The invention relates to a revolver crane, comprising a movable or immovable pedestal mounted or mountable on a supporting base for fixing it on said supporting base,

wherein the pedestal supports a platform ring that is rotatably mounted on the pedestal, and on which platform ring hoisting elements for a load are provided as well as ballast for balancing the load.

Such a revolver crane is known from US-A-4 , 579, 234 , which concerns a heavy-duty revolver crane. The invention is however also applicable to revolver cranes which are not particularly intended for heavy-duty purposes. Further, the invention applies to cranes that are immovably fixed to the supporting base, but also to cranes which are movable and wherein the pedestal of the crane is mounted to the supporting base prior to the crane being placed in operation.

In order -to be able to lift heavy loads, the construction of the known revolver crane must likewise be heavy, and the dimensions of particularly the platform ring must answer to certain minimum requirements resulting in a quite bulky construction of the known revolver crane. Also the weight of the ballast that is applied must be relatively high to enable sufficient outreach of the hoisting elements for the design capacity of the crane. In fact when the hoisting elements are idle, the weight of the ballast induces such a high load of the platform ring on the ring construction that is applied for the ro- tatable mounting of the platform ring on the pedestal, that wear and tear of this ring construction is high.

It is an object of the invention to provide a design of a revolver crane for all load categories, which is provided with a higher loadbearing capacity than a known revolver crane of comparable dimensions and weights. Alternatively it is an object of the invention to provide a design of a revolver crane having comparable capacity as the known revolver crane, however with smaller dimensions and weights.

It is a further object of the invention to provide a design of a revolver crane being less prone to wear and tear.

In order to promote the above mentioned objects and to attain further advantages that may become apparent from the following disclosure, the revolver crane of the invention is provided with controllable force exerting means to selectively apply forces between the platform ring and the pedestal when the pedestal is fixed on the supporting base for assisting or counteracting the load balancing forces of the ballast depending on the duty of the hoisting elements.

The just mentioned features of the revolver crane of the invention enable that said forces between the platform ring and the pedestal can be continuously attuned to the needs that may surface during the operation of the crane so as to relax the loads and reduce wear and tear that applies to the platform ring on which the crane rotates. For this purpose it is beneficial that the said controllable force exerting means to selec- tively apply forces between the platform ring and the pedestal when it is fixed to the supporting base, are arranged to apply forces to the platform ring that pull said platform ring towards the pedestal mounted on the supporting base at the side of the ring where the ballast is located at the time that the hoisting elements are hoisting a load so as to provide additional counterweight to the ballast for balancing the load. In this way the ballast may be designed smaller than in the prior art. It is also possible to construe the platform ring with a smaller diameter which positively impacts of course the overall dimensions of the revolver crane of the invention in a way that it can be designed smaller.

The objects of the invention are further promoted by arranging that the said controllable force exerting means to selectively apply forces between the platform ring and the ped- estal when it is fixed to the supporting base are arranged to apply forces to the platform ring pushing said platform ring away from the pedestal and the supporting base at the side of the ring where the ballast is located when the hoisting elements are unloaded so as to provide counterweight to the bal- last. This contributes to the realization of the above mentioned objectives, and is particularly useful to deter wear and tear of the ring construction connecting the platform ring to the pedestal which otherwise would suffer from the ballast weight, also when the hoisting elements are unloaded.

It is feasible to construe the controllable force ex- erting means to selectively apply forces between the platform ring and the pedestal and/or the supporting base in several different ways, for instance by a motor-powered pinion-and-rack or motor-powered winches. In a preferred embodiment the controllable force exerting means are embodied as a hydraulic cylinder or cylinders mounted between and connected on a first end to the platform ring, and on an opposite end to the pedestal and/or the supporting base. This is a convenient way for embodying the said means to apply the required forces to the platform ring.

Preferably the hydraulic cylinder or cylinders are on said opposite end connected with a bogey or bogeys that are movable on the pedestal and/or the supporting base. This enables that the revolver crane can rotate to any intended position without compromising the possibility to 'apply additional forces to the platform ring. It is then possible that the hydraulic cylinder or cylinders are fixed at the bottom of the platform ring below and in the vicinity of the ballast.

Suitably the bogey or bogeys are movable along a rail that is mounted on the pedestal and/or the supporting base.

Preferably the rail is mounted on the supporting base and is at least in part removable in order to give way to the revolver crane moving on the supporting base to a position encircled by the rail where it is to be fixed to the supporting base .

The invention will hereinafter be elucidated with reference to the drawing of an exemplary embodiment of a revolver crane according to the invention.

In the drawing:

-figure 1 shows a side view of the revolver crane of the invention; and

-figure 2 shows a detailed view of a preferred embodiment of the means to apply forces between the platform ring and the pedestal of the revolver crane shown in figure 1.

Whenever in the figures the same reference numerals are applied, these numerals refer to the same parts.

Figure 1 shows the revolver crane 1 of the invention in a side view. The crane 1 comprises a pedestal 2 mounted or mountable on a supporting base 3. The pedestal 2 supports a platform ring 4 that is rotatably mounted on the pedestal 2, and said platform ring 4 is provided with hoisting elements 5-8 for a load as well as ballast 13 for balancing such a load.

The invention is concerned with the aspect that the crane 1 is further provided with controllable force exerting means 9 to selectively apply forces between the platform ring 4 and the pedestal 2 and/or the supporting base 3 for assisting or counteracting the load balancing forces of the ballast 13 depending on the duty of the hoisting elements 5-8.

The said controllable force exerting means 9 to selec- tively apply forces between the platform ring 4 on the one hand, and on the other hand the pedestal 2 and/or the supporting base 3 are arranged to apply forces to the platform ring 4 pulling said platform ring 4 towards the pedestal 2 at the side of the ring 4 where the ballast 13 is located when the pedestal 2 is fixed to the supporting base 3. This applies when the hoisting elements 5-8 are hoisting a load and provides additional counterweight to the ballast 13 for balancing the load.

Further the said controllable force exerting means 9 to selectively apply forces between the platform ring 4 and the pedestal 2 when it is fixed to the supporting base 3 are arranged to apply forces to the platform ring 4 pushing said platform ring 4 away from the pedestal 2 and the supporting base 3 at the side of the ring where the ballast 13 is located when the hoisting elements 5-8 are unloaded so as to provide at that time counterweight to the ballast 13.

A favourable construction of the controllable force exerting means 9 that provide the required forces between the platform ring 4 and the pedestal 2 and/or the supporting base 3 is shown more clearly in figure 2. Said controllable force ex- erting means 9 are embodied with a hydraulic cylinder or cylinders 10 that are mounted between and connected on a first end 10' to the platform ring 4 and on an opposite end 10' ' (directly or indirectly) to the pedestal 2 and/or the supporting base 3.

Figure 2 further shows that the hydraulic cylinder or cylinders 10 are on said opposite end 10' ' connected with a bogey or bogeys 11 that are movable on the supporting base 3. It is also possible to arrange for movability of the bogeys 11 on the pedestal 2. This is not shown in the figures but the manner in which this can be arranged is clear to the skilled person and requires no further elucidation with reference to a drawing .

As figure 2 shows the bogey or bogeys 11 are movable on the supporting base 3 through the application of a rail 12 that is mounted on the supporting base 3 and along which the bogeys 11 can ride. This construction enables that the hydraulic cylinder or cylinders 10 can be fixedly mounted to the bottom of the platform ring 4. In this embodiment it is also feasible and advantageous that the rail 12 is at least in part removable in order to give way to the revolver crane 1 moving on the supporting base 3 to a position encircled by the rail 12 where it is to be fixed to the supporting base 3. This demonstrates that the invention also applies to movable revolver cranes, as it also does apply to revolver cranes that- are fixed to a supporting base. The (not shown) removable part of the rail 12 can be simply handled by the revolver crane 1 prior to its moving to its eventual position encircled by the rail 12. After it has reached its position encircled by the rail 12, the removable part of the rail can also simply be placed back into position by the revolver crane 1.

The above discussed preferred embodiment of a revolver crane according to the invention is provided merely as elucidation of the appended claims, and should not be construed as limiting the protective scope of said claims. The invention may be varied in many feasible ways, for instance the genus term "controllable force exerting means" as used in the claims, should not be deemed restricted to the example of hydraulic cylinders as provided by the exemplary embodiment. It is also possible to implement the "controllable force exerting means" in other feasible technical ways, for instance by a motor powered rack-and-pinion or by motor powered winches that are construed to apply forces between the platform ring and the pedestal and/or the supporting base of the revolver crane.