US20060042804A1

US20060042804A1 - Work implement rotation control system and method

Info

Publication number: US20060042804A1
Application number: US10/927,306
Authority: US
Inventors: Patrick Pecchio
Original assignee: Caterpillar Inc
Current assignee: Caterpillar Inc
Priority date: 2004-08-27
Filing date: 2004-08-27
Publication date: 2006-03-02
Also published as: DE102005031135A1

Abstract

A system for automatically moving a work implement of a work machine includes a position monitoring system configured to track a position of the work implement relative to a mapped landscape. A controller is configured to change an angle of the work implement relative to a direction of travel of the work machine in response to information from the position monitoring system.

Description

TECHNICAL FIELD

This disclosure is directed to a system and method for controlling the movement of a work implement and, more particularly, to a system and method for controlling the angle of a work implement relative to a direction of travel of the work machine.

BACKGROUND

Work machines such as motor graders, track-type tractors (e.g. bulldozers), wheeled tractors, loaders, excavators, etc. can perform many functions, which may require a control input device. Controlling the many control input devices on a work machine may require a highly skilled operator. Even with a skilled operator, manual control of a work implement to accomplish many earth moving tasks, particularly finish work such as finish grading, is not always accurate and can require multiple trials to achieve a desired result. Such duplication of work can be inefficient, time consuming, and fatiguing to the operator.
Systems have been developed for automating certain functions of a work machine in an attempt to improve efficiency and reduce the skill level required to operate the machine. For example, U.S. Pat. No. 5,375,663 (“the '663 patent”) issued to Teach on Dec. 27, 1994, describes a system and method for automatic control of a bulldozer blade based on mapped information correlated to a worksite. The system of the '663 patent includes various laser devices and sensors to track the height of the blade as the bulldozer traverses the work site landscape. This system is configured to automatically control the blade height based on the location of the blade with respect to the worksite and the desired elevation at that location.
Although the system of the '663 patent may improve grading accuracy, and reduce the level of skill needed to operate the machine, it does not make efficient use of each pass of the blade. For example, while the system of the '663 patent includes automated control of the amount of material cut from a particular location at a worksite, the system does not include automated features for efficient distribution of the material to other areas of the worksite.
The disclosed control system is directed towards overcoming one or more of the problems set forth above.

SUMMARY OF THE INVENTION

In one aspect, the present disclosure is directed to a system for automatically moving a work implement of a work machine. The system includes a position monitoring system configured to track a position of the work implement relative to a mapped landscape. The system may also include a controller, which may be configured to initiate movement of the work implement in response to information from the position monitoring system to change the angle of the work implement relative to a direction of travel.
In another aspect, the present disclosure is directed to a motor grader including a cab, a traction system, a power source, and a work implement positionable at an angle relative to a direction of travel of the motor grader. The position monitoring system may track the position of the work implement. The motor grader may also include a controller, which may be configured to initiate movement of the work implement in response to information from the position monitoring system to change the angle of the work implement relative to the direction of travel.
In another aspect, the present disclosure is directed to a method of controlling a work implement for a work machine. The method includes determining an actual position of a work implement relative to a work site. At least two predetermined areas designated for an elevation change may be located with respect to the actual position of the work implement. An angle of the work implement relative to a direction of travel of the work machine may be controlled in response to a relationship between the at least two predetermined areas designated for an elevation change.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic illustration of a work machine according to an exemplary disclosed embodiment;
FIG. 2 is a diagrammatic exploded view illustration of a drawbar-circle-moldboard assembly according to an exemplary disclosed embodiment;
FIG. 3 a is a diagrammatic top view representation of a work implement blade swivel motion according to an exemplary disclosed embodiment;
FIG. 3 b is a diagrammatic side view representation of a work implement blade tilt motion according to an exemplary disclosed embodiment;
FIG. 3 c is a diagrammatic front view representation of a work implement blade height adjustment according to an exemplary disclosed embodiment;
FIG. 3 d is a diagrammatic front view representation of a work implement blade slope adjustment according to an exemplary disclosed embodiment;
FIG. 3 e is a diagrammatic front view representation of a work implement blade side shift motion according to an exemplary disclosed embodiment;
FIG. 4 is a block diagram representation of a work implement control system according to an exemplary disclosed embodiment;
FIG. 5 is a diagrammatic top view representation of a motor grader at a work site according to an exemplary disclosed embodiment;
FIG. 6 is a flow chart of an exemplary process for controlling work implement angle according to an exemplary disclosed embodiment;
FIG. 7 is a flow chart of another process for controlling work implement angle according to an exemplary disclosed embodiment;

DETAILED DESCRIPTION

FIG. 1 illustrates an exemplary embodiment of a work machine 10, which includes a system for automatically moving a work implement 12. Although-work machine 10 is shown as a motor grader, work machine 10 may include other types of work machines such as, for example, track-type tractors (e.g. bulldozers), wheeled tractors, loaders, excavators, and any other type of work machine. Work machine 10 may include work implement 12, a cab 14, a power source 16, one or more traction devices 18, and position monitoring system components 20, including a controller 22, one or more Global Positioning System (GPS) receivers 24, a processor 26, and a monitor display 28.
In an exemplary embodiment, work implement 12 may include a blade 30. In the case of a motor grader, blade 30 may be attached to a drawbar/moldboard/circle assembly (DMC) 32, as shown in FIG. 2. DMC 32 may include a drawbar 34, a moldboard 36, and a circle 38. Blade 30 may be attached to circle 38, which may be rotatably attached to moldboard 36. Moldboard 36 may be attached to drawbar 34, which may be attached to a front portion 40 of work machine 10 with a pivoting joint 42. Circle 38 may swivel about an axis 44 in a direction 46. Because circle 38 may be rotatably attached to moldboard 36 and fixedly attached to blade 30, rotation of circle 38 may translate into swivel of blade 30.
Blade 30 may be adjusted in several degrees of freedom. FIG. 3 a is a top view of blade 30 showing a swivel motion of blade 30. A dashed element 48 represents blade 30 after it has been swiveled. Swivel of blade 30 results in a change in an angle 50 of blade 30 relative to a direction of travel 52 of work machine 10.
In addition to swivel, blade 30 may also be tilted forward and back. FIG. 3 b is a side view of blade 30 showing a tilt motion of blade 30. A dashed element 54 represents blade 30 after it has been tilted. Tilt of blade 30 occurs when an upper edge 56 of blade 30 and/or a lower edge 58 of blade 30 are shifted forward and/or rearward with respect to one another to change an angle 60 between an axis 62 of blade 30 and direction of travel 52.
For purposes of this disclosure, the term “rotation” refers to either or both of swivel and tilt of work implement 12, as described above. For example, “rotation” of blade 30 may include any motion resulting in a change in angle 50 and/or angle 60.
In addition to rotation, blade 30 may be raised and lowered to adjust a height of blade 30. FIG. 3 c illustrates a change in a height 64 of blade 30 off a work surface 66 (e.g. the ground). A dashed element 68 represents blade 30 after it has been raised.
FIG. 3 d illustrates a change in the slope of blade 30. A dashed element 70 represents blade 30 after a change in slope. Slope is a function of a difference between a height 72 at a first end 74 of blade 30 and a height 76 at a second end 78 of blade 30. The slope may be determined by dividing the difference between height 72 and height 76 by a length 80 of blade 30. Adjusting the slope can change an angle 82 between a longitudinal axis 84 of blade 30 and work surface 66.
FIG. 3 e illustrates a side shift motion of blade 30 by a distance 86. A dashed element 88 represents blade 30 after a side shift.
Referring to FIG. 4, work machine 10 may include a position monitoring system 90, which may be configured to track the position of work implement 12 relative to a mapped landscape. Position monitoring system 90 may include controller 22, GPS receivers 24, processor 26, monitor display 28, a memory 92, an angle position sensor 94, and a slope sensor 96.
Position monitoring system 90 may include memory 92 for storing information. Memory 92 may be incorporated into a unit with controller 22 or with processor 26 or in a single unit including both controller 22 and processor 26. Memory 92 may store maps of a work site. The maps may include elevation maps of the existing landscape, as well as maps reflecting the desired contour of the work site. The maps may also include differential maps illustrating the differences in elevation between the existing landscape and the desired contour of the work site.
The maps may be generated by position monitoring system 90. The maps may be generated by driving around a worksite collecting information along the way. By driving over the entire worksite, position monitoring system 90 may record the actual elevation at each area of the work site. Position monitoring system 90 may generate a map of the worksite from this recorded elevation data.
Also, processor 26 may be configured to superimpose or compare elevation maps of the existing landscape at a worksite to maps of the desired contour of the worksite. From the comparison, processor 26 may generate maps indicating locations of predetermined areas of the mapped landscape that are designated for an elevation change. The designation of areas, at the work site, for an elevation change may be established for the entire work site prior to beginning operation of work machine 10 or may be established as work machine 10 traverses the work site.
In addition, maps may be downloaded or programmed into position monitoring system 90 from an outside source. For example, when a machine is designated for use at a particular work site, pre-established maps of that work site may be downloaded into memory 92. Downloading or programming of information into memory 92 may be performed using external devices such as laptops, PDAs, etc. Information transfer to memory 92 may also be performed wirelessly with a network connection to laptops, PDAs, etc., or to a central server at an offsite location.
Memory 92 may also store other information, such as, for example, positional information about work machine 10, positional information about work implement 12, and positional information about obstacles at the work site. This information may also be incorporated into one or more maps of the worksite.
Position monitoring system 90 may also include monitor display 28 in cab 14 for displaying information to an operator. Monitor display 28 may be any kind of display, including screen displays, such as, for example, cathode ray tubes (CRTs), liquid crystal displays (LCDs), plasma screens, and the like.
Monitor display 28 may display maps stored in memory 92 or maps generated by position monitoring system 90. Monitor display 28 may also represent the past, present, and/or projected future position and orientation of work machine 10 and work implement 12 in relation to the maps. For example, monitor display 28 may show a trail indicating where work machine 10 has traveled within the work site. Similarly, monitor display may show a projected route based on the current heading of work machine 10, or a suggested route for the operator to follow. Monitor display 28 may also display other information unrelated to position monitoring system 90, such as, for example, the amount of time the machine has been operating, work machine systems information (e.g. oil pressure, hydraulic fluid pressure, coolant temperature, etc.), and any other information desired to be displayed to the operator.
Position monitoring system 90 may further include processor 26. Processor 26 may be located at any suitable location on work machine 10. Processor 26 may be contained in its own housing or, alternatively, may be housed with other components of work machine 10.
Processor 26 may receive information from any source from which information is desired to be processed. In particular, processor 26 may receive information about the position and orientation of work implement 12 as well as the speed of work machine 10. Processor 26 may receive this information from GPS receivers 24, angle position sensor 94, slope sensor 96, and a work machine speed sensor. Processor 26 may also receive information from memory 92.
Processor 26 may be configured to determine which movements of work implement 12 are desired and at what rate they should be made, based on information it receives. Processor 26 may send signals to controller 22 communicating these desired movements. Processor 26 may also be configured to send signals to monitor display 28 to display the information that processor 26 receives and/or processes.
Controller 22 may also be located anywhere on board work machine 10. Controller 22 may be contained in its own housing or, alternatively, may be housed with other components of work machine 10, including for example, processor 26. Controller 22 and processor 26 may be independent components if, for example, position monitoring system 90 has been retrofitted to work machine 10, wherein work machine 10 was already equipped with controller 22. As a further alternative, one of controller 22 and processor 26 may be omitted and its functions performed by the other.
In any of the aforementioned arrangements, controller 22 may be configured to receive information from processor 26 regarding the desired movements of work implement 12. Controller 22 may also be configured to initiate movements of work implement 12 in response to information from processor 26. Controller 22 may be configured to initiate swivel, tilt, height adjustment, slope adjustment, side shift, and any other desired movements of work implement 12. In addition, controller 22 may be configured to vary the rate of rotation of work implement 12 as determined by processor 26, based on the speed of work machine 10 and/or a distance to a predetermined cut or fill area.
Position monitoring system 90 may be configured to track the position of work implement 12 in three dimensions. By using this tracking function, position monitoring system 90 may also update the elevation maps of a work site as work implement 12 modifies the contour of the landscape. In order to do this, the height and slope of work implement 12 may be recorded as work implement 12 engages the landscape at each location while work machine 10 traverses the work site. This recorded information may be used to update a map of actual elevation at the work site.
Position monitoring system 90 may also include one or more GPS receivers 24 for receiving signals from one or more GPS satellites 98. A local positioning unit 100 may be used to supplement GPS receivers 24. Local positioning unit 100 may be a reference station, at or near the work site, which enables GPS receivers 24 to more accurately monitor the position of work implement 12.
In operation, each of GPS receivers 24 may communicate with one or more GPS satellites 98 to determine its position with respect to a selected coordinate system. GPS receivers 24 may be attached to one or more locations on work implement 12, preferably at one or both ends.
A single GPS receiver 24 mounted on work implement 12 may determine the position of work implement 12 relative to a mapped landscape. With more than one GPS receiver 24, the orientation of work implement 12 may also be determined. In an exemplary embodiment, work implement 12 may have two GPS receivers 24 mounted on it. The two GPS receivers 24 may be placed at or near the ends of work implement 12, so as to determine the position of each of ends. By knowing the position of each end of work implement 12, processor 26 may determine the orientation of work implement 12. For example, processor 26 may determine swivel angle by determining the position of the two ends of work implement 12 relative to one another. Similarly, processor 26 may determine the slope of work implement 12 by comparing the height of one end of work implement 12 to the height at the other end.
While two GPS sensors 24 may be mounted on work implement 12, certain embodiments may include just one GPS sensor 24 mounted on work implement 12. In an exemplary embodiment, work implement 12 may have a single GPS sensor 24 at one end for determining its location at a work site. Angle position sensor 94 may be included on work implement 12 for determining swivel angle. Work implement 12 may also include slope sensor 96 for detecting the slope of work implement 12. The position and height at one end of work implement 12 may be determined by GPS receiver 24. The swivel angle of work implement 12 may be determined by angle position sensor 94, rather than by determining the position of both ends of work implement 12 with GPS receivers 24. Similarly, the slope of work implement 12 may be determined by slope sensor 96 rather than by comparing heights measured by GPS receivers 24 at both ends of work implement 12.
Local positioning unit 100 may be any system for determining the position of work implement 12 in a coordinate system. Local positioning unit 100 may be placed at a surveyed location with a known position. Local positioning unit 100 may be part of a differential GPS, and may include a GPS receiver 102. GPS receiver 102 may be able to determine the position of local positioning unit 100. Position monitoring system 90 may compare the known (surveyed) position of local positioning unit 100 with the position determined by GPS receiver 102. Position monitoring system 90 may calculate a correction factor for any error in the position determined by GPS receiver 102. This correction factor may be used to correct errors in the positions determined by GPS receivers 24 on work implement 12. Correction of these errors may enable a more accurate position of GPS receivers 24 (and therefore work implement 12) to be determined.
Alternatively, local positioning unit 100 may be a laser-based system for determining the position of work implement 12 in the work site. Local positioning unit 100 may include a transceiver for communicating with work machine 10. Such systems may be used in a similar manner to a differential GPS as discussed above to improve the accuracy of position monitoring system 90.
FIGS. 5-7, which are discussed in the following section, illustrate the operation of a work machine utilizing embodiments of the disclosed system.

INDUSTRIAL APPLICABILITY

The disclosed system may be applicable to a variety of work machines, including motor graders, track-type tractors (e.g. bulldozers), wheeled tractors, loaders, excavators, and any other work machine that may include a work implement. The disclosed system provides automation of work implement motion that can increase efficiency and accuracy of work machine operations. For example, the use of earth-moving work machines can involve the movement of earth or other materials from one place to another. It may be desirable to remove material from one location and deposit the same type of material at a different location. The disclosed control system can automatically move work implement 12 such that, during any given pass of work implement 12, material removed from one location may be automatically deposited at one or more desired locations.
FIG. 5 depicts an exemplary work machine 10 within an exemplary work site. Selection of a desired location to deposit material may depend, at least in part, on its proximity to the location from which the material was removed. For example, processor 26 may analyze information about a work site within a work zone 104, in proximity to work machine 10, to determine which areas within work zone 104 are designated to have material removed and which are designated to have material added.
A work zone may be of any size or shape. In an exemplary embodiment shown in FIG. 5, work zone 104 may be an area around work machine 10, within which work machine 10 could travel during a predetermined period of time. For example, work zone 104 could include all areas that work machine 10 could cover, at its current speed, within the next few seconds or minutes.
Work zone 104 may include at least the area directly ahead of work machine 10, and may be at least as wide as work implement 12. In addition, work zone 104 may also be expanded to include all areas that the machine could cover if it were steered to one side or the other. This expanded portion of work zone 104 may be generally the shape of a baseball diamond, as shown in FIG. 5. Also, because work machine 10 may deposit material to the side of the machine (by swiveling work implement 12 to one side), work zone 104 may be wider than work implement 12.
The size and shape of work zone 104, as well as the predetermined period of time, may be fixed at universally effective values for all operating conditions of work machine 10. As an alternative, these values may be automatically adjusted to suit the current operating conditions of work machine 10. As a further alternative, these values may be chosen by an operator to suit the current task. Further still, modes may be selected between these alternatives to allow an operator to choose between fixed values, automatic adjustment, manual settings, and combinations thereof.
As work machine 10 traverses the work site, processor 26 may analyze the landscape in work zone 104 and determine which areas require elevation changes. Processor 26 may select, from these areas, those that will be involved in the next one or more movements of work implement 12.
Although the located areas may be selected from a collection of predetermined areas within work zone 104, they may, alternatively, be selected in any suitable manner from amongst all areas at the work site that have been designated for an elevation change. In such a case, processor 26 may determine an intended route, covering the entirety of the work site and select predetermined areas designated for an elevation change along the entire route. As yet another alternative, processor 26 may analyze the areas designated for an elevation change for the whole work site and determine an intended route based on the location of those areas.
One method of operation may include determining differences between the actual and desired elevations for at least a first area 106 and a second area 108 designated for an elevation change, as shown in FIG. 5. Swivel of work implement 12 may be controlled to deposit material in the area where the difference is determined to be greatest. In other words, work machine 10 determines which of areas 106 and 108, is furthest below or least above the desired elevation and deposits the material there.
Another method of operation may include selecting a location designated for a decrease in elevation, such as a cut area 110, and a location designated for an increase in elevation, such as area 108, which may be a fill area. Material may be removed (“cut”) from cut area 110 and automatically deposited at area 108 by swiveling work implement 12.
In situations where a selected cut area 110 and fill area, such as area 108, are not directly adjacent one another, it may be desirable to carry material removed from cut area 110 over a distance 112 prior to depositing it at a fill area, such as area 108. In these situations, controller 22 may maintain longitudinal axis 84 of work implement 12 substantially orthogonal to direction of travel 52 after removing the material. Doing so may enable work implement 12 to carry the material over distance 112 prior to automatically swiveling to deposit the material at area 108.
The rate of swivel of work implement 12 may be linked to the speed of work machine 10. For example, the rate of swivel may increase with the speed of work machine 10. Conversely, the rate of swivel may also be decreased as the speed of work machine 10 increases. The relationship may or may not be linear and may be described with many different functions, including, but not limited to, non-linear functions, step functions, and exponential functions. The relationship between rate of swivel and the speed of work machine 10 may be varied during operation of work implement 12. For example, rate of swivel may decrease linearly as the speed of work machine 10 decreases, but, as the speed of work machine 10 approaches zero, the rate of swivel may decrease less rapidly, so as to avoid reducing the rate of swivel too much. Similarly, as the speed of work machine 10 approaches its maximum, the speed of swivel may increase less rapidly, so as to avoid swiveling too fast, or too much.
The rate of swivel may also depend on the distance between work machine 10 and predetermined cut and fill areas. This relationship may vary as greatly as the relationship between rate of swivel and the speed of work machine 10 discussed above. Also, the relationship may be varied during operation of work implement 12. For example, when a cut area, such as cut area 110, as shown in FIG. 5, is relatively close to a fill area, such as area 108, work implement 12 may be required to swivel significantly over a short distance 112 of machine travel. Therefore, initially, the short distance 112 to area 108 would require a relatively fast swivel of work implement 12. However, as work machine 10 approaches area 108 (i.e. as a distance 114 from work machine 10 to area 108 approaches zero) and angle 50 of work implement 12 approaches the desired angle, the rate of swivel would slow down.
The desired change in elevation at any given location may be great enough that the entire change may not be possible to achieve with a single pass of work implement 12. Controller 22 and position monitoring system 90 may be configured to take this into account and limit the amount of material that work implement 12 may remove in a single pass. This may be accomplished by limiting the depth below the actual elevation at which work implement 12 may be set and/or by monitoring the actual load on work implement 12.
The load on work implement 12 during operation may also affect swivel of work implement 12. For example, while material is being carried from one location to another, work implement 12 must remain in contact with the ground. As a result, additional material may be loaded onto work implement 12 during this process. Because of this, it may not be practical to maintain work implement 12 substantially orthogonal to direction of travel 52, if doing so would cause an amount of material to load on work implement 12 that exceeds its load limit. Accordingly, while carrying material, work implement 12 may be automatically swiveled based on the monitored load, in order to deposit some material along the way, so as to maintain an acceptable load on work implement 12.
FIG. 6 illustrates one possible method of depositing material. At step 116, position monitoring system 90 may determine an actual position of work implement 12 relative to a work site. This position may be determined by processor 26, using information from one or more GPS receivers, as discussed above.
At 118, processor 26 may update the actual elevation in one or more maps stored in memory 92. As discussed above, this update may be conducted by recording the height and slope of work implement 12 as work machine 10 traverses the work site.
At 120, position monitoring system 90 may locate, with respect to the actual position of work implement 12, at least two predetermined areas designated for an elevation change. These predetermined areas may be selected from an analysis of the entire work site or a smaller subset thereof.
At 122, processor 26 may determine a first difference between an actual elevation and a desired elevation at a first predetermined area and a second difference between an actual elevation and a desired elevation at a second predetermined area. These differences may be determined by comparing an elevation map of the existing landscape at the work site with an elevation map of the desired contour of the landscape. At 124, a comparison may be made between the first difference and the second difference. Comparing these differences determines which of these two areas is most appropriate for depositing additional material.
At 126, controller 22 may control swivel of work implement 12 based on the comparison between the two differences. Specifically, controller 22 may swivel work implement 12 to deposit material at the predetermined area that is furthest below the desired elevation or least above the desired elevation, in comparison to the other located area or areas. For example, work machine 10 may remove material from a cut area and processor 26 may determine where to deposit the material by determining which of a plurality of fill areas is furthest below the desired elevation at its respective location. The process may repeat, continuously analyzing the landscape and controlling work implement 12 based on that analysis.
FIG. 7 illustrates one possible method of moving material from one location to another. In this method, processor 26 may also follow steps 116-120 described in connection with FIG. 6. In addition, at 128, processor 26 may select a first predetermined location that is designated for a decrease in elevation, and at 130, may select a second predetermined location, forward of work machine 10 that is designated for an increase in elevation. These locations may be selected in a number of ways, as discussed above, from maps of the work site stored in memory 92.
At 132, work implement 12 may be used to remove material from the location designated for a decrease in elevation. As work machine 10 passes over the location designated for a decrease in elevation, the height and slope of work implement 12 may be automatically controlled to remove a desired amount of material.
At 134, controller 22 may maintain longitudinal axis 84 of work implement 12 substantially orthogonal to direction of travel 52 of work machine 10. Work implement 12 can be maintained in this orientation while work machine 10 is proceeding from the first location to the second location to carry the material to the second location as needed.
At 136, with work implement 12 loaded with material, controller 22 may automatically swivel work implement 12 to deposit at least some of the material at the second location to thereby increase the elevation at the second location. This process may repeat continuously as well.
It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed work implement control system without departing from the scope of the invention. Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope of the invention being indicated by the following claims and their equivalents.

Claims

1. A system for automatically moving a work implement of a work machine, comprising:

a position monitoring system configured to track a position of the work implement relative to a mapped landscape; and

a controller configured to change an angle of the work implement relative to a direction of travel of the work machine in response to information from the position monitoring system.

2. The system of claim 1, wherein the controller is further configured to adjust at least one of a slope of the work implement and a height of the work implement in response to the information from the position monitoring system.

3. The system of claim 1, the system further including a memory, and wherein the controller is configured to initiate the change in the angle of the work implement based on a location of at least one predetermined area of the mapped landscape that is stored in the memory and designated for an elevation change.

4. The system of claim 1, wherein the controller is further configured to:

determine a first difference between an actual elevation and a desired elevation at a first location on the mapped landscape;

determine a second difference between an actual elevation and a desired elevation at a second location on the mapped landscape; and

change the angle of the work implement relative to the direction of travel based on a comparison of the first difference and the second difference.

5. The system of claim 4, wherein at least one of the actual elevation and the desired elevation at the first location is pre-stored in a memory, and at least one of the actual elevation and the desired elevation at the second location is pre-stored in the memory.

6. The system of claim 4, wherein the controller is further configured to rotate the work implement such that the work implement deposits material at the first location if the first difference is less than the second difference and at the second location if the second difference is less than the first difference.

7. The system of claim 1, wherein the controller is further configured to:

select a first predetermined location that is designated for a decrease in elevation;

select a second predetermined location designated for an increase in elevation, wherein the second location resides at a position forward of the work machine;

position the work implement to enable removal of material from the first location; and

automatically change the angle of the work implement relative to the direction of travel to deposit at least some of the material at the second location.

8. The system of claim 7, wherein the controller is further configured to vary the rate at which the angle of the work implement is changed based on the speed of the work machine in the direction of travel and the distance to the locations of predetermined cut and fill areas.

9. The system of claim 7, wherein the controller is further configured to:

maintain a longitudinal axis of the work implement substantially orthogonal to the direction of travel after removing the material from the first predetermined location to carry the material over a distance prior to automatically changing the angle of the work implement relative to the direction of travel.

10. The system of claim 1, wherein the work implement includes a blade.

11. The system of claim 10, wherein the blade is attached to a drawbar/moldboard/circle (DMC) assembly.

12. The system of claim 1, wherein the position monitoring system is configured to track the position of the work implement in three dimensions.

13. The system of claim 1, wherein the position monitoring system is configured to generate a three dimensional map of the landscape and store the map in a memory.

14. The system of claim 1, wherein the position monitoring system is configured to make use of a global positioning system (GPS).

15. The system of claim 14, wherein the position monitoring system includes a local positioning unit for supplementing the GPS.

16. A motor grader comprising:

a cab:

a traction system;

a power source;

a work implement positionable at an angle relative to a direction of travel of the motor grader;

a position monitoring system for tracking a position of the work implement relative to a mapped landscape; and

a controller configured to initiate movement of the work implement, in response to information from the position monitoring system, to change the angle of the work implement relative to the direction of travel.

17. The motor grader of claim 16, wherein the work implement includes a circle and the angle change is accomplished by rotation of the circle.

18. The motor grader of claim 16,

wherein the controller is further configured to change the angle of the work implement relative to the direction of travel based on a location of a predetermined area of the landscape designated for an elevation change;

wherein the work implement includes a blade attached to a drawbar/moldboard/circle (DMC) assembly;

wherein the position monitoring system is configured to track the position of the work implement in three dimensions and is configured to generate a three dimensional map of the landscape and store the map in a memory;

wherein the controller is further configured to vary a rate at which the angle of the work implement is changed based on a speed of the work machine in the direction of travel and a distance to the location of the predetermined area; and

wherein the position monitoring system is configured to make use of a global positioning system (GPS).

19. The motor grader of claim 16, wherein the controller is further configured to:

determine a first difference between an actual elevation and a desired elevation at a first location;

determine a second difference between an actual elevation and a desired elevation at a second location; and

20. The motor grader of claim 16, wherein the controller is further configured to:

21. The motor grader of claim 20, wherein the controller is configured to:

22. A method of controlling a work implement for a work machine, comprising:

determining an actual position of a work implement relative to a work site;

locating, with respect to the actual position, at least two predetermined areas designated for an elevation change; and

controlling an angle of the work implement relative to a direction of travel of the work machine in response to a relationship between the at least two predetermined areas designated for an elevation change.

23. The method of claim 22, wherein one or more of the at least two predetermined areas includes a fill area.

24. The method of claim 22, wherein one or more of the at least two predetermined areas includes a cut area.

25. The method of claim 22, wherein the at least one predetermined area designated for an elevation change is stored in a memory.

26. The method of claim 22, wherein controlling an angle of the work implement includes:

determining a first difference between an actual elevation and a desired elevation at a first of the at least two predetermined areas;

determining a second difference between an actual elevation and a desired elevation at a second of the at least two predetermined areas; and

changing the angle of the work implement relative to the direction of travel based on a comparison between the first difference and the second difference.

27. The method of claim 22, further including:

selecting a first predetermined location that is designated for a decrease in elevation;

selecting a second predetermined location designated for an increase in elevation, wherein the second location resides at a position forward of the work machine;

removing material from the first location; and

automatically changing the angle of the work implement relative to the direction of travel to deposit at least some of the material at the second location.

28. The method of claim 27, further including:

maintaining the longitudinal axis of the work implement substantially orthogonal to the direction of travel after removing the material and carrying the material over a distance prior to automatically changing the angle of the work implement relative to the direction of travel.

29. The method of claim 22, further including:

varying a rate at which the angle of the work implement is changed based on at least one of a speed of the work machine in the direction of travel and a distance to one of the at least two predetermined areas designated for an elevation change.

30. The method of claim 22, wherein the work implement includes a blade.

31. The method of claim 30, wherein the blade is attached to a drawbar/moldboard/circle (DMC) assembly.

32. The method of claim 22, further including:

tracking the position of the work implement in three dimensions with a position monitoring system.

33. The method of claim 22, further including:

generating a three dimensional map of the work site; and

storing the map in a memory.

34. The method of claim 22, wherein the position monitoring system is configured to make use of a global positioning system (GPS).

35. The method of claim 34, wherein the position monitoring system includes a local positioning unit for supplementing the GPS.