Dynamic information storage or retrieval – Dynamic mechanism subsystem – Having power driven transducer assembly
Patent
1996-08-06
1998-08-04
Cao, Allen
Dynamic information storage or retrieval
Dynamic mechanism subsystem
Having power driven transducer assembly
360106, G11B 1730, G11B 555
Patent
active
057905096
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a driving mechanism for moving an optical pickup along a recording surface of an optical disk such as a compact disk (hereinafter referred to as "CD") to reproduce or read data recorded on the optical disk.
2. Description of the Related Art
To reproduce music or data from a recording track recorded on an optical disk, e.g., a CD, a laser light beam must be applied to the center of the recording track. A common control method for maintaining a light beam at the center position of a recording track is a 3-beam system in which, as shown in FIG. 2, a recording track T0 is illuminated with 3 beams, i.e., a center beam B0 and side beams B1 and B2. The side beams B1 and B2 are used for detection of a tracking error. If the position of the recording track shifts from the center position T0 to a position T1 or T2 as shown by the dotted lines, the intensity of reflected light from the side beam B1 or B2 changes. Therefore, the intensity change is detected to control the beam application position.
An imaginary straight line connecting the centers of the three beams is inclined at 2 degrees with respect to the center line (tangent) of the recording track, that is, the reference line of the optical pickup. In the 3-beam system, the inclination angle must be maintained at a constant level in an allowable range at all times. In other words, it is necessary to make the reference line of the optical pickup coincident with the tangential direction of the recording track within an allowable range. Therefore, many of conventional 3-beam type optical pickup driving mechanisms have been arranged to cause the optical pickup to move rectilinearly on a linear guide. There has been another type of driving mechanism in which an optical pickup is pivotally moved by a swing arm (see Japanese Utility Model Application Public Disclosure (KOKAI) No. 5-33316).
Regarding the length of time required for an optical pickup to move from the innermost track to the outermost track on a CD, about 3 seconds has heretofore been adequate for conventional musical reproduction systems. However, CD-ROMs, which are used as external storage units for computers, are required to make high-speed access; even an access time of 0.3 second or less is needed for CD-ROMs. The demand for such high-speed access makes it necessary to increase the optical pickup driving speed. The driving mechanism that uses a linear guide requires to increase the output of a driving motor for causing the whole optical pickup to perform an accelerated motion. In addition, the linear guide must be produced with high precision over the entire stroke; this causes the cost to increase. Further, a signal output line which extends from the optical pickup to connect with a stationary-side member also needs to be sufficiently long to cover the entire stroke. Consequently, noise is likely to be induced in the output signal line, and the output waveform is adversely affected. In a quadruple-speed drive system in which data is read from a CD rotating at a quadruple speed, the frequency of the data output signal is also quadrupled. Accordingly, the adverse effect due to the length of the output signal line increases.
In contrast, a driving mechanism in which an optical pickup is fixed on one end of a pivoting arm and pivotally moved about a supporting point for the other end of the pivoting arm needs no linear guide and enables the production cost to be reduced. However, as shown in FIG. 3, the locus D of movement of the optical pickup is a circular arc centered at the supporting point 38, and it is impossible to make the direction of the reference line of the optical pickup coincident with the tangential direction of each particular recording track at all points on the locus. Therefore, this type of driving mechanism cannot employ the 3-beam system for tracking error detection. Accordingly, Japanese Utility Model Application Public Disclosure (KOKAI) No. 5-33316 proposes a driving mechanism in which the pos
Cao Allen
Tam Co., Ltd.
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