Radiant energy – Photocells; circuits and apparatus – Photocell controls its own optical systems
Reexamination Certificate
1999-08-31
2001-05-22
Allen, Stephone B. (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Photocell controls its own optical systems
C369S043000, C360S069000, C360S073010
Reexamination Certificate
active
06236032
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a tracking pull-in circuit for enabling securely pulling a read beam in a tracking servo loop by inhibiting relative velocity in a direction in which the read beam crosses a code track between the read beam and a record medium in pulling in the tracking servo loop in a tracking servo circuit for instructing a code read beam to follow a code track in an information reader represented by a reproducing unit for an optical disk or an optical card and others.
2. Description of the Related Art
In the above information reader, so-called tracking servo control for instructing a code read beam to follow a code track is essential. In such tracking servo control, when a read beam is biased in a direction in which the read beam crosses a code track to follow by disturbance caused due to the eccentricity and others of an optical disk which is a record medium for example, the quantity of the bias, that is, a tracking error signal is detected and feedback control is executed so that such a tracking error signal becomes zero. That is, a tracking servo loop is configured, a read beam is controlled so that it is always on a code track and record information recorded on the code track is read.
In pulling in a tracking servo loop, damping control is executed in a direction reverse to the erroneous direction of a read beam to a code track by a tracking pull-in circuit and after relative velocity between a read beam and a record medium is sufficiently reduced, the tracking servo loop is closed.
The erroneous direction of a read beam to a code track can be acquired based upon a relationship in phase between a tracking error signal and an on-track signal showing that the read beam is in a state (in an on-track state) in which the read beam irradiates the code track.
Generally, a flaw, dust and others exist on a record medium such as an optical disk. Such flaw and dust reduce the luminous energy of the reflected light of a read beam, operate on an on-track signal and a tracking error signal respectively generated based upon such reflected light as a so-called defect and deteriorate its amplitude level.
There is a problem that when the above defect is caused during operation for pulling in a tracking servo loop, the erroneous direction of a read beam to a code track acquired based upon the above phasic relationship between a tracking error signal and an on-track signal is judged by mistake, damping is applied in a direction reverse to a direction for damping to be applied, velocity is increased by mistake and pulling in the tracking servo loop fails.
SUMMARY OF THE INVENTION
The present invention is made to solve the above problem and the object is to provide a tracking pull-in circuit for reducing effect by a defect and enabling securely and promptly pulling in a tracking servo loop.
To achieve the above object, according to a first aspect of the present invention, there is provided a tracking pull-in circuit for reducing relative velocity in the erroneous direction of a code track between a code read beam and a record medium so as to pull a code read beam irradiated on the record medium on which code tracks are formed in a tracking servo loop for instructing the code read beam to follow the code track based upon a tracking error signal, said tracking pull-in circuit comprising: tracking error signal generating means for generating a tracking error signal showing the quantity of the relative bias of a code read beam to a code track, on-track signal generating means for generating an on-track signal showing that a code read beam is on a code track, damping control signal generating means for generating a damping control signal showing either of a damping authorized state or a damping inhibited state based upon the above on-track signal, damping means for damping a code read beam in the erroneous direction of a code track according to a control signal generated based upon the above tracking error signal when the above damping control signal shows a damping authorized state and defect detecting means for detecting a defect on the record medium; wherein the damping control signal generating means forcedly changes the above damping control signal into a damping inhibited state when the above defect is detected.
According to the first aspect of the present invention, the damping control signal generating means forcedly changes a damping control signal into a damping inhibited state in case a defect is detected on a record medium.
Therefore, the wrong discrimination due to a defect of the direction of relative movement between a code read beam and a record medium is prevented beforehand and damping operation in pulling in a tracking loop can be securely executed.
According to a second aspect of the present invention, there is provided a tracking pull-in circuit as set forth in the first aspect of the invention, wherein the above damping control signal generating means is restored to a damping authorized state when the damping inhibited state of a damping control signal continues for predetermined time.
According to the second aspect of the present invention, damping control signal generating means is forcedly restored to a damping authorized state in case a damping inhibited state continues for predetermined time.
Therefore, the stored quantity of low frequency components of a tracking error signal generated when a damping inhibited state, that is, the open state of a tracking loop continues for a long time can be reduced and a damped state can be prevented from being unstable due to the above stored quantity when a damping control signal is restored into a damping authorized state.
REFERENCES:
patent: 4544957 (1985-10-01), Moriya et al.
patent: 4901299 (1990-02-01), Nakatsu
Allen Stephone B.
Pioneer Corporation
Sughrue Mion Zinn Macpeak & Seas, PLLC
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