Abstract:
A sod cutting blade pivotally supported on a plow assembly frame such that the sod cutting blade is able to pivot and pass over an obstruction when encountered during a plowing operation. The plow assembly has a spring that is used to bias the sod cutter into the ground.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of provisional patent application Ser. No. 61/770,024, filed on Feb. 27, 2013, the entire contents of which are incorporated herein by reference. 
     
    
     FIELD 
       [0002]    The present invention relates generally to the field of utility installation and in particular to the use of plows for the installation of underground utilities. 
       SUMMARY 
       [0003]    The present invention is directed to a system for installing a utility underground. The system comprises a mobile power source comprising a work machine frame and a plow assembly connected to the power source. The plow assembly comprises an arm pivotally connected to the work machine frame at a first end of the arm, a shaker box connected to a second end of the arm, a plow blade connected to the shaker box, and a pivotal sod cutting member supported by the arm between the first end of the arm and the second end of the arm ahead of the plow blade. The sod cutting member has a cutting length less than a length of the plow blade and pivots when the sod cutting member engages an underground obstruction. A biasing member is connected to the sod cutting member and the arm to bias the sod cutting member into the ground. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0004]      FIG. 1  is a diagrammatic representation of a vibratory plow and sod cutter. 
           [0005]      FIG. 2  is a diagrammatic representation of a sod cutter of the present invention. 
           [0006]      FIG. 3  is a diagrammatic representation of an alternative sod cutter of the present invention. 
       
    
    
     DESCRIPTION 
       [0007]      FIG. 1  illustrates a vibratory plow machine  10  used for the installation of slender underground utilities (cables, small pipes, etc.). These machines typically have a power unit  14  on wheels  16  or tracks (not shown) for moving the unit. The power unit  14  pulls a plow unit  18  that has a vibratory shaker box  20  and plow blade  22 . The vibratory shaker box  20  will typically feature a set of internal rotating eccentric weights (not shown) that cause a vibratory motion of the shaker box as the weights are rapidly rotated. The shaker box  20  connects to the plow blade  22  extending into the soil  24  which creates a narrow slot in the ground as the machine  14  advances forward. Typically, the utility service is fed into the narrow slot in the ground right behind the plow blade  22 . 
         [0008]    In many instances, this type of machine is used to install services in nicely landscaped areas with established turf. In these instances, the vibratory plow machines  10  commonly run a sod cutter  26  in front of the plow blade  22  to pre-cut the sod  28  in front of the plow blade to minimize the turf damage done as the vibratory plow machine operates. The sod cutter  26  provides a clean cut in Bermuda grass or similar grasses with rhizomes, or “runners” that spread out on the surface of the ground and helps to prevent a pulling and uprooting of the grass as the blade passes. Sod cutter types that have been used include a narrow fixed blade or a rolling disc to cut the sod. 
         [0009]    One problem that can be encountered with the current sod cutters is when an obstacle  30  such as a stone or tree root exists at or close to the surface of the ground. This type of obstacle can damage the sod cutter  26 , and/or cause the shaker box  20  to be lifted up as the sod cutter passes over the obstacle, resulting in an inconsistent burial depth for the installed utility. 
         [0010]    Turning to  FIG. 2 , the sod cutter  32  of the present invention is shown mounted on the lower arm  34  of a vibrator plow assembly  18 . The sod cutter  32  is pinned in place at the pinned pivot location  36  instead of the rolling disc shown in  FIG. 1 . 
         [0011]    In use, the device functions as follows. The sod cutter  32  extends into the surface of the ground  28  (typically about 3″-6″) and cuts the sod in front of plow blade  22 . Springs  38  are attached to a device frame  40  and to an attachment point  42  above the pinned pivot  36  on the blade  32 . In this configuration, the spring  38  provides a measure of preload on the blade  32  to keep it from freely pivoting and moving backward. The preload on the blade  32  is sufficient to allow the blade to cut through normal sod and vegetation as is found in an established lawn without pivoting backward. When an obstacle of sufficient size, such as a large stone or tree root is encountered, the preload on the blade  32  is overcome and the blade may pivot back allowing the sod cutter to pass over the obstacle without damage and without causing the shaker box to be lifted up relative to the ground surface. After passing over the obstacle  30  ( FIG. 1 ), the preload of the spring(s)  38  on the blade causes the sod cutter blade  32  to once again extend into the surface of the ground and continue cutting the vegetation as the machine  14  is advanced forward. 
         [0012]    Continuing with  FIG. 2 , a generalized form of the spring-loaded sod cutter for a vibratory plow is shown. The version illustrated in  FIG. 2  is shown on a frame  40  which may be added or removed from the vibratory plow assembly  18 . Alternatively, the spring loaded sod cutter  32  can be an integral part of the plow assembly  18 . The sod cutter would be mounted on the lower arm  34  of the vibratory plow attachment  18 . The sod cutter  32  is free to pivot about its attachment point  36  as illustrated in  FIG. 2 . A mechanical stop (not shown) may be used to limit the amount of forward rotation of the sod cutter in order to maintain pre-load on the spring  38  used to bias the sod cutter. Spring  38  may be a tension spring The spring may be made from steel. Alternatively, the spring  38  could be an elastomer like rubber or urethane, or a gas filled spring. By altering the geometry slightly, a compression spring made of steel, elastomer, or of a gas-charged design could be used to maintain preload on the blade  32 . Alternatively, a torsion spring could be adapted to provide the necessary preload to hold the sod cutter in its forward position when an obstacle is not encountered. 
         [0013]    The leading edge  44  of the sod cutter  32  will have a semi-sharpened leading edge comparable to a knife blade, and the toe  46 , or leading point, of the sod cutter will extend forward of the pivot point  36  as shown in  FIG. 2 . 
         [0014]      FIG. 3  illustrates an alternative embodiment of the spring-loaded sod cutter. In this embodiment, a rolling disk  26 , “pizza-cutter” style sod cutter illustrated in  FIG. 1  is utilized. However, instead of a fixed mounting as shown in  FIG. 1 , the rolling disk cutter  26  is mounted on an arm  46  which may pivot to allow the sod cutter  26  to float up out of the way of an obstacle  30  ( FIG. 1 ). As illustrated in  FIG. 3 , a compression spring  48  is used to maintain a preload on the pivoting arm  46  to hold the rolling disk cutter  26  in the ground  28  when an obstacle  30  ( FIG. 1 ) is not encountered. The spring  48  could be made of steel, and elastomer, or of a gas-charged design. It will be appreciated that by altering the geometry of the arm  46  and pivot point  50  slightly, a tension spring or a torsion spring could be used to maintain the preload on this style of cutter. 
         [0015]    The present invention is also directed to a method of using the above described devices to cut a trench in the Earth and install a utility. 
         [0016]    Various modifications can be made in the design and operation of the present invention without departing from the spirit thereof Thus, while the principal preferred construction and modes of operation of the invention have been explained in what is now considered to represent its best embodiments, which have been illustrated and described, it should be understood that the invention may be practiced otherwise than as specifically illustrated and described.