KR20010036854A - An actuator of optical pick-up device - Google Patents

Abstract

PURPOSE: An actuator of an optical pick-up device is provided to reduce asymmetrical distortion in driving power of an actuator caused by various deviation of magnets when employing a plurality of magnets in the actuator of an optical pick-up device as well as reducing production costs generated by using the plurality of magnets. CONSTITUTION: A bobbin(20) is provided with a pair of tracking coils(17), a pair of focusing coils(16) and a lens(18). A magnet applies a magnetic flux to the tracking coils(17) and the focusing coils(16) in an outer periphery of the bobbin(20). A yoke(15) surrounds the magnet. An actuator includes the bobbin(20), the magnet, and the yoke(15). The magnet's inside has an empty cylindrical shape. The magnet is formed of multi-electrodes and the magnet's each part generates each magnetic flux. Empty cylindrical permanent magnets(11,12,13,14) are arranged inside the cylindrical yoke(15). The cylindrical bobbin(20) on which the lens(18) is mounted is positioned in a central space of an inside of the actuator surrounded by the permanent magnets(11,12,13,14). The focusing coils(16) for controlling focusing and the tracking coils(17) for controlling tracking are installed to face each other in the outer periphery of the bobbin(20).

Description

Actuator of Optical Pick-up Device {AN ACTUATOR OF OPTICAL PICK-UP DEVICE}

The present invention relates to an actuator of an optical pickup apparatus for optically writing a signal to or reading a signal from a recording medium such as an optical disc.

An optical pickup device mounted on a disc player capable of recording and playing an optical disc can displace a bobbin with an objective lens in a radial direction of the disc in a focusing direction and a tracking direction. Permanent magnets are placed toward each other to control the position of the objective lens with respect to the optical disk by flowing a control current through the electric coil. By moving the objective lens, the light beam emitted from the objective lens is focused on the signal surface of the optical disc, and the light beam is traced to the signal track on the signal surface.

In the optical pickup apparatus, the actuator is a device capable of controlling tracking and focusing of a reproduction signal of an optical disc by moving the mounted objective lens vertically and horizontally. Here, focusing refers to moving the objective lens up and down so that the spot of the beam focused by the objective lens can be exactly coincided with the recording surface of the disc. Tracking means that the spot of the focused beam This means that the objective lens is moved to the left and right so as to track the track of the disc accurately so as to track the track.

The actuator of the conventional optical pickup device is configured by employing a plurality of magnets, which will be described below with reference to the drawings.

As shown in FIG. 1, in the yoke 1 of the actuator base 2, the first fixed magnet 3 and the second fixed magnet 4 and the magnetic pole of which the direction of the magnetic pole is set in the circumferential direction of the yoke 1 are provided. The third stationary magnet 5 is set in which the direction of is set in the diameter (thickness) direction of the yoke 1. In addition, the line segments connecting the centers of the respective magnet pairs facing each other of the first fixed magnet 3 and the second fixed magnet 4 are arranged to be orthogonal to each other, and clockwise, that is, viewed from the first fixed magnet 3. In the right direction of the first stationary magnet 3, at a position of 45 ° from each of the line segment connecting the center of the first stationary magnet 3 and the line segment connecting the center of the second stationary magnet 4, The stator magnet 5 is arranged.

In the pick-up actuator having a structure that employs a plurality of magnets, such as the rotary pick-up actuator, each magnet must be independently processed, magnetized, and assembled, resulting in a cost increase proportional to the number of magnets employed. . In addition, it is caused by accumulating the magnetism characteristic deviation caused by the shape deviation, the assembly position deviation during assembly, and the property difference of the raw materials when magnetizing from several magnets. These deviations cause asymmetry in the magnitude and direction of the Lorentz force, which is the driving force of the pickup actuator, and the self-restoring force, which acts as a spring for supporting the bobbin of the actuator. Each component of the forces due to this asymmetry causes not only translational movement in the plane but also rotational movements such as rolling or pitching, so only two-axis movements of translational movement for focusing and rotational movement for tracking are controlled. These are movements that cannot be controlled with the target rotary actuator. Therefore, these motions cause instability of actuator drive, make it difficult to accurately predict the actuator frequency characteristics at design time, and cause performance deviations between the actuators. Optical pickup actuators need a way to eliminate these movements because rotational movements, such as rolling or pitching, severely affect the reproduction performance of the optical pickup.

An object of the present invention is to reduce the asymmetry of the driving force of the actuator generated from various variations of the magnet by employing a plurality of magnets in the actuator of the optical pickup device as described above. It also has another purpose to reduce the production costs incurred by using multiple magnets.

1 is a perspective view showing a structure employing a plurality of magnets as an actuator of a conventional optical pickup device.

2 is a perspective view showing an actuator of the optical pickup apparatus according to the present invention.

3 is a perspective view illustrating the operation of the actuator according to the present invention.

*** Explanation of symbols for main parts of drawing ***

1: York 3: First fixed magnet

4: 2nd fixed magnet 5: 3rd fixed magnet

11: part of the permanent magnet 12: part of the permanent magnet

13: part of the permanent magnet 14: part of the permanent magnet

15: York 16: focusing coil

17: tracking coil 18: lens

20: bobbin

The optical pickup apparatus includes a bobbin including a tracking coil, a focusing coil, and a lens, a magnet applying magnetic flux to the tracking coil and the focusing coil around the bobbin, and a yoke surrounding the magnet. To provide an actuator.

The magnet has a hollow cylindrical shape, and is multi-pole magnetized for each part of the magnet to generate magnetic flux.

Hereinafter, features and details of the present invention will be described with reference to the accompanying drawings.

As shown in FIG. 2, in the actuator of the optical pickup apparatus of the present invention, cylindrical permanent magnets 11, 12, 13, and 14 are disposed inside the cylindrical yoke 15. In the inner central space surrounded by the permanent magnets 11, 12, 13 and 14, a cylindrical bobbin 20 mounted with a lens 18 is located. On the outer periphery of the bobbin 20, a pair of focusing coils 16 for focusing control and a pair of tracking coils 17 for tracking control are provided facing each other. 3 shows the structure of the bobbin 20 in detail.

The hollow cylindrical magnet has a body and magnetized into four parts 11, 12, 13 and 14. Each magnetized portion of the magnet generates a magnetic flux C in the radial direction of the cylinder. The magnetic poles are the same between the opposing portions of the magnets (eg, 11 and 13), and the magnetic poles are reversed between the neighboring portions (eg, 12 and 13). The iron core 19, the focusing coil 16, and the tracking coil 17 fixed to the bobbin 20 receive magnetic force from the magnet around the bobbin.

In the state where no current is applied to the focusing coil 16 and the tracking coil 17, the respective iron cores 19 are located near A and B in which the magnetic flux directions are changed. Since this position is the position which minimizes the magnetic potential of the system, when the torque in the center of the z-axis for rotating the bobbin 20 or the external force for moving the bobbin 20 on the z-axis are applied, the iron core 19 is the initial position. A self restoring force acts to move around A and B. This self restoring force acts as an equivalent stiffness in the focusing and tracking direction of the actuator of the optical pickup device.

The actuator of the optical pickup device having the above structure is driven in the following operation.

When the current Ia flows through the focusing coil 16, the focusing coil 16 receives a force Fa in the + z direction according to Lorentz's law, F = ∫iB dl. When the direction of the current Ia is reversed, the direction of the force Fa also is reversed. Therefore, the force Fa becomes a driving force component in the focusing direction of the actuator.

Similarly, when the current Ib flows to the tracking coil 17, a force Fb in the θ direction is generated, which acts as a torque for rotating the actuator, and drives the pickup actuator in the tracking direction using this rotational movement.

As described above, the actuator of the optical pick-up apparatus of the present invention generates a magnetic flux using a hollow cylindrical magnet, and performs the tracking control and the focusing control on the bobbin provided with the tracking coil and the focusing coil by the magnetic flux. do. The magnets are integrally processed, magnetized and assembled, which can lead to simplification of the process. In addition, it is possible to prevent the deviation of the magnetization characteristics caused by the shape deviation during processing, the assembly position deviation during assembly, the physical property difference of the raw material when magnetized from a plurality of magnets. Therefore, it is possible to remove in advance the asymmetrical elements in the magnitude and direction of the Lorentz force, which is the driving force of the actuator, or the self-resilience force, which acts as a spring for supporting the bobbin of the actuator, and assure the stability of the actuator driving. It is possible to accurately predict various characteristics of actuators. In addition, the performance deviation between the actuators can be reduced, resulting in an improvement in the reproduction performance of the optical pickup device.

As described above, the present invention removes an asymmetric motion component in which a cumulative deviation of a plurality of magnets used in a conventional rotary method pickup actuator is generated by using a magnet having a hollow cylindrical shape with a multipole magnetization. In addition, it is also possible to reduce production costs than using multiple magnets.

Claims (3)

An actuator of an optical pickup apparatus comprising a bobbin comprising a tracking coil, a focusing coil and a lens, a magnet applying magnetic flux to the tracking coil and the focusing coil around the bobbin, and a yoke surrounding the magnet. 2. The actuator of claim 1, wherein the magnet has a hollow cylindrical shape formed inside the yoke. 2. The actuator of claim 1, wherein the magnet is multipole magnetized for each part.