Parametric descriptions of the actuator model are obtained in a technical specification written by manufactures of an optical pick-up unit. Most of the mechanical and electrical parts have tolerance for error. And various reflectivity and physical characteristics of a disc make an optical system more separate from the nominal system. So the nominal model using the parametric descriptions has a mismatch with an actual system about 30 ~ 50%. To overcome these obstacles against stability and performance, automatic gain-adjustment for a servo loop has been operated in an optical disc drive (ODD). This adjusting algorithm can change the gain of the compensator in order to maximize a phase margin of the servo loop.
© 2011 Optical Society of AmericaPDF Article