| 摘要 |
PURPOSE:To prevent an overcurrent from flowing to a tracking actuator when a tracking error is increased abnormally by comparing a tracking error signal with a reference signal and interrupting a tracking servo loop in response to the result. CONSTITUTION:The tracking error signal (a) from a computing element 4 is compared with reference signals b, b' from reference signal sources 8, 9 for the quantity by a comparator 7. The reference signal (b) is equal to a positive abnormal level of the tracking signal (a) and the reference signal b' is equal to a negative abnormal level of the signal (a). When the level of the signal (a) is at the outside of the level of the reference signals b, b' as the result of comparison, it is discriminated to be a fault of the tracking control to open a switch circuit 6. Thus, the tracking servo loop is interrupted, no error signal is given to a drive circuit 1, and the overcurrent flowing to the tracking actuator 2 due to the abnormal increase in the error signal is prevented.
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