Interactions in Servo Loops of an Optical Disk Drive

In an optical disk drive, three servo loops are typically used to control the focus, fine tracking, and coarse tracking actuators. Optical disk drives have interactions between these servo loops attendant to the characteristics of actuators and the error signal sensing schemes employed. Simple actuators and error signal sensing methods are desirable to reduce the manufacturing costs; however, large interactions, if present may degrade the servo performance. This can result in a degradation in the error rejection ratio, seek time, and seek reliability.