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.

Description:
This application is a continuation application of U.S. patent application Ser. No. 11/970,593, filed Jan. 8, 2008, the entire contents of which are incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     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 
     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. 
     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. 
     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 
     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. 
     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. 
     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 
       Embodiments will now be described more fully with reference to the accompanying drawings in which: 
         FIG. 1  is a perspective view of an interactive whiteboard and boom assembly; 
         FIG. 2  is a side elevational view in cross-section of the boom assembly; 
         FIG. 3  is an enlarged, partly cut-away, perspective view of a portion of the boom assembly; 
         FIG. 4  is a top plan view of a safety device forming part of the boom assembly; 
         FIG. 5  is a safety device moment displacement plot; 
         FIG. 6  is a top plan view of another embodiment of a safety device; 
         FIG. 7  is a cross-sectional view of  FIG. 6  taken along line  7 - 7 ; 
         FIG. 8  is a top plan view of yet another embodiment of a safety device; 
         FIG. 9  is a cross-sectional view of  FIG. 8  taken along line  9 - 9 ; 
         FIG. 10  is a side elevational view of a portion of the boom assembly showing yet another embodiment of a safety device; 
         FIG. 11  is a side elevational view of a portion of the boom assembly showing yet another embodiment of a safety device; 
         FIG. 12  is a side elevational view of the boom assembly showing still yet another embodiment of a safety device; and 
         FIG. 13  is an enlarged, side elevational view of the safety device shown in  FIG. 12 . 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     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. 
     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 . 
     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 . 
     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  102   a  and  102   b  respectively. Each band has pair of laterally spaced holes  104  provided therein. The holes  104  in band  102   a  accommodate fasteners that secure the band  102   a  to the horizontal flange  96 . The holes  104  in band  102   b  accommodate fasteners that secure the band  102   b  to the top of the boom  86 . The bands  102   a  and  102   b  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  102   a  and  102   b . Each chain-link element  110  is positioned on an opposite side of the link  106 . 
     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. 
     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 . 
       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 1  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 2  represents the point at which the chain-like elements  110  fail under the applied moment. 
     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. 
     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  10 . 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. 
     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  202   a  and  202   b  respectively, with each band having a pair of laterally spaced holes  204  provided therein. The holes  204  in band  202   a  accommodate fasteners that secure the band to the horizontal flange  96 . The holes  204  in band  202   b  accommodate fasteners that secure the band to the top of the boom  86 . The bands  202   a  and  202   b  are joined by a generally central mechanical fuse assembly  206 . A pair of elongate coil springs  210  also joins the bands  202   a  and  202   b . 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  202   b  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  202   a  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. 
     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. 
     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  302   a  and  302   b  respectively, with each band having a pair of laterally spaced holes  304  provided therein. The holes  304  in band  302   a  accommodate fasteners that secure the band to the horizontal flange  96 . The holes  304  in band  302   b  accommodate fasteners that secure the band to the top of the boom  86 . The bands  302   a  and  302   b  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  302   a  and  302   b . 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  302   b  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  302   a  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 . 
     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. 
     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 . 
       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. 
     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 . 
     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. 
     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. 
     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.