Damping mechanisms

The invention comprises an adjustable damping mechanism for such as pan and tilt heads comprising two or more mateable surfaces operating with lubrication wherein the pressure of one surface on the other is variable and combines solidity when stationary, drag proportional to velocity in movement up to whip pan velocity after which the drag remains substantially constant.

This invention relates to dampers and more particularly though not 
exclusively to rotary dampers of the type frequently used for damping or 
drag action on instrument support platforms suitable for rotation in the 
pan and/or tilt axis. 
Damping mechanisms in the past have tended towards the use of fluids 
wherein movement of two or more concentric surfaces in the same plane 
relative to each other has caused the molecular shearing of the fluid 
therebetween. Maximum torque has, in these mechanisms, been dependent on 
the viscosity of the fluid, the area of the surfaces and the separation 
distance i.e. the molecular construction of the fluid and its resistance 
to change of shape. Very small clearances, or separation distances, 
increase torque but are difficult to obtain without the concentric 
surfaces touching. 
One problem with some of the prior art type of friction dampers or fluid 
dampers is that of filling them with a thick lubricant. It is normal to 
perform this operation using a high pressure gun which usually forces the 
lubricant through, such as a grease nipple, until all air is expelled from 
a vent hole. The vent hole is then sealed as is the grease nipple. With 
the present invention this problem does not exist as the lubricant is more 
fluid and filling to capacity unnecessary. 
Due to the fact the prior art dampers rely mainly on the molecular shear of 
the fluid for operation very little resistance to movement is encountered 
for very small angular movement about the null, for example, if used in 
the field of television, the cameraman may obtain a fairly steady 
transition during pan or tilt but when the subject is still and the camera 
being neither panned nor tilted, very little resistance is felt in the 
damper and any slight movement of the cameraman may be transmitted to the 
camera. If the damper is tightened, the drag when panning and tilting, 
becomes excessive with only marginal increase to the resistance of very 
small angular movements about the null positions. Furthermore if a whip 
pan is required, that is a rapid movement from one target to another in 
the pan axis, the damper has to be released before this may be achieved. 
A head wherein the combination of stability when on target, stability when 
following a target and the ability to whip pan when necessary to transfer 
to a fresh target without necessary adjustments prior to the action is 
therefore required. 
It is therefore an object of this invention to provide a damping mechanism 
wherein the aforementioned problems are considerably reduced. 
According to the invention we provide a damping mechanism comprising at 
least in part, two or more mateable surfaces, wherein at least one of said 
mateable surfaces is substantially resistive to lubricants and at least 
one other of said mateable surfaces is substantially absorbent of 
lubricants, said two or more mateable surfaces being variably compressible 
one with the other to vary the degree of drag when said two or more 
mateable surfaces are moved in the same plane relative to each other and 
the degree of damping is proportional to the relative velocity of said two 
or more surfaces up to whip pan velocity. 
According to a further aspect of the invention we provide a damping 
mechanism comprising at least in part, two or more mateable surfaces, 
wherein at least one of said mateable surfaces is substantially resistive 
to lubricants and at least one other of said mateable surfaces is 
substantially absorbent of lubricants, said two or more mateable surfaces 
being variably compressible one with the other to vary the degree of drag 
when said two or more mateable surfaces are moved in the same plane 
relative to each other and the degree of damping is proportional to the 
relative velocity of said two or more surfaces up to whip pan velocity and 
wherein frictional resistance is obtained between said two or more 
mateable surfaces when said two or more mateable surfaces are stationary. 
According to a still further aspect of the invention we provide a damping 
mechanism comprising at least in part, two or more mateable surfaces, 
wherein at least one of said mateable surfaces is substantially resistive 
to lubricants and at least one other of said mateable surfaces is 
substantially absorbent of lubricants, said two or more mateable surfaces 
being variably compressible one with the other to vary the degree of drag 
when said two or more mateable surfaces are moved in the same plane 
relative to each other, and the degree of damping is proportional to the 
relative velocity of said two or more surfaces up to whip pan velocity 
wherein frictional resistance is obtained between said two or more 
mateable surfaces when said two or more mateable surfaces are stationary 
and wherein said two or more mateable surfaces will slip one on the other 
when the velocity of movement in the same plane relative to each other 
reaches that of whip pan.

Referring to the drawing, a base (1) has a bearing (2), preferably a 
tapered bearing, with a shaft (3) journalled therein. A frusto-conical 
section of substantially lubricant resistant material (4) preferably of 
P.T.F.E. (Poly-tetra-fluoro-ethylene), or the like, of a P.T.F.E. or the 
like coated material, is concentrically attached to one end of shaft (3) 
for substantially mating engagement with a female frusto-conical section 
(5), the frusto-conical surface of which has a layer of compressible, 
substantially lubricant absorbent, material, such as NEBAR (Registered 
Trade Mark) or the like attached thereto. Locating means (7), such as 
dowels, and securing means (8), such as screws, provide the attachment 
means for the conical section (4) and shaft (3). A bar-nut (9) attached to 
the female frusto-conical section (5) and moveable along two slotted 
keyways (10) and (11) by rotation of a threaded adjusting ring (12) 
determines the amount of compression of the NEBAR (Registered Trade Mark) 
on the P.T.F.E. surface and hence the resistance to movement between the 
two surfaces when shaft (3) is rotated. Preferably the female 
frusto-conical section (5) is located on the bar-nut (9) by such as two 
dowel pins (13) and (14) and secured by such as two screws (15) and (16). 
A cover (17) may be secured, by such as screws, to the base (1). To 
provide a smooth movement between the two surfaces, the surfaces may be 
partially or wholly immersed in a lubricant reservoir and the lubricant 
may be retained within the operating area or reservoir by such as seals 
(18), (19) and (20). 
To provide a greater degree of control over the resistance to movement 
between the mating surfaces the NEBAR (Registered Trade Mark) surface may 
be channelled thus reducing the contact surface area and increasing the 
lubrication of the mating surfaces as a greater surface area for lubricant 
absorption is available within the channels and compression of the 
abutments easier. 
For use on such as a pan and tilt head used for supporting and controlling 
such as a camera, tracking aerial, or surveying instruments, the pan axis 
can be accommodated by utilising a thick cover (17) securable to such as a 
tripod and mounting the pan and tilt head, such as shown in the diagram, 
wherein a thrust race (21) supports the weight of a head (22) and the head 
is attached to the shaft (3) by such as a squared section (23), clamp (24) 
and nuts (25). For the tilt axis the cover (17) may be a thin plate and 
the shaft (3) may be attached to or be a part of the tilt pivots and the 
base (1) may be attached to or part of the main framework in which the 
tilt axis rotates. 
To improve dispersion of the lubricant around the reservoir when the drag 
unit is in operation, holes may be drilled through the female 
frusto-conical section (5) and nut bar (9) to prevent a build up of 
lubricant. 
With the system of the present invention friction between the two surfaces 
maintains the two surfaces in adherance when no intentional movement is 
taking place, the drag between the two surfaces provides a smooth 
resistive transition when following a moving subject and whip pan may be 
achieved, whereas, with fluid drag units quick changes in speed of 
rotation causes either build up of fluid drag and consequent excessive 
torque on a supporting tripod, or the like, or, the stress in the fluid 
caused by viscous shear may be high enough to break down the fluid layer 
and cause a fall-out in the damping rate. 
By friction it is meant the resistance to movement between the two surfaces 
when the surfaces are stationary. 
By drag it is meant the resistance to movement between the two surfaces 
when movement is made and is proportional to the relative velocity of the 
two surfaces. 
By whip pan it is meant that the resistance to movement between the two 
surfaces does not increase when a sufficient relative velocity is reached 
above a given rate.