Modeling and identification of opto-mechanical coupling and backlash nonlinearity in optical disk drives

In an optical disk drive, a bi-directional actuator and a coarse positioning mechanism are servo controlled to position the laser beam spot precisely. Typically the control system is designed based on the models of servomechanisms. Although the models are capable of characterizing the essential part of the system dynamics, they frequently ignore opto-mechanical coupling in the bi-directional actuator and backlash in the positioning mechanism. If the opto-mechanical coupling or backlash is too significant, the control system, when applied to the actual machine, may fail to meet the designated performance specifications. Therefore, to facilitate the design of high performance control systems, this research is devoted to developing models and identification procedures to understand the sources of coupling and measure the backlash size. The results indicate that opto-mechanical coupling is mainly caused by manufacturing tolerances and alignment errors, and the size of backlash for a sample machine is approximately 42.7 μm