Focussing lens operating device

An optical focussing device for an optical information storage system. A hollow cylindrical holder carries a lens at its upper end. The holder is connected to a frame by two thin plates adjacent each other near the upper end and by one thin plate at a lower position. A vibration diminution element is interposed between the upper pair of plates. Each plate is circular with a central opening and several scroll shaped cuts extending from the opening toward the outside edge.

The present invention relates to an apparatus for optically reproducing 
information such as video and/or audio signals recorded on a dis-shaped 
information carrier, and more particularly to a means for supporting a 
focussing unit for such apparatus to be accurately moved in vertical 
direction to the plane of the information carrier for focussing control. 
In the conventional optical information reproducing apparatus, the 
focussing control to keep the beam spot constant on the plane of the 
information carrier is effected by moving the focussing unit including a 
focussing lens in the vertical direction to the plane of the information 
carrier by way of an electro-magnetic controlling means. In such 
apparatus, the focussing unit is supported in resilient suspension 
relative to a frame by means of a single elastic plate arranged around the 
focussing unit. However, since the elastic plate used for suspension of 
the focussing unit is made of a very thin plate and the focussing unit is 
elastically supported on the frame by such single thin plate only, in the 
prior art reproducing apparatus, there is a defect that the focussing unit 
moves accidentally in the lateral or slantwise direction while it is moved 
in upward and downward directions in relation to the plane of the 
information carrier for the focussing control. Due to this defect, in the 
conventional optical information reproducing apparatus, the focussing of 
the light beam on the information carrier is sometimes made errorneously 
and in consequence, the information recorded on the information carrier is 
not correctly obtained.

FIG. 1 shows the first embodiment of a focussing unit operating device in 
which a focussing unit is moved only in one direction for the focussing 
control purposes. Tracking control in this embodiment is performed by a 
pivotable deflecting mirror and for such purposes, the focussing unit is 
not moved. With reference to FIG. 1, designated by the reference numeral 
(1) is a frame. This frame (1) is made of single block of for example 
metal and formed with a comparatively large through bore (2) which extends 
vertically. Within the frame (1), there is arranged a cylindrical holder 
(3). The cylindrical holder (3) is provided on its upper half part with an 
axial through bore (3a) whose lower end communicates with a wider axial 
through bore (3b) formed on the lower half part of the cylindrical holder 
(3). The upper portion of the cylindrical holder (3) mounts a focussing 
lens (4). This focussing lens (4) is adapted to bring a light beam (5) 
from a beam generating means (not shown) into focus on the plane of a 
disc-shaped information carrier (A) to read the information recorded on 
it. The cylinrical holder (3) is resiliently suspended within the through 
bore (2) of the frame (1) by means of thin plates which will be explained 
later in detail. At the bottom of the frame (1), an electro-magnetic 
controlling means is disposed to operate the focussing lens (4) in upward 
and downward directions in relation to the plan of the information carrier 
(A) for the purpose of the focussing control of the light beam (5). The 
electro-magnetic controlling means is constituted by a first and second 
magnetic yokes (6,7), a circular magnet (8) interposed between the 
magnetic yokes (6,7) and a coil (9) which is wound around the outer 
surface of the lower portion of the cylindrical holder (3). The magnetic 
yoke (7) has a center projection (7a) extending into the lower axial 
through bore (3b) of the cylindrical holder (3). This center projection 
(7a) of the magnetic yoke (7) is formed with an axial passage (7b) 
arranged in vertical alignment with the axial through bores (3a,3b) of the 
cylindrical holder (3). Below the axial passage (7b) of the magnetic yoke 
(7), a deflecting mirror (10) is disposed in vertical alignment with the 
focussing lens (4). This deflecting mirror (10) is rotatable for the 
purpose of tracking control of the light beam (5). 
Hereinafter, the above-mentioned thin plates which form a support for 
elastically maintaining the cylindrical holder (3) on the frame (1) will 
be explained in detail. As shown in FIG. 1, the support of the present 
invention is constituted by three thin plates (11) arranged around the 
cylindrical holder (3) in parallel spaced relationship with each other. 
The three thin plates (11) include two upper thin plates (11) arranged on 
the upper portion of the cylindrical holder (3) on which the focussing 
lens (4) is mounted and one lower thin plate (11) arranged around the 
lower portion of the cylindrical holder (3). The two upper thin plates 
(11) are arranged adjacent to each other to leave a small space 
therebetween in which an element which has certain vibration diminution 
chracteristics is interposed. However, they can be arranged in contact 
relation with each other. The three thin plates (11) are made of a thin 
metal plate. In this embodiment, this thin metal plate is made of 
stainless steel and produced by way of a stamping or etching process. This 
thin metal plate can also be made of phosphor bronze. As shown in FIG. 2, 
each thin plate (11) has a circular shape and is formed with a center 
opening (11a) therein. There is further provided three narrow cuts (11b) 
in the form of scroll spreading outwards from around the center opening 
(11a), so that it has an adequete elasticity to support the cylindrical 
holder (3) for focussing control as well as an adequete strength against 
the lateral movement given from the outside, etc. The three thin plates 
(11) having such structure are fixedly attached to the inner wall of the 
frame (1) with their outer periphery (11c) and to the cylindrical holder 
(3) with their inner periphery (11d) thereby supporting the cylindrical 
holder (3) on the frame (1) in resilient suspension. The cylindrical 
holder (3) supported by the three thin plates (11) in this manner is 
moved, when the electro-magnetic controlling means is operated, in the 
upward and downward directions in relation to the information carrier (A) 
through the elastic action of those thin plates (11) to correctly focuss 
the light beam (5) on the information carrier (A). 
In the optical system of this embodiment, the light beam (5) emerged from 
the beam generating means (not shown) is deflected in the vertical 
(upward) direction by the pivotable deflecting mirror (10) and is entered 
into the axial passage (7b) of the magnetic yoke (7). Then, the light beam 
(5) travels through the axial through bores (3a,3b) of the cylindrical 
holder (3) and is converged into a minute spot (12) on the surface of the 
information carrier (A) through the focussing lens (4). In this 
embodiment, the cylindrical holder (3) is moved by the electro-magnetic 
controlling means in the upward and downward directions in relation to the 
plane of the information carrier (A) for the focussing control of the 
light beam (5) when the light beam (5) is out of focus on the information 
carrier (A) due to for example the change of the distance between the 
focussing lens (4) and the plane of the information carrier (A). However, 
in this embodiment the tracking control to correctly project the beam spot 
(12) in desired incident relation upon a track to be read (not shown) on 
the information carrier (A) is effected by deflecting the light beam (5) 
in minute angles through rotation of the reflecting mirror (10). In this 
manner, in this embodiment, the cylindrical holder (3) is moved for the 
focussing control only therefore its lateral or slantwise movements occur 
on that particular occasion. In order that the focussing control of the 
light beam (5) is correctly performed, the cylindrical holder (3) having 
the focussing lens (4) on its upper portion must be accurately moved in 
the vertical direction to the plane of the information carrier (A) and its 
lateral or slantwise movements during such vertical displacement must be 
prevented. The lateral or slantwise movements of the cylindrical holder 
(3) are caused by the portional differences of the thickness thereof made 
in the production process. In the present invention, such lateral or 
slantwise movements of the cylindrical holder (3) which affect a bad 
influence on the correct focussing control are eliminated by assuredly 
supporting it on the frame (1) by means of the three thin plates (11), 
particularly by means of the two upper adjacent thin plates (11) arranged 
on the upper portion of the cylindrical holder (3). By the support of 
those three thin plates (11), the cylindrical holder (3) is maintained 
relative to the frame (1) in the assured manner and in consequence, it can 
move accurately in the vertical direction to the plane of information 
carrier (A) without any lateral or slantwise movements thereof. 
Further, in the present invention, owing to the combination of those three 
thin plates (11), if any of the thin plates (11) is vibrated laterally due 
to for example a shock given from the outside, such lateral vibration can 
be diminished to such degree as not affect a bad influence upon the 
accurate vertical motion of the cylindrical holder (3). Furthermore, as 
described above, since the two upper thin plates (11) are arranged in 
adjacency of each other, they rub against each other in the course of the 
upward and downward diaplacement of the cylindrical holder (3). By such 
friction between the two upper thin plates (11), the lateral vibration of 
each thin plate is further diminished. To make such lateral vibration of 
the thin plates much smaller, an element (18) which has certain vibration 
diminution characteristics can be arranged between the two upper thin 
plates (11) as explained before. In the preferred embodiment, a gelatinous 
silicon grease or Butyl rubber is used as such element and interposed 
between these two upper thin plates (11). Of course, other element which 
has the same vibration diminution characteristics may be used in the 
present invention. As a result of the assured support by the three thin 
plates (11) and the elimination of the lateral vibration of the thin 
plates, the vertical motion of the cylindrical holder (3) is carried out 
in the reliable manner. 
FIG. 3 shows the second embodiment of the focussing unit operating device 
in which the focussing unit is moved in two different directions for the 
purpose of the tracking control as well as for the focussing control. In 
FIG. 3, like elements shown in FIG. 1 are given like reference numerals, 
the cylindrical holder (3) having the focussing lens (4) on the upper 
portion thereof is held in resilient suspension within the frame (1) by 
the three thin plates (11). The structure of the thin plates (11) and the 
support of the cylindrical holder (3) by such thin plates (11) are the 
same with the first embodiment. The electro-magnetic controlling means 
including the first and second magnetic yoke (6,7), circular magnet (8) 
and coil (9) is disposed under the cylindrical holder (3) to operate it 
for the focussing control. A screw (13) is inserted into the center 
projection of the magnetic yoke (7) whose upper end is extended into the 
lower axial through bore (3b) of the cylindrical holder (3). A deflecting 
mirror (14) is disposed within the lower axial through bore (3b) of the 
cylindrical holder (3) and is fixed at the top of the screw (13) at an 
angle of 45.degree. in vertical alignment with the focussing lens (4). The 
cylindrical holder (3) is formed with a cutout (15) on the lateral side in 
horizontal alignment with the deflecting mirror (14) to lead the light 
beam (5) from the beam generating means (not shown) toward the deflecting 
mirror (14). The light beam (5) incident upon the deflecting mirror (14) 
is deflected in the vertical (upward) direction by it and is converged 
into the beam spot (12) on the surface of the information carrier (A). A 
framing unit including the frame (1) is disposed and movably supported in 
an outer case (16). The framing unit is held in suspension within the 
outer case (16) by means of upper and lower rubber pins (17) inserted into 
the framing unit and the outer case (16). 
In this embodiment, the cylindrical holder (3) is moved by the 
electro-magnetic controlling means in the vertical direction to the plan 
of the information carrier (A) for the focussing control of the light beam 
(5) in the same manner with the first embodiment. Further, in this 
embodiment, for the tracking control purposes, the framing unit including 
the frame (1) is displaced horizontally in parallel relationship with the 
plane of the information carrier (A) by way of another electro-magnetic 
controlling means (19). At this time, since the cylindrical holder (3) is 
supported on the frame (1) through the three thin plates (11), it moves 
horizontally in parallel with the plane of the information carrier (A) 
together with the framing unit. By such horizontal displacement of the 
framing unit for the purpose of the tracking control, there occurs far 
larger lateral or slantwise movements of the cylindrical support (3) which 
affect much worse influence upon the vertical motion of the cylindrical 
holder (3). As a result, undesirable movement of the cylindrical holder 
(3) for the focussing control, namely its lateral or slantwise movements, 
is taken place by reaonance with the horizontal displacement of the 
framing unit for the tracking control. In this embodiment, however, the 
cylindrical holder (3) is supported on the frame (1) in the assured manner 
by means of the three thin plates (11) as explained before in connection 
with the first embodiment. Such assured support by the three thin plates 
(11) is much more useful for the prevention of the lateral or slantwise 
movements of the cylindrical holder (3) on such occasion of the horizontal 
displacement of the framing unit for the tracking control. As a result, 
undesirable movement of the cylindrical holder (3) for the focussing 
control is prevented. This assured support of the cylindrical holder (3) 
by the three thin plates (11) is also helpful in performing accurate 
tracking control. 
Further, as mentioned before in connection with the FIG. 3, the thin plates 
(11) are made in the particular patterns to provide a strength against the 
lateral movement which also helps to prevent the lateral or slantwise 
movement of the cylindrical holder (3) in the course of the tracking 
control. In consequence, in this embodiment, both the tracking control and 
focussing control are carried out in good condition and therefore the 
information on the information carrier (A) is correctly obtained. In this 
embodiment, the lateral vibration is also diminished in like manner with 
the first embodiment. 
As mentioned so far, in the present invention, owing to the support of the 
cylindrical holder (3) relative to the frame (1) by means of the three 
thin plates (11), in particular by the two upper adjacent thin plates 
(11), the lateral or slantwise movements of the cylindrical holder (3) is 
prevented not only in such case that the cylindrical holder (3) is moved 
in the vertical direction for the focussing control but also in such case 
that it is moved in both vertical and horizontal directions for the 
focussing and tracking controls.