Abstract:
A method and apparatus for controlling an excavator having a frame, engine, ground supports and an excavation boom with an excavating drum. The method includes fixing the orientation of the boom relative to gravity to approximately control the shape of an excavated ground plane.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application contains disclosure from and claims the benefit under Title 35, United States Code, §119( e ) of the following U.S. Provisional Application: U.S. Provisional Application Ser. No. 60/316,590 filed Aug. 31, 2001, entitled IMPROVED EXCAVATION APPARATUS. 
    
    
     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 the control of 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 to the arrangement of sensors and methods of utilizing sensors, which allows control of the depth of cut, orientation of the resulting new ground surface, and location of the 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 lift 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 pivotally mounted to the frame at a boom mount pivot axis to allow control of the excavation depth. 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 adjusted, relative to the frame and the boom mount pivot axis. 
     Road Bed Preparation 
     The present invention is particularly useful for providing a control system wherein the initial excavation for a road bed can be accomplished in a manner that is accurate and precise allowing the depth of excavation and the related amount of backfill material necessary to be reduced to a minimum. 
     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 an alternative boom; 
     FIG. 2 a  is an enlarged partial side view of a track like that shown in FIG. 2; 
     FIG. 3 is a top view of a track trencher with an alternative boom; 
     FIG. 4A is a preferred embodiment of the hydraulic schematic illustrating an auto down pressure configuration for the boom; 
     FIG. 4B is the preferred embodiment of the hydraulic schematic illustrating an auto down pressure configuration for the stabilizers; 
     FIG. 5 is the preferred embodiment of a hydraulic schematic illustrating the position control configuration; 
     FIG. 6 is the preferred embodiment of a electrical schematic illustrating the pitch control circuit for the boom; 
     FIG. 7 is a schematic illustration of an operator control panel allowing appropriate selection of auto down pressure, position and pitch control; 
     FIG. 8 is a schematic of an alternate embodiment of a control system; 
     FIGS. 9A,  9 B and  9 C are sequential side views that illustrate a trencher traveling along an existing ground surface that includes a bump; and 
     FIGS. 10A,  10 B and  10 C are sequential side views that illustrate a trencher traveling along an existing ground surface that includes a bump like FIGS. 9A,  9 B and  9 C but with the boom set to pitch control using the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings wherein like reference numerals designate identical or corresponding parts throughout the several views, FIGS. 2 and 3 illustrate a track trencher with an alternative excavation boom  100 , as disclosed in co-pending U.S. patent application Ser. No. 10/227,838 Aug. 27, 2002. The track trencher comprises track assemblies  20 , frame  30 , power unit  40 , and excavating boom  100  including head unit  130 , which supports excavation assembly  140 . The orientation of the base machine is defined by the existing ground surface  180 . The areas contacted by the two track assemblies  20  will define the effective ground plane  180 , oriented at an angle relative to gravity, the effective grade. 
     The location and orientation of the excavation assembly  140  will define the new ground surface  182 . This location and orientation is controlled by several elements. The position of the boom  100  relative to frame  30  is controlled with lift cylinders  62 , which effectively rotate boom  100  about axis  114 , defined by frame  30  as parallel to the existing ground surface  180 , to effectively control the excavation depth, relative to the track assemblies  20 . 
     The orientation of the excavation assembly  140 , relative to the frame  30 , is controlled with tilt cylinders  64 , which rotate the head unit  130  about swivel axis  124 . Swivel axis  124 , in this preferred embodiment, is perpendicular to axis  114 , allowing the orientation of the head unit  130  and excavation assembly  140  to be modified relative to axis  114  and the ground plane  180 . Alternatively, a swivel axis, not shown, could be merely parallel with swivel axis  124 . 
     The excavation assembly  140  is designed to be in contact with the ground in order to excavate a certain depth, the difference between the existing ground surface  180  and the new ground surface  182 . The amount of force necessary to hold the excavation assembly  140  in the position to maintain a consistent excavation depth, excavation force, depends greatly on the type of material being excavated. In some conditions the weight of the head unit  130  is sufficient, and the excavation force is equal to the weight of the head unit  130 . At other times additional force is required, and the lift cylinders  62  are utilized to effectively transfer some of the weight of the base machine to the excavation assembly  140 . 
     As shown in FIG. 2, the positioning assembly  170  also affects the loading and position of the excavation assembly  140  relative to the existing ground plane  180 . Stabilizer cylinders  66  extend from the frame of head unit  130  to bogey wheels  172  which may or may not be in contact with existing ground surface  180 . If in contact they carry at least a portion of the excavation load. 
     The positioning assembly  170  (FIGS. 2 and 2 a ) is comprised of a stabilizer frame  176  which connects to the stabilizer cylinder  66  at a pivot point  174 . The stabilizer frame  176  provides mounts for the bogey wheels  172 . The bogey wheel and frame  176  are free to rotate around the pivot point  174 . By freely rotating the pivot point  174  does not need to move as much when encountering relatively small surface irregularities. As illustrated in FIG. 2 a , with certain irregularities, such as bump  185 , the travel of pivot  174  will be approximately ½ the actual height of the bump as can be seen by comparing dimension A to dimension B. 
     The control of the position and orientation of the excavation assembly thus includes appropriate control of the lift cylinders  62 , the tilt cylinders  64  and the stabilizer cylinders  66 . The present invention involves techniques to control the excavation depth, or alternately to control the contour of the new ground surface  182  by coordinated control of these cylinders. 
     One technique for controlling the position of the excavation assembly  140  is to control the excavation force. The excavation force is comprised of a portion of the weight of the excavation boom  100 , that not carried by the base machine, plus the portion of the weight of the base machine transferred to the boom  100  minus the weight borne by the position stabilizer assembly  170 . Controlling the pressure applied to the lift cylinders  62  controls the portion of the weight of the base machine transferred to the boom  100 , a technique known as Auto-Down pressure. The preferred embodiment of the hydraulic circuit  450  that enables this control technique, in the configuration of Auto-Down for the boom  100 , is illustrated in FIG.  4 A. 
     The basic circuit includes a pump assembly  450 , comprising pump  402  and control valves, that are capable of providing pressurized hydraulic fluid to a supply line  452  which transfers the fluid to valve  420 . Valve  420  is a directional control valve, known as a 3-position valve, illustrated directing the hydraulic fluid to port labeled B, and to line  454  which transfers the pressurized fluid to pressure reducing/relieving valve  410 . Valve  420  is controlled to be in this position by energizing solenoid  420 B. 
     The pressure reducing/relieving valve  410  is controlled by valve  456 , a poppet valve. If the solenoid of poppet valve  456  is energized, as illustrated in FIG. 4A, it will open a flow path from the pilot end of valve  410  to relief valve  460  through fluid supply line  458 . The relief valve will control the fluid pressure in fluid supply line  458 , which in turn controls the pressure at which valve  410  effectively operates. Valve  410  effective operates to reduce or relieve the fluid pressure in fluid supply line  462 , to a controlled pressure, as set by the adjustment of relief valve  460 . The fluid, under controlled pressure, in fluid supply line  462  is transferred to poppet valve  464  and counter balance valve  466 . Counter balance valve  466  functions during position control operation, but in the Auto-Down operation is not necessary. Thus, poppet valve  464  effectively bypasses the counterbalance valve  466  by energizing its solenoid at the same time that the solenoid of valve  456  is energized. The two solenoids are simply wired in parallel. 
     As illustrated by this hydraulic schematic of FIG. 4A, the hydraulic fluid is transferred from pump  402  to the cylinders  62  in a manner that the cylinders will exert a constant force, attempting to rotate the boom  100  counterclockwise with the machine as illustrated in FIG.  2 . Hydraulic fluid will flow from the pump  402  to the cylinders  62  at the reduced pressure set by valve  410 , as valve  410  functions as a pressure reducing valve, when the boom  100  rotates counterclockwise. Hydraulic fluid will flow from the cylinders  62  to the tank, as valve  410  functions as a pressure relieving valve, through fluid supply line  468 , when the boom  100  is required to rotate clockwise, as when traveling over a surface irregularity. The desired result is that a nearly fixed amount of force, resulting from the transfer of weight from the base machine to the boom  100 , is applied to the excavation assembly  140 , as the boom  100  is allowed to float to follow the ground surface. 
     FIG. 4B illustrates a preferred embodiment of a hydraulic circuit in a configuration that enables a constant down force on the stabilizer assembly  170 . This circuit operates in a fashion similar to that described for the boom cylinders  62  as illustrated in FIG.  4 A. In the configuration of FIG. 4B, constant down force is applied to the stabilizer assembly  170  by stabilizer cylinders  66 . Hydraulic fluid is transferred from the pump  402  to valve  422  through fluid supply line  452 . From valve  422  the fluid is transferred through counterbalance valve  470 , and pilot operated check valve  472 , both with functions unrelated to the auto down pressure. The fluid is then transferred to pressure reducing/relieving valve  474 . The pressure reducing/relieving valve  474  is controlled by valve  476  and relief valve  460 . 
     As illustrated in FIG. 4B, the solenoid of valve  476  is energized, allowing the pressure in pilot line  458  to effectively control valve  474 . Valve  474  functions to reduce the pressure from the pump  402  to a set value and by relieving the pressure, potentially generated by the cylinders  66 , to that same pressure. This allows the stabilizer cylinders  66  to move, to follow the topography, while maintaining a consistent force. This force is adjustable by adjusting the pressure in fluid transfer line  458 , by adjusting relief valve  460 . The pressure is adjustable from the operator&#39;s station  300  with adjustment  302 , as illustrated in FIG. 7, which effectively adjusts relief valve  460  which is physically located at the control panel. An operator, using pressure gauge  303 , can monitor the pressure in fluid transfer line  458 . 
     The operator&#39;s station  300  also includes a selector switch  304 , with 3 positions  304 A,  304 B and  304 C. In position  304 A Auto-Down is selected to control pressure to the boom, which increases the excavation force by transferring additional weight to the boom with lift cylinders  62 . 
     Still referring to FIG. 7, in position  304 C Auto-Down is selected for the Stabilizer, to apply a controlled pressure to the stabilizer cylinders  66 . The net effect on the excavation force is opposite that described for the auto down pressure for the boom. The controlled pressure is controlling the weight borne by the stabilizer cylinders  66 , which reduces the excavation force. 
     Still referring to FIG. 7, in position  304 B Auto-Down is turned off, resulting in de-energizing of the solenoids for valves  464 ,  456  and  476  to effectively disable the pressure reducing/relieving valves  410  and  474 . Disabling these valves  464 ,  456  and  476  will allow the hydraulic circuit to function in a position control mode, as illustrated in FIG.  5 . 
     In some applications control of position/orientation is useful. The operator station  300  of FIG. 7 illustrates two position control options: pitch control and position control. The preferred hydraulic circuit is illustrated in the configuration for position control in FIG. 5 where valve  420  controls position of the boom  100 , valve  422  controls position of the stabilizer cylinders  66 , and valve  424  controls the tilt cylinders  64 . These valves  422  can be controlled manually by switches  320 ,  322  and  324  as illustrated in FIG. 7, if the valves  422  are actuated by solenoids. Each of the switches  320 ,  322  and  324  has a first position in which the appropriate cylinder  66  will be extended, a second position in which the appropriate cylinder  66  will be retraced and a third, middle, position in which the cylinders  66  are held in position. They could alternately be controlled mechanically through cables or direct linkage. Many techniques of controlling position control valves are well known, any such technique could be utilized. 
     Pitch control is another form of position control, and can be selected from operator station  300  (FIG.  7 ). Switch  326  allows selection of pitch control of the boom  100 , and switch  328  allows selection of pitch control of the tilt cylinders  64 . The pitch control is enabled by the preferred embodiment of electrical circuit illustrated in FIG. 6 for the boom  100 , comprising a four-way, three-position solenoid valve  420 , corresponding to valve  420  illustrated in FIGS. 4A,  4 B and  5 , and a tilt sensor  351 . Tilt sensor  351  includes a center member  356  that freely rotates in housing  358  such that its position is determined by gravity. The tilt sensor  351  is secured to the excavation boom  100 , as illustrated in FIG. 2, contains two sensor pads  352  and  354 . When the housing is tilted clockwise, indicating the boom  100  has rotated clockwise, the center member  356  will contact pad  354 . This will result in energizing solenoid  420 B which will shift valve  420  into a position to direct oil to rotate the excavation boom  100  counterclockwise. Many types of tilt sensors are commercially available including those wherein there is no physical contact, wherein there are magnetic reed switches and the center member includes a magnet that causes the reed switches to close when in close proximity. The type of switch is not important. 
     Solenoid  420 B will remain energized until the boom  100  has rotated counterclockwise far enough such that the center member  356  of tilt sensor  350  is no longer contacting pad  354 . The system operates in a similar manner if the boom  100  is positioned too far counter clockwise wherein pad  352  is contacted, solenoid  420 A is energized resulting in the boom moving clockwise. 
     A similar electrical circuit will enable pitch control for the tilt cylinders  64  with a tilt sensor  350  installed to detect the orientation of the head unit  130  (as illustrated in FIG. 2) and is enabled by switch  328 . 
     Operation 
     In operation, the auto-down control is given precedence. For instance, referring to FIG. 7, the operator can select auto-down pressure for the boom  100 , by positioning switch  304  in position  304 C, and at the same time select pitch control for the boom  100 , by positioning switch  326  in position  326 A. In this scenario, the auto-down pressure overrides, and the tilt sensor is ignored. 
     This precedent relationship can be defined by appropriate wiring techniques, or could alternately be defined using a programmable logic controller of any known type. 
     The purpose of the auto-down control has previously been described in the description of the hydraulic circuits: to provide a consistent force to either the boom, to increase the excavation force, or to the stabilizer cylinders  66  to effectively reduce the excavation force. A preferred operating configuration is to have the auto-down control activated for the boom while the stabilizer cylinders  66  are set at a given position. This provides consistent load on the excavating assembly  140  while providing depth control with the position of the stabilizer cylinders  66 . 
     Referring again to FIG. 7, the pitch control (switch  328 ) for the tilt provides a mechanism to hold the tilt of excavation assembly  140  constant to provide a new ground surface  182  of a consistent pitch or grade. The purpose of the pitch control of the boom  100 , using switch  328 , is to provide a new ground surface  182  that is smoother than the existing ground surface  180 . 
     This is illustrated in FIGS. 9A,  9 B,  9 C,  10 A,  10 B and  10 C. FIGS. 9A,  9 B and  9 C illustrate trencher  10  traveling along an existing ground surface  180  that includes a bump  184 . In these figures, the excavation boom  100  is position controlled and its orientation relative to the base machine is fixed, while the stabilizer cylinders  66  are controlled for auto-down pressure. 
     As illustrated in FIG. 9B, the tracks will initially climb the bump  184 , causing the excavation assembly  140  to be lowered. The machine will continue to travel along the ground and, as illustrated in FIG. 9C, the bump  184  will eventually be under the opposite end of the tracks. In this position the excavation assembly would be raised, to the point it will not even contact the ground. The net effect is that the new ground plane  184  will contain a bump  186  that is larger than the original bump  184  as illustrated in FIG.  9 C. 
     FIGS. 10A,  10 B and  10 C illustrate the same base trencher of FIGS. 9A,  9 B and  9 C traveling over the same bump  184 , but this time with the boom  100  set, using switch  238 , to pitch control. Using the pitch control, the boom  100  is controlled such that its engagement with the ground is improved, and the bump  186  in the new ground surface  184  is less defined than the original bump  184 . In this manner the surface is improved. FIG. 10A looks essentially like FIG.  9 A. However, in FIG. 10B it can be seen that the pitch control has pivoted the boom  100  upwardly compared to the boom  100  shown in FIG. 9B so that the bump  186  is reduced in FIG. 10B compared to bump  186  in FIG.  9 B. In FIG. 10C, the boom  100  is now lowered with respect to the surface  180  compared to the boom  100  in FIG. 9C so that it can better remove bump  184 . 
     FIG. 8 illustrates several alternative embodiments of a control system of the present invention that would provide increased capability. A hydraulic control system  60  includes lift cylinder(s)  62 , tilt cylinder(s)  64  and stabilizer cylinder(s)  66  in addition to control valves  67 . 
     A controller  200  is capable of accepting inputs and controlling outputs to control various mechanical elements of the trencher. The control system would be capable of controlling many systems other than illustrated in this Fig, including the drive motor to the tracks  24  and excavation boom hydraulic motor  52  as disclosed in U.S. Pat. Nos. 5,590,041; 5,574,642; 5,509,220 which are all incorporated herein by reference. For the purpose of explaining the current invention, the control aspects related to positioning the excavating boom are included in FIG.  8 . The primary outputs required for this control are the outputs for controlling valves  67  and display  230 . Inputs could include: 
     1) an indication of the relative position of the head unit  130  as tilted on axis  124 , which can be indicated with a rotary potentiometer  202 ; 
     2) an indication of the relative position of the mount section  110  as tilted on axis  114 , an indication of cutting depth, which can be indicated with a rotary potentiometer  204 ; 
     3) an indication of the position of the stabilizers as indicated with a rotary potentiometer  203 ; 
     4) An indication of the relative height of the right side of the excavating drum  148 R, which can be indicated with a laser target  206 ; 
     5) An indication of the relative height of the left side of the excavating drum  148 L, which can be indicated with a laser target  208 ; 
     6) An indication of the pitch of the new ground surface  172 , which can be indicated by a tilt sensor  210  mounted on the head unit  130  of the excavating boom assembly  100 ; 
     7) An indication of the depth of cut which can be indicated by a tilt sensor  211  mounted in fixed relationship to axis  124 ; 
     8) An indication of the position of the excavating boom assembly  100  which can be indicated by a Global Position Sensor  212  mounted onto the head unit  130 ; 
     9) An indication of the sub-surface conditions can be determined by a GPR unit  214  or other sensors. Techniques of performing these types of subsurface surveys are disclosed in U.S. Pat. Nos. 6,195,922; 6,119,376; 5,704,142; 5,659,985; 5,553,407 and pending application Ser. No. 60/211,431 all of which are hereby incorporated by reference. Mounting the sensors onto the track trencher in an appropriate location will provide the capability to do real-time monitoring and control of the excavating process. 
     10) An alternate and preferable technique is be to mount a GPS sensor  216 , subsurface sensors like a GPR  218  or any other such sensor, possibly a relative height sensor as in a laser target  220  onto a separate cart and perform preliminary surveys. The information generated by the preliminary surveys could be contained in a database  222 , post processed by a planning/analysis system  224  wherein the 3-D contour of the desirable geology is identified. The contours can be evaluated and an optimized excavation route determined optimizing production rates, minimizing travel/turn requirements, minimizing any non-productive activity required, etc. The resulting excavation plan can then be insert into the controller  200  where it may be used to provide a control signal to an operator via display  230 , or alternatively to control the excavator directly. 
     With this or similar arrangements of components the excavation process can be controlled in a variety of manners to achieve various results. 
     If a subsurface survey is completed and a map/plan developed, the inputs which allow determination of the depth of the excavation, the rotary pots  204  and  202  and height sensors  206  and  208 , can be used to control the excavator to excavate to a certain depth while also maintaining control to a set depth of cut. The inputs can be used to control both in a manner to optimize the excavation process. 
     Likewise if the subsurface survey is completed in real-time, the ultimate depth of the excavation, the location of the new ground surface  182 , can be determined in a manner to optimize both the location of that surface and the depth of cut. 
     The result of the various embodiments is an excavation machine that provides a variety of control modes allowing the operator to select the mode best suited for the conditions. The embodiments range from basic switches with no controller, to the most complex system comprising a controller and the ability to incorporate logic. 
     A primary consideration in this excavation process is the quality of the excavated material. The previously described control systems provide a means of varying operation and control associated with depth of cut to affect the quality of this final product. Additionally the depth of cut can be utilized in conjunction with controlling the ground speed of the excavator to optimize the quality of the resulting product. It has been found that operating the machine in a mode of relatively high ground speed, with relatively shallow excavation depth yields the best quality of product and the highest productivity, for certain materials. With the control systems of the present invention the operation of the excavation machine can be controlled to achieve the desired result. 
     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.