JPS58218051A - Optical pickup - Google Patents

Abstract

PURPOSE:To obtain a small sized driving device with a simple construction, by fixing a square coil around a holding cylinder of an objective lens so as to provide an equal angular interval to an optical axis in a plane including the optical axis, and generating two kinds of magnetic fields with one magnet. CONSTITUTION:Four permanent magnets 5 are arranged concentrically around the objective lens holding cylinder 2 to form the magnetic field for coil driving at a gap between the magnets. A focus control coil 3 is fixed to the objective lens holding cylinder 2 with its center shifted to the magnets 5, and its upper side 3' is placed at the gap of the magnets 5. A tracking control coil 4 is a long and narrow square toward the optical axis 1' of the objective lens and a side 4' in parallel with the optical axis 1' is placed in the gap of the magnets 5. Thus, a force toward the optical axis is generated on a side 3' of the coil is generated with the current control of the focus control coil 3 to attain the position control toward the optical direction of the objective lens 1. Further, the force toward vertical direction to the optical axis produced on the side 4' is done with the current control of the tracking control coil 4 and the control of displacement toward the direction at a right angle to the information track of the lens holding cylinder 2 is attained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to driving demolding of an objective lens for tracking and focusing in a pickup of an optical information reading device.

In order to reproduce information from a video disc recording medium that optically records information, light from a light source is passed through an objective lens.
An optical pickup is used in which the reflected light is focused on the recording medium and the reflected light is again focused and detected by the same objective lens.

In such optical pickup, in order to always form a spot on the recording medium, the objective lens is moved in the direction of its optical axis in order to maintain a constant distance between the recording medium and the objective lens.
In order to faithfully follow the track on the recording medium, a tracking drive that drives the objective lens parallel to the recording medium and perpendicular to the track is required.
Ru.

In order to drive the objective lens in two directions, the direction of the optical axis and the direction perpendicular to it, a magnetic field generating magnet is installed in the coil corresponding to each IIK movement direction. It is provided integrally with the objective lens and combined with a magnetic field generator (for example, JP-A-52-1389TL).
Item a) etc. are known.

However, providing drive coils and magnetic field generators corresponding to each driving direction makes the structure of the pickup complicated and large, and a pickup that also functions for drive control in both directions is difficult to use when controlling the objective for tracks. The movement of the lens is a rotational motion, and the optical axis deviates from perpendicular to the recording medium surface, so a large-mouth objective lens is required, which increases the weight 1k, reduces the body vJ ratio, and causes the optical axis to deviate from perpendicular to the recording medium surface. The reflected light intensity changes, and the S/N ratio decreases. Furthermore, the point of application of one rotational force is close to the center of rotation, and the rotational moment is small, resulting in a disadvantage that the tracking driving force is small.

In this D invention, a rectangular coil is placed around the holding tube of the objective lens in a plane including the optical axis, and has an angle of M equal to the optical axis.
[Fix this square □ so that there is a gap.

Sides parallel to the optical axis of the coil: ,,,i,11 By applying a field, drive in the direction perpendicular to the optical axis, and by applying a magnetic field to the side perpendicular to the optical axis, drive in the direction of the optical axis. Thus, it is possible to obtain a two-way drive device that generates force and does not have the above-mentioned drawbacks. Moreover, by selecting the coil shape and viewing position, the two types of magnetic fields mentioned above can be generated with the same magnet, and the book attempts to obtain a compact drive device with a simple structure.

A detailed explanation will be given below with reference to the drawings.

Figure 1 shows the actual product of this invention! FIG. 2 is a perspective view showing the arrangement of the coils and magnets of the A cage, FIG. In this embodiment, a focus control coil 3 and a tracking control coil 4 are fixed to a holding cylinder 2 of an objective lens l with a distance of 90 degrees from each other. The focus control coil 3 has a side 3' perpendicular to the optical axis, that is, parallel to the recording medium surface.
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3", and the magnetic field applied here generates a driving force in the direction of the optical axis l' force of the objective lens l. On the other hand, the one-racking system coil 4 has a side 4' parallel to the optical axis, where vc
4 Optical axis l':', due to the seen magnetic field.

produces a driving force perpendicular to In the embodiment shown in the first figure, the coils 4, 4 are disposed on the recording medium on a diameter perpendicular to the information track, so that the driving force generated therein moves the objective lens holding cylinder 2 at right angles to the track. drive to enable tracking control. It goes without saying that the lens holding cylinder 2 is supported movably by a plate spring or other known means as a pickup.

In the embodiment shown in FIG. 1, as shown in the second part,
Four permanent magnets 5 are arranged concentrically around the objective lens holding cylinder 2, and a magnetic field for driving a coil is formed in the gap between each magnet 5. The focus control coil 3Vi is fixed to the objective lens holding cylinder 2 with its center shifted from the magnet 5, and its upper side 3' is placed in the gap between the magnets □5. The tracking control coil 4 has a rectangular shape elongated in the direction of the optical axis 1' of the objective lens.
The side 4' parallel to the Q optical axis is located in the gap between the magnets.

Therefore, the VIIL flow control of the focus control coil 3 generates a force in the optical axis direction on the side 3' of the coil, making it possible to control the position of the objective lens l in the optical axis direction.

On the other hand, the control of the force in the direction perpendicular to the optical axis generated on the side 4' is turned on by the [fi control of the tracking control coil 4,
It becomes possible to control the displacement of the lens holding cylinder 2 in a direction perpendicular to the information track.

As described above, the focus control coil 3 is shifted downward in a vertical direction with respect to the magnet 5, and its upper side 3' is bent within the magnetic field of the magnet 5. Therefore, two magnets 6 corresponding to the lower side 3 of the coil 3 are arranged below the magnet 5, and the driving force for focus control can be increased. In the embodiments shown in FIGS. 1 and 3, the length of the tracking control coil 4 is short, and the magnets 6 are two permanent magnets extending about half the circumference of the objective lens holding cylinder 2. If the length of the magnet 4 is extended until it crosses the magnet 6, and the number of magnets 6 is made into four pieces like the magnet 5, the driving force of the tracking system can be further increased.

If it is necessary to make the driving force even stronger, the number of driving coils can be further increased. @4 In the embodiment shown in FIG. 4, four focus control coils 3 are arranged around the objective lens holding cylinder 2 every 6tl.

In addition, this is an example in which coils 7 are provided diametrically opposite each other in the direction of the information track shown in FIG. 5, thereby making it possible to perform control t for correcting the time lag in reading information on the track. In the case of a focus control coil, if one pair of focus control coils is sufficient, the coil υ arrangement does not necessarily have equal intensity intervals.

Although a Vi electromagnet permanent magnet is used in the implementation shown in Figure 1,
Although electromagnets may be used, many design variations are possible within the scope of this invention.

In this way, the present invention has a magnet arrangement for driving the coils that is common to adjacent coils, which has good magnetic circuit efficiency and no spatial waste θ, is thin in the optical axis direction, and has a pickup structure. The overall υ direct strength can also be made small. Furthermore, it is possible to provide an inexpensive pickup by standardizing parts such as valley coils and permanent magnets.

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[Brief explanation of drawings]

:1 Figure 1 is a perspective view of the mounting part of one embodiment of the optical pickup of this invention, Figure 2 is its front view, Figure 3 is its bottom view, and Figures 4 and 5 are views of other parts. Conceptual diagram of the embodiment 1: Objective lens 2: Objective lens holding tube 3: Focus control coil 4 Ni tracking control coil 5.6: FB stone
7: Continuing time control coil to special eave appearance Makiniyosha Ricoh 1 □)・. Feeling;

Claims (1)

[Claims] an objective lens that focuses light from a light source onto an information recording medium;
A means for controlling the position of the objective lens in the optical axis direction so that the focused spot by the skeleton objective lens is always on the recording medium surface, and a means for controlling the objective lens so that the focused spot is always located on the information track. The optical axis direction position control means includes a coil having a side perpendicular to the optical axis of the objective lens, and the means for positioning and controlling the position in a direction perpendicular to the track is an optical axis. An original pickup characterized by having a coil with sides parallel to the axis, and the sides perpendicular and parallel to the optical axis being placed in a magnetic field created by a common magnet.