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Description  |
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This invention relates to television camera mounting equipment, or the
like, and more particularly, though not exclusively, to television camera
mounting equipment for studio use.
Television camera mounting equipment such as balanced pedestals at present
in use in television studios cover most of the desirable features, such as
smooth transition of a camera in the vertical direction and, as the
pedestals are normally wheel mounted and operating on a smooth floor, they
also cover smooth transition in the horizontal plane. Some of these
pedestals will also rotate in azimuth and any one of the three movements
may be used independently of the others. However, assuming, for example,
an upward or downward sloping transition were required, and this is
sometimes the case, it is a very hit or miss affair as the operator has to
imagine the changing vertical and horizontal co-ordinates which produce
the line of travel, and endeavour to alter the pedestal height, which
requires a minimal force to overcome inertia, at the same time as the
pedestal is being moved in a straight line across the floor where, due to
the weight difference alone, a comparatively high force is required to
overcome inertia. The resulting wavelike transition which should
preferably be a straight line is, more often than not, far from
acceptable.
This problem is caused by the appreciable difference in the vertical and
horizontal forces required and could be considerably reduced were the
forces equally balanced and only a small guiding force required.
The same type of problem exists when using pedestals in some other
operations, e.g. where a camera needs to be moved in a particular plane.
The horizontal plane can be overcome by moving the balanced pedestal over
the floor on its wheels, but the vertical plane suffers the same problems
as for the angled transition. It is always the problem of applying the
changing vertical and horizontal co-ordinates manually, and hoping for a
smooth transition.
Balanced arms, also used in the art, do not follow a true vertical as does
the pedestal. In many applications an arm is more appropriate for the task
than a pedestal, due to its greater versatility but in the past the lack
of true vertical guidance has caused a problem.
It is also desirable that full counterbalance of the mass, comprising
camera and arm, is maintained at all times in elevation and horizontal
movement or any combinations thereof so that only a minimal force is
required to traverse in any direction within the working envelope of the
arm and yet full stability and rigidity is maintained at all times both
during positional change and at the changed position.
It is a further desirable feature that motion may be constrained to limited
planes or directions, in addition to the aforementioned vertical guidance,
as and when required so that an operator need not concentrate on guidance
and only needs to supply the small force necessary for movement.
A still further desirable feature is that the balanced arm may be easily
operable from a remote site by such as small electric motors, or the like,
controlling the arm movement from remotely controlled signal lines.
It is therefore an object of this invention to provide a fully balanced arm
wherein the desirable features of the pedestal are retained and the
additional desirable features are incorporated thereby substantially
overcoming the problem.
According to the invention we provide a balanced arm for television or the
like comprising, a movable base, a rotatable platform mounted on said
base, a first traversable mounting on said rotatable platform having
vertical control means operable on a control pivot of a pantograph having
its fulcrum arm pivotally located on said rotatable table, a load carrying
platform pivotally located at the end of the pantograph proportional arm,
linkages forming a first parallelogram on said proportion arm wherein one
link is formed on said load carrying platform and a second parallelogram
on said fulcrum arm wherein one link is formed from part of said rotatable
platform and said two parallelograms share a common link; arm mass
counterbalancing means pivotally mounted on a second traversable mounting
on said rotatable platform and having its fulcrum pivotally attached to a
short link of said pantograph, load counterbalancing means operable on
said vertical control means, and guide means for said first and second
traversable mountings wherein said load carrying platform and load retains
verticality and may be traversed with full counterbalance in any plane
within its operational limits.
The invention will now be described, by way of example only, in conjunction
with the accompanying schematic diagrams in which,
FIG. 1 shows a schematic system according to the invention
FIG. 2 shows the mathematical diagram for proving mass balance of structure
and
FIG. 3 shows the mathematic diagram for proving balance of load.
Referring to FIG. 1 a base (1) preferably of a generally triangular shape
for ease of mounting wheels (2) or the like so that the base may be
steered or moved in a crabbing fashion i.e. the base may be traversed
along a straight line in any selected direction with its three wheels in
alignment or may be steered in tricycle fashion. A section (3) which may
be part of the base or attached thereto has a journalled shaft (4) of
preferably large diameter located therein. Mounted on shaft (4) is a
rotatable platform (5) having guides therein (not shown) in which wheels,
rollers or the like (6) may run for controlled movement of traversable
mountings (7) and (8). A fixed mounting, preferably part of platform (5),
provides a fixed link (9) for pivotally mounting the fulcrum (21) of
fulcrum arm (10) of a pantograph comprising, in addition, links (11) and
(12) and proportion arm (13), joined at four pivot points (14), (15), (16)
and (17) so that movement of pivot (14) determines, in conjunction with
rotation of platform (5), the position of the proportion arm (13) and
hence the position of a load carrying platform (18) pivotally located at
the free end (19) of the proportion arm (13). Two parallelograms of links
formed from fixed link (9), fulcrum arm (10), link (20) common link (22)
link (23), pivotally located on the load carrying platform at pivot (24)
to form a short link in conjunction with the pivots (16), (19), (21),
(24), (25), (26) and (27) of the two parallelograms ensures that the load
carrying platform and a load thereon retains its verticality irrespective
of the pantograph position. Pivot point (21), the fulcrum, provides a
fixed reaction point which ensures desirable structural integrity of arms
(10) and (13) with the rotatable platform (5).
A vertical control means, in this example vertical slots milled in
traversable mounting (7) for reception of extended ends of pivot (14)
provides vertical movement of pivot (14) and pivot (14) is acted upon by a
small diameter ram (28) controlled by a gaseous pressure in cylinder (29),
located on traversable mounting (7), provided from a relatively large
reservoir (30) via suitable piping (31). The pressure on ram (28), being
substantially constant, is such that the load on platform (18) is
counterbalanced in all positions of the arm. A bar (32) pivoted at a
suitable point (33) along its length on traversable mount (8) is pivotally
attached at pivot (34) on link (11) of the pantograph and a weight (36) at
the opposite end of the bar (32) is of sufficient mass to counterbalance
the combined mass of the pantograph and parallelogram links, excluding
link (9), and load carrying platform (18) as the combined mass pivots
about combinations of pivots (9), (14) and (21). An advantage of this
arrangement is that it permits the use of unequal length of proportional
arm (13) and fulcrum arm (10) whilst still retaining full counterbalance.
In the case of such as a television camera being the load it is normal
practice to mount the camera on a pan and tilt head, or the like, to
provide additional control. The added weight of the pan and tilt head may
be considered as extra load and be counterbalanced by increasing the
pressure in cylinder (29).
Locking devices which may be of any known type such as cylinder brakes or
friction clamps, may be applied or released at pivot point (14), as
indicated by locking device (40), to lock pivot point (14) in the vertical
plane on traversable mounting (7), at wheels or rollers (6), as indicated
by locking device (42), to lock traversable mounting (7) in the horizontal
plane on rotatable platform (5), and in journalled shaft (4) to lock the
rotatable platform (5) in azimuth. The following table shows the effect of
locking and unlocking, either singly or in combination, any of the
aforementioned locking means.
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Effect on load carrying
Vertical
Horizontal
Azimuth platform
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locked locked locked locked in selected position.
locked locked unlocked peripheral circular motion on
horizontal plane.
locked unlocked locked motion in horizontal line.
unlocked
locked locked motion in vertical line.
locked unlocked unlocked motion on horizontal plane.
unlocked
unlocked locked motion on vertical plane.
unlocked
locked unlocked motion on a cylindrical plane.
unlocked
unlocked unlocked complete freedom of motion.
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Manual positional control of the load carrying platform is preferably
performed directly at the load carrying platform but remote positional
control of the load carrying platform is preferably performed at the
control pivot point of the pantograph and may, as the balanced arm is
fully balanced, be controlled by three small electric motors, or the like;
one for vertical, one for horizontal and one in azimuth; remotely
controlled via signal lines. Control by this method has the added
advantage that the movement of the load is proportional to the control
point displacement provided by the motors.
It will also be obvious to those skilled in the art that various
alterations may be made to the apparatus without departing from the
invention. For example, the mass counterbalancing of the arm by weights
may easily be replaced by a pneumatic or hydraulic system similar to that
for counterbalancing the load or it may be counterbalanced by a spring
system such as disclosed in British Patent Application No. 8122509.
The following calculations, in conjunction with FIGS. 2 and 3, shows the
mathematical proof for balance of the arm and load respectively.
The mass of each element of the structure is represented by M at its centre
of gravity.
Balance of mechanism components
M.sub.1 Mass of links 10, 20 and 22
M.sub.2 Mass of link 11
M.sub.3 Mass of link 12
M.sub.4 Mass of links 13 and 23
M.sub.5 Mass of load platform
F Constant vertical force
In moving from .theta..sub.1 =.theta..sub.2 =0.sup.0, loss of potential
energy of links is:
##EQU1##
Corresponding work done on force F is:
.DELTA.W.sub.F =F{r.sub.1 (l-Cos .theta..sub.1)=x(l-Cos .theta..sub.2)}
Thus the structure will remain in equilibrium if:
Fr.sub.1 +M.sub.1 l.sub.1 +M.sub.2 r.sub.1 +M.sub.3 (r.sub.1
+l.sub.3)+(M.sub.4 +M.sub.5)L.sub.1
and
Fx=M.sub.2 l.sub.2 +M.sub.3 r.sub.2 +M.sub.4 l.sub.4 +M.sub.5 L.sub.2
Balance of variable camera load
M.sub.6 Mass of camera and mounting
P Constant vertical force
Loss of P.E. of M.sub.6 is:
.DELTA.P.E.=M.sub.6 {L.sub.1 (l-Cos .theta..sub.1)+L.sub.2 (l-Cos
.theta..sub.2)}
Work done on force P is:
.DELTA.W.sub.P =P{r.sub.1 (l-Cos .theta..sub.1)+r.sub.2 (l-Cos
.theta..sub.2)
Thus the load will stay in equilibrium if:
Pr.sub.1 =M.sub.6 L.sub.1 and Pr.sub.2 =M.sub.6 L.sub.2
Since P.alpha.M.sub.6 in both equalities, changes in M.sub.6 can be
accommodated by changes in P to maintain conditions for equilibrium.
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