Objective lens driving device and manufacturing method thereof

An objective lens driver in which a movable portion 1 with an objective lens 11 is supported on a fixed portion by two groups of elastic supporting members each being horizontally bent which are disposed on both sides of the objective lens 11 such that each group of elastic supporting members are vertically arranged on each side of the objective lens, and the upper elastic supporting members of the groups of elastic supporting members are spaced from each other horizontally, is improved such that each group of elastic supporting members vertically arranged on each side of the objective lens are not parallel to each other. Further, damping material are fixedly disposed between both ends of the elastic supporting members and stuck onto the elastic supporting members, and the amount of the damping material on one side of the objective lens is different from that of the damping material on the other side of the objective lens, and a method of manufacturing the objective lens driver.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to an optical pick-up device for optically 
writing information into and reading out the same from a recording medium 
layered on an optical disc by projecting a light beam onto the recording 
medium. More particularly, the invention relates to an objective lens 
driver, used for an optical pick-up device, in which a movable portion 
having an objective lens is supported by means of suspension wires. 
2. Discussion of Background Art 
Generally, an optical pick-up device is composed of an objective lens 
driver having an objective lens and an optical system for transmitting 
light to and receiving the same from the objective lens. The optical 
pick-up device is mounted on a mounting table of an optical system block. 
A general objective lens driver, as shown in FIG. 15, includes a movable 
portion 1, a fixed portion 2, and four elastic supporting members 3. The 
movable portion 1 includes an objective lens 11, a focus coil 12 and a 
tracking coil 13. The fixed portion 2 includes a magnetic circuit (magnet 
and others) 21. The elastic supporting members 3 are fastened at both ends 
thereof to the movable portion 1 and the fixed portion 2, and support the 
movable portion 1 in a cantilever fashion. The elastic supporting members 
3 being metal suspension wires are disposed such that pairs of elastic 
supporting members are respectively provided on both sides of the movable 
portion 1 with respect to the objective lens 11. One ends of the pairs of 
the elastic supporting members 3 are soldered to holder plates 15, while 
the other ends of them are soldered to a base plate 23. The holder plates 
15 are provided on the right and left sides of a lens holder 14 holding 
the objective lens 11. The fixed portion 2 is disposed so that the elastic 
supporting members 3 are parallel to a tangential direction of the disc. 
The movable portion 1 may be shifted in a focus direction (perpendicular to 
the disc surface) when current is fed to the focus coil 12, and in a 
tracking direction (radial direction of the disc) when current is fed to 
the tracking coil 13. A measure to damp vibrations of the movable portion 
1 is taken. As well illustrated in FIG. 16, damper cases 24 are provided 
on the front side of the base plate 23 to which the other ends of the 
elastic supporting members 3 are fastened. The other ends of the elastic 
supporting members 3, as shown, are passed through the damper cases 24 and 
the base plate 23, and soldered to the outer side of the base plate 23. 
The damper cases 24 are filled with gel-like damping material 25. In this 
case, the elastic supporting members 3 placed in part are stuck with the 
damping material 25. When the movable portion vibrates, the elastic 
supporting members 3 move through the damping material within the damper 
cases. At this time, viscous flow of the damping material acts on the 
moving elastic supporting members, and the supporting members are 
deformed. The deformation of the supporting members and the viscous flow 
of the damping material are utilized for the damping of the vibrations of 
the movable portion. (This damping technique is disclosed in 
JP-A-2-232824.) 
To secure an exact information writing/reading to and from the optical 
disc, it is required that the optical axis of the objective lens is 
perpendicular to the surface of the disc. If the optical axis of the 
objective lens is tilted with respect to the disc surface during a 
movement of the movable portion (including the objective lens) of the 
objective lens driver in the focus direction, coma occurs in the optical 
system and consequently a signal jitter increases. A tangential 
directional component and a radial directional component make up the tilt 
of the objective lens. To secure an exactness of the information 
writing/reading, tilts of those directional components need to be 
eliminated. 
For this reason, in the objective lens driver, the objective lens is 
mounted on the mounting table such that the optical axis of the objective 
lens is perpendicular to the disc surface. To this end, the supporting 
mechanism of the movable portion is designed such that the angular 
relation of the objective lens of the disc surface is maintained 
irrespective of the moving directions of the movable portion, the focus 
direction and the tracking direction. 
In the objective lens driver, referred to above, in which the movable 
portion is supported by the elastic supporting members, the 
perpendicularity of the optical axis of the objective lens to the disc 
surface is maintained irrespective of the moving direction of the movable 
portion if the elastic supporting members have equal lengths and the 
spatial intervals between both ends of the elastic supporting members are 
equal. 
To prevent the movable portion 1, or the objective lens 11, from being 
tilted when the movable portion is moved in the focus direction or the 
radial direction, the background art mentioned above has the following 
construction: the distances between the fixing ends of the elastic 
supporting members 3 in the movable portion 1 and the fixing ends thereof 
in the fixed portion 2 are selected to be equal and those elastic 
supporting members 3 are disposed to be parallel to one another in the 
vertical and horizontal directions. Further, the amounts of the damping 
material 25 contained in the damper cases 24 are selected to be equal to 
each other on the assumption that the elastic supporting members 3 are 
fixed at predetermined positions. Spring constants of the elastic 
supporting members 3 are selected to be equal to one another. When the 
movable portion 1 is moved in the focus direction, it can be considered 
that a focus-directional drive force acts on the center of gravity of the 
movable portion 1. Hence, the gravity center position is coincident with 
the focus-directional drive center position. 
To suppress the resonance in a low frequency region, damping material is 
put around each wires in the objective lens driver. Use of only the 
damping material fails to satisfactorily suppress the resonance in a high 
frequency region by pitching or yawing, however. To cope with this, 
JP-A-7-105551 and JP-A-9-190636 disclose objective lens drivers in that 
with the intention of improvement of the high-frequency resonance 
suppression, the movable portion 1 is supported with the fixed portion 2 
in a state that the elastic supporting members 3 are bent in advance in 
radial direction, as shown in FIG. 17. 
In the structure where the elastic supporting members 3 are arcuately bent 
in advance, the movable portion 1 unavoidably tilts when the movable 
portion 1 is shifted in the focus direction, even if the spatial intervals 
between the fixing points of the four elastic supporting members 3 are set 
to be equal to one another, and those members are disposed strictly 
parallel to each other. In case where the elastic supporting members 3 are 
bent in the radial direction, for example, when the movable portion 1 is 
shifted in the focus direction, its tilting in the tangential direction 
increases. Particularly when the damping resonating with high frequencies 
is increased by increasing a quantity of the bending of the elastic 
supporting members, a tilt of the movable portion 1 in the tangential 
direction increases. When the tilt of the movable portion 1, i.e., the 
tilt of the objective lens 11, increases, coma is produced and readout 
signal jitter increases. 
Where the quantity of the bending of the elastic supporting members 3 is 
reduced with the intention of reducing the tilt of the movable portion 1 
in the tangential direction when the movable portion 1 is shifted in the 
focus direction, the damping effect for the high frequency resonance is 
lowered. This is problematic when it is assembled into a system. 
Thus, the decrease of the tilt of the movable portion 1 in the tangential 
direction contradicts the increase of the damping for the high frequency 
resonance suppression. 
In the above-mentioned objective lens driver, when the mounting positions 
of the four elastic supporting members 3 are displaced from the correct 
ones, a problem arises. The problem arises even if one mounting position 
is displaced from the correct one. For example, when the space or distance 
between the upper and lower elastic supporting members 3 on the radial (+) 
side is different from that on the radial (-) side, a dynamic balance of 
the structure with respect to the objective lens is lost. When the movable 
portion 1, which is horizontal at the neutral position as shown in FIG. 
19, is shifted in the focus direction, a moment is generated about the 
gravity center of the movable portion 1, and as shown in FIG. 20, the 
movable portion 1 is tilted in the radial direction. Under this condition, 
when the movable portion 1 is shifted in the focus direction, coma is 
produced and the jitter of a readout signal increases. 
For this reason, to prevent the tilt of the movable portion in the radial 
direction, it is required that the elastic supporting members 3 are highly 
accurately positioned. It is very difficult to highly accurately position 
the elastic supporting members 3 in the manufacturing stage. Actually, the 
resultant products inevitably suffer from the tilt of the movable 
portions. A possible measure to correct this is to do over again the 
soldering of the elastic supporting members 3 already fastened by 
soldering. However, the measure is accompanied by the following 
disadvantages: production yield is degraded, perfect correction is not 
always achieved, and product reliability will be impaired at the soldering 
portions of the elastic supporting members 3. 
Next, details of the shift of the movable portion 1 in the focus direction 
will be given. When a focus-directional drive force F causes the movable 
portion 1 to shift in the focus (+) direction (toward the disc) as shown 
in FIG. 21A, a force to cause the elastic supporting members 3L and 3R to 
return to their original positions acts on those members. Let spring 
constants of the elastic supporting members 3L and 3R be Kl and Kr. When 
the movable portion is shifted from the neutral position in the focus 
direction by a distance X, a force Fl (=-Kl*X) acts on the fixing terminal 
of the elastic supporting member 3L and a force Fr (=-Kr*X) acts on the 
fixing terminal of the elastic supporting member 3R. Rotational moments 
generated about the gravity center G of the movable portion 1, caused by 
those forces, is expressed by 
EQU Ml=Fl+L, and Mr=Fr*L 
where L=distance between the gravity center G and the fixing terminal of 
each of the elastic supporting members 3L and 3R. 
Those moments Ml and Mr are opposite to each other with respect to the 
gravity center G. As recalled, the spring constants of the rotational 
moments Ml and Mr are equal to each other. Hence, the rotational moment Ml 
that is caused about the gravity center by the force applied from the 
elastic supporting member 3R is equal to the rotational moment Mr caused 
by the elastic supporting member 3L. Therefore, the movable portion 1 is 
not rotated. 
Then, let us consider a case that the movable portion 1 is shifted in the 
radial direction, specifically, it is shifted a distance "l" to the left. 
In this case, the gravity center G of the movable portion 1 is shifted a 
distance equal to the radial shift of 21" with respect to the 
focus-directional drive center position. As a result of the shift, the 
spring constants Kl and Kr of the elastic supporting members 3L and 3R 
remain unchanged, viz., those are equal to each other. 
The focus-directional drive center position can be considered to be the 
center of the magnetic circuit 21 of the fixed portion 2. Then, if the 
movable portion is shifted in the focus direction after it is shifted the 
distance of the radial shift of "l", a shift of "l" is produced between 
the focus-directional drive center position on which the focus-directional 
drive force F acts and the gravity center G of the movable portion 1. As a 
consequence, a rotation moment Mf (=F*l) is generated about the gravity 
center G in the movable portion 1. The direction of the rotation moment Mf 
is a counterclockwise direction when the movable portion is shifted in the 
focus (+) direction (toward the disc) since the gravity center G is 
located on the left-hand side when it is viewed from the focus-directional 
drive center position on which the focus-directional drive force F acts. 
Therefore, the movable portion 1 is rotated in the counterclockwise 
direction. In contrast with the above case, when the movable portion is 
shifted in the focus (-) direction (apart from the disc), the direction of 
the rotation moment Mf is a clockwise direction. The movable portion 1 is 
turned in the clockwise direction. 
This results in a radial-directional tilt of the movable portion 1. There 
is known a technique that to remove the tilt, the rotational moment is 
balanced when the focus-directional drive center position is radially 
shifted in a manner that a distribution of magnetic flux of the magnetic 
circuit is shaped like a twin-mountain configuration by dividing the 
magnetic circuit in the radial direction (disclosed in JP-A-8-50727, for 
example). 
A complicated magnetic circuit is required for varying the 
focus-directional drive center position in accordance with a quantity of 
its shift. Use of the complicated magnetic circuit cannot reduce the 
rotational moment sufficiently, however. Therefore, the movable portion 1 
is tilted in the radial direction at the time of the radial shift of the 
focus-directional drive center position. This results in coma in the 
optical system, and increase of the jitter of the readout signal. 
SUMMARY OF THE INVENTION 
Accordingly, an object of the present invention is to provide an objective 
lens driver of which an objective lens is not tilted with respect to the 
surface of an optical disc. 
According to one aspect of the present invention is to provide an objective 
lens driver comprising: a movable portion with an objective lens; at least 
four elastic supporting members being fixedly attached at one ends to the 
movable portion while being vertically and horizontally arranged with 
respect to the objective lens, the elastic supporting members being 
bilaterally bent; and a fixed portion to which the other ends of the 
elastic supporting members are fixedly attached; wherein the elastic 
supporting members vertically arranged are not in parallel to each other. 
The thus improved structure reduces a tilt of the movable portion in the 
tangential direction that is caused when the movable portion is shifted in 
the focus direction. 
According to another aspect of the present invention, there is an objective 
lens driver comprising: a movable portion with an objective lens; at least 
four elastic supporting members being fixedly attached at one ends to the 
movable portion while being vertically and horizontally arranged with 
respect to the objective lens; and a fixed portion to which the other ends 
of the elastic supporting members are fixedly attached; wherein damping 
material are fixedly disposed between both ends of the elastic supporting 
members and stuck onto the elastic supporting members, and the amount of 
the damping material on one side of the objective lens is different from 
that of the damping material on the other side of the objective lens. 
In the thus objective lens driver thus constructed, when the movable 
portion is shifted to the radial (+) side, and when the movable portion is 
shifted to the radial (-) side, the damping material is additionally put 
into the damper case on the radial (+) side in accordance with a tilt of 
the movable portion, viz., the amount of the damping material on one side 
is different from that on the other side. This unique structure reduces a 
tilt of the movable portion in the tangential direction that is caused 
when the movable portion is shifted in the focus direction. 
According to another aspect of the invention, there is provided an 
objective lens driver comprising: a movable portion with an objective 
lens; at least four elastic supporting members being fixedly attached at 
one ends to the movable portion while being vertically and horizontally 
arranged with respect to the objective lens; and a fixed portion to which 
the other ends of the elastic supporting members are fixedly attached; 
wherein when the movable portion is shifted in the radial direction, the 
spring constants of the elastic supporting members are varied. 
With such a construction, when the movable portion is shifted in the radial 
direction, the spring constants of the elastic supporting members are 
varied. When the movable portion is shifted in the focus direction, forces 
causing elastic supporting members to restore their original shape are 
generated, and generate rotational moments about the gravity center of the 
movable portion. The rotational moments cancel out a rotational moment 
generated when the focus-directional drive center position is shifted from 
the gravity center.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
&lt;First Embodiment&gt; 
FIG. 1 is a diagram schematically showing an objective lens driver in use 
for an optical pick-up device which is an embodiment of the present 
invention. In FIG. 1, reference numeral 31 is an upper elastic member; 32 
is a lower elastic member 32; A is a fixed interval between the upper and 
lower elastic members 31 and 32 in a movable portion 1 of the objective 
lens driver; and B is a fixed interval between the upper and lower elastic 
members 31 and 32 in a fixed portion 2 of the objective lens driver. 
FIG. 2 shows a variation of a tilt of the movable portion 1 in the 
tangential direction when the movable portion 1 is shifted +0.5 mm in the 
focus direction (from the neutral position to the disc) in a manner that 
the fixed interval A is varied while the fixed interval B is fixed at a 
given value. In this case, wires of phosphor bronze, 0.08 mm in diameter, 
were used for the elastic members 31 and 32. A horizontal interval C 
between the right and left elastic supporting members 3, viz., those 
members when viewed in the radial direction was 10.6 mm; an interval L 
between the fixing points of the elastic members 31 and 32 was 9.0 mm; and 
the fixed interval B was 1.9 mm. Also in FIG. 2, X represents data 
gathered when a quantity D of bending of the elastic supporting member was 
set at 0, and Y represents data when the bending quantity D was set at 
approximately 130 .mu.m. For the meanings of the horizontal interval C and 
the bending quantity D, reference is made to FIG. 17. As seen from the 
graph, where A/B=1 and the bending quantity D=0, a tilt of the movable 
portion 1 in the tangential direction is +2 arcmin (sign+means a tilt of 
the movable portion when it is shifted to the disc). Where A/B=1 and the 
bending quantity D=approximately 130 .mu.m, a tilt of the movable portion 
is +7 arcmin. In this case, the movable portion is greatly tilted in the 
tangential direction. Where A/B=0.97, it is little tilted in the 
tangential direction. The further a value difference of A/B from 0.97 
increases, the larger the tilt in the tangential direction is. 
As seen from this fact, it is possible to prevent the increase of the tilt 
of the movable portion in the tangential direction even if the elastic 
supporting members 3 is bent and the movable portion 1 is shifted in the 
focus direction if the fixed intervals A and B are related as A&lt;B, and the 
ratio of them, A/B, is properly selected so as to compensate for a tilt of 
the movable portion determined by the bending quantity D of the elastic 
supporting member 3. Therefore, the damping effect for the resonance at 
high frequencies can be enhanced by setting the bending quantity D at a 
value irrespective of the tilt of the movable portion 1. 
Description has been made about the objective lens driver in which the 
movable portion with the objective lens is supported on the fixed portion 
in a cantilever fashion by two pairs of elastic supporting members. Those 
elastic supporting members are disposed on both sides of the objective 
lens such that each pair of elastic supporting members are vertically 
arranged as the upper and lower elastic supporting members on each side of 
the objective lens, and the upper elastic supporting members of those 
pairs of the elastic supporting members are horizontally spaced from each 
other. It is readily understood that the invention is applicable to the 
objective lens driver in which the movable portion is supported on the 
fixed portion in a cantilever fashion by two trios of elastic supporting 
members. Those elastic supporting members are disposed on both sides of 
the objective lens such that each trio of elastic supporting members are 
vertically arranged as the upper, middle and lower elastic supporting 
members on each side of the objective lens, and the upper elastic 
supporting members of those pairs of elastic supporting members are spaced 
from each other horizontally. While the movable portion is supported on 
the fixed portion in a cantilever fashion in the above-mentioned 
embodiment, the former may be supported at both ends with the latter. In 
the above-mentioned embodiment, the like members are used for the upper 
and lower elastic members 31 and 32, which are vertically arranged on each 
side of the objective lens and horizontally bent. The elastic supporting 
members that are bent at different curvatures may be used instead of the 
above ones. Further, the elastic supporting members that are horizontally 
and vertically bent may also be used for the elastic members 31 and 32. In 
the above-mentioned embodiment, the fixing points of the upper and lower 
elastic members 31 and 32 on the movable portion 1 are vertically aligned 
with each other. If necessary, those fixing points may be not aligned with 
each other. 
An objective lens driver in which a movable portion with an objective lens 
is supported on a fixed portion by two groups of elastic supporting 
members each being horizontally bent which are disposed on both sides of 
the objective lens such that each group of elastic supporting members are 
vertically arranged on each side of the objective lens, and the upper 
elastic supporting members of the groups of elastic supporting members are 
spaced from each other horizontally, is improved such that each group of 
elastic supporting members vertically arranged on each side of the 
objective lens are not parallel to each other. 
The thus improved structure reduces a tilt of the movable portion in the 
tangential direction that is caused when the movable portion is shifted in 
the focus direction, and enables a designer to properly select a bending 
quantity of each elastic supporting member irrespective of the tilt of the 
movable portion. Therefore, the objective lens driver of the invention 
reduces a tilt of the movable portion in the tangential direction caused 
when the movable portion is shifted in the focus direction, and enhances 
the damping effect for the resonance at high frequencies. 
&lt;Second Embodiment&gt; 
FIG. 3 is a diagram showing a second embodiment of the present invention. 
In FIG. 3, reference numeral 1 is a movable portion; 2 is a fixed portion; 
3 is an elastic supporting member; 24L is a left-hand (left=radial (-) 
side) damper case; 24R is aright-hand (right=radial (+) side) dampercase; 
25L is a damping material filling the left-hand damper case 24L; and 25R 
is a damping material filling the right-hand damper case 24R. 
A quantity of additional damping material and a tilt angle that may be 
corrected will be described. An experiment was conducted for obtaining a 
relationship between a quantity of additional damping material and a tilt 
angle that may be corrected. The result of the experiment is shown in FIG. 
4. This relationship depends on such various factors as kinds and spring 
constants of the elastic supporting members, the volumes of the right- and 
left-hand damper case 24R and 24L, and kinds and initial filling 
quantities of the damping materials 25R and 25L. A typical relationship 
will be described for ease of explanation. Various materials may be used 
for the damping materials 25R and 25L. Of those materials, gel-like 
materials, particularly gel-like materials of silicone or denatured 
acrylate are preferable for the damping materials. In the description to 
follow, a gel-like damping material of silicone will be used for the 
damping materials 25R and 25L. 
Four wires of 80 .mu.m in diameter were used for the elastic supporting 
members 3. A length of the elastic supporting member ranging from the 
fixing point on the movable portion 1 to the fixing point on the fixed 
portion 2 was 9 mm. The right- and left-hand damper cases 24R and 24L are 
each capable of receiving damping material of 7.6 mg. One damper case 24R 
or 24L was used for two wires, upper and lower wires. A tilt of the 
movable portion in the radial direction, which was caused when the movable 
portion was shifted +0.5 mm in the focus direction, was measured. In the 
measurement, the damping material 25R of 6.1 mg was put into the 
right-hand damper case 24R, and the damping material 25L was gradually put 
into the left-hand damper case 24L during the measurement. 
In the graph of FIG. 4, the abscissa represents a quantity of the damping 
material 25L put into the left-hand damper case 24L, and the ordinate 
represents a tilt of the movable portion in the radial direction, which 
was caused when the movable portion was shifted +0.5 mm in the focus 
direction. From the graph, it is seen that the movable portion descends as 
the quantity of the damping material is large. When the quantity of the 
damping material 25R on the right side (=radial (+) side) is larger than 
that of the damping material 25L on the left side (=radial (-) side), the 
right end of the movable portion descends (tilts to the radial (+) side). 
In the reverse case, the left end of the movable portion descends (tilts 
to the radial (-) side). 
The relationship between the quantity of additional damping material and 
the radial-directional tilt is substantially linear. A proportional 
constant of the relationship can be calculated as 4.2 arcmin/mg. 
The relationship between a quantity of additional damping material and a 
tilt angle (FIG. 5) that may be corrected may be derived from the 
measurement results of FIG. 4. In case where a sample manufactured is 
shifted +0.5 mm in the focus direction and the movable portion 1 is tilted 
to the radial (+) side at angle of 4.2 arcmin, the tilt of the movable 
portion 1 can be corrected and the tilt angle can be reduced to zero (0) 
by additionally putting the damping material of 1.0 mg into the left-hand 
damper case 24L of the radial (-) side. 
As seen from the above, the tilt of the movable portion 1 in the radial 
direction can be removed in the following manner. Equal to substantially 
equal amounts of damping material is put into the right-hand damper cases 
24R and 24L. A tilt of the movable portion 1 produced when it is shifted 
+0.5 mm in the focus direction is measured. Damping material is 
additionally put into either of the right- and left-hand damper cases 24R 
and 24L to make the amounts of the damping materials 25R and 25L 
different. 
In an alternative, the right- and left-hand damper cases 24R and 24L are 
empty at first. The operator puts the damping material into those damper 
cases while measuring a tilt characteristic of the objective lens. 
Finally, the amount of the damping material in the right-hand damper case 
24R is made different from that in the left-hand damper case 24L. 
In the instances mentioned above, the tilt adjusting damping material is 
additionally put into the right-hand damper case 24R or 24L. Another 
alternative is shown in FIG. 6. As shown, tilt-adjusting damper cases 4 
are provided on both sides of a movable portion 1. Tilt adjusting material 
is put into one or both the damper cases 4. In this instance, the damper 
cases 4 are mounted on both side surfaces of a lens holder 14. If 
necessary, those cases 4 may be fastened onto holder plates 15. One 
tilt-adjusting damper case 4 is provided for two elastic supporting 
members, the upper and lower elastic supporting members. The 
tilt-adjusting damper case may be provided for the elastic supporting 
member in one-to-one correspondence fashion. The tilt-adjusting damping 
material 5 is additionally put into both the tilt-adjusting damper cases 
4. This is based on the assumption that no tilt-adjusting damping material 
5 is put into the tilt-adjusting damper cases 4 all along. When the 
tilt-adjusting damping material 5 is already put in the tilt-adjusting 
damper cases, adding of the tilt-adjusting damping material 5 to the 
damping material already present in either of the tilt-adjusting damper 
cases 4 will do. 
Another tilt-adjusting contrivance is illustrated in FIG. 7. As shown, 
tilt-adjusting damper cases 6 are separately provided on the side surfaces 
of the base plate 22 of the fixed portion 2. Tilt-adjusting damping 
material 7 is additionally applied to one or both of the tilt-adjusting 
damper cases 6. In this tilt-adjusting contrivance, one tilt-adjusting 
damper case 6 is provided for two elastic supporting members 3, the upper 
and lower elastic supporting members. If required, the tilt-adjusting 
damper case 6 is provided for each of the elastic supporting members 3. 
An additional tilt-adjusting contrivance is shown in FIG. 8. In this 
tilt-adjusting contrivance, the tilt-adjusting damper cases are not used, 
but tilt-adjusting damping material 8 is directly applied to the elastic 
supporting members 3 by coating. The tilt-adjusting damping material 8, 
together with the elastic supporting members 3, is held by the movable 
portion 1. Places onto which the tilt-adjusting damping material 8 is 
stuck are the side surfaces of the lens holder 14. If necessary, the 
holder plates 15 are extended, and the tilt-adjusting damping material 
maybe applied to the extended holder plates 15. In the illustrated 
instance, the two, upper and lower elastic supporting members are secured 
onto the same place, or the movable portion 1. If necessary, the upper 
elastic supporting members may be stuck to the movable portion 1 and the 
lower elastic supporting members may be stuck onto the fixed portion 2, 
and vice versa. Further, the tilt-adjusting damping material 8 may be 
applied to one or both of the elastic supporting members 3. 
A kind of the tilt-adjusting damping material may be different from that of 
the damping material already filled in. 
The embodiment uses two types of damping materials. The first type of 
damping material is first loaded into the right- or left-hand damper case 
24R or 24L, and the second type of damping material is additionally loaded 
into the damper case. Therefore, the amount of damping material to be 
loaded into the right- and left-hand damper case 24R or 24L is reduced. 
The fact implies that the depth of the right- and left-hand damper case 
24R or 24L may be reduced, and hence its size in the tangential direction 
may be reduced. 
A mechanical unbalance, e.g., difference of the interval between the upper 
and lower elastic supporting members 3 on the radial (+) side portion of 
the movable portion 1 from that on the radial (-) side portion thereof, 
can be removed by adjusting the spring constant or constants of the 
elastic supporting member or members. To the adjustment, the 
tilt-adjusting damping material is additionally loaded into the damper 
case or cases. If so adjusted, the elastic supporting members 3 on the 
radial (+) side are uniformized with those on the radial (-) side. As a 
result, when the movable portion is shifted in the focus direction, the 
elastic supporting members uniformly act and move in parallel with each 
other. Hence, the movable portion 1 never tilts in the radial direction. 
In the description thus far made, the tilt of the movable portion is caused 
by dimensional errors of the elastic supporting members. However, the 
movable portion will be tilted by other causes, for example, when the 
magnet is shifted in the radial direction. The tilt-adjusting means 
mentioned above may be applied to the correction of the tilts produced by 
the latter cause. 
There is a case where the movable portion of the product tends to tilt 
because of the characteristic of the tool used for assembling the product. 
The tilt-adjusting means of the invention effectively operates to correct 
such a tilt peculiar to the product without correcting the tool 
characteristic. In this case, different but properly selected amounts of 
damping material are loaded into to the damper cases. 
Description has been made about the objective lens driver in which the 
movable portion with the objective lens is supported on the fixed portion 
in a cantilever fashion by two pairs of elastic supporting members. Those 
elastic supporting members are disposed on both sides of the objective 
lens such that each pair of elastic supporting members are vertically 
arranged as the upper and lower elastic supporting members on each side of 
the objective lens, and the upper elastic supporting members of those 
pairs of the elastic supporting members are horizontally spaced from each 
other. It is readily understood that the invention is applicable to the 
objective lens driver in which the movable portion is supported on the 
fixed portion in a cantilever fashion by two trios of elastic supporting 
members. Those elastic supporting members are disposed on both sides of 
the objective lens such that each trio of elastic supporting members are 
vertically arranged as the upper, middle and lower elastic supporting 
members on each side of the objective lens, and the upper elastic 
supporting members of those pairs of elastic supporting members are spaced 
from each other horizontally. While the movable portion is supported on 
the fixed portion in a cantilever fashion in the above-mentioned 
embodiment, the former may be supported at both ends with the latter. 
The present invention, which has been described, is incorporated into the 
objective lens driver in which even if the movable portion 1 is shifted in 
the focus direction, the movable portion 1 is not tilted in the radial 
direction. The invention may be incorporated into a method of 
manufacturing the objective lens driver in which even if the movable 
portion 1 is shifted in the focus direction, the movable portion 1 is not 
tilted in the radial direction. There is provided a manufacturing method 
of an objective lens driver in which a movable portion with an objective 
lens is supported on a fixed portion by two groups of elastic supporting 
members which are disposed on both sides of the objective lens such that 
each group of elastic supporting members are vertically arranged on each 
side of the objective lens, and the upper elastic supporting members of 
the groups of elastic supporting members are spaced from each other 
horizontally, the manufacturing method wherein after an objective lens 
tilt characteristic is inspected, tilt-adjusting damping material is added 
to damping material stuck onto the elastic supporting members fixed at 
both ends and arranged therebetween in accordance with a detected tilt of 
the objective lens. 
As seen from the foregoing description, the present invention may be 
defined by an objective lens driver in which a movable portion with an 
objective lens is supported on a fixed portion by two groups of elastic 
supporting members which are disposed on both sides of the objective lens 
such that each group of elastic supporting members are vertically arranged 
on each side of the objective lens, and the upper elastic supporting 
members of the groups of elastic supporting members are spaced from each 
other horizontally, the improvement being characterized in that damping 
material are fixedly disposed between both ends of the elastic supporting 
members and stuck onto the elastic supporting members, and the amount of 
the damping material on one side of the objective lens is different from 
that of the damping material on the other side of the objective lens, and 
a method of manufacturing the objective lens driver. With such a 
construction, even if the movable portion 1 is shifted in the focus 
direction, the movable portion 1 is not tilted in the radial direction. 
The novel and unique construction of the invention accrues to the 
following advantages. There is no need for the work of accurately 
positioning the elastic supporting members for preventing the objective 
lens tilt. There is eliminated the work to do over again the soldering of 
the elastic supporting members 3 already fastened by soldering, the work 
essential to the accurate positioning. Further, there is no need for the 
apprehension of the reliability on the soldering portions. 
&lt;Third Embodiment&gt; 
FIG. 9 shows a diagram useful in explaining a third embodiment of the 
present invention. In the figure, reference numeral 1 is a movable 
portion; 3L is a left-hand elastic supporting member; and 3R is a 
right-hand elastic supporting member 3R. 
The right- and left-hand damper cases 24R and 24L are shaped to be 
bilaterally symmetrical with each other as shown in FIG. 10. A portion 24A 
of the right-hand damper case 24R (24L) at which the left-hand elastic 
supporting member 3R (3L) is to be placed is shaped like V; the inner side 
of the portion 24A narrows in the focus direction, and the outer side 
thereof expands in the focus direction. With the thus shaped portions 24A, 
when the movable portion 1 is shifted in the radial direction, the amount 
of damping material 25 loaded into between the right-hand damper case 24R 
and the right-hand elastic supporting member 3R becomes different from 
that of the damping material loaded into between the left-hand damper case 
24L and the left-hand elastic supporting member 3L. 
When the movable portion 1 is shifted a distance 1 to the left as shown in 
FIG. 3, a distance between the wall of the right-hand damper case 24R 
(24L) filled with the damping material 25 and the right-hand elastic 
supporting member 3R (3L) varies in the focus direction as shown in FIG. 
12. The left-hand elastic supporting member 3L attached in the shift 
direction is put in a place where the amount of the damping material 25 is 
increased in the focus direction. Therefore, its compression by the 
left-hand damper case 24L is lessened, so that its spring constant Kl 
becomes small. 
The right-hand elastic supporting member 3R attached in the direction 
opposite to the shift direction is put in a place where the amount of the 
damping material 25 is decreased. Therefore, its compression by the 
left-hand damper case 24L is increased, so that its spring constant Kl 
becomes large. 
When the movable portion 1 is merely shifted in the focus direction, the 
amounts of the damping materials 25, which fills in between the right- and 
left-hand damper cases 24R and 24L and the right- and left-hand elastic 
supporting members 3R and 3L, are equal to each other. Therefore, the 
spring constants Kl and Kr are equal to each other. 
When the movable portion 1 is shifted in the radial direction and then in 
the focus direction, forces are generated which cause the right- and 
left-hand elastic supporting members 3R and 3L to restore their original 
shape. When the movable portion is shifted from the neutral position in 
the focus direction by a distance X, a force Fl (=-Kl*X) acts on the 
fixing end of the left-hand elastic supporting member 3L (FIG. 3). 
Further, a force Fl (=-Kr*X) acts on the fixing end of the right-hand 
elastic supporting member 3R. Those forces cause respectively rotational 
moments about the center of gravity of the movable portion. The rotation 
moments are given by 
EQU Ml=Fl*L and Mr=Fr*R 
where L=distance between the gravity center G and each of the elastic 
supporting members 3R and 3L. Therefore, the smaller the spring constant 
of each elastic supporting member is, the smaller the rotational moments 
are. On the other hand, the larger the spring constant of each elastic 
supporting member is, the larger the rotational moments are. 
The gravity center G is located to the left when viewed from the right-hand 
elastic supporting member 3R, and to the right when viewed from the 
left-hand elastic supporting member 3L. 
Therefore, the directions of the rotational moments Ml and Mr are opposite 
to each other. The rotational moment Mr caused by the right-hand elastic 
supporting member 3R is larger than the rotational moment Ml by the 
left-hand elastic supporting member 3L. Therefore, when the movable 
portion 1 is shifted in the focus (+) direction (toward the disc, the sum 
of the rotational moments Mr and Ml (=Mr-Ml) causes the movable portion 1 
to turn in the clockwise direction. In contrast with this, when it is 
shifted in the focus (-) direction (apart from the disc), the movable 
portion 1 will turn in the counterclockwise direction. 
When the movable portion 1 is shifted in the radial direction, the 
focus-directional drive center position on which the focus-directional 
drive force F acts is shifted from the gravity center G of the movable 
portion 1. When the movable portion 1 is shifted in the focus direction 
under this condition, a rotational moment Mf is generated about the 
gravity center: Mf=f.times.l, where l=shift of the focus-directional drive 
center position and the gravity center. The gravity center G is positioned 
to the left when viewed from the focus-directional drive center position 
on which the focus-directional drive force F acts. Therefore, when the 
movable portion 1 is shifted in the focus (+) direction (toward the disc), 
the rotation moment Mf causes the movable portion 1 to turn in the 
counterclockwise direction. When it is shifted in the focus (-) direction 
(apart from the disc), the rotation moment Mf causes the movable portion 1 
to turn in the clockwise direction. 
The rotational moment (Mr-Ml) is opposite in direction o the rotational 
moment Mf. Therefore, the former cancels out the latter. Therefore, if the 
rotational moment (Mr-Ml) is selected to be equal to or slightly smaller 
or larger than the rotational moment Mf, when the movable portion 1 is 
simultaneously shifted in both the focus and radial directions, the 
rotational moment is extremely small and hence a tile of the movable 
portion is 0 or approximate to 0. 
EXAMPLE 
A radial directional tilt of the movable portion 1 caused when the movable 
portion is shifted in the radial direction, and then shifted a distance of 
+0.4 mm in the focus direction, is shown in FIG. 13. In the figure, Y 
indicates a conventional objective lens driver and X indicates an 
objective lens driver by the invention. A sample constructed by the 
conventional technique is shown in FIG. 14A. In the sample, the depth of 
the damper case 24 was 2.0 mm. An elongated hole of 1.8 mm wide and 3.45 
mm high was formed in the damper case 24. Elastic supporting members 3 are 
located within the elongated hole while being spaced at intervals A (=0.65 
mm), B (=2.15 mm) and C (=1.0 mm). Another sample constructed according to 
the present invention is shown in FIG. 14B. In the sample, the depth of 
the damper case 24 was 2.0 mm. An elongated hole of 0.95 mm wide and 3.45 
mm high was formed in the damper case 24. V-shaped grooves are formed in 
the inner left surface of the elongated hole while being spaced at 
intervals A (=0.65 mm) and B (=2.15 mm). Elastic supporting members 3 are 
located within those V-shaped grooves, respectively. Each elastic 
supporting member 3 was 90 .mu.m in diameter and 9.0 mm long. A distance 
between the right and left elastic supporting members 3 was 9.6 mm. 
Damping material loaded into the damper case 24 was silicone gel. 
As seen from the graph of FIG. 13, in the conventional driver, a 
radial-directional tilt is 8.2 arcmin when the radial shift is 0.2 mm, 
while it is 2.5 arcmin in the driver of the invention. The tilt is greatly 
reduced in the invention driver. 
In the objective lens driver of the invention, with a mere modification of 
the damper case, the rotation moment generated about the gravity center is 
sufficiently reduced even if the movable portion is shifted simultaneously 
in both the radial and focus directions. Therefore, the tilt of the 
movable portion 1 is reduced to 0 or extremely reduced while not making 
the magnetic circuit complicated, and hence no coma is produced and the 
jitter of the readout signal is improved. 
Description has been made about the objective lens driver in which the 
movable portion with the objective lens is supported on the fixed portion 
in a cantilever fashion by two pairs of elastic supporting members. Those 
elastic supporting members are disposed on both sides of the objective 
lens such that each pair of elastic supporting members are vertically 
arranged as the upper and lower elastic supporting members on each side of 
the objective lens, and the upper elastic supporting members of those 
pairs of the elastic supporting members are horizontally spaced from each 
other. It is readily understood that the invention is applicable to the 
objective lens driver in which the movable portion is supported on the 
fixed portion in a cantilever fashion by two trios of elastic supporting 
members. Those elastic supporting members are disposed on both sides of 
the objective lens such that each trio of elastic supporting members are 
vertically arranged as the upper, middle and lower elastic supporting 
members on each side of the objective lens, and the upper elastic 
supporting members of those pairs of elastic supporting members are spaced 
from each other horizontally. While the movable portion is supported on 
the fixed portion in a cantilever fashion in the above-mentioned 
embodiment, the former may be supported at both ends with the latter. 
As seen from the foregoing description, the present invention may be 
defined by an objective lens driver in which a movable portion with an 
objective lens is supported on a fixed portion by two groups of elastic 
supporting members which are disposed on both sides of the objective lens 
such that each group of elastic supporting members are vertically arranged 
on each side of the objective lens, and the upper elastic supporting 
members of the groups of elastic supporting members are spaced from each 
other horizontally, the manufacturing method wherein when the movable 
portion is shifted in the radial direction, the spring constants of the 
elastic supporting members are varied. Forces causing elastic supporting 
members to restore their original shape are generated when the movable 
portion is shifted in the focus direction. Those forces act on the movable 
portion and generate rotational moments about the gravity center of the 
movable portion. The rotational moments cancel out a rotational moment 
generated when the focus-directional drive center position is shifted from 
the gravity center. Therefore, the tilt of the movable portion 1 is 
reduced to 0 or extremely reduced while not making the magnetic circuit 
complicated, and hence no coma is produced and the jitter of the readout 
signal is improved.