Patent Application
20090073818
The present invention generally relates to a seeking control system and method of an optical disc drive for stably controlling the seeking operation.
The DVD-RAM type disc employs a wobbled Land/Groove recording method, which is different from the wobbled Groove recording method employed by the other discs, such as CD-RW, DVD-RW or DVD+RW. The data is recorded in both the groove and land of each spiral track on the DVD-RAM disc; therefore a high track density is obtained. However, it results in some difficulties for an optical disc drive to access the DVD-RAM disc.
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Generally, an optical disc drive seeks (or called search) the target position first then could follow the track to access the optical disc. This seeking or searching is called a seeking operation. The optical disc drive adopts the reflected signal by the PUH 102 to control the movement of the PUH 102. The reflected signal is converted and amplified into servo signals by the RF Amp 112. The servo signals at least include a TE (Tracking Error) signal and a Tcs (central servo) signal. A servo controller 114 receives these servo signals and generates a TRO (Tracking Output) signal and a FMO signal (a sled motor control signal) to a motor driver 116 to drive the tracking coil 108 and the sled motor 106 so as to move the PUH 102 to the target position. In the seeking operation, the servo controller 114 always tries to keep the tracking coil in the middle of the sled motor, so the TRO signal is generated by compensating the Tcs signal. But as closing to the end of seeking operation, the pickup head 102 would be sometimes controlled to move forward or backward then reduced a “reverse” of the pickup head.
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As aforementioned, the reverse of the PUH 102 happens sometimes if only Tcs control is employed. If the optical disc is CD-RW, DVD-RW or DVD+RW, which is wobbled Groove recording type, even the reverse does happen, the RFZC and TEZC signal can be a clue to determine the TE polarity, but in DVD-RAM, which is wobbled Land/Groove recording type, when a reverse of the PUH 5 occurs, the polarities of the TE signals corresponding to the Land/Groove of the disc also reverses. As a result, the aforesaid phenomenon makes the seeking control unstable.
The present invention provides a seeking control system and method of an optical disc drive for controlling a pickup head stably in a seeking operation. The system comprises a servo controller, a velocity control unit and a switch unit. The servo controller receives a central servo signal (Tcs) to output a first tracking control signal for controlling the tracking coil. The servo controller also provides a sled motor control (FMO) signal for controlling the sled motor. The velocity control unit receives a tracking error (TE) signal to determine the velocity of the pickup head. Then, the velocity control unit compares the velocity of the pickup head with a predetermined velocity profile to generate a second tracking control signal for controlling the tracking coil. The switch unit couples to the servo controller and the velocity control unit. It selects to output one of the first tracking control signal and the second tracking control signal according to the TE signal or the FMO signal.
The switch unit makes a selection between the first and the second tracking control signals by comparing a predetermined frequency with the frequency of the TE signal or by comparing a predetermined number with the number of the pulses of the FMO signal. Alternatively, the switch unit selects to output the second tracking control signal if the seeking operation is in the last portion of the sled motor control signal.
Furthermore, the velocity of the pickup head is obtained from the pulses of the sled motor control signal if a stepping motor is generally used as the sled motor. The pulses supplied to the motor can be employed as a reference for position and velocity of the controlled motor. The switch unit switches from first tracking control signal to the second tracking control signal as the TRO signal to the motor driver to control the pickup head steadily moving without reverse occurring when approaching the ending of the seeking operation.
Accordingly, the seeking control system and the method thereof according to the present invention provides a velocity estimation capable of controlling the pickup head moving steadily without reverse occurring in the seeking operation, especially for the wobbled Land/Groove recording type optical disc. Furthermore, the present invention efficiently prevents the runout event happening while the eccentric optical disc is accessed.
The foregoing aspects and many of the attendant advantages of this invention will become more readily appreciated as the same becomes better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein:
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When the optical disc drive 200 performs a seeking operation, the servo controller 302 receives the TE signal and the Tcs signal from the RF Amp 112, and generates a FMO signal and a first tracking control signal accordingly. The first tracking control signal is generated by compensating the Tcs signal for controlling the tracking coil 108 in the middle of the sled motor 106. As description above, a FMO signal is used to control the sled motor 106 to move the PUH 102 to the target position. The FMO signal is generated by referring to a Flexible Macroblock Ordering profile, which provides the pulses arrangement for the sled motor 106. The FMO signal can be generated by the servo controller 302 or by the other servo element in the optical disc drive 200 which is not restricted according to the present invention.
The present invention also employs a velocity control unit 304 and a switch unit 306 in the seeking control system 300. The velocity control unit 304 receives the TE signal and determines a velocity of the PUH 102 accordingly. In one embodiment, the velocity of the PUH 102 could be the frequency of the TE signal. The velocity control unit 304 makes a velocity estimation to generate the second tracking control signal. The velocity estimation is to compare velocity of the PUH 102 with a predetermined velocity profile. The second tracking control signal is generated by compensating errors between the velocity of the PUH 102 and the predetermined velocity profile. The predetermined velocity profile could be a predetermined frequency, a frequency profile, or the FMO signal. In one embodiment, the predetermined frequency can be the runout frequency for the optical disc. Regarding the DVD-RAM disc, 20 k Hz is preferably used.
Both the servo controller 302 and the velocity control unit 304 are coupled to a switch unit 306. Once the frequency of the tracking error signal (TE) gets slower than the predetermined frequency, a predetermined number of the pulses of the FMO signal for a long seeking is going to reach, or the seeking operation gets in the last portion of the velocity profile of the FMO signal, the switch unit 306 switches connection from the servo controller 302 to the velocity control unit 304. That is, the TRO signal is switched from the first tracking control signal to the second tracking control signal to force the pickup head 102 into a stable velocity control mode. Thereafter, as the seeking operation is close to the end, the pickup head 102 moves stably without reverse. In one embodiment, the switch unit 306 could be a multiplexer.
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In step 410, generating a first tracking control signal for controlling the tracking coil according to a central servo signal;
In step 420, determining a velocity of the pickup head according to a tracking error signal;
In step 430, comparing the velocity of the pickup head with a predetermined velocity profile to generate a second tracking control signal for controlling the tracking coil; and
In step 440, selecting to output one of the second tracking control signal and the first tracking control signal according to the tracking error signal or the sled motor control signal.
In conclusion, the seeking control system and method of an optical disc drive according to the present invention prevent the PUH from happening of the “reverse” and then the optical disc drive becomes unstable, therefore, the present invention prevent can control a pickup head stably in a seeking operation. Therefore, failure of the servo control can be avoided.
As is understood by a person skilled in the art, the foregoing preferred embodiments of the present invention are illustrative rather than limiting of the present invention. It is intended that they cover various modifications and similar arrangements be included within the spirit and scope of the appended claims, the scope of which should be accorded the broadest interpretation so as to encompass all such modifications and similar structure.
