Some advances in loop shaping controller design with applications to disk drives

This paper presents two new concepts for assisting control engineers with the design of high performance servo systems with applications to disk drives. Classical loop shaping concepts are the basis for the two methods. The first idea is a modification of the traditional Bode plots to provide closed-loop frequency response information as graphed as contours along with the usual open-loop magnitude and phase response graphs. The concept can reduce the trial and error needed to obtain a good design by more clearly showing the relationship between the open-loop and closed-loop frequency responses. The second idea is to use complex conjugate poles and zeros as a modification to the classical double lead compensator. The damping ratio of the complex poles and zeros provides the flexibility to reduce the ratio of the high frequency gain to low frequency gain and to sharpen the phase peak without changing the magnitude of the peak. The paper shows a design example employing both methods.