This paper considers modeling and correction signal design for self servowriting in disk drives. Self-servowriting is a process whereby the position and timing burst information are written on the disk surface by using the servo information from a previously written track as a reference (seed) for writing the burst information on a subsequent track, and repeating the process. An obstacle to this process is radial error propagation, whereby the distortion in the successive written tracks builds up. In this paper, a reference correction signal is designed which when added to the position error signal (PES) prevents the radial error propagation. The design of the correction signal is carried out through a repetitive systems approach and does not require several revolutions of track following in order to compute it. The analysis is verified by means of simulations which show the containment of radial error propagation.
A receding time horizon linear quadratic optimal control approach is formulated for multi-axis contour tracking problem. The approach employs a performance index with fixed weights on quadratic contouring error, tracking error, and control input over a future finite horizon. The problem is then cast into a standard receding horizon LQ problem with time varying weighting matrices, which are functions of the future contour trajectory within the horizon. The formulation thus leads to a solution of time varying state feedback and finite preview gains. Stability is proven for the linear trajectory case. Experimental and simulated results for an X-Y motion control problem are presented, which demonstrate the effectiveness of the control scheme and the effects of the key controller design parameters. [S0022-0434(00)01202-8]
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