System for setting the sheet length on a crosscutter for webs of material

In a system for setting the sheet length on a cross-cutter for webs of material which comprises a feeding means including a pair of feed rolls, cutting means including a pair of cutter rolls preceded by an irregular-motion mechanism and an positioning element associated therwith, a common drive motor, and a sheet-size adjusting mechanism disposed between the feeding means and the irregular-motion mechanism and including a speed-changing mechanism and a continuously variable speed transmission and positioning elements associated therewith, the improvement comprising:

• first means forming a first control loop for the positioning element of the irregular-motion mechanism;
• second means forming a second control loop for the positioning element of the speed transmission;
• means for producing a positioning signal for one speed corresponding to the desired sheet length and for applying same to the first control loop, the positioning element of the speed changing mechanism and to the second control loop, wherein the desired values correspond to the desired sheet length, and wherein the second control loop of the continuously variable speed transmission includes means receptive, as an actual value, the sheet length for specifying to the associated positioning element the positioning time on the basis of the deviation of the actual value from the desired value and of the speed selected and for making another comparison of actual value with desired value only at the completion of each positioning operation.