JPH0341629A - Focus actuator - Google Patents

Abstract

PURPOSE:To enlarge a focus control band to a high area side by composing a driving mechanism of almost rectangular coils in the shape of planes and a pair of permanent magnets arranged to face to the respective coils. CONSTITUTION:A driving mechanism 30 is composed of almost rectangular coils 31 and 32 in the shape of planes fixed on the both side faces of an objective lens holding member 21 and arranged so that two faced sides can be orthogonal to an optical axis 26 of an objective lens 22 and a pair of permanent magnets 33 and 34 arranged to face to the respective coils 31 and 32 for applying mutually reverse magnetic fluxes to the two sides of a pair of the almost rectangular coils 31 and 32. Accordingly, since the objective lens holding member 21 is not fitted into a magnetic gap in structure, the number of vibration to widely resonate mechanical characteristic can be widely rised. Thus, the number of resonance vibration for the objective lens holding member 21 can be widely rised and the band, where focus control can be executed, can be improved.

Description

[Detailed Description of the Invention] [General Shell] Regarding the force actuator applied to optical discs 1!7, the purpose is to enable expansion of the focus control band to the high frequency side, and to hold the objective lens. an objective lens holding member that supports the objective lens holding member, a support mechanism consisting of a pair of parallel plate springs that support the objective lens holding member, and a drive a1a mechanism that drives the objective lens holding member to focus the disk. In the focus actuator II, the drive structure described above is
a flat plate-shaped coil fixed to both sides of the objective lens holding member and disposed such that two opposing sides are perpendicular to the optical axis of the objective lens; A pair of permanent 11 stones are arranged facing each of the above-mentioned coils in order to apply magnetic fluxes in opposite directions to the above-mentioned two sides of the medium-shaped coil. do.

[Fields of use for cancer specialists]

The present invention relates to a focus actuator applied to optical disc mounting.

It is desired that the focus actuator has good vibration characteristics up to a high frequency range. 100)
In addition to the primary resonance of the leaf spring that exists below -1z,
It is assumed that high-order resonance does not exist up to a frequency of 0 KHz or higher, that is, that there is no peak in gain and that the delay of the other phases is not 1 unit.

[Conventional technology]

FIG. 7 shows a conventional focus actuator 1. As shown in FIG.

A cylindrical objective lens holding member 2 holds the objective lens 3.

4 is a support mechanism, which includes a single leaf spring 5 arranged in parallel.
6, the objective lens holding member 2 is connected to the objective lens 3.
is supported so as to be movable in the direction of the optical axis 7.

Reference numeral 8 denotes a drive mechanism, which includes a bottomed cylindrical yoke 9, a central columnar yoke 10, a radially magnetized annular permanent magnet 11 fixed inside the yoke 9, and an objective lens holding member. [!] between the annular permanent magnet 11 and the columnar yoke 10. It consists of a coil 13 attached inside i12.

A magnetic field is formed within the gap 12, and the coil 13 is located within the magnetic field.

When a current corresponding to the focus error signal is applied to the coil 13, a driving force in the direction of arrow Z+, 22, is generated according to Fleming's law.

Due to this driving force, the objective lens holding member 2 is moved by the leaf spring 5.
6, the objective lens 3 is displaced in the direction of the optical axis 7, and focus control is performed.

The leaf spring 5.6 mentioned above is a solid metal plate such as Be Cu.

Further, the width q of the gap 12 is narrow. Along with this, the bobbin portion 2a of the objective lens holding member 2 around which the coil 3 is wound
The thickness t is 0.5M or less, and the mechanical rigidity of the bobbin portion 2a is low.

(Problems to be Solved by the Invention) The vibration characteristics of the focus actuator 1 having the above configuration were measured, and the results were as shown in FIG.

In the figure, line 15 shows the frequency-gain special case, and line 16 shows the frequency-phase characteristic.

In the figure, 1QkHz f” as shown by the symbol 16a t-
A phase delay begins to occur near 1.

This is considered to be due to the resonance of the bobbin portion 2a of the objective lens holding member 2, which has low mechanical rigidity.

Also, as shown by symbols 15a and 16b, 1.5kHz
(There was one resonance near 4.

This is considered to be due to the higher mode Jl+ of the holding mechanism 4.

In this way, in the force actuator 1, the mechanical resonance at low frequency is the focus control mechanism.
This has been a problem in extending the ll band to the high frequency side.

The present invention aims to provide a focus actuator that enables expansion of the focus flIJIIl band to the high frequency side. A focus actuator comprising a holding member, a support l141N made up of a pair of parallel plate springs that support the objective lens holding member, and a drive mechanism that drives the objective lens holding member to focus on the disk, The drive 1@ is a flat plate-shaped and approximately ψ-shaped coil fixed to both side surfaces of the objective lens holding member and disposed such that two opposing sides are orthogonal to the optical axis of the objective lens. and a pair of permanent 11 stones arranged opposite each of the coils to apply magnetic flux in opposite directions to the two sides of the pair of substantially rectangular coils.

[Effect]

Since the objective lens holding member is not fitted into the magnetic gap, the objective lens holding member has a large mechanical rigidity and can considerably increase the frequency at which it resonates.

〔Example〕

FIG. 1 shows a focus actuator 20 according to an embodiment of the present invention.

Reference numeral 21 denotes an objective lens holding member, which is approximately the size of a cube, and has an objective lens 22 fixed in a shell through hole 21a at the center.

Since the objective lens holding member 21u is not configured to fit into a magnetic gap like the conventional structure, it does not need to have a particularly thin structure and has mechanical rigidity per minute as a whole.

23 is a support mechanism, which includes a pair of leaf springs 2 arranged in parallel.
4.25, supports the objective lens holding member 21 so as to be movable in the direction of the optical axis 26 of the objective lens 22, that is, in two directions.

As shown in FIG. 2, the leaf spring 24 is made of silicone rubber, which is a viscoelastic material, and has a thickness of 0.05 m (IF!). One layer 27 is made of Be Cu with a thickness t2 of 0.03 m.
It has a sandwiched structure between metal plates 28 and 29 made of

Another leaf spring 25 also has the same I m as the leaf spring 24 described above.

In addition to the above-mentioned silicone rubber, polyurethane rubber, polyimide resin, natural rubber, etc. can be used for the intermediate layer 271. However, silicone rubber is the most excellent in terms of thermophilicity, and as the intermediate layer M27, Silicone rubber is preferable.

Reference numeral 30 denotes a drive mechanism, which includes flat plate-shaped and elongated rectangular coils 31.32 fixed to the side surfaces 21b and 21C on both sides of the objective lens holding member 21, and closely opposed to each of A and 31.32. It consists of fixedly arranged permanent magnets 33 and 34. .

Coil 31kt, two opposing long sides 31a.

31b is orthogonal to the optical axis 26 mentioned above.

Another coil 32 is also oriented in the same direction as the coil 31.

As shown in FIGS. 3 and 4, the permanent magnet 33 has a structure consisting of a permanent magnet piece 35 having an isosceles trapezoidal cross section and a pair of beams 36 and 37 having a right triangular cross section. It is.

The permanent magnet C 35 is magnetized in a direction parallel to the bottom surface 35a, with one slope 35b being the north pole and the slope 35 on the opposite side being the north pole.
5c is the south pole.

35d is the top surface.

The yokes 36 and 37 have slopes 36a and 37a as slopes 35b, which are magnetic pole surfaces of the permanent magnet pieces 35, respectively.

35c, and the permanent magnet pieces 35 are sandwiched and fixed from both sides.

The il[lJ south 36b and 37b of the yokes 36 and 37 coincide with the top surface 35d of the permanent magnet moon 35.

The above permanent 11 stones 33 are the side 3 of each cork 36.37
6d and 37d are the long sides 31a and 31b of the coil 31, respectively.
A 1° magnetic flux disposed at a position opposite to flows as shown by the reference numeral 38 in FIG.

That is, it comes out from the slope 35b which is the north pole, passes through the inside of the yoke 36, comes out vertically into the air from the side surface 36b, and interlinks the long side 31a of the coil 31 from the center to the right in the figure.

The magnetic flux 38 further passes through the inside of the objective lens holding member 21 and heads toward the yoke 37.

In this process, another long side 31b of the coil 31 is interlinked in the opposite direction to the above long side 31a, that is, from right to left in the figure.

The magnetic flux 38 enters the yoke 37 from the vertical surface 37b, passes through the yoke 37, and reaches the slope 35c, which is the south pole.

Another permanent magnet 34 also has a structure in which a permanent magnet moon 40 and a yoke 41, 42 are joined together, like the permanent magnet 33 described above, and interlinks with each side of the magnetic flux field 32.

Next, the operation of the focus actuator 20 having the above configuration will be explained.

A current corresponding to the focus error device is applied to the coils 31 and 32.

Regarding the coil 31, the direction of current is opposite between the long sides 31a and 31b. -7J This is opposite to the direction of the magnetic flux 38 acting on the long sides 31a and 31b. As a result, an upward force in the Z direction is generated on both the long sides 31a and 31b according to Fleming's law.

As for the coil 32 on the opposite side, the coil 31
A force in the same direction is generated.

This force causes the objective lens holding member 21 to spring against the leaf spring 24,
The objective lens 22 is displaced in the direction of the arrow Z7J with a bending deformation 25, and the objective lens 22 is displaced in the direction of the optical axis 26, thereby performing focus control.

The vibration characteristics of the focus actuator 1-20 described above were measured and the results were as shown in FIG.

In the figure, a line 40 indicates the frequency-gain characteristic. Line 41 shows the frequency-phase characteristics.

Lines 40 and 41 are both gentle from 90 days 2 to 40 kHz. It can be seen from this that high-order resonance is not observed up to 40 kHz.

This is because, firstly, the entire objective lens holding member 22 has high mechanical rigidity, and secondly, the leaf springs 24 and 25 themselves are susceptible to high-order mode vibrations. +! This is thought to be due to the fact that it has the ability to perform

As can be seen from the vibration characteristic diagram shown in FIG.
Focus control is possible over a wide frequency band up to Hz, and the focus control band is significantly expanded compared to the conventional case.

Next, the focus actuator 20 is driven li! !
IaI 30 days, furthermore] t le.

The coil 31 is included in the magnetic flux 38 generated by the permanent magnet 33.
There is also a magnetic flux passing through the coil 3 in its axial direction, which causes the coil 3 to
1, a moment about the Y axis in FIG. 1 is generated. However, this moment is balanced by a moment similarly generated in the coil 32 on the opposite side. Therefore, there is no effect on the movement of the objective lens holding member 21! figure,
The objective lens 22 is displaced in the direction of its optical axis 26.

Regarding the permanent magnet 33, as shown in FIG. 4, the width W1 of the magnetic path in the coil 31 is the vertical plane 36b of the yoke 36 and 37, respectively.

It corresponds to the width W2 of 37b and is wide.

Therefore, among the 'iIi wires forming the long sides 31a and 31b of the coil 31, the number of electric wires interlinked with the magnetic flux 38 increases.

Further, the magnetic path from the upper surface of the permanent magnet 33 along the surface 35a to the lower surface is longer than the magnetic path from 36b to 37b, and the magnetic resistance is human. Therefore, the amount of leakage magnetic flux flowing along the magnetic path along the surface 35a is several percent of the total magnetic flux hl generated by the permanent magnet 33, and most of it flows along the surface 35d side. Therefore, most of the magnetic flux generated by the permanent magnet 33 intersects with the coil 31.

Further, the thickness T of the permanent magnet g35 on the surface 35a side is large, and the magnetomotive force of the permanent magnet piece 35 is large.

Also, the magnetic flux path is from magnetic pole N to yoke 36 to yoke 37.
-→The path from the yoke 36 to the yoke 37 is 5, which is the path that leads to the magnetic pole S.
6a to the vertical surface 37a of the cork 37,
It is considerably shorter than the path from the upper surface of the yoke 36 to the lower surface of the yoke 37. Therefore, the magnetic circuit is short.

The yoke 36 has the role of reducing magnetic paper folding between the magnetic pole S and the vertical surface 36a, and the role of causing the magnetic flux to flow out in a direction perpendicular to the plane of the coil 31.

The yoke 37 also has the same role as the yoke 36.

As mentioned above, the magnetomotive force of the permanent magnet 35 is human, and most of the generated magnetic flux flows to the coil 31 side, and the magnetic circuit is short, so the magnetic flux density at the coil 31 is high.
The force generated in the lens 31 per focus error current is sufficiently large, and focusing $Qm is performed efficiently.

In addition, in the above permanent magnet 33, the coil 311QI
The reason why surface 35d was left on J is due to Rizan below.

The strength of the magnetic field 11 along the surface of the permanent magnet 33 on the coil 31 side is as shown by the line 45 in FIG.

The symbol 46S indicates a portion where the magnetic field strength is zero.

This portion 46 is due to the existence of the surface 35d.

Due to the existence of this portion 46, even if the coil 31 is displaced in the Z1 direction and part of it enters the portion 46 during focus control, no force will be applied to the coil in that portion, and the focus will be maintained. Does not affect control.

The width 1↑W3 of 35d is set to be approximately twice the displacement dimension of the coil 31.

(Effects of the Invention) As explained above, according to the invention of claim 1, since the objective lens holding member does not have a structure fitted into a narrow magnetic gap, the objective lens holding member can be made into a structure with high mechanical rigidity. As a result, the resonance frequency of the objective lens holding member can be considerably increased, and the band in which focus ti+160 is possible can be increased.

According to the invention of claim 2, by making the permanent magnet have a composite structure of a permanent magnet piece and a yoke, it is possible to increase the magnetic flux density at the coil portion, and to efficiently obtain the deformation force for focus control. I can do it.

According to the invention of claim 3, since the leaf spring itself is made of a $100 structure that can suppress vibrations, it is possible to prevent higher-order mode vibrations of the leaf spring, thereby increasing the band in which no-occurrence control is possible. I can do it.

[Brief explanation of drawings]

Fig. 1 is a perspective view of a focus actuator according to an embodiment of the present invention, Fig. 2 is a diagram showing the structure of a leaf spring, Fig. 3 is an exploded perspective view of a permanent magnet, and Fig. 4 is a perspective view of a permanent magnet and a coil. A diagram illustrating the relationships between
Figure 1 shows the vibration characteristics of the focus actuator, Figure 6 shows the distribution of the magnetic field strength on the side facing the permanent magnet coil, and Figure 7 shows the conventional focus actuator 11-1. FIG. 8 is a diagram illustrating the vibration characteristics of the focus actuator of FIG. 7, which is a partially cutaway view of an example. In the figure, 20 is a focus actuator, 21 is an objective lens holding member, 22 is an objective lens, 23 is a supporting mechanism, 24 and 25 are leaf springs, 26 is an optical axis, 27 is a silicone rubber intermediate layer, 28 and 29 are metal plates. , 30 is a drive mechanism, 31.321. L coil, 31a and 31b are long sides, 33.34 is a permanent magnet, 35 G is a permanent magnet piece, 35a is a bottom surface, 35b and 35c are slopes, 35d is a top surface, 36.37 is a yoke, 36a and 37a are 36b and 37b are side surfaces, and 38 is a magnetic flux. Vi Revised Applicant Fuji Co., Ltd. Attorney, Attorney Figure 2
i5 Figure 4 Difficulty (Hz) #l圀*rr-:zxT74%:c-pn-□ishow-m
Figure 5 Figure 6 (Hz)

Claims (3)

[Claims] (1) An objective lens holding member (21) that holds an objective lens (22), a support mechanism (23) consisting of a pair of parallel leaf springs that supports the objective lens holding member, and a focus lens on the disk. In a focus actuator comprising a drive mechanism (30) that drives the objective lens holding member to achieve alignment, the drive mechanism (30) is fixed to both side surfaces of the objective lens holding member, and is attached to two opposing sides (31a). , 31b) is the objective lens (22
) flat and substantially rectangular coils (31, 32) disposed perpendicularly to the optical axis (26) of A focus actuator comprising a pair of permanent magnets (33, 34) arranged to face each of the coils to apply magnetic flux. (2) The pair of permanent magnets (33) each have a trapezoidal cross section and a permanent magnet main body (35) which is magnetized so that each slope (35b, 35c) side becomes a magnetic pole, and a triangular cross section. A pair of yokes (35b, 35c) are joined to each of the slopes (35b, 35c) and fixed with the permanent magnet main body in between.
36, 37), and the top surface (35d) of the permanent magnet body is connected to the coil (31
), and the pair of yokes are disposed so as to respectively oppose the two sides of the coil. (3) An objective lens holding member that holds the objective lens; a support mechanism that supports the objective lens holding member and includes a pair of parallel plate springs; and a drive mechanism that drives the objective lens holding member to focus on the disk. In the focus actuator, the pair of leaf springs (24, 25) of the support mechanism are replaced by an intermediate layer (27) having viscoelasticity, and a pair of metal plates (28,
A focus actuator characterized by having a sandwich structure with 29).