GB2031842A

GB2031842A - A load rotating device

Info

Publication number: GB2031842A
Application number: GB7931667A
Authority: GB
Original assignee: Peiner Maschinen und Schraubenwerke AG
Current assignee: Terex Peiner GmbH
Priority date: 1978-09-13
Filing date: 1979-09-12
Publication date: 1980-04-30
Also published as: GB2031842B; NL184610B; DE2839723A1; FR2436096B1; BE878693A; DD145908A5; DE2839723C2; NL7906226A; FR2436096A1; NL184610C

Abstract

A load rotating device 1 has a rotary drive for operative connection with a load 3 via load connecting means and a power take-off. The device is suspended via one or more cables 2. It has been found that in consequence of the inertia of the load actuation of the device produces a torque or prestress in the cables which when the load is displaced through the rotary drive tends to rotate the load beyond its desired position. The present invention applies a torque or prestress to the cable in the opposite direction to the desired rotation, which subsequently initiates motion of the load in the desired direction. When the desired position for the load is reached, the rotary coupling between the load and the cable is disengaged whereby the torque or prestress in the cable can be released whilst the load remains at the desired position. In one embodiment the transmission between the rotary drive and load is de-coupled hydraulically and in a further embodiment decoupling is effected through an electromagnetic clutch. <IMAGE>

Description

SPECIFICATION A load rotating device This invention relates to a load rotating device comprising a rotary drive which is in an operative connection with the load via a power take-off for the purpose of transmitting rotary forces, which load is suspended via the load rotating device from at least one cable, preferably from four cables, so that the load rotating device, after being actuated, as a consequence of the inertia of the load produces, in opposition to the desired direction of rotation of the load, a cable prestress (in the case of one cable) or a cable field prestress (in the case of a plurality of cables), which then causes the rotation of the load.

It is known that load rotating devices are necessary for rotating and thus positioning heavy loads such as tree-trunks, bundled pine logs, pipes, containers and the like which are transported by means of a crane. The load rotating devices themselves are suspended from at least one crane cable and in the majority of cases are so constructed that, for the purpose of producing a large take-off torque, a mechanical gear is used which is connected on its drive side to an electric motor of relatively low power.

To enable other electric or electro-hydraulic consumer units (such as grabs, tongs, etc.) to be connected to the load rotating device for the purpose of picking up the load, a spur wheel group is usually provided after the mechanical gear. By suitably constructing the drive shaft as a hollow shaft, electrical power lines or liquid lines may be passed through the shaft to the consumer unit.

It has already been mentioned that the load rotating devices are suspended from at least one cable. In practice, a plurality of cables is usually provided, a cable base as wide as possible being aimed at for the purpose of accepting the reaction torque. The wide cable base means that the cables, from which the load rotating device is suspended, are at relatively large distances from one another.

A rotation and accurate orientation of large loads which possess large moments of inertia - is accompanied by the problems explained below.

When the load rotating device is switched on to rotate the load, the load cannot immediately accompany the rotation on account of its large mass moment of inertia. Let it be assumed that the load rotating device is suspended from only one cable.

Since the load has a larger inertia then the cable, when the rotational movement is initiated it is not the load but the cable that commences to rotate. If the load rotating device is suspended from several, e.g. four cables, a comparable effect occurs in that a corresponding cable field twisting takes place between the load rotating device and the crane jib though which the cables are passed. As explained in more detail below, the term cable field twist means that the area bounded by the cables and lying in one plane is twisted.

When a load rotating device is switched on, an acceleration torque cannot become effective on the load to be rotated until the corresponding twist of the cable field between the load rotating device and the crane jib has taken place as a consequence of the reaction torque in the opposite driven rotational direction. To assist in understanding, it may be imagined that four cables hang down from a firm slab and that the points of attachment of the cables to the slab are the corner points of a square. Let a heavy load be suspended from the cables, the points of attachment of the lower ends of the cables to the load constituting the corner points of the same square. If the load is now rotated by hand, a twisting of the cable field between load and slab takes place.

This cable field twist results in a torque which is manifested in that the released load moves in opposition to the rotational movement previously applied by hand. Rotating by hand can be carried out until a so-called "collapsing" of the cable field occurs. The collapsing is reached when the four cables touch one another and become twisted together if rotation is continued.

If one now turns back from this theoretical example to the load rotating device, its drive must be switched off after a specific switched-on period in order to avoid the aforementioned possible collapsing of the cable group. For a desired rotation of load through an angle of, for example, 90 , it is favourable to execute the above-described twisting of the cable field, if indeed possible, only as far as an angle of twist of approximately 45 between load rotating device and cable suspension (crane jib). When this angle of twist is reached the drive should be off in order that the cable field torque which has built up can act upon the load rotating device and thus upon the load itself in an accelerating manner.After acceleration has taken place, the load which is in rotation must then be retarted by an approximately equal braking torque. This only becomes possible if, with the drive switched off, a twisting of the cable field now again occurs, but on this occasion in the direction of the current rotation of the load. When the load rotational speed n = 0 is reached, i.e. when the rotation of the load has been braked by the cable group twist built up by it, a cable field twist angle once again of large magnitude and thus a cable field twist between the load rotating device and cable suspension is however reached.As a consequence of this cable field twisting, a repeated acceleration of the load in the undesired, opposite rotational direction now commences Unless there is further inter vention,the described operations continue until oscillation of the load has died down. Accurate orientation of large loads is thus possible, if indeed at all, only with great expenditure of time, with the result that economic handling of the goods is out of the question.

In order to overcome this problem it has been disclosed that special cable stressing devices may be provided for the purpose of rotational stabilization on the crane jib (preprint from Peine & Salzgitter Report No. 1/75, special volume for Hanover Fair 1975 bearing the title "New Development - Selfstabilized Rotational Device", pages 1 and 2). Rotational stabilization is here achieved by the cable stressing device applying a counter-torque. From the aforementioned preprint it is also known that a rotational stabilization may be achieved by a shears (compare same preprint, page 2, paragraph 2). The known devices are, however, frequently very troublesome in operation. Also, by virtue of their own weight, they reduce the useful lift of the crane.

From the aforementioned preprint a self-stabilized rotational device has also been disclosed (see preprint page 3) by which the initially described problems can be avoided. However, the self-stabilized rotational device, though advantageous in itself, cannot be used without restrictions. When relatively large loads are involved and therefore high moments of inertia occur, the necessary self-stabilized rotational device becomes too large and much to great a lifting capacity is required from the crane to lift the rotational device itself, so that the useful lifting capacity of the crane is seriously and adversely reduced. A still acceptable limit for the use of self-stabilized rotational devices is at about 32 t weight for the load. Beyond this, self-stabilized rotational devices can no longer be used for reasons of economy.

The present invention seeks to provide embodiments of a load rotating device which avoids the disadvantages of the hitherto disclosed devices for rotating loads. It is further sought to provide an embodiment of a load rotating device which permits rotation and accurate positioning of the load in a simple manner and thus makes possible economical handling of goods and wherein the time necessary for rotating the load is as short as possible.

According to the present invention there is provided a load rotating device comprising a rotary drive which is in operative connection with the load carrying means via a power-take-offfortransmitting rotary forces, which load carrying means is suspended via the load rotating device from at least one cable, so that, in use, the load rotating device, after being actuated, as a consequence of the inertia of a load carried by the load carring means produces a cable prestress (for one cable) or a cable field prestress (for a plurality of cables) in opposition to the desired direction of rotation of the load, which prestress then causes the rotation of the load, wherein the operative connection between the rotary drive of the load rotating device and the load carrying means is constructed to be capable of disengagement and re-engagement as desired so that at selectable instants the existing cable prestress or cable field prestress may be suddenly reduced.

In the descriptive introduction it has already been mentioned that an acceleration moment initiating the rotation of the load cannot become effective until a corresponding twisting of the cable field between the load rotating device and the cable suspension has occured. As a result thereof, a cable field torque is produced, which can act in an accelerating manner upon the load and it has further been mentioned that the load which then is in rotation produces an opposite twisting of the cable field in the direction of the instantaneous rotation of the load. This cable field twist then produces a repeated acceleration of the load in the undesired, opposite rotational direction etc. When the load, as a consequence of its rotation, is correctly positioned, a residual cable field torque is consequently still present in the majority of cases.In embodiments of the invention, the operative connection between the rotary drive of the load rotating device and the load is now constructed to be capable of disengagement and re-engagement. By the releasing of the operative connection comparable to a decoupling, the cable prestress still present or cable field prestress - and thus the residual cable field torque still present - is suddenly reduced at the desired instant.

No cable field torque is then any longer present, if the cable prestress or cable field prestress is sudderily reduced at the instant at which, as a result of the rotational movement of the load, the initial prestress has first been reduced and then an opposite prestress has been built up and the latter has braked the rotation of the load and thus the load no longer executes any rotational movement. The braked load remains at this instant in its position.

In a preferred embodiment of the invention the load rotating device contains a hydraulic motor with a suction side and a pressure side, the power take-off of which is operatively connected to the load for the purpose of force transmission and which (hydraulic motor) is supplied with pressurized fluid from a pump. Between the suction and pressure side of the hydraulic motor a connection for the pressurized fluid can be made, as a result of which a sudden reduction in the existing cable group prestress can be achieved. For this purpose, in an advantageous manner, there is disposed between the suction and pressure sides of the hydraulic motor a 2/2-way valve, by which a connection can be made as desired between the suction and pressure sides.

In a second advantageous embodiment there is provided, as drive for the load rotating device, an electric motor which drives, via an electromagnetic disc clutch, a spur wheel set connected to the load for the purpose of force transmission. Here the sudden reduction in the cable prestress or cable field prestress is achieved by the fact that the power train or operative connection between the electric motor and load is interrupted by releasing the electromagnetic disc clutch. The electromagnetic disc clutch is, in an advantageous manner, connected to the electric motor via a hydrodynamic coupling and a double worm gear.

Embodiments of the invention will now be described by way of example only, with reference to the accompanying drawings, in which: Figure 1 shows schematically a load rotating device suspended from four cables with a load secured thereto; Figure 2 shows schematically a first embodiment of a load rotating device; and Figure 3 shows schematically a second embodiment of a load rotating device.

In Figure 1, a load rotating device 1 is suspended from four cables 2. The upper ends of the cables 2 lead to a cable suspension, not shown, for example a crane jib of a slewing crane, not shown, for lifting loads. The load rotating device 1 is here illustrated diagrammatically as a rectangular box, although in the majority of cases they are of round construction.

It is also possible to suspend the load rotating device 1 from more than four cables, for example from eight cables, or from only one cable. The load rotating device 1 itself is connected by load carrying means, here shown as a hook (not referenced) and cables 3a for the purpose of force transmission to a load 3, which is to be rotated and positioned. The load 3 may, for example, be a heavy container.

Tree-trunks, bundles of pine logs, pipes etc, may however also be considered. The connection between the load rotating device 1 and the load 3 is provided in Figure 3 by cables 3a. The aforementioned load carrying means connecting the load to the load rotating device for force transmission may, however, be realized in other ways. It is only necessary to ensure that a force can be transmitted to the load from the rotary drive (see 9 and 25 in Figures 2 and 3).

Between the cables 2, a plane area 2a is drawn in broken line, the corner points of which are formed by the cables 2. This area is termed the cable field. If, instead of the four cables 2, only two cables were used, then instead of the cable field a so-called cable line would be situated between these two cables.

Opposite directions of rotation are denoted by the two arrows 4 and 5.

Let is now be assumed that the load rotating device 1, the construction of which is explained further below with reference to Figure 2 and 3, is switched on. The rotational direction of the load rotating device 1 is indicated by the arrow 4. As a consequence of its large moment of inertia, the load 3 cannot immediately follow this rotational direction.

Instead, the load 3 initially remains in its initial position. As a consequence of the rotary drive of the load rotating device 1, a cable field twist of the cable field 2a takes place, however, between the load rotating device 1 and the cable suspension, not shown here. As indicated by the arrow 5, this cable field twist takes place in opposition to the rotational direction 4 of the load rotating device 1.

Let it further be assumed that the load rotating device 1 is switched off after it has executed a rotation of 45 . At this instant, therefore, the opposite cable field twist is also 45 . As a consequence of the cable field twist of the cable 2a, a cable field torque is built up, which now acts as an acceleration torque on the hitherto not yet rotated load 3 and, as a consequence of this acceleration torque, the load 3 commences to rotate in the direction indicated by 'the arrow 4. As a result of the rotating load 3, the original cable field twist is reduced. At the instant at which the cable field twist is zero, The rotating load 3 is, however, not stationary.As a consequence of its mass inertia it continues its rotation and now for its part builds up a cable field twist, and thus a cable field torque, the cable field twist takes place in the direction of the current rotation of the load. As a result, a braking moment is produced, which brakes the rotation of the load. If, as a consequence of the braking moment, the load 3 is now sufficiently braked so that it just stops and, as a consequence of the built-up cablefield twist just tends to rotate back again in the opposite direction, then a rapid restoring of the prestressed cable field 2a takes place, so that the state illustrated in Figure 1 is achieved, in which the cable field 2a is not twisted. The load 3 then remains stationary in its braked position.The aforementioned restoration is achieved by the fact that the operative connection between the rotary drive (9 and 25 in Figure 2 and 3) and the load 3 is released in the manner described below.

Without the sudden reduction in the cable field twist when the load 3 is correctly positioned, this load would again oscillate back in the opposite rotational direction after being braked, as has already been described in detail. Since such a swingback is avoided when this embodiment of the invention is used and the load can be positioned correctly in a relatively short time, economical handling of materials is achieved.

The use of this embodiment of the invention is especially advantageous when, as just described, the sudden reduction of the cable field prestress takes place at the instant of the braked load.

However, this sudden reduction in the cable field prestress can also be carried out at other instants, for example just before the braked condition is reached.

After the operative connection between the rotary drive and the load 3 is released, the operative connection is then again made. In this case, the load 3 does indeed move onwards a little in its previous direction of rotation, but since the speed of movement is only slight the subsequent rotation is negligible. Also, the subsequent oscillation of the load can be neglected, if it is considered in relation to the oscillation that would occurwithoutthe embodiment. In every case, a desired rotation and positioning is achieved in a relatively short time. In Figure 2 an example of embodiment of a load rotating device is illustrated, which is suitable for carrying out the described rotation of loads. The illustrated load rotating device comprises a drive motor 6, a pump 7 connected thereto and hydraulic motor 9, which drives a spur wheel set 16.When the drive motor 6 is switched on and the pump 7 connected thereto starts up, this pump delivers a pressurized fluid, such as oil, into a line 8. Through a controllable non-return valve 10, the pressurized fluid passes to the pressure connection of the hydraulic motor 9.

Through the spur wheel set 16 the rotational movement is transmitted to the take-off shaft 24 and thus a load rotation is initiated. The rotational drive of the power take-off shaft 24 can therefore be effectively transmitted to the load 3.

The pressurized fluid emerging from the lowpressure side of hydraulic motor 9 passes, via a regulated non-return valve 17, to the suction side of the pump 7 via line 8a. Pressurized fluid which is missing on account of leaks is made up via a non-return valve 18 from a pressurized fluid container 11. The leakage oil occuring at the hydraulic motor 9 is supplied to this pressurized fluid container 10 via a line 21.

To make possible a rotation in the two possible directions, the rotational direction of the drive motor 6 is reversible. With the reversal of direction of the drive motor 6, the delivery direction of the pump 7 is also changed and thus also the take-off rotational direction of the take-off shaft 24 is reversed in accordance with the above described function. In this case, missing pressurized fluid due to leakage losses is made up via the non-return valve 19.

The securing of the hydraulic system against excess pressure is provided by two alternately operating non-return valves 12 and 13 and via a pressure-limiting valve 14. The two alternately operating non-return valves 12 and 13 are disposed between the suction and pressure sides of the hydraulic motor 9 and the pressure limiting valve 14 is connected via a line to the common connection point of the two non-return valve 12 and 13. The relieved pressurized fluid is supplied to the pressurized fluid container 11.

If the drive motor 6 is switched off, the take-off shaft 24 also comes to a stop. When the non-return valves 10 and 17 are closed, a rigid connection is made between the rotating device 1 and the load 3.

As described with reference to the Figure 1, the accelerating or retarding of the load can therefore occur only via the built-up or building up cable field.

When the load is correctly positioned, a cable field moment is usually still present. This residual cable field torque is suddenly reduced in this embodiment of the invention. Therefore, the load rotating device illustrated in Figure 2 contains a 2/2-way valve 15 connected in parallel with the hydraulic motor, which valve is controllable via a magnet 23. When the 2/2-way valve 15 is actuated a connection is made between the suction side 22 and the pressure side 20 of the hydraulic motor 9. As a result, a rapid restoration of the still present residual cable field torque is obtained without effect upon the positioned load. By the making of the connection between the suction and pressure sides 22 and 20 of hydraulic motor 9, the drive connection between the load rotating device and the load is disengaged, so that the still existing cable field torque can be suddenly reduced.

In Figure 3 a further example of embodiment of a load rotating device is illustrated. The drive of the take-off shaft 24 is here provided by the switching on of an electric motor 25. Energy transmission takes place via a hydrodynamic coupling 26, a doubleworm gear 27, an electromagnetic disc clutch 28 and the spur wheel set 16. As already described previously, when the electric motor 25 is switched on, a prestressing of the cable field at first takes place.

When the electric motor 25 is switched off, the take-off shaft 24 is rigidly connected to the rotating device as a consequence of the self-locking of the double-worm gear 27. The accelerating or retarding of the load can now take place via the built-up or building up cable field. When the load is correctly positioned, then as a consequence of the necessary cable braking torque, a residual cable field torque is present, which can indeed adopt a maximum value.

A sudden reduction in this cable field torque is absolutely necessary, if the stationary load is not again to be accelerated but in this case in the opposite direction.

The sudden reduction in the cable field torque in the load rotating device of Figure 3 is achieved by the fact that an interruption of the power train between the load and the rotary drive can be effected by releasing the electromagnetic disc clutch 28. Thus a rapid restoration of the twisted or prestressed cable field can be achieved without effect upon the correctly positioned load.

These embodiments have hitherto been described on the assumption that the load rotating device 1 is suspended from a plurality of cables 2. The device of these embodiments is however utilisable also where only one cable is provided, because even one cable can itself generate a torque like the hitherto discus-sed cable field if, as a consequence of the original rotation of the load rotating device 1, this cable becomes twisted. It has however been found that the use of a plurality of cables, for example 2,4 or 8 cables, is more advantageous in the majority of cases than the use of only one cable.

Claims

1. A load rotating device comprising a rotary drive which is in operative connection with the load carrying means via a power take-off for transmitting rotary forces, which load carrying means is suspended via the load rotating device from at least one cable, so that in use, the load rotating device, after being actuated as a consequence of the inertia of a load carried by the load carring means produces a cable prestress (for one cable) or a cable field prestress (for a plurality of cables) in opposition to the desired direction of rotation of the load, which prestress then causes the rotation of the load, wherein the operative connection between the rotary drive of the load rotating device and the load carrying means is constructed to be capable of disengagement and re-engagement as desired so that at selectable instants the existing cable prestress or cable field prestress may be suddenly reduced.

2. A load rotating device as claimed in Claim 1, comprising a hydraulic motor with a suction side and pressure side, the power take-off of the hydraulic motor being operatively connected for the purpose of force transmission with the load carrying means and the hydraulic motor being supplied by a pump with pressurized fluid, and wherein a connection is provided selectively connecting the pressurized fluid between the suction and pressure sides of the hydraulic motor.

3. A load rotating device as claimed in Claim 2, wherein a 2/2-way valve is arranged between the suction and pressure sides of the hydraulic motor which enables the connection between the suction and pressure sides to be made as desired.

4. A load rotating device as claimed in either Claim 2 or Claim 3, wherein the pump for supplying the pressurized fluid is connected at its delivery side and its suction side respectively via a respective line with the pressure and suction sides of the hydraulic motor and wherein each line contains a controllable non-return valve.

5. A load rotating device as claimed in Claim 4, wherein the suction side of the pump is connected via a line containing a non-return valve with a pressurized fluid container containing pressurized fluid.

6. A load rotating device as claimed in either Claim 4 or Claim 5, comprising a drive motor for driving the pump, wherein the direction of delivery of the pump is reversible.

7. A load rotating device as claimed in any one of Claims 2 to 6, wherein two alternately operating non-return valves are disposed in series between the suction and pressure sides of the hydraulic motor and wherein a common connection point of the two non-return valves is connected to the pressurized fluid container via a line containing a pressure limiting valve.

8. A load rotating device as claimed in any one of Claims 2 to 7 wherein oil is used as pressurized fluid.

9. A load rotating device as claimed in any one of Claims 2 to 8, wherein leakage fluid occurring at the hydraulic motor is conducted via a line to the pressurized fluid container.

10. A load rotating device as claimed in any one of Claims 2 to 9, wherein the hydraulic motor is connected to the load carrying means via a spur wheel group for the purpose of force transmission.

11. A load rotating device as claimed in Claim 1, comprising an electric motor for the rotary drive, said electric motor driving, via an electromagnetic disc clutch, a spur wheel group connected to the load carrying meansforthe purpose of force trans- mission, and wherein the force train or operative connection between the electric motor and the load can be interrupted by releasing the electromagnetic disc clutch.

12. A load rotating device as claimed in Claim 11, wherein the electromagnetic disc clutch is connected via a hydrodynamic coupling and a double-worm gear with the electric motor.

13. A load rotating device as claimed in any one of the preceding Claims, wherein the load rotating device is suspended via a plurality of cables.

14. A load rotating device as claimed in Claim 13, wherein said number of cables is two or a multiple of two.

15. A load rotating device substantially as herein before described with reference to Figures 1 and 2 or Figures 1 and 3 of the accompanying drawings.