Abstract:
A lens device includes a plurality of lens groups, a lens holder for holding each lens group, a cam barrel for receiving the lens holder therein so as to allow axial movement of the lens holder, and a cam mechanism having cam slots formed in the cam barrel and cam followers provided on the lens holder in slide engagement with the cam slots, respectively, through which rotation of the cam barrel causes the axial movement of the lens holder. The lens holder includes a lens mounting frame for fixedly mounting the lens group therein; and a union collar fixedly coupled to the lens mounting frame; and the cam followers are fix to the union collar.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to an optical lens device including a plurality of lens groups movably mounted in a cam barrel so as to move in an axial direction following rotation of the cam barrel, and, more particularly, to improvement of a structure of a lens holder for mounting a lens group in a cam barrel, and a process of assembling the lens device.  
         [0003]     2. Description of Related Art  
         [0004]     Various types of zoom lenses are nowadays widely used for optical instruments such as photographic cameras and optical projectors. Such a zoom lens comprises an optical lens system consisting of a plurality of lens groups and lens barrels mounting the lens groups therein so as to cause relative movement of the lens groups in an axial direction for focusing and zooming by rotating one or more lens barrels. Each lens group consisting of one or more optical lens elements is fixedly held in a lens holder provided with a plurality of, for example three, cam followers disposed at regular angular intervals and extending radially from the peripheral surface of the lens holder. The lens barrels include a zooming cam barrel having zooming cam slots and a stationary cam barrel having rectilinear guide cam slots. These zooming cam slots and rectilinear guide slots receive the cam followers of the lens holder, respectively, so as to move the lens holder rectilinearly in an axial direction according to rotated angles of the zooming cam barrel. Zoom lenses of this type are known from, for example, Published Japanese Patent Application Nos. 11-326734 and 2000-321476.  
         [0005]     In order to form high quality images, the zoom lens should consists of lens groups precisely aligned an optical axis of the zoom lens system. It is essential for achieving such precise alignment of the lens groups to mount each lens group in a lens holder formed with high parallelism and having cam followers arranged precisely in position The lens holder is generally formed of plastic using injection molding. Because the lens holder has an undercut between a lens holding portion and a cam follower mounting portion, it is conventional to use slide molds in the injection molding.  
         [0006]     Since the injection molding with slide molds encounters not only deterioration in molding accuracy, it has been hard to mold a lens mounting member and cam followers of the lens holder with high accuracy but also an increase in molding cost.  
       SUMMARY OF THE INVENTION  
       [0007]     It is therefore an object of the present invention to provide a high precision, low cost lens holder for a lens device that is capable of being installed in a lens barrel with high accuracy.  
         [0008]     The foregoing object is accomplished by a lens holder comprising a lens mounting frame for fixedly mounting a lens or a lens group therein and a union collar coupled to the lens mounting frame. The union collar is provided with a plurality of cam followers arranged on an outer periphery thereof. The union collar and the lens mounting frame are coupled to each other preferably by press-fitting. Otherwise, the union collar and the lens mounting frame may be coupled together through coupling means such as comprising retainer claws formed on either one of the lens mounting frame and the union collar and flexible hooks formed on the other or comprising projections extending radially outward from both lens mounting frame and union collar and resilient fasteners for fastening respective pairs of the projections of the lens mounting frame and the union collar, or may be coupled together with an adhesion bond or set screws.  
         [0009]     The process for assembling the lens device equipped with the lens holder includes the steps of assembling the union collars into a cam barrel and fixedly coupling the lens mounting frames with lens groups fixedly mounted therein, respectively, to the union collars together, respectively. Upon assembling the union collars into the cam barrel, the union colors are detachably mounted on a fixture in predetermined positions, respectively, and assembled into the cam barrel by inserting and snugly fitting the fixture in predetermined axial position in the cam barrel.  
         [0010]     According to the lens holder for a lens device that comprises the lens mounting frame for fixedly mounting a lens or a lens group therein and the union collar with cam followers prepared separately eliminates the use of slide molds for formation of the lens holder, realizes high accuracy, low cost lens holders and easily improves optical performance of the lens device. Further, since the union collar is provided commonly to lens holders for a plurality of lenses or lens groups, it is realized to reduce initial cost. Furthermore, in the case where a lens group has high sensitivity on its optical design, the separate structure of the lens holder enables eccentricity adjustment between the lens mounting frame and the union collar, so that fine optical axis alignment of the lens device is accomplished. This leads to enhanced image quality. Coupling of the lens mounting frame and the union collar is easily achieved by press-fitting, a simple structure of coupling means, adhesion bond or set screws.  
         [0011]     Since the assembling process comprises the steps of assembling the union collars into a cam barrel and, thereafter, fixedly coupling the lens mounting frames to the union collars together, the union collar is assembled to the cam barrel with high accuracy, so that the lens mounting frame and the cam barrel are coupled with increased accuracy. The use of the fixture upon assembling a plurality of the union collars to the cam barrel enables easy positional adjustment between the cam barrel and the union collars and between the union collars themselves. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]     The foregoing and other objects and features of the present invention will be clearly understood from the following detailed description when reading with reference to the accompanying drawings, wherein the same reference signs have been used to denote same or similar parts throughout the drawings, and in which:  
         [0013]      FIG. 1A  is a cross sectional view of an image projection unit including a zoom lens according to an embodiment of the present invention;  
         [0014]      FIG. 1B  is an enlarged cross sectional view of a cam followers of a zooming cam barrel;  
         [0015]      FIG. 1C  is an enlarged cross sectional view of a coupling structure between a lens mounting frame and a union collar of a lens holder,  
         [0016]      FIG. 1D  is an enlarged cross sectional view of a cam followers of a union collar of a lens holder,  
         [0017]      FIG. 2  is an exploded perspective view of lens barrels and its associated parts for a zooming mechanism;  
         [0018]      FIG. 3  is an exploded perspective view of a lens holder for a second lens group;  
         [0019]      FIG. 4  is an exploded perspective view of a lens holder for a third lens group;  
         [0020]      FIG. 5  is a flowchart illustrating a process of assembling the zoom lens;  
         [0021]      FIG. 6  is a perspective view of an external appearance of a fixture used in the zoom lens assembling process;  
         [0022]      FIG. 7  is a perspective view showing the step of assembling union collars into a zooming cam barrel;  
         [0023]      FIG. 8  is a cross sectional view showing the step of assembling cam followers to the union collars;  
         [0024]      FIG. 9  is a cross sectional view showing the step of assembling second and third lens mounting frame to the union collars; and  
         [0025]      FIGS. 10A through 10D  are cross-sectional views showing alternative coupling structures for coupling a lens mounting frame and a union collar together. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0026]     Referring to the accompanying drawings in detail, and in particular, to  FIGS. 1A through 1D  showing an image projection unit  2  of a projector (not shown), the image projection init  2  comprises a zoom lens  3 , a dichroic prism  4 , a transmission image display  5  such as a liquid crystal display (LCD), and a projection lamp  6 . Light emanating from the projection lamp  5  filters out the transmission image display  5  and impinges on the dichroic prism  4 . Three primary color images (R, G and B images) displayed on the transmission image display  5  are combined as a color image by the dichroic prism and projected by the zoom lens  3  onto a screen remote from the projector. The zoom lens  3  has a zoom lens system comprising four lens groups, namely a first lens group  9  comprising a lens  9   a  that that is operative as a front converter or focusing lens, a second lens group  10  comprising a lens  10   a  that is operative as a variater lens, a third lens group  11  comprising a lens  11   a  that is operative as a compensator lens, and a fourth lens group  12  comprising first and second lenses  12   a  and  12   b  that are operative as a relay lens. The zoom lens system is mounted within a lens barrel including a stationary lens barrel  14 , a focusing lens barrel  15 , a relay lens barrel  16 , an external barrel  17 , a manually operative focusing ring  18 , a zooming cam barrel  19  and a manually operative zooming ring  20 . The zoom lens  3  is detachably mounted to the projector including the dichroic prism  4 , the transmission image display  5  and the projection lamp  6  through the external barrel  17 . It is preferred that the zoom lens  3  is mounted so that the external barrel  17  is hidden inside the projector housing. Zooming is performed by manually rotating the zooming ring  20  so as to move the second lens group  10  and the third lens group  11  relatively to each other in an axial direction Focusing is performed by manually rotating the focusing ring  19  so as to move the first lens group  9  in an axial direction.  
         [0027]     Referring to  FIG. 2 , the stationary barrel  14  has three circumferential zooming cam slots  24  arranged at regular angular intervals in a circumferential direction in the wall, and three rectilinear axial guide slots  25  extending axially and arranged at regular angular intervals in a circumferential direction in the wall. The zooming cam barrel  19  has three circumferential zooming cam slots  38  arranged at regular angular intervals in a circumferential direction in the wall for the second lens group  10  and three circumferential zooming cam slots  39  arranged at regular angular intervals in a circumferential direction in the wall for the third lens group  10 . The stationary barrel  14  holds the first lens group  9  and the fourth lens group  12  at its front and rear ends, respectively. Specifically, the first lens group  9 , namely the focusing lens  9   a , is fixedly mounted in the focusing lens barrel  15 . The fourth lens group  12 , namely the relay lenses  12   a  and  12   b , is fixedly mounted in the relay lens barrel  16 . The focusing lens barrel  15  is rotationally and axially movably mounted within the stationary barrel  14  through helicoid coupling between external helicoid  30  threads on a rear wall of the focusing lens barrel  15  and internal helicoid threads on a front wall of the stationary barrel  14 . The focusing ring  18  fixedly mounted on the focusing lens barrel  15  is manually operated to rotate the focusing lens barrel  15  so as to move the focusing lens  9   a  back and forth in an axial direction for focusing the zoom lens  3  on an intended object. The focusing lens barrel  15  is prevented from coming off from the stationary barrel  14  in a well known manner. The stationary barrel  14  and the relay lens barrel  16  are fixedly mounted within the external barrel  17 .  
         [0028]     The zooming cam barrel  19  is provided with three cam followers  33  arranged at regular angular intervals in a circumferential direction in the wall and is rotationally mounted within the stationary barrel  14 . The cam followers  33  are received for slide movement in the circumferential zooming cam slots  24  of the stationary barrel  14 . Each of the cam followers  33  comprises a cam follower seat  35  secured to the zooming cam barrel  19  by a set screw  35  and a cam follower roller  36  supported for rotation between the cam follower seat  35  and the set screw  34 . The cam follower roller  36  rotates within the circumferential zooming cam slot  24  so as to allow smooth slide movement of the cam follower  33  in the circumferential zooming cam slot  24  during relative rotation between the zooming lens barrel  19  and the stationary barrel  14 . As shown in  FIG. 1B . The cam follower  33  extends passing through the circumferential zooming cam slot  24  of the stationary barrel  14  and is received for slide movement in a rectilinear axial groove  20   a  formed in the interior wall of the zooming ring  20 . The zooming ring  19  is manually operated to rotate the zooming cam barrel  19 , so as thereby to move the zooming cam barrel  19  back and forth in an axial direction according to relative angular positions of the zooming cam barrel  19  relative to the stationary barrel  14 .  
         [0029]     The second lens group  10 , namely the lens  10   a , is fixedly mounted in a lens holder  45  provided with three cam followers  40  arranged at regular angular intervals in a circumferential direction on the external wall as will be described in detail later. The cam followers  40  extend passing through the circumferential zooming cam slots  38  of the zooming cam barrel  19 , respectively, and are received in the rectilinear axial guide slots  25 , respectively. Similarly, the third lens group  11 , namely the lens  11   a , is fixedly mounted in a lens holder  57  provided with three can followers  41  arranged at regular angular intervals in a circumferential direction on the external wall as will be described in detail later. The cam followers  41  extend passing through the circumferential zooming cam slots  39  of the zooming cam barrel  19 , respectively, and are received in the rectilinear axial guide slots  25 , respectively. Relative rotation between the zooming cam barrel  19  and the stationary barrel  14  that is caused by manual operation of the zooming ring  20  causes axial movement of the second and third lens holders  45  and  57 , and hence the second and third lenses  10   a  and  11   a , independently according to angular positions of the cam followers  40  and  41  with respect to the circumferential zooming cam slots  38  and  39 , respectively. As a result, the second and third lens groups  10  and  11  move in an axial direction so as thereby to change an axial distance therebetween for linearly varying the focal length of the zoom lens system.  
         [0030]     Referring to  FIG. 3 , the lens holder  45  for the second lens group  10  comprises a generally cylindrically-shaped lens mounting frame  46  having a tail covert  46   a  formed as one integral piece so as to fixedly mount the lens  11   a  therein and a union collar  47 . The union collar  60  is tightly coupled to the cylindrical lens mounting frame  46  together by press-fitting the union collar  47  onto the tail covert  46   a  as will be described later. Further, the lens holder  45  is provided with three cam followers  40  arranged at regular angular intervals in a circumferential direction on the external wall of the annular coupling frame  47 . Each of the corn followers  40  comprises upper and lower cam follower rollers  53  and  54  which are supported for rotation a cam seat  52  by a set screw a set screw  51  engaged with a threaded boss  52  secured to the external wall of the union collar  47 . The upper and lower cam follower rollers  53  and  54  rotate independently within the circumferential zooming cam slot  38  of the zooming cam barrel  19  and the rectilinear axial guide slots  25  of the stationary barrel  14 , respectively, so as thereby to allow smooth slide movement of the cam follower  40  in the circumferential zooming cam slot  38  and the rectilinear axial guide slots  25 .  
         [0031]     The union collar  47  is press fitted onto the cylindrical lens mounting frame  46 . As shown in  FIG. 1C , the annual frame  47  is provided with circumferential protrusions  47   b  and  47   c  formed over the internal wall thereof. Each of the circumferential protrusions  47   b  and  47   c  has an external diameter slightly smaller than an external diameter of the tail covert  46   a  of the cylindrical lens mounting frame  46  so as to be coupled to the tail covert  46   a  through shrink fitting. Further, the annual frame  47  is provided with circular protrusions  47   d  formed on the end wall thereof. The circular protrusion  47   d  is brought into abutment against a vertical shoulder of the lens mounting frame  46   a  so as thereby to position the union collar  47  in the axial direction with respect to the lens mounting frame  46 .  
         [0032]     Referring to  FIG. 4 , the lens holder  57  for the third lens group  11  comprises a generally cylindrically-shaped lens mounting frame  59  having a tail rear covert  59   a  formed as one integral piece so as to fixedly mount the lens  11   a  therein and a union collar  60 . The union collar  60  is tightly coupled to the cylindrical lens mounting frame  59  together by press-fitting the union collar  60  onto the tail covert  46   a  Further, the lens holder  57  is provided with three cam followers  41  arranged at regular angular intervals in a circumferential direction on the external wall of the union collar  60 . Similarly to the cam followers  40  of the lens holder  45  for the second lens group  10   a , each of the corn followers  41  comprises upper and lower cam follower rollers  53  and  54  which are supported for rotation a cam seat  52  by a set screw  51  engaged with a threaded boss  52  secured to the external wall of the union collar  60 . As shown in  FIG. 1D  in detail, The upper and lower cam follower rollers  53  and  54  rotate independently within the circumferential zooming cam slot  39  of the zooming cam barrel  19  and the rectilinear axial guide slots  25  of the stationary barrel  14 , respectively, so as thereby to allow smooth slide movement of the cam follower  41  in the circumferential zooming cam slot  39  and the rectilinear axial guide slots  25 .  
         [0033]     Each of lens holders  45  and  57  are formed in injection molding, not as one integral piece as it always has been in the past, but as two separate pieces in this embodiment. If these cylindrical lens mounting frame  46 ,  59  and union collar  47 ,  60  were formed as one integral piece, the mold needs a number of slide parts which are often causative of a cost rise and deterioration in injection accuracy. However, since these cylindrical lens mounting frame  46 ,  59  and union collar  47 ,  60  are formed separately as two independent pieces, the molds for these individual parts are made simple in configuration. This simple configuration of the molds leads to in a reduction of manufacturing cost. Furthermore, in the case where the zoom lens system has high group sensitivity on its optical design, the separate structure of the lens holder  45 ,  57  enables eccentricity adjustment of the lens  10   a ,  11   a  so as to realize fine optical axis alignment of the zoom lens system. Furthermore, these union collars  47  and  60  including the cam followers  40  and  41  may be identical to each other so as to reduce an initial cost of the zoom lens.  
         [0034]      FIG. 5  shows a flowchart illustrating an assembling process of the zoom lens  3 . In the assembling process, a fixture  63  is used. The fixture  63 , that is made of plastic or metal and finished to high dimensional accuracy, comprises two cylindrical sections, namely a cylindrical positioning head  63   a  and a cylindrical shank  63   b . The cylindrical positioning head  63   a  is shaped in conformity with the bore of the stationary barrel  14  so as to be snugly fitted into said cam barrel  14  from the front (on opposite side to the projector). As shown in  FIG. 6 , the cylindrical shank  63   b  is shaped so as to receive and snugly mount the union collars  47  and  60  thereon and has positioning lines, namely axial positioning lines  63   c  and  63   d  and a circumferential positioning line  63   e  drawn thereon. First of all, in first step S 1 , the union collars  47  and  60  with the threaded bosses  50  secured thereto are detachably mounted onto the cylindrical shank  63   b  of the fixture  63  in strict accordance with the axial positioning lines  63   c  and  63   d , respectively, and adjusted in circumferential position by putting the threaded bosses  50  along the circumferential positioning line  63   e  as shown in  FIG. 7 . Subsequently, in step S 2 , the fixture  63  is inserted into the stationary barrel  14  in which the zooming cam barrel  19  is assembled beforehand until the positioning head  63   a  is snugly fitted in the stationary barrel  14  as shown in  FIG. 8 . The positioning head  63   a  at its rear edge is stopped by an internal shoulder  14   a  behind the internal helicoid threads  28  of the stationary barrel  14 . In this state, the threaded bosses  50  of the union collars  47  and  60  are positioned in line with the zooming cam slots  38  and  39  of the zooming cam barrel  19 , respectively, in an axial direction. Simultaneously, the fixture  60  is turned until the circumferential positioning line  63   e  is viewed through the rectilinear axial guide slot  25  of the stationary barrel  14 . In this way, both union collars  47  and  60  are correctly positioned in the axial and circumferential directions. In this state, the cam followers  40  and  41  are assembled to the union collars  47  and  60 , respectively, by screwing the set screws  51  into the threaded bosses  50 . The use of the positioning fixture  63  makes it quite easy and precise to assemble the union collars  47  and  60  to the zooming cam barrel  19  in the stationary barrel  14 . Furthermore, it is allowed to divert the union collars  47  and  60  to different zoom lenses when the zoom lens include lens groups different but similar in shape to the second and third lens groups  10  and  11 , respectively. In such a case, it is suffice to modify the lens holders  45  and  57  only.  
         [0035]     In step S 3 , after removing the positioning fixture  60  from the zooming cam barrel  19 , the lenses  10   a  and  11   a  fixedly mounted in the lens mounting frame  46  and  59  of the lens holders  45  and  57 , respectively, are inserted into the zooming cam barrel  19  from the front and the back, respectively, and then coupled to the union collars  47  and  60  together, respectively, by press fitting the tail coverts  46   a  and  59   a  into the union collars  47  and  60 , respectively. Since the union collars  47  and  60  have been precisely positioned, the lenses  10   a  and  11   a  are consequently placed respectively in position. This is contributive to increasing optical performance of the lenses  10   a  and  11   a  as parts of the zoom lens system. Thereafter, in steps S 4  through  7 , the zoom ring  20 , the relay lens barrel  16  with the relay lenses  12   a  and  12   b  fixedly mounted therein, the focusing barrel  15  and the focusing ring  18  are assembled to the zoom lens  3  preferably in this order.  
         [0036]     Although, in the above embodiment, coupling of the union collar  47  to the lens holder  45  together is performed by press fitting the union collar  47  onto the tail covert  46   a  of the lens mounting frame  46 , alternative coupling means may be employed as shown in FIGS.  10 (A) through  10 (D).  
         [0037]     As shown in  FIG. 10A , a lens holder  45 A for a lens  10   a  (a second lens group  10 ) comprises a generally cylindrically-shaped lens mounting frame  46 A and a union collar  47 A similar to the lens mounting frame  47  and union collar  47  of the previous embodiment, respectively. However, the lens mounting frame  46 A having a tail covert  46 Aa is provided with three retainer claws  71   a  formed as integral part extending radially outward from a rear edge thereof and arranged at regular angular intervals. The union collar  47 A is provided with three flexible hooks  71   b  formed as integral parts extending forward and arranged at regular angular intervals alternately with cam followers (not shown). The union collar  47 A is coupled to the lens mounting frame  46 A together by engaging the flexible hooks  71   b  with the retainer claws  71   a , respectively.  
         [0038]     As shown in  FIG. 10B , a lens holder  45 B for a lens  10   a  (a second lens group  10 ) comprises a generally cylindrically-shaped lens mounting frame  46 B and a union collar  47 B similar to the lens mounting frame  47  and union collar  47  of the previous embodiment, respectively. The lens mounting frame  46 B having a tail covert  46 Ba is provided with three retainer projections  73   a  formed as integral part extending radially outward from a rear edge thereof and arranged at regular angular intervals. The union collar  47 B is provided with three projections  73   b  formed as integral parts extending radially outward from a front edge thereof and arranged at regular angular intervals alternately with cam followers (not shown). The union collar  47 B is coupled to the lens mounting frame  46 A together by holding tight the projections  73   a  and  73   b  by resilient metal fasteners  73   c.    
         [0039]     As shown in  FIG. 10C , a lens holder  45 C for a lens  10   a  (a second lens group  10 ) comprises a generally cylindrically-shaped lens mounting frame  46 C having a tail covert  46 Ca that may be just the same as the union collar  46  of the previous embodiment and a union collar  47 C similar to the union collar  47  of the previous embodiment. The union collar  47 C is provided with three holes  75   b  arranged at regular angular intervals alternately with cam followers (not shown). The union collar  47 C is coupled to the lens mounting frame  46 A together by infusing adhesion bonds  75   c  into the holes  75   b  so as thereby to join the union collar  47 C to the tail covert  46 Ca of the lens mounting frame  46 C with the adhesive bonds  75   c.    
         [0040]     As shown in  FIG. 10D , a lens holder  45 D for a lens  10   a  (a second lens group  10 ) comprises a generally cylindrically-shaped lens mounting frame  46 D having a tail covert  46 Da that may be just the same as the union collar  46  of the previous embodiment and a union collar  47 D similar to the union collar  47  of the previous embodiment. The union collar  47 D is provided with three bosses with internal threads  77   b  preferably formed as integral parts extending radially outward and arranged at regular angular intervals alternately with cam followers (not shown). The union collar  47 D is coupled to the lens mounting frame  46 D together by fastening set screws  77   c  into the boss  77   b  until the set screws  77   c  bears against the tail covert  46 Da of the lens mounting frame  46 D.  
         [0041]     In the case of using an adhesion bond or set screws in order to couple the lens mounting frame and the union collar together, it is preferred to form slots or bores as access ways to the union collar in both stationary barrel and zooming cam barrel.  
         [0042]     Although, the above description has been directed to the zoom lens for use with projectors, nevertheless, the zoom lens of the present invention is suitably used in combination with optical instruments such as photographic cameras.  
         [0043]     It is to be understood that although the present invention has been described with regard to a preferred embodiments thereof, various other embodiments and variants may occur to those skilled in the art, which are within the scope and spirit of the invention, and such other embodiments and variants are intended to be covered by the following claims.