JPH033123A - Objective lens drive device - Google Patents

Abstract

PURPOSE:To facilitate the positioning fixation of a coil for tracking and simultaneously, to prolong an effective coil length and to improve the driving efficiency by making the sectional shape of the coil for tracking into the approximately cylindrical shape of an approximate quadrangle and attaching four coils approximately symmetrically to a rotary shaft to a lens holder. CONSTITUTION:A system to obtain the driving in a tracking direction T by turning arround a shaft 3 as a center is adopted, and for four coils 5a-5d for tracking, the sectional shapes are the approximately cylindrical shapes of the approximate quadrangle, and the coils are fitted approximately symmetrically to the shaft 3. Two surfaces to be opposite of one side of each of the coils 5a-5d are made approximately parallel in the tracking direction T, and two surfaces to be opposite of the other side are made approximately perpendicular to an optical axis direction F. Consequently, both driving forces generated on two surfaces to be opposite of the coils 5a-5d for tracking can be utilized as the driving force in the tracking direction T, and the effective length of the coil can be prolonged. When the fitting part of a holder 2 is made into a cylindrical shape to be mutually fitted in, the positioning fixation of the coil for tracking can be facilitated.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an objective lens driving device for an apparatus for optically writing or reading information on a disc-shaped recording medium.

Conventional technology Objective lens drive devices move the objective lens in a direction parallel to the surface of the recording medium in order to correct focus shifts caused by vertical movements of warped disk-shaped recording media such as compact discs, and tracking shifts caused by eccentricity. It is driven along two axes: an optical axis direction (hereinafter referred to as a focus direction F) and a radial direction parallel to the recording medium surface (hereinafter referred to as a tracking direction T).

A conventional objective lens driving device of this type has a structure as shown in FIG.

That is, driving in the focus direction F is performed by the objective lens 21.
The lens holder 22 with the attached lens is moved along the axis 23 by an electrodynamic transducer in which a focusing coil 28 is placed in the gap of a magnetic circuit consisting of magnets 25a, 25b and magnetic yokes 26a, 26b provided on a base 29. It is obtained by sliding motion. Drive in the tracking direction T is achieved by placing tracking coils 27a, 27b in the gap of a magnetic circuit consisting of magnets 25a, 25b and magnetic yokes 26a, 26b, in which a lens holder 22 with an objective lens 21 attached is provided on a base 29. This is obtained by rotational movement about the axis 23 using an electrodynamic transducer. In addition, the entire objective lens driving device is access-driven by a motor in the access direction Ac () the same direction as the ranking direction T) on the recording medium.

Problems to be Solved by the Invention However, in the objective lens drive device having the structure as shown in FIG.
The magnetic flux generated by the magnetic circuit 26b is directed toward the center of the shaft. therefore,
In order to use a common magnetic circuit for focus drive and tracking drive, tracking coils 27a, 27
The opposing portion of b has to be taken out of the magnetic circuit, and at the same time, since it is a flat type, the effective coil length for obtaining the driving force in the tracking direction T cannot be long, resulting in poor coil utilization efficiency. Further, there was a problem that positioning and fixing to the focusing coil 28 was difficult.

Therefore, in view of the above problems, the present invention provides an efficient objective lens drive device in which the tracking coil can be easily positioned and fixed, and the effective coil length is long.

Means for solving the problem The technical means for solving the above problem are as follows.

That is, the trunking coil has a substantially cylindrical shape with a substantially quadrangular cross section, and one of the two opposing surfaces is substantially perpendicular to the focusing direction F, and the other two opposing surfaces are directed in the tracking direction T. The four tracking coils are mounted on the movable part so as to be substantially parallel to the axis, and the four tracking coils are substantially symmetrical to the axis, and of the two planes of the tracking coils that are substantially parallel to the tracking direction T, The magnetic flux generated by a part of the magnet constituting the opposing focus direction magnetic circuit crosses the surface near the center of rotation in the axial direction approximately parallel to the tracking direction T, and the surface far from the center of rotation The magnetic circuit is configured such that the magnetic flux generated by the opposing tracking direction magnets has a component substantially perpendicular to the tracking direction T and the focus direction F and crosses in a direction away from the axis.

action The effects of the above technical means are as follows.

In an objective lens drive device configured to rotate around an axis, by adopting the magnetic circuit configuration described above, the driving force generated on the two opposing surfaces of the tracking coil is used as driving force in the tracking direction T. The effective length of the coil can be increased. In addition, since it is not a flat type, the effective length of the coil for obtaining the driving force in the tracking direction T can be long, and the coil can be utilized efficiently and sensitivity can be improved. Since the tracking coil is wound into a substantially cylindrical shape, the tracking coil can be easily positioned and fixed by forming a part of the lens holder into a cylindrical shape that can fit into the tracking coil.

EXAMPLE Hereinafter, an objective lens driving device according to an example of the present invention will be described with reference to the drawings.

In FIG. 1, (A) is a front view of an objective lens driving device according to an embodiment of the present invention, FIG. 1(B) is a cross-sectional view taken along line A-A in FIG. 1(A), and FIG. FIG. 3 is a front view of main parts showing the state of driving.

As shown in FIG. 1, the drive in the focus direction F is such that the lens holder 2 to which the objective lens 1 is attached is focused into the gap of a magnetic circuit consisting of magnets 7a, 7b provided on a base 9 and magnetic yokes 8a, 8b. A shaft 3 whose one end is fixed to a base 9 by an electrodynamic transducer equipped with a coil 6 for
obtained by sliding movement along the As shown in FIG. 3, the cross-sectional shape of the tracking coil 5C is a rectangular cylindrical shape, and one of the two opposing surfaces 11
c, the lid is approximately parallel to the tracking direction T, and the four tracking coils 5a to 5d are
(shown in FIG. 1(A)) is attached to the movable part so as to be approximately symmetrical with respect to the axis 3, and the balance weight 4
The center of gravity of all movable parts is partially located at the center of the shaft. As shown in FIG. 2, the surface 11c closer to the center of rotation has a magnetic flux B1 substantially parallel to the tracking direction T generated by a part of the magnet 7b constituting the focus direction magnetic circuit and a current 11 flowing through the surface 11c. The lid on the side far from the center of rotation, which generates a driving force of Fl, generates a driving force of F2 by a magnetic flux B2 collected by the opposing tracking direction magnet 10c and a current 2 flowing through the surface lid. Drive in the tracking direction T is obtained by rotating the lens holder 2 to which the objective lens 1 is attached about the shaft 3 by the driving forces F1 and F2. In addition, the entire objective lens driving device is moved in the access direction AC (same direction as the tracking direction T) on the recording medium.
Access is driven by a motor.

By adopting the magnetic circuit configuration as shown in FIG. 2, the driving forces F1 and F2 generated on the two opposing surfaces of the tracking coil can both be used as driving forces in the tracking direction T, and sensitivity can be improved. Since it is not a flat type, the effective coil length for obtaining the driving force in the tracking direction T can be long, and the coil utilization efficiency is improved.

In addition, as shown in Figure 3, since the tracking coil is wound into a substantially cylindrical shape, if a part of the lens holder is made into a cylindrical shape that can fit into the tracking coil, the tracking coil can be positioned and fixed. can be easily done.

Needless to say, since the driving in the focus direction F is a closed magnetic circuit, the sensitivity can be improved. Furthermore, the focusing magnets 7a, 7b and 7b are arranged so that the sum of the magnetic flux generated by the surface magnetic field of a portion of the focusing magnets 7a, 7b and the magnetic flux generated by the tracking magnets 10a-10d becomes almost zero with respect to the recording medium surface. Alternatively, if the magnetic flux of the trunking magnets 10a-10d is adjusted, recording will not be affected, even in the case of a recording medium in which information is recorded magneto-optically, such as a magneto-optical disk.

Effects of the Invention This is an objective lens drive device that obtains drive in the tracking direction by rotating around an axis, and the tracking coil has a substantially rectangular cylindrical cross section, and one of the two opposing surfaces is in the focus direction F. so that the other two opposing surfaces are approximately parallel to the tracking direction T, and the four tracking coils are approximately symmetrical about the axis. The magnetic flux generated by a part of the focusing magnet is attached to the movable part of the tracking coil, and the magnetic flux generated by a part of the focusing magnet is placed on the side near the center of rotation of the two surfaces substantially parallel to the tracking direction T of the tracking coil. The magnetic flux collected by the opposing tracking magnets crosses the surface in parallel toward the axis and away from the center of rotation in a direction away from the axis with components substantially perpendicular to the tracking direction T and focus direction F. By configuring the magnetic circuit in this way, the driving forces generated on the two opposing sides of the tracking coil can both be used as driving forces in the tracking direction T, the effective length of the coil can be increased, and sensitivity can be improved. Since it is not a flat type, the effective length of the coil for obtaining the driving force in the tracking direction T can be long, and the efficiency of use of the coil is improved. In addition, since the tracking coil is wound into a substantially cylindrical shape, if a part of the lens holder is made into a cylindrical shape that can be fitted into the tracking coil, the tracking coil can be easily positioned and fixed. An objective lens drive device with good performance can be realized.

[Brief explanation of the drawing]

FIG. 1(A) is a front view showing an embodiment of the objective lens driving device of the present invention, FIG. 1(B) is a cross-sectional view taken along line A-A in FIG. 1(A), and FIG. FIG. 3 is a front view of a main part showing how an embodiment of the objective lens drive device is driven in the tracking direction; FIG. Figure 4 (
A) is a front view of a conventional objective lens drive device, and FIG. 4 (B)
) is a sectional view taken along line BB in FIG. 4(A). ■... Objective lens, 2... Lens holder, 3... Axis, 4...=- Balance weight, 5a to 5d... Tracking coil ,6
...Focusing coil, 7a, 7b...
... Focusing magnet, 8a, 8b... Focusing magnetic yoke, 9... Base, 10a-1
0d... Tracking magnet, F...
Focus direction, 11, 12... Current, T tracking direction, Bl, B2... Magnetic flux, Ac...
...Access direction, Fl, F2...Driving force.

Claims (4)

[Claims] (1) The objective lens of a device for optically writing or reading information onto or from a disc-shaped recording medium is aligned in a radial direction parallel to the recording medium surface of the disc-shaped recording medium and in a direction parallel to the recording medium surface. has a mechanism for driving in the perpendicular optical axis direction, and is configured such that a movable part consisting of the objective lens and a lens holder that holds the objective lens is rotatable in the radial direction about an axis, four radial drive coils for driving the movable part in the radial direction; one optical axis drive coil for driving the movable part in the optical axis direction; and one radial drive coil for driving the movable part in the optical axis direction. Equipped with a plurality of optical axis direction magnetic circuits for applying magnetic flux to the drive coil,
The drive coil for the optical axis direction has a substantially cylindrical shape with a substantially quadrangular cross section, and one opposing two surface is substantially perpendicular to the optical axis direction, and the other opposing two surface is substantially perpendicular to the optical axis direction. The four radial drive coils are attached to the movable part so as to be substantially parallel to the radial direction, and the four radial drive coils are substantially symmetrical to the axis, and drive in the optical axis direction. is obtained by an electrodynamic converter in which the optical axis direction drive coil is arranged in a gap of a magnetic circuit for the optical axis direction consisting of a magnet and a magnetic yoke, and the drive in the radial direction is achieved by the radial direction drive coil. Of the two surfaces substantially parallel to the radial direction, the magnetic flux generated by a part of the magnet constituting the opposing magnetic circuit for the optical axis direction is made substantially parallel to the radial direction on the surface near the rotation center. The magnetic flux generated by the opposing radial direction magnets extends away from the axis with a component substantially perpendicular to the radial direction and the axial direction, on the side that traverses the axial direction and is far from the center of rotation. An objective lens driving device characterized in that it is obtained by an electrodynamic transducer by traversing. (2) The magnetic flux of the radial direction magnet and/or the optical axis direction magnetic circuit is adjusted so that the sum of the magnetic fluxes generated on the recording medium surface by the radial direction magnet and the optical axis direction magnetic circuit becomes zero. The objective lens driving device according to claim 1, characterized in that: (3) The objective lens drive device according to claim (1), wherein the lens holder is provided with a substantially rectangular parallelepiped-shaped protrusion for positioning and fixing the radial drive coil. (4) The dimension of the magnet constituting the optical axis direction magnetic circuit in the direction perpendicular to the optical axis direction and the radial direction is longer than the dimension of the magnetic yoke of the optical axis direction magnetic circuit. The objective lens driving device according to claim (1).