Abstract:
A system for performing a variable function such as a variable spring resistance comprises a plurality of selectively operable spring devices and movable actuator means for selecting/deselecting devices over a range of movement of the actuator means. The actuator means includes stepped drives for selecting/deselecting at least one of the spring devices at a predetermined ratio with respect to another of the devices whereby spring devices can be selected to operate individually or in combination by movement of the actuator means to provide multiple levels of spring resistance.

Description:
BRIEF DESCRIPTION OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to variable function devices and particularly although not exclusively to variable counter-balance devices for use in T.V. or video camera pan and tilt heads for controlling tilt movement of the head. 
     2. Description of the Prior Art 
     U.S. Pat. No. 4,447,033 (Sachtler GmbH Filmtechniche Gerate) discloses a mechanism or support for a television or movie camera which allows the camera to be tilted or pitched upwardly and downwardly. The weight or torque applied by the camera when tilted from its neutral position is counterbalanced by means of a series of accumulators or spring elements placed between a rotor of the camera support camera and a stator portion of the support. The elements are adapted to be selectively engaged between the rotor and stator depending on the weight of the camera being used. Each accumulator offers a restoring torque that is different from that of the other accumulators such that by selective engagement of various combinations of accumulators, many different weights of cameras can be accommodated. 
     Individual accumulators are locked with the staters by means of a central operating handle which is rotatably located over the cylindrical stator and has on its inner periphery several cams. These cams serve to press lock pins into recesses of the respective accumulators when the handle is rotated. 
     By a planned placement of cams on the inner surface of the central operating handle, one or more lock pins can be selectively engaged with their respective individual accumulators by appropriate positioning of the handle. In order to achieve all possible combinations of accumulators it is necessary to be able to re-select accumulators at different positions of the movement of the handle and whilst two or four positions of engagement can be accommodated, difficulties arise in providing eight or more positions which may be necessary to maximise the number of combinations possible from a given set of accumulators. 
     SUMMARY OF THE INVENTION 
     This invention provides a system for performing a variable function comprising a plurality of selectively operable devices which provide a required function, actuator means for selecting/deselecting devices over a range of movement of the actuator means, the actuator means including stepped drives for selecting/deselecting at least one of the devices at a predetermined ratio with respect to another of the devices whereby devices can be selected to operate individually or in combination by movement of the actuator means to provide multiple levels of the function. 
     Preferably the actuator means comprise at least 35 two rotary shafts each having means for selecting/deselecting one or more devices with rotation of the shafts, and drive means coupling the shafts in a predetermined drive ratio whereby the devices are selected singly or in possible combination to provide a range of accumulated functions from the devices. 
     More specifically the drive ratio between the shafts maybe 2:1. 
     In one embodiment according to the invention the drive between the shafts may comprise a belt drive extending around wheels of different diameters on the shafts to provide the required drive ratio. 
     In any of the above arrangements at least one of the actuator drives may have a plurality of devices associated with the drive for selection/deselection. 
     More specifically drives may select and deselect a plurality of devices. 
     Further, said stepped drive is preferably arranged to select said devices singly and in all possible combinations through its cycle of movement. 
     In any of the above arrangements the respective 20 devices may provide progressively increasing functional. 
     For example the functional effect provided by respective devices may increase in a progression by a factor of two from the lowest function to the highest function. 
     In one particular application of the invention the function provided by the devices may be a torque resistance to rotation to provide counter-balance in a mechanism for use in a tiltable camera mounting system. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The following is a description of some specific embodiments of the invention, reference being made to the accompanying drawings in which: 
     FIG. 1 is a perspective view of a pan and tilt head for mounting a video or T.V. camera; 
     FIG. 2 is a perspective view of part of a counterbalancing mechanism for tilt movement of a TV or video camera including a plurality of rotary resistance devices; and 
     FIG. 3 is a detailed view of one of the rotary resistance devices and a mechanism for rendering the device operative/inoperative. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The arrangement shown in FIGS. 2 and 3 of the drawings is part of a variable resistance counterbalancing mechanism for use in controlling tilt movement of a TV or video camera mounting head as illustrated in FIG.  1 . Mountings of the construction in which the counterbalancing mechanism may be incorporated are described and illustrated in our UK Patent Publication Nos 2189043 and 2102757. 
     A typical TV or video camera mounting head has a fixed stator element  5  and a rotor element  6  and a platform  7  on the rotor element on which the camera is mounted to rotate about a horizontal axis with respect to the stator to provide a range of tilt movement for the camera/mounting about an axis indicated at  8 . The mounting has a horizontal or neutral position (as shown) in which the camera is supported with its optical axis extending horizontally and can be tilted to either side of the horizontal to enable the camera to be pointed upwardly or downwardly as required. 
     The camera is mounted offset from the axis  8   30  about which it tilts on the mounting and a counterbalancing force is required to stabilise the camera and provide “perfect” balance when tilted which will vary according to the particular weight of the camera and the ancilliary equipment such as lenses mounted on the camera. 
     Referring now to FIG. 2 of the drawings, the rotary element of a tiltable head for a TV or video camera mounting is coupled to a shaft  10  which rotates with the head. The shaft carries four bidirectional rotatable torque resistance devices  11 ,  12 ,  13  and  14  of progressively increasing strength preferably increasing by a factor of 2 between each pair of devices. One of the variable resistance devices is illustrated in greater detail in FIG.  3  and comprises an inner ring  15 , an outer concentric ring  16  and a loosely wound spiral spring ( 17 ) located between the inner and outer rings and attached at its ends to the respective inner and outer rings. The spring provides a resistance to rotation of the inner ring with respect to the outer ring which increases in direct proportion to the rotation of the inner ring in either direction from the neutral position. 
     As indicated above, the inner ring of each torque resistance device is secured to the shaft  10  and the outer ring is formed with a deep notch  18  to receive a detent for locking the outer ring against rotation when the torque resistance device is required to be operative. The mechanism also comprises a further shaft  21  extending parallel to shaft  10  and having a control knob  22  at one end thereof and two cams  23 ,  24  secured to the shaft. 
     The cam  23  is illustrated in greater detail in FIG. 3 to which reference will again be made. The cam has first, smaller diameter section  25  extending a little over 180 degrees around the axis of the shaft  21  and a second, larger diameter section  26  extending over the remaining portion of the cam. The ends of the smaller and larger diameter portions of the cam  25 ,  26  are joined by radial steps  27 . For each cam there is a cam follower  28  pivotally mounted at  29  about an axis parallel to the shaft  21 . One end of the cam follower has a rounded nose  30  which bears on the cam and the other end of the cam follower has a projecting stop  31  engageable in a notch  18  in a ring  16 . A compression spring  32  acts between the cam follower on the opposite side of the projection  31  and a fixed abutment to bias the cam follower towards the ring  16  of the variable resistance device. 
     Rotation of the shaft  21  by the knob  22  rotates the cam past the nose  20 . When the nose engages the smaller diameter portion  25  of the cam, The stop  31  at the end of the cam is urged by the spring  32  into the notch  18  in the outer ring  16  of the rotary torque resistance device. The outer ring is then locked against movement and rotation of the shaft  10  as the camera is tilted on its mounting will be resisted by the spring of the rotary torque resistance device. When rotation of the shaft  21  by the knob  22  brings the larger diameter portion  26  of the cam into engagement with the nose  30 , the cam follower is tilted about the pivotal axis  29  to withdraw the stop  31  from the notch  18  and thereby to release the outer ring  16  of the torque resistance device. The device then ceases to provide any resistance to rotation of the shaft  10 . If the shaft  21  is rotated by the knob  22  to move the nose  30  from the larger diameter portion of the cam  26  to the smaller diameter portion  25  the notch  18  on the outer ring  16  of the rotary resistance device may not be in register with the stop  31 . By tilting the mounting the stop  31  will ride around the outer surface of the ring  16  until it comes into alignment with and then engagement in the notch. Once engaged the device will provide a torque resistance to further tilting movement of the head. 
     Shaft  21  carries a further cam  24  acting through a similar cam follower  28  on a second rotary torque resistance device  12  on the shaft  10  similar in construction to the device  11 . In this case, the cam  35  is an elongate bar  33  having rounded ends  34  which the nose  30  of the follower engages. 
     The cam  23  provids one 180° sector  25  over which the stop  31  can engage in the notch  18  and one 180° sector  26  over which the stop  31  is withdrawn from the notch  18 . Cam  24  provides engagement of the associated stop  31  with the corresponding notch  18  in a rotary resistance device  12  when the nose  30  is engaged with one or other of the elongate sides of the cam and disengagement of the stop  31  from the notch when the nose is engaged in one or other of the rounded ends  34  of the cam. 
     Thus, one full rotation of the knob  22  engages the stop for half a turn and disengages the stop for the other half of the turn. On the other hand, cam  24  provides engagement with its associated resistance device twice per turn and disengagement twice per turn. Thus, the cams can be phased to provide engagement of neither rotary resistance device  11  or  12 ; 
     engagement of one or other of the rotary resistance devices  11  and  12 ; 
     or engagement of both rotary resistance devices  11  and  12  in the course of one 360 degree revolution of the knob  22 /shaft  21 . 
     The shaft  21  also carries a sprocket  40  having a belt drive  41  to a second smaller diameter sprocket  42  mounted on a further shaft  43  parallel with shafts  10  and  21 . The sprockets are arranged to provide a 2:1 drive between shaft  21  and shaft  43 . Shaft  43  carries further cams  23  and  24  similar to cams  23  and  24  on shaft  21  and operating cam followers  28  which engage the further rotary torque resistance devices  13  and  14  on shaft  10 . 
     The 2:1 drive ratio between shafts  21  and  23  couples and decouples the resistance devices  13  and  14  at twice the rate as the resistance devices  11  and  12  with rotation of the knob  22  to provide combinations of neither resistance device  13  and  14 , one of the resistance devices  13  and  14  or both resistance devices  13  and  14  with each of the combinations provided by the resistance devices  11  and  12 . 
     The following is a table of the possible 5 combinations provided by the mechanism: 
     
       
         
               
             
               
               
               
               
               
               
               
             
               
               
               
             
               
               
               
               
               
               
               
             
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                   
               
               
                 Combination switching 
               
             
          
           
               
                 Modules 
                 1 
                 2 
                 3 
                 4 
                  5 
                 . . . n 
               
               
                 Magnitude 
                 1 
                 2 
                 4 
                 8 
                 16 
                 . . . 2 n-1   
               
               
                 No. of combinations (inc zero) 
                 2 
                 4 
                 8 
                 16  
                 32 
                 . . . 2 n   
               
               
                   
               
             
          
           
               
                   
                   
                 Modules 
               
             
          
           
               
                   
                 Magnitude 
                 1 
                 2 
                 3 
                 4 
                 5 
               
               
                   
                   
               
               
                   
                  0 
                 * 
                 * 
                 * 
                 * 
                 * 
               
               
                   
                  1 
                 1 
                 * 
                 * 
                 * 
                 * 
               
               
                   
                  2 
                 * 
                 2 
                 * 
                 * 
                 * 
               
               
                   
                  3 
                 1 
                 2 
                 * 
                 * 
                 * 
               
               
                   
                  4 
                 * 
                 * 
                 4 
                 * 
                 * 
               
               
                   
                  5 
                 1 
                 * 
                 4 
                 * 
                 * 
               
               
                   
                  6 
                 * 
                 2 
                 4 
                 * 
                 * 
               
               
                   
                  7 
                 1 
                 2 
                 4 
                 * 
                 * 
               
               
                   
                  8 
                 * 
                 * 
                 * 
                 8 
                 * 
               
               
                   
                  9 
                 1 
                 * 
                 * 
                 8 
                 * 
               
               
                   
                 10 
                 * 
                 2 
                 * 
                 8 
                 * 
               
               
                   
                 11 
                 1 
                 2 
                 * 
                 8 
                 * 
               
               
                   
                 12 
                 * 
                 * 
                 4 
                 8 
                 * 
               
               
                   
                 13 
                 1 
                 * 
                 4 
                 8 
                 * 
               
               
                   
                 14 
                 * 
                 2 
                 4 
                 8 
                 * 
               
               
                   
                 15 
                 1 
                 2 
                 4 
                 8 
                 * 
               
               
                   
                 16 
                 * 
                 * 
                 * 
                 * 
                 16 
               
               
                   
                 17 
                 1 
                 * 
                 * 
                 * 
                 16 
               
               
                   
                 18 
                 * 
                 2 
                 * 
                 * 
                 16 
               
               
                   
                 19 
                 1 
                 2 
                 * 
                 * 
                 16 
               
               
                   
                 20 
                 * 
                 * 
                 4 
                 * 
                 16 
               
               
                   
                 21 
                 * 
                 * 
                 4 
                 * 
                 16 
               
               
                   
                 22 
                 * 
                 2 
                 4 
                 * 
                 16 
               
               
                   
                 23 
                 1 
                 2 
                 4 
                 * 
                 16 
               
               
                   
                 24 
                 * 
                 * 
                 * 
                 8 
                 16 
               
               
                   
                 25 
                 1 
                 * 
                 * 
                 8 
                 16 
               
               
                   
                 26 
                 * 
                 2 
                 * 
                 8 
                 16 
               
               
                   
                 27 
                 1 
                 2 
                 * 
                 8 
                 16 
               
               
                   
                 28 
                 * 
                 * 
                 4 
                 8 
                 16 
               
               
                   
                 29 
                 * 
                 * 
                 4 
                 8 
                 16 
               
               
                   
                 30 
                 * 
                 2 
                 4 
                 8 
                 16 
               
               
                   
                 31 
                 1 
                 2 
                 4 
                 8 
                 16 
               
             
          
           
               
                   
                 Switch Cycles: 
                 
                   
                             
                     
                         
                         
                     
                   
                 
                 4 
                 
                   
                             
                     
                         
                         
                     
                   
                 
               
               
                   
                   
               
               
                   
                 Shaft ratio: 
                 X2 
                 X1 
                 X1/4 
               
             
          
           
               
                   
                 Cycles per rev: 
                 2 
                 1 
                 1 
                 2 
                 1 
               
               
                   
                   
               
             
          
         
       
     
     The mechanism generates 16 different levels of resistance (including zero resistance) from the four torque resistance devices to provide a large number of discrete steps of adjustment. Moreover, the mechanism due to its simplicity can be made extremely compact and therefore easy to accommodate in a confirmed space in a camera mounting. 
     The same or a similar mechanism can also be used to operate a switching mechanism for controlling a display showing the current level of resistance provided by the mechanism for the convenience of the operator.