US3534995A - Device for damping the oscillatory motion of the hoisting ropes of a crane - Google Patents

Description

Oct. 20, 1970 u. J. HEIKKINEN 3,534,995

DEVICE FOR DAMPING THE OSCILLATOR! MOTION OF THE HOISTING ROPES OF A CRANE Filed April 5, 1968 United States Patent DEVICE FOR DAMPING THE OSCILLATORY MOTION OF THE HOISTING ROPES OF A CRANE Urho Johannes, Heikkinen, Ida Ahlhergintie 4 A 11,

Helsinki 40, Finland Filed Apr. 3, 1968, Ser. No. 718,430

Claims priority, application Finland, Feb. 14, 1968, 381/68 Int. Cl. B66c 1/34 U.S. Cl. 29478 6 Claims ABSTRACT OF THE DISCLOSURE A device is provided for damping the oscillatory motion of the hoisting ropes of a crane by which a gripping element engaging the load to be hoisted has been suspended. The gripping element is designed to act as a pendulum, by dividing it vertically into two or more parts which are joined together by links or pivots and the parts are furthermore interconnected by one or more cylinders damping the relative oscillatory motion of the parts.

A difficult problem in crane operation is how to check the oscillatory motion of the hoisting ropes. It is necessary for the gripping element to be lowered without oscillation upon the load which it is to engage. On the other hand, the gripping element and the load carried by it have to be deposited on a base of some kind without oscillations. One way in which the oscillatory motion may be damped is that the hoisting ropes are not carried downward from the crane in a vertical direction but that they enclose an angle with each other instead. The damping achieved is greater, the larger angle. But the angle cannot be large when the hoisting height is great. Considerable hoisting heights are necessary e.g. in harborside cranes, where the ropes reaching from the point of the jib deep down into the ships hold may be several tens of metres in length.

It takes a long time to wait for the oscillatory motion to subside. Checking the motion by manpower, again, requires additional men on the site.

An object of the present invention is to provide a device by means of which the oscillatory motion is made to subside in a very short period of time. The invention is characterized in that the gripping device is designed so as to act as a pendulum, by dividing it vertically into two or several parts which are joined together with links or pivots, and in addition the parts are interconnected by means of one or more cylinders damping the oscillatory motion of the parts relative to each other.

It is thus to be understood that in a device according to the invention there is formed as a continuation of the hoisting ropes, another pendulum, but which has a length only a fraction of the length of the ropes. As a consequence, its period of oscillation is also much shorter. The pendulum consisting of the ropes induces an oscillatory motion of the pendulum which the gripping element constitutes and imparts vibratory energy to the latter.

The cylinder in the gripping element continuously dissipates vibratory energy as such energy is imparted to the pendulum formed by the gripping element by the pendulum which consists of the ropes. Even under most adverse conditions the oscillatory motion of the ropes will thus be checked within some tens of seconds. The invention is in fact based on the phenomenon well-known from childrens swings, namely, that it is possible to stop the swing rapidly by exerting pressure on the ropes with the hands in the direction of the momentary movement.

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The invention is described, for illustration, in the following with reference to the attached drawing, in which FIG. 1 shows the gripping element in side elevational view, and

FIG. 2 shows the gripping element, in end elevation v1ew.

The gripping element in the drawing is intended to be suspended by ropes attached to the loops 1 from a harborside crane. The gripping element is employed to hoist containers. In FIG. 1 the ends of the long body 2 engaging the container have not been shown.

The gripping element has been designed to act as a pendulum in the plane of FIG. 1 by dividing it vertically into two parts 9, 10 which are joined together with pivoted arms. The upper and lower parts are moreover interconnected by means of a cylinder 4. The cylinder 4 is mounted on the lower part 10 and its piston rod 5 is fixed to the upper part 9. The piston inside the cylinder 4 has a throttling orifice through which the medium in the cylinder can pass from one side of the piston to the other.

When the loaded or unloaded gripping element is hoisted with the aid of the ropes indicated by arrows 6 and displaced horizontally, the pendulum formed by the hoisting ropes together with the gripping element begins to oscillate, as indicated by arrows 7. But at the same time the pendulum formed by the gripping element itself tends to oscillate about the pivot point 8. The last-mentioned pendulum has a length only a fraction of that of the pendulum constituted by the hoisting ropes. Accordingly, its period of oscillation is also considerably shorter. The pendulum formed by the hoisting ropes continuously gives off oscillatory energy to the pendulum formed by the gripping element. When this latter pendulum oscillates, the beam of the upper part 9 and the beam of lower part 10 remain parallel but are laterally displaced with reference to each other. This lateral motion, or the oscil latory motion of the pendulum, is counteracted by the cylinder 4 mounted perpendicular to the linkage arms 3, because the medium cannot pass rapidly enough through the restricting orifice in the piston. The cylinder 4 thus continuously dissipates the oscillatory energy imparted to the pendulum formed by the gripping element by the pendulum which is formed by the ropes, until the energy has been used up and all oscillatory motions have ceased, This takes an astonishingly short time to accomplish.

The efiiciency of the device shown in FIG. 1 is further increased if the cylinder 4 is made double-acting, that is, if the crane operator may supply actuating medium alternatively to either side of the piston. He may in that case actively contribute to the checking of the ropes oscillatory motion. There is, of course, no orifice in the piston in such instances. If the oscillatory motion of the hoisting ropes is, for instance, to the right in FIG. 1, the crane operator will supply medium to the left side of the piston, which causes the linkage arms 3 to be rotated in a clockwise direction by a certain amount. After the oscillatory motion of the hoisting ropes has reversed itself, the operator will start to supply medium to the opposite side of the piston. The crane operator has ample time for these manipulations, because the long pendulum has a long period of oscillation.

The invention was tried out in conditions consistent with actual practice. The hoisting wires, on the lower end of which a gripping element as shown in FIG. 1 was suspended, had a length of 20 metres. The pendulum was caused to oscillate with an amplitude of its lower end of :2 metres. If nothing was undertaken and the pendulum was allowed to free oscilate, a time of 30 minutes was necessary for the oscillation of the lower end to diminish to the acceptable amplitude of :02 metres. When the cylinder 4, with a restricting orifice in its piston, was

mounted in place, 2.5 minutes were required for the motion of the pendulum to subside to the acceptable amplitude. When the cylinder 4 Was made double-acting and actively operated by the crane operator, the motion of the pendulum was reduced to the acceptable amplitude within 20 seconds.

As can be seen from FIG. 2, the gripping element shown in the drawing furthermore incorporates a device which damps the oscillatory motions in the plane perpendicular to that considered above. Now, too, the gripping element has been designed to act as a pendulum by dividing it vertically into two parts joined together with a pivot 11. A cylinder 12 is mounted in the gripping element and connected in parallel with the pivot 11, this cylinder being mounted on a lug 13 of the lower part and its piston rod 14 being fixed to a lug 15 on the upper part. In order that the cylinder 12 may be comparatively long, the lug 13 is elongated in the downward direction. In this case, too, the piston of cylinder 12 may have a restricting orifice for passage of the medium from one side of the piston to the other, or the cylinder may also be double-acting so that it may be operated by the crane operator. The principle of action of the device shown in FIG. 2 is completely identical to that described in connection with FIG. 1.

It is to be understood that different embodiments of the invention may vary within the scope of the attached claims. For instance, the gripping element may differ considerably in its other details of design from what has been shown in the drawing.

I claim:

1. An improvement in a device for damping oscillatory motion of the hoisting ropes of a crane by which a gripping element engaging the load to be hoisted is suspended, wherein according to the improvement the gripping element includes two vertically spaced parts and links joining said parts to form a pendulum therewith, and a hydraulic cylinder interconnecting said parts for damping relative oscillatory motion of the parts, said cylinder including a double-acting piston which is adapted for being compulsority operated to dampen each swing of oscillatory movement.

2. A device according to claim 1 wherein said links and cylinder extend perpendicular to one another.

3. A device according to claim 1 wherein said cylinder has a restricting orifice for passage of hydraulic medium from one side of the piston to the opposite side.

4. A device according to claim 1 wherein said gripping element includes means forming a second pendulum pivotable about an axis perpendicular to the first pendulum.

5. A device according to claim 4 wherein said means forming the second pendulum comprises two divided elements constituting one of said parts, further links connecting said divided elements and a further hydraulic cylinder connecting said divided elements.

6. A device according to claim 5 wherein said cylinders extend perpendicular to one another.

References Cited UNITED STATES PATENTS 3,086,661 4/1963 De Stasi 2l2-125 3,254,775 6/1966 Bevard 21214 FOREIGN PATENTS 561,436 4/1957 Italy.

EVON C. BLUNK, Primary Examiner D. D. WATTS, Assistant Examiner

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