Optical disk unit

There is disclosed an optical disk unit. Optical parts, including a laser unit and objective, are integrally mounted on a bobbin, and focusing coils and tracking and feed coils are mounted on the bobbin. The bobbin is resiliently supported, and is slidable along guide shafts extending radially of an optical disk loaded on the optical disk unit. The bobbin is moved by the focusing coils and the tracking and feed coils, thereby effecting a focusing drive, a tracking drive and a feed drive. With this construction, the optical disk unit can be compact in size, and light in weight.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to an optical disk unit which reads information from 
a recording medium, such as an optical disk and a opto-magnetic disk, or 
reads and writes information relative to such a recording medium. 
2. Description of Related Art 
Recently, optical disk units have become compact and thin in size, and are 
of a high performance design so that they can be mounted on a smallsize 
information processing device. 
A conventional optical disk unit will now be described. FIG. 20 is a view 
showing important portions of the conventional optical disk unit, and FIG. 
21 is a view showing a pickup head of the conventional optical disk unit. 
As shown in FIG. 20, the optical disk unit comprises a spindle motor 2 for 
rotating an optical disk (recording medium) 1, a fixed optical portion 3 
and a movable optical portion 4 which reproduce data stored in the optical 
disk 1, or record and reproduce such data, and a feed portion 5 for moving 
the movable optical portion 4 in a direction radially of the optical disk 
1. A laser beam emitting means for applying a laser beam to the optical 
disk 1, a photo detector means for detecting the light or beam reflected 
from the optical disk 1, and other optical parts are mounted on the fixed 
optical portion 3. Optical parts which direct the laser beam, applied from 
the fixed optical portion 3 to the optical disk 1, and also condense or 
converge the laser beam, a focusing drive means, and a tracking drive 
means are mounted on the movable optical portion 4. In FIG. 21, an 
objective lens 6 for converging the laser beam, emitted from the fixed 
optical portion 3, onto the optical disk 1, a bobbin 7 supporting an 
objective lens 6, focusing coils 8 and tracking coils 9 are mounted on the 
bobbin 7. The bobbin 7 is resiliently supported by suspension springs 10 
for movement in a focusing direction (direction of an arrow A) and a 
tracking direction (direction of an arrow B) relative to a head base 11. 
Opposite ends of each suspension spring are fixedly secured to the head 
base 11 and the bobbin 7, respectively. A pair of magnets 12 are fixedly 
mounted on the head base 11 in opposed relation to the focusing coils 8 
and the tracking coils 9. The pickup head shown in FIG. 21 is mounted on a 
carriage base 13 shown in FIG. 20, and guide rollers 14 mounted on the 
carriage base 13 are held in engagement with two guide shafts 15, so that 
the pickup head is slidable, together with the carriage base 13, in a 
direction radially of the optical disk 1. Feed magnets 16 are fixedly 
mounted respectively on back yokes 17 of a ferromagnetic material. An 
opposed yoke 18 made of a ferromagnetic material is provided in opposed 
relation to a respective one of the feed magnets 16. The feed magnet 16, 
the back yoke 17 and the opposed yoke 18 jointly constitute a magnetic 
circuit of the feed portion 5. A pair of feed coils 19 are mounted on the 
carriage base 13, and the opposed yokes 18 extend through these feed coils 
19, respectively. 
The operation of the optical disk unit of the above construction will now 
be described. A laser beam, emitted from the laser beam emitting means 
mounted on the fixed optical portion 3, is directed to the objective lens 
6 by an upwardly-directing mirror and other associated parts mounted on 
the head base 11 of the movable optical portion 4, and is converged onto 
the optical disk by the objective lens 6. On the other hand, reflection 
light from the optical disk 1 is fed via the objective lens 6 and the 
upwardly-directing mirror and other associated part to the photo detector 
means mounted on the fixed optical portion 3. Using a signal outputted 
from this photo detector means, data stored in the optical disk 1 is 
reproduced. In order to satisfactorily reproduce the data stored in the 
optical disk 1, the objective lens 6 needs to be moved in the focusing 
direction (direction of the arrow A) and the tracking direction (direction 
of the arrow B) so as to accurately converge the laser beam, emitted from 
the laser beam emitting means mounted on the fixed optical portion 3, onto 
the optical disk 1. With respect to the movement of the objective lens 6 
in the focusing direction, the focusing drive is effected by an 
electromagnetic effect, achieved by the focusing coils 8 and the magnets 
12, against the bias of the suspension springs 10. With respect to the 
movement in the tracking direction, the tracking drive is similarly 
effected by an electromagnetic effect achieved by the tracking coils 9 and 
the magnets 12. The carriage base 13 is moved along the guide shafts 15 by 
an electromagnetic effect achieved by the feed coils 19 and the feed 
magnets 16. By thus driving the carriage base 13, a feed drive is effected 
such that the objective lens 6 moves over an entire data area of the 
optical disk 1. 
By the above focusing drive, tracking drive and feed drive, the laser beam, 
emitted from the fixed optical portion 3, is accurately converged onto a 
required position of the optical disk 1 through the objective lens 6. 
In the above conventional construction, however, the carriage base 13 is of 
such a construction that the opposite sides thereof are disposed close to 
the pair of guide shafts 15, respectively, and therefore the carriage base 
13 is large in size and heavy in weight. As a result, the carriage base 13 
can not be driven at high speed in the tracking direction. Further, two 
drive portions are required, that is, the tracking drive portion 
constituted by the tracking coils 9 and the magnets 12 for moving only the 
bobbin 7, having the objective 6 mounted thereon, in the tracking 
direction and the feed drive portion constituted by the feed coils 19 and 
the feed magnets 16 for moving the entire movable optical portion 4, 
including the carriage base 13, in the tracking direction. Thus, the 
number of component parts increases, and therefore it is difficult to 
provide a small-size design and to reduce the cost. Further, since the 
fixed optical portion 3 is separate from the movable optical portion 4, it 
has been necessary to achieve such a positional accuracy that the laser 
beam, emitted from the laser beam emitting means, can be directed to the 
objective lens 6. Thus, high precision of the parts and means for making 
adjustments during assembly are required. Furthermore, in the magnetic 
circuit constituted by the magnets 12, the focusing coil 8 and the 
tracking coil 9 are disposed in overlapping relation to each other, and 
therefore a gap in the magnetic circuit is increased by an amount 
corresponding to the thickness of this overlap, which has resulted in 
decreasing the efficiency with which the actuator is driven. 
SUMMARY OF THE INVENTION 
With the above problems of the conventional construction, it is an object 
of this invention to provide an optical disk unit which is compact in 
size, less costly, and high in reliability. 
According to the present invention, there is provided an optical disk unit 
comprising: 
light-converging means for converging light, emitted from emitting means, 
onto a recording medium loaded on the optical disk unit; 
a bobbin having the light-converging means mounted thereon; 
a pair of guide members mounted respectively on opposite sides of the 
bobbin for guiding the bobbin in a direction radially of the recording 
medium; 
a pair of slide members slidably mounted on the pair of guide members, 
respectively; 
a connecting member fixedly secured to the bobbin and the slide members to 
resiliently support the bobbin relative to the slide members; 
focusing drive means for moving the bobbin in a direction perpendicular to 
the surface of the recording medium; and 
tracking drive means for moving the bobbin along the guide members. 
The slide members mounted on the pair of guide members are connected 
together through the bobbin and the connecting member, and therefore the 
slide members, movable radially of the optical disk together with the 
bobbin, can be lightweight.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
First Embodiment 
A first embodiment of the present invention will now be described with 
reference to the drawings. FIG. 1 is a plan view of the first embodiment 
of an optical disk unit of the present invention, FIG. 2 is a perspective 
view of the optical disk unit of the first embodiment, FIG. 3 is an 
exploded perspective view of the optical disk unit of the first 
embodiment, and Figs. 4, 5, 6, 7 and 8 are cross-sectional views taken 
along the lines IV--IV, V--V, VI--VI, VII--VII and VIII--VIII of FIG. 1, 
respectively. In FIGS. 1, 2 and 3, reference numeral 21a denotes a bobbin. 
A laser unit 20 for emitting and detecting a laser beam as shown in FIG. 
4, an objective lens 22 for converging the laser beam onto an optical disk 
1, and a pair of reflecting mirrors 23 (FIG. 4) for directing the laser 
beam, emitted from the laser unit 20, to the objective lens 22, are 
mounted on the bobbin 21a. Even if only one or none of the reflecting 
mirrors 23 is provided, a layout of the laser unit 20 and the objective 
lens 22 is possible. Two guide shafts 25 are mounted on a carriage base 
24, and extend in a direction radially of the optical disk 1. Actuator 
magnets 26 for moving the bobbin 21a are mounted on the carriage base 24 
in parallel relation to the guide shafts 25. A back yoke 27 made of a 
ferromagnetic material is fixedly secured to each of the actuator magnets 
26 in contiguous relation thereto. In this embodiment, the guide shafts 25 
are made of a ferromagnetic material, and with this construction, the 
guide shaft 25, the actuator magnet 26 and the back yoke 27 constitute a 
magnetic circuit. Focusing coils 28a for moving the bobbin 21a in a 
focusing direction (direction of an arrow C) are fixedly mounted on the 
bobbin 21a in opposed relation to the actuator magnets 26, as shown in 
FIG. 5. Tracking and feed coils 29a for moving the bobbin 21a in a 
tracking/feed direction (direction of an arrow D) are fixedly mounted on 
the bobbin 21a, and are disposed in opposed relation to the actuator 
magnets 26, respectively, as shown in FIG. 6, the guide shafts 25 passing 
through the tracking and feed coils 29a, respectively. Main shaft sliders 
30 and guide sliders 31 are supported on the guide shafts 25, 
respectively. As shown in FIG. 7, the main shaft sliders 30 are slidable 
along one guide shaft 25, and the guide sliders 31 are slidable along the 
other guide shaft 25, and are movable along the surface of the optical 
disk 1 in a direction perpendicular to the axis of this guide shaft 25. 
Suspension springs 32a are fixedly secured to the bobbin 21a and the main 
shaft sliders 30 and the guide sliders 31, as shown in FIG. 7, and the 
bobbin 21a is resiliently supported by these suspension springs 32a for 
movement in the focusing direction (direction of the arrow C (FIG. 2)). A 
signal flexible cable 33 for transferring an electrical signal between a 
control board for controlling the disk unit and the laser unit 20 is 
connected to the laser unit 20, and is fixed to the carriage base 24. An 
actuator flexible cable 34 for transferring signals from the control panel 
to the focusing coils 28a and the tracking and feed coils 29a is connected 
to the focusing coils 28a and the tracking and feed coils 29a, and is 
fixed to the carriage base 24. As shown in FIG. 8, a spindle motor portion 
for rotating the optical disk 1 comprises a bearing 35 mounted on the 
carriage base 24, a spindle coil 36 provided around the bearing 35, a 
spindle shaft 37 rotatably supported by the bearing 35, a turntable 38 
fixedly mounted on the spindle shaft 37 for supporting the optical disk 1, 
and a spindle magnet 39 mounted on the turntable 38 in opposed relation to 
the spindle coil 36. 
The operation of the optical disk unit of the above construction will now 
be described. First, a laser beam, emitted from a semiconductor laser 
provided at the laser unit 20, is reflected by the pair of reflecting 
mirrors 23, and is fed to the objective lens 22, as shown in FIG. 4. The 
laser beam is converged or decreased in diameter by the objective lens 22 
so that data can be read from the optical disk 1. Reflection light from 
the optical disk 1 passes through the objective lens 22, and is reflected 
by the reflecting mirrors 23 to a photo detector provided at the laser 
unit 20, and is outputted as an electrical signal. 
Next, the focusing drive for detecting the data recorded on the optical 
disk 1 will now be described. The focusing coils 28a are located in the 
magnetic circuit constituted by the actuator magnet 26, the back yoke 27 
and the guide shaft 25, as shown in FIG. 5. When the focusing coils 28a 
are energized, the bobbin 21a and the objective lens 22 (FIG. 2) are 
driven, together with the focusing coils 28a, in the focusing direction 
(direction of the arrow C) by an electromagnetic effect. At this time, 
since the bobbin 21a holding the objective lens 22 is supported on the 
main shaft by sliders 30 and the guide sliders 31 through the pair of 
upper and lower suspension springs 32a, the main shaft sliders 30 are 
angularly moved about the guide shaft 25, and the guide sliders 31 are 
angularly moved about the guide shaft 25, and also are moved in a 
direction perpendicular to the axis of the guide shaft 25, and as a result 
the suspension springs 32a are deformed, so that the bobbin 21a moves in 
the focusing direction (direction of the arrow C). When the bobbin 21a is 
moved in the focusing direction (direction of the arrow C), the main shaft 
sliders 30 are angularly moved about the guide shaft 25, and the guide 
sliders 31 are angularly moved about the guide shaft 25, and also move in 
a direction perpendicular to the axis of the guide shaft 25, and therefore 
the deformation of the suspension springs 32 a is effected smoothly. 
In this embodiment, the suspension spring 32a is formed by a leaf spring. 
With this construction, when the bobbin 21a is moved in the tracking/feed 
direction (direction of the arrow D), the suspension springs 32a are not 
deformed, and the tracking drive, the feed drive and the focusing drive 
can be effected accurately. 
In the first embodiment, the suspension spring 32a is of such a 
construction that a spring portion, interconnecting the bobbin 21a and the 
main shaft sliders 30, is integral with a spring portion interconnecting 
the bobbin 21a and the guide sliders 31. However, this suspension spring 
may be of such a construction that a spring portion interconnecting the 
bobbin 21a and the main shaft sliders 30 is separate from a spring portion 
interconnecting the bobbin 21a and the guide sliders 30, as in a 
suspension spring 32b shown in FIG. 9. 
Next, the tracking and feed operation will now be described. Like the 
focusing coils 28a, the tracking and feed coil 29a held on the bobbin 21a 
is located in the magnetic circuit constituted by the actuator magnet 26, 
the back yoke 27 and the guide shaft 25. When the tracking and feed 
actuator coils 29a are energized, the bobbin 21a and the objective lens 22 
are driven, together with the tracking and feed coils 29a, in the 
tracking/feed direction (direction of the arrow D) by an electromagnetic 
effect. The objective lens 22 can be moved radially of the optical disk 1 
over the entire recording area of the optical disk 1 by this tracking and 
feed drive. The main shaft sliders 30 and the guide sliders 31, movable 
radially of the optical disk 1 together with the bobbin 21a holding the 
objective lens 22, are slidably mounted respectively on the pair of guide 
shafts 25, and are connected to the bobbin 21a by the suspension springs 
32a. With this arrangement, the main shaft sliders 30 and the guide 
sliders 31 movable together with the objective lens 22 can be lightweight, 
and with this lightweight design, the bobbin 21a can be moved at high 
speed together with the main shaft sliders 30 and the guide sliders 31, 
and therefore the tracking drive portion and the feed drive portion can be 
jointly constituted by one drive portion. 
With respect to the spindle drive, when the spindle coil 36 shown in FIG. 8 
is energized, the turntable 38 is rotated together with the optical disk 1 
by an electromagnetic effect achieved by the cooperation of the spindle 
coil 36 with the spindle magnet 39. 
By the above focusing drive, tracking and feed drive, and spindle drive, 
the data recorded on the optical disk 1 is reproduced. 
As described above, in this embodiment, the optical system, including the 
laser unit 20 for emitting and detecting a laser beam and the objective 
lens 22 for converging the laser beam from the laser unit 20 onto the 
optical disk 1, is integrally mounted on the bobbin 21a. Therefore, there 
will not occur a change of the position of the objective lens 22 relative 
to the laser unit 20 in accordance with the movement of the bobbin 21a, 
which change has been encountered in the prior types of construction in 
which only an objective lens is mounted on a bobbin movable along an 
optical disk. Therefore, a high-precision manufacture of the guide members 
for the bobbin 21a, as well as a position adjustment, is less severe, and 
the optical performance is enhanced, and the assembling can be simplified. 
Furthermore, the focusing coils 28a and the tracking and feed coils 29a 
are mounted on the bobbin 21a holding the objective lens 22, and both the 
tracking drive and the feed drive are effected by the tracking and feed 
coils 29a, and the magnetic circuit for effecting the focusing drive, the 
tracking drive and the feed drive constituted by the actuator magnet 26, 
the back yoke 27 and the guide shaft 25. Therefore, the actuator can be of 
a compact size, and the optical disk unit is reliable and inexpensive. 
In the first embodiment, although the focusing coils 28a and the tracking 
and feed coil 29a are located in the magnetic circuit constituted by the 
actuator magnet 26, the back yoke 27 and the guide shaft 25, it is also 
contemplated that a focusing coil 28b and a tracking and feed coil 29b in 
FIGS. 10 and 11 be located in a circuit subjected to a magnetic influence 
of an actuator magnet 26a. In the first embodiment, the pair of guide 
shafts 25 extend through the tracking and feed coils 29a, respectively, 
and the actuator magnet 26 and the back yoke 27 are provided outwardly of 
each of the pair of guide shafts 25. However, as shown in FIGS. 10 and 11, 
an actuator magnet 26a and a back yoke 27a may be provided inwardly of 
each of a pair of guide shafts 25a, in which case a bobbin 2lb, suspension 
springs 32c, main shaft sliders 30a and guide sliders 31a are arranged as 
illustrated. 
As described above, in the present invention, the optical disk unit 
comprises the bobbin having the light converging means for converging 
light onto the loaded optical disk, the pair of guide members provided 
respectively on the opposite sides of the bobbin for guiding the bobbin 
radially of the optical disk, the pair of slide members slidably mounted 
on each of the guide members, the connecting members connecting the bobbin 
to the slide members in a manner to allow the bobbin to move in a 
direction perpendicular to the surface of the optical disk, the focusing 
drive means for moving the bobbin in a direction perpendicular to the 
surface of the optical disk, and the tracking and feed drive means for 
moving the bobbin along the guide members. In this construction, the slide 
members mounted on the pair of guide members are connected together by the 
bobbin and the connecting members, and therefore the slide members, 
movable with the bobbin in the direction radially of the optical disk, can 
be lightweight, and the slide members and the bobbin can be moved radially 
of the optical disk only by the tracking and feed drive means mounted on 
the bobbin. Therefore, the optical disk unit can be of a small-size and 
lightweight construction. 
Second Embodiment 
A second embodiment of the present invention will now be described with 
reference to the drawings. FIG. 12 is a plan view of the second embodiment 
of an optical disk unit of the present invention. FIG. 13 is a perspective 
view of the optical disk unit of the second embodiment. FIG. 14 is an 
exploded perspective view of the optical disk unit of the second 
embodiment, and FIGS. 15, 16 and 17 are cross-sectional views taken along 
the lines XV--XV, XVI--XVI and XVII--XVII of FIG. 12, respectively. In 
FIGS. 12, 13 and 14, reference numeral 21c denotes a bobbin. A laser unit 
20 for emitting and detecting a laser beam shown in FIG. 15, an objective 
lens 22 for converging the laser beam onto an optical disk 1, and a pair 
of reflecting mirrors 23 for directing the laser beam, emitted from the 
laser unit 20, to the objective lens 22, are mounted on the bobbin 21c. 
Even if only one or none of the reflecting mirrors 23 is provided, the 
foregoing layout of the laser unit 20 and the objective lens 22 is 
possible. Two guide shafts 25 are mounted on a carriage base 24, and 
extend radially of the optical disk 1. Actuator magnets 26 for moving the 
bobbin 21c are mounted on the carriage base 24 in parallel relation to the 
guide shafts 25. A back yoke 27, made of a ferromagnetic material, is 
fixedly secured to each of the actuator magnets 26 in contiguous relation 
thereto. In this embodiment, the guide shafts 25 are made of a 
ferromagnetic material, and with this construction the guide shaft 25, the 
actuator magnet 26 and the back yoke 27 constitute a magnetic circuit. 
Focusing coils 28c for moving the bobbin 21c in a focusing direction 
(direction of the arrow C (FIG. 13)) are fixedly mounted on the bobbin 21c 
in opposed relation to the corresponding actuator magnets 26, as shown in 
FIG. 16. Tracking and feed coils 29c for moving the bobbin 21c in a 
tracking/feed direction (direction of the arrow D (FIG. 12)) are fixedly 
mounted on the bobbin 21c, and are disposed in opposed relation to the 
corresponding actuator magnets 26. The guide shafts 25 pass through the 
corresponding tracking and feed coils 29c. Main shaft sliders 30 and guide 
sliders 31 are supported on the guide shafts 25, respectively. As shown in 
FIG. 17, the main shaft sliders 30 are slidable along one guide shaft 25, 
and the guide sliders 31 are slidable along the other guide shaft 25. 
Sliders 30 and 31 are movable along the surface of the optical disk 1 in a 
direction perpendicular to the axis of guide shaft 25. Suspension springs 
32a are fixedly secured to the bobbin 21c and to the main shaft sliders 30 
and the guide sliders 31, as shown in FIG. 17. Bobbin 21c is resiliently 
supported by suspension springs 32a for movement in the focusing direction 
(direction of the arrow C (FIG. 13)). A signal flexible cable 33 for 
transferring an electrical signal for controlling the disk unit between a 
control board and the laser unit 20 is connected to the laser unit 20, and 
is fixed to the carriage base 24. An actuator flexible cable 34 for 
transferring signals from the control panel to the focusing coils 28c and 
the tracking and feed coils 29c is connected to the focusing coils 28c and 
the tracking and feed coils 29c, and is fixed to the carriage base 24. 
The operation of the optical disk unit of the above construction will now 
be described. A laser beam, emitted from a semiconductor laser provided at 
the laser unit 20, is reflected by the pair of reflecting mirrors 23, and 
is fed to the objective lens 22, as shown in FIG. 15. The laser beam is 
converged or decreased in diameter by the objective lens 22 so that data 
can be read from the optical disk 1. Reflection light from the optical 
disk 1 passes through the objective lens 22, and is reflected by the 
reflecting mirrors 23 to a photo detector provided at the laser unit 20, 
and is outputted as an electrical signal. 
Next, the focusing operation for detecting the data recorded on the optical 
disk 1 will be described. The focusing coils 28c are located in the 
magnetic circuit constituted by the actuator magnet 26, the back yoke 27 
and the guide shaft 25, as shown in FIG. 16. When the focusing coils 28c 
are energized, the bobbin 21c and the objective lens 22 are driven, 
together with the focusing coils 28c, in the focusing direction (direction 
of the arrow C) by an electromagnetic effect. At this time, since the 
bobbin 21c holding the objective lens 22 is supported on the main shaft 
sliders 30 and guide sliders 31 through the pair of upper and lower 
suspension springs 32a, the main shaft sliders 30 are angularly moved 
about the guide shaft 25, and the guide sliders 31 are angularly moved 
about the guide shaft 25, and also are moved in a direction perpendicular 
to the axis of the guide shaft 25. As a result, the suspension springs 32a 
are deformed, so that the bobbin 21c moves in the focusing direction 
(direction of the arrow C). In the second embodiment, each of the upper 
and lower suspension springs 32a is of such a construction that a spring 
portion, interconnecting the bobbin 21c and the main shaft sliders 30, is 
integral with a spring portion interconnecting the bobbin 21c and the 
guide sliders 31. However, this suspension spring may be of a construction 
that a spring portion interconnecting the bobbin 21c and the main shaft 
sliders 30 is separate from a spring portion interconnecting the bobbin 
21c and the guide sliders 30. 
Next, the tracking and feed operation will be described. Like the focusing 
coils 28c, the tracking and feed coils 29c, held on the bobbin 21c, are 
located in the magnetic circuit constituted by the actuator magnet 26, the 
back yoke 27 and the guide shaft 25. When the tracking and feed actuator 
coils 29c are energized, the bobbin 21c and the objective lens 22 are 
driven, together with the tracking and feed coils 29c, in the 
tracking/feed direction (direction of the arrow D) by an electromagnetic 
effect. The tracking and feed coils 29c are mounted on the bobbin 21c so 
that those surfaces of the tracking and feed coils 29c facing the actuator 
magnet 26 and those surfaces of the focusing coils 28c facing the actuator 
magnet 26 are disposed in a common plane. Therefore, the spacing between 
the actuator magnet 26 and the guide shaft 25 can be reduced, and a 
magnetic flux density acting on the focusing coils 28c and the tracking 
and feed coils 29c is increased, thus enhancing the driving efficiency of 
the actuator. The objective lens 22 can be moved radially of the optical 
disk 1 over the entire recording area of the optical disk 1 by this 
tracking and feed operation. The main shaft sliders 30 and the guide 
sliders 31, movable radially of the optical disk 1 together with the 
bobbin 21c holding the objective lens 22, are slidably mounted 
respectively on the pair of guide shafts 25, and are connected to the 
bobbin 21c by the suspension springs 32a. With this arrangement, the main 
shaft sliders 30 and the guide sliders 31 are movable together with the 
objective lens 22, and can thus be compact and lightweight. With this 
lightweight design and the enhanced drive efficiency of the actuator, the 
bobbin 21c can be more stably driven at high speed together with the main 
shaft sliders 30 and the guide sliders 31 than in the first embodiment. 
As described above, in the second embodiment, those surfaces of the 
focusing coils 28c facing the actuator magnet 26 and those surfaces of the 
tracking and feed coils 29c facing the actuator coil 26 are disposed in a 
common plane, and with this arrangement the spacing between the actuator 
magnet 26 and the guide shaft 25 can be reduced. Therefore the actuator 
can have a higher drive efficiency, and can be of a smaller size than in 
the first embodiment. Therefore, the optical disk unit is highly reliable 
and inexpensive. 
In the second embodiment, although the focusing coils 28c and the tracking 
and feed coil 29c are located in the magnetic circuit constituted by the 
actuator magnet 26, the back yoke 27 and the guide shaft 25, it is only 
necessary that the focusing coils and the tracking and feed coils shown as 
at 28d and 29d in FIGS. 18 and 19 be located in a circuit subjected to a 
magnetic influence of an actuator magnet 26a, and that those surfaces of 
the focusing coils 28d and the tracking and feed coils 29d facing the 
actuator magnet 26a be disposed in a common plane. In the second 
embodiment, the pair of guide shafts 25 extend through the corresponding 
tracking and feed coils 29c, and the actuator magnet 26 and the back yoke 
27 are provided outwardly of each of the pair of guide shafts 25; however, 
as shown in FIGS. 18 and 19, an actuator magnet 26a and a back yoke 27a 
may be provided inwardly of each of a pair of guide shafts 25a. 
As described above, in the present invention, the optical system, including 
the means for emitting and detecting a laser beam and the objective lens 
for converging the laser beam onto the optical disk, is integrally mounted 
on the bobbin. Therefore, there will not occur a change of the position of 
the objective lens relative to the laser beam emitting and detecting means 
in accordance with the movement of the bobbin, which change has been 
encountered in the type of construction in which only an objective lens is 
mounted on a bobbin. Therefore, a high-precision manufacture of the guide 
members for the bobbin, as well as a position adjustment, is less severe, 
and the optical performance is enhanced, and the assembling can be 
simplified. Furthermore, the focusing coils and the tracking and feed 
coils are mounted on the bobbin holding the objective lens, and the 
tracking drive and the feed drive are effected by the tracking and feed 
coils, and the magnetic circuit for effecting the focusing drive, the 
tracking drive and the feed drive is constituted by the single magnetic 
circuit means. Moreover, those surfaces of the focusing coils facing the 
actuator magnet and those surfaces of the tracking and feed coils facing 
the actuator magnet are disposed in a common plane. Therefore, the 
magnetic circuit constituted by the actuator magnet can be highly 
efficient, and the actuator can be of a compact size, and there can be 
provided the optical disk unit which is reliable and inexpensive.