| 摘要 |
An optical disk drive system having a means for detecting off-track conditions with high reliability under conditions causing the objective lens to deviate from optimal focus, such as in the presence of external mechanical shocks. As the lens travels out of focus, the ability to resolve features decreases due to the lose of image contrast, causing a loss of tracking error signal (TES) gain. A digital signal processor (DSP) compensates for this loss by continuously determining an adjustable TES threshold representing the same desired percentage off track and same percentage of TES amplitude. A straight line approximation of this ideal adjustable threshold is used as a threshold to determine if the beam is within the desired amount off track. Alternatively, the DSP amplifies the TES by an amplification function to maintain the TES at a constant value while the objective lens travels out of focus. The TES amplification function is a straight line approximation of an ideal amplification function. The amplified TES is then compared against a fixed TES threshold to determine if the beam is within the desired amount off track. The DSP compensates for head optics astigmatism by shifting the adjustable TES threshold and adjustable TES amplification to a corrected position corresponding to the optimum TES. Dual adjustable and fixed TES thresholds are utilized to filter noise glitches on smaller off track conditions and simultaneously provide fast detection of large off track excursions.
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