Abstract:
A telescopic boom is disclosed having a plurality of generally tubular boom sections each having its corners defined by angled corner plates converging upwardly and inwardly at equal angles relative to a central vertical plane containing the longitudinal axes of all boom sections when properly aligned. Boom shoes secured to the outer surfaces and near the inner ends of the angled corner plates of all boom sections except the largest section slidably engaging the adjacent angled corner plates of the next larger boom section; and similar boom shoes secured to the inner surfaces of the angled corner plates near the outer end of all boom sections except the smallest section slidably engaging the outer angled surfaces of the next smaller section. The lower outer shoes and the upper shoes cooperate with their associated angles corner surfaces to define inclined planes which maintain the longitudinal axes of the boom sections horizontally aligned with the vertical plane when the tip section is loaded and is subjected to a side force.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application is related to the following United States applications, which applications are assigned to the assignee of the present invention: 
     Rathe et al application Ser. No. 293,728 filed on Aug. 17, 1981 and entitled ENTENSIBLE BOOM WITH MANUAL STORED IN BASE. 
     Rathe application Ser. No. 293,729 filed on Aug. 17, 1981 and entitled COUPLING AND LATCHING MECHANISM FOR EXTENSIBLE BOOM. 
     Cozad application Ser. No. 293,727 filed on Aug. 17, 1981 and entitled LOW DROOP MULTI-PART PENDANT SUPPORTED BOOM. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a crane having a multi-section extensible telescopic boom; and more particularly relates to a telescopic boom having angled corner sections with boom shoes slidable in said corner sections. 
     2. Description of the Prior Art 
     Conventionally the boom sections of telescopic booms for cranes or the like have been generally rectangular in transverse cross-section. Boom shoes, which are the contacting surfaces between the boom sections, are generally arranged in two sets, one set being disposed between adjacent vertical walls and the other set being disposed between adjacent horizontal walls. Because of the clearance required between the vertical boom walls and the associated side shoes, a horizontal side load applied to the tip of boom will cause the longitudinal axis of the tip section, as well as the axes of all other intermediate sections, to deflect out of alignment with the longitudinal axis of the base section in the direction of application of the side load. This side deflection or &#34;kink&#34; between the several boom sections increases with shoe wear and with multisection booms creates a large tip offset. The tip offset results in offset loading and increased side bending forces being applied to the boom resulting in detrimental side deflecting and stresses. 
     An additional problem occurs when the boom is swung about its vertical axis with a load suspended therefrom. The swinging action may cause the tip section to shift from one side to the other side of the longitudinal axis of the base section causing the suspended load to swing excessively making it difficult for the operator to accurately control the load and place the load in tight spots when swinging of the boom is required. With clearance between the side shoes and the vertical walls, as is conventional, the offset of the outer boom sections will cause additional side bending loading of the boom. Such side bending loading severely stresses welds or the like in the corners of the boom sections. 
     In addition to booms that are generally rectangular in cross-section, other boom shapes are known. For example, U.S. Pat. No. 3,708,937 which issued to Sterner on Jan. 9, 1973 discloses a trapezoidal boom section; Eiler et al Pat. No. 3,802,136 which issued on Apr. 9, 1974 discloses truncated triangular boom sections used in interconnected pairs; U.S. Pat. No. 3,985,234 which issued to Jouffray on Oct. 12, 1976 illustrates a boom section with the lower wall being V-shaped; and Lester et al Pat. No. 4,171,597 which issued on Oct. 23, 1979 discloses boom sections having external configurations which are generally octagonal. U.S. Pat. No. 4,257,201 which issued to Landolt et al on Mar. 24, 1981 discloses boom sections having slide pad assemblies that include cylindrical outer surfaces at their corners. 
     SUMMARY OF THE INVENTION 
     The telescopic boom of the present invention comprises a plurality of boom sections including a base section and a tip section. Each boom section includes a pair of upper angled corner members and a pair of lower angled corner members which extend substantially the full length of the associated boom sections. Each angled corner member includes a planar shoe contacting plate with an outer surface and an inner surface. 
     The upper shoe contacting angle corner plates converge upwardly and inwardly at equal but opposite angles relative to a longitudinally extending vertical plane containing the longitudinal axis of each boom section; while the lower angled shoe contacting plates converge downwardly and inwardly at equal but opposite angles relative to said plane. Front boom shoes at the forward end of all of the boom sections except the tip section are secured to the inner surfaces of the associated angle corner plates, and rear boom shoes located near the rear end of all boom sections except the base section are secured to the outer surfaces of the angled corner plates. 
     When a load is applied to the tip section during operation vertical forces are applied to the boom sections such that the front boom shoes tend to slide up or down the associated converging inclined planar shoe contacting surfaces and the rear boom shoes tend to slide up or down the associated inclined planar shoe contacting surfaces thus maintaining the longitudinal axes of the several boom sections aligned in said vertical plane. When side loadings are now applied to the tip section (whether by wind loads or by swinging of the boom) the horizontal forces between the sections cannot produce any boom offset or &#34;kink&#34; because the side clearance has been taken-up by the action of the shoes moving up or down the angled corners which in effect has &#34;wedged&#34; the sections maintaining the alignment of the boom section axes. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a diagrammatic side elevation of the preferred embodiment of a crane which incorporates the telescopic boom of the present invention, the boom being shown fully extended and in an elevated operative position. 
     FIG. 2 is a diagrammatic vertical central section of the boom of FIG. 1 with the boom being retracted and positioned horizontally. 
     FIG. 3 is a diagrammatic section taken along lines 3--3 of FIG. 2 illustrating the transverse cross-section of the boom. 
     FIG. 4 is a perspective view of the boom sections, with portions being broken away, illustrating the relationship of the boom shoes with angled corners of the boom sections. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The telescopic boom 10 (FIG. 1) with angled corner construction of the present invention is illustrated as a component of a self-propelled truck crane 12 having a lower works or chassis 14 supported on wheels 16 for movement from place to place under the control of an operator in a cab 17. An upper works 18 includes a second cab 19 and is mounted on the chassis by a bearing 20 for rotation about a vertical axis A. The upper works supports the boom for pivotal movement about a horizontal axis B. The upper works 18 also carries power means (not shown) which drives a hydraulic pump (not shown) that provides power to a boom hoist winch or drum 22 (FIG. 1), a load hoist drum 24, one or more pendant take-up drums 26, and other standard components of the crane 12. 
     In general, the telescopic boom 10 includes at least two sections. However, the boom 10 is preferably a four section boom (FIGS. 1 and 2) which includes a base section 30 pivoted to the upper works about the horizontal axis B, a manual section 32 slidably received within the base section 30, a mid section 34 slidably received in the manual section 32, and a tip section 36 which is slidably received in the mid section 34 and includes head machinery 37 on its outer end for supporting a load L by means of a load line 24a. 
     The boom 10 is preferably extended and retracted by a single hydraulic ram 38 (FIG. 2) aided by two pair of extend cables 40 and retract cables 40A (FIGS. 2 and 3). The manual section 32 is selectively locked in a retracted position or in one of a plurality of extended positions, to the base section 30 during different phases of the boom extension and retraction operation by means not shown. The piston rod 42 of the ram 38 is selectively connected to the manual section 32 or to the base section 30 by a coupling mechanism (not shown). 
     The preferred structure for supporting the boom 10 (FIG. 1) about axis B is accomplished by means of a pair of pendant lines 50 which are trained around sheaves 52 journaled on the outer end of the base section 30 (FIG. 1), around sheaves 54 journaled on the upper end of a live mast 56, and around sheaves 58 journaled on the head machinery 37. The pendant lines 50 then enter the tubular boom, and engage the under surface of sheaves 62. The pendant lines are then trained around sheaves 60 journaled on the inner end of the tip section 36, back around the triple groove sheaves 62 journaled on a bracket 63 secured to the outer end of the cylinder case 64 of the ram 38, around sheaves 66 journaled on the rear end of the manual section 32 and are then anchored to the outer end of the base section at 68. The other ends of the pendant lines 50 are anchored to the base section 30 at 70 (FIG. 1). The boom 10 is raised and lowered by controled operation of the winch 22 which is connected to the upper end of the live mast 56 by a boom hoist line 72. This boom elevating structure is described in more detail in the aforementioned Cozad application, which application is incorporated by reference herein. 
     The specific details of the structure for extending and retracting the boom sections, and for locking the sections to one another as above described are fully disclosed in the aforementioned Rathe application which application is incorporated by reference herein. 
     An important feature of the present invention is the configuration of the structure for supporting the tubular, telescopic boom sections 30,32,34,36 (FIGS. 1 and 2) for extension and retraction relative to each other while maintaining the longitudinal axis of each boom section aligned with a vertical plane P (FIG. 3) containing the longitudinal axis of the base section even when substantial side forces are being applied to the section 36 by a suspended load. 
     In the preferred embodiment of the invention and as best shown in FIG. 3, the base section 30 of the boom 10 includes an upper wall 90, a lower wall 92, a pair of spaced side walls 94,96, a pair of upper angled corner plates 98, 100 which connect the upper wall 90 to the side walls 94, 96, and a pair of lower angled corner plates 102,104 which connect the lower wall 92 to the side walls 94,96. The upper wall 90 and angle corner plates 98,100 are preferably formed integrally from a single plate with outer edge portions 106,108 directed downwardly and welded to the side walls 94,96. Similarly, the lower wall 92 and lower angled corner plates 102,104 are preferably formed integrally from a single plate with the outer edge portions 110,112 bent upwardly and welded to the side walls 94,96. It will be appreciated that the preferred construction of the upper and lower walls minimize the amount of welding required and also eliminates welds in the highly stressed corners. 
     The upper angle corner plates 98,100 converge upwardly and inwardly at the same angle but in opposite directions toward the vertical plane P. The lower angle corner plates 102,104 converge downwardly and inwardly at the same angle but in opposite directions toward the plane P. 
     The cross-sectional construction of the manual section 32, the mid section 34 and the tip section 36 are substantially the same as the base section except that the boom sections are progressively smaller in cross-section. Accordingly, the cross-sectional construction of the manual section 32, the mid section 34 and the tip section 36 will not be described in detail but parts of these sections which are equivalent to those of the base section 30 will be identified by the same numerals followed by the letters &#34;a&#34;, &#34;b&#34; and &#34;c&#34;, respectively. 
     Having reference to FIGS. 2, 3 and 4, upper outer boom shoes 130,132 and lower outer boom shoes 134,136 are rigidly secured near the outer end of the base section 30 as by bolting to the inner surfaces of the upper angle corner plates 98,100 and to the lower angle corner plates 102,104, respectively. These boom shoes 130,132,134,136 slidably engage the outer surfaces of the angle corner plates 98a, 100a, 102a, 104a of the manual section 32, respectively. 
     Other outer boom shoes 130a, 132a, 134a and 136a are rigidly secured to the inner surfaces of the angle corner plates 98a,100a, 102a and 104a, respectively near the outer end of the manual section 32 and slidably engage the outer surfaces of the angled corner plates 98b,100b, 102b and 104b, respectively. Similarly, boom shoes 130b, 132b, 134b and 136b are rigidly secured to the inner surfaces of the angled corner plates 98b, 100b, 102b and 104b, respectively, and slidably engage the outer surfaces of the angled corner plates 98c, 100c, 102c, and 104c, respectively. 
     Similar pairs of upper and lower boom shoes 140, 142; 140a,142a; and 140b,142b (FIG. 4) are located near the rear of the boom sections. The rear shoes are bolted to outer surfaces of the angled corners and slidably engage the inner surface of the adjacent angle plates of the next largest boom section. 
     More particularly, upper rear shoes 140 are bolted to the outer surfaces of the angled corner plates 98a, 100a (FIG. 3) of the manual section 32 and slidably engage the inner surfaces of the angled corner plates 98,100 of the base section 30, the two lower shoes 142 are bolted to the outer surface of the angle corner plates 102a, 104a (FIG. 3) of the manual section 32 and slidably engage the inner surfaces 102,104 of the base section 30. 
     The upper and lower shoes 140a, 142a (FIG. 2) are secured to the outer surfaces of the upper and lower angle corner plates 98b,100b and 102b, 104b, respectively, near the rear end of the mid section 34 and slidably engage the inner angled corner surfaces of the next larger boom section, i.e., the manual section 32. 
     The upper and lower shoes 140b and 142b are likewise secured to the outer surfaces of the upper and lower angled plates 98c, 100c and 102c, 104c respectively, near the end of the tip section 34 and slidably engage the inner angled corner surfaces of the mid section 34. 
     As illustrated in FIG. 3, the bracket 63 is pinned to the outer end of the ram 38 and has the aforementioned pendant sheaves 62 and extend line sheaves 152 journaled thereon. Four ram alignment shoes 154 are bolted to the angle bracket 155 and slidably engage the inner surfaces of the angled shoe contacting plates 98c, 100c, 102c and 104c of the tip section. 
     In operation, the boom 10 (FIG. 1) is pivotally raised and lowered about pivot axis B by means of the pendant lines 50, boom hoist line 72 and actuation of the winch 22 in the proper direction. The boom is pivoted about vertical axis A of bearing 20 by conventional means (not shown); the boom 10 is extended and retracted upon actuation of the hydraulic ram 38; and a load L may be connected to the load line 24A for suspension from the boom. All of the above operations are performed under the control of an operator. 
     With the boom extended and supporting load L, it will be appreciated that the lower outer shoes 134, 134a, 134b and 136, 136a, 136b will act like inclined planes causing the outer surfaces of the angled corner plates 102a, 102b, 102c and 104a, 104b, 104c to slide downwardly and toward the central vertical plane P thereby compensating for clearance and shoe wear at the forward or outer end of all of the boom sections causing the forward portion of all boom sections to remain centered on the plane P. 
     The rear pairs of upper shoes 140, 140a, 140b (FIG. 4) at the rear ends of the manual section 32, mid section 34 and tip section 36 will be forced upwardly due to the load L suspended from the tip section. The angled corner plates 98,100 of the base section, the angled corner plates 98a, 100a of the manual section 30, and the angled corner plates 98b, 100b of the mid section 34 will also act as inclined planes which cause the rear end of the sections to slide upwardly and toward the center of the vertical plane P thereby compensating for clearance and wear to the rear shoes. 
     With the upper shoes at the rear end of the boom sections raised upwardly against the associated angled corner plates, and with the lower angled corner plates engaging the associated inclined shoes on the outer ends of the boom sections 30,32 and 34, all boom sections remain in horizontal transverse alignment with their axes within or substantially within the vertical plane P even though substantial side forces are applied to the tip section of the boom. 
     Although the angled corner sections of the preferred embodiment have been illustrated as being integral with the associated upper or lower walls, it will be understood that the corner plates may be otherwise connected to the adjacent walls as desired. 
     From the foregoing description it is apparent that the boom construction of the present invention provides boom shoes secured to angled corner plates and slidably engaging other angled boom sections at the bottom of the forward end of the boom which compensates for clearance and shoe wear thereby maintaining the forward end of the boom sections in alignment with a vertical plane; and that a similar construction at the upper rear end of the boom sections maintains the rear portions of the boom sections in alignment with said vertical plane. If the boom is not subjected to a load sufficient to raise the rear end of the boom sections or if the geometry of the boom system and the resultant vertical forces result in the rear end of the boom dropping and the front end of the boom raising relative to the next section, the lower shoes at the rear end of the boom sections will maintain alignment with the vertical plane. 
     Although the best mode contemplated for carrying out the present invention has been shown and described, it will be apparent that modification and variation may be made without departing from what is regarded to be the subject matter of the invention.