Patent ID: 7613081
Filing Date: 2009-11-03
Classification: G11B

Abstract:
1. A method for controlling a stepper motor in an optical disc system, comprising the steps of: (A) measuring a static offset level of a center error signal with a laser beam of said optical disc system turned off; (B) measuring a maximum value, minimum value and an average value of said center error signal in response to rotating an optical disc while both (i) said laser beam is turned on and controlled to say on a particular track of said optical disc and (ii) no control is applied to said stepper motor; (C) computing upper threshold values and lower threshold values based upon said static offset level, said maximum value, said minimum value and said average value of the center error signal by (i) calculating a first upper threshold value and a first lower threshold value when said laser beam stays on said particular track of said optical disc, (ii) calculating a second upper threshold value and a second lower threshold value when said laser beam moves across one or more tracks towards a center of said optical disc, and (iii) calculating a third upper threshold value and a third lower threshold value when said laser beam moves across one or more tracks away from said center of said optical disc; (D) selecting one of the upper threshold values and a corresponding one of the lower threshold values computed in step (C) based upon a direction of movement of said laser beam; (E) sampling said center error signal; (F) comparing a sample of said center error signal to the selected upper and lower threshold values; and (G) computing a control output to control said stepper motor in response to a result of comparing said sample of said center error signal to the selected upper and lower threshold values.