GB2265693A - Stop mechanism, particularly for use with extending ladder systems - Google Patents

Abstract

A stop mechanism (100) for arresting movement of a member e.g. a rope comprises guide means (102) movable between a first and a second position; at least one stop means (108) juxtaposed the guide means defining a stop surface which surface is movable relative to the guide means (102) and is biased away from the guide means by first bias means; and second bias means (114) acting on the guide means and arranged to urge the guide means towards the stop means. In use the member is disposed on the guide means between the guide means (102) and the stop means (108). <IMAGE>

Description

STOP MECHANISM This invention relates to a stop mechanism. Stop mechanisms embodying the invention are particularly suitable for use in the field of extending ladder systems, but may also be used in yachting and many other fields.

Conventional extending ladder systems comprise two or more rigid ladders which slide relative to each other to extend or retract the extending ladder system.

Often, particularly when the extending ladders are for use on fire engines and the like, it is highly desirable for an operator to be able to extend and retract the extending ladder system without moving from a position adjacent the base of the system.

Conventionally, this is done by a simple pulley system. In the case of a two ladder system in which a second, or upper, ladder slides along a first, or base, ladder, a rope is attached to the bottom of the second ladder. The rope then extends around a pulley at the top of the first ladder and an operator holds the free end of the rope at a location at or close to the base of the first ladder. When the operator pulls on the rope, hauling the rope in, this causes the second ladder to slide up the first ladder thus extending the ladder system.If the system includes a third ladder disposed to slide on the second ladder, a fixed length of wire extends from the top of the first ladder over a pulley at the top of the second ladder to the bottom of the third ladder: the movement of second ladder sliding up and along the first ladder, then causes the third ladder to slide up and along the second ladder.

With a system as described above, if the operator releases the rope, when the extending ladder system is partly or fully extended, the second and third ladders will tend to come crashing down under the action of gravity unless they are locked into position.

Various means are known for locking such ladder systems. Mechanical means which dispose a stop member between the rungs of one or other of the ladders can be used, but with this method the ladders can, depending on rung spacing, drop a significant distance before locking occurs: also the forces involved can damage the rungs and the locking mechanism. Pawls have been used, but these cannot be controlled on the upper sections of extending ladder systems where the extending ladder system is controlled by a single rope. Also while parts may be effective to prevent the ladders crashing downwards as the system is extended when such pawls are disengaged to allow the second and other, if any, ladders to descend, if the rope is released the ladders will still come crashing down.

It is an object of the present invention to provide an improved stop mechanism which, inter alia, may be used to alleviate some or all of the above-mentioned problems.

Thus, according to the present invention, there is provided a stop mechanism for arresting movement of a member comprising: guide means for the member; and at least one movable stop means disposed adjacent to the guide means wherein, in use, the member is disposed to travel along the guide means between said guide means and the stop means, characterised in that limited movement of the guide means relative to the stop means is allowed, in that said guide means are biased to move relatively towards the stop means, and in that movement of the stop means away from the guide means is allowed.

With the stop mechanism of the present invention, when the member is moved along the guide means in one direction the member may move along the guide means substantially unrestricted by one stop means; when the member is moved along the guide means in the opposite direction, the movement of the member and contact between the member and the one stop means causes the one stop means to move towards the guide means, and arrest movement of the member when an equilibrium is reached preventing further movement of the guide means or when the guide means reaches the limit of its allowed movement away from the stop means; and when the guide means have been moved away from the stop means the member may move along the guide means in either direction.

Typically, the stop means are provided by the cam surface of a cam member mounted on a pivot adjacent to the guide means in an overcentre orientation so that rotation of the cam in one direction causes the cam surfaces/stop means to move towards the guide means.

When the stop mechanism is applied to an extending ladder system of the type described, the guide means is provided by the pulley and the stop means by a cam as described supra. The "member" is the rope and the cam surface is toothed to improve its grip on the rope. The pulley is mounted on an arm which pivots about the same axis as that which the cam rotates about. Thus, relative rotation of the cam and arm causes the cam surface to move towards the pulley. The cam member is biased to rotate the cam about the pivot against a stop to move its cam surfaces away from the guide means to prevent uncontrolled jamming of the stop mechanism.

In other embodiments the guide means may be a flat plate or may define a curved surface.

Two stop means may be provided, one being arranged to act to arrest movement of the member in the one direction, another stop means being arranged to arrest movement of the member in the opposite direction so that the member may only be moved if a nett force is applied to move the guide means away from the stop means.

Specific embodiments of the invention will now be described, by way of example only, and with reference to the accompanying drawings in which: Figures 1A, B, C and D illustrate a first stop mechanism incorporating a circular guide member and a cam; Figure 2A is a front view of a stop mechanism for an extending ladder system; Figure 2B is a side view of the stop mechanism of Figure 2A; Figure 2C is a bottom view of the stop mechanism of Figure 2A; Figure 2D illustrate the use of the mechanism of Figure 2A on an extending ladder system; Figures 3A, B, C and D illustrate a second stop mechanism similar to that of Figure 1 but incorporating a second cam; Figures 4A, B, C and D illustrate a yet further stop mechanism; Figures 5A, B, C and D illustrate a stop mechanism in which there is a flat guide member; and Figures 6A, B, C and D illustrate a stop mechanism similar to the mechanism shown in Figures 1A, B, C and D but in which the cam is replaced by an alternative stop means.

Figures 1, 3, 4, 5 and 6 [A to D] are schematic drawings which are intended to be illustrative of the principles of the present invention whereas Figures 2A to D show a working embodiment of the invention.

Referring to the drawings, Figures fA to D show an automatic stop mechanism. It comprises a guide member 1 which is constrained for limited movement between a first and a second position along the axis A-B and which is biased to move towards a cam 10. The cam is generally semi-circular in shape and is mounted on a pivot 12 located adjacent the guide member generally along axis A-B. Bias means, not shown, are provided to bias the cam to rotate about the pivot 12 in direction C, away from the guide member. A flexible member 14 is disposed for movement along the guide member between said guide member 1 and cam 10.

In use, when the member 14 is pulled along the guide means in the direction D as shown in Figure 1B friction between the member 14 and the cam 10 tends to pull the cam clockwise about pivot 12 in the direction E against the cam's bias means. This tends to close the gap between the cam 10 and the guide means 1 and pushes the guide means in the direction B until the guide means reaches the limit of its movement in that direction. When guide member A has reached the limit of its travel or when an equilibrium is reached preventing further movement of the guide means, member 14 is trapped between cam 10 and guide member 1. Thus further movement of member 14 in response to force E is prevented.

In contrast, referring to Figure 1C, when a force G is applied to the other side of the flexible member to cause the member 14 to move across the guide means in the opposite direction to that shown in Figure 1B, the flexible member 14 may move along the guide means with substantially no restriction since friction between the member 14 and the cam member does not cause the cam member to move towards the guide 1 but reinforces the action of the bias means to move the cam 10 away from the guide means.

Finally, referring to Figure 1D, when a force D and a force G are simultaneously applied to the member 14 coupled with a force F biasing pulley wheel A away from cam member B with force D being initially greater or equal to force G to release the member from engagement with cam 10, guide member 1 moves in the direction B, away from cam 10, and flexible member 14 moves out of contact with cam 10, allowing member 14 to traverse guide member 1 in either direction. Force F need not be provided as a separate force on the guide means but may be a resultant force provided by D and G.

Figures 2A, 2B and 2C show a stop mechanism generally shown at 100 for use on a rope and pulley arrangement for an extending ladder system of the type described.

Figure 2D is illustrative of the use of the stop mechanism on such a system.

The mechanism comprises a pulley wheel 102 which is mounted an axle 103 located on one end of an arm 104.

The axle 103 passes through the central axis 103A of the pulley which is mounted so that it is free to spin about that central axis 103A. The arm comprises two generally flat arm elements 104A and 104B, one arm element being disposed to one side of the pulley, the other arm element being disposed on the other side of the pulley.

The other end 105 of the arm 104 is mounted on an axis 106. The arm is arranged to rotate about the axis 106, so that the pulley 102 can, for example, move to position 102' shown in dotted outline in Figure 2B.

A cam 108 is also mounted on the axis 106 between the arm elements 104A and 104B. The cam is able to rotate about that axis. As is best seen in Figure 2B, the cam is generally semi circular and is toothed to improve its grip on a rope (not shown) disposed on the pulley 102 between the pulley and the cam.

The axis 106 is mounted on a frame or bracket 110. The frame defines a space 111 between itself and the axis, in which the rung or part of a ladder can be inserted.

The frame includes holes 112, for fixing the frame and hence the cam and pulley, to the rung of the ladder.

The cam is biased by a spring to rotate in the K (anticlockwise) direction. Figures 2A and 2B shows the cam in its rest position where it has rotated in the K direction as far as it can before coming to rest against part 113 of the frame 110 after which it can rotate no further. The cam is mounted in an overcentre position, so that as it rotates round the axis 106 in the J (clockwise) direction, the surface of the cam moves towards the pulley wheel 100. Thus rotation of the cam and pulley, relative to each other, about the same axis, causes the gap between them, in which the rope is in, to change.

The arm 104 is also biased to move in the K direction; this is done by means of a spring 114 one end of which is mounted on a bracket 116 attached to the (pulley) end of the arm remote from axis 106, the other end being attached to the same rung of the ladder to which the frame 110 is mounted at a distance from the frame.

The schematic drawing Figure 2D illustrates the stop mechanism being used to control an extending ladder system comprising a first base ladder 122 and a second ladder 124 mounted on, and, in sliding engagement with, the base ladder.

One end 126A of a rope 126 is attached to the base of the second ladder; the rope passes over the pulley 102 of the stop mechanism 100, which is fixed to the top of the base ladder. The rope then extends to the base of the first ladder where its other free end 126B is held by an operator of the the extending ladder system.

With reference to Figure 2B, the stop mechanism is arranged so that the weight of the second ladder acts in the direction W with a pull exerted by the operator acting in the "opposite" direction P. Thus the cam 108 is disposed above the pulley.

In use, to extend the ladder pull P is exerted by the operator and providing it is sufficient to overcome weight W the rope and pulley will move about the axis 103A in the clockwise direction as shown in Figure 2B, the operator will haul the rope in and the ladder system will extend.

In practice various mechanisms may be used to give the operator a mechanical advantage to assist him/her in overcoming weight W, but the principle of the operation remains the same.

If the operator lets go of the rope, weight W alone will act. Friction between the rope and the toothed cam 108 will try to turn the cam in the J direction.

This will tend to close the gap between the pulley and the cam and jam the rope between the cam and pulley thus preventing the second ladder from coming crashing downwards. Jamming occurs either when the forces pulling the guide means generally downwards reaches equilibrium with the force in the spring pulling it generally upwards or when the guide means reaches the end of its travel.

To allow the second ladder to descend a pull P must be applied to the free end of the rope simultaneously with weight W (in this embodiment "W" is always applied because the ladder will always weigh substantially the same) with pull W being initially greater than pull P to disengage the rope from the cam allow the cam to rotate back to its rest position against frame 113 and allow the arm 102 to rotate away from the cam in the J direction to allow the ladder to descend in a controlled manner. If at any time the operator lets the rope go, the stop mechanism will act to lock the rope between the cam and pulley in the manner described above with reference to extension of the ladder system.

Thus not only the system fall safe in both when extending and retracting the system but is also operable by controlling the pull on a single rope.

Figures 3A to D, illustrate a third embodiment of the present invention. In this embodiment the guide member 1 is identical to that of Figure 1 however instead of one cam, two cams 16 and 18 are provided.

Each cam is biased about its respective pivot 17 and 19 to rotate the cam away from guide means 1 in directions C and E respectively. In use, as illustrated in Figures 3B and 3C, when member 14 is pulled around guide member 1 by a force D or G, in either direction one or other of the cam means 16, 18 will operate to arrest movement of member 14 in the same manner as the cam. Only when a force F is applied to move the guide means away from the cams, (16, 18), can member 14 move in either direction about that guide member 1.

Figures 4A to D, illustrate a stop mechanism which operates in a similar manner to that shown in Figures 3A to D, the cam 30 being pivoted about an axis 32 on one end 34 of an arm 36, the other end of which is mounted on a pivot 38. The cam is biased to be positioned as shown in Figures 4A and 4D. When the member 14 is in contact with the cam and either a force D (Figure 3B) or a force G (Figure 3C) is applied the arm and pivots allow the cam surfaces to move towards guide member 1 thus forcing guide means in the direction B until guide member reaches the limit of its travel and member 14 is trapped between the cam and the guide means as shown in Figures 4B and 4C. Thus, a nett force F has to be applied to move the guide means away from the cam before the member 14 can be moved over the guide means.

Figure 5A to D, illustrate the use of a flat guide means 40 which is constrained to move along an axis A-B and operates in a similar manner to the stop mechanism shown in Figure 1A to D.

Figures 6A to D, illustrate an alternative stop mechanism in which the guide member is as shown in Figure 1 but in which the cam is replaced by a stop member or trapezoidal block 50 defining an inclined surface 52. The stop member is constrained to move along an axis H-I and is biased to move away from the guide member in the direction I. When as shown in figure 6B, a force D is applied to the member 14 friction between the member 14 and the stop member 50 causes the stop member to move against its biasing means towards guide member 1. Inclined surface 52 pushes the guide member downwards in direction B and when guide A reaches the end of its movement, member 14 is trapped between block 50 and the guide 1.

Movement of the flexible member to traverse the guide means in the opposite direction is permitted as shown in Figure 6C, and as shown in Figure 6D, when force F is applied to the guide means simultaneously with forces E and D to move the flexible member away from the cam surface then the flexible member may traverse the guide means in either direction.

Although the cams described in the embodiments of Figures 1, 3, 4 and 5 have been described as being semicircular, clearly any configuration of cam could be used provided that the cam surfaces are configured to move the guide means in the correct direction as the cam rotates.

In certain embodiments a pull "F'2 has been described.

The skilled man will realise, particularly by reference to the embodiments of Figure 2 that no separate force is necessary for the guide means but as in the embodiment of Figure 2, a nett force F can be provided by forces on the members 14 themselves.

In yachting, the stop mechanism may be used as a jamming cleat for setting sails and the like.

Claims (2)

1. A stop mechanism for arresting movement of a member comprising: guide means movable between a first and a second position; at least one stop means juxtaposed the guide means defining a stop surface which surface is movable relative to the guide means and is biased away from the guide means by first bias means; and second bias means acting on the guide means and arranged to urge the guide means towards the stop means wherein, in use, the member is disposed on the guide means between the guide means and the stop means, the arrangement is such that when a force is exerted on the guide to overcome the second bias means and move the guide means away from the stop means, the member is able to traverse the guide means; and that when insufficient force to overcome the second bias means is applied, the second bias means urges the guide means towards the stop means until the member is in contact with both the guide means and the stop means and that traversing of the member along the guide means in at least one direction overcomes the second bias means thus causing the stop surface to move towards the guide means, so that the member is held between the stop means and the guide means after the guide means has reached the end of its travel towards the stop means or when equilibrium occurs.

2. A stop mechanism as claimed in claim 1 wherein, the stop means are provided by the cam surface of a cam member mounted on a pivot juxtaposed the guide means in an overcentre orientation so that rotation of the cam in one direction causes the cam surface to move towards the guide means.

2. A stop mechanism as claimed in claim 1 wherein, the stop means are provided by the cam surface of a cam member mounted on a pivot juxtaposed the guide means in an overcentre orientation so that rotation of the cam in one direction causes the cam surface to move towards the guide means.

3. A stop member as claimed in claim 1 wherein the stop means comprise a cam pivoted about an axis on an arm which arm is itself mounted on a pivot.

4. A stop member as claimed in claim 1 wherein the stop means defines a generally planar surface which intersects the axis along which the guide means moves at a non-perpendicular angle so that movement of the stop member towards and away from the guide means causes the stop surface to move towards or away from the guide means.

5. An extending ladder system including a stop mechanism as claimed in claim 1 or claim 2 wherein the guide means comprises a pulley mounted juxtaposed the upper part of a first ladder and the stop means comprise a cam and the member is a rope one end of which is attached to the lower part of a second ladder which ladder arranged to slide on the first ladder.

6. A stop mechanism as claimed in claim 1 or 2 wherein the guide means defines a substantially flat surface.

7. A stop mechanism as claimed in any preceding claim wherein two stop means are provided, one being arranged to act to arrest movement of the member over the guide in one direction, another stop means being arranged to arrest movement of the member in an opposite direction so that the member may only be moved if a nett force is applied to move the guide means away from the stop means.

8. A stop mechanism as claimed in any preceding claim wherein the first or second bias means comprise a spring.

Amendments to the claims have been filed as follows move the guide means away from the stop means, the member is able to traverse the guide means; and that when insufficient force to overcome the second bias means is applied, the second bias means urges the guide means towards the stop means until the member is in contact with both the guide means and the stop means and that traversing of the member along the guide means in at least one direction overcomes the first bias means thus causing the stop surface to move towards the guide means, so that the member is held between the stop means and the guide means after the guide means has reached the end of its travel towards the stop means or when equilibrium occurs.