Digital Implementation Issues of Electronic Line Shafting

Electronic line shafting (ELS) is a control methodology for reproducing the desirable intershaft stiffness dynamics of a physical line shaft while adding some features that cannot be achieved with a physical line shaft. There are important challenges that must be addressed before ELS can be implemented. Asynchronous sampling between drives will cause perceived distortion, which negatively affects the degree of motion and tension control available. Relative-state motion control requires high position information resolution to be able to accurately measure and correct for small differences in motion between shafts. In addressing these issues, ELS can be implemented correctly to achieve much more precise tension and speed control in paper machines. The asynchronism between drive sampling frequencies is addressed using a novel observer-based compensation mechanism. This method is shown to work in both simulation and experimentation. The resolution of motion information is increased using a sine/cosine encoder in conjunction with an optical-signal-tracking observer. The improvements are shown both in simulation and experimentation.