1. Field of the Invention
The present invention relates to a mechanism for moving an optical pickup radially along a disc. Particularly, the invention is concerned with an optical pickup moving mechanism suitable for the reduction of cost and weight.
2. Description of the Prior Art
In a disc unit which, with use of an optical pickup, records and reproduces information to and from a disc such as CD (compact disc), MD (minidisc), or DVD (digital versatile disc), an optical pickup moving mechanism as shown in FIG. 7 is provided for moving the optical pickup radially along the disc.
In the same figure, an optical pickup P0 is principally composed of an objective lens 2, a drive mechanism (not shown) for actuating the objective lens 2, and a base 1 which carries thereon the objective lens 2, the objective lens drive mechanism and an optical device for radiating a laser beam to a disc D through the objective lens 2. The base 1 is disposed between a guide shaft 3 and a screw shaft 4. The guide shaft 3 and the screw shaft 4 are arranged in an opposed parallel relation to each other on a mechanical chassis (not shown). The screw shaft 4 is rotated in both forward and reverse directions by means of a thread motor (not shown). Bearing portions 1a and 1b as portions to be guided are projected from both sides of the base 1. One bearing portion 1a is in abutment against a peripheral surface of the guide shaft 3, while the other bearing portions 1b are loosely fitted on the screw shaft 4. A plate spring 5 is screwed in a cantilevered fashion to the base 1 and a female screw member 6 called half nut is fixed to a free end side of the plate spring 5. The female screw member 6 is toothed over an approximately semicircle. This toothed portion remains in contact with the threaded portion of the screw shaft 4 due to the resilience of the plate spring 5.
In the optical pickup transfer mechanism thus roughly constructed, when the screw shaft 4 is rotated in either forward or reverse direction, the rotational force thereof is converted to a linear motion and transferred to the base 1 by means of the female screw member 6, so that the base 1 moves in the thrust direction (right and left direction in FIG. 7) of the guide shaft 3 and the screw shaft 4. As a result, the whole of the optical pickup 2 is moved radially along the disc D through the base 1, thus permitting information recording and reproducing operations for the disc.
Recently, for promoting the reduction of cost and weight of the optical pickup moving mechanism, studies have been made about a technique wherein the base of the optical pickup is formed by molding a synthetic resin instead of using such a metallic material as die casting aluminum, and the guide shaft is formed by molding a synthetic resin as a substitute for a metallic shaft such as a stainless steel shaft. If, however, the base and the guide shaft are each formed by molding a synthetic resin, the bearing portion of the base, which is always kept in sliding contact with the guide shaft at the same portion thereof, becomes worn-out. This may result in tilting of an optical axis of the objective lens mounted on the base, which deteriorates the recording or reproducing function.
In the case of a vehicular disc unit, it is necessary to select a material superior in both rigidity and heat resistance. With a synthetic resin material, PPS (polyphenylene sulfide) with glass fibers incorporated therein is used. If both base and guide shaft repeat sliding, their constituent synthetic resins are apt to wear more rapidly. Such a problem is also true of the case where the screw shaft as the other movement guide member is formed by molding a synthetic resin.
The present invention has been accomplished in view of the above-mentioned circumstances and it is an object of the invention to provide an optical pickup moving mechanism wherein even if a base of an optical pickup and a movement guide member are each formed from a synthetic resin, it is possible to suppress the growth of wear caused by sliding contact between their constituent synthetic resins, and which can attain the reduction of cost without impairing the reliability.
According to the present invention, for achieving the above-mentioned object, there is provided an optical pickup moving mechanism including an optical pickup and a movement guide member, the optical pickup having a base with an objective lens mounted thereon and with a to be guided portion being projected sideways thereof, the movement guide member having a guide surface which is extended in a predetermined direction and supporting the base slidably through the to be guided portion, the base being slid along the guide surface of the movement guide member, thereby allowing the optical pickup to move radially of a disc, wherein the to be guided portion and the movement guide member are each formed from a synthetic resin and a metallic slide member is disposed in the to be guided portion at a position opposed to the guide surface so that an outer peripheral surface of the slide member comes into sliding contact with the guide surface.
According to the optical pickup moving mechanism of the above construction, since the base which includes the to be guided portion and the movement guide member which supports the base slidably are each formed by molding a synthetic resin, it is possible to attain the reduction of cost and weight, and since the metallic slide member disposed in the to be guided portion is brought into sliding contact with the guide surface of the movement guide member, it is possible to suppress the growth of wear caused by sliding contact between their constituent synthetic resins and hence possible to ensure a high reliability.
In the above optical pickup moving mechanism, by disposing a resilient member for urging the to be guided portion in a direction in which the slide member comes into pressure contact with the guide surface of the movement guide member, the slide member is allowed to slide on the guide surface always under a moderate pressing force without leaving the guide surface.
It is preferable that the slide member be a metal pin of a generally circular section. As such a metal pin of a generally circular section there may be used, for example, a commercially available parallel pin made of stainless steel which is inexpensive and high in dimensional accuracy. Thus, it is not necessary to newly provide a special mold for the metal pin; in other words, the metal pin itself does not become a cause of increase in cost. If the metal pin of a generally circular section is reciprocated in the optical pickup moving direction while being kept in sliding contact with the guide surface of the movement guide member, lubricating oil (grease) applied to the guide surface stays in wedge-like gaps formed before and behind the sliding contact position of the metal pin, thereby functioning as grease sumps and thus giving rise to an advantage that a smooth sliding motion of the metal pin is ensured.
In connection with the above optical pickup moving mechanism, if there is adopted a structure wherein a recess is formed in the to be guided portion at a position opposed to the guide surface and the metal pin is fitted in the recess, the metal pin mounting workability for the to be guided portion is improved. Further, if the recess is formed with a flat inner bottom surface and is narrower on its side close to the guide surface and if the metal pin is fitted in the recess while its outer peripheral surface is brought into abutment against the inner bottom surface of the recess, the metal pin can be fitted in the recess with the inner bottom surface of the recess as a reference. Here, the position of the bottom surface can be easily defined relative to the guide surface. This allows for improved relative positional accuracy between the metal pin and the guide surface and easier dimensional management in a design stage or in an assembling stage.
In connection with the above optical pickup transfer mechanism, if a through hole is formed in the to be guided portion so as to communicate with the recess and open to a side of the metal pin which side is not opposed to the guide surface, and if an adhesive is poured from this through hole into the recess to fix the metal pin within the recess, the metal pin fitted in the recess can be fixed firmly to the to be guided portion with the adhesive by using a slight force. Additionally, the assembling work efficiency can be improved because there is no fear that the adhesive may adhere to the guide surface side of the metal pin.
Preferably, the metal pin is disposed so that its longitudinal direction is substantially orthogonal to the extending direction of the guide surface. According to this arrangement, the base can be moved while keeping the contact area between the metal pin and the guide surface to a minimum, so that the sliding resistance between the metal pin and the guide surface becomes extremely small and hence it is possible to prevent the occurrence of such an inconvenience as the metal pin is caught on the guide surface during movement of the optical pickup and tilting of the optical pickup results. For example, if the guide surface of the movement guide member is arcuate in section, then by disposing a metal pin in a direction approximately orthogonal to a generator of the circular arc it is made possible to maintain the metal pin and the guide surface in a state of point contact.