Rotary shafts – gudgeons – housings – and flexible couplings for ro – Fluid coupling
Reexamination Certificate
1998-06-18
2001-01-23
Browne, Lynne H. (Department: 3629)
Rotary shafts, gudgeons, housings, and flexible couplings for ro
Fluid coupling
C464S030000, C188S290000, C192S058410
Reexamination Certificate
active
06176783
ABSTRACT:
This invention relates to a rotary drag device for providing a coupling having a selected speed/torque characteristic between two relatively rotatable members. The invention is particularly applicable to TV/video camera mountings such as pan and tilt heads.
Devices which produce drag or damping by means of either friction or viscous shear between relatively moving elements are well known. The former typically comprise a friction clutch attached to one element and contacting a 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 therefore 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 a stationary position to an initial level 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.
A particularly important application of a drag/damper device 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 resistance torque not to rise in proportion necessitating application of an increasing force to move the camera.
U.S. Pat. No. 4,955,568 discloses a camera mounting pan and lift head, including fluid drag systems or resisting pan and tilt movement and a counterbalance system in supporting the camera in equilibrium in any position in its range of tilt movement. The fluid drag systems each include a drag disc assembly secured to the rotating shaft and drag section assemblies pivotally mounted on the housing and disposed about the circumference of the disc assembly to define the space containing discus fluid. The level of drag exerted may be adjusted by pivoting the sector assemblies towards or away from the disc assembly to vary the space containing viscous fluid. In this system is the drag provided will rise more or less linearly with relative rotational speed of the components of the drag system so that at very high speed, there is high drag force.
In applications such as a 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:
1. The rate of change of the damping/speed relationship should tend to zero at high speed to permit relatively fast movements to be accomplished without unreasonable restraint, whilst providing adequate damping control at low speeds.
2. For fine control at the commencement of movement and during reversals, the unit should produce zero damping at rest and a high rate of change of damping with speed at low speed.
Our UK Patent Application number 9018312.0 describes and illustrates a rotary damper comprising two torque resisting rotary damping devices coupled together in series, one of said rotary damping devices having an input, an output and a viscous fluid coupling to provide a resistance torque to relative rotation between the input and output which is zero when the relative speed between the input and output is zero and which rises generally linearly with relative speed between the input and output. The other of the rotary damping devices has an input and an output and a torque resistant friction coupling which resists relative rotation between the input and output up to a certain torque and above which the friction coupling allows slippage with a substantially constant torque resistance. Thus the two rotary damping devices together provide a combined speed/torque characteristic in which the resistance torque generated by the viscous coupling rises with speed to a certain level at which the torque causes the friction coupling to slip whereafter the resistance offered by the damper remains substantially constant for higher speeds.
Providing separate friction and viscous couplings in series does however result in a complicated arrangement which is difficult to pack into a restricted space. The space available for drag devices in a camera mounting is normally limited and it is highly desirable therefore to make the drag devices as compact as possible.
This invention provides a rotary drag device having relatively rotatable members one of which has a plurality of closely spaced, thin-walled flexible annular plates peripherally mounted thereon to provide annular running faces and a viscous fluid filling the spaces between the plates, and the other of which members has a plurality of segmental elements having part-annular running faces interleaved with the annular plates to slide between the plates with relative rotation of the members and means to permit release of viscous fluid from between the plates as fluid pressure rises ahead of the segmental plates with increasing relative speeds between the members, the flexibility of the annular plates allowing the plates to close together accommodating the loss of viscous fluid from between the plates whereby the damping characteristic of the device can vary between viscous drag between the relative running surfaces of the annular and segmental plates at low relative speeds of the members and, with loss of viscous fluid from between the plates, can change to boundary lubrication between the running surfaces of the respective plates at higher relative speeds of rotation of the members.
In one arrangement according to the invention the means to permit release of viscous fluid between the plates includes apertures in the annular plates outside the running surfaces thereof for the viscous fluid to flow axially between the plates.
More specifically the apertures may comprise elongate arcuate slits spaced around the annular plates outside the running surfaces thereof.
In one particular arrangement according to the invention the elongate arcuate slits may comprise inner and outer sets of arcuate slits staggered with respect to each other to provide flexible beam elements between the respective ends of the inner and outer slits to allow the running surface part of the annular plate to move axially with respect to the peripheral mounting of the plate whereby the spacing between the running surfaces of the annular plates can vary with the amounts of viscous fluids between the plates.
In any of the arrangements referred to above the segmental elements may have means to permit limited axial movement of the running faces of the elements to accommodate axial movement of the running faces of the annular plates.
For example, the means in the segmental plates to permit axial movement of the running faces thereof may comprise inner and outer rows of annular slits, outside the running faces of the plates with the slits in the outer set staggered with respect to the slits in the inner set to provide beam elements between the respective ends of the slits which can flex to allow limited axial movement of the running faces of the segmental elements with respective to their respective mountings.
In any of the above arrangements the annular plates may be mounted on said one member of the device around their outer peripheral edges and the segmental elements are mounted on said other member within the annular plates.
Also in any of the above arrangements means are provided for adjusting the overlap between the running faces of the segmental elements and
Lindsay Richard Arthur
Sayer Robin Andrew
Browne Lynne H.
Kenyon & Kenyon
Thompson Kenneth
Vitec Group PLC
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