Device for supporting object lens in optical head

Abstract: A device for supporting an object lens in an optical head includes a substantially parallelepipedic link mechanism (5), a rotatable member (16) rotatable in the parallelepiped, a second hinge member (15) connecting the rotatable member (16) to the inner wall of one plate (10) of the link mechanism (5) to make it possible to rotate the rotatable member about an axis parallel to the optical axis of the object lens (1), a lens holding member (2) supported by the rotatable member (16) and holding the object lens (1), and a base (17} for stationarily holding another plate (12) of the link mechanism.

Description: This invention relates to an optical head employed in an optical information recording/reproducing apparatus such as an optical disk player, and more particularly, to an improvement in a device for supporting an object lens. Fig. 1 is a longitudinal sectional view of an optical head disclosed in the Japanese Patent Laying-Open No. 283430/1987, and Fig. 2 is an exploded perspective view of the optical head shown in Fig. 1. Referring to these figures, a yoke member 112 formed from a sheet material is attached to a base 111. A link member 113 cast in a mold is attached via pins 114 to the yoke member 112. A holding member 117 holding an object lens 115 and a semiconductor device 116 is attached to the forward end of the link member 113. A lid 118 having an opening 118a is attached to the holding member 117. A mirror 121 is attached to the lid 118 for closing the opening 118a. The semiconductor device 116 includes a semiconductor laser for emitting a laser beam 143 and a photosensor for sensing the laser beam reflected from a disk 144. The link member 113 includes hinges 113a for swinging the holding member 117 along the direction of the optical axis of the object lens 115, as indicated by chain dotted lines in Fig. 1, for effecting focusing adjustment, and also includes a hinge 113b for swinging the holding member 117 along the direction normal to the optical axis of the object lens 115, for effecting tracking adjustment. Also, for preventing the holding member 117 from being turned about the hinge 113b in case when the optical head is tilted in its entirety, a counterbalance 122 is provided to the holding member 117 at a portion opposite to the object lens 115 with respect to the hinge 113b. The yoke member 112 is provided with upstanding plate sections 112a, 112b, formed by bending, and a magnet 123 is mounted to a surface of the upstanding plate section 112a confronting to the upstanding plate section 112b. A focusing coil 124 is attached to the holding member 117 for surrounding the upstanding plate section 112b. A tracking coil 125 is attached to the focusing coil 124 for confronting to the magnet 123. Two sets each of the upstanding plate sections 112a, 112b, magnet 123, focusing coil 124 and tracking coil 125 are arranged symmetrically to each other with respect to the hinge member 113. The semiconductor device 116, focusing coil 124 and the tracking coil 125 are connected electrically to the outside through a flexible wiring board or substrate 126. The hinge member 113 and the holding member 117 are covered by a cap 127 having an opening 127a at a position above the object lens 115. A similar optical head is disclosed in EP-A-212 941. In the above described conventional supporting device for supporting the object lens of the optical head, the link member 113, hinge 113b and object lens 115 are arrayed along a straight line in this sequence without overlapping. Hence, the object lens supporting device has a longer length, resulting in a larger size of the overall optical head. Also, the counterbalance 122 need be inserted in the link mechanism to complete the object lens supporting device, after the formation of the link mechanism including the link member 113 and the hinge 113a, thus complicating the manufacture process for the object lens supporting device. JP-A-60-160032 describes an objective lens driver of an optical recording and reproducing device in which the objective lens is able to move in tracking direction by a grooved part having one end fixed to a substrate and the other end, which carries the object lens portion rotatable about a constructed portion. In accordance with the present invention, there is provided a lens supporting device for use in an optical head in which an objective lens is displaceable both in a first direction along its optical axis and in a second direction normal to said optical axis, said device comprising a link mechanism including a support member rigidly mountable on a base, a pair of parallel link elements extending between said support member and an intermediate member and each hinged by a respective pair of first hinges to said support and intermediate members to permit movement of said intermediate member in said first direction, a lens mounting means mounted for movement in said first direction with the intermediate member and for rotation about a second hinge means between the lens mounting means and the intermediate member for lens movement in said second direction characterised in that the pivot axis of the second hinge means is disposed in the space between the link elements and in that the lens mounting means comprises an attachment member which is also disposed in the space between said link elements, the second hinge means being disposed between said attachment member and said intermediate member, and a substantially ring-shaped lens mounting member surrounding the link mechanism. Hence, in the object lens supporting device of the present invention, the object lens may be displaced along the optical axis by the link mechanism, and also in a direction normal to the optical axis by the second hinge means. Also, in the object lens supporting device of the present invention, the second hinge means is accommodated in the link mechanism, so that the lens supporting device is more compact in size than the conventional device. Embodiments of the present invention provide a device for supporting an object lens in an optical head, which has an advantage of being compact in size and easily assemblable. The foregoing and other features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings. Fig. 1 is a longitudinal sectional view diagrammatically showing a conventional optical head. Fig. 2 is an exploded perspective view of the optical head shown in Fig. 1. Fig. 3 is an exploded perspective view of a lens supporting device according to an embodiment of the present invention. Fig. 4 is an enlarged side elevation showing the link mechanism and second hinge means shown in Fig. 1. Fig. 5 is a top plan view showing the link mechanism and second hinge means shown in Fig. 4. Referring to Fig. 3, an object lens 1 is fixed to a lens supporting member 2. The lens supporting member 2 is substantially ring-shaped, and a counterbalance 4 is affixed to the side of the member 2 opposite to the object lens 1 with respect to an opening 3. A link mechanism 5 is inserted into the opening 3. The both ends of a rotatable plate 16 connected to the link mechanism 5 are inserted and fixed in a pair of slots 6 formed on the inner wall of the opening 3, whereby the lens supporting member 2 is supported by the link mechanism 5. Focusing coils 7 and tracking coils 8 are attached to the lens supporting member 2 and are connected to an external circuit through a flexible print board or substrate 9. As shown in more detail in Figs. 4 and 5, the link mechanism 5 is molded from a soft synthetic resin material. Four link plates 10, 11, 12 and 13 are arranged in the form of a parallelepiped and interconnected by four hinges 14a, 14b, 14c and 14d of a first hinge group having a first rotatable axis. A rotatable plate 16 is connected to the inner lateral side of the link plate 10 by a hinge 15 of a second hinge group having a second rotatable axis parallel to the surface of the link plate 10 and normal to the first axis of the first group hinges 14a to 14d. The rotatable plate 16 has its both ends inserted and fixed in the pair of slots 6 formed in the lens supporting member 2. The link plate 12 facing to the link plate 10 is provided with a through-hole 18 and pins 19 for engaging with the base 17. The base 17 has a pin 20 and holes 21 for engaging with the hole 18 and the pins 19 of the link plate 12, respectively. The link mechanism 5 is securely held on the base 17 through the intermediary of these engaging means 18-21. The base 17 is also provided with yokes 22a, 22b and magnets 23 constituting magnetic circuits in cooperation with the focusing coils 7 and the tracking coils 8. As seen from Fig. 4, the parallelepipedic link mechanism 5, constituted by the link plates 10 to 13 and the first group hinges 14a to 14d, can be displaced as indicated by chain dotted lines. Thus, the link plate 10 can be moved up and down as indicated by an arrow mark A with respect to the link plate 12 secured to the base 17, whereby the object lens 4 can be displaced along the optical axis, as indicated by an arrow mark Y in Fig. 3, together with the lens supporting member 2. The rotatable plate 16 can be rotatively displaced, with the second group hinge 15 as center, as indicated by chain dotted lines and by an arrow mark B in Fig. 5. Thus, the object lens 1 can be rotated along with the lens supporting member 2 about the second group hinge 15 as center, this displacement being that in the tracking direction as indicated by an arrow mark X in Fig. 3. Thus, the object lens 1 can be displaced in both the focusing direction X and the tracking direction Y, and the focusing and tracking can be controlled appropriately under the driving force of magnetic circuits constituted by the coils 7, 8, yokes 22a, 22b and magnets 23. In the device shown in Fig. 3, inasmuch as the second group hinge 15 and the rotatable plate 16 are provided in the parallelepipedic link mechanism 5 made up of the link plates 10 to 13 and the first group hinges 14a to 14d, the lens supporting device may be made more compact than the conventional device. There is also no necessity of inserting the counterbalance 4 into the link mechanism 5 for assembling. Hence the counterbalance 4 can be attached to the lens supporting member 2 in a process step which is separate from the step of securing the link mechanism 5 to the base 17. It is also possible to have the counterbalance 4 formed simultaneously with the lens supporting member 2. The ring-shaped lens supporting member 2 has a mechanical strength higher than that of the conventional lens supporting member. In the above embodiment, the link plate 12 of the link mechanism 5 is secured to the base 17 and the rotatable plate 16 holds the lens supporting member 2.

Claims: A lens supporting device for use in an optical head in which an objective lens (1) is displaceable both in a first direction along its optical axis and in a second direction normal to said optical axis, said device comprising a link mechanism (5) including a support member (12) rigidly mountable on a base (17), a pair of parallel link elements (11, 13) extending between said support member (12) and an intermediate member (10) and each hinged by a respective pair of first hinges (14a/14d, 14b/14c) to said support and intermediate members to permit movement of said intermediate member (10) in said first direction, a lens mounting means (2, 16) mounted for movement in said first direction with the intermediate member and for rotation about a second hinge means (15) between the lens mounting means and the intermediate member for lens movement in said second direction characterised in that the pivot axis of the second hinge means (15) is disposed in the space between the link elements (11, 13) and in that the lens mounting means (16) comprises an attachment member (16) which is also disposed in the space between said link elements (11, 13), the second hinge means (15) being disposed between said attachment member (16) and said intermediate member (10), and a substantially ring-shaped lens mounting member (2) surrounding the link mechanism (5). The lens supporting device according to claim 1 wherein said link mechanism (5) is cast integrally by molding a soft synthetic resin material. The lens supporting device according to claim 1 or 2 wherein said link mechanism (5), said second hinge means (15) and said attachment member (16) are cast integrally by molding a soft synthetic resin material. The lens supporting device according to any one of claims 1 to 3 wherein said attachment member (16) comprises a bar (16) disposed with each end inserted in a respective one of a pair of slots (6) formed in the surrounding wall of the lens mounting means (2). The lens supporting device according to any preceding claim wherein said lens holding means (2) is provided with a counterbalance (4) for counterbalancing with respect to the pivot axis of said second hinge means (15). The lens supporting device according to any preceding claim wherein the support member (12) is secured to the base (17) by interengaging pin means (19, 20) and hole means (18, 21).

Inventors: NISHIHARA HIKARU, NISHIMURA KAORU, OGATA HIROSHI, YOSHIMUNE TATSUHIRO, NISHIHARA, HIKARU, NISHIMURA, KAORU, OGATA, HIROSHI, YOSHIMUNE, TATSUHIRO
Applicants: SHARP KK, SHARP KABUSHIKI KAISHA
Application year: 1989
Main classification: G11B7
IPC codes: G11B7