Robust following control design for hard disk drives

This paper presents an example of a robust control design for a hard disk drive (HDD) that has resonant mode(s) around the Nyquist frequency. The design is based on a continuous-time μ-analysis and synthesis. Over-sampling discretization is introduced in order to have the discretized controller meet the continuous time domain specification. The design technique of a temperature-dependent filter derived from the original controller is also introduced in order to tighten the error rejection specification. We have conducted experiments using a 3.5" HDD with a sampling frequency of 11 kHz, and have confirmed that the open loop bandwidth as well as the positioning quality can be improved 10 to 20 percent compared to conventional controller performance