Falling object protective structure
BACKGROUND OF THE INVENTION 
     The present invention relates to the field of overhead protective structures for excavating machines such as hydraulic excavators and shovels to protect the machine and the machine operator from falling objects such as rocks and bolders dislodged during excavation operations. It is well known to provide protective structures for the top of such machines. However, since they may be subjected to high impact compressive forces and bending moments, such structures must be mounted on the machine frame by heavy mounting members sufficient to withstand such bending moments. The required heavy mounting members increase the weight and complexity of such protective structures and interfere with vision from the operator&#39;s cab. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a falling object protective structure for hydraulic excavators and the like that avoids the requirements for heavy support members extending from the main vehicle frame upward past the operator&#39;s station to the canopy assembly of the structure to improve visibility and eliminate the weight and complexity of such mounting structures. The foregoing objectives are realized in the present invention, which provides a protective structure including a canopy mounted on the top of the excavator operator&#39;s cab at the front and back thereof directly over the front and back vertical cab structure members to avoid imparting bending moments thereto. The mounting means at the front of the cab includes laterally resilient pivot means whereby bending moments imparted to the canopy assembly of the protective structure by the impact of falling objects will not be transmitted to the cab structure. Since the cab structure will not be subjected to such bending moments, it may be employed as an integral means for mounting the protective structure on the top of the cab, eliminating any requirements for heavy mounting members mounting the protective structure to the vehicle frame, and thus reducing weight, avoiding needless components and complexity of the machine and enhancing visibility from the operator&#39;s cab. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an elevational view of the portion of a hydraulic excavator showing a falling object protective structure embodying the present invention mounted thereon; 
     FIG. 2 is an enlarged view of the protective structure and extreme cab top shown in FIG. 1; 
     FIG. 3 is a sectional view of the front mounting means of the present invention taken along the line 3--3 of FIG. 2; 
     FIG. 4 is a top plan view of the protective structure of the present invention; 
     FIG. 5 is a sectional view of the front mounting means of the present invention taken along the line 5--5 of FIG. 2; 
     FIG. 6 is a sectional view of the rear mounting means of the present invention taken along the line 6--6 of FIG. 2; and 
     FIG. 7 is a sectional view of the rear mounting means of the present invention taken along the line 7--7 of FIG. 6. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIG. 1, a hydraulic excavator is shown at 10 as comprising an undercarriage assembly 12, a frame 14 pivotally mounted on the undercarriage assembly, an engine compartment 16 mounted on the frame, a boom 18 shown in fragment pivotally mounted on the frame and having a distal end, now shown, adapted for fitting with a digging implement such as a bucket, a boom jack 20 pivotally connected to the frame and the boom for actuation thereof, and an operator&#39;s cab 22 mounted on the frame and adapted for accomodation of the excavator operator and controls. 
     As shown in FIG. 2, cab 22 typically comprises upstanding support members 24 and 26 supporting a top 28 thereon. A falling object protective structure embodying the present invention is shown generally at 30 mounted on top 28 and comprises a front mounting means 32 attached to cab top 28 near the front thereof directly above upstanding support member 26, a rear mounting means 34 attached to top 28 near the rear thereof directly above upstanding support member 24, and a canopy assembly 36 mounted on said front and rear mounting means. The canopy assembly comprises front and rear U-shaped channel members 38 and 40, respectively, joined by side channel members 42 and 44. The plate 54 is a U-shaped member (50, 52 and 54 being all one piece) and does not have front and rear plates 45 and 47. The dashed lines in FIG. 4 represent the channel members 38 and 40, as shown in FIG. 2. The four channel members are covered on the top by a top plate 46 having downwardly extending side portions 48 and 50, as shown in FIG. 6, and a central opening 56 provided for upward visibility from the cab. A plurality of spaced parallel bars 58 are mounted on top plate 46 and extend forwardly thereof to a front bar 60 which may be an integral proportion of side bars 62. 
     The canopy assembly is mounted to the top of cab 22 at the front and rear thereof by front mounting means 32 and rear mounting means 34, respectively, on each side of the cab. The front mounting means includes brackets 64 which depend from channel members 42 and 44, and have a bore 66 provided therein. Fitted within bore 66 is a bushing assembly 68 which comprises a rubber bushing 70 having outer and inner sleeves 72 and 74 at the outer and inner diameters thereof, respectively. Attached to the top of cab 22 by means of bolts 76 is a plate 78 to which is welded an upstanding rectangular bracket 79 having parallel walls 80 arranged on each side of depending bracket 64 and having coaxial bores 82 disposed therein in alignment with the axis of inner sleeve 74. Brackets 64 and 78 are joined by a bolt 84 secured by a washer 86 and a nut 88. Thus, front mounting means 32 provides for pivotal resilient connection of the canopy assembly to the cab at the front thereof. 
     At the rear of the cab the canopy assembly is attached to the cab by means of bolts 90 which extend through suitable holes 92 provided in channel members 42 and 44, through plates 94 provided on the top of the cab and through cab top 28 where they are secured by nuts 96. U-shaped members 98 extend between plates 94 and channel members 42 and 44 for suitable spacing of the canopy assembly from the cab top. Front plates 99 complete the enclosure of bolts 90. Spacers 100 and washers 102 are provided on bolts 90 between top 46 and channel members 42 and 44, and additional washers 104 are provided on top of the assembly. 
     Since the front and rear mounting means of the present invention are provided on the cab top directly above the front and rear upstanding cab top support members, vertical forces imparted to the protective structure of the present invention will not cause any shear or bending moments in the cab top. 
     Moreover, if bending moments are imparted to the canopy assembly by the impact of falling objects, the canopy assembly is allowed to pivot around bolts 84 preventing the bending moments from being transmitted to the structure of cab 22. Resilient bushing assembly 68 allows transverse displacement of bolts 90 during bending of the canopy assembly to further prevent bending moments in the structure of cab 22. 
     While the invention has been described in connection with specific embodiments thereof, it will be understood that it is capable of further modification, and this application is intended to cover any variations, uses or adaptations of the invention following, in general, the principles of the invention and including such departures from the present disclosure as come within known or customary practice in the art to which the invention pertains and as may be applied to the essential features hereinbefore set forth, and as fall within the scope of the invention and the limits of the appended claims.