Abstract:
A lens barrel having inner and outer cam rings which are configured to rotate relatively each other so as to shift one or more lens element of a lens system installed therein is equipped with an axial movement restraint mechanism for restraining axial play of one of the two cylindrical barrels relative to the other of the two cylindrical barrels while allowing relative rotation between them, the axial movement restraint mechanism comprising a radial jaw or a radial flange formed integrally with one of the inner and outer cam rings and a peripheral groove formed on another cam ring for receiving the jaw or the flanges and, if necessary, a spring disposed between the inner and outer cam rings for forcing the inner and outer cam rings in opposite axial directions, respectively.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a lens barrel, and in particular, to a lens barrel having a rotatable cylindrical ring with a curvilinear cam groove or slot and a stationary cylindrical ring with a linear cam groove or slot which are arranged coaxially with each other and a lens holder with a cam follower pin in engagement with both curvilinear cam groove and linear cam groove so as to move linearly along the linear grooved cam following movement of the curvilinear grooved cam when rotating either one of the rotatable cylindrical rings relative to the other. 
     2. Description of the Related Art 
     Typically, there are numerous lens barrel s that drive optical lens elements, such as a zooming lens element and a focusing lens element, by an manually operated ring or a motor driven ring. Such a lens barrel comprises at least a cylindrical ring with a linear cam groove or slot (which is referred to as a cylindrical linear cam ring) in which lens holders holding focusing lens elements or zooming lens elements is installed and a cylindrical ring with a curvilinear cam groove or slot (which is referred to as a cylindrical curvilinear cam ring) that is fitted externally on and coaxialy with the inner cylindrical ring. These cylindrical cam rings are configured such that either one of the cylindrical cam rings rotates relatively to the other. The lens holder is provided with a cam follower pin which extends radially into the curvilinear cam groove of the cylindrical curvilinear cam ring passing through the linear cam slot of the cylindrical linear cam ring. The lens barrel thus constructed moves the lens holders in an axial direction following rotation of either the cylindrical linear cam ring or the cylindrical curvilinear cam ring. 
     The this type of lens barrel restricts these cylindrical cam rings in axial position relative to a stationary cylindrical ring of the lens barrel by means of a restrictive ring or a restrictive plate while allowing them to rotate about the optical axis. This construction of the lens barrel has a drawback in an increase in cost that is induced by a large number of parts and an increased man-hour for assembling the lens barrel. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide an optical scanning device which is accurate in scanning operation. 
     It is another object of the present invention to provide a lens barrel which provide a reduction in the number of parts and man-hour for assembly with an effect of reducing production costs. 
     The foregoing objects of the present invention are accomplished by a lens barrel that comprises an inner cam barrel, an outer cam barrel disposed coaxially with the inner cam barrel so as to be rotatable relatively to the inner cam barrel, a lens holder for holding a lens element of the optical lens system which has a radial cam follower pin which passes through an inner cam slot of the inner cam barrel and is received in an outer cam slot of the outer cam barrel and is shiftable alongside both inner and outer cam slots in an axial direction following relative rotation between the inner and outer cam barrels so as thereby to cause axial movement of the lens element for adjusting optical operating condition of the optical lens system, and axial movement restraint means for restraining the inner and outer cam barrels from axially moving relatively to each other during relative rotation between the inner and outer cam barrels. The axial movement restraint means comprises a peripheral groove which is formed on either one of the inner and outer cam barrels and a radial jaw which is formed on the other one of the inner and outer cam barrels and received in the peripheral groove for contact slide movement. The axial movement restraint means further comprises elastic means disposed between the inner and outer cam barrels for forcing the inner and outer cam barrels in opposite axial directions so as thereby to press the axial jaw against a wall of the peripheral groove. 
     Because of the simple structure of the axial movement restraint means which is formed by the jaw and the groove only and, if necessary, the elastic member incorporated between the cam barrels which eliminates axial play usually occurring between the cam barrels, while the number of parts necessary for the lens barrel is reduced and, in consequence, man-hour necessary for assembling the lens barrel is considerably cut, which are always desirable for cutting production costs of the lens barrel, the lens barrel is precise in operation, as compared with conventional lens barrels. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects and features of the present invention will be more apparent from the following detailed description in connection with a preferred embodiment thereof when reading in conjunction with the accompanying drawings, in which: 
     FIG. 1 is a cross-sectional view of a varifocal lens barrel in accordance with a preferred embodiment of the present invention; and 
     FIG. 2 is a perspective view showing an outer appearance of a linear cam ring of the varifocal lens barrel of FIG.  1 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to the drawings in detail, and in particular to FIG. 1 showing of a lens barrel with a varifocal lens system installed therein in accordance with a preferred embodiment of the present invention, a varifocal lens  10  comprises a lens barrel  10 A and a varifocal lens system  10 B installed in the lens barrel  10 A. The varifocal lens system  10 A comprises a focusing lens element  12 , a zooming lens element  14  and a master lens element  16  arranged in order from an object end along an optical axis P. The lens barrel  10 A has a stationary cylindrical barrel  22 , namely a stationary cam ring which is formed by two integral parts, i.e. a larger diameter front part and a smaller diameter rear part, a rotatable cylindrical barrel  24 , namely a focusing cam ring, which is externally fitted onto the larger diameter front part of the stationary cam ring  22  for rotation relative to the stationary cam ring  22 , a rotatable cylindrical barrel  34 , namely a zooming ring, which is externally fitted onto the larger diameter front part of the stationary cam ring  22  for rotation relative to the stationary cam ring  22 , a rotatable cylindrical barrel  32 , namely a zooming cam ring, which is internally fitted into the smaller diameter rear part of the stationary cam ring  22  for rotation relative to the stationary cam ring  22 , The focusing cam ring  24  is arranged coaxially with and in front of the zooming ring  34  in the axial direction P and operationally linked to the zooming ring  34  by means of a linking mechanism (not shown) so as to keep the varifocal lens system  10 B remaining focused on an object. Such a linking mechanism is known in various forms in the art and may take any well known form. The stationary cam ring  22  is formed with a plurality of linear cam slots  22 A (only two linear cam slots are shown in FIG. 1) formed and arranged at regular angular intervals in the larger diameter front part thereof and extend in the axial direction P, a plurality of internal curvilinear cam grooves  22 B (only one curvilinear cam groove is shown in FIG. 1) formed in the smaller diameter part thereof, an external peripheral groove  22 C formed in the larger diameter front part thereof, a flange  22 D extending radially outward from the front end thereof, and an annular shoulder  22 E formed at the rear end thereof. 
     The focusing cam ring  24  is formed with a plurality of internal curvilinear cam grooves  24 A (only two linear cam grooves are shown in FIG. 1) arranged at regular angular intervals so as to spatially intersect the linear cam slots  22 A of the stationary cam ring  22 , respectively, and has a rear annular flange  24 B extending radially inward. The zooming cam ring  32  is formed with a linear cam slot  32 A which extends along the entire length of the zooming cam ring  32  in the axial direction P and has a front annular flange  32 C extending radially outward to a vertical connecting wall  22 F between the larger and smaller diameter parts of the stationary cam ring  22  and a rear contact jaw  32 B extending radially outward so as to be received by the annular shoulder  22 E of the stationary cam ring  22 . These front annular flange  32 C and the rear contact jaw  32 B are preferably formed integrally with the zooming cam ring  32  and, however, may be separately made and secured to the zooming ring. 
     A moveable annular lens holder  18  which the focusing lens element  12  fixedly holds therein is provided with a plurality of cam follower pins  20  (only two cam follower pins are shown in FIG. 1) which radially extend and is installed within the large diameter front part of the stationary cam ring  22  with the cam follower pins  20  passing through the linear cam slots  22 A of the stationary cam ring  22 , respectively, and received in the curvilinear cam grooves  24 A of the focusing cam ring  24 , respectively. A moveable annular lens holder  28  which fixedly holds the zooming lens element  14  therein is provided with a plurality of cam follower pins  30  (only one can follower pin is shown in FIG. 1) which radially extends and is installed within the zooming cam ring  32  with the cam follower pins  30  passing through the linear cam slot  32 A of the zooming cam ring  32  and received in the internal curvilinear cam grooves  22 B of the stationary cam ring  22 . A stationary lens holder  36  which holds the master lens  16  is fixedly put between a mounting ring  38  by which the varifocal lens  10  is detachably mounted to a camera (not shown) and a stationary part  40  of the lens cylindrical ring  10 A where an iris diaphragm  42  is installed. This iris diaphragm  42  is driven by a built-in electric motor  44 . 
     The focusing cam ring  24  is fitted onto the stationary cam ring  22  with the rear annular flange  24 B in slide engagement with the peripheral groove  22 C, so that it is allowed to rotate with respect to the stationary cam ring  22  but kept from axial movement. A corrugated ring spring  23  is put between an top end of the focusing cam ring  24  and the radial flange  22 D of the stationary cam ring  22  so as to force the focusing cam ring  24  rearward and in consequence press the rear annular flange  24 B against a rear wall of the peripheral groove  22 C of the stationary cam ring  22  with an effect of eliminating axial play of the focusing cam ring  24  and being conducive to smooth rotation of the focusing cam ring  24  to a nicety. Selection of the spring constant of the corrugated ring spring  23  provides appropriate rotational torque of the focusing cam ring  24 . The focusing cam ring  24  is provided with an operating lever (focusing lever)  26  extending radially outward passing through a peripheral slot  11 A for external access. When turning the focusing cam ring  24  by pushing sideways the operating lever  26  in one of opposite directions, the focusing cam ring  24  forces the cam follower pins  20  of the lens holder  18  received in the curvilinear cam grooves  24 A, so that the cam follower pins  20  of the lens holder  18  is shifted forward or rearward in the linear cam slot  22 A of the stationary cam ring  22  following the curvilinear cam grooves  24 A according angles of rotation of the focusing cam ring  24 . As a result, the focusing lens element  12  is shifted along the optical axis P for focusing the varifocal lens system  10 B on a desired object. 
     The zooming ring  34  is integrally formed with a connecting ring  37  extending forward partly from the rear end thereof. Through the connecting ring the zooming ring  34  is operationally linked to the zooming cam ring  32 . The zooming ring  34  is provided with an operating lever (zooming lever)  27  extending radially outward passing through a peripheral slot  11 B for external access. When turning the zooming ring  34  by pushing sideways the operating lever  27  in one of opposite directions, the zooming ring  24  forces the zooming cam ring  32 , so as to force the cam follower pins  30  of the lens holder  28  to turn about the optical axis P and shift in the axial direction P following the curvilinear cam grooves  22 B of the stationary cam ring  22  according angles of rotation of the zooming ring  34 . As a result, the zooming lens element  14  is shifted along the optical axis P for adjusting the focal length of the varifocal lens system  10 B. As was previously described, the focusing cam ring  24  is operationally linked to the zooming ring  34  through the linking mechanism which causes rotation of the focusing cam ring  24  accompanying rotation of the zooming ring  34  such that the focusing lens  12  is shifted relatively to the axially moving zooming lens  14  so as to keep the varifocal lens system  10 B remaining focused on an object even during adjusting the focal length of the varifocal lens system  10 B. 
     The zooming cam ring  32  is fitted in the stationary cam ring  22  by holding the smaller diameter rear part of the stationary cam ring  22   32 B in the axial direction between the front annular flange  32 C and the rear contact jaw  32 B. A corrugated ring spring  33  is put between the front annular flange  32 C of the zooming cam ring  32  and the vertical connecting wall  22 F of the stationary cam ring  22  so as to force the zooming cam ring  32  forward and in consequence press the rear contact jaw  32 B against a front wall of the annular shoulder  22 E of the stationary cam ring  22  with an effect of eliminating axial play of the zooming cam ring  32  and being conducive to smooth rotation of the zooming cam ring  32  to a nicety. Selection of the spring constant of the corrugated ring spring  33  provides appropriate rotational torque of the zooming ring  34 . In this instance, in order to allow the rear contact jaw  32 B of the zooming cam ring  32  to pass through the interior of the stationary cam ring  22 , the linear cam slot  32 A extends from end to end of the zooming cam ring  32 . 
     In operation of the varifocal lens  10  thus constructed, when operating the zooming level  27  sideways to turn the zooming ring  34  in one of opposite directions, the zooming cam ring  34  is turned in the same direction with the rear contact jaw  32 B thereof keeping sliding contact with the annular shoulder  22 E of the stationary cam ring  22 . This contact slide between the contact jaw  32 B and the annular shoulder  22 E, which works as axial movement restraint means, eliminates the necessity of using a pressure member such as a brace ring for restraining axial play of the zooming cam ring  32  and keeping it in a given axial position relative to the stationary cam ring  22 . Moreover the zooming cam ring  32  is rotated with the contact jaw  32 B pressed against the wall of the shoulder  22 E by means of the corrugated ring spring  33  put between the stationary cam ring  22  and the zooming cam ring  32 , so as to keep the zooming cam ring  32  from rotation accompanied by axial play. On the other hand, when operating the focusing lever  26  sideways, the focusing cam ring  24  is turned with the rear annular flange  24 B remaining in engagement with the external peripheral groove  22 C of the stationary cam ring  22 . This engagement between the rear annular flange  24 B and the external peripheral groove  22 C, which works as axial play restraint means, eliminates the necessity of using a pressure member such as a brace ring for restraining axial play of the focusing cam ring  24  and keeping it in a given axial position relative to the stationary cam ring  22 . Moreover the focusing cam ring  24  is rotated with the rear annular flange  24 B pressed against the rear wall of the external periphery groove  22 C by means of the corrugated ring spring  23  put between the stationary cam ring  22  and the focusing cam ring  24 , so as to keep the focusing cam ring  24  from rotation accompanied by axial play. 
     In the lens barrel  10 A described above, the focusing cam ring  24  may be placed inside the stationary cam ring  22 . Further, the rear annular flange  24 B of the focusing cam ring  24  and the external periphery groove  22 C of the stationary cam ring may be replaced with each other. Further, the axial play restraint means may be provided in either one of the focusing cam ring and the zooming cam ring. The corrugated ring spring  23  or  33  may be replaced with any type of spring that forces the focusing cam ring  24  or the zooming cam ring  32  in the axial direction. 
     Although the present invention has been described in connection with the lens barrel  10 A of the varifocal lens  10  which remains focused on an object even during adjusting the focal length thereof, it is applicable to lens barrels which comprises at least two cam rings for shifting lens component of a lens system installed in the lens barrel. 
     It is to be understood that although the present invention has been fully described by way of the preferred embodiments thereof with reference to the accompanying drawings, various variant and other embodiments may occur to those skilled in the art. Unless these variants and embodiment depart from the scope of the present invention, they are intended to be covered by the following claims.