Improved speed control for a casting drum drive

This paper addresses the issue of speed holding capability for a casting drum drive used in a high-quality film production process. The quality of the product is reduced by film profile variations, which are caused by changes in the casting drum speed, resulting from: forces transmitted through the film, mechanical imbalance of the drum, backlash in gearboxes, and torque ripple from the electric drives. Techniques for counteracting film-transmitted forces are described and tested using a laboratory facility, which replicates the behaviour of a production plant. It is shown that system modelling must include the effects of creep and slip between the drive belt and pulleys. Using the system model in speed and load torque observers allows the development of new controllers, which improve speed holding capability by a factor of 10.