Of all the features of a drive system, the most popular by far is "stop to length." This feature is particularly appreciated by operators of older lines in which the operator had to be vigilant to prevent winding a long or oversized roll.
Some techniques for stopping to length affect the quality of the wound roll and productivity of the slitter more than others. Slowly reducing the speed so that the targeted length may be reached is the worst method as the slitter is stopped with a varying acceleration. Slowing the slitter to a safe slow speed at a preset length count 1 is a pretty good option, but the slitter runs a long time at slow speed with resulting productivity losses. The optimum stopping method is to use a calculation to determine the optimum instant to stop the slitter and have it end at the target length.
It is quite simple to measure the instantaneous wound length of a roll. This is generally done with a surface wheel and encoder. The problem is in initiating a stop at a correct time to end the roll at the correct length. The length to be added to a roll depends on the integration of the speed as the line ramps down to a stop. Web gauge is not part of the length during stopping.
In web handling, we do not use linear ramps because they introduce tension variations, so we need to integrate an S-ramp. The S-ramp consists of 3 segments. These segments are rounding into the linear portion, the linear deceleration portion, and the rounding out to a stop. These are non-trivial and complexity is increased if the speed is too low to achieve the linear portion of the deceleration ramp.
Most S-ramps begin with acceleration. This is a segmented curve in the shape of a trapezoid. The sloped portions cover the rounding time. The S-ramp integrates the acceleration to produce a speed reference in the shape of a tilted “S." To stop to length, the speed is integrated over the 3 segments to get the total length.
Your drive controller is capable of this calculation in the hands of the right programmer.