Adaptive equalization for disk drives

This paper discusses the design and simulation of adaptive equalization applied to disk drive servo systems. The adaptive equalizer is an add-on compensator placed in series after the existing controller and before the plant. The objective of adaptive equalization is to identify uncertain dynamics (lightly damped resonances in this case) and to equalize (remove) them from the control loop. This can improve the stability margin and increase the closed loop tracking bandwidth of the disk drive servo system. The proposed adaptive equalizer is simulated with a detailed disk drive model with nonlinearities and both internal and external disturbances. Simulation results show that the adaptive equalizer can successfully identify the disk drive resonances and equalize them when particular adaptive algorithm modifications are implemented and additional "probing" excitation is added