Focus servo loop off-set compensation

Claim 2

In an optical disk data storage system including head means having lens means for focusing a beam of radiant energy on a surface of said disk and means for adjusting the point of focus by moving the head, said system further including a feedback servo means, including means for supplying a focus error signal, for maintaining the head at a position of best focus, said system being characterized in that it comprises : means for supplying an indicating signal when the head is at its best focus position; means responsive to said indicating signal supplying means and to said focus error signal supplying means for sensing said focus error signal when the head is at its best focus position; means for supplying a correction signal having a value equal to said sensed focus error signal; and means for supplying a focus drive signal to said adjusting means including means for combining said focus error signal and said correction signal to cancel out said sensed focus error signal.

Claim 3

The system as claimed in claim 1 further comprising: means for selectively disconnecting said focus error signal from said combining means; means for varying said correction signal to move the head to its best focus position; and means for reconnecting said focus error signal to said combining means.

Claim 4

The system as claimed in claim 2 wherein said correction signal varying means includes: means for causing said correction signal to assume a value to move the head to one limit of its travel; and means for changing said correction signal value monotonically in a direction to cause the head to move to its other limit.

Claim 5

Information storage and retrieval system including: a beam of radiant energy; recording means for storing information having values manifested by variations in reflectivity; , focusing means for causing said beam to converge on a recorded surface of said recording means in a plane at which said information is recorded; focus control means responsive to a portion of radiant energy reflected from said recording means for providing a control signal to said focusing means to keep said beam converged on said recording means; and differentiating means responsive to a read signal derived from reflected radiant energy for supplying a feedback signal, said system being characterized in that it further includes :: means for decoupling said control signal from said focusing means; means for providing an off-set correction signal to said focus control system to maintain convergence of said beam on said recording means including: means coupled to said focusing means for driving said means from one limit to the other; means responsive to said feedback signal for supplying a pulse when a peak is detected in said feedback signal; and means responsive to said control signal and said pulse for storing the value of said control signal coincident with said pulse; means for coupling said control signal to said focusing means; and means for subtracting the stored value of said control signal from said control signal value.

Claim 6

Information storage and retrieval system including: a beam of radiant energy; recording means for storing information having values manifested by variations in reflectivity; , focusing means for causing said beam to converge on a recorded surface of said recording means in a plane at which said information is recorded; focus control means responsive to a portion of radiant energy reflected from said recording means for providing a control signal to said focusing means to keep said beam converged on said recording means; and differentiating means responsive to a read signal derived from reflected radiant energy for supplying a feedback signal, said system being characterized in that it further includes :: means for decoupling said control signal from said focusing means; means for providing an off-set correction signal to said focus control system to maintain convergence of said beam on said recording means including: means coupled to said focusing means for driving said means from one limit to the other; means responsive to said feedback signal for supplying a pulse when a peak is detected in said feedback signal; and means responsive to said control signal and said pulse for storing the value of said control signal coincident with said pulse; means for coupling said control signal to said focusing means; and means for subtracting the stored value of said control signal from said control signal value.