Method of controlling the length of corrugated fins

A method of using a machine for forming corrugated ribbon parts from sheet stock, said machine having forming rolls for corrugating the sheet stock, stuffing rolls for compressing the corrugated ribbon to a pitch smaller than the desired product pitch, metering rolls for feeding the compressed ribbon followed by pullout rolls driven by a servomotor for stretching the ribbon out to a desired nominal pitch, and cutter means following the pullout rolls for severing the ribbon into discrete parts;

• the method of accurately controlling the part length to a target length comprising the steps of:
• operating the servomotor to drive the pullout rolls in phase with the metering rolls to maintain the desired nominal pitch;
• measuring with high resolution the length of the most recently cut part;
• comparing the measured part length to the target part length to determine the amount of any error;
• determining from the error amount of the servomotor adjustment required to attain the target part length by multiplying the amount of error by a proportional gain constant to create a servomotor adjustment that is at least in part proportional to the error amount and which can correct said error without overshoot to create an opposite error;
• and
• correcting the error for subsequent parts by momentarily changing the servomotor speed according to the said motor adjustment to effect a phase change between the pullout rolls and the metering rolls.