Dynamic information storage or retrieval – With servo positioning of transducer assembly over track... – Optical servo system
Reexamination Certificate
1999-10-28
2002-08-27
Huber, Paul W. (Department: 2651)
Dynamic information storage or retrieval
With servo positioning of transducer assembly over track...
Optical servo system
C369S053300
Reexamination Certificate
active
06442111
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a track jump apparatus for jumping a position of an actuator to a position corresponding to a target recording track so as to irradiate the target recording track with a laser beam spot to be irradiated to a predetermined recording track on a recording medium via an objective lens of the actuator, the track jump apparatus being used in an information reproducing apparatus, information recording apparatus or information recording/reproducing apparatus using a recording medium such as an optical disk.
2. Description of the Related Art
Conventionally, feed-forward type open control method has been employed for control on track jump in a compact disk (CD) player and the like, in which acceleration pulse of a predetermined amount is applied to an actuator drive at the same time when a jump start instruction is dispatched and deceleration pulse of a predetermined amount is applied to that drive at a desired timing.
However, with current increased density of an optical disk like DVD, as the track pitch is narrowed, the following problem occurs in an open control of a conventional feed forward method. First, because blind zone and a delay of reaction time exist in the driving system and detecting system of the tracking servo, even if a deceleration pulse is applied, sometimes actual driving is delayed or detection of deceleration and servo close timing is delayed. If a sufficient jump time is secured like a case of CD or a so-called capture range which is a range capable of obtaining an effective tracking error signal at the time of lead-in after a servo close is wide, the delay of the driving system or detecting system does not affect stabilization of the tracking servo largely.
However, if the same amount of pulse is used for the acceleration pulse and deceleration pulse like the conventional track jump in case of a narrow track pitch, the jump time decreases. Thus, the aforementioned blind zone and a rate of the delay with respect to the jump time increase so that stabilization of the tracking servo is largely affected. If the track pitch is narrow, the aforementioned capture range is also narrow. As a result, the frequency of overshoot caused at the servo close increases so that it is out of the servo band. Thus, no braking is applied so that the jump fails or it takes long until stabilization is accomplished.
As a method for preventing such a unstable condition of the track jump, a method in which the same amount of pulse is not used for the acceleration pulse and deceleration pulse but after a predetermined amount of the acceleration pulse is applied, an interval between a jump start and zero cross of the tracking error is measured and then the amount of the deceleration pulse is adjusted based on a deviation between a measured zero cross interval and an appropriate zero cross interval, has been proposed.
To measure the zero cross point accurately, some extent of measuring time is required. If the same amount of the acceleration pulse and deceleration pulse is applied when the track pitch is narrow, the jump time becomes shorter than the conventional case, so that a necessary measuring time cannot be obtained. Therefore, the accuracy of the measured zero cross point deteriorates so that a deceleration pulse calculated from the zero cross interval based on this zero cross point becomes not appropriate, thereby further disturbing stabilization of the tracking servo.
Recently, a servo system for digital processing with digital signal processor (DSP) has been developed. In this system, the tracking error signal is sampled upon a track jump and then the output timing of the deceleration pulse and close timing of the tracking servo are determined based on the sampled value, so that a delay of a timing of one sampling at the maximum occurs.
Therefore, if the track pitch is decreased, the jump time becomes shorter, so that the delay of the timing of one sampling affects largely, thereby not only making a unstable jump but also the jump operation not functioning properly sometimes leading to a jump failure.
On the other hand, to prevent an occurrence of a problem due to shortening of the jump time as described above, a method for reducing the acceleration/deceleration amounts can be considered. However, generally if the acceleration pulse and deceleration pulse are decreased, relatively an influence of a disturbance increases. The disturbance is caused by a deflection, a change of slider state, shock or the like and a size of an estimated disturbance is almost determined. Because the track jump method is carried out by open control as described above, basically this is weak against the disturbance. Therefore, even if the acceleration/deceleration amount is decreased in the conventional track jump method, the influence of the disturbance is so strong that the track jump cannot be stabilized.
Thus, a method in which feed back control is carried out even during a track jump by feed forward control to achieve a stabilized jump with some extent of jump time secured has been proposed (Japanese Patent Application Laid-Open No. HEI 9-167357). According to this method, even if the disturbance such as a deflection of disk occurs, a stabilized tracking servo lead-in is possible after the track jump ends.
However, although according to the method disclosed in the aforementioned Patent Application, a trajectory of a beam position at a jump time needs to be provided as an object value for feed back control, because feed forward control of applying a deceleration pulse just after the acceleration pulse ends is carried out, the trajectory of the aforementioned beam position becomes a shape like quadratic curves are combined. As a result, because the object value itself is high in view of band, an effect of the feed back control cannot be expected so high. That is, because according to this method, the constant deviation is relatively large, it is difficult to stabilize the tracking servo in a short time.
SUMMARY OF THE INVENTION
Accordingly, the present invention has been achieved in views of these problems, and therefore, it is an object of the invention to provide a track jump apparatus capable of achieving a stabilized track jump with some extent of jump time secured even if the track pitch is narrow and further stabilizing the tracking servo in a short time.
A track jump apparatus in accordance with the present invention is an apparatus for making an actuator jump in order to move a spot position of a laser beam emitted through an objective lens of the actuator from a current position to an object position corresponding to a desired recording track on a recording medium. The track jump apparatus includes: an actuator driving device that moves the actuator in accordance with a driving signal; a tracking error signal detecting device that detects a tracking error signal on the basis of a change of return light from the recording medium caused by a change of the spot position of the laser beam relative to the recording track; a feed-forward control device that applies an acceleration pulse and a deceleration pulse to the actuator driving device; and a position control device that controls a position of the actuator using a feedback of the driving signal so as to reduce a difference between an object value and the tracking error signal detected by the tracking error signal detecting device, when making the actuator jump in order to move the spot position of the laser beam from the current position to the object position. The feed-forward control device sets a constant speed period during which neither of the acceleration pulse and the deceleration pulse is applied to the actuator driving device between an acceleration period during which the acceleration pulse is applied to the actuator driving device and a deceleration period during which the deceleration pulse is applied to the actuator driving device.
In the track jump apparatus in accordance with the present invention, when receiving an instruction of the track j
Takahashi Kazuo
Tateishi Kiyoshi
Huber Paul W.
Morgan & Lewis & Bockius, LLP
Pioneer Corporation
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