JPH054732B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus for reading information by projecting a reading light spot onto an information track recorded spirally or concentrically on a recording medium. A recording medium having an information track is generally called a video disk, and encoded video signals and audio signals are recorded as optical information such as optical transmission characteristics, reflection characteristics, and phase characteristics.

While rotating the video disk at high speed, laser light emitted from a laser light source is focused and projected onto the video disk to read optical information.

Such recording media are characterized by extremely high information density. Therefore, the width of each information track is extremely narrow, and the intervals between successive information tracks are also extremely narrow. Therefore, the diameter of the reading light spot is also extremely small.

In order to accurately read the original information from such a narrow information track in width and pitch, it is necessary to minimize the relative positional deviation between the reading light spot and the information track, that is, the tracking error. To this end, tracking control has conventionally been performed in which the relative positional deviation between the reading light spot and the information track is detected, and the reading light spot is displaced in the width direction of the information track based on this tracking error signal. ing.

There is a method of displacing the optical axis of the objective lens in a direction perpendicular to the information track based on a tracking error signal using an elastic member integrally formed with the objective lens.

In this method, a thin plate-shaped elastic member is generally used as the elastic member integrally formed with the objective lens.

Examples of driving devices using elastic members include a method using an electromagnet or a method using a piezoelectric element.

However, in order to improve tracking response characteristics, it is necessary to make the device as small and lightweight as possible.

In addition to such tracking errors, video disk devices also suffer from focusing errors in which a light spot is not correctly focused on an information track.

In order to correct this focusing error, a focusing means for displacing the objective lens in the optical axis direction is required. This focusing means is generally arranged above the tracking means from a functional point of view.

In order to perform this focusing correction well, the tracking means needs to be small and lightweight. As a tracking means, there is a method of moving using an electromagnet as described above. This method of performing tracking correction using an electromagnet is suitable for obtaining the necessary force and for reducing size and weight. However, although this method of moving using an electromagnet can achieve a reduction in size and weight, it has the drawback of resonance due to the relationship between the current flowing through the coil and the amount of displacement of the objective lens. In addition, the elastic member has the disadvantage of causing buckling development in relation to focusing correction and tracking correction.

The objective lens drive device of the present invention includes an objective lens support means for movably supporting the objective lens in a first direction substantially perpendicular to its optical axis and an information track, and a movable magnetic member that moves together with the objective lens. , first and second fixed magnetic members disposed opposite to each other so as to sandwich the movable magnetic member in a second direction substantially perpendicular to the first direction;
It has first and second tracking coils wound around the first and second fixed magnetic members, respectively, and generates a magnetic field passing through the first and second fixed magnetic members and the movable magnetic member. permanent magnets are arranged between the first and second fixed magnetic members to constitute two sets of magnetic circuits, which extend in a third direction parallel to the optical axis and which are connected to the objective lens light. Two flat elongated leaf springs arranged in parallel so as to sandwich the axis and having different dimensions in the extending direction are connected between the magnetic member and a coil holding member to which the focusing coil is fixed, and the coil Connecting the holding member and the base with an elastic member,
A permanent magnet disposed between the focusing coil and the coil holding member is fixed to a base, and the ends of the two leaf springs are separated by a step along the third direction. It is characterized by being fixed to the surface.

The configuration of the present invention will be explained below based on the drawings.

FIG. 1 is a plan view showing the position of an elastic member supported by an objective lens in an information track reading device embodying the present invention, with half of the surface being taken in longitudinal section.

FIG. 2 is a schematic plan view showing the top surface of FIG. 1.

FIG. 3 is an enlarged plan view of an elastic member integrally constructed with the objective lens shown in FIG. 1.

Figures 4a and 4b are resonance frequency tables in tracking operation.

A ring-shaped permanent magnet 2 fixed to an outer frame 1 and ring-shaped yokes 3 and 4 are integrally constructed.

Inside the yokes 3 and 4 is a double cylindrical coil holding cylinder 5.
A pair of plate-shaped elastic members 19, 19' are provided at the base end 6 of the objective lens 16, facing the optical axis of the objective lens 16.
A cylindrical holding member 7 in which grooves are formed for insertion into each of the holding members 7 is fixed with an adhesive or the like.

One of the pair of elastic members 19 and 19' is formed into a long shape. That is, the elastic member 19' is formed long by the elastic member 19, and serves as a damper for correcting resonance. A cylindrical holding member 7 that holds the end of the elastic member 19'
forms a notch 21 on the circumference, and the notch 2
A groove is formed on the top surface of the elastic member 19', into which the end of the elastic member 19' is fitted and fixed with adhesive or the like.

Further, the outer periphery of the outer cylinder of the coil holding cylinder 5 faces the above-mentioned permanent magnet 2 around which the movable coil 8 is wound.

The inner periphery of a circular spiral spring 9 that operates in the form of a plate and whose outer periphery is fixedly supported by a spacer 11 disposed in the frame 1 is fixed to the end extending upward of the inner cylinder of the coil holding cylinder 5. ing. This spiral spring 9 is plate-shaped and has strip-shaped long holes 24, 24', 24'', 2
4, and a light flux hole 25 is formed in the center.

Further, the inner periphery of a spiral spring 10 having the same shape as the spiral spring 9 is fixed to the end face of the base end 6 of the coil holding cylinder 5 with adhesive, and the outer periphery thereof is fixed to a spacer 12 provided in the frame 1. are doing.

Above the spiral spring 9, a fixed yoke 14 and a fixed magnet 15 are attached to a retaining ring 13 attached to the frame 1.
is attached as a single unit. A fixed coil 17 for driving the objective lens 16 is wound around the fixed yoke 14 . A lens frame 18 equipped with the objective lens 16 is disposed at the center surrounded by the fixed yoke 14 and the fixed magnet 15, and a magnetic ring 20 that operates for tracking is fitted onto the outer periphery of the lens frame 18. .

A gap is formed between the lens frame 18 and the magnetic ring 20 fitted and attached, and plate springs 19, 1 made of elastic members are formed.
The end portion of the lens 9' is inserted and mounted to form an integral structure with the objective lens 16.

The elastic members 19, 19', namely the leaf springs 19, 1
The resonance correction at 9' will be explained with reference to FIGS. 4a and 4b. Figure 4a shows the leaf spring 19,1
9' represents the resonance frequency when the same length, thickness, and width are required.

FIG. 4b shows leaf springs 19, 19' according to the invention.
FIG. 3 is a diagram showing the resonance frequency in a rectangular shape.
As is clear from comparing a and b, the waveform Q shown in figure a is smaller than the waveform Q shown in figure b. However, the waveform shown in figure b is small and has a plurality of waveforms. This has a configuration in which the peak amount of resonance is divided into two, with the peak amount of resonance being made large and small.

In the present invention constructed as described above, when a focusing signal is applied to the coil 8, the spiral springs 9 and 10 are actuated to displace the objective lens 16 in the optical axis direction via the leaf springs 19 and 19'. Further, when a tracking signal is applied to the coils 17, 17', the objective lens 16 can be displaced in a direction perpendicular to the optical axis.

As described above, by forming the elastic members 19, 19' into a long shape according to the strength of resonance as described above, accurate information reading is possible without harmful resonance operation due to tracking operation. Become.

[Brief explanation of the drawing]

FIG. 1 is a plan view showing a half section of an information reading device embodying the present invention. FIG. 2 is a plan view showing the configuration of the upper surface of FIG. 1. FIG. 3 is an enlarged plan view of the elastic member integrally constructed with the objective lens shown in FIG. 1. Figure 4a,
b is a diagram showing the resonance frequency in tracking operation. 1...Frame, 2...Permanent magnet, 3...Yoke, 4
... Yoke, 5 ... Coil holding cylinder, 7 ... Holding member, 8 ... Moving coil, 9 ... Spiral spring, 10 ...
... Spiral spring, 13 ... Holding frame ring, 14 ... Fixed yoke, 15 ... Fixed magnet, 16 ... Objective lens,
17...Fixed coil, 18...Mirror frame, 19,1
9′...Elastic member (plate spring), 20... Magnetic ring.

Claims (1)

[Scope of Claims] 1. Objective lens support means for movably supporting an objective lens in a first direction substantially perpendicular to its optical axis and an information track; a movable magnetic member that moves integrally with the objective lens;
first and second fixed magnetic members arranged opposite to each other so as to sandwich the movable magnetic member in a second direction substantially perpendicular to the first direction; two permanent magnets each having a first and second tracking coil wound thereon and generating a magnetic field passing through the first and second fixed magnetic members and the movable magnetic member; and a fixed magnetic member of the objective lens to form two sets of magnetic circuits, the magnetic circuits extend in a third direction parallel to the optical axis and are arranged parallel to each other so as to sandwich the optical axis of the objective lens. Two flat long leaf springs with different dimensions in the orientation direction are connected between the magnetic member and a coil holding member to which the focusing coil is fixed, and an elastic member is further connected between the coil holding member and the base. At the same time, a permanent magnet disposed between the focusing coil and the focusing coil is fixed to a base, and the ends of the two leaf springs are separated by a step along the third direction. An objective lens drive device, characterized in that it is fixed to the surface of a coil holding member.