Focussing Lens Operating Device

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.

It is therefore an object of the present invention to provide a simple means for supporting the focussing unit to be reliably moved in the vertical direction to the surface of the information carrier. Other objects, advantages, and features of the invention will be apparent from the following detailed description of the preferred embodiments thereof when read in connection with the attached drawings, in which:

FIG. 1 is a longitudinal sectional view of the focussing unit operating device using a focussing unit supporting means according to the invention;

FIG. 2 is a longitudinal sectional view of the second embodiment of the focussing unit operating device using the same focussing unit supporting means of FIG. 1; and

FIG. 3 is a top plan view of one embodiment of the diaphragm used in the focussing unit supporting means according to the invention.

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.