The present application claims priority from Australian Provisional Patent Application No 2008901588 filed on 2 Apr. 2008, the content of which is incorporated herein by reference.
This invention relates to an improved pulley apparatus.
Pulleys are used for raising and lowering objects and/or people. In particular, pulleys may be used for lowering equipment or rescue workers from helicopters and lowering equipment or workers down shafts. A typical standard pulley comprises a wheel or sheave for carrying a rope, the sheave being rotatably mounted on an axle or the like which turns in a frame or block. Pulling at one end of the line (the haul end), will raise the weight or object attached at the other end of the line. Standard pulleys run very freely. When very heavy loads are being lowered, such free running of the pulley is disadvantageous, as the operator on the haul end of the line may have little control over the object at the other end of the line, particularly if the object is heavy or if the object accelerates and starts to descend rapidly. This control problem can be overcome by fixing the wheel/sheave, so that it is not able to turn and the rope merely slides over the surface of the sheave with the resultant increase in friction providing a greater degree of control for the operator. The sheave may comprise an elongate drum so that the line may be wrapped around the drum several times to increase the friction and consequently, increase the ease of control.
The problem with this approach, however, is that although a greater degree of control is provided when lowering an object, the increase in friction makes it more difficult to raise an object using fixed pulley. To solve this problem, it is known to provide one-way pulleys where the drum will turn in one direction only. Such pulleys can be used as either static pulleys or standard (free running) pulleys.
A further problem which arises with pulleys, is the tendency for the ropes to overrun which occurs when the ropes that are wrapped around the drum rub against each other and ride up over each other. This problem not only increases wear and tear on the rope, but may also reduce the control the operator has at the haul end of the line over the object being raised or lowered. It is known to put one or more pins at the top of static pulleys act as a rope guide. It is also known to mount a blade adjacent the top of a standard pulley to guide the rope and prevent screwing of the rope on the drum. The problem with this is that it limits the number of turns of rope that may be wound round the drum to one turn, where one blade is provided.
A yet further problem with existing pulleys, is that while pulleys are useful for lowering objects, a lack of mechanical advantage in existing pulleys means that it is usually difficult to raise and lower an object or person, except by using a lower pulley having two or more sheaves below the main pulley. However the problem with this is that more rope is needed passing between the main pulley and sheaves of the lower pulley.
The present invention seeks to alleviate some of the above mentioned problems of existing pulleys.
Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is solely for the purpose of providing a context for the present invention. It is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed before the priority date of each claim of this application.
In accordance with the present invention there is provided a pulley apparatus, including a drum having a central axis mounted between two side plates for receiving a rope passing around the drum, the drum defining a cylindrical surface for receiving a rope or line, the pulley being mounted between the two side plates, the pulley apparatus including a means for hanging or supporting the pulley and a rope guide means disposed on the underside of the pulley adjacent the drum and passing over the cylindrical surface of the drum for guiding the line to wrap around the central part of the drum for inhibiting overrun of ropes, and wherein a second sheave is mounted to the apparatus, disposed below the guide means in use.
Typically the second sheave is a single sheave and is freely rotatable. It is typically pivotally mounted to one or both of the side plates by a arm having a fixed length. It may be mounted between the lower ends of two plates whose upper ends are pivotally mounted to the side plates.
The guide means may be defined by two curved blades which extend from the side plates and bow out towards the centre of the drum to define a convergent-divergent wasp-waisted passage for the line to pass through.
It has been found that the provision of such a guide means at the bottom of the pulley where the line meets the drum provides sufficient correction to the line to ensure that it wraps properly around the drum and tends not to bunch or overrun. This contrasts with applying a correction to the line at the top of the drum by which point some twisting of the line might already have occurred making correction more difficult to effect.
It is preferred that a guide ring or the like, is provided adjacent each of the curved blades.
The pulley may be a static pulley with a fixed sheave, a standard pulley having a rotatable sheave or a one way pulley.
In a preferred embodiment, one side plate is fixed relative to the sheave, and the other plate is rotatable relative to the first plate for ease of threading a line around the sheave.
A specific embodiment of the present invention will now be described, by way of example only, and with reference to the accompanying drawings in which:
Referring to the drawings,
As can be seen from
As is best seen in
Also shown in
This ensures better alignment of the rope when the pulley is in use and in co-operation with the rope guide means helps prevent over-run of the rope.
In use, and as shown in the Figure, a rope 120 is attached to the upper hole 104 of the lower pulley and passes up towards the lower sheave 40 of the main pulley 10, passing around that sheave 40 and down towards the lower pulley and around the movable sheave 102 of that lower pulley. The rope 120 then travels upwards, passes through one guide ring 52 and is wound three times around the one way sheave 12 before passing through the other guide ring 50.
By providing the second lower sheave 40 hanging from the main pulley, a mechanical advantage of 3 to 1 is provided without a major increase in required rope length. By pulling on the free or haul end of the rope the lower pulley and a person or object attached to the pulley can be safely and easily raised (by virtue of the 3 to 1 mechanical advantage) as well as lowered.
The diameter of the rope determines the number of turns which will fit side by side in the gap 34. The described embodiment is best suited to 12 mm diameter rope or similar.
It has been found that the provision of such a guide means 30, 32 at the bottom of the pulley where the line winds on to the drum provides sufficient correction to the line to ensure that it wraps properly around the centre of the drum and tends not to contact the side rims 13 of the drum or the cheeks 14 and 16 and which does not bunch, overrun. or screw to tightly onto the drum. This provides less unwanted rubbing and reduces the wear and tear on the line and provides more control of the pulley for an operator.
It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as shown in the specific embodiments without departing from the scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.
Number | Date | Country | Kind |
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2008901588 | Apr 2008 | AU | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/AU2009/000399 | 4/1/2009 | WO | 00 | 11/18/2010 |
Publishing Document | Publishing Date | Country | Kind |
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WO2009/121136 | 10/8/2009 | WO | A |
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3326819 | Feb 1985 | DE |
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779312 | Jul 1957 | GB |
Number | Date | Country | |
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20110068311 A1 | Mar 2011 | US |