Patent Publication Number: US-7216774-B2

Title: Crane

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a crane whose lowest boom of a boom can be used both for a tower crane and a normal crane. 
   2. Description of the Related Art 
   In general, in a crane whose lowest boom portion of the boom which consists of several boom portions is used both for the tower crane and the standard crane (hereinafter usually referred to as a normal crane), the respective minimum distances between spreaders (distance between upper and lower spreaders) Sa and Sb are determined when the boom is raised maximally while the tower crane is considered as a standard, and the distances Sa and Sb are set approximately equal both for the cranes. 
   However, the maximum boom raise angle of the boom depends on the respective cranes, and thus, the distance is longer for the tower crane, and shorter for the normal crane when the boom is laid on the ground. 
   Consequently, if an upper spreader is lowered on a rear surface of the boom, the spreader is lowered on a second boom exceeding beyond the lowest boom. 
   As a result, when the boom is disassembled for the tower crane, it is necessary to relocate the upper spreader which has bee lowered on the second boom to a spreader retainer of the lowest boom. 
   In addition, when the boom is assembled, it is necessary to relocate the upper spreader from the spreader retainer to a position on the second boom where a boom guyline can be connected. 
   For the relocation of the upper spreader, there are required employment of another crane, maintenance of a boom raising/lowering rope at a proper tension at the same time, and the like, and this operation is thus very troublesome. Consequently, overall work efficiency of the assembly/disassembly of the boom decreases. 
   SUMMARY OF THE INVENTION 
   It is an objective of the present invention to provide a crane where an upper spreader can be directly lowered on a spreader retainer of the lowest boom either for a tower or normal crane when a boom is disassembled. 
   The crane according to the present invention has the following principle constitution. 
   Namely, the crane according to the present invention is comprised of a base machine, a boom pivotedly attached to the base machine in such a manner that the boom is raised and lowered, and a boom raising/lowering apparatus that raises/lowers the boom. A tower boom for a tower crane specification, or a normal boom with a maximum raising angle of the boom smaller than that of the tower boom for a normal crane specification is respectively attached as the boom. A spreader retainer is attached on a rear surface of a lowest boom portion of the boom used both for the tower boom and the normal boom in common. The boom raising/lowering apparatus is comprised of a gantry, a lower spreader provided on a top of the gantry, an upper spreader disposed closer to an extreme end of the boom than the lower spreader, and a boom raising/lowering rope wound between the upper spreader and the lower spreader. In the crane having the above principle constitution, the distance between both the spreaders is S 1  when the boom is maximally raised for the tower crane specification, and S 2  when the boom is maximally raised for the normal crane specification, the length of the lowest boom portion is L, and S 1 , S 2 , and L are set such that the upper spreader is lowered to the position of the spreader retainer if the boom raising/lowering apparatus lays the boom on the ground for assembling/disassembling the boom for either of the specifications. 
   According to the present invention, since the distances between the spreaders S 1  and S 2 , and the length of the lowest boom portion L are set such that the upper spreader is lowered to the position of the spreader retainer if the boom raising/lowering apparatus lays the boom on the ground either for the tower crane or the normal crane, it is not necessary to relocate the upper spreader from the second boom to the lowest boom portion for the tower crane. 
   As a result, when the tower crane is assembled/disassembled, it is possible to eliminate the troublesome operation where an additional crane is used to relocate the upper spreader between the second boom portion and the lowest boom portion while the tension of the boom raising/lowering rope is being observed. Consequently, it is possible to significantly simplify the assembly/disassembly of the boom. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic side view of a tower crane according to an embodiment of the present invention; 
       FIG. 2  is a schematic side view of a normal crane according to the embodiment of the present invention; and 
       FIG. 3  describes a state where an upper spreader is lowered if a boom is disassembled for either of the cranes. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   A crane according to the present invention has a principle constitution including a base machine, a boom attached to the base machine for being raised and lowered, and a boom raising/lowering apparatus that raises/lowers the boom. A tower boom for a normal crane specification, or a normal boom with the maximum raise angle of the boom smaller than that of the tower boom for a normal crane specification is attached as the boom. The boom raising/lowering apparatus is comprised of a gantry, a lower spreader provided on a top of the gantry, an upper spreader, and a boom raising/lowering rope wound between the upper spreader and the lower spreader. A spreader retainer is attached on a rear surface of the lowest boom used both for the tower boom and the normal boom. When the boom is assembled/disassembled, the lowest boom is raised/lowered by the boom raising/lowering apparatus while the upper spreader is retained by the spreader retainer. The distance between both the spreaders is S 1  when the boom is maximally raised for the tower crane specification, and S 2  when the boom is maximally raised for the normal crane specification, the length of the lowest boom is L, and S 1 , S 2 , and L are set such that the upper spreader is lowered to the position of the spreader retainer if the boom raising/lowering apparatus lays the boom on the ground for either of the tower crane and normal crane specifications. 
   A crane according to the present invention, compared with a crane, wherein the length of the lowest boom is La for the both specifications, and spreader distances Sa and Sb corresponding to the respective specifications are approximately equal to each other, S 1 , S 2 , and L satisfy the following conditions: 
   (i) S 1  and Sa are approximately the same; 
   (ii) S 2  is larger than Sa and Sb; and 
   (iii) L is larger than La. 
   A description will now be given of an embodiment of the present invention with reference to  FIGS. 1 to 3 . 
     FIG. 1  and  FIG. 2  respectively show a tower crane and a normal crane according to the embodiment. 
   Both of the cranes use a common base machine A including a crawler type lower traveling body  1  and an upper rotating body  2 . A tower boom  3  or a normal boom (normal type boom)  4  is attached to a front section of the upper rotating body  2  respectively for the tower crane or the normal crane. 
   As the tower crane, a jib  5  extends from a extreme end of the tower boom  3 , and an operation is generally carried out by raising/lowering the jib  5  while the tower boom  3  is maintained to a constant angle (approximately 90°). 
   Alternatively, as the normal crane, an operation is generally carried out by raising/lowering the normal boom  4 . In the operation, the maximum boom raise angle is limited to a value smaller than that of the tower boom  3  (80°, for example). 
     FIG. 1  shows an example where the tower boom  3  is constructed by using the lowest boom  6  as a first boom, and sequentially joining second to forth booms  7 ,  8 , and  9  thereto.  FIG. 2  shows an example where the normal boom  4  is constructed by using the lowest boom  6  as a lower boom, and joining an upper boom  10  thereto. It should be noted that the number of the booms joined to the lowest boom  6  may be variously selected/changed according to a required lifting height. 
   The boom raising/lowering apparatus  11  which raises/lowers the tower boom  3  and normal boom  4  includes a gantry  12  upwardly provided on the upper rotating body  2 , a lower spreader  13  provided on a top of the gantry  12 , an upper spreader  14 , and a boom raising/lowering rope  15  wound between respective sheaves of the lower and upper spreaders  13 ,  14 . The upper spreader  14  is connected to a boom extreme end through a boom guyline  16 . The booms  3 ,  4  are raised/lowered by winding/rewinding the boom raising/lowering rope  15  by means of a raising/lowering winch  17  in this configuration. 
   In  FIGS. 1 and 2 , reference numeral  18  denotes a suspension hook suspended down from a extreme end of the jib  5  in the tower crane;  19 , a suspension hook suspended down from a extreme end of the boom  4 ;  20 , a winding rope which raises/lowers the suspension hook  18  or  19  on either of the cranes;  21 , a jib raising/lowering strut;  22 , a jib guyline;  23 , a jib raising/lowering rope; and  24 , a counterweight provided on a rear end of the upper rotating body  2 . 
   Both in the tower and normal cranes, when the booms  3 ,  4  are disassembled, the booms  3 ,  4  are first laid on the ground by the boom raising/lowering apparatus  11  as dash double dot lines show in  FIGS. 1 ,  2 . 
   Then, the boom raising/lowering rope  15  is loosened to lower the upper spreader  14  on a rear surface of the boom. 
   Behind a extreme end of the lowest boom  6  is provided a spreader retainer (bracket)  25 . The upper spreader  14  is retained by the spreader retainer  25  with a pin to achieve an assembly/disassembly attitude which can secure the boom raising/lowering states, the boom guyline  16  is detached from the upper spreader  14 , and the upper booms are then detached from the lowest boom  6  while boom raising/lowering action is property carried out. 
   After the disassembly, the base machine A and the lowest boom  6  are conveyed on a trailer while they are still in the assembly/disassembly attitude. 
   The assembly of the booms  3  and  4  is carried out by a procedure/operation inverse to that of the above disassembly. 
   Both in the tower and normal cranes, the minimum distance between both the lower and upper spreaders  13 ,  14  of the boom raising/lowering apparatus  11  (more precisely, the distance between the respective sheaves) is set as a distance which secures a fleet angle of the boom raising/lowering rope  15  equal to or lower than a certain angle. 
   In the present embodiment, the distance between both the lower and upper spreaders  13 ,  14  of the boom raising/lowering apparatus  11  is S 1  for the maximum boom raising of the tower crane specification, and is S 2  for the maximum boom raising of the normal crane specification, and the length of the lowest boom (distance between the center of the boom foot and the extreme end of the boom) is L. Both in the tower crane and normal crane specifications, S 1 , S 2 , and L are set such that the upper spreader  14  is lowered to the position of the spreader retainer  25  while the booms  3 ,  4  are laid on the ground by the boom raising/lowering apparatus  11  as shown in  FIGS. 1 and 2 . 
   For the tower crane specification, the maximum boom raise angle is approximately 90°. In this case, this angle is larger than that of the normal crane (approximately 80°), the amount of the winding for the boom is thus large, and both the spreaders  13 ,  14  are consequently the closest to each other. Therefore, the distance between the spreaders S 1  on this occasion is set to a dimension which can secure the desired fleet angle. 
   Based on this determined inter-spreader distance S 1 , the length of the lowest boom L (position of the spreader retainer  25 ) is determined such that the upper spreader  14  is directly lowered to the position of the spreader retainer  25  as shown in  FIG. 3  if the boom raising/lowering rope  15  is loosened while the tower boom  3  is laid on the ground for the boom disassembly as shown in  FIG. 1 . In place of adjusting the length L of the lowest boom, the position of the spreader retainer  25  may be adjusted such that the upper spreader  14  is directly lowered to the position of the spreader retainer  25 . 
   Also for the normal crane specification, the inter-spread distance S 2  for the maximum boom raise is determined such that the upper spreader  14  is lowered to the position of the spreader retainer  25  as for the tower crane specification. 
   It is preferable S 2  is determined to be larger than S 1 . 
   Compared with both of the crane specifications described in “THE RELATED ART” where the inter-spreader distances Sa and Sb are set as approximately equal to each other, S 1  and S 2  are set so as to satisfy the following conditions (i) to (iii). It is assumed that the length of the lowest boom  6  is La in “THE RELATED ART”.
     (i) S 1  and Sa are approximately the same.   (ii) S 2  is larger than Sa and Sb.   (iii) L is larger than La of the lowest boom  6  in “THE RELATED ART”.   

   It should be noted that the relationship between S 2  and Sb is shown in  FIG. 2 . in terms of the above condition (ii). 
   As a result of the setting described above, both on the tower and normal cranes, the upper spreader  14  can be directly lowered on the extreme end (spreader retainer  25 ) of the lowest boom  6 , and can be retained by the spreader retainer  25  without the necessity of relocating the upper spreader  14  in the longitudinal direction of the boom  6 . 
   Namely, for the tower crane, it is not necessary to relocate the upper spreader  14  lowered on the second boom  7  to the lowest boom  6  (spreader retainer  25 ) when the boom is disassembled, and to relocate the upper spreader  14  back when the boom is assembled as described in “THE RELATED ART”. 
   Consequently, it is possible to eliminate the troublesome operation where the upper spreader  14  is relocated using another crane while the tension of the boom raising/lowering rope  15  is being observed for the assembly/disassembly of the boom. 
   In the crane according to the embodiment, the spreader retainer  25  on the lowest boom  6  is disposed at the position farther from the boom foot than that in “THE RELATED ART” as described above, and it is thus necessary to increase the length of the lowest boom  6  compared with that in “THE RELATED ART”. 
   Consequently if the transport is simply carried out in the assembly/disassembly attitude on a trailer, the overall length will become longer. If this causes a problem, this problem may be solved by reducing the overall length of the upper rotating body  2  by an amount corresponding to the increase of the lowest boom, and increasing the weight of an upper section of the counterweight  24  by an amount corresponding to a resulting decrease in counter balance capability. 
   Although the invention has been described with reference to the preferred embodiment in the attached figures, it is noted that equivalents may be employed and substitutions made herein without departing from the scope of the invention as recited in the claims.