Dynamic information storage or retrieval – With servo positioning of transducer assembly over track... – Optical servo system
Reexamination Certificate
1998-11-09
2001-10-09
Huber, Paul W. (Department: 2651)
Dynamic information storage or retrieval
With servo positioning of transducer assembly over track...
Optical servo system
C369S124050
Reexamination Certificate
active
06301206
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical disc drive and its control method and in particular, to a servo control method and an optical disc drive appropriate for implementing the control method.
2. Description of the Related Art
A conventional optical disc drive usually uses a servo signal processor circuit (hereinafter, referred to as an SSP) as hardware for carrying out a servo processing. An error signal outputted from an optical unit is supplied to the SSP so as to be compared to a target value and a difference between the error signal and the target value is corrected for carrying out the servo processing.
FIG. 8A
is a block diagram showing configuration example of an optical disc drive for carrying out such a servo processing with hardware.
Referring to
FIG. 8A
, according to a reproduction signal read out from an optical disc
1
by an optical unit
2
, an RF circuit
4
creates a servo signal and an SSP
6
carries out a servo processing via a driver circuit
3
such as a focus servo, tracking servo, sled servo, and spindle servo. A microcomputer
5
carries out a system control such as a servo control sequence, disc information management, key-in information fetch, display control, and other system control.
The SSP
6
for the servo processing is constituted by hardware for carrying out the servo processing in parallel processing method. In this case, a filter calculation for determining a control amount for correcting the aforementioned difference between an error signal and a target value is carried out by combining an fs process with an 1
fs process. The fs process is carried out for each sampling frequency (hereinafter, referred to as fs), and the 1
fs process is carried out 1
times of the sampling frequency. That is, a focus servo and a track servo need be controlled at a high speed, whereas a spindle servo need not be controlled at such a high speed as the focus and tracking servo. Accordingly, as shown in
FIG. 9
, the calculation amount varies depending on the sampling timing as follows: only an fs processing, or an fs processing in combination with a ¼ fs processing, or an fs processing in combination with a ¼ fs processing and ⅛ fs processing, and the like.
It should be noted that for carrying out a servo processing through hardware, there is also an optical disc drive using the SSP
6
and the microcomputer
5
which are made as a unitary block. In this case also, the system control of the servo control is carried out by the microcomputer portion and the servo processing is carried out by hardware.
In the optical disc drive shown in block diagrams of FIG.
8
A and
FIG. 8B
, the SSP
6
is hardware for carrying out a servo processing in a parallel processing method. However, it is desired to perform the servo processing with microcomputer software. If the servo processing is carried out by software, it becomes easy to modify the filter form such as the calculation order and calculation amount for general purpose. For example, a CD has been the main optical disc widely used, but recently new discs such as a PD (private disc, writable CD) and DVD (digital versatile disc) have been developed and are now in use. A servo processing through software would enable a single servo LSI to be used for various types of media.
However, if the servo processing which has been conventionally carried out by hardware is simply transferred to a microcomputer software, it is necessary to employ a microcomputer having a considerably high speed. This is because the processes carried out in parallel in the conventional hardware need be carried out in series in software, requiring a long calculation time at once. Moreover, as shown in
FIG. 9
, down sampling processes are concentrated in a particular sampling timing, and the time required for calculation greatly varies depending on the sampling timing.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a servo control method in which a servo processing load per one sampling is averaged to reduce the maximum calculation amount. This enables to obtain a servo control and a system control at a sufficiently practical speed even by using a microcomputer having a comparatively low speed, and an optical disc drive apparatus appropriate for implementing the servo control method.
The present invention provides an optical disc drive apparatus for carrying out a servo processing and system control by software using a microcomputer. Moreover, the present invention provides an optical disc drive control method characterized in that an interrupt is generated at a servo processing sampling period for carrying out a digital servo processing, and the remaining time is used for carrying out a system control.
In a servo processing of the optical disc drive according to the present invention, down sampling processes are not concentrated at a particular sampling timing. That is, the down sampling processes are classified according to the sampling frequency and the function (such as focus and tracking). Head addresses of the classified down sampling processes are stored in a servo table which will be detailed later with reference to FIG.
5
. Using this servo table and a counter value which is incremented by each sampling, a sampling process to be performed is selected from the servo table each sampling timing (step
22
in FIG.
6
).
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Nomura Akihisa
Shimone Toshiaki
Tanaka Hiroyuki
Huber Paul W.
NEC Corporation
Sughrue Mion Zinn Macpeak & Seas, PLLC
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