Methods and apparatus for compensatng step distance in a stepping motor driven label printer

In a barcode label printer having a printhead positioned to print barcodes on labels moving thereunder, a drive roller positioned to move a plurality of labels carried by a backing strip under the printhead for printing thereon, and a stepping motor driving the drive roller so as to accurately control longitudinal label registration as a function of steps of the stepping motor, apparatus for dynamically adjusting the steps of the stepping motor to compensate for changes in effective step length effecting longitudinal registration of barcodes printed on the labels comprising:

• a) a sensor outputting a first signal upon sensing a leading edge of a just-printed label and outputting a second signal upon sensing a first bar of a barcode of said just-printed label;
• and,
• b) control logic connected to said sensor to receive said first signal and said second signal for,
• b1) outputting a number of steps to the stepping motor to move each label from a known longitudinal position to a registered position under the printhead,
• b2) continuously sensing a start of label point and a start of barcode point on each label just printed and counting steps of the stepping motor required to move each just printed label from the start of label point to the start of barcode point,
• b3) comparing the number of steps of the stepping motor required to move each just printed label from the start of label point to the start of barcode point to a baseline value, and
• b4) adjusting the number of steps to the stepping motor employed to move one label from the known longitudinal position to the registered position under the printhead as a function of any change between a latest counted value of the number of steps of the stepping motor required to move each just printed label from the start of label point to the start of barcode point to a baseline value.