Abstract:
A lens barrel of the present invention includes a first zoom frame and a second zoom frame which are moved frontward and rearward by a cam frame. The first zoom frame holds a first lens group, and the second zoom frame contacts and presses a second-group frame. Four guide shafts are fixed to the first zoom frame, and directly and slidably support the second-group frame which holds a second lens group or a third-group frame which holds a third lens group. Therefore, the deviation between the optical axes of the second lens group and the third lens group from the first lens group is reduced. In the lens barrel, the supporting structure of the frame members is simplified, the supporting accuracy of the frame members is increased, and the misalignment of the optical axes of the lens groups is prevented.

Description:
[0001]    This application claims benefit of Japanese Application No. 2001-101497 filed in Japan on Mar. 30, 2001, the contents of which are incorporated by this reference.  
         BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates to the structure of frontward and rearward movable frame members which constitute a lens barrel.  
           [0004]    2. Related Art Statement  
           [0005]    A zoom lens barrel disclosed in Japanese Unexamined Patent Application Publication No. 11-64714 concerning the configuration of a lens barrel includes a first-group tube for supporting a first lens group, and a second-group tube for supporting a second lens group (focusing lens). The first-group tube is supported by a cam frame, and the second-group tube is supported by a zoom tube via a guide shaft. The zoom tube is supported by the cam frame.  
           [0006]    In the above zoom lens barrel, multiple supporting members, such as the first-group tube, the cam frame, the zoom tube, and the guide shaft, are interposed between the first lens group and the second lens group, as described above. Therefore, a deviation between optical axes of the first lens group and the second lens group may increase, and this makes it difficult to achieve a high optical performance.  
         SUMMARY OF THE INVENTION  
         [0007]    The present invention has been made to overcome the above problems, and an object of the invention is to provide a lens barrel with a simple configuration in which frame members are supported with high precision and in which a deviation between the optical axes of lens groups is reduced.  
           [0008]    In order to achieve the above object, according to an aspect of the present invention, there is provided a lens barrel having a plurality of lens groups including at least a first lens group and a second lens group which are movable along an optical axis, and also comprising a cam frame having a first cam and a second cam for driving the first lens group and the second lens group along the optical axis during a zooming operation, a first moving frame which holds the first lens group and is driven along the optical axis by the first cam, a second moving frame which is driven along the optical axis by the second cam, a third moving frame which holds the second lens group and is supported by the first moving frame so that it can move along the optical axis relative to the first moving frame, and a driving device mounted in the second moving frame so as to drive the third moving frame relative to the first moving frame and the second moving frame along the optical axis.  
           [0009]    According to another aspect of the present invention, there is provided a lens barrel having a plurality of lens groups including at least a first lens group, a second lens group, and a third lens group which are movable along an optical axis, and also comprising a first-lens-group moving frame which holds the first lens group, a first and a second guide members formed in the first-lens-group moving frame so as to extend along the optical axis, a second-lens-group moving frame which holds the second lens group and which is guided slidably only along the optical axis relative to the first-lens-group moving frame while the positional accuracy of the second lens group with respect to the optical axis of the first lens group is ensured to be within a predetermined range by the first guide member, and a third-lens-group moving frame which holds the third lens group and which is guided slidably only along the optical axis relative to the first-lens-group moving frame while the positional accuracy of the third lens group with respect to the optical axis of the first lens group is ensured to be within a predetermined range by the second guide member.  
           [0010]    Further objects, features, and advantages of the present invention will become apparent from the following description of the preferred embodiments with reference to the attached drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    [0011]FIG. 1 is a schematic view showing the configuration of a zoom lens barrel serving as a lens barrel according to an embodiment of the present invention.  
         [0012]    [0012]FIG. 2 is a sectional view showing a state in which a guide shaft is fixedly bonded to a zoom frame in the zoom lens barrel shown in FIG. 1.  
         [0013]    [0013]FIG. 3 is a sectional view showing a state in which a sleeve is fixedly bonded to a second-group frame or a third-group frame in the zoom lens barrel shown in FIG. 1. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0014]    An embodiment of the present invention will be described below with reference to the attached drawings.  
         [0015]    [0015]FIG. 1 is a schematic view showing the configuration of a zoom lens barrel serving as a lens barrel according to an embodiment of the present invention, FIG. 2 is a sectional view showing a state in which a guide shaft is fixedly bonded to a zoom frame in the zoom lens barrel shown in FIG. 1, and FIG. 3 is a sectional view showing a state in which a sleeve having the guide shaft slidably fitted therein is fixedly bonded to the zoom frame in the zoom lens barrel. In the following description, the object side is designated the front side, and the image formation side is designated the rear side.  
         [0016]    A zoom lens barrel  1  principally comprises a fixed frame  50  having a linear guide  2 , a cam frame  3  serving as a cam member, a first zoom frame  4  serving as a first moving frame (frame member) Which holds a first lens group  21 , a second zoom frame  5  serving as a second moving frame (frame member), a linear key member  6  which moves linearly, a second-group frame  7  serving as a third moving frame which holds a second lens group  22 , and a third-group frame  8  serving as a fourth moving frame (frame member) which holds a third lens group  23 . In the FIGS., C 1  to C 10  denote portions where the components are fixed.  
         [0017]    The cam frame  3  comprises a portion  51  which rotationally slides on the linear key member  6 , portions  52  and  53  which rotationally slide on the first zoom frame  4  and the second zoom frame  5 , respectively (more specifically, a fitting portion between the inner peripheral surface of the cam frame  3  and the outer peripheral surface of the zoom frame  4 , and a fitting portion between the inner peripheral surface of the cam frame  3  and the second zoom frame  5 ), a first cam  54 , and a second cam  55 . The cam frame  3  is rotationally driven by a cam-frame driving mechanism  58  so that it moves frontward and rearward relative to the fixed frame  50  between a collapsed position and a picture-taking position, and further it rotates at the picture-taking position so as to perform a zooming operation.  
         [0018]    The linear key member  6  is supported slidably along an optical axis O by the linear guide  2  of the fixed frame  50  via a guide portion  31  with its rotation regulated. Since the linear key member  6  is engaged with the rotational sliding portion  51  of the cam frame  3 , it moves frontward and rearward along the optical axis O together with the cam frame  3 .  
         [0019]    The first zoom frame  4  includes a peripheral sliding portion which is slidably fitted in the rotational sliding portion  52  of the cam frame  3 , a cam follower  56  fixed to the peripheral sliding portion, and a linear guide portion  32  slidably engaged with the linear key member  6 .  
         [0020]    The second zoom frame  5  includes a peripheral sliding portion slidably fitted in the rotational sliding portion  53  of the cam frame  3 , a cam follower  57  fixed to the peripheral sliding portion, and a linear guide portion  33  slidably engaged with the linear key member  6 .  
         [0021]    The cam followers  56  and  57  are respectively fitted to the first cam  54  and the second cam  55  of the cam frame  3 . When the cam frame  3  rotates, the first zoom frame  4  and the second zoom frame  5  are moved frontward and rearward along the optical axis O with the rotation thereof regulated by the linear key member  6 .  
         [0022]    Guide shafts  9  and  11  serving as sticklike guide members for movably supporting the second-group frame  7 , and guide shafts  12  and  14  serving as sticklike guide members for movably supporting the third-group frame  8  along the optical axis O are fixed to the first zoom frame  4  in parallel with the optical axis O.  
         [0023]    When fixed to the first zoom frame  4 , as shown in FIG. 2, the guide shafts  9 ,  11 ,  12 , and  14  are inserted into guide-shaft holding holes C 5 , C 6 , C 7 , and C 8  serving as fixing portions of the first zoom frame  4  with a clearance therein, and are supported together with the first zoom frame  4  by an assembly jig  101 . The guide shafts are held in parallel with the optical axis O while the positional accuracy thereof with respect to the optical axis of the first lens group  21  is ensured. An adhesive is applied into the clearance with the positional accuracy maintained, so that the first zoom frame  4  and the guide shafts are bonded to each other.  
         [0024]    The second-group frame  7  is supported slidably along the optical axis O by the guide shaft  9  and the guide shaft for preventing the rotation  11 . The guide shaft  9  is slidably fitted in a sleeve  34  fixed to the second-group frame  7 , and the guide shaft  11  is slidably engaged with an antirotation portion  35  of the second-group frame  7 . A second-group spring  10  made of a compression spring for serving as a forcing member is fitted on the guide shaft  9 . The second-group frame  7  is constantly forced rearward by the force of the second-group spring  10 .  
         [0025]    When fixed to the second-group frame  7 , the sleeve  34  is inserted into a sleeve-holding hole C 9  serving as a fixing portion of the second-group frame  7  with a clearance therein, and the second-group frame  7  and the guide shaft  9  fitted in the sleeve  34  are supported by an assembly jig  102 , as shown in FIG. 3. The sleeve  34  is held with a predetermined accuracy at a predetermined position relative to the optical axis of the second lens group  22  of the second-group frame  7  in parallel therewith. An adhesive is applied into the clearance in the sleeve  34  in the above holding state, so that the sleeve  34  and the second-group frame  7  are bonded to each other.  
         [0026]    The third-group frame  8  is supported slidably along the optical axis O by the guide shaft  12  and the guide shaft  14  for preventing the rotation. The guide shaft  12  slidably supports a sleeve  36  fixed to the third-group frame  8 , and the guide shaft  14  slidably supports an antirotation portion  37  of the third-group frame  8 . A third-group spring  13  made of a compression spring for serving as a forcing member is fitted on the guide shaft  12 . The third-group frame  8  is constantly forced rearward by the force of the third-group spring  13 .  
         [0027]    When fixed to the third-group frame  8 , the sleeve  36  is inserted into a sleeve-holding hole C 10  serving as a fixing portion of the third-group frame  8  with a clearance therein, and the third-group frame  8  and the guide shaft  12  fitted in the sleeve  36  are supported by the assembly jig  102 , as shown in FIG,  3 . The sleeve  36  is held with a predetermined accuracy at a predetermined position relative to the optical axis of the third lens group  23  of the third-group frame  8  in parallel therewith. An adhesive is applied into the clearance in the sleeve  36  in the above holding state, so that the sleeve  36  and the third-group frame  8  are bonded to each other.  
         [0028]    The second zoom frame  5  has a nut portion  41  formed along the optical axis O, and a feed screw  42 , which is rotationally driven by a focus driving section  59  incorporated in the second zoom frame  5 , is screwed in the nut portion  41 . A distal end portion  43  of the feed screw  42  is in contact with the second-group frame  7  in the optical axis direction.  
         [0029]    The cam frame  3  rotates, the second zoom frame  5  is moved frontward and rearward in the optical axis direction by the second cam  55 . With the frontward and rearward movement, the second-group frame  7  is pressed by the feed screw distal end portion  43 , and is moved frontward and rearward against the force of the second-group spring  10 . During the focusing operation, the feed screw  42  is rotationally driven by the focus driving section  59 , and the second-group frame  7  is pressed against the force of the second-group force  10 , thereby performing the focusing operation.  
         [0030]    When the zoom lens barrel  1  with the above-described configuration is placed in a picture-taking position, the third-group frame  8  is pressed rearward relative to the first zoom frame  4  by the force of the third-group spring  13 , and the sleeve  36  is held in contact with a stopper  38  formed at one end of the guide shaft  12 .  
         [0031]    When the zoom lens barrel  1  is placed in the collapsed position, the cam frame  3 , the first zoom frame  4 , and the second zoom frame  5  are retracted into the fixed frame  50  via the first and second cams  54  and  55  by the rotation of the cam frame  3 . The second-group frame  7  and the third-group frame  8  are moved forward closer to the first zoom frame  4  in the optical axis direction by a contact member (not shown), by which the second-group frame  7  and the third-group frame  8  are pressed, thereby compressing the springs  10  and  13 .  
         [0032]    In order to move the zoom lens barrel  1  from the collapsed position to the picture-taking wide-angle position, the cam frame  3  is rotationally driven by the cam-frame driving mechanism  58 , and the first zoom frame  4  is moved forward to the wide-angle position by the first cam  54 . In this case, the third-group frame  8  is also moved forward in contact with the stopper  38  while being forced rearward by the third-group spring  13 . The second zoom frame  5  is moved forward by the second cam  55 , and the second-group frame  7  is.,pressed and moved forward to the wide-angle position via the distal end portion  43  of the feed screw  42 , so that it is placed in a picture-taking state.  
         [0033]    In order to perform zooming from the wide-angle position to the telephoto position, the first zoom frame  4 , the second-group frame  7 , and the third-group frame  8  are moved forward to the telephoto position by rotating the cam frame  3 .  
         [0034]    For focusing operation, the feed screw  42  is rotated by the focus driving section  59 . Then, the distal end portion  43  is shifted by the rotation of the feed screw  42 , the second-group frame  7  is shifted by being pressed by the distal end portion  43 , and the relative distance between the second-group frame  7  and the first zoom frame  4  is changed, thereby carrying out focusing.  
         [0035]    In the above-described zoom lens barel  1  of this embodiment, the guide shafts  9 ,  11 ,  12 , and  14  are fixed to the first zoom frame  4  for holding the first lens group  21  with a predetermined accuracy. The second-group frame  7  which directly holds the second lens group  22  is slidably supported by the guide shafts  9  and  11 , and the third-group frame  8  which directly holds the third lens group  23  is slidably supported by the guide shafts  12  and  14 . This makes it possible to achieve a zoom lens barrel with high optical accuracy in which a deviation of the respective optical axis of the second lens, group  22  and the third lens group  23  from the optical axis of the first lens group  21  is minimized. Since the second-group frame  7  and the third-group frame  8  are directly supported by the first zoom frame  4 , as described above, assembly can be easily performed.  
         [0036]    The second-group frame  7  and the third-group frame  8  are not directly driven by the cam frame  3 , but are moved frontward and rearward via the second-zoom frame  5  or the first zoom frame  4 . Since vibrations resulting from the driving by the cam frame  3  are not directly transmitted to the second lens group  22  and the third lens group  23 , the frontward and rearward movement thereof is made smooth.  
         [0037]    Since the focus driving section  59  for driving the second-group frame  7  for focusing is not placed between the first zoom frame  4  and the second-group frame  7 , unnecessary components are not placed therebetween, the optical axis of the first lens group  21  and the optical axis of the second lens group  22  are not prone to be displaced from each other, the structure is simplified, and the supporting accuracy is enhanced.  
         [0038]    As described above, according to the lens barrel of the present invention, the supporting accuracy of a plurality of lens groups which are movably supported is enhanced, and the structure of the frame members for supporting the lens groups is simplified.  
         [0039]    While the present invention has been described with reference to what is presently considered to be the preferred embodiment, it is to be understood that the invention is not limited to the disclosed embodiment. On the contrary, the invention is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. The scope of the following claims is to be accorded with the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.