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BACKGROUND OF THE INVENTION
1. Field of the Invention:
This invention relates in general to extensible and retractable masts and
specifically to support systems for anchoring such masts.
Extensible and retractable masts are well known in the prior art. Such
devices are typically utilized in communications to support antennae,
fruit harvesting, fire hose elevation and many other applications in which
temporary elevation or support is required. Known portable mast systems
generally utilize telescoping or other extension methods and many such
systems include masts which are mounted upon a portable base or trailer to
facilitate movement of the mast from location to location.
2. Description of the Prior Art:
An excellent example of the current state of the art in portable extensible
mast systems can be seen in U.S. Pat. No. 4,625,475 issued to Henry J.
McGinnis. The system disclosed in that patent teaches an extensible mast
which is formed by orienting and uniting flexible strips of material.
A problem which exists in all known extensible mast systems is the
provision of stability as the mast is deployed or retracted. Guy wire
systems are well known in the art; however, unlike fixed mast units which
may be simply supported by fixed guy wires, an extensible system requires
a guy wire system which can be continually adjusted as the mast is
deployed. The solution utilized by most extensible mast systems known in
the prior art involves the utilization of multiple guy wires which must be
individually controlled to ensure vertical stability of the mast. The
problems associated with accurately controlling multiple individual guy
wires have made erection of such systems unduly complex and such systems
often require a large number of assistants to operate.
It should therefore be apparent that a need exists for an extensible mast
support system which may be simply and easily utilized to provide
stability for an erect mast. Further, a need exists for an extensible mast
support system which may be adapted to provide continual stability during
both extension and retraction of a portable mast.
SUMMARY OF THE INVENTION
It is therefore one object of the present invention to provide an improved
extensible mast support system.
It is another object of the present invention to provide an improved
extensible mast support system which provides vertical stability during
extension and retraction of the mast.
It is yet another object of the present invention to provide an improved
extensible mast support system which provides vertical stability during
extension and retraction of the mast and which may be easily and simply
operated by a single operator.
The foregoing objects are achieved as is now described. The extensible mast
system of the present invention includes a plurality of anchor points
which are preferably disposed at equidistant points radially distant from
the base of the mast. A support bracket is mounted to the mast and serves
as a mounting point for multiple metering sprockets. A single continuous
length of cable is threaded from a single supply reel coupling each anchor
point and the support bracket. A plurality of strain measurement devices
are utilized to measure the strain on each span of cable between an anchor
point and the support bracket and the output of these strain measurement
devices is utilized to control the paying out of cable during mast
extension and retraction. The length of cable utilized is beaded with a
plurality of beads which engage with the metering sprockets to restrict
variations in length between spans despite variations in strain from span
to span. In this manner, the geometry of the guy wires is retained despite
the utilization of a single continuous length of cable and vertical
stability is ensured.
BRIEF DESCRIPTION OF THE DRAWINGS
The novel features believed characteristic of the invention are set forth
in the appended claims. The invention itself; however, as well as a
preferred mode of use, further objects and advantages thereof, will best
be understood by reference to the following detailed description of an
illustrative embodiment when read in conjunction with the accompanying
drawings, wherein:
FIG. 1 is a perspective view of a portable extensible mast system utilizing
the support system of the present invention;
FIG. 2 is a partial view of one side of the cable drive and supply section
of the extensible mast support system of the present invention;
FIG. 3 is a partial view of the other side of the cable drive and supply
section of the extensible mast support system of the present invention;
FIG. 4 is a perspective view of the support bracket and metering sprockets
of the extensible mast support system of the present invention; and
FIG. 5 is a bottom view of the metering sprocket drive system of the
extensible mast support system of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
With reference now to the figures and in particular with reference to FIG.
1, there is depicted a perspective view of a portable extensible mast
system which utilizes the support system of the present invention. As can
be seen, the portable mast system includes a mast 10 which has been
erected from a movable base 12 to support a communications antennae 16. In
the depicted embodiment movable base 12 is implemented utilizing a small
trailer having an axle 18 and wheels 20 so that mast 10 may be moved from
site to site prior to erection. As is taught in the McGinnis Patent, mast
10 may be erected utilizing a plurality of flexible metal members which
are coiled within reel housings 22, 24 and 26. To ensure additional
structural soundness in the depicted mast system, rotatable reels 28 are
utilized to Wrap mast 10 in an elongate flexible material of a type and
nature disclosed in the aforementioned patent.
The support system of the present invention utilizes a plurality of anchors
including cable supply anchor base 30 and two additional anchor bases 32.
Each anchor base 30 or 32 is preferably placed at a radially disposed
location which is equidistant from the base of mast 10. Additionally, each
anchor base 30 or 32 is radially spaced equally about mast 10. That is,
with three anchor bases as depicted, each base is located at a one hundred
and twenty degree angle from an adjacent anchor base. While three anchors
are depicted in this embodiment, upon reference to this specification
those skilled in the art will appreciate that at least two anchors must be
utilized and that any greater number may also be utilized in accordance
with the teaching of the present invention. Additionally, it should be
clear that multiple sets of anchors may be utilized, each set serving to
anchor a different vertical section of mast 10. It should also be apparent
that many methods exist for anchoring anchor bases 30 or 32 to the earth.
Upon each anchor base 30 or 32 there is mounted a stanchion 38 which serves
to support additional system elements. Cable supply anchor base 30 and its
associated stanchion 38 serve to support supply reel 40 which is utilized
to store and collect cable 42. In the depicted embodiment of the present
invention cable 42 comprises a flexible metallic cable which includes a
plurality of beads 66 which are formed thereon at substantially
equidistant locations. The function of beads 66 will be explained in
greater detail herein; however, it will be apparent that other physical
discontinuities in cable 42, if utilized in accordance with the novel
system of the present invention, may serve a similar function to that of
beads 66.
Cable supply anchor base 30 also serves to support controllable drive motor
58 which is preferably an electric motor. Controllable drive motor 58,
through transmission 62, and as directed by control device 60, serves, in
a manner described below, to operate cable drive 64. Also mounted to each
cable supply anchor base 30, and anchor bases 32, are strain measurement
devices 36 which are utilized in accordance with the present invention to
measure the strain present in spans 44, 46 and 48 of cable 42. The output
of each strain measurement device 36 may be utilized, as explained herein,
to control the paying out and rewinding of cable 42 during extension and
retraction of mast 10. Anchor bases 32 also serve to mount detent pulleys
34 which each serve to receive and return a length of cable 42. After a
review of the following disclosure, those skilled in the art will
appreciate that each detent pulley 34 must be mounted to stanchion 38 at
substantially the same vertical position and that this vertical position
should be equal to the position of the source of cable 42 as it pays out
of cable drive 64.
Still referring to FIG. 1, there is also depicted a support bracket 50
which is preferably mounted in a selected position to mast 10. Support
bracket 50 serves to mount metering sprockets 52, 54 and 56 along with
various guidance and synchronization equipment illustrated below. As can
be seen, the mast support system of the present invention utilizes a
single continuous length of cable 42 which is threaded from supply reel 40
through cable drive 64 to metering sprocket 54 on support bracket 50 along
span 44. From metering sprocket 54 cable 42 is threaded through detent
pulley 34 at anchor base 32 and back to metering sprocket 56 along span
46. Similarly, cable 42 is threaded from metering sprocket 56 through
detent pulley 34 at anchor base 32 and back to metering sprocket 52 along
span 48. Finally, cable 42 is threaded from metering sprocket 52 to
stanchion 38 on cable supply anchor base 30 along span 43. Of course, it
will be apparent upon reference to FIG. 1, that each anchor base also
includes a strain measurement device 36 which is coupled to a section of
the cable span near that anchor point.
With reference now to FIG. 2, there is depicted a partial view of one side
of cable supply anchor 30 of the present invention. As can be seen, supply
reel 40 is mounted to stanchion 38 by means of reel support bracket 76.
Controllable drive motor 58 is mechanically coupled, through transmission
62 ,to cable drive 64. As those skilled in the art will appreciate,
controllable drive motor 58 may be selectively operated to rotate cable
drive pulley 70 which is coupled to reel drive pulley 72 by means of
flexible drive belt 74. In this manner, operation of cable drive 64 will
cause rotation of supply reel 40. While it is obvious that extension of
mast 10 and pay out of cable 42 by cable drive 64 could be accomplished
without the necessity of driving supply reel 40, it should be recalled
that automatic rewind of cable 42 is required during retraction of mast 10
(see FIG. 1). Thus, during rewind of cable 42 drive belt 74, co-acting
with cable drive pulley 70 and reel drive pulley 72 will serve to rewind
cable 42 on supply reel 40.
Pivotally mounted to cable drive 64 by members 68 is strain measurement
device 36. The depicted embodiment of strain measurement device 36 can
best be understood by simultaneous reference to both FIGS. 2 and 3. As can
be seen, strain measurement device 36 includes two fixed tension rollers
78, which are preferably pulleys or other devices adapted with detents to
receive each bead 66 of cable 42. Movable tension roller 80 is similarly
constructed and is preferably mounted in a manner which will permit
movement in a substantially vertical manner when disposed as depicted in
FIG. 3.
As can be seen, a spring 83 and adjustment screw 81 are provided and may be
utilized to bias the initial position of movable tension roller 80 in a
raised position. It should be apparent from reference to the foregoing
that while cable 42 is not under tension or strain, movable tension roller
so will move upward in response to the bias of spring 83, deflecting cable
42 upward from the depicted horizontal position. As longitudinal tensile
strain is increased on cable 42, movable tension roller 80 will be forced
downward, against the bias provided by spring 83. Those skilled in this
art will appreciate that the movement of movable tension roller 80 may by
utilized to operate a potentiometer or make an electrical contact to
provide an indication of the strain present in cable 42. This indication
may be provided remotely by electrically coupling each strain measurement
device 36 to a central control device 60.
Referring more specifically now to FIG. 3, the operation of cable drive 64
may be illustrated. As is depicted, cable drive 64 preferably includes a
plurality of detent rollers similar to those present in each strain
measurement device 36. Two of such rollers are preferably idler drive
rollers 82 while a third roller, drive roller 84, is operatively coupled
through transmission 62 to controllable drive motor 58. It should be
apparent that during rotation of drive roller 84 cable 42 may be driven
through cable drive 64 in either direction. As illustrated below, control
device 60 may be utilized to direct the operation of controllable drive
motor 58 in response to the outputs of strain measurement devices 36, or
in an alternate embodiment, a human operator may observe the outputs of
strain measurement devices 36 and direct controllable drive motor 58
manually.
With reference now to FIG. 4, there is depicted a more detailed perspective
view of support bracket 50 of the novel support system of the present
invention. As is illustrated, support bracket 50 is preferably fixedly
mounted to mast 10 by utilization Of a plurality of bolts 98.
Additionally, multiple mounting pins 100 may also be utilized in
conjunction with apertures in mast 10 to ensure support bracket 50 remains
in a stable position on mast 10. Support bracket 50 is preferably mounted
to mast 10 at a selected point as mast 10 is erected. As disclosed
earlier, in applications in which mast 10 will achieve a sufficient height
it may be desirable to attach a second support bracket 50 to mast 10 is to
serve in conjunction with a second set of anchor points. Fixedly mounted
to support bracket 50 are multiple metering sprockets 52, 54 and 56. As
can be seen, each metering sprocket includes a plurality of detents, each
adapted to receive a bead 66 when cable 42 is threaded through the
metering sprockets.
As previously described in less detail, cable 42 may be threaded along span
44 to a guide roller 86 which is rotatably mounted to guide roller support
88. Cable 42 then engages metering sprocket 54 and passes over a second
guide roller to form span 46. Upon returning from detent pulley 34 (see
FIG. 1) span 46 engages another guide roller 86 and is threaded into
contact with metering sprocket 56. Another pair of guide rollers 86 are
utilized to form span 48 and cable 42 is finally coupled to metering
sprocket 52 from whence it returns to cable supply anchor base 30 as span
43.
As may be partially viewed in FIG. 4, metering sprockets 52, 54 and 56 are
each directly coupled by a shaft (not shown) to a respective metering
sprocket drive gear 90, 92 and 94 (not shown). A chain belt 96 is then
utilized to synchronize rotation of metering sprockets 52, 54 and 56 in a
manner consistent with the disclosure of the present invention. The
operation of metering sprocket drive gears 90, 92 and 94 and further
advantages of this invention may be more easily understood upon reference
to FIG. 5.
FIG. 5 depicts a bottom view of support bracket 50 of the novel support
system of the present invention and clearly illustrates the interaction of
metering sprocket drive gears 90, 92 and 94. As may be seen, although
metering sprockets 52, 54 and 56 are of substantially identical diameters,
metering sprocket drive gears 90, 92 and 94 vary in diameter in a precise
relationship. This relationship is responsible for the novel manner in
which a single length of continuous cable 42 may be utilized to provide
multiple independent guy wires. As illustrated, metering sprocket drive
gear 92 includes five gear teeth, metering sprocket drive gear 90 includes
fifteen gear teeth and metering drive gear 94 includes forty-five gear
teeth, each gear tooth being spaced a substantially equal distance from
its adjoining gear teeth in each metering sprocket drive gear by varying
the diameter thereof so that a single chain belt can drive each metering
sprocket drive gear.
Chain belt 96 couples each metering sprocket drive gear together and limits
independent rotation of any individual metering sprocket drive gear. Thus,
each rotation of metering drive gear 90 will Cause three rotations of
metering sprocket drive gear 92 and one-third of one rotation of metering
sprocket drive gear 94. Recalling that metering sprockets 52, 54 and 56
are directly coupled to their associated metering sprocket drive gear and
that each metering sprocket is substantially identical in diameter, it
should be apparent that longitudinal movement along each span of cable 42
will vary in accordance with the gear ratios depicted.
It will facilitate the understanding of this aspect of the present
invention if the reader will consider the paying out of additional cable
42 from cable supply reel 40 to each individual pan in a discreet
step-by-step manner. Thus, should cable 42 pay out from supply reel 40 a
total of six beads 66, the forced rotation of metering sprocket drive gear
92 will cause metering sprocket 54 to advance five beads 66 to span 46,
leaving the length of span 44 incremented by one bead.
Next, the rotation of metering sprocket drive gear 90 (in actuality
occurring simultaneously with the rotation of metering sprocket drive gear
92) will drive metering sprocket 56, advancing three beads 66 and
augmenting the length of span 46 by one bead 66 on each leg thereof.
Finally, metering sprocket drive gear 94 also rotates, driving metering
sprocket 52 and advancing one bead 66 onto span 43, augmenting the length
of span 48 by one bead on each leg thereof. In this manner, each guy wire
formed by a span of cable 42 has been incremented by an equal amount of
length.
It should now be apparent that while cable drive 64 is immobilized,
metering sprocket drive gears 90, 92 and 94 will similarly be immobilized.
It follows then that metering sprockets 52, 54 and 56 will remain at rest,
engaging various beads 66 from cable 42 and substantially restricting
length variation in each span of cable 42 despite variations which may be
present in the strain at each span.
The foregoing teaching is quite important as it is necessary to retain the
desired geometry of all guy wires despite unequal strain present therein.
For example, should a single span 46 be exposed to a tensile strain by a
wind, it is necessary to prevent span 46 from increasing in length and
consequently shortening the length of spans 48 and 44. The novel support
system of the present invention allows this independent relationship to
occur despite the utilization of a single length of continuous cable 42.
By solving this problem, the Applicant has made the utilization of a
single length of cable 42 and its concomitant ease of operation possible
for multiple guy wire support systems.
The utilization of stress measurement devices 36 will now be described in
conjunction with the erection or retraction of mast 10. As may be
apparent, the necessary position of support bracket 50 will vary with
climatic conditions and the height of mast 10 which is desired. It will
however be necessary to fasten support bracket 50 to mast 10 during
erection and pay out cable 42 as support bracket 50 rises with the
erection of mast 10. Conversely, it will be necessary to rewind cable 42
as support bracket 50 is lowered while mast 10 retracts. A simple
algorithm which may be easily adapted to automatic control is utilized to
control the paying out and rewinding of cable 42 during extension or
retraction of mast 10.
The output of each strain measurement device 36, in accordance with the
present invention, is constantly scrutinized during erection and
retraction of mast 10. During erection of mast 10, cable drive 64 will
only pay out cable 42 when all three strain measurement devices 36
indicate cable 42 is under tension. During retraction of mast 10, cable
drive 64 will rewind cable 42 when any one of strain measurement devices
36 indicates cable 42 is not under tension. In this manner, mast 10 may be
erected or retracted, raising or lowering support bracket 50 while the
novel support system of the present invention ensures that each span of
cable 42 remains equal in length.
Although the invention has been described with reference to a specific
embodiment, this description is not meant to be construed in a limiting
sense. Various modifications of the disclosed embodiment as well as
alternative embodiments of the invention will become apparent to persons
skilled in the art upon reference to the description of the invention,. It
is therefore contemplated that the appended claims will cover any such
modifications or embodiments that fall within the true scope of the
invention.
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