Abstract:
An optical pickup sending device comprises: an optical pickup for reading information from an information recording medium; a rack member provided in connection with the optical pickup; and a screwed shaft engaged with the rack member for sending the optical pickup along the screwed shaft. In particular, the rack member is formed with a plurality of curved teeth each having a radius of curvature larger than that of the screwed shaft.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to an optical pickup sending device for freely moving back and forth an optical pickup within an information recording/reproducing apparatus such as a disc player so as to read information from an information recording medium such as an optical disc. 
     There have been known several types of conventional pickup sending devices such as those disclosed in Japanese Utility Model Unexamined Publication No. 5-61861 and Japanese Patent Unexamined Publication No. 6-68619. 
     FIG. 6 is used to schematically indicate the structure of a conventional pickup sending device disclosed in Japanese Utility Model Unexamined Publication No. 5-61861. As shown in FIG. 6, the sending device comprises a pair of guide shafts  2  and  3  for slidably supporting an optical pickup body  1 , a screwed shaft  4 , a rack member  6  supported by two arm members  5  extending from the pickup body  1 . The teeth  6   a  of the rack member  6  are engaged with the screwed shaft  4 . When the screwed shaft  4  is rotated, a relative positional relationship between the teeth  6   a  and the screw shaft  4  will he changed, so as to cause the pickup body  1  to freely move back and fourth along the guide shafts  2  and  3 , i.e., in a radial direction of an optical disc such as a CD (Compact Disc) mounted on a turntable (not shown). 
     With the pickup sending device shown in FIG. 6, although the rack member  6  is elastically urged by the screw shaft  4  through a least spring  6   b  provided in parallel with the arm members  5 , since the teeth  6   a  of the rack member  6  are simply engaged with a part of the circumferential surface of the screwed shaft  4 , an engagement between the teeth  6   a  of the rack member  6  and the screw shaft  4  is apt to collapse even due to a small vibration. As a result, it is difficult for the optical pickup  1  to read information from the optical disc in a correct manner and hence there will be some defects in the obtained information read by the optical pickup  1 . 
     FIG. 7 is used to schematically indicate the structure of another conventional pickup sending device disclosed in Japanese Patent Unexamined Publication No. 6-68619. As shown in FIG. 7, the sending device comprises two guide shafts  8  and  9  for slidably supporting an optical pickup body  7  in a manner such that the pickup body  7  can be freely moved back and forth in the radio direction of an optical disc. A support member  10  is provided on the pickup body  7 . The support member  10  has an engaging pin  12  provided at a front end thereof which is capable of engaging with a screw portion  11  formed integrally with the guide shaft  8 . When the guide shaft  8  is rotated, a relative positional relationship between the engaging pin  12  and screw portion  11  will be changed, so as to cause the optical pickup body  7  to freely move back and fourth along the guide shafts  8  and  9 . 
     With the pickup sending device shown in FIG. 7, since only the front end of the engaging pin  12  is engaged with the screw portion  11  of the shaft  8 , an engagement between such two members  8  is apt to collapse even due to a small vibration. As a result, it is difficult for the optical pickup  7  to read information from the optical disc in a correct manner and hence there will be some defects in the obtained information read by the pickup  7 . 
     In order to solve the problems existing in the above conventional devices shown in FIGS. 6 and 7, there has been suggested an improved structure shown in FIG.  8 . Referring to FIG. 8, a half-nut  14  engaged with a screwed shaft  13 , is integrally formed with a holding member  16  extending outwardly from the pickup main body  15 . The inner diameter of the half-nut  14  is made almost the same as that of the screwed shaft  13 , so that it is sure to prevent the half-nut  14  from getting off the screwed shaft  13 . 
     However, if there is a relative deviation between a pair of guide shafts  17 ,  18  on one hand and the screwed shaft  13  on the other, an undesired gouging force will happen since it is difficult to absorb a dislocation caused by the above deviation between the screwed shaft  13  and the half-nut  14 . As a result, there will he an unduly increased load on a driving motor (not shown) for driving the screwed shaft  13 , hence undesirably causing an increase in the starting voltage of the driving motor. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide an improved optical pickup sending device capable of solving the above-mentioned problems peculiar to the above-discussed prior arts. 
     According to the present invention, there is provided an optical pickup sending device, comprising: an optical pickup for reading information from an information recording medium; a rack member provided in connection with the optical pickup; and a screwed shaft engaged with the rack member for sending the optical pickup along the screwed shaft. In particular, the rack member is formed with a plurality of curved teeth each having a radius of curvature larger than that of the screwed shaft. 
     In one aspect of the present invention, the rack member is integrally formed with a holder so as to be supported thereby, said holder is engaged in a frame structure which is integrally formed with an arm member extending from he optical pickup and facing towards the screwed shaft. 
     In another aspect of the present invention, a coil spring is attached onto the holder in a manner such that the rack member is elastically urged against the screwed shaft. 
     The above objects and features of the present invention will become better understood from the following description with reference to the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 is an explanatory plane view indicating the structure of an optical pickup sending device made according to the present invention. 
     FIG. 2 is an exploded plane view indicating in more detail how a rack member may be attached to an optical pickup main body. 
     FIG. 3 is a back view indicating the rack member. 
     FIG. 4 is a longitudinally sectional view taken along A—A line in FIG.  1 . 
     FIG. 5 is an explanatory view indicating an engaging relationship between a screwed shaft and the rack member. 
     FIG. 6 is a perspective view indicating an optical pickup sending device made according to a prior art. 
     FIG. 7 is a plane view indicating another optical pickup sending device made according to a prior art. 
     FIG. 8 is a perspective view indicating a further optical pickup sending device made according to a prior art. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     An embodiment of the present invention will be described in the following with reference to the accompanying drawings. 
     FIG. 1 is an explanatory plane view indicating the structure of an optical pickup sending device made according the present invention. 
     In FIG. 1, reference numeral  100  is used to represent an optical disc such as CD (Compact Disc), DVD (Digital Video Disc or Digital Versatile Disc). Reference numeral  101  is used to represent a turntable provided on a chassis  102  for mounting the optical disc  100  when the optical disc is being reproduced or new information is being recorded thereon. Further, reference numerals  103  and  104  are used to represent a Pair of guide shafts disposed on the chassis  102 . In addition, a screwed shaft  105  serving as a pickup sending means and a driving motor  106  are also provided on the chassis  102 . 
     In detail, the guide shafts  103 ,  104  and the screwed shaft  105  are arranged in parallel with one another, with the guide shafts  103  and  104  fixed on the chassis  102  by means of fixing members  107 - 110 . The screwed shaft  105  is rotatably supported by bearing members  111  and  112  which are fixed on the chassis  120 . 
     In more detail, one end face of the screwed shaft  105  is elastically urged by a thrust member  113  consisting of a leaf spring, in a manner such that it is sure to prevent a possible vibration of the screwed shaft  105  in the longitudinal direction thereof. Further, a driven gear  114  engaged with a driving gear  115  for transmitting a driving force from a driving motor  106  to the screwed shaft  105 , is secured on the screwed shaft  105 . 
     An optical pickup body  116  is slidably supported on the guide shafts  103  and  104 , an objective lens  117  (for emitting a light beam on to the information recording surface of the optical disk  100  and for collecting its reflected light so as to read information from the disc) is provided on the upper surface of the pickup body  116 . 
     Further, an arm member  118  (FIG.  1  and FIG. 2) is provided extending from the pickup body  116  towards the screwed shaft  105 , a rack member  120  is provided in connection with the arm member  118  in a manner such that it receives an elastic force from a coil spring  119  provided therebetween and thus gets in contact with the screwed shaft  105 . 
     FIG. 2 is an exploded plane view indicating in more detail how a rack member  120  may be attached to the pickup body  116 . FIG. 3 is a back view indicating the rack member  120 . FIG. 4 is a longitudinally sectional view taken along A—A line in FIG.  1 . 
     In FIG. 2, the arm member  118  extending from the pickup body  116  is integrally formed with a frame structure  121  which includes two mutually facing side walls  121   a ,  121   b  and one rear wall  121   c . The side walls  121   a  and  121   b  are formed with through-holes  121   d  and  121   e , and a support pin  122  is inserted there through. 
     The rack member  120  has an integrally formed holder  120   a  adapted to be engaged into the frame structure  121 , an elongate through hole  120   b  allowing insertion of the support pin  122  is formed through the holder  120   a . On the back surface of the rack member  120  there are formed curved teeth  120   c  capable of engaging with the screwed shaft  105 . 
     Then, the holder  120   a  with the coil spring  119  wound thereon is engaged into the frame structure  121 , with one end  119   a  thereof fixed on the rear wall  121   c  and the other end thereof on the rack member  120 , so that the support pin  122  is inserted in the through holes  121   d ,  121   e  and elongated through hole  120   b.  In this way, as shown in FIG. 4, the rack member  120  may be attached in a proper position with respect to the pickup body  116 , and will be elastically urged against the screwed shaft  105  by virtue of the coil spring  119 . 
     In detail, as shown in FIG. 5, the semi-diameter R (radius of curvature) of the curved teeth  120   c  formed on the rack member  120  is set to be larger than the semi-diameter r (radius of curvature) of the screwed shaft  105 , so that the screwed shaft  105  is allowed to be covered by the curved teeth  120   c.    
     An operation of the optical pickup sending device having the above structure will be described in the following with reference to FIG.  1  and FIG.  4 . 
     After an optical disc  100  is mounted on the turntable  101 , the driving motor  106  is started so as to cause the rotation of the screwed shaft  105  through the gear  115  and the gear  114 . For this reason, there will be a change in a relative positional relationship between the curved teeth  120   c  and the screwed shaft  105 , thereby causing the pickup body  116  to move back and forth along the guide shafts  103  and  104  in the radial direction of the disc  100 , thus enabling the optical pickup to read information from the information recording surface of the disc. 
     Here, since the curved teeth  120   c  has a larger semi-diameter than that of the screwed shaft  105 , the screwed shaft  105  may be covered by the curved teeth  120   c  in the radial direction thereof, thereby making it possible to absorb a deviation or a dislocation possibly occurred in the engagement between the curved teeth  120   c  and the screwed shaft  105 . 
     In this way, since it is sure to prevent a possible deviation or dislocation in the engagement between the curved teeth  120   c  and the screwed shaft  105 , there will not be an unduly increased load on the driving motor  106 , thus avoiding an undesired increase in the starting voltage of the driving motor. 
     Further, the pickup body  116  has a predetermined moving range depending upon the length of the guide shafts  103  and  104 . However, when the pickup body  116  arrives at a terminal position closest to the turntable  101  or arrives at the opposite terminal position farthest from the turntable  101 , since the curved teeth  120   c  will go beyond the teeth portion of the screwed shaft  105  against the elastic force of the coil spring  119 , it is allowed to exactly prevent an unduly increased load on the driving motor  106 . 
     In this way, with the use of the above embodiment, since a good and stable engagement may be maintained between the screwed shaft  105  and the rack member  120 , the pickup body  116  is allowed to move back and forth in the radial direction of the disc  100  with an improved precision. 
     As may be understood from the above description, with the use of the optical pickup sending device made according to the present invention, since the rack member  120  is formed with curved teeth  120   c  which has a larger semi-diameter than that of the screwed shaft  105 , even if a deviation or a dislocation occurs between the curved teeth  120   c  and the screwed shaft  105 , such kind of deviation or dislocation will be effectively absorbed. For this reason, it is sure to prevent an undesired gouging force possibly occurred due to the above deviation or dislocation. Further, even if there is a vibration occurred between the rack member  120  and the screwed shaft  105 , such a vibration will not cause the rack member  120  to move away from the screwed shaft  105 . In this way, since a good and stable engagement may be maintained between the rack member  120  and the screwed shaft  105 , the pickup body  116  may be moved in accordance with a rotating amount of the screwed shaft  105  in a more stable manner and with a higher precision. 
     While the presently preferred embodiments of the invention have been shown and described above, it is to be understood that these disclosures are for the purpose of illustration and that various changes and modifications may be made without departing from the scope of the invention as set forth in the appended claims.