A tension observer for nonlinear web-winding systems with air entrainment

This paper presents a tension observer for web-winding systems such as tape drives, using a nonlinear model where reel radii vary with time. The observer is unique in a certain sense, and when the spring and damping parameters of the system are known the observed tension converges exponentially to the true tension. In practice, air entertainment makes the spring and damping parameters difficult to know, and in this case the observer uses estimates. Assuming only that the unknown parameters satisfy certain bounds (but may vary in time), the maximum observer error is derived via an interesting and exactly solvable problem in variational calculus. This error depends upon the quality of the spring and damping parameter estimates. A simulation shows observer performance.