IMPROVEMENTS IN OR RELATING TO ROTARY LOAD COUNTERBALANCING MECHANISMS

Abstract: The disclosure relates to a rotary counterbalancing mechanism comprising a rotatable input (19, 22), a pair of aligned linearly movable outputs (24, 25), means (23) to convert rotation of said input into sinusoidal oscillation of said outputs between minimum and maximum displacement positions and 90 DEG out of phase with each other and spring means (29) for resisting said oscillating movement of the outputs away from said minimum positions. The means to convert rotary motion of the input into linear movement of said two outputs comprise a rotatable cam (23) mounted to rotate about a fixed axis and the outputs comprise two cam followers (30) engaging the cam on opposite sides thereof and mounted for linear movement along a common line of action with each other which passes through the axis or rotation of the cam, said spring means (29) acting on the respective followers biasing the followers towards the cam to resist rotation of the cam.

Description: 8/36208 IMPROVEMENTS IN OR RELATING TO ROTARY LOAD COUNTERBALANCING MECHANISMS This invention relates to rotary load counterbalancing mechanisms and more particularly, although not exclusively, to tilt mounting heads for counterbalancing the torque caused by the out of balance mass of a camera or the like mounted thereon when rotated about the tilt axis. Many load counterbalancing mechanisms are known including hydraulic or pneumatic devices and springs loaded through lever or cam arrangements. Our UK Patent Specification No. 2102757 discloses a multiple spring and lever arrangement which provides true balance and is also capable of adjustment to accommodate different loads but is relatively complex and bulky and can therefore be difficult to accommodate. An important requirement of a counterbalancing mechanisms and particularly mechanisms to be embodied in a tilt mounting for a camera is that the mechanism should be compact so that the overall bulk of the mounting can be kept to a minimum. This invention provides a rotary counterbalancing mechanism comprising a rotatable input, a pair of aligned linearly movable outputs, means to convert rotation of said input into sinusoidal oscillation of said outputs between minimum and maximum displacement positions and 90s out of phase with each other and spring means for resisting said oscillating movement of the outputs away from said minimum positions. Preferably the means to convert rotary motion of the input into linear movement of said two outputs comprise a rotatable cam mounted to rotate about a fixed axis and the outputs comprise two cam followers engaging the cam on opposite sides thereof and mounted for linear movement along a common line of action with each other which passes through the axis of rotation of the cam, said spring means acting on the respective followers biasing the followers towards the cam to resist rotation of the cam. More specifically the cam may be heart shaped having a recessed region in one part of its periphery and a peak at a diametrically opposite location, the cam being symmetrical on either side of a line joining the centre of the recess to the peak through the axis of rotation of the cam, the datum position of the cam being a position in which one of the cam followers engages in the recess and the other is in engagement with the peak. In any of the above arrangements, the spring means may be arranged to resist the movement of the cam followers in compression. In one particular example according to the invention, the spring means are arranged parallel to one another with one end of each spring means anchored and the other end coupled to a respective cam follower. The following is a specific embodiment of the invention, reference being made to the accompanying drawings in which: Figure 1 is a side elevation view of a rotary load counterbalancing mechanism suitable for a tilt mounting for a TV or cinematograph type camera; and Figure 2 is an end view of the mounting. Referring firstly to Figure 1 of the drawings, there is shown a mounting for a television or video camera comprising an elongate horizontally extending base indicated generally at 10 on which a platform 11 is mounted to pivot about a horizontal axis 12 extending through the housing in the direction of the arrows 13 and on which a camera indicated diagrammatically at 14 is mounted. The housing 10 is of elongate horizontally extending hollow box form having a rectangular cross- section. The housing has side walls 15 top and bottom walls 16, 17 and end walls 18. A horizontally extending shaft 19 extends through the housing and is mounted in bearings (not shown) in the side walls 15 of the housing but support the shaft for rotation about the aforesaid axis 12. The ends of the shaft project from the side walls 15 of the housing as indicated at 21 and a pair of parallel arms 22 are secured at their lower ends to the projecting ends of the shaft. The platform 11 is mounted at the upper ends of the arms. The platform and its camera are therefore supported on the arms 22 to pivot about the axis 12 to either side of the vertical, as indicated by the arrows 13. Pivotal movement of the platform is controlled by a counterbalancing arrangement mounted in the housing 10 whereby the platform can be moved to any position in its range of tilt about the housing and an appropriate counterbalancing force is automatically generated to support the platform in position. The counterbalancing mechanism will now be described. A detailed mathematical analysis of a filling platform carrying a certain mass and resisted by a pair of springs is to be formed in our aforesaid UK Patent Specification No. 2102757 to which reference should be made. The counter-balancing mechanism comprises a cam 23 is mounted on the shaft 21 within the housing, the cam having a heart shaped profile which is symmetrical about a horizontal axis extending through the pivot axis 12 when the arms 22 are in the neutrally vertical position as shown in Figure 1. Two similar cam followers indicated at 24 and 25 act on opposite sides of the cam. Each follower comprises a plunger 26 mounted in a horizontal bore 27 in an end wall 18 of the housing to slide towards and away from the cam. Each plunger has an end plate 28 fixed to the end of a plunger and a compression spring 29 acts between the plate and end wall to force the plunger towards the cam. The end of the plunger has a roller 30 mounted therein on a spindle 31 to provide smooth rolling engagement with the cam surface as the cam rotates between the respective plungers. It will be appreciated that the cam followers engage opposing halves of the cam as it rotates on the shaft with tilting of the platform. Each half of the cam is shaped to provide full cycle of sinusoidal movement of the cam follower with 1802 rotation of the cam, the movements of the respective cam followers being 90s out of phase with one another. The cam followers are held against the cam by the compressive forces of the springs 29 which will therefore vary sinusoidally with angle of tilt from the vertical of the platform/arm assembly. The resulting force resisting rotation of the cam 23 from its neutral position corresponding to the vertical position of the arms 22 provides a counterbalancing force equal to and opposite the out of balance force of the mass/platform assembly so that the platform is supported fully counterbalanced at any position of tilt to which it is adjusted. It will be appreciated that a variety of other similar forms of mechanism can be utilised to provide two sinusoidally varying 902 out of phase forces to provide the counterbalancing affect indicated above. For example, a swash plate mechanism could be utilised.

Claims: CLAIMS 1. A rotary counterbalancing mechanism comprising a rotatable input, a pair of aligned linearly movable outputs, means to convert rotation of said input into sinusoidal oscillation of said outputs between minimum and maximum displacement positions and 90s out of phase with each other and spring means for resisting said oscillating movement of the outputs away from said minimum positions. 2. A rotary counterbalancing mechanism as claimed in claim 1, wherein the means to convert rotary motion of the input into linear movement of said two outputs comprise a rotatable cam mounted to rotate about a fixed axis and the outputs comprise two cam followers engaging the cam on opposite sides thereof and mounted for linear movement along a common line of action with each other which passes through the axis of rotation of the cam, said spring means acting on the respective followers biasing the followers towards the cam to resist rotation of the cam. 3. A rotary counterbalancing mechanism as claimed in claim 1 or claim 2, wherein the cam is heart shaped having a recessed region in one part of its periphery and a peak at a diametrically opposite location, the cam being symmetrical on either side of a line joining the centre of the recess to the peak through the axis of rotation of the cam, the datum position of the cam being a position in which one of the cam followers engages in the recess and the other is in engagement with the peak. 4. A rotary counterbalancing mechanism as claimed in any of the preceding claims, wherein said spring means are arranged to resist the movement of the cam followers in compression. 5. A rotary counterbalancing mechanism as claimed in claim 4, wherein the spring means are arranged parallel to one another with one end of each spring means anchored and the other end coupled to a respective cam follower.

Inventors: LINDSAY RICHARD ARTHUR, LINDSAY, RICHARD, ARTHUR
Applicants: LINDSAY RICHARD ARTHUR, VITEC GROUP PLC, LINDSAY, RICHARD, ARTHUR
Application year: 1997
Main classification: F16M11
IPC codes: F16M11