Application of Mixed H₂/H_∞ Data Driven Control Design to Dual Stage Hard Disk Drives

A data driven control design approach in the frequency domain is used to design track following feedback controllers for dual-stage hard disk drives using multiple data measurements. The advantage of the data driven approach over model based approach is that, in the former approach the controllers are directly designed from frequency responses of the plant, hence avoiding any model mismatch. The feedback controller is considered to have a Sensitivity Decoupling Structure. The data driven approach utilizes H_∞ and H₂ norms as the control objectives. The H_∞ norm is used to shape the closed loop transfer functions and ensure closed loop stability. The H₂ norm is used to constrain and/or minimize the variance of the relevant signals in time domain. The control objectives are posed as a locally convex optimization problem. Two design strategies for the dual-stage hard disk drive are presented.