Method and apparatus for time synchronized measurement correction of multidimensional periodic effects on a moving web

摘要

An improved measuring system used with a process control system provides substantially real time correction of aliasing effects in a system having moving equipment that exhibits periodic parameters while being monitored. The measuring/control system can be used with a rotating equipment process line, such as used in a paper mill, in which a measurement scanner travels in the cross direction of a moving web of material, while that same moving web of material continues to move in a longitudinal direction (the machine direction) transverse to the cross direction. The measuring/control system begins by acquiring data utilizing a time synchronous monitoring system that produces a count matrix and a measurement matrix of readings from the measurement scanner. After a sufficient number of data samples have been acquired, a correction matrix can be built. Each sample of data can be adjusted for the contribution of each of the rotating elements at the data processing level before the raw reading is processed into a measurement or a profile. In this manner, the aliasing effect of all mapped rotating elements can be removed from the measurement. The output measurement matrix element values are converted by the measuring/control system to deviations from the average, caused by each rotating element. These values are then used by a correction algorithm. Each rotational element has its own correction map generated, and the CD position of the scanner is known at each data collection interval, and further the rotational position of each rotating element is also known at each data collection interval. The measuring/control system can use these raw sensor readings and correct them for each CD and MD positional effect, or for each rotational element. The measuring/control system can provide immediate correction for rotational effects at the time of sampling, before the data is averaged or used in any other way. This permits the rotational effects of multiple rotating elements to be removed deterministically in real time.