Patent Publication Number: US-9845227-B2

Title: Mobile crane

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a mobile crane comprising a frame which, in its upper part, is provided with a main support structure and which, in its lower part and on opposite sides of the lower part of the frame, is provided with lower beam structures transverse to the main support structure, and upright legs between the main support structure and the lower beam structures; at least one wheel or wheel arrangement at both ends of the lower beam structures, i.e. in each lower corner of the crane; a trolley arranged to move along the main support structure and provided with a hoisting member; at least one hoisting mechanism; at least one rope drum arranged to be run by the hoisting mechanism; at least one rope arranged from the rope drum of the hoisting mechanism to the hoisting member for running the hoisting member. 
     Such yard gantry cranes for storage areas in container terminals are designed for arranging and handling containers in a container storage yard. They move along paths parallel with container rows, either on rails or rubber wheels. 
     Typically, the hoisting mechanism of such a crane is located in a trolley moving on top of the main support structure of the crane, in which case the masses to be moved are quite large, which has a substantial influence on the dimensioning of the support structures of the entire crane. 
     The known cranes on a mobile platform are susceptible to accelerations and decelerations as well as, in ports, typically, the influence of wind and stormy weather, and they are expected to be stable against falling down. 
     A known solution also requires demanding service and maintenance procedures to be taken into consideration in high places whereto the necessary, possibly heavy and large spare parts also have to be moved in connection with service operations. 
     SUMMARY OF THE INVENTION 
     An object of the invention is to provide a crane so as to enable the above-described problems to be solved. This object is achieved by a crane according to the invention, which is characterized in that the rope drum is further provided with at least one hoisting rope connected to at least one counterweight. Preferred embodiments of the invention are disclosed in the dependent claims. 
     When utilizing at least one counterweight in the hoisting mechanism, it is possible to dimension the hoisting mechanism smaller, thus enabling savings in materials and costs to be achieved in the form of structures, motors, instrumentation, and energy supply cables. 
     When a crane lifts a load, i.e. typically a container, into an upper position, the counterweight is at the same time lowered into a lower position. In this position, the crane is ready to move the container, and the crane is subjected to accelerations and decelerations in a direction of travel. Consequently, the stability of the mobile crane is better than without the implemented counterweights. Correspondingly, when the counterweight(s) is/are up, and the container is down, the container is not typically moving in the direction of travel but is usually positioning the container with gentle movements, i.e. lateral (the travel direction of the crane) accelerations and decelerations do not much influence the crane. 
     When the counterweight(s) is/are located in connection with the upright legs, it is possible to achieve a long and substantially vertical path for the counterweight to travel, supported and controlled. The upright leg provides the counterweight with a sufficiently stiff structure also in the crosswise direction for changes in acceleration and deceleration caused by movements in the travel direction. The upright leg is not absolutely vertical upwards but provides a slightly inclined surface for the counterweight to travel. The counterweight is thus lightly supported downwards against the surface of the upright leg, in which case it is prevented from swinging incessantly by its rope. Consequently, the movement of the counterweight is smooth, causing no noise, and no peenings nor flashes occur in the guide surfaces that would hinder the travel of the counterweight. 
     When the control cabin is located close to the ground level, exactly in front of the loading area, in the lower part of the leg structure at one end of the crane, in other words in connection with the aforementioned lower beam structure, it is possible to control the loading and unloading operations of trucks and carriages requiring special accuracy from a short distance and from the best possible monitoring site providing a crane operator with the shortest seeing distance to the loading area. This enables the operation to be made as safe as possible. An additional advantage herein is that the crane operator does not have to climb all the way to the main support level since the working height is at a substantially lower level than in a conventional yard gantry crane. 
     Similarly, when the hoisting mechanism is also located close to the ground level in connection with the other lower beam structure, it is possible to place them close to the main power source, making electrisation simpler and improving the weight distribution of the crane. Items in need of servicing are more easily available and the necessary spare parts can be easily brought thereto by means of a fork-lift truck, for instance. When the control cabin thus at the same time remains in connection with the lower beam structure located on a side opposite to the crane, the control cabin is situated far away from the sources of noise and vibration. While handling the load, when the container is lowered or lifted substantially at the level of the control cabin, the container itself forms a temporary noise wall between the machine unit and the control cabin. 
     When the machinery and the control cabin are moved from the trolley to be located close to the ground level, the trolley becomes light in structure, enabling also the support structure of the crane to be made lighter. At the same time, of course, the centre of gravity of the crane becomes to be situated lower, stabilizing the travel of the crane. Also, fewer passageways and platforms are required in the upper part when no emergency exits are necessary from top to bottom in case of fires or other accidents. 
     The parts of the crane are designed such that they can be packed and transported as modules in containers to the installation site. This makes the transportation easier to plan, when no large structural steel parts and components have to be transported separately as general cargo. The main support structure and the legs are built from interconnectable beam parts to be interconnected at the installation site. The rest of the parts are designed in a similar manner so as to be packed in containers. 
    
    
     
       LIST OF FIGURES 
       The invention is now explained in closer detail with reference to the accompanying drawings, in which 
         FIG. 1  is a perspective view showing a crane according to the invention, 
         FIG. 2  shows a counterweight, in its guides, according to the invention, and 
         FIG. 3  shows an arrangement of a rope system according to the invention in a crane. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to the figures, a mobile crane according to the invention has a frame  1  which, in its upper part, is provided with a main support structure  2  and which, in its lower part and on opposite sides of the lower part of the frame  1 , is provided with lower beam structures  3   a  and  3   b  transverse to the main support structure  2 . The main support structure  2  is connected to the lower beam structures  3   a  and  3   b  by upright legs  4 . The upright legs  4  are deflected from the vertical direction at least in one lateral direction in order to improve the stability of the crane. The main support structure  2  herein comprises two main supports  2   a  travelling, spaced apart from one another, parallelly and connected to one another by upper beam structures  5   a  and  5   b.    
     Ends of the lower beam structures  3   a  and  3   b  are provided with bogie structures  6 , each comprising two successive wheels  7 . The total number of bogie structures  6  is thus four, one in each lower corner of the crane. In this example, the wheels are rubber wheels and, typically, one of the wheels  7  of each bogie  6  is a drive wheel while the other is a driven wheel. In connection with a rubber wheel crane, the wheels  6  are preferably also swivelable. Alternatively, the number of wheels  7  could be four in each bogie structure  6  (two pairs of wheels in succession), or only one wheel  7  could be provided in each lower corner (in which case the structure is not a bogie structure). As already stated above, the wheels of the crane could also be (nonswivelable) wheels travelling on rails. 
     Along the main support structure  2 , a trolley  8  is arranged to move, a hoisting member or spreader  9  hanging therefrom. 
     The crane further comprises hoisting mechanisms  10 , rope drums  24  arranged to be run by the hoisting mechanisms  10 , and ropes M 1  and M 2  arranged from the rope drums  24  of the hoisting mechanisms  10  to the hoisting member  9  for running the hoisting member  9 . The crane also has a main power source  11  and a control cabin  12  for the crane&#39;s operator. The control cabin  12  is located in connection with one lower beam structure  3   a  while the hoisting mechanism  10  is located in connection with the other lower beam structure  3   b ; to be more precise, in this example the control cabin  12  is located on top of the lower beam structure  3   a  and the hoisting mechanism  10  on top of the lower beam structure  3   b . The control cabin  12  is located in the middle of the lower beam structure  3   a . The main power source  11 , in turn, is located in connection with the same lower beam structure  3   b  as the hoisting mechanism  10 . Preferably, the control cabin  12 , the hoisting mechanism  10 , and the main power source  11  are modular structures to be installed in the crane. 
     According to the invention, the rope drums  24  are further provided with hoisting ropes  23  connected to counterweights  20  which herein are arranged to move in guides  21 ,  22  arranged in side surfaces of the upright legs  4 . The rope drums  24  and the counterweights  20  are arranged to alternately run one another through the hoisting ropes. These counterweights  20  may also be modular structures to be installed in the crane. In the overall arrangement of the hoisting ropes  23  it is appropriate that on opposite sides of the trolley  8  the hoisting mechanism  10  is located on one side while the rope system led to the counterweight  20  resides on a side opposite thereto, i.e. preferably on the side of the control cabin  12 . Thus, the force provided by the counterweight  20  is transmitted through the rope drum  24  to the hoisting mechanism  10 , in which case the hoisting capacity required from the hoisting mechanism  10  is smaller than if the structure were built with no counterweights  20 . Typically, a counterweight  20  is always supported by a hoisting rope  23 , i.e. it is not lowered onto a separate platform or the like; consequently, the hoisting rope  23  is always subjected to a gravity force on account of the counterweight  20 . 
     On the side surface of the upright leg  4 , the guides  21 ,  22  reside in a protected slot in order to prevent the counterweight  20 , which moves up and down, from creating a compressing jaw. The slots, already at their bottom, are appropriately at least of the same height as the control cabin  12  in the vicinity of the control cabin  12  but may also all the way to the top be protected by protective plates  25 . A space to be reserved for the travel of the counterweight  20  and the guides  21 ,  22  may also be provided inside the upright leg  4  with a box-type structure, in which case no separate structure in the form of protective plates  25  is necessary. 
     Preferably, the number of counterweights  20  including their guides  21 ,  22  is two, i.e. both the upright leg  4  and the hoisting mechanism  10  in question are provided with one of their own. Two counterweights  20  enable such an advantage to be achieved that in the hoisting mechanisms  10  it is possible in the run of the hoisting rope  23  to carry out independent rope movements and forces, in which case the inclination and skew of the container to be attached to the hoisting member  9  and the hoisting member  9  can be controlled accurately in order to achieve a correct inclination and skew around the vertical axis so as to ensure that grabbing and releasing the container take place in a safe and quick manner. 
     The guides  21 ,  22  are located such that a first guide  21  supports the counterweight on the upright leg  4  sideways (the direction of travel of the crane) while a second guide  22  supports the counterweight  20  in the direction of the main support structure  2  of the crane. Thus, the counterweight is supported in two substantially transverse directions. The guides  21 ,  22  may also be implemented such that when the counterweight is arranged between the guides, they both restrict lateral movement. The movement parallel with the main support structure  2  is restricted such that the counterweight  20  is provided with a groove  28  wherein the guide  21 ,  22  is arranged, as shown in  FIG. 2 . The controlled support of the counterweight  20  may naturally be implemented in many different ways by using different profiles or bars capable of providing a sufficient support in x and y directions of a three-dimensional coordinate system when the counterweight moves in z direction in the direction of the upright leg  4 . It is also possible to install between the counterweight  20  and the upright leg  4  a sliding plane  30  to support the counterweight  20  for instance by its face when the direction of the upright leg  4  slightly differs from the vertical surface. The sliding plane  30  enables a suitable kinetic friction to be provided to prevent the counterweight  20  from swinging freely, which would cause noise. The friction may naturally also be arranged by means of the guides  21 ,  22  or bars. The sliding plane  30  may be the same as the surface of the upright leg  4  between the guides  21 ,  22 , or it may further be provided with an appropriate additional material for forming a suitable friction coefficient of the sliding plane  30 . 
     The number of counterweights  20  may also be only one, in which case a force-balancing member has to be arranged separately, i.e. balancing scales, a wheel or a joint has also to be provided if the controlled inclination and skew around the vertical axis are to be implemented. As far as the distribution of the load of the crane is concerned, it is optimal for the wheels  7  when the counterweight  20  resides in the frame  1  on a side opposite to that of the hoisting mechanism  10 . This enables dead mass to be distributed on both wheel rows. It is possible to arrange the counterweight  20  on the same side as the hoisting mechanism  10 , though. 
     It is also possible to provide the counterweight  20  with a space or a framework to enable for instance tools or spare parts to be loaded therein for service. When a counterweight  20  in the lower position is provided with a hatch or a door in the protective plate  25 , it is possible to lift up heavy objects by means of the counterweight  20  and the hoisting mechanism  10  for servicing the crane when a corresponding access is provided in the upper position through the protective plate  25  to the counterweight  20 . 
       FIG. 3  shows how a rope system implemented with a counterweight  20  is arranged in a mobile crane. The viewing angle in  FIGS. 1 and 3  is the same, so the reference numerals are found in substantially the same places, excluding the different height position of the counterweights  20  used on account of the properties of the drawing. The rope system is symmetrical with respect to a centre line CL, so only one rope system line is described herein. In order to operate the hoisting member  9 , the ropes M 1 , M 2  are run from the rope drum  24  via upper rope pulleys B 1 , B 2  to the hoisting member  9  hanging underneath the trolley  8 . From the hoisting member  9 , the ropes are led back up and, remaining up there, they keep further running forward in the direction of the main support structure  2 , ending up at a mechanism J for controlling the skew of the hoisting member  9 . This control mechanism J may be used for controlling the skew occurring around the vertical axis of the hoisting member  9 . By means of two rope runs and two hoisting mechanisms  10  parallel with respect to the centre line CL, both being provided with the ropes M 1 , M 2 , it is possible to implement the inclination of the hoisting member  9  so that the ends of the hoisting member  9  (and thus the ends of the container being handled) may be brought in mutually different height positions, which may be a property necessary to utilize when lowering the container for instance onto a slightly slanting truck trailer or onto a slanting ground. It is also necessary to be able to grab a slanting container to be lifted. 
     From the rope drum  24 , also the hoisting rope  23  is led which runs mainly alongside with the ropes M 1 , M 2 . The hoisting rope  23  is led from the rope drum  24  via a rope pulley C 1  past the trolley  8  and, further, alongside with the main support structure  2 , to rope pulleys K 1 . Therefrom, the hoisting rope  23  continues downwards to a rope pulley L 1 , rises back to a rope pulley K 2  rotatably fastened to the frame  1 , further descends to a rope pulley L 2 , and returns back up again to a fastening point of the hoisting rope  23 , which may be located for instance in connection with the hub of a rope pulley K 2 . The rope pulleys L 1 , L 2  are rotatably fastened to the counterweight  20 , they may rotate irrespective of one another and differ in diameters. 
     This solution enables the rope force provided by the counterweights  20  to be transmitted to the rope drum  24 . The counterweights  20  are always suspended by the hoisting rope  23 , so the hoisting rope  23  stays naturally tight. It is also possible to arrange rope pulleys (not shown) parallel with the main support structure  2  to support the run of the hoisting rope  23 . 
     The hoisting rope  23  and the ropes M 1 , M 2  differ clearly from one another, a first difference being the different direction of rotation of the rope on the rope drum  24 . This difference in the direction of rotation enables the rope force provided by the counterweight  20  to be transmitted directly to the hoisting mechanism. The next difference is in passing the trolley  8 , i.e. the hoisting rope  23  does not run via the hoisting member  9  but continues directly to the counterweights  20 . Consequently, it has nothing to do with the mechanism J for controlling the skew of the hoisting member  9 , either. When the counterweights  20  are located on a side opposite to that of the rope drum  24  and the hoisting mechanism  10 , the distribution of mass becomes advantageous on both sides of the crane, evening out the wear of the wheels  7  and, also, the control of the crane being driven. 
     By utilizing the additional force provided by the counterweight  20 , the hoisting mechanisms  10  can be dimensioned to be smaller in their structure and energy supply cables and, further, the arrangement saves energy. 
     Typically, the mass of a counterweight  20  may be dimensioned so that the rope force provided thereby substantially corresponds to the mass of an empty hoisting member  9 . This enables a considerable improvement to be achieved in energy use as the crane lifts and lowers an empty hoisting member  9  for a considerably long stretch of time during its work cycles. It is preferable that the rope rotation between K 1 -L 1 -K 2 -L 2  in connection with the counterweight  20  equals in number that provided between the trolley  8  and the hoisting member  9 . The examples shown in  FIGS. 1 and 3  both employ a solution with four ropes. In such a case, the hoisting height of the hoisting member  9  and the counterweight  20  is substantially the same, thus making dimensioning easy. 
     It is preferable to provide the trolley  8  and the hoisting member  9  with cameras (not shown) to enable the container handling procedures in the storage area to be carried out sufficiently accurately, as the crane operator no longer monitors the storage sites obliquely downward. 
     Typically, such a crane is large, in which case the main support structure  2  extends over a plurality of lines of containers. In order to be able to further move the centre of gravity of the crane lower, it is preferable to make the main supports  2   a  reside close to one another, in which case the upper beam structures  5   a  and  5   b  become shorter and, thus, lighter. Thus, the upright legs  4  then obliquely join the lower beam structures  3   a  and  3   b , when viewing the crane from its side. This, of course, at the same time saves material, stabilizes the entire crane and makes the structure stiffer. 
     This structural entity according to the invention enables the advantages described in detail above to be achieved. 
     The above description of the invention is only intended to illustrate the basic idea of the invention. A person skilled in the art may thus vary its details within the scope of the attached claims. It is to be noted that the main power source may alternatively also comprise a cable drum and a guide bar, in which case the appearance of the crane differs from the structure being shown in the drawing. In such a case, the crane depends on an external energy source, and it is supplied by an electric cable following the surface of the ground and being uncoiled by the crane onto the large cable drum. This embodiment may be relevant in connection with a crane travelling on rails.