GB2296481A

GB2296481A - Zero fleet angle winch

Info

Publication number: GB2296481A
Application number: GB9423979A
Authority: GB
Inventors: Michael Barnet
Original assignee: Stage Tech Ltd
Current assignee: Stage Tech Ltd
Priority date: 1994-11-28
Filing date: 1994-11-28
Publication date: 1996-07-03
Also published as: GB9423979D0

Abstract

A winch comprises a frame 12 a carriage 36 adapted for movement with respect to the frame and a cylindrical drum 14 mounted on the carriage for rotation with respect to the carriage about an axis extending generally axially of the drum. A cable 16 is attached to the drum 14 and adapted to be wound around a circumferential surface thereof. Drive means 18 is mounted on the carriage for rotating the drum about the axis and means are provided for moving the carriage with respect to the frame in a linear direction axially of the drum such that upon each rotation of the drum the drum moves axially relative to the frame by a distance equal to that separating adjacent turns of the cable when measured parallel to the drum axis. As shown the latter means comprises a rotatable threaded rod 58 engaging a threaded bore 34 on the frame. Alternatively the threaded rod may be fixed and a rotatable nut mounted on the carriage. <IMAGE>

Description

ZERO FLEET ANGLE WINCH The present invention relates to winches and in particular, but not exclusively, to winches for use in theatres for moving various items of scenery.

In the past winches have comprised a cylindrical drum which is rotatably driven about a substantially horizontial shaft which extends axially of the drum.

A cable is wound around a circumferential surface of the drum to which it is attached at one end.

Typically the cable passes over a pulley and the opposite end of the cable is attached to an item to be moved by the winch so that, for example, as the cable is wound onto the drum the item to be moved is drawn in the direction of the winch.

In order to guide the cable on to the drum and prevent the cable from slipping with respect to the circumferential surface in a direction parallel to the drum axis, the circumferential surface of the drum is often provided with a helical groove of sufficient dimensions to accommodate the cable. Even so, the fleet angle, that is the angle subtended between the cable and a plane perpendicular to the axis of the drum, must be smaller than three degrees to prevent the cable from riding up out of the helical groove and slipping axially of the drum. For a typical winch where the drum has a diameter of 0.3m this has necessitated placing the pulley at least 2m from the drum. This distance between the drum and the pulley represents dead or unusable space which, for example, in a theatre setting where space is restricted, represents a considerable problem.If the drum were to be replaced with one having a smaller diameter then the pulley would need to be placed even further away while if the diameter of the drum were to be increased there would need to be a corresponding increase in the size of the motor and gear box through which the drum is rotatably driven. Thus in the past it has been accepted that a winch must of necessity be of a certain size that cannot be significantly reduced.

In a theatre setting any winch is typically accommodated beneath the stage. Quite clearly however, the size of the winch has a significant impact on the cost of installation and its applicability for the performance of certain tasks.

In order to reduce the amount of dead space between the pulley and the drum, a number of attempts have been made to devise a winch which maintains a zero fleet angle. One such attempt has involved moving the drum in an axial direction as it rotates so that for each revolution the drum moves axially by a distance equal to the pitch of the helical groove.

However, such an arrangement requires the shaft about which the drum is rotated to slide with respect to the gearbox in order that it may accommodate the axial movement of the drum. Unfortunately this has led to problems with wear which have rendered the resulting winch impracticable.

In another attempt to produce a zero fleet angle winch, the pulley has been positioned at the takeoff point at which the cable leaves the drum. The pulley has then been moved axially so that for each revolution of the drum the pulley moves by a distance equal to the pitch of the helical groove. This arrangement however suffers from the fact that the pulley is exposed to increased loads of typically up to half a ton.

The present invention is directed at least in part to overcoming some of the problems associated with the prior art.

According to the present invention there is provided a winch comprising a frame, a carriage adapted for movement with respect to the frame, a cylindrical drum mounted on the carriage for rotation with respect to the carriage about an axis extending generally axially of the drum, a cable attached to the drum and adapted to be wound around a circumferential surface thereof, drive means mounted on the carriage for rotating the drum about said axis, and means for moving said carriage with respect to the frame in a linear direction axially of the drum such that upon each rotation of the drum said drum moves axially relative to the frame by a distance equal to that separating adjacent turns of the cable when measured parallel to the drum axis.

In this way it will be apparent to those skilled in the art that the present invention provides a zero fleet angle winch which is neither exposed to excessive wear or transmits an increased load to the pulley. Furthermore, by providing a satisfactory zero fleet angle winch, it has become possible to reduce the diameter of the drum without increasing the associated dead space between the drum and the pulley.

Having reduced the diameter of the drum it has then been possible to reduce the size of the gearbox and drive means for rotating the drum which in turn has led to an overall reduction in the size of the winch.

This size reduction enables savings in both manufacturing costs and the cost of installation.

Finally, by providing a winch which is reduced in size, it is possible for the winch to find use in applications where heretofor such use would not have been possible such as, for example, in situations where the available space is severely limited.

An embodiment of the present invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 is a cross sectional view of a prefered embodiment of the present invention; and Figure 2 is an end view of the embodiment of Figure 1.

Referring to Figures 1 and 2, there is shown a winch 10 comprising a frame 12, a cylindrical drum 14 mounted to the frame, a cable 16 attached to the drum and drive means 18 for rotating the drum with respect to the frame.

Looking in more detail at Figure 2, the frame 12 can be seen to comprise two longitudinally extending side walls 20, 22 which are held in spaced relationship by means of a pair of cross braces 24, 26 welded to their under surfaces. The two side walls 20, 22 are both of substantially c-shaped cross section and so define respective longitudinal channels 28 and 30 which open inwardly of the side walls. An upstanding projection 32 is provided on a first of the cross braces 24 centrally of the side walls 20 and 22 and defines a threaded through bore 34.

In addition to the upstanding projection 32, there is also disposed between the two side walls 20 and 22, a carriage 36. The carriage 36 comprises a supporting platform in the form of plate 38 having a lateral dimension which enables the plate when placed centrally between the side walls 20 and 22 to define respective slots 40 and 42 which extend longitudinally between the cross braces 24 and 26. The carriage 36 is supported for longitudal movement with respect to the frame 12 by means of four flanged wheels 44 which are received within the channels 28 and 30. As can be seen from Figure 2, each wheel 44 is mounted in a set of bearings 46 for rotation with respect to an axle assembly 48 which in turn depends from an undersurface of the supporting plate 38.

In addition to the four axle assemblies 48, the supporting plate 38 is also provided on its undersurface with a depending projection 50 which is located centrally of the side walls 20 and 22 and rearwardly of the upstanding projection 32. Like the upstanding projection 32, the depending projection 50 defines a through bore 52 which is in axial alignment with the threaded through bore 34.

At a forward end of the carriage 36, the supporting plate 38 is provided with a front wall 54 which both extends upwardly from the plate and downwardly in the direction of the cross brace 26.

This downwardly extending portion is provided with a further through bore 56 in axial alignment with that provided in the depending projection 50 and the threaded through bore 34 provided in the upstanding projection 32. A longitudingly extending ACME screw threaded member 58 is received within the threaded through bore 34 and is supported between the depending projection 50 and the front wall 54. The ACME screw threaded member 58 is provided at opposite ends with a respective one of a pair of axially extending smooth stub portions 60, 62 which are of reduced diameter and which are received within the through bores 52 and 56.

Respective bearings 64 and 66 are provided in association with each of the through bores 52 and 56 and facilitate the rotation of the ACME screw threaded member 58 with respect to the carriage 36.

The upwardly extending portion of the front wall 54 is also provided with a through bore 68 which receives the stub like end projection 70 of a longitudinally extending shaft 72. At an opposite end, the shaft 72 is received within an axially aligned through bore 74 provided in a rear wall 76 which, like the front wall 54, extends upwardly from the supporting plate 38. Intermediate the front and rear walls 54 and 76, the supporting plate 38 is provided with its own upstanding projection 78 and this also defines a through bore 80 in axial alignment with that provided in the upwardly extending portion of the front wall. All three through bores 68, 74 and 78 are each associated with a respective set of bearings 82, 84 and 86 to facilitate the rotation of the shaft 72 with respect to the carriage 36.

As can be seen from Figure 1, the cylindrical drum 14 is arranged co-axially of the shaft 72, intermediate the front wall 54 and the upstanding projection 78. In order to reduce the weight of the drum 14 and so minimise the power requirements of the drive means 18, the drum is formed as a hollow cylinder 88 and joined to the shaft 72 by means of a pair of axially spaced discs 90, 92 each having a central through bore 94 dimensioned to receive the shaft 72 and a diameter corresponding to the interior diameter of the cylinder 88. One end of the cable 16 is secured to a first of the axially spaced disks 90 by means of a threaded bolt 96 which is received within an appropriately threaded apperture 98. The cable 16 then passes exteriorly of the hollow cylinder 88 through an appropriately dimensioned through bore 100.

The circumferential surface of the hollow cylinder 88 is provided with a helical groove 102 which is dimensioned so as to be capable of receiving the cable 16. To this end the groove 102 preferably has a depth substantially equal to the radius of the cable and a width parallel to the drum axis slightly greater than its diameter.

The cylindrical drum 14 is rotatably driven with respect to the carriage 36 by means of a drive means 18 in the form of an electric motor 104 and gear box 106. The electric motor 104 is supported by the rear wall 76 and communicates with the shaft 72 by way of the gear box 106. The gear box 106 is located between the rear wall 76 and the upstanding projection 78 and is keyed to the shaft 72 by means of an appropriate keyway 108.

At an end of the shaft 72 remote from the gear box 106, the stub like end projection 70 carries a flanged gear wheel 110 which is secured to, and rotates with, the stub like end projection by means of a grub screw 112. A second gear wheel 114 is secured to that part of the stub portion 62 of the ACME screw threaded member 58 which projects through the through bore 56 provided in the downwardly extending portion of the front wall 54. The two gear wheels 110 and 114 are drivingly interconnected by means of a drive chain 116.

In use, when it is desired to wind the cable 16 onto the cylindrical drum 14 the electric motor 104 is actuated by means of a suitable switch (not shown).

The rotational movement generated within the electric motor 104 is transmitted to the shaft 72 by means of the gear box 106 and this in turn causes the rotation of the hollow cylinder 88. Depending on the direction of rotation, the cable 16 is then drawn onto the cylindrical drum 14 passing through the frame 12 between the cross braces 24 and 26 and through the longitudinal slots 40 and 42.

As well as causing the rotation of the cylindrical drum 14, the rotation of the shaft 72 also causes the rotation of the first of the two gear wheels 110. This motion is in turn transmitted to the second gear wheel 114, and hence to the ACME screw threaded member 58, by way of the drive chain 116. As the ACME screw threaded member 58 rotates its engagement with the threaded through bore 34 of the outstanding projection 32 causes the entire carriage 36 including the cylindrical drum 14, electric motor 104 and gear box 106, to move longitudinally of the frame 12. This movement is facilitated by means of the rolling engagement of the four flanged wheels 44 within the channels 28, 30 of the side walls 20, 22.

Because of the gearing that exists between the first gear wheel 110 and the second gear wheel 114, each time the cylindrical drum 14 completes one rotation the carriage 36 moves longitudely by a distance equal to the pitch of the groove 102 provided in the circumferential surface of the drum 14. In this way the cable take off point remains fixed with respect to the frame 12 enabling the cable 16 to extend away from the cylindrical drum 14 in a plane which is always at right angles to the axis of rotation of the shaft 72.

By ensuring that the cable 16 maintains a zero fleet angle, the described winch 10 is no longer subject to the dead space requirement associated with winches of the prior art. As a result it becomes practicable to reduce the diameter of the cylindrical drum 14 which in turn enables a reduction in both the size and power of the electric motor 104 and gear box 106. Thus, in a prefered embodiment the hollow cylinder 88 has a diameter of 0.125 metres. The overall reduction in the size of the winch 10 enables it to be both manufactured and installed at a reduced cost. At the same time the described winch is capable of operating in a limited space environment which until now has not been practicable.

It will be apparent to those skilled in the art that the longitudinal movement of the cylindrical drum 14 and its associated drive means 18 may be accomplished by some means other than the rotation of an ACME screw threaded member such as that described above. For example, the drive for this longitudinal movement may be provided directly from the electrical motor 104 by way of a second output shaft from the bear box 106 or from an additional motor (not shown).

Likewise, it will be apparent that the synchronisation between the rotation of the cylindrical drum 14 and the longitdudinal movement of the carriage 36 may be achieved in some way other than by way of a drive chain 116. For example, this synchronisation could be achieved by use of a timing belt or else by causing the rotational movement of the shaft 72 to be transmitted to the ACME screw threaded member 58 by way of one or more intermeshing gear wheels.

Claims

1. A winch comprising a frame, a carriage adapted for movement with respect to the frame, a cylindrical drum mounted on the carriage for rotation with respect to the carriage about an axis extending generally axially of the drum, a cable attached to the drum and adapted to be wound around a circumferential surface thereof, drive means mounted on the carriage for rotating the drum about said axis, and means for moving said carriage with respect to the frame in a linear direction axially of the drum such that upon each rotation of the drum said drum moves axially relative to the frame by a distance equal to that separating adjacent turns of the cable when measured parallel to the drum axis.

2. A winch in accordance with claim 1, wherein said means for moving said carriage comprises a member mounted to the carriage for rotation with respect thereto and in threaded engagement with the frame, and means for rotating said member so as to move said carriage with respect to the frame.

3. A winch in accordance with claim 1, wherein said means for moving said carriage comprises a member mounted to the frame for rotation with respect thereto and in threaded engagement with the carriage, and means for rotating said member so as to move said carriage with respect to the frame.

4. A winch in accordance with claim 2 or claim 3, wherein said means for rotating said member comprises geared means rotatably interconnecting said drum and said member.

5. A winch in accordance with claim 4, wherein said geared means includes a drive chain.

6. A winch in accordance with claim 4, wherein said geared means includes a timing belt.

7. A winch in accordance with claim 4, wherein said geared means includes one or more intermeshing gear wheels.

8. A winch in accordane with claim 1, wherein said means for moving said carriage comprises additional drive means and means for synchronising the movement of the carriage with the rotational movement of the drum.

9. A winch in accordance with claim 1, wherein the drive means for rotating the drum also serves to move the carriage with respect to the frame, the winch further comprising means for synchronising the movement of the carriage with the rotational movement of the drum.

10. A winch in accordance with claim 1, wherein a helical groove is provided in the circumferential surface of the drum and the means for moving the carriage is such that upon each rotation of the drum said drum moves axially relative to the frame by a distance equal to the pitch of the groove.

11. A winch substantially as herein described with reference to the accompanying drawings.