Abstract:
A lens barrel having a cam barrel is disclosed. The cam barrel is molded by die-cutting in radial and other directions relative to the optical axis so as to have raised cams without undercuts if the raised cams are even partially lined up fore and behind one another along the optical axis, and there is no parting line in either the cam grooves nor the raised cams. The cam barrel has its outer surface provided with raised cams and is made of synthetic resin, and each of the raised cams has at least one of cam faces inclined toward an opposite cam face off a radial direction relative to an optical axis of the cam barrel.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a lens barrel and a cam barrel molding die, and more particularly, it relates to a lens barrel included in a zoom lens and having movable multi-barrel and multi-lens built-in in combination with a cam barrel of synthetic resin, and a molding die used to produce such a cam barrel. 
     BACKGROUND ART 
     Japanese Patent Laid-Open No. H09-203850 discloses a mechanical assembly of a zoom adjusting element of a zoom lens which is made of synthetic resin and integrated with a cam element or a cam follower of cam mechanism. 
     Japanese Patent Laid-Open No. H09-203851 discloses a zoom lens which has a movable frame provided with a cam in relation with a first group of lenses, and a zoom adjusting ring having its inner surface formed with a cam follower in relation with the first group of lenses and also formed with a cam in relation with a second group of lenses, so that simply regulating the zoom adjusting ring enables the first and second groups of lenses to move relative to an optical axis. 
     Japanese Patent No. 2773586 discloses a zoom lens including a cam ring which has its raised cams molded with opposite cam faces, respectively, by die-cutting in directions along the optical axis, and the invention is characterized in that the cam face shaped by a static member of the die and the cam face shaped by a movable member of the die meet each other at parting line or seam along a raised portion made by the static and movable members of the die. 
     Japanese Patent Application No. H11-265765 discloses a zoom lens which has a cam barrel made of synthetic resin and formed with a cam in relation with a first group of lenses and cams in relation with at least two more groups of lenses, i.e., second, third, and so forth. 
     The cam ring having raised cams as described in Japanese Patent No. 2773586, which is suitable for use in a zoom lens, is molded by die-cutting in directions along the optical axis, and this unable to create the raised cams even partially lined up fore and behind one another along the optical axis, which resultantly disturbs down-sizing as having strongly been demanded recently. 
     The zoom lens set forth in Japanese Patent Application No. H11-265765 is configured to have the cam barrel provided with the cam in relation with the first group of lenses and the two or more cams in relation with the second and other groups of lenses. With this configuration, as can be seen in FIG. 6, the die is adapted to radially slide under a certain restriction in direction so as not to leave undercuts in locations of raised cams for the respective lens groups, and such restriction to and a design of the die lead to a creation of parting line  202  in cam surfaces of cam grooves  200  defined in the molded cam barrel. Consequently, in adjusting for the zooming, studs fitted in the cam grooves  200 , while sliding along the cam surfaces of the cam grooves  200 , bump into the parting line  202  with slight impact, namely, a light shock of tapping. 
     The present invention is intended to overcome the above-mentioned disadvantages of the prior art lens barrel of synthetic resin, and it is an object of the present invention to provide a lens barrel having a cam barrel which is molded by die-cutting in radial and other directions relative to the optical axis so as to have raised cams without undercuts if the raised cams are even partially lined up fore and behind one another along the optical axis, and a cam barrel molding die in which a cause of an undercut is eliminated. 
     It is another object of the present invention to provide a lens barrel having a cam barrel where there is no parting line in either the cam grooves nor the raised cams, and a cam barrel molding die to produce such a cam barrel. 
     SUMMARY OF THE INVENTION 
     A lens barrel according to the present invention includes a cam barrel which has its outer surface provided with raised cams and is made of synthetic resin, and in the cam barrel, each of the raised cams has at least one of cam faces inclined toward an opposite cam face off a radial direction relative to an optical axis of the cam barrel. 
     In another aspect of the present invention, a cam barrel, which is included in a lens barrel and made of synthetic resin, has cam grooves and raised cams in its outer surface, and each of the raised cams has at least one of cam faces inclined toward an opposite cam face off a radial direction relative to an optical axis of the cam barrel. 
     Furthermore, a die according to the present invention is designed to mold a cam barrel of synthetic resin which is suitable for use in a lens barrel and has raised cams in its outer surface, and each of the raised cams has at least one of cam faces inclined toward an opposite cam face off a radial direction relative to an optical axis of the cam barrel, so as not to leave an undercut in the raised cams. 
     In another aspect of the present invention, a die is designed to mold a cam barrel of synthetic resin which is suitable for use in a lens barrel and has cam grooves and raised cams in its outer surface, and each of the raised cam s has at least one of cam faces inclined toward an opposite cam face off a radial direction relative to an optical axis of the cam barrel, so as not to leave an undercut in either the cam grooves or the raised cams. 
     These embodiments of the present invention are commonly characterized in that one of the cam faces extends in a radial direction relative to the optical axis. If both the cam faces of each of the raised cams are inclined toward the opposite cam faces off the radial direction relative to the optical axis, both the cam faces and cam followers must be shaped with high precisions. Additionally, short shot in molding is likely to occur where fused resin is insufficient at the top of the raised cam that is to be tapered in shape, which results in the truncated top of the raised cam being unsatisfactory in hardness. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a sectional view showing an exemplary embodiment of a zoom lens according to the present invention being in wide-mode; 
     FIG. 2 is a sectional view showing the zoom lens being in tele-mode; 
     FIG. 3 is a perspective view showing an exemplary cam barrel for the zoom lens according to the present invention; 
     FIG. 4 is an exploded view illustrating the cam barrel for the zoom lens in FIG. 3; 
     FIG. 5 is a partial sectional view taken along the line V—V of FIG. 4, showing a raised cam portion formed in the cam barrel for the zoom lens according to the present invention; and 
     FIG. 6 is a perspective view showing a prior art embodiment of a lens barrel. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Optics of the zoom lens consists of a first group  10  of lenses having a positive power attribute for focusing, a second group  12  of lenses having a negative power attribute, and a third group  14  of lenses having a positive power attribute. 
     A zoom lens barrel  20  has a plurality of roughly cylindrical members which are mutually telescopic, including a first fixed barrel  22  fixed to a mount  24  and guiding the second and third groups  12  and  14  of lenses in parallel with the optical axis O, a cam barrel  26  sliding over the outer surface of the first fixed barrel  22 , a barrel  28  in relation with the first group of lenses wand sliding over the outer surface of the fist fixed barrel  22 , a second fixed barrel  30  fixed to the mount  24 , a focus adjusting ring  40  rotating and simultaneously sliding over the outer surface of the second fixed barrel  30 , and a zoom adjusting ring  44  rotating and simultaneously sliding over the outer surface of the second fixed barrel  30  behind the focus adjusting ring  40 . The zoom adjusting ring  44  is coupled to the cam barrel  26  in proximal position or at the mount  24  to be a unit and pivot together about the optical axis O. 
     In the first fixed barrel  22 , there are defined grooves  54  shared for linear movement by both the second and third groups  12  and  14  of lenses, and the barrel also has its front end embedded with a first stud  80  for linear movement. The first stud  80  is fitted in a groove  82  defined in the inner surface of the barrel  28  for linear movement of the first group of lenses. 
     The cam barrel  26  of synthetic resin, as illustrated in FIGS. 3 and 5, includes raised cams  60  in relation with the first group of lenses and trapezoidal in vertical cross-section, second cam grooves  62  in relation with the second group of lenses and widened toward the outer circumference of the cam barrel, and third cam grooves  64  in relation with the third group of lenses and widened toward the outer circumference. 
     As shown in FIG. 5, each the raised cams  60  in relation with the first group of lenses has two faces opposite to each other, namely, a vertical face  63  radially extending outward from the optical axis O or perpendicular to a tangential plane with the curved outer surface of the cam barrel  26 , and a tapering face  61  inclined to meet the vertical face  63 . Such a raised cam  60  in relation with the first group of lenses does not have to have both of its respective cam faces and cam followers shaped with high precision, and short shot in molding is not caused; that is, fused resin might not be insufficient at the top of the raised cam that is to be tapered in shape, which is additionally advantageous in that the truncated top of the raised cam  60  is hard enough to resist impact. 
     The barrel  28  in relation with the first group of lenses, which supports a frame  70  holding the first group  10  of lenses, includes a helicoid inner barrel  90  and a helicoid outer barrel  92  which is screwed over and mated with the inner barrel and fixedly supports the frame  70  holding the first group of lenses. In the helicoid inner barrel  90 , as shown in FIG. 2, the groove  82  is defined for linear movement of the first stud  80  fitted therein, beyond and ahead of the cam barrel  26  fixed to the first fixed barrel  22 . The helicoid outer barrel  92  has its hind portion coupled to the focus adjusting ring  40  by a rotating member (not shown) so as to slide along the optical axis O relative to the second fixed barrel  30 , and the barrel is also engaged with the ring  40  to receive rotational movement from the same. 
     The barrel  28  in relation with the first group of lenses has its helicoid inner barrel  90  provided with cam followers  93  that are engaged with the raised cams  60  in relation with the first group of lenses. The frame  102  holding the second group  12  of lenses is fixed with pins  104  in relation with the second group of lenses and partially shaped in upside-down truncated cones, which slide in the cam grooves  62  in relation with the second group of lenses and in the grooves  54  for linear movement of the second and third groups of lenses. The frame  110  holding the third group  14  of lenses is fixed with pins  112  partially shaped in upside-down truncated cones, which slide in the cam grooves  64  in relation with the third group of lenses and in the grooves  54 . 
     An operation of the zoom lens having the aforementioned configuration will now be described. In zooming, the zoom adjusting ring  44  is turned to rotate the cam barrel  26  over the first fixed barrel  22 . As the cam barrel  26  rotates, the barrel  28  in relation with the first group of lenses, which is restricted in its rotational movement due to the engagement of the stud  80  with the groove  82 , moves around the optical axis O, following a trajectory determined by the cam mechanism, by virtue of the engagement of the raised cams  60  with the cam followers  93 . The frame  102  holding the second group of lenses, which is restricted in its rotational movement due to the engagement of the pins  104  for the second group of lenses with the grooves  54  for linear movement of the second and third groups of lenses, moves relative to the optical axis O, following a trajectory determined by the cam mechanism, by virtue of the engagement of the pins  104  with the cam grooves  62 . 
     In addition to that, the frame  110  holding the third group of lenses, which is restricted in its rotational movement due to the engagement of the pins  112  with the grooves  54  for linear movement of the second and third groups of lenses, moves relative to the optical axis O, following a trajectory determined by the cam mechanism, by virtue of the engagement of the pins  112  with the cam grooves  64 . In this way, the zooming is performed. 
     In focusing, the focus adjusting ring  40  is turned to make a rotation member (not shown) transmit the rotation to revolve the helicoid outer barrel  92 . Meanwhile, the helicoid inner barrel  90  is restricted in its rotational movement due to the stud  80  fixed to the first fixed barrel  22  and the groove  82  for linear movement, and instead, the helicoid outer barrel  92  holding the frame  70  in relation with the first group of lenses, while screwing on and off the helicoid inner barrel  90 , moves relative to the optical axis O along a trajectory determined by the cam mechanism. In this way, the focusing is attained. 
     Thus, according to the present invention, there are provided a lens barrel having a cam barrel which can be molded without undercuts, and a molding die to produce such a cam barrel. 
     Also, according to the present invention, there is provided a lens barrel having a cam barrel where there is no parting line in either the cam grooves nor the raised cams, and a cam barrel molding die to produce such a cam barrel. 
     These objects, advantages, and features of the present invention have been given only by way of examples but not for limitations, and therefore, it should be noted that any person having ordinary skills in the art would appreciate that there should be a variety of variations and modifications of the best modes as described above, without departing the true spirit and scope of the present invention as defined in the appended claims.