Optical pickup actuator with an objective lens fixing part suspended by an elastic members

In an optical pickup, a yoke of a supporting part has a flat bottom and both side walls upwardly bent at both ends thereof. Magnets are installed on inner surfaces of both side walls of yoke. Laser-penetrating hole is made in the plat botom and a guide projector are formed to the flat bottom. A spring is put around the guide projector. An objective lens fixing part is elastically supported by a spring in an inside of the yoke. In a main body of the objective lens fixing part, an objective lens and a through hole are installed in corresponding positions with the laser-penetrating hole and the guide projector, respectively. Coils are wound around side walls of the main body for tracking and focusing servos. The objective lens fixing part is elastically supported by the spring in a state that the guide projector is inserted into the through hole.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to an optical pickup actuator. More 
particularly, the present invention relates to an optical pickup actuator 
which has a suspension using an elastic member for simplification of the 
construction and manufacturing process. 
2. Description of the Prior Art 
Data recording/reproducing apparatuses using optical disks such as a laser 
disk (LD) and a compact disk (CD) have been commercially available in 
recent years. In order to read out data from an optical disk, a laser beam 
is irradiated onto a data recording track (to be referred to as a "track" 
hereinafter), and data are reproduced based on the beam reflected by the 
track. 
When the tracks are helically formed on the optical disk, since the sectors 
of a single track are not equidistant from the center of the rotation of 
the disk, tracking (radial) control is necessary in the read mode to 
accurately irradiate the track with a laser beam. 
This tracking control has been conventionally performed by a one beam 
method or a three beam method. Tracking errors are detected from the laser 
beam reflected by an optical disk. Tracking control operation is conformed 
by transferring the objective lens in response to the tracking error 
signals derived by these tracking error signals. The objective lens is 
normally supported and fixed by a spring on an optical head housing. A 
tracking actuator is energized to move the lens for the tracking control. 
When the tracking actuator is deenergized, the lens is held at a 
mechanically neutral point balanced by a spring force. 
Meanwhile, since the distance from the optical pickup to disk shifts 
minutely in the read mode in which the disk is rotated, it is difficult to 
correctly read data due to the shift, thus rendering focusing control 
essential. This focusing control has been conventionally performed by 
astigmatic method using astigmatism or a knife edge method. 
For focusing control, focusing errors are detected from the laser beam 
reflected by an optical disk, and focusing control operation is conformed 
by transferring the objective lens in response to the focusing error 
signals derived by these focusing error signals. The objective lens is 
normally the same lens that is used for the tracking control. A focusing 
actuator is energized to move the lens for the focusing control. When the 
focusing actuator is deenergized, the lens is held at a mechanically 
neutral point balanced by a spring force. 
The conventional optical pickup actuators are generally classified into 
actuators of two types in the arrangement of coils. The objective lens is 
moved in vertical (focusing) direction and horizontal (tracking) direction 
using an optical pickup actuator. For example, there is one type in which 
focusing and tracking coils are placed in the orthogonal and parallel 
directions, respectively. There is the other type in which the two coils 
are placed in directions which are 45.degree./45.degree. against an 
optical axis as in Noiman's cutter head, respectively. 
These conventional optical pickup actuators for moving the objective lens 
in vertical and horizontal directions for focusing and tracking control as 
shown above are described in U.S. Pat. No. 5,103,438 (issued to Masunaga 
et al.), U.S. Pat. No. 5,182,738 (issued to Yoshigawa), etc. 
As shown in FIGS. 1 and 2, two suspension wires 2 extend in parallel with 
each other in a horizontal direction. One end of each of the suspension 
wires 2 is connected to an upstanding wall portion of an actuator base 1. 
Further, a holder 4 is positioned above the actuator base 1 for supporting 
an objective lens 3, and the holder 4 is connected to each end of the 
suspension wires 2. Therefore, the holder 4 is movably supported on the 
suspension wires 2 in a cantilevered fashion. 
Magnets 5A and 5B are fixed to the holder 4. Further, focusing coils 7A and 
7B and tracking coils 8A and 8B are mounted on yokes 6A and 6B which stand 
vertically from the actuator base 1. One magnet 5A confronts the focusing 
coil 7A and tracking coil 8A, and the other magnet 5B confronts the 
focusing coil 7B and tracking coil 8B. The combination of the holder 4, 
the coils 7, 8, the magnets 5, and the suspension wires 2 is generally 
referred to as an actuator. 
With such an actuator, the suspension wires 2 are formed of extremely 
flexible materials having low elastic modulus so as to insure precise 
movement of the holder 4 in response to the magnetic forces. Stated 
differently, in the conventional actuator, a sufficiently high magnetic 
flux density has not been obtainable, and therefore, the suspension wires 
2 have required extremely high flexibility so that the wires 2 do not 
restrain movement of the holder 4 in response to the generated magnetic 
attractive force. 
According to the optical pickup actuator having the wire type suspension, 
the laser beam generated from the laser diode is incident on the recording 
pit, and the laser reflected from the recording pit is received on the 
photo detector. In consequence, information recorded on the recording pit 
is read out. The tracking and focusing conditions on the recording pit are 
detected by the laser beam reflected from the recording pit. 
When focusing control is required, a current is supplied to the focusing 
coils 7A and 7B in clockwise and counterclockwise directions. At that 
time, electromagnetic force acts in a direction of the support shaft 6 
(focusing direction X). Accordingly, the objective lens is axially moved 
in correspondence with a change in surface level of the optical disc, so 
that the beam spot follows the recording surface of the disc. 
When tracking control is required, a current is supplied to the tracking 
coils 8A and 8B in one direction or in the reverse direction thereof. At 
that time, an electromagnetic force acts in an orthogonal direction with 
the support shaft (tracking direction Y). Accordingly, the beam spot 
traces the recording tracks in accordance with the eccentricity of the 
tracks. 
Thus, the predetermined currents flow into focusing and tracking coils, 
which respectively move the holder 4 in the focusing direction X or the 
tracking direction Y. As a result, the focusing and tracking servos are 
carried out. 
According to the optical pickup actuator having the wire type suspension, 
the optical pickup actuator is produced through a difficult and precise 
process in which fine through holes are drilled through the actuator base 
and yokes and wires are inserted and fixed therethrough. Such a process is 
a very difficult one, and thus productivity is decreased. 
Furthermore, the suspension wire should be made of special materials, i.e., 
extremely flexible materials having low elastic modulus, and therefore, 
the manufacturing cost is increased. 
SUMMARY OF THE INVENTION 
The present invention is intended to overcome the above-mentioned and 
numerous other disadvantages and deficiencies of the prior art. Therefore, 
it is an object of the present invention to provide an optical pickup 
actuator which has a suspension using an elastic member for simplification 
of the construction and manufacturing process. 
To achieve the above object of the present invention, there is provided an 
optical pickup actuator which comprises: 
a supporting part having 
a yoke which has a flat bottom and both side walls upwardly bent at both 
ends thereof; magnets which are oppositely installed on inner surfaces of 
both side walls, respectively; a laser-penetrating hole made in one 
portion of the flat bottom; a guide projector made in another portion of 
the flat bottom; and an elastic member into which the guide projector is 
inserted; and 
an objective lens fixing part having 
a main body having a flat plate shape which allows for upward and downward 
movement along both side walls of the yoke; an objective lens installed in 
a corresponding position with the laser-penetrating hole; a through hole 
installed in a corresponding position with the projector and penetrated by 
the guide projector; and focusing control coil portion and tracking 
control coil portion installed on side walls of the main body; 
wherein the objective lens fixing part is provided on a top of the elastic 
member in a state that the guide projector is inserted into the through 
hole, so that the objective lens fixing part is to be elastic by the 
elastic member. 
The guide projector has a truncated cone shape of which an outer surface is 
bent inwardly so that the elastic member can elastically move for tracking 
and focusing in a stable state. 
The elastic member comprises a spring. 
A first groove is formed around the guide projector on the bottom of the 
yoke, into which a lower end of the elastic member is inserted and fixed, 
so that the elastic member can elastically move for tracking and focusing 
in a stable state when the lower end is fixed. 
The through hole of the objective lens fixing part has a second groove 
formed around into which an upper end of the elastic member is inserted 
and fixed, so that the elastic member can elastically move for tracking 
and focusing in a stable state when the lower end is fixed. 
According to the optical pickup actuator, the objective lens fixing part 
having the objective lens is elastically supported by a spring over the 
yoke, and tracking and focusing servos are carried out with elastic motion 
in vertical (focusing) and horizontal (tracking) directions, and thereby 
the construction of the optical pickup actuator is simplified and the 
manufacturing process becomes easy.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Hereinafter, the preferred embodiments of this invention will be described 
in detail with reference to the accompanying drawing. 
FIG. 3 is a perspective view showing the optical pickup actuator of the 
present invention. FIG. 4 is an exploded cross-sectional view showing the 
optical pickup actuator of FIG. 3. 
A yoke 110 of a supporting part 100 has a flat bottom and both side walls 
upwardly bent at both ends thereof. Magnets 160 are oppositely installed 
on inner surfaces of both side walls of yoke 110, respectively. A 
laser-penetrating hole 120 is made in one predetermined portion of the 
flat bottom. A guide projector 140 is formed in the portion which is 
symmetric to the portion of laser-penetrating hole 120 of the flat bottom. 
A spring 150 is put around the guide projector 140. The diameter of the 
spring 150 from bottom to top gradually becomes smaller. A first groove 
190 is formed around the guide projector 140 on the bottom of the yoke 
110. A lower end of the spring 150 is inserted and fixed into the first 
groove 190, so that the spring 150 can elastically move for tracking and 
focusing in a stable state when the lower end is fixed. The guide 
projector 140 has a truncated cone shape of which an outer surface is bent 
inwardly, so that the spring 150 can elastically move for tracking and 
focusing in the stable state. 
An objective lens fixing part 200 has a main body having a flat plate 
shape. An objective lens 220 is installed in a corresponding position with 
the laser-penetrating hole 120 on the main body. A through hole 240 is 
installed in a corresponding position with the projector 140. The through 
hole 240 is penetrated by the guide projector 140. A second groove 290 is 
formed around the through hole 240 of the objective lens fixing part 200. 
An upper end of the spring 150 is inserted and fixed into the second 
groove 290, so that the objective lens fixing part 200 can be elastically 
supported by the spring 150 in the stable state when the lower end is 
fixed. A focusing control coil 260 is wound around the side walls of the 
main body 210. When the current is applied to the focusing control coil 
260, the electromagnetic force is biased in a vertical direction (focusing 
direction). Furthermore, a tracking control coil 261 is installed on side 
walls of the main body 210. When the current is applied to the tracking 
control coil 261, the electromagnetic force is biased in a horizontal 
direction (tracking direction). A PCB 270 is connected to the objective 
lens fixing part 200 for transferring input and output signals to the 
focusing and tracking coils 260 and 261 in case that the focusing and 
tracking controls are needed. 
Hereinafter, an operation of the optical pickup of the present invention 
will be described. 
As shown in FIG. 3, in the state that the objective lens fixing part 200 is 
elastically supported by the spring 150 fixed on the yoke 110 of the 
supporting part 100, a laser beam goes through the objective lens 220 via 
the laser penetrating hole 120 from below. The laser beam is focused on a 
recording pit to be reflected. The reflected laser beam is returned to the 
objective lens 220 and the laser penetrating hole 120. After that, the 
beam is received on a photodetector (not shown) via the predetermined 
optics (not shown). Focusing and tracking conditions of the recording pit 
are detected by the received beam. 
When focusing servo is required, a focusing control current is supplied to 
the focusing coil 260 via PCB 270 from a servo system (not shown). At that 
time, since the focusing control coil 260 is wound around the side walls 
of the main body 210 in parallel with the surface of the main body 210, an 
electromagnetic force acts in a vertical direction against the surface of 
the main body 210. Accordingly, the objective lens 220 and the objective 
lens fixing part 200 are forced in a vertical direction, and thereby the 
focusing servo is carried out. 
When tracking servo is required, a tracking control current is supplied to 
the tracking coil 261 via PCB 270 from a servo system (not shown). At that 
time, since the tracking control coil 261 is wound vertical to the surface 
of the main body 210 at the side walls of the main body 210, an 
electromagnetic force acts in a parallel direction with the surface of the 
main body 210. Accordingly, the objective lens 220 and the objective lens 
fixing part 200 is forced in a horizontal direction, and thereby the 
tracking servo is carried out. 
According to the optical pickup actuator, the objective lens fixing part 
having the objective lens is elastically supported by a spring over the 
yoke, and tracking and focusing servos are carried out with elastic motion 
in vertical (focusing) and horizontal (tracking) directions, and thereby 
the construction of the optical pickup actuator is simplified and the 
manufacturing process becomes easy. 
It is understood that various other modifications will be apparent to and 
can be readily made by those skilled in the art without departing from the 
scope and spirit of this invention. Accordingly, it is not intended that 
the scope of the claims appended thereto be limited to the description as 
set forth herein, but rather that the claims be constructed as 
encompassing all the features of patentable novelty that reside in the 
present invention, including all features that would be treated as 
equivalents thereof by those skilled in the art to which this invention 
pertains.