Apparatus and method for calculating registration error of a rotary die

A rotary die apparatus comprising:

• a rotary die having a quantity of pattern protrusions extending outward therefrom and configured to cut, emboss, or stamp a pattern onto a strip of material, the quantity being greater than 1;
• a motor coupled to the rotary die and configured to rotate the rotary die;
• an encoder coupled to at least one of the rotary die and the motor and configured to output a particular number of pulses per revolution of the rotary die;
• a sensor configured to sense one or more pre-defined fiducials on the strip of material and to output a signal each time the sensor senses one of the fiducials;
• and
• a control system configured to receive signals from the encoder and the sensor, increment a pulse count each time a signal from the encoder is sensed if the pulse count is less than a pattern length, reset the pulse count if the pulse count is greater than or equal to the pattern length, determine an actual rotational position of the rotary die based on the pulse count when the fiducial is detected, set an actual variable to correspond with the actual rotational position, and calculate a registration error based on a difference between the actual variable and a registration target, and the pattern length is equal to the number of signals sensed from the encoder per revolution of the rotary die divided by the quantity of pattern protrusions,
• wherein the pulse count is reset for each one of the plurality of patterns of the rotary die;
• wherein the registration target is a value corresponding to a desired rotational position of one pattern protrusion of the quantity of pattern protrusions on the rotary die;
• and
• wherein the registration target is a constant value regardless of which pattern protrusion of the quantity of pattern protrusions occupies the desired rotational position.

A computer-readable medium encoded with a nontransitory computer program for determining a registration error in a length-wise direction on a strip of material between a desired location of a pattern applied to the strip of material by a rotary die and an actual location of the pattern applied by the rotary die, the computer program configured to perform the following steps:

• sensing pulses from an encoder corresponding with rotation of the rotary die;
• incrementing a pulse count each time a pulse from an encoder is sensed by the control system if the pulse count is less than a pattern length, wherein the pattern length corresponds to a number of pulses per revolution of the rotary die divided by the number of pattern protrusions on the rotary die;
• resetting the pulse count if the pulse count is greater than or equal to the pattern length;
• sensing a signal from a sensor configured to detect when a fiducial is sensed on the strip of material;
• determining an actual rotational position of the rotary die based on the pulse count when the fiducial is detected;
• and
• calculating the registration error based on a difference between the actual rotational position and a registration target,
• wherein the pattern is one of a plurality of patterns spaced in even increments around the rotary die such that the quantity of patterns applied to the strip of material per revolution of the rotary die is greater than 1 and the pulse count is reset for each one of the plurality of patterns of the rotary die;
• and
• wherein the registration target is a value corresponding to a desired rotational position of the pattern;
• and
• wherein the registration target is a constant value regardless of which pattern of the plurality of patterns occupies the desired rotational position.