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CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is a Divisional of U.S. patent application Ser. No. 11/236,104 filed Sep. 26, 2005, now U.S. Pat No. 7,152,348 which is incorporated by reference herein in its entirety. 

   STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
   Not Applicable 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   One aspect of the present invention relates generally to an excavator for breaking-up hard soils, rock, or concrete into manageable sized pieces for subsequent handling or processing. The excavator acts on an existing ground surface, acting on a layer of material to define a new ground surface that is below the original. The process is used for road construction and mining. This aspect of the present invention relates more particularly the apparatus, which allows control of the depth of cut and of the orientation of the resulting new ground surface. 
   2. Description of the Related Art 
   Road Bed Preparation 
   In the preparation of a road bed one critical function is to establish the proper lateral grade. In most cases the desired lateral grade is level, with the exception of regions where the road curves and a banking effect is desirable. In both cases, when constructing new roads the grade of the native topography will typically need to be modified to achieve the desired grade. Certain ground conditions prohibit excavation in a manner wherein very fine adjustments can be made. These include conditions of rock and very hard soils. In these conditions the surface is typically excavated below the desired level, and finer more manageable materials backfilled to bring the grade to the desired level. 
   The process of replacing a damaged road surface often begins with the step of removing the existing road surface. The current methods of removing existing road surfaces of concrete are complicated by the existence of steel reinforcing rod that is integral to the concrete road surface. Current techniques of breaking up the road surfaces are slow and labor intensive often including the use of some form of impact wherein the existing road surface is struck from the above and broken into smaller pieces, and at the same time separating the reinforcing rod. 
   Mining 
   Many types of non-metallic rock are mined from shallow open-pit mines called quarries. The process is known as quarrying, open cast or surface mining. One quarrying technique involves drilling and blasting to break the rock. When usable rock is found, the surface is cleared to expose the desired rock. The area being mined is then drilled and blasted, a large number of low-powered explosives detonated at the same time to shatter the rock. The drillings are controlled to a depth to stay within the strata of desirable rock, as may have been determined by preliminary exploratory drillings. A single blast produces as much as 20,000 tons of broken stone. The broken stone is then loaded by handling equipment and transported to additional equipment to be crushed into smaller pieces and separated into uniform classes by screening methods. During that time the broken stone is exposed to the elements and some may be affected by weathering damage. This process is relatively labor intensive, produces work-in-process subject to damage. New techniques are recently being developed. 
   One such technique of quarrying is labeled as percussive mining in U.S. Pat. No. 5,338,102. In this reference a percussive mining machine is utilized to successively strike or impact the material with a cutting tool. In this case the cutting tools are mounted to a rotating drum that is propelled on a mining machine. The mining machine illustrated includes components representative of many machines which have recently been developed for this application. The machines typically include some form of ground drive, supporting frame for the drum, power unit to provide power to rotate the drum, a conveyance mechanism and some form of height control, to control the position of the drum. Examples of other machines, built specifically for this application, can be found in U.S. Pat. Nos. 5,092,659; 5,577,808; and 5,730,501. These machines are highly specialized, with limited additional use. 
   An example of a more versatile machine, built on a more generic platform, can be found in U.S. Pat. No. 4,755,001. This reference discloses an excavating machine that consists of a digging head mounted to an elongated digging member, both mounted to a main frame. The main frame resembles machines currently known as track trenchers. 
   Track trenchers, as is illustrated in  FIG. 1 , were originally designed for forming trenches for the installation of drainage lines or other utilities in open trench installations. The basic components of a Track Trencher  10  include:
     1) a main frame  30 ,   2) a set of ground engaging track assemblies  20  which are fixedly supported by the main frame  30  in a manner that allows the drive sprocket  22  to be driven to propel the machine along the ground,   3) a power unit  40  typically a diesel engine, and   4) an excavation boom assembly  50  which is relatively narrow, as compared to its length, as most trenches are much deeper than they are wide.   

   The power unit  40  provides power to the driven/drive components of the machine. This is typically comprised of a diesel engine and a hydraulic system. The hydraulic power is transferred to various actuators mounted on the machine to perform the desired operations including:
         1) a hydraulic motor  24  mounted onto the track drive frame that drives the track drive sprockets  22 ,   2) a hydraulic motor  52  mounted on frame  30  that supports and drives a sprocket which drives the excavation chain  54  that is supported on an idler sprocket  56  which is supported by the boom frame  51 , and   3) a hydraulic system that includes cylinders  62  to raise and lower the excavation assembly.       

   In trenching the primary parameter that needs to be controlled is the depth of the trench. The machine provides this control by controlling the position of the boom relative to the ground engaging tracks, typically allowing the boom to pivot around an axis defined by the machine frame. This pivot is designed robustly to handle the severe loading, particularly experienced when excavating rock. Typically the only movement of the boom relative to the frame is provided by pivoting about this axis. 
   Controlling the height of each ground drive unit, track, independently allows the frame to be kept level and thus the orientation of the resulting trench can also be controlled. However, this technique of orientation is not ideal in that the entire machine is being controlled resulting in higher power requirements and reduced responsiveness. 
   BRIEF SUMMARY OF THE INVENTION 
   The present invention relates generally to an excavation machine having a frame and an excavation boom. The excavation boom is rotatably mounted to the frame at a boom mount pivot axis. The excavation boom includes an excavating chain that drives an excavating drum, both rotating about an excavation axis. The boom further includes an integral pivot that allows the position and/or orientation of the excavating drum to be independently adjusted, relative to the frame and the boom mount pivot axis. The excavating drum and the excavating chain both include cutters mounted in a predetermined pattern. The predetermined pattern involves the placement of the drum cutters in relation to the chain cutters. The predetermined pattern does not change as the chain and drums are operated. 
   Road Bed Preparation 
   The apparatus of the present invention is particularly useful for the preparation of a road bed with its ability to control the orientation of the final ground surface along with the excavation depth. In addition the excavating drum&#39;s width, relative to the width of the ground engage tracks and the arrangement of the cutting teeth on the excavating drum make it particularly useful in demolition of an existing road surface in preparation to install a new road surface. 
   Mining 
   The apparatus of the present invention is particularly useful for certain types of mining operations with its ability to control the excavating drum to optimize the orientation of the ground surface and the excavating parameters. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a side view of the prior art track trencher with a standard boom; 
       FIG. 2  is a side view of a track trencher with the boom of the current invention; 
       FIG. 3  is side view of the new boom; 
       FIG. 4  is a cross-section of the main pivot taken along line  4 - 4  of  FIG. 2 ; 
       FIG. 5  is an isometric view of the main pivot; 
       FIG. 6  is a cross-section of the swivel of the present invention taken along line  6 - 6  of  FIG. 3 ; 
       FIG. 7  is an enlarged side view of the head assembly of the new boom; 
       FIG. 8  is an end view of the head assembly of the new boom taken along line  8 - 8  of  FIG. 7 ; 
       FIG. 9  illustrates the hydraulic drive motor and drive sprocket for the excavation chain; 
       FIG. 10  is a cross section through the head shaft and the excavation drums of the present invention taken along line  10 - 10  of  FIG. 7 ; 
       FIG. 11  is a perspective view of a portion of the excavation chain assembly; 
       FIG. 12  is an exploded view of the base plates assembled onto the excavation chain; 
       FIG. 13  illustrates the pattern of the cutters mounted on the excavation chain and drums; 
       FIG. 14  is a top view of a track trencher with the boom of the current invention; and 
       FIG. 15  is an end view of a portion of the track trencher and excavation boom of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring now to the drawings, like reference numerals designate identical or corresponding parts throughout the several views. 
   The current invention includes a track trencher with a new excavation boom. A preferred embodiment is illustrated in  FIGS. 2 and 3 . In  FIG. 2  the track trencher includes the basic components of the main frame  30 , track assemblies  20 , power unit  40 ; all with similar functions as described for the prior art track trencher. The excavation boom is replaced by a new excavation boom  100  of the present invention. 
   The new excavation boom  100  is illustrated in  FIG. 3  and includes a mounting section  110 , swivel  120  and head unit  130 . The mounting section  110  includes a mount frame  112  that will mate with the main frame  30  as illustrated in  FIG. 4  and  FIG. 5 . The main frame  30  includes two coaxial holes with an array of tapped bolt holes, bolt patterns  32 , which define the main pivot axis  114 . Bolt pattern  32  is defined as including both the large diameter pilot hole  332  and the array of tapped holes  232  that fall on a bolt circle that is aligned with the pilot hole. 
   Outer pivot rings  113  attach to the main frame  30  with bolts  115  that are mated with bolt holes defining bolt pattern  32 . Inner pivot rings  116  mate with the outer pivot rings  113 , in a manner that they can freely rotate relative to the outer pivot rings  113  and frame  30 . The inner pivot rings  116  attach to the mount frame  112  at bolt pattern  117  defined by pilot hole  317  and an array of tapped holes  217 . There are two bolt patterns  117 , one on each side of mount frame  112 , that define an axis that passes through the centers of the two bolt patterns  117 . This joint is assembled by first inserting the mount frame  112  into the main frame  30 , then installing the inner pivot rings  116  into the pilot holes  317  though the sides of the frame  30 . The inner pivot rings  116  are then attached to the mount frame  112  by installing bolts  118  that mate with tapped holes  217 . The outer rings  113 , which are constructed in  3  sections, are then installed and attached to the main frame  30  by installing bolts  115  that engage tapped holes  232 . The excavation boom is thus able to pivot around the axis  114  to allow control of its position relative to the main frame. 
     FIG. 6  illustrates swivel  120  which includes a frame section  123 , swivel shaft  128 , inner pivot rings  126 ,  127 , and outer pivot rings  125 . The pivot rings  125 ,  126 , and  127  form two rotary supports  122   a  and  122   b  defining a swivel or pivot axis  124 . The rotary support  122   a  comprises an outer pivot ring  125  and an inner pivot ring  126 . Rotary support  122   b  comprises an outer ring  125  and an inner ring  127 . The outer rings of both rotary supports are constructed to be bolted to the frame section  123 . The inner rings  126  and  127  are constructed to be bolted to swivel shaft  128 . In this manner they provide both radial and longitudinal support of the swivel shaft  128 . Frame section  123  is constructed to fit within the mount frame  112  of mounting section  110 . It is secured to mount frame  112  with bolts  121  passing through the mount frame  112  at slots  119  such that the swivel or pivot axis  124  is perpendicular to and substantially aligned with main pivot axis  114 , defined by the main frame  30  and substantially parallel to the ground surface, or the plane defined by the two track assemblies  20 , as illustrated in  FIG. 3 . 
   As illustrated in  FIG. 3  positioning the swivel axis  124  perpendicular to main pivot axis  114  allows the orientation of the head unit  130 , which mounts on the swivel shaft, to be modified relative to main frame and ultimately the ground surface. 
     FIGS. 7 and 8  illustrate the head unit  130 . It includes a frame section  132 , an excavation assembly  140 , and positioning assembly  170 . The excavation assembly  140  comprises a center excavation chain  142 , drive sprockets  144 , driven sprockets  146  mounted on drums  148  which are rotatably mounted on head shaft  150  that is fixedly supported by extendable end section  152  of frame  132 . The centerline of head shaft  150  defines the excavation head shaft axis  151 . Power is transferred from the excavation hydraulic motors  52 , that have been mounted onto the frame section  132  of head unit  130 . Drive sprockets  144  are mounted onto motor shaft  145  which is supported in bearing assemblies  133  supported by frame  132 . Hydraulic motors  52  are mounted onto motor shaft  145  and held from rotating by torque arms  53  as illustrated in  FIG. 9 . The drive sprockets  144  propel the excavation chain  142  which subsequently powers rotation of the sprockets  146 . Sprockets  146  are fixedly mounted onto drums  148  such that whenever the sprocket rotates, the drums are also rotated. The excavation drums  148  are rotatably mounted onto head shaft  150  by bearings  147 , as illustrated in  FIG. 10 . The extendible end section  152  is attached to the frame section  132  at joint  153 . Joint  153  allows the extendible end section  152  to be moved perpendicular to the axis of rotation of the output shaft of drive motor  52  such that the distance between the drive sprockets  144  and the driven sprockets  146  can be adjusted to control chain tension. 
   Excavation chain  142  comprises external flanged side bars  141  and internal side bars  143  and rollers  143   a , as illustrated in  FIG. 11 , and base plates  156 , as illustrated in  FIG. 12 . Base plates  156  are typically bolted to the external flanged side bars  141  with bolts  158  and nuts  159  and include mounts  155  for supporting cutters  154 . Cutters  154  are known in a variety of configurations. It is well known to attach such cutters to chain. Similar cutters are also known to be attached to rotatable drums. The type of cutter or method of mounting are not a portion of this invention, and any such cutter or mount would be useful. 
     FIG. 13  illustrates the outer circumference of the two excavation drums  148  shown as  148 R and  148 L, corresponding to one drum on the left and one on the right, along with the base plates  156  of the excavation chain  142 . The pattern of the cutters  154 , their location and placement and the coordination of this placement for the three separate components, has been found to be critical in optimizing the excavation efficiency of the assembly. One aspect includes the arrangement of the cutters  154  into rows  160  and columns  162 . The columns  162  are parallel to the excavation axis, and spaced to coincide with the base plates  156 . As the chain is rotated the outer circumference illustrated in this  FIG. 13  effectively moves from right to left. Thus, column  162   a  contacts the ground surface first followed by  162   b , followed by  162   c  etc. 
   Following one row  160   a , the first cutter  154   a  is on column  162   h . As the chain and drums are rotated this first cutter  154   a  will contact the ground surface, fracturing the surface and creating a groove. At column  162   i  the second cutter  154   b  is longitudinally spaced, away from the center of the base plate  156 , towards the outer edge, as compared to the first cutter  154   a . This longitudinal spacing defines the angle of the rows  160 . The material contacted by the second cutter  154   b  will have been previously affected by the first cutter  154   a  on one side while on the other side the material will be less affected by any previous cutters. Thus, if any material fractures, there is a higher probability that it will be material between the groove created by the first cutter  154   a  and the groove now being created by the second cutter  154   b , material on the inside of the second cutter  154   b , than on the outside of the second cutter  154   b . Thus material fractured by the second cutter  154   b  will tend to fracture towards the center of the base plates. As the chain and drum continue to rotate the cutters impacting the ground continue to move closer to the edge of the drum, in this case to the edge of drum  148 R. As that row  160  approaches the edge, the longitudinal spacing of the last few cutters is decreased to approximately zero. This is necessary due to the fact that the loading at the ends will be influenced by the sides of the excavated trench. When plunge cutting there will be walls on each side of the excavation assembly  140 . These walls will tend to force material against the outside teeth in such a manner that the loading is higher on these outside teeth. 
   The speed of the outer surface of excavation chain  142  must be coordinated with the speed of the outer surface of the drums  148 R and  148 L in order to maintain the relationship between the cutters mounted to the chain and the cutters mounted to the drums. To achieve this coordination the drums are sized to a specific outer diameter such that the one revolution of the excavation chain results in exactly an integer number of revolutions of the excavation drums. The pattern shown as  148 R includes  28  cutters  154  and represents one complete rotation of the excavation drum  148 . The pattern shown in  FIG. 13  represents exactly ½, ⅓, or ¼ of the total length of the chain. Looking at an individual column there are always six cutters in each column, two on drum  148 L, two on excavation chain  142  and two on drum  148 R. 
   This cutter spacing and the coordination of the excavation chain length with outer diameter of the excavation drums results in consistent placement of the cutters  154  on the excavation drums relative to the cutters  154  on the excavation chain  142 . There is an identical number of cutters  154  in each vertical row, and slightly increased density of cutters  154  on the two outside edges of the excavating drums  148 L and  148 R. Many patterns can be developed, the disclosed pattern comprising a V wherein the legs of the V-pattern pass from the chain to each of the drums, is one example but many others are possible. 
   In operation the track trencher with the new excavation boom of the present invention is useful in surface mining or in surface preparation for road construction. The use of the track trencher for these applications is enhanced by the fact that the excavation assembly  140  always cuts wider than the tracks. One configuration is illustrated in  FIG. 14  where the excavation assembly  140  is positioned with the excavation axis  151  parallel to the main pivot axis  114 . 
   Another configuration is illustrated in  FIG. 15  where the excavation assembly is tilted to its extreme position and excavation axis  151  is at the maximum angle to the tracks  20 . In this configuration the swivel or tilt axis  124  is parallel to the longitudinal axis of the machine. Even in this extreme position the drum  148  will excavate wider than the tracks  20 . 
   Obviously many modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

Summary:
An excavating apparatus having a prime mover with a longitudinal centerline and a main frame with an engine, a ground drive system and an excavation boom operatively attached thereto wherein the excavation boom has a first end and a second end. The first end of the boom is operatively pivotally attached to the main frame along a main frame pivot axis. The main frame pivot axis is transverse to the longitudinal centerline of the prime mover. A head shaft operatively rotatably attached to the second end of the boom and is operatively pivotally attached to the second end of the boom. Also, the excavation drum is mounted onto the head shaft in a manner that the excavation drum cooperates with the excavation chain and a fixed cutter pattern of the excavation chain to stay in consistent alignment with the fixed cutter pattern of the excavation drum.