U.S. patent application number 11/970593 was filed with the patent office on 2009-07-09 for safety device for a cantilevered beam and boom assembly incorporating the same.
This patent application is currently assigned to SMART TECHNOLOGIES INC.. Invention is credited to Paul Auger, Amir Butmir, Gregory G. Forrest, Andrew MacAskill, James Jacob Remple, Matthew Sean Rodgers.
Application Number | 20090173856 11/970593 |
Document ID | / |
Family ID | 40843811 |
Filed Date | 2009-07-09 |
United States Patent
Application |
20090173856 |
Kind Code |
A1 |
Auger; Paul ; et
al. |
July 9, 2009 |
Safety Device For A Cantilevered Beam And Boom Assembly
Incorporating The Same
Abstract
A safety device for a cantilevered beam pivotally mounted
adjacent one end thereof to a support surface is adapted to bridge
the beam and the support surface and is structured so that when
coupled to the beam and support surface, the safety device
maintains the beam in a substantially fixed cantilevered condition
until a downward force exceeding a threshold is applied to the beam
and thereafter controls downward pivoting of the beam.
Inventors: |
Auger; Paul; (Osgoode,
CA) ; Butmir; Amir; (Ottawa, CA) ; Rodgers;
Matthew Sean; (Stittsville, CA) ; Remple; James
Jacob; (Calgary, CA) ; MacAskill; Andrew;
(Calgary, CA) ; Forrest; Gregory G.; (Calgary,
CA) |
Correspondence
Address: |
KATTEN MUCHIN ROSENMAN LLP;(C/O PATENT ADMINISTRATOR)
2900 K STREET NW, SUITE 200
WASHINGTON
DC
20007-5118
US
|
Assignee: |
SMART TECHNOLOGIES INC.
Calgary
CA
|
Family ID: |
40843811 |
Appl. No.: |
11/970593 |
Filed: |
January 8, 2008 |
Current U.S.
Class: |
248/222.52 ;
248/291.1 |
Current CPC
Class: |
F16M 2200/066 20130101;
F16M 11/10 20130101; F16M 2200/041 20130101 |
Class at
Publication: |
248/222.52 ;
248/291.1 |
International
Class: |
F21V 21/00 20060101
F21V021/00 |
Claims
1. A safety device for a cantilevered beam pivotally mounted
adjacent one end thereof to a support surface, said safety device
being adapted to bridge said beam and said support surface and
being structured so that when coupled to said beam and support
surface, said safety device maintains said beam in a substantially
fixed cantilevered condition until a downward force exceeding a
threshold is applied to said beam and thereafter controls downward
pivoting of said beam.
2. A safety device according to claim 1 wherein said safety device
comprises first structure to maintain said beam in said
substantially fixed cantilevered condition and second structure to
control downward pivoting of said beam.
3. A safety device according to claim 2 wherein said first
structure is physically altered when a downward force exceeding
said threshold is applied to said beam.
4. A safety device according to claim 3 wherein said first
structure is at least one elongate link.
5. A safety device according to claim 4 wherein said at least one
elongate link breaks when a downward force exceeding said threshold
is applied to said beam.
6. A safety device according to claim 4 wherein said at least one
elongate link stretches to a point of non-recovery when a downward
force exceeding said threshold is applied to said beam.
7. A safety device according to claim 5 wherein said at least one
elongate link has a region of weakness formed along its length.
8. A safety device according to claim 7 wherein said region of
weakness is a region of reduced dimension.
9. A safety device according to claim 5 wherein said second
structure comprises at least one beam-pivoting resisting
element.
10. A safety device according to claim 9 wherein said at least one
beam-pivoting resisting element is selected from (i) at least one
chain-link element, (ii) at least one spring element, and (iii) at
least one dashpot.
11. A safety device according to claim 10 comprising a plurality of
beam-pivoting resisting elements.
12. A safety device according to claim 10 wherein said
beam-pivoting resisting elements comprise a combination of at least
two of (i) a chain-link element, (ii) a spring element, and (iii) a
dashpot.
13. A safety device according to claim 10 further comprising a
plurality of elongate links.
14. A safety device according to claim 3 wherein said safety device
is a metal strap comprising said first and second structure.
15. A safety device according to claim 14 wherein said first
structure is at least one elongate link and said second structure
is at least one beam-pivoting resisting element.
16. A safety device according to claim 15 wherein said at least one
elongate link has a region of weakness formed along its length.
17. A safety device according to claim 16 wherein said region of
weakness is a region of reduced dimension.
18. A safety device according to claim 15 wherein said at least one
beam-pivoting resisting element is selected from (i) at least one
chain-link element, (ii) at least one spring element, and (iii) at
least one dashpot.
19. A safety device according to claim 18 comprising a plurality of
beam-pivoting resisting elements.
20. A safety device according to claim 3 wherein said first
structure comprises a shear pin and retainer assembly.
21. A safety device according to claim 20 wherein said second
structure comprises at least one beam-pivoting resisting element
selected from (i) at least one chain-link element, (ii) at least
one spring element, and (iii) at least one dashpot.
22. A safety device according to claim 21 comprising a plurality of
beam-pivoting resisting elements.
23. A safety device according to claim 22 wherein said
beam-pivoting resisting elements comprise a combination of at least
two of (i) a chain-link element, (ii) a spring element, and (iii) a
dashpot.
24. A boom assembly comprising: a boom pivotally coupled adjacent
one end to a support surface; and a safety device acting between
said boom and said support surface, said safety device maintaining
said boom in a substantially horizontal orientation but failing
when a downward force exceeding a threshold is applied to said boom
to permit said boom to pivot downwardly, after failure said safety
device controlling downward pivoting of said boom.
25. A boom assembly according to claim 24 wherein said safety
device comprises first structure coupling said boom and support
surface that is physically altered when subjected to a downward
force exceeding said threshold and second structure coupling said
boom and support surface that controls downward pivoting of said
boom.
26. A boom assembly according to claim 25 wherein said first
structure breaks when subjected to the downward force exceeding
said threshold.
27. A boom assembly according to claim 26 wherein said first
structure and second structure are integrally formed on a strap
extending between and secured to said boom and support surface.
28. A boom assembly according to claim 27 further comprising a
mounting bracket to which the one end of said boom is pivotally
coupled, said mounting bracket being fastened to said support
surface.
29. A boom assembly according to claim 28 wherein said strap is
fastened adjacent one end thereof to said boom and adjacent an
opposite end thereof to said mounting bracket.
30. A boom assembly according to claim 29 wherein said first
structure comprises at least one elongate link having a region of
weakness thereon and wherein said second structure comprises at
least one beam-pivoting resisting element.
31. A boom assembly according to claim 30 wherein said at least one
beam-pivoting resisting element is selected from (i) at least one
chain-link element, (ii) at least one spring element, and (iii) at
least one dashpot.
32. A boom assembly according to claim 31 comprising a plurality of
beam-pivoting resisting elements.
33. A boom assembly according to claim 29 wherein said first
structure comprises a shear pin and retainer assembly and wherein
said second structure comprises at least one beam-pivoting
resisting element.
34. A boom assembly according to claim 33 wherein said at least one
beam-pivoting resisting element is selected from (i) at least one
chain-link element, (ii) at least one spring element, and (iii) at
least one dashpot.
35. A boom assembly according to claim 34 comprising a plurality of
beam-pivoting resisting elements.
36. A boom assembly according to claim 26 further comprising a
mounting bracket to which the one end of said boom is pivotally
coupled, said mounting bracket being fastened to said support
surface.
37. A boom assembly according to claim 36 wherein said first
structure comprises a shear pin and retainer assembly coupling said
boom and mounting bracket.
38. A boom assembly according to claim 37 wherein said shear pin is
affixed to said boom and said retainer is affixed to said mounting
bracket.
39. A boom assembly according to claim 38 wherein said second
structure is at least one dashpot coupling said boom and mounting
bracket.
40. A boom assembly according to claim 38 wherein said second
structure is at least one spring element coupling said boom and
mounting bracket.
41. A boom assembly according to claim 36 wherein said first
structure comprises a rotatable spool and tether arrangement
coupling said mounting bracket and boom, said spool being inhibited
from rotation prior to failure of said safety device.
42. A boom assembly according to claim 41 wherein said spool is
locked by a retaining pin that fails when a downward force
exceeding the threshold is applied to the boom.
43. A boom assembly according to claim 42 wherein said spool is
mounted on said mounting bracket, said tether being wound about
said spool and affixed adjacent one end thereof to said boom.
44. A boom assembly according to claim 43 wherein said second
structure lo is a brake acting on said spool.
Description
FIELD OF THE INVENTION
[0001] The present invention relates generally to cantilevered
assemblies and in particular, to a safety device for a cantilevered
beam and boom assembly incorporating the same.
BACKGROUND OF THE INVENTION
[0002] Wall mounted cantilevered assemblies such as for example
projector mounts are known in the art. U.S. Pat. No. 5,490,655 to
Bates discloses a video/data projector and monitor ceiling/wall
mount. The wall mount includes a wall support assembly fixedly
secured to a wall surface. A pair of struts extends horizontally
from the wall support assembly. A projector/monitor adapter is
supported by the ends of the struts. The wall support assembly
includes a strut adapter that rests between a pair of adapter
plates extending from a wall plate. A fastener secures the strut
adapter to the adapter plates in a manner to permit rotation of the
adapter plate and hence, the struts about a vertical axis. Although
Bates discloses an assembly for supporting a projector that is to
be secured to a wall surface, the Bates wall mount suffers
disadvantages. When a load is placed on the wall mount, the entire
load is taken up by the wall mount and the wall surface due to the
fact that the wall mount is static. If the load is significant, the
load may cause damage to the wall mount and/or the wall surface. In
addition, if it is necessary to service the wall mount and/or the
projector supported thereon, a ladder or other similar device must
be used to gain access to the wall mount and/or projector.
[0003] U.S. Pat. No. 6,540,366 to Keenan et al. discloses an
overhead projection system comprising an overhead projector support
assembly extending generally horizontally from a generally vertical
support surface. A display screen having a display surface is
mounted on the support surface beneath the projector support
assembly. A projector is mounted on the projector support assembly
and is aimed to project images onto the display surface of the
display screen. The projector support assembly comprises a governor
in the form of a damper and spring arrangement to control downward
pivotal movement of the projector support assembly when a load is
placed on the projector support assembly and to return the
projector support assembly to its generally horizontal orientation
when the load is removed. Although this overhead projection system
has proven to be very effective and overcomes the deficiencies
associated with the Bates assembly, it is expensive. In some
environments where cost is of primary concern, most cost effective
solutions are desired.
[0004] It is therefore an object of the present invention at least
to provide a novel safety device for a cantilevered beam and to a
boom assembly incorporating the same.
SUMMARY OF THE INVENTION
[0005] Accordingly, in one aspect there is provided a safety device
for a cantilevered beam pivotally mounted adjacent one end thereof
to a support surface. The safety device is adapted to bridge the
beam and the support surface and is structured so that when coupled
to the beam and support surface, the safety device maintains the
beam in a substantially fixed cantilevered condition until a
downward force exceeding a threshold is applied to the beam and
thereafter controls downward pivoting of the beam.
[0006] In one embodiment, the safety device comprises first
structure to maintain the beam in the substantially fixed
cantilevered condition and second structure to control downward
pivoting of the beam. The first structure is physically altered
when a downward force exceeding the threshold is applied to the
beam. In one form, the first structure is at least one elongate
link that breaks when the downward force exceeding the threshold is
applied to the beam. In another form, the first structure comprises
a shear pin and retainer assembly. The second structure comprises
at least one beam-pivoting resisting element. The at least one
beam-pivoting resisting element may be selected from (i) at least
one chain-link element, (ii) at least one spring element, and (iii)
at least one dashpot.
[0007] According to another aspect there is provided a boom
assembly comprising a boom pivotally coupled adjacent one end to a
support surface. A safety device acts between the boom and the
support surface. The safety device maintains the boom in a
substantially horizontal orientation but fails when a downward
force exceeding a threshold is applied to the boom to permit the
boom to pivot downwardly. After failure, the safety device controls
downward pivoting of the boom.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] Embodiments will now be described more fully with reference
to the accompanying drawings in which:
[0009] FIG. 1 is a perspective view of an interactive whiteboard
and boom assembly;
[0010] FIG. 2 is a side elevational view in cross-section of the
boom assembly;
[0011] FIG. 3 is an enlarged, partly cut-away, perspective view of
a portion of the boom assembly;
[0012] FIG. 4 is a top plan view of a safety device forming part of
the boom assembly;
[0013] FIG. 5 is a safety device moment displacement plot;
[0014] FIG. 6 is a top plan view of another embodiment of a safety
device;
[0015] FIG. 7 is a cross-sectional view of FIG. 6 taken along line
7-7;
[0016] FIG. 8 is a top plan view of yet another embodiment of a
safety device;
[0017] FIG. 9 is a cross-sectional view of FIG. 8 taken along line
9-9;
[0018] FIG. 10 is a side elevational view of a portion of the boom
assembly showing yet another embodiment of a safety device;
[0019] FIG. 11 is a side elevational view of a portion of the boom
assembly showing yet another embodiment of a safety device;
[0020] FIG. 12 is a side elevational view of the boom assembly
showing still yet another embodiment of a safety device; and
[0021] FIG. 13 is an enlarged, side elevational view of the safety
device shown in FIG. 12.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0022] Turning now to FIG. 1, an interactive whiteboard (IWB) is
shown and is generally identified by reference numeral 50. In this
embodiment, the IWB 50 is a 600i series interactive whiteboard
manufactured by SMART Technologies ULC, of Calgary, Alberta,
Canada, assignee of the subject application. As can be seen, the
IWB 50 comprises a touch screen 70 having a touch surface 72
surrounded by a bezel 74. A tool tray 76 is affixed to the bezel 74
adjacent the bottom edge of the touch surface 72 and accommodates
one or more tools that are used to interact with the touch surface.
The touch screen 70 is mounted on a wall surface 78 via mounting
brackets (not shown). The touch screen 70 may be one of a number of
types including but not limited to analog resistive, capacitive,
camera-based, electromagnetic, surface acoustic wave etc.
[0023] A boom assembly 82 is also mounted on the wall surface 78
above the touch screen 70 via a mounting bracket 84. The boom
assembly 82 comprises a generally horizontal boom 86 that extends
outwardly from the mounting bracket 84. The boom 86 supports a
projector 88 intermediate its length and a mirror 89 adjacent its
distal end. The projector 88 is aimed at the mirror 89 so that the
image projected by the projector 88 is reflected by the mirror 89
back towards the touch screen 70 and onto the touch surface 72.
[0024] The mounting bracket 84 comprises a pair of laterally
spaced, vertical flanges 90 between which a pivot pin 92 extends.
The pivot pin 92 is accommodated by a cup 94 provided on the
underside of the boom 86 thereby to enable the boom to pivot
downwardly in a vertical plane. The mounting bracket 84 also
comprises a horizontal flange 96 that extends outwardly from the
mounting bracket above the boom 86. A safety device 100 is secured
at one end to the horizontal flange 96 and at its opposite end to
the top surface of the boom 86. The safety device 100 maintains the
boom 86 in its substantially horizontal orientation unless a
downward force exceeding a threshold is applied to the boom 86. If
such a downward force is applied to the boom 86, the safety device
100 releases the boom allowing the boom 86 to swing downwardly. In
this manner, damage to the wall surface 78 and/or mounting bracket
84 is avoided. Even though the safety device 100 releases the boom
86, the safety device 100 controls downward pivotal movement of the
boom to avoid injury to anyone and/or damage to anything beneath
the boom 86 as well as to avoid damage to the projector 88 and the
mirror 89 supported by the boom 86.
[0025] Turning now to FIGS. 2 to 4, the safety device 100 is better
illustrated. As can be seen, the safety device 100 in this
embodiment is in the form of a metal strap formed of steel or other
structurally suitable material comprising a pair of spaced bands
102a and 102b respectively. Each band has pair of laterally spaced
holes 104 provided therein. The holes 104 in band 102a accommodate
fasteners that secure the band 102a to the horizontal flange 96.
The holes 104 in band 102b accommodate fasteners that secure the
band 102b to the top of the boom 86. The bands 102a and 102b are
joined by a generally central link 106 having a region of weakness
108 midway along its length. The region of weakness 108 in this
embodiment is a region of reduced width that acts as a mechanical
fuse. A pair of elongate boom-pivoting resisting elements in the
form of chain-link elements 110 also joins the bands 102a and 102b.
Each chain-link element 110 is positioned on an opposite side of
the link 106.
[0026] The operation of the safety device 100 will now be
described. When the boom 86 is normally loaded, the safety device
100 is placed in tension as the safety device acts to maintain the
boom 86 in its horizontal orientation. During normal loading, the
integrity of the safety device 100 remains intact keeping the boom
86 in position. However, if the boom 86 is overloaded as a result
of one or more individuals pulling down on or hanging from the
boom, when the load placed on the boom reaches a threshold, the
region of weakness 108 provided along the link 106 fails thereby
releasing the boom and permitting the boom 86 to pivot downwardly.
Failure of the region of weakness 108 along the link 106 provides
clear visual evidence that the boom 86 has been overloaded. The
point at which the region of weakness 108 along the link 106 fails
is selected to meet safety standard requirements and to avoid
damage to the wall surface 78 from occurring as a result of the
mounting bracket 84 being pulled from the wall surface 78. In
typical applications, the link 106 is designed so that it fails at
the region of weakness 108 under an applied load in the range of
from about 50 lbs to about 80 lbs. For example, when supporting a
typical projector 88, the link is designed so that it fails at the
region of weakness 108 under an implied load equal to about 62
lbs.
[0027] During downward swinging of the boom 86 under continued
application of the applied load and/or under its own weight, the
chain-link elements 110 bend while resisting downward pivoting of
the boom 86 thereby to control the descent of the boom 86 in a
manner to avoid injury to anyone and/or damage to anything beneath
the boom 86 as well as to avoid damage to the projector 88 and the
mirror 89 supported by the boom 86. As will be appreciated, the
configuration of the region of weakness 108 can be tailored to
adjust the point at which the link 106 fails under load applied to
the boom 86. Also, the configuration of the chain-like elements 110
can be tailored to adjust the manner by which the boom 86 swings
downwardly. After failure of the safety device 100, the boom
assembly 82 can be reset and returned to its normal operating
condition by removing the failed safety device, pivoting the boom
86 upwardly to its generally horizontal orientation, and fastening
a replacement safety device 100 to the boom 86 and horizontal
flange 96.
[0028] FIG. 5 is a moment displacement plot showing the moment
applied to the boom 86 in foot-pounds versus the extension of the
safety device 100 in inches. As can be seen, initially as the
moment applied to the boom 86 increases, the safety device 100
retains its integrity and extends very little. When the applied
moment reaches the threshold, the region of weakness 108 along the
link 106 begins to fail and the safety device 100 extends. Point F,
represents the point at which the region of weakness 108 fails
under the applied moment. Once the region of weakness 108 fails,
the chain-link elements 110 extend as the boom 86 pivots
downwardly. Point F.sub.2 represents the point at which the
chain-like elements 110 fail under the applied moment.
[0029] If desired, the link 106 can be configured so that rather
than breaking, the link stretches to a point beyond recovery when
the boom 86 is subjected to a load exceeding the threshold. Also,
the region of weakness 108 along the link 106 can take other forms.
For example, the region of weakness 108 can be formed by
perforating the link 106. Alternative safety device configurations
are also possible.
[0030] For example, although the safety device 100 is shown as
including a single link 106 positioned between a pair of chain-link
elements 110, those of skill in the art will appreciate that many
variations are permissible. The safety device 100 may include a
single link 106 and a single chain-link element 110. Alternatively,
the safety device 100 may comprise a single chain-link element 110
and a plurality of links 106 or a plurality of both chain-link
elements 110 and links 106. When the safety device 100 comprises a
plurality of chain-link elements 110 and a plurality of links 106,
the links and chain-link elements can be arranged in an alternating
pattern or other desired arrangement. Of course other structure can
be used to maintain the boom 86 in its horizontal orientation and
control downward pivoting of the boom 86 after the boom has been
overloaded.
[0031] Turning now to FIGS. 6 and 7, another embodiment of a safety
device is shown and is generally identified by reference numeral
200. In this embodiment, the safety device 200 comprises a pair of
spaced bands 202a and 202b respectively, with each band having a
pair of laterally spaced holes 204 provided therein. The holes 204
in band 202a accommodate fasteners that secure the band to the
horizontal flange 96. The holes 204 in band 202b accommodate
fasteners that secure the band to the top of the boom 86. The bands
202a and 202b are joined by a generally central mechanical fuse
assembly 206. A pair of elongate coil springs 210 also joins the
bands 202a and 202b. Each coil spring 210 is positioned on an
opposite side of the mechanical fuse assembly 206. The mechanical
fuse assembly 206 comprises an arm 212 integral with the band 202b
that terminates midway between the bands. The distal end of the arm
212 is configured to form a recess 214. An arm 216 integral with
the band 202a terminates with its distal end accommodated in the
recess 214. A shear pin 218 passes through the arms 212 and 216 and
the recess 214 thereby to interconnect and retain the arms and
inhibit their separation.
[0032] Similar to the previous embodiment, during normal loading
the integrity of the safety device 200 remains intact keeping the
boom 86 in its generally horizontal orientation. However, if the
boom 86 is overloaded as a result of one or more individuals
pulling down on or hanging from the boom, when the load placed on
the boom 86 reaches the threshold, the shear pin 218 fails thereby
to allow the arms 210 and 214 to separate and permit the boom 86 to
pivot downwardly. The point at which the shear pin 218 fails is
selected to avoid damage to the wall surface 78 from occurring as a
result of the mounting bracket 84 being pulled from the wall
surface. During downward swinging of the boom 86 under continued
application of the applied load and/or under its own weight, the
springs 210 extend thereby resisting downward pivoting of the boom
86 and controlling the descent of the boom 86 in a manner to avoid
injury to anyone and/or damage to anything beneath the boom 86 as
well as to avoid damage to the projector 88 and the mirror 89
supported by the boom 86. As with the embodiment of FIGS. 1 to 5,
the number and arrangement of mechanical fuse assemblies and coil
springs 210 can be varied.
[0033] Turning now to FIGS. 8 and 9, yet another embodiment of a
safety device is shown and is generally identified by reference
numeral 300. The safety device 300 in this embodiment is very
similar to that shown in FIGS. 6 and 7. As can be seen, the safety
device 300 comprises a pair of spaced bands 302a and 302b
respectively, with each band having a pair of laterally spaced
holes 304 provided therein. The holes 304 in band 302a accommodate
fasteners that secure the band to the horizontal flange 96. The
holes 304 in band 302b accommodate fasteners that secure the band
to the top of the boom 86. The bands 302a and 302b are joined by a
central mechanical fuse assembly 306. A pair of dashpots 310 (i.e.
pneumatic or hydraulic cylinder and piston arrangements) also joins
the bands 302a and 302b. Each dashpot 310 is positioned on an
opposite side of the central mechanical fuse assembly 306. The
mechanical fuse assembly comprises an arm 312 integral with the
band 302b that terminates midway between the bands. The distal end
of the arm 312 is configured to form a recess 314. An arm 316
integral with the band 302a terminates with its distal end
accommodated in the recess 314. A shear pin 318 passes through the
arms 312 and 316 and the recess 314 thereby to interconnect and
retain the arms and inhibit their separation. As will be
appreciated, the safety device 300 functions in a manner almost
identical to that of safety device 200 except that during downward
swinging of the boom 86, the dashpots 310 control the descent of
the boom 86.
[0034] Each of the safety devices need not carry a single type of
mechanical fuse or boom-pivoting resisting element. If desired,
each safety device may comprise a variety of boom-pivoting
resisting elements and/or a variety of mechanical fuses. For
example, the safety device may comprise one or more chain-link
elements as well as one or more spring elements and/or dashpots.
The safety device may also comprise one or more elongated links and
one or more mechanical fuse assemblies.
[0035] Turning now to FIG. 10 yet another embodiment of a safety
device is shown and is generally identified by reference numeral
400. In this embodiment, the safety device 400 comprises a shear
pin 420 extending upwardly from the top surface of the boom 86
adjacent the mounting bracket 84. A retainer 422 in the form of a
triangular ring extends from the mounting bracket 84 and surrounds
the shear pin 422. A coil spring 424 is secured at one end to the
mounting bracket 84 and at its opposite end to the top surface of
the boom 86. Similar to the embodiment of FIGS. 6 and 7, during
normal loading, the shear pin 420 remains intact thereby trapping
the retainer 422 and keeping the boom 86 in its generally
horizontal orientation. However, if the boom 86 is overloaded, when
the load placed on the boom reaches the threshold, the shear pin
420 fails thereby releasing the retainer 422 and permitting the
boom 86 to pivot downwardly. During the downward swinging of the
boom 86, the coil spring 424 controls the descent of the boom
86.
[0036] FIG. 11 shows still yet another embodiment of a safety
device 500. In this embodiment, the safety device 500 is very
similar to that shown in FIG. 10. As can be seen, the safety device
500 comprises a shear pin 520 extending upwardly from the top
surface of the boom 86 adjacent the mounting bracket 84. A retainer
522 in the form of a triangular ring extends from the mounting
bracket 84 and surrounds the shear pin 520. A dashpot 524 is
secured at one end to the mounting bracket 84 and at its opposite
end to the top surface of the boom 86. As will be appreciated, the
safety device 500 functions almost identical to that of safety
device 400 except during downward swinging of the boom 86, the
dashpot 524 controls the descent of the boom.
[0037] Turning now to FIGS. 12 and 13 still yet another embodiment
of a safety device is shown and is generally identified by
reference numeral 600. In this embodiment, the safety device
comprises a spool 602 rotatably mounted on the mounting bracket 84.
A tether 604 is wound about the spool 602 and is attached at its
free end to the boom 86. A retaining pin 606 extends through the
spool 602 thereby to inhibit rotation of the spool and hence,
paying out of the tether 604. A brake 608 exerts force on the spool
602.
[0038] In operation, during normal loading the integrity of the
retaining pin 606 remains intact thereby locking the spool 602 and
tether 604 and keeping the boom 86 in its generally horizontal
orientation. However, if the boom 86 is overloaded, the retaining
pin 606 fails allowing the spool 602 to rotate and pay out the
tether 604 thereby permitting the boom 86 to pivot downwardly.
During the downward pivoting of the boom 86, the brake 608, which
exerts a force on the spool 602, resists the downward pivoting of
the boom 86 thereby to control the descent of the boom.
[0039] Those of skill in the art will appreciate that use of the
safety device is not limited to a boom assembly 82 supporting a
projector 88 and mirror 89. Other equipment such as for example
camera assemblies, mirrors, microphones etc. may be supported by
the boom assembly. In fact, the safety device may be used in
virtually any environment where a cantilevered beam may be
subjected to overloading.
[0040] Although embodiments have been described, those of skill in
the art will appreciate that variations and modifications may be
made without departing from the spirit and scope thereof as defined
by the appended claims.
* * * * *