signal from the set of calibration actuation signals; d) actuating the drive motor to cause the roller to displace the medium over a distance of the nominal calibration step corresponding to the selected calibration actuation signal; e) printing a next reference mark besides the first reference mark in a direction perpendicular to the medium displacement direction; f) optically reading the first and the next reference mark; g) determining an achieved medium displacement step from the read reference marks; and h) repeating steps b) to g) for all available calibration actuation signals in the set of calibration actuation signals, wherein the set of calibration actuation signals comprises at least one calibration actuation signal that actuates the drive motor to make one full revolution and one calibration actuation signal that actuates the drive motor to make a rotation larger than one full revolution, but smaller than two full revolutions, and determining a relation between the calibration actuation signals and the difference between the achieved medium displacement steps and the nominal calibration steps, based on a finite series of basis functions.