Feedforward Control to Attenuate Tension Error in Time-varying Systems

This paper presents two feedforward control algorithms to attenuate the tension error in digital tape systems. Tape systems are time-varying because not only do the radii of both reels change as a result of tape winding from one reel to the other but reels also have eccentricities. We address the time-varying nature of the reel radii due to tape winding by introducing a time-varying feedforward filter for the reference input. To attenuate the periodic tension error caused by reel eccentricities, we investigate the error in previous periods and calculate the compensation input that cancels it. This input is then fed forward to the system for future periods. Simulations show that the time-varying reference input achieved from the feedforward filter leads to zero tension error if the variations in the radius are known. With unknown reel eccentricities, the feedforward compensation input reduces the tension error by about 3 orders of magnitude when the system is periodic.