The invention concerns a method of controlling the operations of a crane, in which the movements made by the crane's lifting carriage are controlled by an open control system that aims to minimize the swing of the load. The invention also concerns the equipment needed to dampen the swing of the crane's load, which will include an open control system designed to control the movements made by the crane's lifting carriage and to minimize the swing of the load. The invention further concerns the crane arrangements, which will include a lifting carriage designed to move on one track, a control cabin designed to move on a second track, parallel to the first, and an open control system for controlling the movements of the lifting carriage and minimizing the swing of the load.

Methods and equipment as described above in which an open control system is used to control the movements of a crane's lifting carriage are known, for example, from FI patent publication 44036 and FI patent application 925212. In these systems, the movement of the crane's lifting carriage is controlled by adjusting the revolutions of the motor that transfers the lifting carriage, with the result that the swing of the load suspended from the crane is minimized. In these cases, control is based on mathematical models of the load's swing. Because it concerns a so-called open control method, the actual movements of the load are not measured at all. Therefore, these systems do not always work satisfactorily in all circumstances. For example, a sudden gust of wind may cause load swing that cannot be noticed or taken into account by a swing dampening system that is based on this kind of open control method.

On the other hand, various methods of mechanically dampening the swing of the crane's load are known. These methods are generally based either on hydraulic dampeners and/or diagonal cable suspension. The objective of these systems is to dampen load swing caused by the movements of the crane's lifting carriage completely and as rapidly as possible. The problems related to these mechanical dampening systems include interruptive load swing, which results

from the mechanical dampening, and the technical complexity of the dampening system, which is reflected in high prices and maintenance costs. As loads transferred by container cranes are very large, typically about 55 tonnes for example, a considerable amount of energy, well over 10 kW, is needed to dampen the swing.

The purpose of the present invention is to devise a new method and equipment for controlling the operations of a crane, without any of the drawbacks of the above-described types of dampening system. This is achieved by a method according to the invention, characterized in that an ideal plan of movements is calculated for the said open control system, and at least something of the crane's mechanical, mobile part is controlled on the basis of the ideal plan of movements.

In the first embodiment of the invention, the equipment that mechanically prevents load swing is controlled so as to allow swing that is in harmony with the ideal plan of movements and dampen only the swing that deviates from this ideal plan of movements.

In the second embodiment of the invention, when the lifting carriage is operated on one track and the control cabin on another track, parallel to the first, the movements of the crane's control cabin will follow the said ideal plan of movements in order that the locations of the control cabin and the load in the direction of the tracks will remain essentially unchanged with respect to each other.

In the method according to the first embodiment of the invention, therefore, the open control system controlling the movements of the lifting carriage is combined with a mechanical swing dampening system which, nevertheless, is controlled in a way which clearly differs from the conventional mechanical swing dampening system. According to the invention, only the load swing that deviates from the said ideal plan of movements in the open control system is dampened. By so doing it is possible to construct a mechanical swing prevention system that is substantially lighter and simpler than has been known, while still achieving a more effective overall swing dampening system than has been known earlier. At the same time, there is decreased wearing of the mechanical swing prevention equipment and reduced

maintenance costs.

Regarding the equipment according to the invention designed to dampen the swing of a crane's load, it is characteristic that, in addition to the open control system controlling the movements of the crane's lifting carriage and aiming to minimize the swing of the load, the equipment includes a means of calculating the ideal plan of movements with the aid of the open control system, and a means of mechanical swing prevention, and a means to control the dampening behaviour of the mechanical swing prevention equipment, in order that they allow load swing in accordance with the said ideal plan of movements and dampen only the swing that deviates from this ideal plan of movements.

When the mechanical swing prevention equipment consists of swing dampening cables, the means of controlling the dampening behaviour consists of equipment for adjusting the length of the swing dampening cables.

If the mechanical swing prevention equipment consists of a hydraulic dampening system, the means of controlling the dampening behaviour of this hydraulic dampening system consists of equipment for adjusting the dampening induced by the hydraulic cylinders of the dampening system.

If the mechanical swing prevention equipment consists of an electromechanical dampening system, the means of controlling the dampening behaviour consists of equipment for adjusting the dampening induced by the electromechanical actuators.

Regarding the crane arrangement according to the invention, which consists of a lifting carriage designed to move on the first track and a control cabin designed to move on the second track, parallel to the first, and an open control system aiming at minimizing the swing of the load, it is characteristic that it consists of equipment for calculating the ideal plan of movements with the aid of the open control system, and equipment for controlling the movement of the control cabin according to the said ideal plan of movements in order

that the locations of the control cabin and the load in the direction of the tracks will remain essentially unchanged with respect to each other.

The following is a more detailed description of the method and equipment according to the invention, with reference to the appended drawing in which

Figure 1 presents in schematic form a crane arrangement to which the method and equipment according to the invention may be applied,

Figure 2 presents in schematic form the first embodiment of equipment according to the invention, and

Figure 3 presents in schematic form the hydraulic part of the second embodiment of equipment according to the invention.

Figure 1 presents a crane arrangement, which consists of a lifting carriage 1 designed to move on the first track 8 and a control cabin 10 designed to move on the second track 9, parallel to the first track 8. The lifting carriage 1 carries the load 2 by means of the cable system 15. The crane arrangement also includes an open control system which controls the movements of the lifting carriage 1 and aims to minimize the swing of the load, and which may be, for example, a system as described in the above-mentioned publications. In accordance with the invention, this arrangement also includes equipment, such as a suitable microprocessor or microcomputer, which calculates the ideal plan of movements of the load 2 to be achieved with the aid of the said open control swing dampening system. In accordance with the invention this movement information is utilized in the control of some mechanical, moving part of the crane, such as control cabin 10 or the mechanical swing dampening system.

Figure 1 shows that control cabin 10 is separate from lifting carriage 1. In order that this control cabin 10 may move in such a way that the operator can follow the movements of load 2 as well as possible, the control cabin is controlled according to the said ideal plan of

movements calculated for the load, so that the locations of control cabin 10 and the load 2 in the direction of tracks 8 and 9 are maintained essentially unchanged with respect to each other. In practice it is possible with this method to have control cabin 10 remain above load 10 for example. The particular advantage with this method is that the control cabin does not move with the lifting carriage but with the swing of the load which is considerably more peaceful in terms of acceleration than the movements of lifting carriage 1.

Figure 2 presents as an example some known equipment for the dampening of the swing of a crane's load. This equipment includes the bearing cables 11 and 12 drawn over idler wheels 13 and 14 and attached at both free ends to points on opposite sides of the load, so as to form the shape of a V between them. In addition, load 2 is carried by bearing cables 3 and 4 which are formed by the swing dampening cables. In equipment according to the invention, which therefore consists of an open control system controlling the movements of the lifting carriage and aiming at minimizing the swing of load 2, and related equipment for calculating the ideal plan of movements to be achieved with the aid of the open control system, the length of the said swing dampening cables 3 and 4 is adjusted so as to allow load swing according to the said ideal plan of movements and to dampen only the swing that deviates from this ideal plan of movements. The means of adjusting the length of swing dampening cables 3 and 4 is not, for reasons of clarity, presented in Figure 2, but may be included in the control circuits of the motors driving the drums around which the cables are wound. The purpose is to lengthen and shorten the swing dampening cables so that they allow a residual swing arising ideally from the use of the open control system, but do not however allow other kinds of load swing. The purpose, therefore, of length adjustments of swing dampening cables 3 and 4 according to the operating principle of equipment in accordance with the invention, is to dampen all interruptive swing, or swing caused by faulty operation of the open control system controlling the movements of the lifting carriage, which deviates from the ideal plan of movements to be achieved by the said open control system. Thus the loading of these swing dampening cables 3 and 4 is

relatively small, compared with the situation where they would dampen the swing of a freely swinging load.

Figure 3 presents a second type of mechanical swing dampening system that is known in terms of its basic principle and which can be adapted to a load suspension system as in Figure 2. In this case the swing dampening cables 3 and 4 can be omitted from the arrangement. According to the schematic presentation in Figure 3, the idler wheels 13 and 14 of the load-bearing, crossed cables 11 and 12 are suspended from the piston drivers of the hydraulic cylinders 5 and 6. The cylinder spaces of these hydraulic cylinders 5 and 6 are in turn joined with a hydraulic hose 16, equipped with a pressure relief valve 7 for adjusting pressure. By adjusting this pressure relief valve 7, it is possible to control the dampening behaviour of the described hydraulic dampening system. If the pressure relief in valve 7 is set at zero, there will be no dampening effect at all. This situation occurs in equipment according to the invention when the movement of the load corresponds to the movement ideally achieved by the open control system. In practice this means that the flow of hydraulic fluid in hose 16 is of a certain magnitude and direction. If the rate or direction of flow of the hydraulic fluid deviates from this ideal situation, the pressure relief valve 7 is directed to limit the flow. Thus the hydraulic system is capable of dampening the load swing that deviates from the ideal plan of movements achieved by the open control system.

Electromechanical actuators can also act as mechanical swing dampening equipment. An example of this kind of solution is a system in which the load is carried by a suspension cable which is drawn around an idler wheel at the load end. When the load swings, the said idler wheel rotates around its axle. This rotation can be adjusted according to the invention by, for example, an electric motor connected to the axle of the idler wheel, so that its operations are controlled with an electromechanical brake when the load swing deviates from the ideal plan of movements achieved by the open control system. In this case, such braking moments must be used that the suspension cable does not begin to slip with relation to the idler wheel. This is possible in equipment according to the invention, because the mechanical swing dampening system is limited, in

equipment according to the invention, to a much smaller swing than is normal in systems in which the load swing is dampened only by mechanical arrangements.

The above method and equipment according to the invention for the controlling of a crane's operations, as well as the crane arrangements, are described only with the aid of some exemplary embodiments, and it is thus understandable that the invention may be fulfilled by arrangements differing from the foregoing without, however, departing from the protected area defined by the appended patent claims and from the basic idea of the invention, according to which a mechanical swing dampening system is used to dampen only that movement which deviates from the ideal plan of movements arising from the open control system that controls the movements of the lifting carriage. Thus this mechanical swing dampening system concerns nearly all known types of mechanical swing dampening system which can be modified according to the invention to limit only the swing that deviates from the ideal plan of movements arising from the open control system that controls the movements of the lifting carriage. Mechanical swing dampening systems are understood to mean all swing dampening that is not based on the electrical control of the movements of the lifting carriage.