GB2178716A - Load handling equipment - Google Patents

Abstract

Equipment for handing a load, said equipment including a load support (2) which is suspended from an overhead structure (1) by a plurality of lengths of cable (9, 10). A pair of the cable (9, 10) lengths engages with the load support (2) at locations which are spaced apart in a of the cables are variable by a first dimension. The effective lengths winding drum (6) and motor (7) so as to enable the load support (2) to be raised and lowered relative to the overhead structure (1). To oppose swinging movement of the load pport (2) in said first dimension, a spur of rotary drums is provided around which each of said cables (9, 10) is wound such that displacement of the load support (2) in said first dimension at a predetermined position relative to the overhead structure is opposed by the tendency of the pair of cable lengths to rotate each of the pair of drums respectively in opposite directions at the same time. <IMAGE>

Description

SPECIFICATION Load handling equipment The present invention relates to equipment used for handling loads, particularly, although not exclusively, loads that are handled by overhead cranes.

One of the difficulties of handling loads suspended from an overhead crane or other overhead handling equipment (hereinafter referred to simply as a crane) by means of a system of cables, ropes, chains or the like (hereinafter referred to simply as cables), is the limited ability of the crane to transmit forces in certain directions, in particular, the forces that are required to maintain the load in, or close to, a given relationship with the crane. One particular problem is the tendency for a load or a support used to engage the load, suspended by a system of cables to swing relative to the crane, especially when the crane is set into motion, or when such motion is arrested.

Equipment to overcome this problem has been previously proposed in British Patent Application No. 8515700 in which load handling equipment is described in the form of an overhead crane and comprises an overhead structure including an upper framework and a lower framework, the lower framework defining a load support. A winding drum is mounted rotatably on the upper framework and two lengths of cable are wound round in the same sense onto the winding drum such that rotation of the winding drum winds both cables on or off the winding drum. A rotary control drum is rotatably mounted on the lower framework and comprises a means for opposing swinging of the lower framework relative to the upper framework the cables pass from the winding drum over an arrangement of pulleys to the control drum.The cables are wound around the control drum and thence around further pulley arrangements back up to anchor points on the upper framework to which the cables are attached. The cables are wound round the control drum in such a way that displacements of the lower framework from a predetermined position relative to the upper framework is opposed by the tendency of the cables to rotate the control drum in opposite directions at the same time. Both cables are wound around the control drum such that they are substantially locked together and during raising and lowering, the cables precess along the control drum. However, when the height of lift required is great this precession would require a long control drum which is often difficult to accommodate on the lower framework.A further problem is encountered in that, with a large precession, unbalanced forces can develop on the lower framework causing it to rotate slightly in the horizontal plane. This might present difficulties when lowering loads into fixed guides.

The main cause of precession is the presence of complete turns of cable around the central drum which are required to allow the cable to grip the control drum sufficiently.

It is an object of the present invention to provide load handling equipment which obviates or mitigates the problems outlined above and provide a method of resisting sway which does not require complete turns of cable around a control drum yet which allows equivalent resistance to sway.

According to the present invention, there is provided equipment for handling a load, said equipment including a load support which is suspended from an overhead structure by a plurality of lengths of cable (as defined herein), the pair of said cable lengths engaging with said load support at locations which are spaced apart in a first dimension, means for varying the effective lengths of the cables so as to enable the load support to be raised and lowered relative to the overhead structure, and means for opposing swinging movement of the load support in said first dimension, said opposing means including a pair of rotary members around which each of said cables is wound such that displacement of the load support in said first dimension at a predetermined position relative to the overhead structure is opposed by the tendency of said pair of cable lengths to rotate each of said pair of rotary members respectively in opposite directions at the same time.

Preferably, the pair of rotary members is mounted on the load support. However, with a suitable configuration of the cables, said pair of rotary members can be mounted on the overhead structure with the same advantages.

Said pair of rotary members may take the form of a pair of drums having substantially parallel axes of rotation, each of said pair of cable lengths forming at least one loop around said pair of drums.

It is particularly preferred that the cables are wound around the drums in such a way that no complete turns are formed around any one drum, the cables being wound around both of said pair together. It is also preferred that the cables are constrained within annular grooves provided around the peripheral surfaces of the drums.

An embodiment of the present invention will now be described, by way of example, with reference to the accompanying figure which is a schematic perspective view of one embodiment of load handling equipment according to the present invention.

Referring now to the figure, the load handling equipment illustrated therein takes the form of an overhead crane and comprises an overhead structure including an upper framework 1, and a lower framework defining a load support. The upper framework 1 includes brackets 3 upon which supporting wheels 4 are mounted. The wheels 4 allow the said upper framework 1 to travel along or be driven a long a suitable overhead beam 20, said beam having flanges 21 that,act as rails for said supporting wheels 4. The upper framework 1 and the wheels 4 together define an overhead carriage.

The lower framework 2 has a number of load attaching points 5.

Mounted rotatably on the upper framework 1 is a winding drum 6 which is under the control of a motor 7 and brake apparatus 8.

Preferably, the winding drum is grooved in the normal manner. Wound in the same sense on the winding drum 6 are two lengths of cable 9 and 10 which extend from opposite sides of the drum so that clockwise rotation (as viewed in the figure) of the winding drum 6 winds both cables 9 and 10 onto the winding drum 6.

A pulley 11 is rotatably mounted close to one end of the upper framework 1. In a similar manner a pulley 12 is mounted close to the other end of the upper framework 1.

Cable anchors 13 and 14 are pivotally attached at locations part way along the upper framework 1.

Close to one end of the lower framework 2, two pulleys 15 and 16 are rotatably mounted.

Close to the opposite end of the lower framework 2, two pulleys 17 and 18 are rotatably mounted.

Two rotary control drums 22, 23 are rotatably mounted at locations on the lower framework 2 intermediate the pulleys 15 and 16, and 17 and 18. Preferably, the control drums 22, 23 are provided with mutually parallel annular grooves (not shown) extending around their peripheries to receive the cables and prevent precession. These rotary control drums comprise a means for opposing swinging of the lower framework 2.

From the winding drum 6, the cable 9 is passed over the pulley 11 down to and under pulley 15 and thence to the control drums 22, 23. The cable 9 passes under control drum 22, is wound for a half turn around control drum 23 and is led back towards control drum 22. The cable 9 is then wound for a half turn around control drum 22 and is led back towards control drum 23. The cable 9 is then wound for a further half turn around contrtol drum 23 and is led back over control drum 22 and then led to and around pulley 18 and thence up to the anchor 13 to which the cable 9 is attached.

Cable 9 is wound around the control drums 22 and 23 in such a direction, that when the winding drum 6 is rotated in a clockwise direction, in order to wind in cable 9 and so raise the lower framework 2, the control drums 22, 23 are caused to rotate in an anticlockwise direction (as viewed in the figure).

From the winding drum 6, the cable 10 is passed over the pulley 12 and is then led down and under pulley 17 and thence to the control drums 22, 23. The cable 10 is led over the control drum 23 and is wound for a half turn around control drum 22 and led back towards control drum 23. The cable 10 is then wound for a half turn around control drum 23 and is led back towards control drum 22. The cable 10 is then led around control drum 22 for a further half turn and is led back under control drum 23 and is then led to and around pulley 18 and up to the anchor 14 to which the cable 10 is attached.

The cable 10 is wound around the control drums 22, 23 in such a direction that, when the winding drum 6 is rotated in a clockwise direction, in order to wind in cable 10 and so raise the lower framework 2, the control drums 22, 23 are caused to rotate in an anticlockwise direction (as viewed in the figure).

Thus, during the raising of the lower framework 2, and, if any, the load, both the action of cable 9 and the action of cable 10 cause the control drums 22,23 to rotate in the same direction, in the case illustrated, this is an anticlockwise direction (as viewed in the figure).

Hence the presence of the control drums 22, 23 does not significantly affect the raising and lowering operation ultimately controlled by the winding drum 6 and motor 7.

It should be noted that the rotational axes of he various drums and pulleys described above are all substantially parallel to each other but substantially perpendicular to the "first dimension" referred to hereinafter. Minor variations may be introduced in order to ease the path of certain portions of the cables 9 and 10. The cable carrying pulleys are mounted as close to the central plane of the system as is practicable. It is preferable that the portions of the cables 9 and 10 passing between the upper framework 1 and the lower framework 2 are so arranged as to be symmetrical and be inclined to the vertical substantially the same angle. In this embodiment, the angle is about 15 to the vertical.

However, it is possible for this angle to be 4" to 40 , and is preferably 10"--20", depending upon the circumstances of use. It is also possible for the angles to be mutually different.

For example, the portion of the cable 9 between pulleys 11 and 15 and the portion of the cable 10 between the pulleys 12 and 17 may be inclined at an angle of 0 to the vertical whilst the portion of the cable 9 between the pulley 16 and the anchor 13 and the portion of cable 10 between the pulley 18 and the anchor 14 may be inclined at an angle of 30 to the vertical. The above angles are the intended angles of inclination when the lower framework 2 is in its lowermost position of use. Such angles are adopted when the lower framework 2 is in the desired position in the horizontal plane relative to the upper framework 1.

In operation the upper framework 1 may need to move along the rail 20. In order to maintain the lower framework 2 in a fixed relative position to the upper framework 1, during such movements, accelerating and decelerating forces will need to be applied in the directions marked "forwards" and "backward" in Fig. 1. Such directions are in what is referred to herein as a first dimension.

This is the dimension in which the longitudinal directions of extent of the upper and lower frameworks exist and in which the upper framework moves along the beam 20.

If a disturbing force is applied to the lower framework 2 in the "forwards" direction, the cable system associated with cable 9 would tend to rotate the control drums 22,23 in an anticlockwise direction, whereas, the cable system associated with cable 10 would tend to rotate the control drums 22,23 in a clockwise direction. Thus equal, or near equal, but opposed rotational forces are applied to the control drums 22, 23 at the same time.

Since the control drums 22, 23 are effectively locked together by means of the cables 9 and 10, relative rotation cannot occur and in effect, the cable systems associated with cables 9 and 10 are locked together by the control drums 22, 23. A similar situation arises if a disturbing force is applied in the "backward" direction. This feature prevents any significant relative movement in the first dimension between the lower framework 2 and the upper framework 1.

In the event of a massive sway (e.g due to collision of the load with some object) the cables 9 and 10 may slip. Even after such a slip, however, the lower framework 2 still remains substantially horizontal, but its centre line is horizontally displaced from its previous centre line and requires re-setting.

The cables 9 and 10 are constrained on the control drums 22, 23 by fixed grooves and in this way precession of the cables 9 and 10 along the control drums 22, 23 is prevented.

This is especially significant in cases where the height of lift is great, and should this precession be allowed to occur, long control drums would be required which may be difficult to accommodate on the lower framework 2.

The provision of two control drums means that a cable can contact the same area of drum in two half turns as it can in one complete turn around a single drum yet there is no precession as the cables are lead onto and off each drum from opposite sides thereof.

It will be clear that this twin control drum arrangement may be applied, mutatis mutandis to the arrangements shown in our co-pending Application No. 8515700.

Claims (6)

1. Equipment for handling a load, said equipment including a load support which is suspended from an overhead structure by a plurality of lengths of cable (as defined herein), the pair of said cable lengths engaging with said load support at locations which are spaced apart in a first dimension, means for varying the effective lengths of the cables so as to enable the load support to be raised and lowered relative to the overhead structure, and means for opposing swinging movement of the load support in said first dimension, said opposing means including a pair of rotary members around which each of said cables is wound such that displacement of the load support in said first dimension at a predetermined position relative to the overhead structure is opposed by the tendency of said pair of cable lengths to rotate each of said pair of rotary members respectively in opposite directions at the same time.

2. Equipment as claimed in claim 1, wherein the pair of rotary members is mounted on the load support.

3. Equipment as claimed in claim 1 or 2, wherein said pair of rotary members takes the form of a pair of drums having substantially parallel axes of rotation, each of said pair of cable lengths forming at least one loop around said pair of drums.

4. Equipment as claimed in claim 3, wherein the cables are wound around the drums in such a way that no complete turns are formed around any one drum, the cables being wound around both of said pair together.

5. Equipment as claimed in claim 3 or 4, wherein the cables are constrained within annular grooves provided around the peripheral surfaces of the drums.

6. Equipment for handling a load, substantially as hereinbefore described with reference to the accompanying drawing.