Evaluation of Lens Actuators in the Optical Disk Drives in Consideration of Friction.

A sliding and rotary type of lens actuator is popularly employed in the optical disk drives nowadays. One of the points to be considered in designing this type of actuator is non-linearity caused by the friction between a shaft and a sleeve. This paper presents a model of the focusing servo loop which includes the lens actuator, assuming the friction to be a Coulomb's friction. With this model the influence of the friction on the actuator performance is analyzed and it is confirmed that the analytical results are in good agreement with experimental results. The results of this evaluation are as follows : (1) The velocity of lens at the lead-in mode is a function of friction, the fluctuation of driving force and viscous damping constant. (2) When the loop is closed, the increase of the friction brings about a rectangular shaped error of the focusing servo. (3) When the dynamic friction factor is around 0.15 to 0.3, the influence of the friction on the focusing performance is negligibly small.