For webs that stretch or shrink during processing, it is difficult to know in real time the amount of distortion in the web. Roll size, position in the roll, environmental conditions and tension all affect how much the web can shrink or stretch during processing. Each stage of converting can impart additional distortion in a flexible web. The RYECO Distortion Monitoring System makes it possible to know in real time how much a web stretches or shrinks during processing.
The system usually consists of a RYECO Registration Marking System for making the marks and a RYECO Distortion Monitoring System for detecting the marks. The Registration Marking System places short marks on the web at defined length intervals; for example, a mark might be placed every 5 yards or meters. The system uses an encoder to accurately place the marks evenly along the web at a point where the substrate is most stable. If an encoder is not available, registration marks can also be printed based on a set time interval. At any point downstream or in subsequent converting stages, the spacing of the marks is checked with a Distortion Monitoring System. Any variations are translated into web distortion in the form of the percentage of stretch or shrinkage. The values are displayed in real time on the operator’s screen.
The value of stretch or shrinkage can be sent serially to another process control system. Limits can be set by an operator to trigger alarms when action needs to be taken. A trend display shows distortion over time and in the case of multiple lanes the stretch can be displayed as a profile. The marks are normally placed along the edge of the web where they can be trimmed off.