Digital tracking servo system with multi-track seek with track zero crossing detection
A servo system with a multi-track seek algorithm with a zero crossing detector is presented. The zero crossing detector indicates when the tracking error signal crosses zero. In some embodiments, a delay is executed between adjacent detections of zero crossings in the tracking error signal, for example half a cycle. In some embodiments, a zero crossing is detected when the tracking error signal passes through a range around zero, the range having a positive value above zero and a negative value below zero.
1. A method of detecting zero crossings in a tracking error signal, the method comprising:
delaying for a time period of a half of a cycle of the tracking error signal before detecting when the tracking error signal crosses zero;
detecting when the tracking error signal crosses zero; and,
providing a zero crossing signal that changes state when the tracking error signal crosses zero.
2. The method of claim 1 , wherein detecting when the tracking error signal crosses zero includes detecting when the tracking error signal passes through a range around zero, the range having a positive value above zero and a negative value below zero.
3. A method of multi-track seeking, comprising:
calculating a tracking error signal from digitized optical signals from an optical pick-up unit;
delaying for a time period of a half of a cycle of the tracking error signal before detecting when the tracking error signal crosses zero;
detecting zero crossings in the tracking error signal;
counting the number of zero crossings to form a count;
calculating a reference velocity from the count;
determining a time period between successive zero crossings;
calculating a velocity from the time period;
calculating a velocity error signal between the reference velocity and the velocity;
adjusting a control signal so that the velocity follows the reference velocity; and,
applying the control signal to an actuator coupled to adjust the position of the optical pick-up unit over an optical media.
4. The method of claim 3 , wherein detecting zero crossings in the tracking error signal includes:
detecting when the tracking error signal crosses zero; and,
providing a zero crossing signal that changes state when the tracking error signal crosses zero.
5. The method of claim 4 , wherein detecting when the tracking error signal crosses zero includes detecting when the tracking error signal passes through a range around zero, the range having a positive value above zero and a negative value below zero.
6. A servo system, comprising:
an optical pick-up unit;
an analog processor coupled to receive signals from detectors in the optical pick-up unit and provide digital signals;
at least one processor coupled to the digital signals, the processor calculating a control signal; and
a driver coupled to control a position of the optical pick-up unit in response to the control signal;
wherein the at least one processor executes an algorithm that detects zero crossings in a tracking error signal by
delaying for a time period of a half of a cycle of the tracking error signal before detecting when the tracking error signal crosses zero;
detecting when a tracking error signal crosses zero, and
providing a zero crossing signal that changes state when the tracking error signal crosses zero.
7. The method of claim 6 , wherein detecting when the tracking error signal crosses zero includes detecting when the tracking error signal passes through a range around zero, the range having a positive value above zero and a negative value below zero.
8. An optical disk drive, comprising:
means for generating a tracking error signal from digital signals received from an optical pick-up unit;
means for delaying for a time period of a half of a cycle of the tracking error signal before detecting when the tracking error signal crosses zero; and,
means for detecting a zero crossing of the tracking error signal.