JPS60226031A - Objective lens driving device - Google Patents

Abstract

PURPOSE:To increase an allowance for focusing control while using straightly leaf springs having high rigidity by adding magnetic cores in such a way that the force generated by the leaf springs and the force in the direction countering said force are generated. CONSTITUTION:Respective one ends of two sheets of the leaf springs 6, 7 facing each other are fixed to the base plate 5 of an optical pickup and a yoke 12 consisting of a rectangular plate is fixed to the end face on the outside of a movable frame 8. Two magnets 13, 14 made into a square columnar shape are juxtaposed to the surface thereof in the direction intersecting orthogonally with an arrow A direction. While a coil 15 to which the circular cylindrical magnetic cores 16, 17 are fixed is in the nonconducting state, the coil 15 is in the relative position where the coil faces the magnets 13, 14. The centers of the cores 16, 17 are stable in the position where said centers face the center between the magnets 13 and 14. The distance between the cores 16, 17 and the magnet 13 or the magnet 14 decreases and the attraction force between both increases with an increase in a displacement position (x) if electricity is conducted to the coil 15 so as to displace upward or downward an objective lens 11. The smaller force to be acted on the leaf springs 6, 7 by the coil 15 is thus required.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an objective lens driving device that can be applied to a main pickup of an optical recording/reproducing device.

For example, PCM recorded as a line of focus on a disk
When optically reading and reproducing signals, the objective lens is supported movably in the optical axis direction, and high-precision focusing servo is performed so that the focal point of the objective lens is always located on the recording surface of the disk. There is a need. In order to stably perform this focusing servo, the objective lens drive device is required to have vibration characteristics suitable for the disk runout standard. At the same time, if the objective lens is tilted with respect to the optical axis when it is driven up and down, aberrations will occur in the disk sub-node, so a support function is also added to prevent the lens from tilting with respect to the optical axis. required.

Electromagnetic driving means is known as a means for performing such focusing servo. This electromagnetic drive means, for example, has one end of a leaf spring fixed to an immovable base constituting the optical pickup, and an objective lens attached to the free end of the leaf spring via a support.

Then, fix two magnets to this support, and attach a coil to the surface of the base facing these two magnets. Then, due to the electromagnetic force generated by energizing this coil and the magnetic force acting between the two magnets, the objective lens is deformed like a leaf spring to perform focusing control.

In Figure 7, reference numeral 1.2 indicates a leaf spring, and reference numeral 6 indicates a support for the objective lens 3a. Further, the direction of arrow A is taken as the forkampfugu control direction. In this example, the objective lens is supported by a leaf spring 1.2, but if the leaf spring 1.2 is set to have a small elastic force so that it is driven by a small electromagnetic force from a coil, it may cause torsion or Rigidity against other undesirable deformations is weakened, resulting in a lack of stability in the direction shown by arrow B.

Therefore, an object of the present invention is to obtain a sufficient amount of deformation of the leaf spring to perform focusing control even if the electromagnetic force generated by the coil is small, and to ensure sufficient rigidity against torsion and other undesirable deformations. The object of the present invention is to provide an objective lens driving device that can drive an objective lens.

According to the above object of the present invention, there is provided an objective lens driving device in which the apparent elastic force of the leaf spring is reduced.

An example of the present invention will be explained below.

Referring to Figures 1 to 6, reference numeral 5 indicates the base of the optical pickup. One end of each of two opposing leaf springs 6 and 7 is fixed to this base 5.

And, at each other free end of these leaf springs 6.7,
Prism, charging element, etc.? The built-in movable frame 8 is attached to the adhesive plate 9.
They are integrally attached via 10. An objective lens 11 is mounted on the upper adhesive plate 9 among these adhesive plates 9 and 10.
is fixed, and the optical relationship position with the prism, photoelectric element, etc. within the movable frame 8 is determined.

A rectangular plate yoke 12 is fixed to the outer end surface of the movable frame 8, and two prismatic magnets 13 and 14 are mounted on the surface of the yoke 120 in a longitudinal direction perpendicular to the direction of arrow A. They are arranged side by side.

The movable frame 8, adhesive plates 9, 10, yoke 12, etc. fixed to the free end sides of the leaf springs 6, 7 directly or indirectly support the objective lens 11, so these members are collectively referred to as the objective lens. It is called the lens support.

Next, the base 5 facing the magnets 13, 14, etc. at intervals
On the 0 side, a coil 15 consisting of a single winding body is connected to the insulating plate 1.
It is fixed through 9.

As a conventional objective lens driving device, there is one having a structure similar to that described above. In this example, we added a magnetic core to the above conventional structure. Added. That is, cylindrical magnetic cores 16 and 17 are placed inside the coil 15 and on the fixed surface of the coil 15.
; is fixed.

When the coil 15 is in the de-energized state, the coil 15 and the magnet 13. 14 are located in opposing relational positions, and magnetic core 1
/), the center of 17 is stable at a position aligned with the center between magnet 16 and magnet 14.

In such a structure, the leaf springs 6, 6,
7 is deformed and the objective lens can be controlled in the four force song control direction.

Here, magnetic core 16. In a situation where 17 does not exist,
Assuming that the leaf springs 6 and 7 are deformed only by the electromagnetic force between the coil 15 and the magnets 13 and 14, the relationship between the elastic force generated in response to this deformation and the amount of displacement is shown in Figure 5. Draw the characteristic as shown by line 20.

That is, as shown in Figure 4, a current is passed through the coil 15, and the center of the objective lens 11? When the leaf spring VCX is displaced upward by X, the elastic restoring force of the leaf spring VCX increases proportionally as the amount of displacement increases. Therefore, it can be seen that a large electromagnetic bar is required to obtain a large amount of displacement.On the other hand, as in this example, the magnets 13, 14 and the magnetic core 16,
Considering the magnetic force acting between the leaf spring and the leaf spring 17, as shown by the line 21 in Figure 5, as the displacement increases, the force in the direction opposite to the restoring direction of the leaf spring tends to increase. This force is greatest at the position where the magnetic core 16.17 faces either the magnet 16 or the magnet 14.

In this example, since magnetic cores 16 and 17 are provided, the relationship between the magnitude of the force required to deform the leaf springs 6 and 7 and the amount of displacement can be determined by combining @2o and line 21 in Figure 5. The resulting characteristic shown by line 22 is followed.

Therefore, conventionally, the more you try to displace the objective lens 11 upward or downward, the more the amount of displacement of the leaf springs 6 and 7 increases, so a large force is required to obtain that amount of displacement, and the coil 15
However, in this example, as the amount of displacement increases, the magnetic core 16, 17
Since the distance between the magnet 15 or the magnet 14 becomes closer and the attractive force between them increases, the force that should be applied to the leaf spring by the coil 15 can be small.

In this way, in this example, the apparent elasticity of the leaf spring 6.7 can be achieved as shown by the reference numeral 22 in Fig.
Even a large displacement amount of 1 can be dealt with with a relatively small electromagnetic force. As a result, the leaf spring itself can be sufficiently resistant to deformation such as torsion that is undesirable in terms of the supporting function of the objective lens, and focusing control can be performed with a small electromagnetic force.

For example, for a certain disk, the standard value of the disk, which is indicated by the amplitude of the disk surface corresponding to the vibration frequency, is
Assuming that the area is set as the area indicated by reference numeral 26 in FIG. 6, the amplitude in the low frequency band is considerably larger than that in the high frequency band.

When a magnetic core as in this example is not used, the follow-up characteristic of the leaf spring approaches the upper limit of the standard value as indicated by the line 20' in Fig. 6, and the margin for focusing control is small.

On the other hand, when the magnetic cores 16 and 17 are used as in this example, even if the electromagnetic force generated by the coil 15 is the same as when the magnetic cores are not used, the characteristics shown by the line 20' are lower. Can adapt to large amplitudes.

This characteristic is shown by line 22'. Therefore, margin for focusing control can be increased.

In this example, two magnetic cores are used for magnet 13.
This is to maintain balance between the left and right sides since the width of 14 in the lateral direction is somewhat wide, and in principle, there is no problem functionally even if one is provided in the center.

Also, magnet 13. 14, the coil 15, and the magnetic core 16 and 17 may be interchanged in the positions shown in FIG. However, since a conducting wire for conducting current is led out to the coil 15, it is easier to dispose the coil 15 on the fixed side for convenience of assembly and the like when processing this conducting wire. However, in a soil that achieves basic functions, there is no problem even if 15 coils are placed on the movable side.

In this way, the present invention creates a force in the opposite direction to the force generated by the leaf spring in the magnetic circuit for electromagnetic drive in order to increase the driving efficiency of the objective lens while maintaining the rigidity of the leaf spring. Since a magnetic core is added and the apparent spring constant is lowered by the combined force of these, it is possible to increase the margin for focusing control by using a highly rigid leaf spring as is.

The apparent repulsion constant can be set to any value by changing the dimensions and arrangement of the magnetic core, the dimensions between the magnetic core and the magnet, etc.

In the present invention, it is possible to use a leaf spring with high rigidity, which is advantageous because it is possible not only to avoid torsional deformation during focusing control, but also to reduce distortion and misalignment of the leaf spring during assembly. .

[Brief explanation of the drawing]

Is Figure 1 an objective lens drive device that is an example of the present invention? The front view explained together with the cross section of the coil, Figure 2 is a perspective view of the objective lens support in the same figure as above, Figure 6 is a perspective view of the coil and magnetic core, and Figure 4 is a front view of the objective lens drive device in the leaf spring displacement state. Figure 215 is a graph explaining the apparent spring characteristics, Figure 6 is a graph explaining the follow-up characteristics of the leaf spring with respect to the standard value of the disk, and Figure 7 is a graph explaining the torsional deformation of the leaf spring in the conventional technology. FIG. 13.14... Magnet, 15... Coil, 16. 1
7...Magnetic core.

Claims (1)

[Claims] A pickup for an optical recording/reproducing device in which an optical system is attached to a base via a leaf spring, and is an electromagnetic drive means formed by arranging a coil and at least two magnets facing each other. One member of the electromagnetic driving means is a support for an objective lens supported on the free end side of a leaf spring, and the other member is arranged and fixed to a base so as to face each other. In the objective lens driving device of
An objective lens driving device characterized in that a magnetic core is disposed on the coil fixing surface at a position facing the center between the two magnets.