Patent ID: 7283436

Claim:
A layer change method for an optical medium, the method comprising: measuring a needed time from where a focus point of the optical medium breaks away from a current layer to where the focus point arrives at a desired layer; and controlling a focus driving voltage needed to pull the focus point of the optical medium into the desired layer, and an output time to output the focus driving voltage by using the needed time; wherein the measuring of the needed time comprises: measuring a first needed time of a kick interval in which the focus point breaks away from the current layer; and measuring a second needed time of an inertia interval from where the kick interval ends to where the focus point arrives at the desired layer, separately from the measuring of the first needed time, and wherein the controlling of the focus driving voltage and the output time to output the focus driving voltage comprises: controlling the output time to output the focus driving voltage according to the first needed time of the kick interval and whether the focus point is pulled into the desired layer; and controlling the focus driving voltage according to the second needed time of the inertia interval and whether the focus point is pulled into the desired layer.