Patent Publication Number: US-10308486-B2

Title: Overhanging storage mechanism for jib

Description:
CROSS REFERENCE TO PRIOR APPLICATION 
     This application is a National Stage Patent Application of PCT International Patent Application No. PCT/JP2016/000486 (filed on Feb. 1, 2016) under 35 U.S.C. § 371, which claims priority to Japanese Patent Application No. 2015-115021 (filed on Jun. 5, 2015), which are all hereby incorporated by reference in their entirety. 
     TECHNICAL FIELD 
     The present invention relates to a jib overhanging storage mechanism. In more detail, the present invention relates to a jib overhanging storage mechanism used in jib overhanging/storing work. 
     BACKGROUND ART 
     PTL 1 discloses a mechanism including a guide attached to a lower part of a distal end portion side surface of a base end boom, and a guide roller attached to a substantially central portion of a jib. Further, PTL 1 discloses a mechanism including a boom side pin socket attached to a lower part of a side surface of the central portion of the base end boom, and a jib side fixing pin that is attached to a distal end portion of the jib. 
     In order to perform jib overhanging work, a jib base end portion and a boom distal end portion are connected first. Subsequently, a boom is raised. When the boom is slightly extended next, the jib side fixing pin is detached from the boom side pin socket. When the boom is further extended, a guide roller rolls along a sloping surface of a guide, and the jib slowly separates from a bottom surface of the base end boom. When the guide roller is completely detached from the guide, the jib is brought into a state where the jib is suspended from the boom distal end portion. Finally, tension is generated in a tension rod, and thereby the jib is overhung. 
     Jib storage work is performed in the reverse order of the jib overhanging work. When the boom is contracted in a state where the jib is suspended from the boom distal end portion, the guide roller rolls along the guide, and the jib is pulled toward the bottom surface of the base end boom. When the boom is further contracted, the jib side fixing pin is inserted into the boom side pin socket. Thereby, the jib can be fixed to the boom. 
     There is a need for applying the mechanism described in PTL 1 also to large cranes. The jib loaded on a large crane is long and has a heavy weight, and therefore has large deflection. In addition, each part has large play in a large crane. Consequently, even when the jib is pulled toward the bottom surface of the base end boom by the guide roller and the guide in jib storing work, the position of the jib side fixing pin is deviated by deflection and play. Hence, there is a problem that the jib side fixing pin cannot be inserted into the boom side pin socket, and the jib cannot be stored. 
     In recent years, a so-called round boom is often used in which the sectional shape of a boom bottom portion is formed in a circular arc shape for the purpose of reducing the weight and increasing rigidity (for example, PTL 2). In a round boom, which is weaker to constrain rotation than the booms having quadrangular and hexagonal sectional shapes, the distal end boom easily rotates with respect to the base end boom. The position of the jib side fixing pin is also deviated by the rotation, so that the jib side fixing pin cannot be inserted into the boom side pin socket. 
     CITATION LIST 
     Patent Literature 
     PTL 1 
     Japanese Patent Application Laid-Open No. 2000-44173 
     PTL 2 
     Japanese Patent Application Laid-Open No. 2010-235250 
     SUMMARY OF INVENTION 
     Technical Problem 
     In the light of the above described circumstances, an object of the present invention is to provide a jib overhanging storage mechanism with which a jib can be stored even if deflection or the like occurs to the jib during jib storing work. 
     Solution to Problem 
     A jib overhanging storage mechanism according to a first aspect of the invention is a mechanism for overhanging/storing a jib with respect to a boom having a base end boom, the mechanism including; a guide roller that is provided at the jib or the base end boom; a guide that is provided at the base end boom or the jib, and guides the guide roller; a jib fixing pin that is provided at the base end boom or the jib; and a pin socket that is provided at the jib or the base end boom, and has an insertion hole into which the jib fixing pin can be inserted, in which: the guide is configured such that the jib is pulled toward a bottom surface of the base end boom, and subsequently the jib moves along the base end boom, by the guide roller being guided with contraction of the boom; the jib fixing pin and the insertion hole are disposed such that when the jib moves along the base end boom with contraction of the boom, the jib fixing pin is inserted into the insertion hole; and an inside dimension of a front end opening portion of the insertion hole is larger than an outside dimension of the jib fixing pin. 
     The jib overhanging storage mechanism according to a second aspect of the invention is the mechanism according to the first aspect, in which; the jib fixing pin has a distal end portion formed in a conical shape; the pin socket has a front end rib and a rear end rib; a front end insertion hole configuring a front end opening portion of the insertion hole is formed in the front end rib; a rear end insertion hole configuring a rear end opening portion of the insertion hole is formed in the rear end rib; and an inside dimension of the rear end opening portion is substantially a same as the outside dimension of the jib fixing pin. 
     The jib overhanging storage mechanism according to a third aspect of the invention is the mechanism according to the first or the second aspect, in which the front end opening portion of the insertion hole is a vertical hole along a vertical direction of the boom, in a state where the jib is pulled toward the bottom surface of the base end boom. 
     Advantageous Effects of Invention 
     According to the first aspect of the invention, the inside dimension of the front end opening portion of the insertion hole is larger than the outside dimension of the jib fixing pin, so that the positional deviation between the jib fixing pin and the insertion hole can be absorbed. Consequently; the jib fixing pin can be inserted into the insertion hole, and the jib can be stored. 
     According to the second aspect of the invention, the jib fixing pin can be roughly positioned by the jib fixing pin being inserted into the front end insertion hole. The position of the jib fixing pin can be finely adjusted by the jib fixing pin being inserted into the rear end insertion hole. 
     According to the third aspect of the invention, the front end opening portion is a vertical hole, so that the positional deviation in the vertical direction in which the influence of deflection of the jib is large can be absorbed. Further, the jib fixing pin can be positioned in the lateral direction in which the influence of deflection of the jib is small. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a side view of mobile crane C in a state where jib  15  is stored; 
         FIG. 2  is a left side view of jib  15  and boom  14  in a state where jib  15  is disposed in a lower hanging position of boom  14 ; 
         FIG. 3  is a right side view of jib  15  and boom  14  in the state where jib  15  is disposed in the lower hanging position of boom  14 ; 
         FIG. 4  is a plan view of jib  15  and boom  14  in the state where jib  15  is disposed in the lower hanging position of boom  14 ; 
         FIG. 5  is a side view of guide member  30 ; 
         FIG. 6  is a perspective view of first jib support member  40 ; 
         FIG. 7A  is a sectional view taken along line VIIa to VIIa seen in an arrow direction in  FIG. 6 , and  FIG. 7B  is a sectional view taken along line VIIb to VIIb seen in an arrow direction in  FIG. 6 ; 
         FIG. 8  is a perspective view of second jib support member  50 ; 
         FIG. 9  is a side view of a state where jib  15  is overhung; 
         FIGS. 10A to 10C  are a side view of jib  15  and boom  14  illustrating respective steps of jib storing work; and 
         FIGS. 11A to 11D  are explanatory views of a step of inserting jib fixing pin  43  into insertion holes  48  and  49 . 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Next, embodiments of the present invention will be described based on the accompanying drawings. 
     A jib overhanging storage mechanism according to one embodiment of the present invention is applied to mobile crane C illustrated in  FIG. 1 , for example. The jib overhanging storage mechanism of the present embodiment can be applied to various cranes, without being limited to mobile crane C illustrated in  FIG. 1 . 
     (Mobile Crane) 
     First, a basic structure of mobile crane C will be described. 
     Reference sign  11  in  FIG. 1  designates a travelling vehicle body, which is equipped with wheels for travelling. Rotating platform  12  is loaded on travelling vehicle body  11 , and can rotate 360° within a horizontal plane by a rotating motor. Driver&#39;s cab  13  is provided on rotating platform  12 . 
     Boom  14  is attached to rotating platform  12  to be capable of hoisting and lowering. A base end portion of boom  14  is pivotally supported by rotating platform  12  with a pin. A hoisting and lowering cylinder is attached to between boom  14  and rotating platform  12 . When the hoisting and lowering cylinder is extended, boom  14  is raised, whereas when the hoisting and lowering cylinder is contracted, boom  14  is lowered. 
     Boom  14  is a multistage boom constructed in a telescopic manner, and includes base end boom  14   a , an intermediate boom and distal end boom  14   b . Boom  14  extends/contracts by an extending/contracting cylinder. The number of stages of boom  14  is not specially limited. Boom  14  may be of a two-stage type without an intermediate boom, or may have the configuration with four stages or more including a plurality of intermediate booms. 
     Boom  14  of the present embodiment is a so-called round boom in which a sectional shape of a bottom portion is formed in a circular-arc shape. Accordingly, distal end boom  14   b  has a property of being easy to rotate around a center axis with respect to base end boom  14   a . Booms having quadrangular and hexagonal sectional shapes may be used. 
     From distal end portion  14   c  of boom  14  (distal end boom  14   b ), a wire rope equipped with a hook not illustrated is suspended, and the wire rope is guided to rotating platform  12  along boom  14  to be wound on a winch. The winch rotates in forward and reverse directions by drive of a hoist motor, winds up the wire rope and pulls it out, and thereby can raise and lower the hook. 
     By combining rotation of rotating platform  12 , hoisting and lowering and extension and contraction of boom  14 , and raising and lowering of the hook, loading and unloading in a three-dimensional space are enabled. 
     Mobile crane C is equipped with jib  15 . Jib  15  is an elongated rod-shaped member as a whole, and base end portion  15   a  thereof is in a bifurcated shape. Jib  15  is used when a lifting range/operation radius larger than a lifting range/operation radius with a boom length of boom  14  which is fully extended is obtained. When not in use, jib  15  is stored along a side surface of boom  14  (see  FIG. 1 ). When in use, base end portion  15   a  of jib  15  and distal end portion  14   c  of boom  14  are connected, and jib  15  is overhung forward of boom  14  (see  FIG. 9 ). 
     (Jib Connection Structure) 
     Next, a jib connection structure will be described. 
       FIGS. 2, 3 and 4  are a left side view, a right side view and a plan view of a state where jib  15  is disposed in a lower hanging position along a bottom surface of base end boom  14   a . As will be described later, in jib overhanging/storing work, connection/disconnection of boom distal end portion  14   c  and jib base end portion  15   a  is performed in the state where jib  15  is disposed in the lower hanging position. 
     As illustrated in  FIG. 4 , in the state where jib  15  is disposed in the lower hanging position, jib base end portion  15   a  is located at boom distal end portion  14   c , and a distal end portion of jib  15  is in an offset disposition in which the distal end portion is located sideward of boom  14 . The distal end portion of jib  15  is located at an opposite side of driver&#39;s cab  13  with respect to boom  14 . Hereinafter, a side at which the distal end portion of jib  15  is located in the offset disposition will be referred to as a left side, and an opposite side to the left side (driver&#39;s cab  13  side) will be referred to as a right side. However, an embodiment in which the left and the right are reversed may be adopted. 
     Boom distal end portion  14   c  is provided with jib connection shafts  21  and  21  that overhang horizontally at both sides thereof. As illustrated in  FIGS. 2 and 3 , jib base end engagement portions  22  and  22  are provided at respective end portions of jib base end portion  15   a  in the bifurcated shape. 
     Jib base end engagement portion  22  is formed in a U-shape, and allows jib connection shaft  21  to be fitted therein. Further, an insertion hole is formed in a distal end portion of jib base end engagement portion  22 . Jib connection shaft  21  is fitted in jib base end engagement portion  22 , and pin  23  is inserted into the insertion hole, whereby jib connection shaft  21  is prevented from being disengaged. Thereby, jib base end engagement portion  22  and jib connection shaft  21  can be connected. 
     (Jib Overhanging Storage Mechanism) 
     Next, a jib overhanging storage mechanism of the present embodiment will be described. 
     The jib overhanging storage mechanism of the present embodiment is a mechanism for overhanging/storing jib  15  with respect to boom  14  in mobile crane C as described above. The jib overhanging storage mechanism includes guide member  30 , first jib support member  40  and second jib support member  50 . Guide member  30  is provided at a right side of boom  14 . First jib support member  40  and second jib support member  50  are provided at a left side of boom  14 . Hereinafter, the respective members will be described in order. 
     (Guide Member  30 ) 
     Guide member  30  is a member for guiding a posture of jib  15 , with extension and contraction of boom  14 , in jib overhanging/storing work. As illustrated in  FIG. 5 , guide member  30  includes guide roller  31 , and guide  32  that guides guide roller  31 . 
     An arm  33  protruded to a bottom surface side is provided on a base end portion side surface of jib  15 . Guide roller  31  is rotatably provided at a distal end portion of arm  33 . In  FIG. 5 , jib  15  is disposed in a state where a bottom surface thereof faces base end boom  14   a.    
     Guide  32  is provided on a distal end portion side surface of base end boom  14   a  in a state where the guide  32  is protruded to the bottom surface side. Guide  32  has first raceway track member  34  and second raceway track member  35 . An alternate long and short dash line in  FIG. 5  shows side wall  36  constructing guide  32 . Side wall  36  serves to support first raceway track member  34  and second raceway track member  35 , and to restrict movement in a lateral direction (direction perpendicular to the paper surface) of guide roller  31 . For convenience of explanation, only an outer shape of side wall  36  is shown by the alternate long and short dash line. 
     A surface of first raceway track member  34  is referred to as first raceway surface  34   s , and a surface of second raceway track member  35  is referred to as second raceway surface  35   s . Jib  15  is guided by guide roller  31  rolling on raceway surfaces  34   s  and  35   s.    
     First raceway surface  34   s  has an inclination to a top surface from a bottom surface of boom  14  toward the base end from a distal end of boom  14 . Consequently, as will be described later, guide roller  31  rolls on first raceway surface  34   s  with extension of boom  14  in the jib overhanging work, whereby jib  15  is separated from the bottom surface of base end boom  14   a . Further, in the jib storing work, guide roller  31  rolls on first raceway surface  34   s  with contraction of boom  14 , whereby jib  15  is pulled toward the bottom surface of base end boom  14   a.    
     Second raceway surface  35   s  is parallel with a center axis of boom  14 , and is connected to a base end side end portion of first raceway surface  34   s . Consequently, as will be described later, in the jib overhanging/storing work, guide roller  31  rolls on second raceway surface  35   s  with extension and contraction of boom  14 , and thereby jib  15  moves along base end boom  14   a  in a state where jib  15  is pulled toward the bottom surface of base end boom  14   a.    
     While in the present embodiment, guide roller  31  is provided at jib  15 , and guide  32  is provided at base end boom  14   a , guide roller  31  may be provided at base end boom  14   a , and guide  32  may be provided at jib  15  instead of this. 
     (First Jib Support Member  40 ) 
     First jib support member  40  is a member for supporting jib  15  in a stored state. Further, first jib support member  40  has a function of rotating jib  15  between a storage position along the side surface of boom  14  and the lower hanging position. 
     As illustrated in  FIG. 6 , bracket  41  is pivotally supported on a bottom portion side surface in a substantially center of base end boom  14   a . Hydraulic cylinder  42  is attached to between an upper portion side surface of base end boom  14   a  and bracket  41 . By extension and contraction of hydraulic cylinder  42 , bracket  41  rotates with respect to base end boom  14   a.    
     Bracket  41  is provided with jib fixing pin  43 . Jib fixing pin  43  is in a columnar shape, and a distal end portion thereof is formed into a conical shape. Jib fixing pin  43  is parallel with the center axis of jib  15 , and is disposed with a distal end portion thereof directed to the distal end of boom  14 . Jib fixing pin  43  may be disposed parallel with a center axis of boom  14 . 
     A pin socket  45  is provided on a bottom surface in a substantially center of jib  15 . In  FIG. 6 , jib  15  is disposed with a bottom surface thereof facing base end boom  14   a . Pin socket  45  has front end rib  46  and rear end rib  47 . Front end rib  46  has front end insertion hole  48  formed therein, and rear end rib  47  has rear end insertion hole  49  formed therein. Jib fixing pin  43  is capable of being inserted into front end insertion hole  48  and rear end insertion hole  49 . Front end insertion hole  48  and rear end insertion hole  49  are disposed in such a manner that center axes thereof are parallel with the center axis of jib  15  in a state where jib  15  is pulled toward the bottom surface of base end boom  14   a . Front end insertion hole  48  and rear end insertion hole  49  may be disposed in such a manner that center axes thereof are parallel with the center axis of boom  14 . 
     Front end insertion hole  48  and rear end insertion hole  49  correspond to “insertion hole” described in the claims. Front end insertion hole  48  configures a front end opening portion of the insertion hole, and rear end insertion hole  49  configures a rear end opening portion of the insertion hole. Here, in the jib storing work, a part into which jib fixing pin  43  is inserted first is set as a “front end”, and a part into which jib fixing pin  43  is inserted later is set as a “rear end”. 
     As illustrated in  FIG. 7A , front end insertion hole  48  is a round hole, and an inside diameter thereof is larger than an outside diameter of jib fixing pin  43 . When jib  15  deflects by weight, pin socket  45  goes down with respect to jib fixing pin  43 . Further, jib fixing pin  43  and pin socket  45  are disposed sideward of base end boom  14   a . Consequently, when distal end boom  14   b  rotates with respect to base end boom  14   a  by the weight of jib  15  and the like, pin socket  45  goes down with respect to jib fixing pin  43 . In short, positions of jib fixing pin  43  and pin socket  45  deviate in the vertical direction due to deflection of jib  15  and the like. Front end insertion hole  48  has the inner diameter that can allow the deviation. 
     As illustrated in  FIG. 7B , rear end insertion hole  49  is a round hole, and an inside diameter thereof is substantially the same as the outside diameter of jib fixing pin  43 . Here, “substantially the same” includes not only a case where the inside diameter of rear end insertion hole  49  is the same as the outside diameter of jib fixing pin  43 , but also a case where the inside diameter of rear end insertion hole  49  is slightly larger than the outside diameter of jib fixing pin  43 . Note that an “inside dimension” described in the claims includes the inside diameter, and an “outside dimension” includes the outside diameter. 
     Front end insertion hole  48  may be formed into a vertical hole. In more detail, front end insertion hole  48  may be formed into a vertical hole along a vertical direction (a direction toward the top surface from the bottom surface) of boom  14  in the state where jib  15  is pulled toward the bottom surface of base end boom  14   a . Front end insertion hole  48  is a long hole along a direction of the deviation due to deflection of jib  15 . Consequently, front end insertion hole  48  can absorb a positional deviation in the vertical direction in which an influence of deflection of jib  15  is large. Jib fixing pin  43  can be positioned in a lateral direction in which the influence of deflection of jib  15  is small. A shape of front end insertion hole  48  is not specially limited, and a center axis of jib fixing pin  43  may deviate from a center axis of front end insertion hole  48 , if front end insertion hole  48  has enough room for jib fixing pin  43  to be inserted therein. 
     Jib fixing pin  43  is not limited to a circular column shape, but may be a rectangular column shape. In this case, the distal end portion of jib fixing pin  43  may be formed in a pyramid shape. Further, front end insertion hole  48  and rear end insertion hole  49  may be formed as square holes. An inside dimension of front end insertion hole  48  is made larger than an outside dimension of jib fixing pin  43 , and an inside dimension of rear end insertion hole  49  may be made substantially the same as an outside dimension of jib fixing pin  43 . 
     The insertion holes for jib fixing pin  43  may be formed as a single insertion hole instead of a component including front end insertion hole  48  and rear end insertion hole  49 . In this case, an inside dimension of a front end opening portion of the insertion hole can be made larger than the outside dimension of jib fixing pin  43 , and an inside dimension of a rear end opening portion may be made substantially the same as the outside dimension of jib fixing pin  43 . The front end opening portion and the rear end opening portion may be configured to be continuously connected. Here, at jib storing work, of the opening portions at both ends of the insertion hole, the opening portion into which jib fixing pin  43  is inserted is set as the “front end opening portion”, and the opening portion from which the distal end of jib fixing pin  43  protrudes is set as the “rear end opening portion”. 
     While in the present embodiment, jib fixing pin  43  is provided at base end boom  14   a , and pin socket  45  is provided at jib  15 , instead of this, jib fixing pin  43  may be provided at jib  15 , and pin socket  45  may be provided at base end boom  14   a.    
     (Second Jib Support Member  50 ) 
     Second jib support member  50  is a member for supporting jib  15  in the stored state. As illustrated in  FIG. 8 , arm  51  is provided at a bottom surface side portion in a base end portion of base end boom  14   a . Auxiliary pin  52  is provided at a distal end portion of arm  51 . Auxiliary pin  52  is in a circular column shape with a small diameter and a short length, and a distal end portion thereof is formed in a conical shape. Auxiliary pin  52  is parallel with the center axis of boom  14 , and the distal end portion thereof is disposed to be directed to the distal end of boom  14 . 
     At the distal end portion of jib  15 , second pin socket  53  is provided on a bottom surface. In  FIG. 8 , jib  15  is disposed in a state where a bottom surface thereof faces base end boom  14   a . Second pin socket  53  has rib  54 . In rib  54 , auxiliary insertion hole  54   h  into which auxiliary pin  52  can be inserted is formed. 
     (Jib Storing Work) 
     Next, jib storing work will be described. 
     (1) As illustrated in  FIG. 9 , in the state where jib  15  is overhung, jib  15  is substantially in line with boom  14 . 
     (2) Tilt cylinder  15   c  is mounted on jib  15 . A rod of tilt cylinder  15   c  is connected to tension rod  15   b . Tension of tension rod  15   b  is loosened by contracting tilt cylinder  15   c . Thereupon, as illustrated in  FIG. 10A , jib  15  rotates forward with jib connection shaft  21  as center, and is brought into a state where jib  15  is suspended from boom distal end portion  14   c.    
     (3) in a step illustrated in  FIG. 10A , boom  14  is raised, a hoisting/lowering angle is adjusted to an appropriate angle, and boom  14  is slightly extended. When boom  14  is contracted from this state, guide roller  31  is guided by guide  32 , and thereby jib  15  is pulled toward the bottom surface of base end boom  14   a  ( FIG. 10B ). When boom  14  is further contracted, jib  15  moves along base end booms  14   a , jib fixing pin  43  is inserted into insertion holes  48  and  49 , and subsequently, auxiliary pin  52  is inserted into auxiliary insertion hole  54   h . Thereby, first jib support member  40  and second jib support member  50  are connected ( FIG. 10C ). 
     (4) Next, boom  14  is lowered. Next, pin  23  is removed from the insertion hole of jib base end engagement portion  22 , and jib base end engagement portion  22  and jib connection shaft  21  are disconnected (See  FIGS. 2 and 3 ). Thereupon, jib  15  is brought into a state where jib  15  is supported by first jib support member  40  and second jib support member  50 . 
     (5) Finally, hydraulic cylinder  42  of first jib support member  40  is contracted, and thereby jib  15  is rotated to a storage position from a lower hanging position. Thereupon, as illustrated in  FIG. 1 , jib  15  is stored along the side surface of boom  14 . 
     Next, based on  FIGS. 11A, 11B, 11C and 11D , details at a time of jib fixing pin  43  being inserted into insertion holes  48  and  49  in step (3) in the above described jib storing work will be described. 
     As described above, jib  15  that is mounted on a large crane has a long length, and a heavy weight, and therefore has large deflection. In addition, a large crane has large play in each part. Furthermore, in a round boom, distal end boom  14   b  easily rotates with respect to base end boom  14   a . Consequently, even if jib  15  is pulled toward the bottom surface of base end boom  14   a  by guide roller  31  and guide  32 , the positions of jib fixing pin  43 , and insertion holes  48  and  49  deviate from one another. 
     As illustrated in  FIG. 11A , center axis O 1  of jib fixing pin  43  and center axis O 2  of insertion holes  48  and  49  deviate vertically. However, if only the apex of the distal end portion of jib fixing pin  43  is within the range of front end insertion hole  48 , jib fixing pin  43  can be inserted into front end insertion hole  48 . As illustrated in  FIG. 11B , the inside diameter of front end insertion hole  48  is large, so that even when the positions of jib fixing pin  43  and insertion holes  48  and  49  deviate in the vertical direction, the apex of the distal end portion of jib fixing pin  43  is in the range of front end insertion hole  48 . That is, a positional deviation between jib fixing pin  43  and front end insertion hole  48  in the vertical direction in which the influence of deflection of jib  15  is large can be absorbed. Consequently, jib fixing pin  43  can be inserted into front end insertion hole  48  without jib fixing pin  43  and front end rib  46  interfering with each other. 
     When an entire section of jib fixing pin  43  is not in the range of front end insertion hole  48 , a distal end portion of the conical shape of jib fixing pin  43  contacts an edge of front end insertion hole  48 . When jib fixing pin  43  is further inserted from this state, pin socket  45  is adjusted in position by the inclination of the distal end portion of jib fixing pin  43 . In this way, jib fixing pin  43  can be roughly positioned by jib fixing pin  43  being inserted into front end insertion hole  48 . 
     As illustrated in  FIG. 11C , when jib fixing pin  43  is further inserted, the distal end portion in the conical shape of jib fixing pin  43  sometimes contacts an edge of rear end insertion hole  49 . When jib fixing pin  43  is further inserted from this state, pin socket  45  is adjusted in position by the inclination of the distal end portion of jib fixing pin  43 . An inside diameter of rear end insertion hole  49  is substantially the same as the outside diameter of jib fixing pin  43 . Consequently, the position of jib fixing pin  43  can be finely adjusted by jib fixing pin  43  being inserted into rear end insertion hole  49 . 
     As illustrated in  FIG. 11D , in a state where jib fixing pin  43  is completely inserted into insertion holes  48  and  49 , jib fixing pin  43  can be fixed to pin socket  45 . 
     (Jib Overhanging Work) 
     Jib overhanging work is performed in the reverse order of the jib storing work. In the jib overhanging work, after jib  15  is disposed in the lower hanging position to connect jib base end engagement portions  22  and jib connection shafts  21 , boom  14  is raised, and the hoisting and lowering angle is adjusted at an appropriate angle ( FIG. 10C ). 
     Next, boom  14  is extended, and with this, auxiliary pin  52  and jib fixing pin  43  are removed from the respective insertion holes in the mentioned order. Thereby, connection of first jib support member  40  and second jib support member  50  is released ( FIG. 10B ). When boom  14  is further extended, guide roller  31  rolls on first raceway surface  34   s , and jib  15  is slowly separated from the bottom surface of base end boom  14   a  ( FIG. 10A ). 
     When tilt cylinder  15   c  is extended thereafter, tension rod  15   b  can be caused to generate tension, and jib  15  can be overhung forward with jib connection shaft  21  as center (see  FIG. 9 ). 
     REFERENCE SIGNS LIST 
     
         
           14  Boom 
           14   a  Base end boom 
           15  Jib 
           30  Guide member 
           31  Guide roller 
           32  Guide 
           40  First jib support member 
           43  Jib fixing pin 
           45  Pin socket 
           48  Front end insertion hole 
           49  Rear end insertion hole 
           50  Second jib support member