Abstract:
A motion control system is provided where a rotatable driven gear is held by bearings. The bearings are held inside a rotatable cam, where the cam has eccentricity between the outside and inside diameter. The outside diameter is held in a case that contains a driving gear. The backlash of the system is controlled by rotating the cam, which adjusts the center to center distance between the driving and driven gear.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 61/809,053, filed Apr. 5, 2013, the disclosure of which is hereby incorporated by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    Motion control systems are commonly used in the photographic and videographic industries to provide controlled movement to various types of equipment. For instance, for a given scene, a director may require a camera to move while the camera is tilted and panned all while the focus is being adjusted. While an operator could perform all of these functions manually by holding and manipulating the camera, a high level of precision and reproducibility is difficult, if not impossible. As such, mechanized motion control systems have been developed which allow for precise and repeatable movements. 
         [0003]    One basic element of a motion control system is a rotatable axis. The rotatable axis allows movement about one axis, such as a pan axis or a tilt axis. In a common embodiment, these rotatable axes are driven by a worm gear. As with any geared system, slop between the teeth of the respective gears can result in backlash, or lash, which can cause a jittery or uneven rotation. This slop can be minimized in a number of ways and has been the subject of many previous inventions. The prior art systems fail for difficulty in assembly and residual slop or binding of the gears. In many cases, prior systems include a pair of members, one above the worm gear and one below the worm gear, both being independently adjusted to move the worm gear toward or away from the worm. If these two members are adjusted differently, the worm and the worm gear can become unaligned and bind or cause wear on the system. As such, these previous structures are difficult to assemble and maintain. As such, an improved motion control system is needed. 
       SUMMARY OF THE INVENTION 
       [0004]    The present disclosure describes a motion control system having a worm and a gear. The worm is driven by a motor and transfers rotation to the worm gear, which in turn transfers motion to an external element, such as a pan or tilt head. Both the worm and the gear have teeth which interlock. For smooth motion, the gear must be located at a precise distance from the worm; having the worm and gear at an improper distance will result in binding, jittering or wear on the system. The cam controls the center to center distance between the driving and driven gear by moving the bearings that hold the driven gear. The cam moves both bearings in concert to maintain proper alignment. This prevents binding and improper gear mesh, which frequently happens when bearings are adjusted individually. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]    A preferred embodiment of this invention has been chosen wherein: 
           [0006]      FIG. 1  is a perspective view of the motion control system with the case in transparent; 
           [0007]      FIG. 2  is an exploded view of the gear assembly; 
           [0008]      FIG. 3  is section view  3 - 3  of the motion control system in  FIG. 1 ; 
           [0009]      FIG. 4  is a perspective view of the motion control system; 
           [0010]      FIG. 5  is a top view of the motion control system without the case; 
           [0011]      FIG. 6  is a side view of the motion control system without the case; and 
           [0012]      FIG. 7  is a top view of the cam from  FIG. 2  showing eccentricity. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0013]    The present disclosure describes a motion control system  10  which is suitable for providing precise and repeatable rotation to an object as is shown in  FIG. 1 . For purposes of illustration, the present motion control system  10  is described as used to rotate (such as pan or tilt) photographic equipment. Any reference to such camera equipment is merely illustrative of one use of the motion control system of the present disclosure. 
         [0014]    The motion control system  10  described herein is made up of a case  24  and a gearset  18 ,  FIG. 2 . The case  24  and gearset  18  are shown in  FIG. 4  and  FIG. 2 . The case includes a worm gear  12  which is driven by a motor  14  as shown in  FIG. 1 . The worm gear  12  has a central axis  15  about which the worm gear  12  may rotate. The case  24  has a central bore  84  as shown in  FIG. 3 . The worm gear  12  drives a gear  46  which is housed in a gearset  18 . For simplicity, the worm gear  12  and the gear  46  are shown with simplified teeth, though it is appreciated that as built, the worm gear  12  and the gear  46  will both include proper teeth as is well known in the art. 
         [0015]    The gearset  18  as shown as an exploded gear assembly in  FIG. 2  comprises an upper sleeve  20 , an upper oil seal  30 , an upper bearing  54 , a gear  46 , a cam  34 , a lower bearing  56 , a lower oil seal  32 , and a lower sleeve  22 . Once assembled as shown in  FIG. 3 , the gearset  18  is axially constrained with respect to the case  24  on the top by an upper sleeve  20  and on the bottom by a lower sleeve  22 . The upper and lower sleeves  20 ,  22  include threading  26 ,  28  around the outer perimeter which is mateable with corresponding threading formed in the upper and lower portions of the case  24 . The upper sleeve  20  circumscribes an upper oil seal  30 , such that the upper oil seal  30  nests in the upper sleeve  20 . Similarly, the lower sleeve  22  circumscribes a lower oil seal  32 , such that the lower oil seal  32  nests in the lower sleeve  22 . The sleeves  20 ,  22  also provide an axial surface for the top surface of the bearings. The bearings  54 ,  56  are typically ball bearings, but can be a roller bearing or a bushing. By applying a sufficient thrust pressure on the bearings  54 ,  56 , axial movement of the gear  46  is reduced or eliminated. The sleeves  20 ,  22  have sufficient clearance to the outside diameter of the cam  76  so that the cam  76  may be selectively rotated, as is shown in  FIG. 3 . 
         [0016]    The cam  34  is axially constrained on the upper end by the upper sleeve  20  and on the lower end by the lower sleeve  22 . The cam  34  is generally cylindrical having an upper face  38  and a lower face  40 . 
         [0017]    The cam  34  is a hollow cylinder defined by an internal diameter  78  and an outer diameter  76 . The internal diameter  78  has a first axis  80  and the outer diameter  76  has a second axis  82 . The first and second axes  80 ,  82  are spaced apart as shown in  FIG. 7  to generate an eccentricity to the cam  34 . The cam  34  includes a series of apertures  36  formed in both the upper and lower faces of the cam  34 . The circle defined by the inner diameter  78  is eccentric relative the circle defined by the outer diameter  76 . As is shown in  FIG. 7 , the thickness of the wall on the left side is different than the thickness of the wall on the right side. The outside diameter  76  of the cam is sized to rotatably mate with the central bore  84 ,  FIG. 3  of the case to allow selectively lockable rotation of the cam  34  with respect to the case  24 . 
         [0018]    The gear  46 ,  FIG. 2  is carried within the cam  34 . The gear  46  is generally shaped as a hollow cylinder with a series of protrusions in the outer wall. The most prominent protrusion is the gear teeth  48  that are centrally located on the outer diameter of the gear  46 . The teeth of gear  46  mesh with the teeth on worm gear  12 . Spaced above and below the teeth  48  on gear  46  are upper and lower protrusions  50 ,  52 , which form a pair of shoulders which locate the inner ring of an upper bearing  54  and a lower bearing  56  respectively. The gear  46  has a central axis  47 , center of the teeth  48 , and shoulders that locate inner rings of upper and lower bearings  54 ,  56 . The upper and lower bearings  54 ,  56  are carried within the cam  34  and axially constrain the gear  46 . The upper and lower bearings  54 ,  56  are sized to contact both the inner diameter of the cam  34  and the outer wall of the gear  46 , such that the gear is fixed from lateral movement with respect to the inside diameter  78  of the cam  34 . The bearings precisely locate the gear  46  within the cam  34 . Bushings could also be used in place of bearings. The gear  46  is coaxial with the first axis  80  of the cam  34 . The bore  84  in the case is coaxial with the second axis  82  of the cam  34  and when the cam  34  is locked from rotation, it is fixed from lateral movement with respect to the bore  84 . 
         [0019]    The upper sleeve  20  and lower sleeve  22  each include slots  58  formed therethrough. These slots  58  provide access to the apertures  36  formed in the cam  34  when the assembly  10  is assembled as is shown in  FIG. 5 . By passing a tool (not shown) through the slots  58  into the apertures  36 , the cam  34  can be rotated relative the case  24 , which rotation causes the gear  46  to move toward or away from the worm  12  due to the eccentricity of the cam. Rotating the cam changes the distance between the central axis  47  of the gear  46  and the worm gear  12 . In this way, rotation of the cam  34  allows for proper positioning of the gear teeth  48  relative the worm gear  12  so as to allow smooth and consistent rotation. The teeth on worm gear  12  and the teeth  48  on gear  46  are involute shaped teeth moving the axes  47 ,  15  nearer to each other may be used to eliminate push. While the cam  34  provides for lateral adjustment of the axis  47  of gear  46 , the worm gear  12  is fixed from lateral movement with respect to the case. The cam  34  includes an elongate window  60  as shown in  FIG. 2 , through which window  60  the worm gear  12  can contact the gear teeth  48  as shown in  FIG. 3 . The window  60  allows the cam  34  to rotate within a certain range while still allowing the worm gear  12  to contact gear teeth  48 . The cam  34  is structured and the window  60  is sized such that the cam  34  is sufficiently rigid to maintain a consistent inside diameter  78  and outside diameter  76  as show in in  FIG. 7 . With the cam  34  positioned as desired, the cam is locked into place by a series of set screws  62  as shown in  FIG. 1 . With the upper sleeve positioned as desired, the upper sleeve  20  is locked in place by a set screw  64 . A corresponding set screw  66  locks the lower sleeve  22  in place. 
         [0020]    Rotation of the cam  34  provides for lateral positioning of the gear teeth  48  relative the worm gear  12  by only making one adjustment. Smooth operation with long life requires both upper bearing  54  and lower bearing  56  to always be coaxial. Previous systems required independent adjustments of mechanisms on the both the top and bottom of the gear, and if the mechanisms are adjusted improperly, the worm gear  12  and the gear  46  would bind, prematurely wear, or otherwise not function ideally. The present system solves this problem by allowing for unitary adjustment of the top and bottom of gear  46 , which simplifies assembly and assures proper functioning. 
         [0021]    The case  24  contains a drive motor  14  that is connected to the worm gear  12  via coupling  74 . The case  24  also contains mounting and bearings  68  to constrain the worm axially and laterally. The axial endplay of the worm is controlled through a preload screw  70  and is held in place with a set screw  72  as is shown in  FIGS. 1 and 5 . The case also can contain controls and electronics for position feedback and control of the motor  14 . Mounting means are also included such that the system  10  can be mounted to an external structure. Setscrews are threaded into the case  24  that contact the cam  34 , upper sleeve  20  and lower sleeve  22  as is shown in  FIG. 4 . The setscrews  62  maintain the rotated position of the cam along with setscrews  64 ,  66  to maintain the position of the sleeves  20 ,  22  after adjustment is performed. 
         [0022]    It is understood that while certain aspects of the disclosed subject matter have been shown and described, the disclosed subject matter is not limited thereto and encompasses various other embodiments and aspects. No specific limitation with respect to the specific embodiments disclosed herein is intended or should be inferred. Modifications may be made to the disclosed subject matter as set forth in the following claims.