Patent ID: 7427848

Claim:
A method of controlling a system for correcting skew of a web of material being fed through a machine, wherein the system comprises first and second pinch assemblies placed at a distance transversely to a direction of feeding; first and second stepper motors that drive the first and second pinch assemblies, respectively; a control that provides first and second pulse trains to drive the first and second stepper motors, respectively; and a device that determines a value for the skew of the web of material, said method comprising the steps of: establishing first and second corrective pulse train sections for the first and second stepper motors, respectively, in accordance with a determined skew value; providing first and second pulse trains for driving the first and second stepper motors, respectively, wherein the first pulse train includes the first corrective pulse train section and a subsequent periodic succession of pulses at a pre-determined nominal frequency, and wherein the second pulse train includes the second corrective pulse train section and a subsequent periodic succession of pulses at a pre-determined nominal frequency; and establishing the first and second corrective pulse train sections to commence the periodic successions of pulses with phases differing between the first and second pulse trains in accordance with the determined skew value.