Experimental investigation of disc drive seek control when subject to a nonlinear magnetic bias

The research experimentally investigates the design and performance capabilities of a voice-coil motor actuator (VCMA) for a disc drive with a nonlinear magnetic bias. A magnetic bias feature is independently designed on the actuator arm to compensate for non-operational shock. Because the resulting bias is nonlinear and uncertain, a model-based adaptive controller was developed to meet seek performance requirements and simultaneously handle effects of the nonlinear bias. Although exact characterization of the bias was unknown, bounds could be determined from geometric tolerance analysis. A projection algorithm was implemented to maintain the bias estimate within the known bounds. The performance criteria was based on minimizing the time required for a seek maneuver without controller saturation. Extensive experiments were conducted to characterize the VCMA physical parameters and verify the controller performance. Additionally, efforts were made to investigate the effects of sample rate variation and bias modeling errors. A representative sample of the results is presented and discussed.