Abstract:
A zoom lens guide system employs air bearings to reduce mechanical shift of the zoom lens components, thus reducing measurement error. The air bearings provide greater stiffness, resulting in the reduction of mechanical shift. Orifice type or porous media air bearings can be used to provide a thin film between an external surface of the bearing and an inner surface of a barrel of the system, the bearing being mounted about a lens housing within the barrel. Guide pins include feed tubes connect the air bearings to an air supply while engaging a guide slot in the barrel and a cam slot in a zoom ring to effect selective axial motion of a lens housing.

Description:
BACKGROUND AND SUMMARY  
       [0001]     This invention relates to optical lens zoom systems, and more particularly to an improved guiding mechanism for controlling the moving parts or elements in such a lens system. It has long been customary in zoom lens systems of the type described, to employ ball bearing rollers for guiding moving parts of a zoom lens within the lens barrel. It has also been customary heretofore to employ in such lens barrel various parts which are mounted for sliding movement relative to each other to effect variation in magnification of an observed object. Lenses of the type described are frequently employed in motion picture photography and television broadcasting, which usually demand the highest of image quality. Typically such a zoom lens system includes in the lens barrel two moveable sets of lenses, the first or forward group of lenses being disposed to vary the angle of view, the second set being operative to restore the focus upon adjustment of the first group.  
         [0002]     Among the disadvantages or prior such zoom lenses has been the difficulty encountered in accurately, and in some instances quietly, moving the respective sets of lenses. Such prior art devices also require a nearly polished finish on the inner bore wall of the lens barrel, thus contributing significantly to the manufacturing costs of the lens systems.  
         [0003]     Accordingly, it is an object of this invention to provide an improved optical zoom lens system of the type described in which the lenses can be moved accurately and with precision not heretofore available.  
         [0004]     Still another object of this invention is to provide an improved guiding mechanism for moving parts of an optical zoom lens system of the type described, which mechanism is easier to manufacture and is longer lasting than prior such guiding mechanisms.  
         [0005]     Other objects of the invention will be apparent hereinafter from the specification and from the recital of the appended claims, particularly when read in conjunction with the accompanying drawings.  
         [0006]     In typical metrological setups, mechanical bearings are used to support and actuate a zoom lens. However, mechanical shift of the zoom components can generate an optical images shift that is an error of measurement in the optical measuring machine. Various designs of mechanical bearings have been made to attempt to overcome this problem, but the shift and resultant error remain. For example, U.S. Pat. No. 6,507,705 to Kasha, the disclosure of which is hereby incorporated by reference in its entirety, discloses one of the most accurate guiding mechanisms available for moving parts in a zoom lens system. The tubular barrel of a zoom lens mechanism has secured in the bore thereof a plurality (three in the embodiment illustrated) of elongate, circular rods which are secure to the inner peripheral surface of the barrel to extend axially thereof and in angularly spaced relation to each other. Each of a plurality of cylindrically shaped lens housings are mounted coaxially in the bore of the barrel for axial adjustment therein by means of a plurality of sets of rollers on each housing, each of which sets on each housing has rolling, point engagement with a different one of the rails. One set of rollers on each housing is urged resiliently into rolling engagement with the associated rail, while the other two sets of rollers in such housing are rotatable about axes which are fixed with respect to the associated housing. Each housing has thereon a pin which projects through a slot in the barrel and into a cam groove formed in one of two different zoom or camming rings which are rotatably mounted on the barrel. The rolling point contact between the rails and the rollers on the housing, significantly improve the accuracy and life of the mechanism. However, even this system can suffer measurement error when mechanical shift of its mechanical bearings occurs.  
         [0007]     Embodiments offer an alternative to the mechanical bearings of the prior art. Air bearings are used in embodiments to guide a zoom lens, eliminating mechanical bearings and the related mechanical and image shift. The air bearings have higher stiffness than the mechanical bearings of the prior art, minimizing the shift of moving components in the lens system. Thus, the zoom lens system guided by an air bearing system results in greater accuracy, overcoming the problems of the prior art. 
     
    
     BRIEF DECRIPTION OF THE DRAWINGS  
       [0008]      FIG. 1  is a cross sectional view of an elongate cylindrical lens barrel according to embodiments containing two zoom lens housings or cells and the improved mechanism for adjusting the housings longitudinally of the lens barrel, the zoom ring containing the cam slots for manipulating the lens housings being shown only fragmentarily.  
         [0009]      FIG. 2  is an end view of the lens barrel and associated parts as seen when looking in the lower end of the lens barrel as shown in  FIG. 1 .  
         [0010]      FIG. 3  is an elevation of an air bearing used in embodiments.  
         [0011]      FIG. 4  is an elevation taken generally along the line  4 - 4  in  FIG. 1  looking in the direction of the arrows, and illustrating the pins/air supply posts of the two lens housings mounted for adjustment in the lens barrel and the cams in which they sit according to embodiments.  
         [0012]      FIG. 5  shows a schematic diagram of an air bearing based guiding mechanism according to embodiments.  
         [0013]      FIG. 6  shows a more detailed schematic diagram of another air beating of embodiments.  
         [0014]      FIG. 7  shows a schematic diagram of an air supply system for an air bearing of embodiments. 
     
    
     DETAILED DESCRIPTION  
       [0015]     This description sets forth an exemplary embodiment with reference to the accompanying Figures. This exemplary embodiment is not limiting, and variations are encompassed by embodiments.  
         [0016]     Referring now to the drawings in which like reference numerals refer to like parts, an optical gaging/metrological apparatus (not shown) of variable magnification includes a mechanism for positioning and optical component control. The optical components of embodiments can include a zoom lens optical imaging system  1  comprising a tubular lens barrel  10  with an inner sleeve portion  12  extending between flanges  13 ,  14  formed on opposite ends of the barrel  10 . The barrel  10  includes an inner bore wall  15 , and a mounting formation  16  can be included in one of the flanges  14  for mounting a component (not shown), such as a front lens. The barrel  10 , inner sleeve portion  12 , flanges  13 ,  14 , and inner bore wall  15  are all preferably coaxial in embodiments.  
         [0017]     In embodiments, at least one substantially cylindrical lens housing or cell  21  mounted for axial adjustment within the bore of barrel  10 . The lenses and mountings thereof in the housing(s)  21  may be of conventional design and therefore are not described in detail herein. In a manner to be described in greater detail, each lens housing  21  is supported by an air bearing  30  for axial adjustment in the lens barrel  10 . Each housing  21  can employ the same type of air bearing  30  in the same fashion, so the mounting arrangement will be described in detail in connection with only one lens housing  21  for convenience.  
         [0018]     Rotational motion between the at least one housing  21  and the barrel  10  is undesirable, so to prevent such rotational motion, a substantially cylindrical guide pin  22  is provided for each housing  21 , each pin  22  being secured at one end to one of the housings  21 . The other end of each pin  22  projects slidably into an elongate guide slot  17  in the inner sleeve portion  12  of the barrel  10 , the elongated slot  17  allowing motion/extension of the lens (housings)  21  longitudinally within the barrel  10 . Each of the pins  22  can additionally project beyond the slot  17  in the sleeve portion  12  of the barrel  10  and into a respective cam slot  41  formed in at least one zoom ring  40  rotatably mounted on the sleeve portion  12  of the barrel  10  for effecting axial adjustment of the housing  21  within the barrel  10 . In such a formation, the pin  22  becomes a cam follower, the cam slot  41  of the zoom ring  40  being the cam. The zoom ring  40  is mounted on section  12  of the lens barrel  10  for rotation relative thereto in a known manner to effect corresponding axial movements of the lens housings  21  in barrel  10 . While a single zoom ring  40  is shown in the FIGS. as operating two housings  21 , it should be apparent that one ring  40  could be used for each lens housing  21 . Further, it should also be apparent that only one or more than two lens housings  21  could be employed with corresponding guide pins  22 , air bearings  30 , and cam slots  41 .  
         [0019]     As noted above, embodiments improve upon the problems associated with mechanical bearings in a zoom lens system by using air bearings  30  in place of mechanical bearings. The air bearings  30  provide a fluid movement with more accurate positioning with negligible friction losses. To accomplish this, embodiments provide that the guide pin  22  of each housing  21  is hollow, with a feed tube  31  extending therethrough. Each guide pin  22  can be connected to an air supply  60  via a supply line  61 . To enhance retention of the supply line  61  on the guide pin  22 , ridges  62  can be formed on the guide pin  22 . Since the pin  22  can move along the longitudinal axis of the optical system in the slot  17 , the air supply lines  61  are preferably flexible enough to continue supplying air at all operating positions of the system.  
         [0020]     The feed tube  31  conducts air from the supply line  61  to the air being  30  through the guide pins  22 . Embodiments preferably employ porous media type air bearings for the air bearings  30 , though air bearings of the orifice type can also be employed. Where porous media air bearings are used, the feed tube  31  delivers air to the porous medium  32 , which conducts the air through itself and forms an air film  33  between an external surface  34  of the air bearing  30  and the inner surface  15  of the sleeve portion  12  of the barrel  10 . Where orifice type air bearings are used, the feed tube  31  delivers air to an internal distribution system that conducts the air to one or more orifices  35  to form the air film  33  between the outer surface  34  of the air bearing  30  and the inner surface  15  of the barrel  10 . As is known in the bearing art, the thin film  33  of pressurized air formed in the air bearing  30  supports a load, and, in this case, provides fluid, highly controlled movement. Air bearings are different from mechanical bearings in that there is no contact between the supported and supporting surfaces during operation. The thin film of pressurized air between these solid surfaces supplies the vehicle for force transfer.  
         [0021]     Both the porous media and orifice types of air bearings are designed so that while air is constantly dissipating from the bearing site, pressurized air is flowing into the bearing to maintain the pressure and support the solid surfaces. In embodiments, the air dissipates through the film and pressurized air flows into the bearing via the feed tube  31 . Air bearings thus provide a substantially frictionless load-bearing interface between surfaces that would otherwise be in contact with each other. Since air bearings are non-contact, they avoid the traditional bearing-related problems of friction, wear, and the need for a lubricant.  
         [0022]     The air bearing  30  of embodiments can be mounted, for example, on the external surface a respective lens housing  21 . Air from the supply  60  thus travels through the supply lines  61  through the pins/cams  22  to the air bearings  30 , which maintain the housings  21  substantially at a desired distance from the barrel inner surface  15 . Where the air bearings  30  are of the porous medium type, embodiments can have a ring of the porous medium  32  arranged on the external surface of each housing  21  with the air film side facing the inner surface  15  of the barrel  10 . To ensure proper distribution of pressurized air to the porous medium, an air conduit  36  can be formed along an inner surface of the ring of porous medium and operatively connected to the air supply  60  via the pin  22 . As seen in  FIG. 6 , the porous medium  32  conducts the air to its outer surface to form the air film between the external surface of the bearing  30  and the inner surface  15  of the barrel  10 . In embodiments where the air bearings  30  are of the orifice type, the air bearings  30  can each include an air conduit  36  and a plurality of substantially equally-spaced orifices  35  directed at the barrel  10  to form the supportive air film  33 , as seen in  FIG. 5 . To further enhance air film distribution, more than one ring can be used.  
         [0023]     An air supply, preferably a remote air supply  60 , is fluidically connected to the air bearings via the cam followers/pins  22  extending through the slots in the barrel. The air supply in embodiments is controlled and monitored by a regulator  62  and filtered by a particle filter  63  to prevent contamination of the system. When the zoom ring  40  mounted on the barrel  10  rotates, the cam/slot  41  controls the axial position of the lens housing  21 , resulting in longitudinal, reciprocal motion of the cam follower/pin  22 . The longitudinal/reciprocal motion of the cam follower/pin  22  controls the magnification produced by the lens system. As seen, for example, in  FIG. 7 , an air supply system usable with embodiments can include a supply  60 , such as a compressor, a regulator/coarse filter  62 ,  63 , a fine filter  64 , and supply lines  61 .  
         [0024]     From the foregoing it will be apparent that the present invention provides a very accurate and smooth mechanism or means for repeatedly and accurately adjusting the zoom lenses of the type carried by a housing  21  accurately to achieve the desired magnification and focus of the mechanism. The elimination of contact between the lens housings  21  and the barrel  10  not only reduces wear of the equipment during axial adjustment of the housings  21 , but also reduces the effort required to make such adjustments and error introduced by contact. The air bearing arrangement of embodiments provides precision motion of the lens housings  21  without requiring the extremely hard, smooth contact surfaces and/or highly polished finish on the interior surface  15  of the barrel  10  necessary for the mechanical arrangements of the prior art.  
         [0025]     It will be appreciated that various of the above-disclosed and other features and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. Also that various presently unforeseen or unanticipated alternatives, modifications, variations or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following claims.