Abstract:
A pan and tilt head for supporting a payload such as a TV, video or motion picture camera comprising a base and a tiltable support including a platform for receiving a payload pivotally mounted on the base to tilt about a horizontal axis to either side of a neutral position in which the platform is generally horizontal. A balancing mechanism for the platform includes an adjustable spring mechanism mounted on the base to enable a pre-load in the spring mechanism to be varied and means coupling the tilting support to the spring mechanism. Adjustable mounting for one end of the spring mechanism includes an upright post mounted on the base and having rotary height adjustment. A manually operable rotary thumb wheel is mounted on the base for rotation about an upright axis.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The application claims priority to United Kingdom Patent Application No. 0905470.1 filed 30 Mar. 2009 which is incorporated herein by specific reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. The Field of the Invention 
         [0003]    This invention relates to pan and tilt heads for supporting a payload such as a TV, video or cine camera on a tripod, pedestal or other form of mounting. 
         [0004]    2. The Relevant Technology 
         [0005]    Our UK Patent Publication No. 2189042 discloses a tiltable mounting for a TV or video camera comprising a base, a tiltable support member pivoted thereto and reactionary moment producing means located between and operated from said base and tiltable support member to produce a reaction equal to the out of balance moment generated by the weight of an article mounted on said tiltable support member as said centre of gravity moves about the vertical. The means for producing the reactionary moment comprises a horizontally extending spring guide mounted on the base carrying a compression spring acting between a slide and an end stop. The slide is excentrically coupled to the support member with respect to the tilt axis so that tilting of support member with respect to the tilt axis so that tilting of the support causes the slide to compress the spring and produce a force to counterbalance the out of balance moment produced as the centre of gravity of an article mounted on the tiltable support member rotates about the vertical. The spring guide has a rotary adjusting device connected to the guide by a lead screw to preload the spring in relation to the weight and position of the centre of gravity of the article on the support which is located on a vertical member of the space on the rearward side of the head. Since very high loads are required in the spring to provide the requisite counterbalancing force, the effort required to rotate the adjustment device is considerable. Moreover the tiltable support covers the adjustment device when the support is tilted rearwardly making it impossible to effect an adjustment when the supported is in that position. 
       SUMMARY OF THE INVENTION 
       [0006]    This invention provides a pan and tilt head for supporting a payload (such as a TV, video or cine camera) the head comprising a base, a tiltable support including a platform for receiving a payload pivotally mounted on the base to tilt about a horizontal axis to either side of a neutral position in which the platform is generally horizontal and a balancing mechanism for the platform comprising an adjustable spring mechanism adjustably mounted at one end on the base to enable a pre-load in the spring mechanism to be varied and means to couple the tilting support to the spring mechanism so that tilting of the support produces a reaction force in the spring which fully counterbalances the support throughout its range of tilt to either side of the neutral position, wherein adjustable mounting for one end of the spring mechanism includes an upright post mounted on the base and having a rotary height adjustment mechanism to raise and lower the post to vary a pre-loaded spring force in the spring mechanism to suit the payload on the support, and a manually operable rotary member mounted on the base for rotation about an upright axis having a stepped down drive to the height adjustment mechanism to provide a mechanical advantage in the rotation of the height adjustment mechanism for ease of operation of the mechanism. 
         [0007]    In one arrangement according to the invention the height adjustment mechanism for the post may comprise a screw jack on the base acting on the lower end of the post. 
         [0008]    According to a further feature of the invention the stepped down drive from the manually operable rotary member to the rotary height adjustment mechanism may comprise a stepped down gear train, a chain and sprocket drive, or a belt and wheel drive. 
         [0009]    In the case where the stepped drive is a gear train between the manually operable member and the rotary adjustment device, the gear train may comprise a pinion mounted on the axis of rotation of the member engaging in an internal ring gear connected to the height adjustment mechanism. 
         [0010]    In the latter arrangement the height adjustment mechanism may comprise a lead screw mounted on the base for rotation about an upright axis, and an internal screw thread in the lower end of the post with which the lead screw engages for adjustment of the post height and thereby the pre-load the spring mechanism. 
         [0011]    More specifically the ring gear may be co-axial with and connected to the lead screw of the height adjustment mechanism. 
         [0012]    In either of the latter arrangements the spring mechanism may comprise an elongate guide member pivotally connected at one end to the upright post of adjustment mechanism and having an end stop for a spring at the other end, a compression spring encircling the guide member engaging the end stop at one of the spring and a slide member on the guide engaging the other end of the spring, the slide member being pivotally mounted to the tiltable support eccentrically from the axis of rotation of the support whereby rotation of the support moves the slide along the guide member to compress the spring and thereby generate the resistance to tilting of the support to counterbalance the support fully in any position of adjustment to which it is moved. 
         [0013]    In any of the above arrangements the manually operable rotary member may be a thumb wheel mounted for rotation on the base of the head. 
         [0014]    More specifically the base may have a housing enclosing the height adjustment mechanism and a slot is provided in the housing wall on one side of the base from which a peripheral part of the thumb wheel projects for operation of the thumb wheel. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIG. 1  is a perspective view of a pan and tilt head for a TV, video camera showing one side and the rear of the head; 
           [0016]      FIG. 2  is a rear view of the head as shown in  FIG. 1 ; 
           [0017]      FIG. 3  is a side view of the head as shown in  FIG. 1 ; 
           [0018]      FIG. 4  is a similar view to  FIG. 1  with a housing and part of the platform for a camera removed to expose a balancing mechanism for the head; 
           [0019]      FIG. 5  is a section through the head on the line  5 - 5  on  FIG. 3 ; and 
           [0020]      FIGS. 6 to 8  show the essential parts of the platform counterbalancing mechanism in neutral and tilted position to either side of neutral. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0021]    As indicated above, this invention relates to tiltable mountings, and more particularly, though not exclusively, to tilting mountings for supporting articles such as television cinematograph or electronic news gathering cameras in such a manner that the articles may be smoothly and easily tilted, i.e., the extremities of the article in a longitudinal plane change their angle of elevation relative to the C of G; i.e. centre of gravity; of the article. A camera panning head has the further function of permitting a camera to be panned i.e. turned to and fro, or rotated about, a vertical axis. Hereinafter the invention is described with reference to a camera, but it will be understood that other articles may be mounted on such tilting mountings. 
         [0022]    In our GB-A-2096345, incorporated herein by reference, we disclose an apparatus providing such a tiltable mounting. 
         [0023]    Referring to GB Patent No. 2096345, page 2, lines 24-39 the energy stored in the spring is given as Ka 2 (1-Cos θ s ) where “a” is the lengths of links AC and CD. In this application if AC and CD are made unequal e.g. “a” and “b”, then the energy stored in the spring for angle ACD changing from 0 to θ s  is 
         [0000]      Energy stored=Kab (1-Cos θ s ) 
         [0000]    and the amount of compensation to obtain counterbalance may be varied by adjusting dimensions “a” or “b” or by changing the rate of the spring or any combination thereof. By permitting “a” and/or “b” to be variable a simplified structure may be manufactured. 
         [0024]    In our GB-A-2189042, incorporated herein by reference, we disclose a tiltable mounting comprising a base, a tiltable support member pivoted thereto and reactionary moment producing means located between and operated from said base and tiltable support member to produce a reaction equal to the out of balance moment generated by the weight of an article mounted on said tiltable support member as said C of G moves about the vertical. More specifically the tiltable mounting comprises a base, a tiltable support member pivoted thereto, mounting means on said tiltable support member for excentrically locating a pivotable slide means, mounting means on said base for pivotably locating a spring guide means having a spring compression means thereon, and a spring located on said spring guide means compressible between said slide means and said spring compression means wherein the reactionary moment at the tiltable support member produced by the action of the pivotable slide means and spring combined is equal to the out of balance moments produced as the C of G of an article mounted on said tiltable support member rotates about the vertical. 
         [0025]    Reference is now made to  FIGS. 1 to 8  of the accompanying drawings which illustrate a pan and tilt head in accordance with the present invention. 
         [0026]    The pan and tilt head comprises a base indicated generally at  10  comprising a chassis on which components of the base are mounted including a base plate  11  below which there is a mounting  12  on which the base plate is rotatable about a vertical axis for pan movement of the head. The mounting is adapted to be secured in the head of a tripod, pedestal or other mounting arrangement. A platform  13  for receiving a TV, video or cinematic camera is pivotably mounted about a horizontal axis on the chassis to provide tilt movement of the camera which is fully counterbalanced by an adjustable spring mechanism. 
         [0027]    As indicated above, the head  10  is supported on the mounting  12  by a bearing arrangement which provides rotation of the head about a vertical axis for pan movement of the camera on the platform. The pan movement is controlled by a variable drag/damper arrangement of the type described and illustrated in our Euro (UK) Patent Publication No. 0850382 acting between the chassis and mounting  12 . 
         [0028]    The base  10  has a lower housing indicated at  17  mounted on the base plate  11  and an upper housing indicated at of part annular form located on the lower housing and disposed below the platform  13  to house the mechanisms for controlling pan and tilt movement of the head. The lower housing  17  has side walls  19  and  20  and front and rear walls  21  and  22 . The drag/damper device for controlling pan movement of the head is adjusted by a thumb wheel  23  a portion of the periphery of which projects through a slot  24  formed in the rear wall  22  of the housing to be adjusted by the camera operator as required. 
         [0029]    The base  11  of the chassis of the head has a pair of upstanding side walls  25 ,  26  as best seen in  FIG. 5  in which a pair of large diameter ball race bearings  27 ,  28  respectively are mounted coaxially on horizontal axis  29  in the upstanding side walls  25  and  26  of the chassis. 
         [0030]    The platform  13  has a dependent annular housing  31  on one side of the platform formed with a projecting stub shaft  32  which engages and is supported for rotation in bearing  28 . The other side of the platform  13  has a dependent flange  33  having a stub shaft  34  at its lower end which engages in the bearing  27 . The platform is thereby supported for tilting movement about the horizontal axis  29  on the chassis. 
         [0031]    The mechanism for counterbalancing the tilt of the platform and camera mounted on the platform so that the camera can be tilted to any position in its range of travel and will stay in that position is generally as described and illustrated in GB-A-2189042, incorporated herein by reference, except that in the case of the present invention the spring arrangement which resists tilting of the platform is aligned generally vertically rather than horizontally as in the previous arrangement. The arrangement of the present invention will now be described in greater detail with reference to  FIGS. 3 to 8 . 
         [0032]    An internal gear  40  is mounted on the chassis above the base plate  11  and the underside of the hub  41 . The hub projects into an annular cavity  42  formed in the lower part of the chassis and a roller bearing  43  is mounted at the bottom of the cavity to support the annular hub  41  for rotation about the vertical axis indicated at  44 . 
         [0033]    At the centre of the hub  41  there is an upright post comprising an upstanding lead screw  45  which engages in an internally threaded upwardly extending sleeve  46  to provide a vertically acting screw jack. Vertical travel of the sleeve part of the post is limited by a horizontally extending pin  47  mounted on the chassis and engaging in a vertical slot  48  in the sleeve. 
         [0034]    The sleeve has a forked upper end  49  which has a hinged connection to a lower end of an elongate slide member  50  by a horizontal pin  51 . The upper end of the slide  50  has an end cap  52  secured by a bolt  53 . A slide in the form of a sleeve  55  is located on slide member  50 . The sleeve has a cup shaped seat  56  at its lower end to receive the lower end of a heavy compression spring  57  the upper end of which engages the cap  52 . 
         [0035]    The cup shaped housing  56  is formed with an outwardly extending pair of pivot pins  56   a  which engage in bearings  58  formed in eccentric bores  59  in the  32  and  34 . 
         [0036]    Referring to  FIGS. 6 to 8  of the drawings, as the platform  13  tilts in one direction on its bearings  27  and  28 , the pivot pins  56   a  will turn with the platform but because they are located eccentrically with respect to the axis  29  of rotation of the platform, the pins will cause the housing  56  to tilt the slide member  50  about pin  51  and, because of the geometry of the arrangement, to rise up the slide member  50  compressing the spring  57 . The resulting reaction force counterbalances the platform so that the platform will remain stationary in any position to which it is moved throughout its range of travel.  FIG. 6  shows the platform in the “neutral”, horizontal position with slide  50  vertical and  FIGS. 7 and 8  show the platform tilted at 40° to either side of neutral with the slide  50  tilted in the respective opposite direction. Reference should be made to our GB-A-2189042 for a more detailed explanation of the geometry and manner in which the arrangement provides a perfectly balanced platform throughout its range of tilt movement. 
         [0037]    The lead screw  45  rotated by the ring gear  40  at the lower end of the housing adjusts the position of the slide  50  with respect to the housing  56  and thereby adjusts the initial compression of the spring  54  to cater for cameras of different weights on the platform so that whatever the camera weight, the platform can be perfectly balanced. The ring gear is itself adjusted by a pinion  60  governed by a thumb wheel  61 . The thumb wheel is mounted to rotate about an axis  62  on the chassis offset laterally from the axis  44  of the ring gear so that a portion of the thumb wheel projects outwardly from the side of the chassis through an aperture  63  formed in the side wall  19  of the lower housing. The gearing between the pinion  60  and ring gear provides a substantial step down in ratio from the pinion to the ring gear and this coupled with the large diameter of the thumb wheel  61  provides a substantial mechanical advantage for the operator in rotating the lead screw  45 . It will be appreciated that the lead screw  45  is subjected through the sleeve  46  to substantial axial force by the compression spring  57  and so the substantial mechanical advantage provided for the thumb wheel  61  significantly enhances the ease by which the preload in the spring  54  can be adjusted by the operator. In addition because the thumb wheel is acted on from the side of the housing rather than the rear wall of the housing as in the arrangement of our British Patent Specification No. 2189042, the spring force can always be adjusted whatever the position of tilt of the platform is moved to. 
         [0038]    The chassis has an upstanding side housing  70  outside the annular hub  31  of the platform  13  in which a further drag device for controlling hand movement of the head is mounted. The housing has an aperture  71  from which a further thumb wheel for adjusting the drag/damper device projects. The housing also carries control members  73 ,  74  for locking the pan and tilt head against pan and tilt movement when required through conventional locking arrangements. 
         [0039]    It will be appreciated that many modifications may be made to the above described embodiment without departing from the scope of the invention. Other forms of linear resistance devices can be used in place of a coil spring and the spring could be operated in tension rather than compression. In addition parallel spring arrangements could be used as described in our British Patent Publication No. 2189042. Also different stepped drives could be provided between the thumb wheel for adjusting the lead screw for the slide such as a chain and sprocket drive or a toothed wheel and belt drive in which the sprocket or wheel sizes are selected to provide the required step down ratio from the thumb wheel to the lead screw. Also other forms of member can be provided for rotating the pinion such as a lever.