Supports – Stand – To hold a particular article
Patent
1993-01-13
1994-11-22
Foss, J. Franklin
Supports
Stand
To hold a particular article
248181, 354 81, F16M 1112
Patent
active
053661931
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
Invention relates to a drag/damper device for providing a coupling having a selected angular speed/torque characteristic between two relatively rotatable members. The invention is of particular application to TV/video camera mountings such as pan and tilt heads.
BACKGROUND OF THE INVENTION
Devices which produce drag or damping by means of either friction or viscous shear between relatively moving elements are known. The former typically comprise a friction clutch, attached to one element and contacting the relatively moving element under pressure, such that energy is dissipated by the resulting sliding contact. The magnitude of the damping force is dependent upon the friction contact pressure and is readily varied.
The torque/speed characteristic of a friction damper may be modified by the choice of friction materials and/or the provision of a fluid at the friction surface to provide boundary lubrication of the sliding contact in which case the damping force may rise with increasing speed from an initial stationary position and thereafter remain substantially constant irrespective of speed.
Viscous dampers typically comprise multiple interleaved plates alternately attached to each of the relatively moving elements, each plate being separated from adjacent plates by a small gap occupied by a viscous fluid. Relative movement of the plates causes viscous shear to take place in the fluid. The damping force generated, tends to increase substantially linearly with speed but at rest is zero.
One particular and important application of drag/damper devices is in pan and tilt heads for cameras, especially television cameras. In this application it is advantageous, to avoid "jerking" when making very slow camera movements from rest, for the torque to be substantially zero at near zero speed. On the other hand, for increasingly fast camera movements above a certain speed, it is advantageous for the torque not to become increasingly high.
In applications such as camera mounting, where the purpose of the damping device is to enhance the smoothness and control of manual movements, the following characteristics are therefore desirable: an high speed to permit relatively fast movements to be accomplished without unreasonable restraint, whilst providing adequate damping control at low speeds. the unit should produce zero damping at rest and a high rate of change of damping with speed at low speeds.
It is a general object of this invention to provide a drag/damper unit which possesses these characteristics.
It is another object of the invention to provide an improved pan/tilt head for a camera mounting, which possesses the above characteristics.
Preferably the amplitude of any damping is variable.
It is a further object of the invention to produce a drag/damper unit (and/or a pan/tilt camera mounting head) in which the amplitude of damping is infinitely variable between limits.
THE INVENTION
According to one aspect of the invention a drag/damper device comprises in combination a friction damper in series with a viscous damper.
The invention thus refines the characteristics of a friction damper by the inclusion of viscous damping characteristics predominently at commencement and reversal of movement.
Preferably the viscous damper possesses a high rate of change of damping relative to speed.
Preferably the friction damper includes means for adjusting contact pressure between relatively moving parts (normally plates) within the friction damper.
According to one embodiment of the invention, there is provided a drag/damper device providing a coupling having a selected angular speed/torque characteristic between two relatively rotatable members, comprising a central shaft fixed to one member and a housing surrounding the shaft and fixed to the other member, the housing accommodating a first set of spaced plates fixed to the shaft, a second set of spaced plates fixed to the housing, a third set of spaced plates floatingly interleaved with the plates of the first and second sets, and a viscous fluid in
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Foss J. Franklin
Vinten Group plc
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