| 摘要 |
An information track centering system comprises a source (14) of radiation, an optical media recording disk (12) and a diffraction grating (22) interposed between said radiation source and said optical media recording disk. The diffraction grating is oscillated so that spots (32,40) produced on the optical media recording disk by a leading first order radiation beam (24) and a trailing first order radiation beam (38) created by the diffraction grating are caused to wobble radially, inwardly and outwardly about the centre of an information track on the optical media recording disk in opposite directions, respectively, while a zero order radiation beam spot is unaffected by the oscillation. First and second detectors (50, 52) are arranged to detect radiation beams reflected from the optical media recording disk by the leading and trailing first order radiation beams. Circuitry (56) forms a time averaged difference signal with respect to output signals of the first and second detectors to produce a difference signal representative of the difference in amplitude in information bits as detected by the first and second detectors. A band pass filter (58) removes from said difference signal any unwanted signal outside the frequency spectrum for error detection and correction. A synchronous amplifier-detector (48) is connected to receive the output of the band pass filter to produce an error signal having an amplitude representative of the distance the information track is off centre and switched in synchronisation with the frequency of oscillation of said diffraction grating so that the error signal contains information representative of the direction in which said information track is off centre. |
