Optical media tracking method and apparatus for optical storage system

A multiple beam optical apparatus for reading an optical disc having at least one concentric reference track and circular data tracks comprising,

• tracking optical means including a tracking objective lens for directing a tracking beam onto a concentric reference track carried by a rotating optical disc,
• data optical means including a data objective lens for directing a data beam onto a circular data track carried by the disc, the beam axes of the tracking and data beams adjacent the disc being substantially parallel,
• substantially continuously operable closed loop control means for simultaneously moving said tracking and data optical means relative to said disc so as to cause the tracking beam to follow the reference track,
• means for rotating the data beam axis about the tracking beam axis so as to cause the data beam to follow circular data tracks, said data lens being rotatably movable about the optical axis of the tracking lens by said means for rotating the data beam axis about the tracking beam axis.

A multiple beam optical apparatus for reading an optical disc having at least one concentric reference track and circular data tracks comprising,

• tracking optical means for directing a tracking beam onto a concentric reference track carried by a rotating optical disc,
• data optical means for directing a data beam onto a circular data track carried by the disc,
• substantially continuously operable closed loop control means for simultaneously moving said tracking and data optical means relative to said disc so as to cause the tracking beam to follow the reference track, said tracking and data optical means including a single objective lens for focusing the tracking and data beams onto the optical disc, through which lens said tracking and data beams pass at an angle with each other,
• means for moving the data beam relative to the tracking beam by varying the angle between the tracking and data beams so as to cause the data beam to follow circular data tracks,
• said data and tracking optical means including first and second lasers operable at first and second frequencies, respectively, and a dichroic mirror for reflecting the data beam and transmitting the tracking beam, and
• said means for varying the angle between the tracking and data beams comprising means for pivoting the dichroic mirror for varying the angle at which the data beam is reflected therefrom and varying the angle between the tracking and data beams.

An optical head positioning system for positioning tracking and data optical means carried on a carriage relative to a rotatable optical disc having at least one concentric reference track and circular data tracks thereon, comprising

• a carriage for carrying tracking optical means and data optical means having parallel tracking and data beams, respectively, directed onto the disc, the tracking beam being fixed relative to the carriage and the data beam being movable relative to the carriage,
• means for supporting said carriage for translational movement radially relative to said disc,
• closed loop control means including a servomotor for moving said carriage and tracking and data optical means carried thereby so as to maintain the tracking beam on the reference track, and
• means for steering the data beam relative to the carriage by movement of the data beam axis along at least a portion of an orbital path about the tracking beam axis so as to follow a selected data track.