Telescoping boom assembly with longitudinally displaceable base boom section
BACKGROUND OF THE INVENTION 
     Reference is made to the following pending U.S. patent applications which were filed on the same date the instant application was filed, are owned by the assignee of the present application, and which relate to the same commercial apparatus on which this instant invention is employed: Ser. No. Ser. No. 807,616, U.S. Pat. No. 4,705,450, Ser. No. 807,573, U.S. Pat. No. 4,700,802, and Ser. No. 807,617, U.S. Pat. No. 4,705,295. 
     FIELD OF THE INVENTION 
     The present invention relates to material handling apparatus having a telescoping boom and, in particular, to an apparatus for allowing such a boom to have a longer effective operating length. 
     DESCRIPTION OF THE PRIOR ART 
     In various material handling applications it has proven expedient to provide a work implement on the end of a boom means. Frequently, such a boom means is pivotally mounted to a structure which may be supported by a truck chassis. The truck chassis is capable of being driven over the road or highway under control of an operator in the main truck cab. The material handling mechanism is supported on an upper structure which is mounted on a swing bearing through which a center pin extends for relative movement with respect to the truck chassis. The material handling device will preferably include a boom and a work implement. An upper structure operator&#39;s cab is provided on the upper structure to move with the material handling mechanism. During operation at a construction site, an operator in the upper structure operator cab can control movement of the truck chassis and also of the material handling mechanism. 
     In the case of a material handling apparatus such as an excavator, a hydraulically operated, telescoping boom means is preferably vertically pivotally mounted on the upper structure. The boom means is typically capable of being raised or lowered by means of a hydraulic cylinder connected between the boom support and the upper structure. In addition to the extension and raising of the boom, such booms are also capable of being tiltable about their axis. In addition, the work implement, such as a bucket, is preferably operable. For example, the bucket may be displaced between open and closed conditions. 
     Also, as indicated above, the upper structure is preferably horizontally pivotable upon the lower chassis in order that materials may be handled at distances remote from the vehicle and located on virtually any side thereof. A problem which frequently arises in connection with the manipulation of objects remote from the vehicle is the ability of the extended boom means to be of sufficient length to allow the material handling implement to reach the desired locale. It appears that in many instances it would be preferable to provide a boom of greater extended length. However, it will be readily appreciated that the provision as standard equipment on a material handling apparatus of an inordinately lengthy boom would add significantly to the initial cost and weight of the material handling apparatus. As such, those skilled in the art have determined that the provision of an additional telescoping member or of an exceptionally long boom means is not feasible due to the infrequency with which such additional boom length is required. 
     One prior art means of providing added length to a boom without requiring the initial construction of the boom to be of exceptional length is to provide a boom extension. Such a boom extension is typically provided as an optional, extra cost feature to the material handling apparatus and usually comprises a length of boom that may be affixed between the usual end of the boom and the material handling implement. However, it must be appreciated that this practice of providing a boom extension is also plagued with certain difficulties. For example, the purchasers of material handling implements typically prefer not to incur the additional added expense of purchasing the optional boom extension. In addition, it is frequently inconvenient for the material handling apparatus to carry the boom extension with it from job site to job site. Hence, an outside means of transporting the boom extension is required. An additional and principal concern of users of material handling apparatus which require employment of a boom extension is the excessive time required for the material handling implement to be removed from the current end of the boom, for the boom extension to be attached to the end of the boom and for the material handling implement to be connected to the end of the boom extension. It will be readily appreciated that the time required for an operator to add the additional length of a boom extension may be seen as excessive and causes unprofitable down-time for the material handling apparatus itself. 
     The subject invention is directed toward a means for providing an additional length to the boom of a material handling apparatus which overcomes, among others, the above-discussed problems and which provides an effective, efficient, inexpensive and readily utilized means for extending the effective length of such a boom without requiring the use of boom extensions or the provision of an inordinately lengthy standard boom. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention there is provided apparatus for extending the effective length of the boom of a material handling apparatus. A telescoping boom of a material handling apparatus is supported by a vertically tiltable boom cradle which is pivotally attached to an upper structure of a material handling vehicle. A hydraulic cylinder means is provided to motivate the pivoting of the boom cradle with respect to the upper structure of the material handling apparatus. 
     The boom itself consists of a first boom section which is affixed to the boom cradle and a second boom section which is provided to telescope within the first boom section and is supported thereby by rollers intermediate the first and second boom sections. A movable material handling implement, such as a bucket, is provided on the free end of the second boom section. The boom cradle includes upstanding front and rear brackets which, by means of pivotable support pins, support front and rear cradle arms. While the first boom section is supported by the cradle arms, front and rear retaining straps are provided to pass around the first boom section and are bolted to the front and rear cradle arms, respectively. A hydraulic cylinder is provided between the rear cradle arm and the boom cradle itself which allows the pivoting of the boom about an axis passing through the support pins. 
     A first pair of stop blocks is affixed to the lower portion of first boom section intermediate the length thereof so as to extend downwardly therefrom. A second set of stop blocks is provided at the trailing end of the first boom section and also extends downwardly therefrom. In normal operation, the first boom section is affixed to the boom cradle by means of dual straps which pass around the first boom section and which are rigidly attached to the boom cradle. In addition, when the boom is in its normal operating position, bolts are caused to pass between the first stop blocks and the front cradle arm to further secure the first boom section thereto. 
     When, however, it is desired to add additional effective length to the boom, the bucket affixed to the end of the boom is set into the ground and the engine is stopped. The bolts intermediate the first stop blocks and the front cradle arm are then removed and the bolts securing the retaining straps to the boom cradle are loosened. The engine is started and the boom retracted which effectively causes the boom to be displaced relative to the boom cradle until the second stop blocks engage the boom cradle. At this point, the bolts are inserted between the second stop blocks and the rear cradle arm and the bolts of the securing straps are tightened thereby resecuring the boom to the boom cradle. 
     In the event that it is desired to add additional effective length to the boom, but not to the full extent of the distance between the first and second stop blocks less the length of the boom cradle due to the lifting limitations thereby imposed on the boom, it is also possible, according to the present invention, to add a portion of such length. In that event, spacer bars having a face plate on each end thereof are inserted between the appropriate stop blocks and the corresponding cradle arm. Cap screws are then affixed between one face plate of the spacer bar and the appropriate stop block and between the other face plate of the spacer bar and the corresponding cradle arm. By the use of such spacer bars, an additional effective length less than the maximum length available may be employed. 
     Accordingly, the present invention provides solutions to the aforementioned problems connected with material handling vehicles. As this invention provides an effective means of adding additional working length to the boom of a material handling apparatus the operating length thereof is effectively increased without requiring the provision of boom extensions or of the additional weight and cost involved with an inordinately long standard boom. 
     These and other details, objects and advantages of the invention will become apparent as the following description of the present preferred embodiment thereof proceeds. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a left side elevation view of a truck mounted extensible boom hydraulic excavator; 
     FIG. 2 is a right side view of the excavator shown in FIG. 1; 
     FIG. 3 is a right side elevation view of the extensible boom means of a material handling apparatus; 
     FIG. 4 is a plan view of the boom means shown in FIG. 3; 
     FIG. 5 is a more detailed right-side elevation view of the boom means; 
     FIG. 6 is a detailed rear elevation view of the boom means provided herein; 
     FIG. 7 is a detailed front elevation view of the boom means of the present invention; 
     FIG. 8 is a perspective view of the boom adjustment spacing means herein provided; and, 
     FIGS. 9a, 9b and 9c are left elevation, front elevation and plan views of the spacing means disclosed herein. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to the drawings wherein the showings are for purposes of illustrating the present preferred embodiment of the invention only and not for purposes of limiting same, the figures show a mobile material handling apparatus 10 which, for purposes of the present DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS, will be described as an extensible boom hydraulic excavating apparatus, also called an excavator. 
     More particularly and with reference to FIG. 1 there is shown an excavator 10 which includes a lower truck chassis 12 and an upper structure 14 rotatably supported thereon by means of a swing bearing 16 through which passes a center pin. Lower chassis 12 is provided with a truck cab 18 mounted beside an engine (not shown). A front axle (not depicted) supports the end of lower chassis 12 nearest truck cab 18 on front wheels 24 while a rear axle (not shown) supports the rear of lower chassis 12 on rear wheels 28. 
     The upper structure 14 includes a platform, generally indicated as 30, on one end of which is mounted a remote operator cab 32. In addition, an extensible boom, generally 34, is mounted to a boom support cradle 36 which is pivotally attached to an upstanding support member 37 of upper platform 30 by means of pins 38. As such, boom cradle 36 allows boom 34 to be vertically pivotable with respect to upper platform 30. Such vertical pivoting of boom 34 is accomplished by means of hydraulic hoist cylinder 39 attached between boom cradle 36 and the end of upper platform 30 remote from operator cab 32. 
     Boom 34 includes a base or first section 42 mounted to boom cradle 36 and a second extensible boom section 44 which is provided to be supportable by and hydraulically retractable within first section 42. However, it is to be understood that boom 34 may consist of any number of sections, one of which is attached to boom cradle 36. A material handling implement 46, such as a bucket, is preferably movably attached to the free end of second boom section 44 by means of a pivotable support 48 which will preferably include a means, such as a hydraulic cylinder for pivoting bucket 46 relative to boom 34. 
     With respect to the general operation of excavator 10, truck cab 18 is occupied by an operator during over the road or distant movement of the excavator 10 to a selected job site. Operator cab 32 is occupied by the operator for control of excavator 10 around a given job site and when it is desired to manipulate a work implement such as a bucket 46 or to rotate upper structure 14 in a manner known in the art. The movement of lower chassis 12 can be provided by either a two wheel drive system in which only rear wheels 28 are preferably driven or a four wheel drive system in which all wheels 24 and 28 are driven. General operating characteristics and functional capabilities of a material handling apparatus 10 are similar to those disclosed in U.S. Pat. Nos. 3,587,886; 3,599,814 and 3,666,125. 
     Boom cradle 36 includes left and right side panels 50 and 52, respectively, which are secured to an inner box member 54. In addition, left and right brackets 56 and 58, respectively, are provided intermediate the spaces between side panels 50 and 52 and box member 54. As such, coaxial apertures are provided through left side panel 50, left bracket 56, both sides of inner box member 54, right bracket 58 and right side panel 52 to receive the pivot pin 38 which functions to movably support boom cradle 36, and hence, boom 34 by means of vertically extending support bracket 37 extending upwardly from upper structure 14. Further, apertures are provided through the rearwardly extending portions of hoist cylinder mounting bracket 59 to receive a pivot pin 62 which attaches boom cradle 36 to hydraulic hoist cylinder 39 effective to accomplish the hoisting of boom cradle 36 relative to upper structure 14. 
     Front and rear boom support brackets 64 and 66, respectively, are provided to extend upwardly from the upper surface of inner box member 54. In order to pivotally support boom 34, there are provided a laterally extending front cradle arm 68 and a rear cradle arm 70 on the upper surfaces of each of which rests first boom section 42. First boom section 42 is secured to boom cradle 36, in part, by means of a front clamping means such as a strap 72 which passes around the upper portions of boom section 42 and which has extended ears which are secured to front cradle arm 68 by means of cap screws 74. Similarly, a rear clamping means such as a strap 76 which also passes around boom section 42 and has extended ears, is thereby secured to rear cradle arm 70 by means of cap screws 78. A front tilt pin 80 is provided to pass intermediate apertures in front cradle arm 68 and front boom support bracket 64 and rear tilt pin 82 is provided between apertures in rear cradle arm 70 and rear boom support bracket 66. As such, an axis of pivot for boom 34 parallel to its axis but spaced therefrom is provided along front and rear tilt pins 80 and 82, respectively. A tilt cylinder 83 is preferably provided operatively between inner box member 54 and rear cradle arm 70 so as to provide the tiltability of boom 34 about the axis defined by front tilt pin 80 and rear tilt pin 82. 
     Also provided on the lower surface of first boom section 42 approximately intermediate its length are left front stop block 84 and right front stop block 86. Cap screws 88 are provided to pass between left front stop block 84 and the left side of front cradle arm 68 and between right front stop block 86 and the right side of front cradle arm 68 so as to further secure first boom section 42 to cradle 36. The position in which the front stop blocks 84 and 86 engage the front cradle arm 68 will be referred to as the standard operating position. In addition, left rear stop block 90 and right rear stop block 92 are secured to the lower portion of first boom section 42 adjacent the trailing end thereof. As such, if the boom 34 were displaced forwardly with respect to cradle 36, left rear stop block 90 and right rear stop block 92 may be secured to the rear portions of rear cradle arm 70 by means of cap screws 88, thereby effectively increasing the operating length of boom 34. The &#34;available additional length&#34; as used herein will be that length equal to the distance between the front stop blocks 84 and 86 and the rear stop blocks 90 and 92 minus the distance between the outermost faces of front cradle arm 68 and rear cradle arm 70. Such distance may consist of a substantial portion of the length of base boom section 42 and will preferably be of at least three feet. 
     In operation, therefore, to effectively increase the length of boom 34, the operator of excavator 10 positions the upper structure 14 with the boom 34 extending over one side or over the end of lower chassis 12. Second boom section 44 is extended and the edge of bucket 46 is placed level into the ground. With the engine stopped, cap screws 88 are removed from between left front stop block 84 and front cradle arm 68 and from between right front stop block 86 and front cradle arm 68. In addition, cap screws 74 which secure front strap 72 to front cradle arm 68 and cap screws 78 which secure rear strap 76 to rear cradle arm 70 are loosened but preferably not removed. The operator then restarts the engine of the vehicle 10 and operates the appropriate control to cause the second boom section 44 to be retracted relative to the first boom section 42 which, due to the bucket 46 being imbedded in the ground, causes the first boom section 42 to slide forward relative to second boom section 44 until rear stop blocks 90 and 92 contact rear cradle arm 70. The engine is then stopped and the cap screws 88 previously removed from front stop blocks 84 and 86 are securely installed between left rear stop block 90 and rear cradle arm 70 and between right rear stop block 92 and the other end of rear cradle arm 70. The cap screws 74 which attach front strap 72 to front cradle arm 68 and cap screws 78 which attach rear strap 76 to rear cradle arm 70 are then tightened to the required torque. Due to this operation, the boom is positioned in an effectively extended position and is able to continue operation with an extended reach but a decreased capacity. It will be clear to those in the art that the above-described procedure may be reversed to return the boom 34 to its standard operating position. 
     It will be appreciated that as the effective length added to boom 34 is increased the capacity thereof decreases. As such, it may, in order to maintain a specified loading capacity of the boom 34, be desired to only increase its effective length an amount less than the full range available which length will be referred to as the modified additional length. In that instance, spacer bars 100 may be employed. Spacer bars 100 preferably each comprise an elongated metallic bar 101, which may assume an angle-like cross section, having a first face plate 102 affixed to one end thereof and a second face plate 104 affixed to the other end thereof. As such, face plates 102 and 104 extend perpendicularly of the axes of spacer bars 100. The spacer bars 100 are of equal length which length is less than the available additional length. By means of example only, if the available additional length is three feet and the length of spacer bars 100, including face plates 102 and 104, is one foot the modified additional length may be one or two feet. In order to provide a modified additional length of one foot, the bucket 46 is secured to the ground, the engine 20 is stopped and the cap screws 88 are removed from between the front stop blocks 84 and 86 and the front cradle arm 68 and the cap screws 74 and 78 loosened. The engine 20 is started and the second boom section 44 is retracted relative to base boom section 42 an amount greater than the length of spacer bars 100. The engine 20 is stopped and the spacer bars 100 are installed by securing first face plates 102 by means of cap screws 88 to front stop blocks 84 and 86, respectively. The engine is then restarted and second boom section 44 is extended until front cradle arm 68 meets face plates 104 of spacer bars 100. Cap screws 74 and 78 are retightened and additional cap screws 106 are then secured between front cradle arm 68 and face plates 104 thereby providing a modified additional length of one foot. 
     In the event it is desired to provide a modified additional length of two feet from the standard operating position using spacer bars 100 which are one foot in length, the engine 20 is stopped and the cap screws 74 and 78 loosened. The cap screws 88 are removed from the position between front stop blocks 84 and 86 and the front cradle arm 68. The spacer bars 100 are then installed by securing second face plates 104 to rear stop blocks 90 and 92 by means of cap screws 88. The engine 20 is restarted and the second boom section 44 is retracted relative to base boom section 42 until rear cradle arm 70 meets the second face plates 104 of spacer bars 100. The engine 20 is then stopped and cap screws 106 installed intermediate rear cradle arm 70 and first face plates 102 of spacer bars 100. The cap screws 74 and 78 on the front and rear straps 72 and 76, respectively, are tightened and the boom 34 is prepared for operation with a modified additional length of two feet. 
     It will be understood that various changes in the details, materials and arrangements of parts which have been herein described and illustrated in order to explain the nature of the invention, may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims.