Design of track following controller of dual actuated HDD servo for 10 Tb/in2 magnetic recording

One of the obstacles to achieving high recording density in hard disk drives (HDDs) is servo performance limitation. As HDD is a mass produced commodity, the challenge is not only achieving high performance for nominal models but with all the uncertainties and variations in HDD models for thousands of HDDs in a batch of production line. This paper presents the implementation results of a novel technique based on the H_∞ probabilistic robust approach for the track-following controller of HDD servo systems. The objective is to design and implement an H_∞ dynamic output feedback controller that achieves robust stability in the presence of various parametric uncertainties. We consider uncertainty as a random variable with uniform probability distribution. Then a randomized algorithm based on gradient iteration is preformed to compute design parameters. The proposed controller is implemented in real-time on a commercially available drive and the results are compared with the conventional H_∞ approach. The results reveal that with a very small risk of violation of the cost function, the proposed method can achieve much better performance compared to the conventional robust methods.