AU767416B2

AU767416B2 - Load limiting device

Info

Publication number: AU767416B2
Application number: AU47167/00A
Authority: AU
Inventors: Brian Eugene Whelan
Original assignee: Individual
Current assignee: Individual
Priority date: 1999-07-12
Filing date: 2000-07-12
Publication date: 2003-11-06
Anticipated expiration: 2020-07-12
Also published as: AU4716700A

Description

S&FRef: 515147

AUSTRALIA

PATENTS ACT 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT

ORIGINAL

Name and Address of Applicant: Brian Eugene Whelan 16 Greenfield Avenue Middle Cove New South Wales 2068 Australia Brian Eugene Whelan Actual Inventor(s): Address for Service: Spruson Ferguson St Martins Tower 31 Market Street Sydney NSW 2000 Load Limiting Device Invention Title: ASSOCIATED PROVISIONAL APPLICATION DETAILS [33] Country [31] Applic. No(s) AU PQ1566 AU PQ3345 The following statement is a full description of this invention, performing it known to me/us:- [32] Application Date 12 Jul 1999 11 October 1999 including the best method of 5815c [R:\LIBW]00745 .doc:MAA LOAD LIMITING DEVICE Technical Field The present invention relates to load limiting devices. More particularly, though not exclusively, the invention relates to load limiting devices for use with suspended work platforms.

Background of the Invention Modern cities and towns include an ever increasing number of buildings and structures of various heights from the ground. These dwellings and/or structures require maintenance and repair work on a regular basis at varying heights up and down the structure. Accordingly, it has become common to use suspended work platforms, swinging stages or the like, lowered from the top of a structure and thereby allowing workers a platform upon which they may safely work on the side of the building or •structure.

Many accidents occur every year during the use of these platforms due to factors such as excessive loads and stresses upon the cables from which the platform is lowered and raised. It is also common for the platform, whilst being elevated, to snag on protruding objects such as ledgers or sills on the side of a structure. Accordingly, it has become necessary for these types of stages to include an automatic fail safe should the platforms exert an overloading or overstressing condition on the cables and their supporting roof rig.

an attempt to overcome these problems a number of fail safe devices have been developed and are presently on the market. However, these prior art devices are too cumbersome, complicated in design, unreliable, expensive and require constant servicing.

Accordingly, it would be desirable to have a simple load limiting device which can automatically fail safe an elevated platform safely and securely.

Object of the Invention It is an object of the present invention to overcome or ameliorate some of the disadvantages of the prior art, or at least to provide a useful alternative.

Summary of the Invention Accordingly, in a first aspect the invention provides a swinging stage assembly having: [R:\IJ B1I09805.doc: KEH at least one rig support to be mounted on a structure and having attachment means; an swinging stage suspended from the rig support; an electrically driven winch attached to the stage, said winch having an electric motor and having at least one cable by which the stage is suspended, the winch being operable to raise and lower the stage; and a load limiting device connecting the cable to the attachment means, the load limiting device being electrically connected to the winch to selectively deliver electric power thereto, the device being operable to electrically isolate said winch when a lo predetermined load is applied to said device by said cable to thereby limit the load that can be lifted by the winch.

Preferably, the load limiting device includes: a body having attachment means to which a load is applied; a switch mounted on the body and operable to connect the motor to a supply of electric energy, the switch being in a first configuration to deliver said energy; a shaft movably mounted in the body for axial movement relative the body, the shaft also having attachment means via which the load is applied to said shaft; p oso a striking means fixed to the shaft so as to be movable therewith between a first ••go position allowing the switch to remain in the first configuration, and a second position in which the switch is in a second configuration, said switch in said second configuration electrically isolates said motor; and resilient means urges said striking means to the first position thereof, the resilient means being resiliently deformed to permit movement of the striking means to the second position upon said load exceeding a predetermined load.

Preferably, the resilient means includes a plurality of resilient discs surrounding the shaft.

•Preferably, the resilient means includes a multi-cushioned rubber mount.

Preferably, the device includes one or more spacers located about said shaft and attached to said body for preselecting the first position.

S 30 Preferably, the body includes a guide bush to facilitate the axial movement of the shaft.

[R:\LIBLL]09805.doc:KEH:caa:KEH Preferably, the spacers include colour coded indicia to indicate the predetermined load.

Preferably, the device is adapted for attachment to a roof rig support.

Preferably, the device is adapted to positively open circuit a main supply of a i winch motor and/or platform.

Preferably, the device is adapted for attachment to any style or make of roof rig support.

Preferably, the device is simple to maintain, and simple to adjust after an initial factory calibration.

1o Preferably, the device is robust and can withstand rough treatment.

Preferably, the device has an optional audible alarm.

The invention at least in a preferred embodiment directly limits the load that the hoist imposes on the suspension rod and rig, as it directly connects the rope to the rig, and directly disconnects power to the hoist once the load on the rope reaches the limit. The is device is necessary as the stalling load of the hoist is significantly higher than the working load for which it is rated.

Known existing devices limit the load imposed on the rope and rig indirectly, for example by limiting the current draw in the hoist, or by limiting the load suspended from the hoist (in this embodiment the device is connected between the hoist and the platform).

Brief Description of the Drawings A preferred form of the present invention will now be described, by way of example only, with reference to the accompanying drawings, wherein: Figure 1 is a schematic perspective view of a load limiting device according to the invention, in situ.

Figures 2A and 2B are cutaway plan and side views, respectively, of a load limiting device according to an embodiment of the present invention; Figures 3A to 3E are plan, rear, front and left and right side views, respectively, of the body shown in Figures 2A and 2B; Figures 4A and 4B are front and side views, respectively, of the attachment means and shaft shown in Figures 2A and 2B; Figure 5 is a plan view of the striker plate shown in Figures 2A and 2B; IR:\llL1.09805.doc:IKBH Figures 6A and 6B are side and plan views, respectively, of the guide bush shown in Figures 2A and 2B; Figure 7 is a side view of the shaft shown in Figures 2A and 2B; Figure 8 is a plan view of the spacer shown in Figures 2A and 2B; Figures 9A, 9B and 9C are plan, front and side views, respectively, of a side wall for the body shown in Figures 2A and 2B; Figure 10 is a cut away side view of a load limiting device according to another embodiment of the invention; Figure 11 is a cut away side view of a load limiting device according to a further 1o embodiment of the invention; Figure 12 is a cut away side view of a load limiting device according to a further "embodiment of the invention; Figures 13A to 13C are front, side and plan views, respectively, of the striker plate shown in Figure 11; Figures 14A to 14E are plan, bottom, front, left and right side views, respectively, of the body shown in Figures 11 and 12; Figure 15 is a side view of the attachment means as shown in Figures 11 and 12; Figures 16A and 16B are side and plan views, respectively, of the guide bush shown in Figures 11 and 12; Figure 17 is a side view of the shaft shown in Figures 10 to 12; Figures 18A and 18B are plan and side views, respectively, of a side wall for the body shown in Figures 11 and 12; Figures 19A and 19B are side and plan views, respectively, of the guide bush shown in Figures 10 to 12; Figures 20A to 20C are plan, front and side views, respectively, of the attachment means shown in Figure Figures 21A and 21B are plan and side views, respectively, of the spacer shown in Figures 10 to 12; Figures 22A and 22B are plan and side views, respectively, of the attachment means shown in Figure 12; and Figure 23 is an exploded parts perspective view of the body shown in Figures 11 I and 12.

IR:\ALIBL]09805.doc: KEH Detailed Description of the Preferred Embodiments In the accompanying drawings, and in particular Figure 1, there is illustrated a swinging stage assembly 1 being lowered from the top of a building 2. The assembly I includes two roof rig supports 3 having complimentary counterweights 4 at one end and attachment means 5 at the other. The attachment means 5 are each respectively secured to a load limiting device 6 which in turn is attached to a cable 7. The cable 7 extends downwardly feeding into a winch 8 which is fixedly attached to the swinging stage 9.

The winch 8 includes a winch motor 10 for increasing and decreasing the length of the cable 7 and thereby raising and lowering the stage 9. A power distribution board 11 is 1o attached in the centre of the swinging stage 9 and includes cables 12 connected to each of winch motors 10. The main power cable 13 extends from the top of the roof and is electrically connected to each of the load liming devices 6 before terminating at the power distribution board 11. Because the device 6 has a preset overload mechanism inside, when tripped the device 6 will break the electrical circuit to the lifting motors 10 until 1s such time as the overload situation is remedied. The device 6 then automatically rests and restores normal power to allow winch 8 operation once more.

The invention 6 positively open circuits the main power supply to the hoists (winch 8) such that no hoist on the platform 9 can be driven in any direction if the load on oooo any rope (cable 7) exceeds the limit.

Known existing devices are wired into the direction switching circuit of the hoist and as such permit the operation of one hoist on a platform while another hoist on the platform is in an overload condition.

Figure 2A illustrates a load limiting device 6 to deliver electric energy to an electric motor 10. The device 6 includes: a body 14 having attachment means 15 to which a load is applied. A switch 16 is mounted on the body 14 and is operable to connect the motor (not shown) to a supply of electric energy. The switch 16 being in a first configuration (as shown in Figure 2A) to deliver the energy. A shaft 17 is movably mounted in the body 14 for axial movement relative the body 14. The shaft 17 also has attachment means 18 via which the load is applied to the shaft 17. A striking means 19 is 3o fixed to the shaft 17 so as to be movable therewith between a first position (as shown in Figure 2A) allowing the switch 16 to remain in the first configuration, and a second position (not shown) in which the switch 16 electrically isolates the motor 10. A second I R:\lH I,L1985.doc: K Ell configuration (not shown) in which resilient means 20 urges the striking means 19 to the first configuration thereof, the resilient means 20 includes a plurality of resilient discs 21 surrounding the shaft 17. The discs 21 being resiliently deformed to permit movement of the striking means 19 to the second position upon the load exceeding a predetermined load.

From Figures 2A, 4A and 7, it can be seen that shaft 17 is threaded at each end.

This allows shaft 17 to secure striking means 19 and attachment means 18 by use of a combination of a nut 21 and slit pin 22. In order to allow a particular load to be preselected, a guide bush 23 and a spacer 24 are positioned between the extremities of the 1o shaft 17. The spacer 24 is preferably colour coded to the load rate required. By installing different thickness spacers 24 the travel required of the striking means 19 to activate the limit switch 16 will be preset. This in turn will cut power to the main power board 11 and .oooo) hence the winch motors 10 will stop.

The invention permits the limit to be simply and readily varied within a range (for a hoist rated at 500 kg the range might be between 400 kg and 650 kg for example) without need for recalibration.

Known existing devices (such as devices that limit current) can only be varied through an iterative process requiring calibration.

The resilient means 20 as best indicated in Figure 2A are shown in the form of a plurality of disc springs 21. These disc springs 21 are selected to allow setting of the striking means 19 to activate the limit switch 16 once a desired overload point is reached.

As shown in Figures 9A-9E the body 14 may include side walls 25 to shield body 14 from the outside elements.

Figure 10 illustrates a further embodiment of a load limiting device 30 according to the present invention. The device 30 is similar to that shown in Figure 2 and includes: a body 32 (as shown in Figures 14A to 14E and 23) having attachment means 34 to which a load is applied. A switch 36 is mounted on the body 32 and is operable to connect the motor (not shown) to a supply of electric energy. The switch 36 being in a first configuration (as shown in Figure 10) to deliver the energy. A shaft 38 (Figure 17) is movably mounted in the body 32 for axial movement relative the body 32. The shaft 38 also has attachment means 40 (as shown in Figures 20A to 20C) via which the load is applied to the shaft 38. A striking means 42 (as shown in Figures 13A to 13C) is fixed to I I(ALIBLL]09805.doc: KI-E the shaft 38 so as to be movable between a first position (as shown in Figure 10) allowing the switch 36 to remain in the first configuration, and a second position (not shown) in which the switch 36 electrically isolates the motor. A second configuration (not shown) in which resilient means 44 urges the striking means 42 to the first configuration thereof, the resilient means 44 (as best shown in Figures 19A and 19B) being, for example, a multi-cushioned rubber mount surrounding the shaft 38. The multi-cushioned mount being resiliently deformed to permit movement of the striking means 42 to the second position upon the load exceeding a predetermined load.

From Figures 10 and 17, it can be seen that shaft 38 is threaded at each end.

This allows shaft 38 to secure striking means 42 and attachment means 40 by use of a combination of nuts 21, washers 23 and slit pins 22. In order to allow a particular load to be preselected, a guide bush 46 (as shown in Figures 16A and 16B) and spacer 48 (as shown in Figures 21A and 21B) are positioned about the shaft 38. The attachment means S.o. 40 may include a pin 49 for the attachment of wire ropes.

The device 30 shown in Figure 10 is controlled by a multi-cushion mount selected to allow setting of the trip lever (striker plate) to activate a limit switch once the selected overload point is reached. This overload point can be adjusted to suit by turning an adjustment screw. This will preset the travel required of the trip lever (striker plate) to activate the limit switch. This in turn, will cut power to the main power board and hence the winch motors.

Figure 11 illustrates a further embodiment of a load limiting device 50 to deliver electric energy to an electric motor. The device 50 is similar to that of device 30 shown in Figure 10, however, the attachment means 52 (as best shown in Figure 15) is in the form of an eye bolt attached to body 32 by nut 21, washer 53 and slit pin 22. The device 2s 50 shown in Figure 11 also includes a bolt 54 and nut 55 combination attached to the striking means 42 above the switch 36. By varying the length of thile shaft of the nut 54 extending through the striking means 42 the travel required by the striking means 42 to activate the limit switch 16 will be preset. This in turn will cut power to the main power board and hence the winch motors will stop.

Figure 12 illustrates another embodiment of a load limiting device 60 according to the present invention. The device 60 is similar to the device shown in Figure 11, however, the body 32 includes a Skylock switch trip lever arrangement 62. This I R:\L113LI1.09805doc:KEHarrangement 62 includes a resilient means 64 surrounding the lever 62 and is held in place by a washer and slit pin 65, 66. The eyelet 69 (as best shown in Figure 22A) surrounds the cable (not shown) attached to the shaft 38. The eyelet 69 acts as a buffer protecting the shaft 38 from being damaged by a cable mount (not shown). When a cable mount comes into contact with the eyelet 69 the striker lever 62 engages the switch 36 cutting the power.

Turning to Figure 23 an exploded parts perspective view of the body 32 is shown. Figure 32 shows the use of gaskets, o-ring seals and washers in typical locations.

The side walls 67 (as best shown in Figures 18A and 18B) are also clearly shown.

The present invention, at least in the preferred embodiments has the following :'ooo. advantages: compact total weight approximately 2.5 kg; can be fitted to any style or make of roof rig support system; is simple to maintain; is simple to adjust, does not need factory setting; robust can withstand rough treatment from the industry; has automatic reset does not need manual re-adjustment; relatively inexpensive and is weatherproof.

1 5 Although the invention has been described with reference to specific examples, it will be appreciated by those skilled in the art that the invention may be embodied in many other forms.

I R:\LIBLI109805.doc: KEH

Claims

1. A swinging stage assembly having: at least one rig support to be mounted on a structure and having attachment means; an swinging stage suspended from the rig support; an electrically driven winch attached to the stage, said winch having an electric motor and having at least one cable by which the stage is suspended, the winch being operable to raise and lower the stage; and a load limiting device connecting the cable to the attachment means, the load limiting device being electrically connected to the winch to selectively deliver electric power thereto, the device being operable to electrically isolate said winch when a predetermined load is applied to said device by said cable to thereby limit the load that can be lifted by the winch.

2. The assembly according to claim 1, said load limiting device further including: a body having attachment means to which a load is applied; a switch mounted on the body and operable to connect the motor to a supply of electric energy, the switch being in a first configuration to deliver said energy; cOO• a shaft movably mounted in the body for axial movement relative the body, the shaft also having attachment means via which the load is applied to said shaft; a striking means fixed to the shaft so as to be movable therewith between a first position allowing the switch to remain in the first configuration, and a second position in which the switch is in a second configuration, said switch in said second configuration electrically isolates said motor; and resilient means urges said striking means to the first position thereof, the resilient means being resiliently deformed to permit movement of the striking means to the second position upon said load exceeding a predetermined load.

3. The assembly according to claim 2, wherein the resilient means includes a plurality of resilient discs surrounding said shaft. S 30 4. The assembly according to claim 2, wherein the resilient means includes a multi-cushioned rubber mount. [R:\LIBLL]09805.doc:KEH:caa:KEH The assembly according to any one of claims 2 to 4, wherein the device includes one or more spacers located about said shaft for preselecting the first position.

6. The assembly according to any one of claims 2 to 5, wherein the body includes a guide bush to facilitate the axial movement of the shaft. s 7. The assembly according to claim 5, wherein the spacers include colour coded indicia to indicate the predetermined load.

8. The assembly according to any one of claims 2 to 7, wherein the device is adapted for attachment to a roof rig support.

9. The assembly according to any one of claims 2 to 8, wherein the device io is adapted to positively open circuit a main supply of a winch motor and/or platform. The assembly according to claim 2, wherein the device is adapted for attachment to any style or make of roof rig support.

11. The assembly according to any one of the preceding claims, wherein the device is simple to maintain, and simple to adjust after an initial factory calibration.

12. The assembly according to any one of the preceding claims, wherein the device is robust and can withstand rough treatment.

13. The assembly according to any one of the preceding claims, wherein the device has an optional audible alarm.

14. The assembly, substantially as herein described with reference to any one of the embodiments of the invention shown in the accompanying drawings. Dated 16 September 2003 Brian Eugene Whelan Patent Attorneys for the Applicant/Nominated Person SPRUSON FERGUSON [R:\LIBLL]09805.doc:KEH:caa:KEH