Patent Publication Number: US-2016237630-A1

Title: System and Method for Determining a State of Compaction

Description:
TECHNICAL FIELD 
     This disclosure relates generally to machines that compact material, and more particularly, to a system and method for determining a state of compaction of a work material at a work site. 
     BACKGROUND 
     Compacting machines or compactors are commonly used to compact work materials (such as soil, gravel, asphalt) to a desired density while constructing buildings, highways, parking lots, and other structures. In addition, compactors are often used to compact recently moved and/or relatively soft materials at mining sites and landfills. The process often requires a plurality of passes over the work material to reach the desired density. 
     Determining whether the desired level of compaction has been reached is often estimated in a variety of manners. In some instances, the compaction may be approximated by a state of compaction system that measures the amount of power required to move the compactor along the surface of a work site. The state of compaction system may determine a state of compaction relative to an absolute scale or a maximum amount of compaction. This type of system typically requires an operator to calibrate the machine while operating on a flat, hard surface. Operation of the machine on a slope rather than a flat surface will change the amount of power used by the machine as compared to the flat surface. As a result, the system may include an adjustment to compensate for changes due to the slope on which the machine is operating. 
     U.S. Pat. No. 6,188,942 discloses a method and apparatus for use with a compactor to determine the compaction performance of a material. The compaction performance may be determined as a function of the compactive energy or as a function of the propelling power of the compactor. 
     The foregoing background discussion is intended solely to aid the reader. It is not intended to limit the innovations described herein, nor to limit or expand the prior art discussed. Thus, the foregoing discussion should not be taken to indicate that any particular element of a prior system is unsuitable for use with the innovations described herein, nor is it intended to indicate that any element is essential in implementing the innovations described herein. The implementations and application of the innovations described herein are defined by the appended claims. 
     SUMMARY 
     In a one aspect, a system for determining a state of compaction of a work material during a compaction operation includes a roller associated with a machine and configured to engage and compact the work material, a speed sensor associated with the machine operative to determine a speed of the machine, a pitch angle sensor associated with the machine operative to determine a pitch angle of the machine, and a power loss sensor associated with the machine operative to determine a power loss of the machine. A controller is configured to determine a plurality of hard earth calibration data points based upon the speed of the machine, the pitch angle of the machine, and the power loss of the machine as the machine moves along a hard earth calibration surface with the plurality of hard earth calibration data points corresponding to a plurality of different speeds and a plurality of different pitch angles. The controller is further configured to determine a three-dimensional hard earth power map based upon the plurality of hard earth calibration data points, determine at least one soft earth calibration data point based upon the speed of the machine, the pitch angle of the machine, and the power loss of the machine as the machine moves along a soft earth calibration surface, determine a soft earth calibration factor based upon the at least one soft earth calibration data point, and determine the state of compaction of the work material based upon the speed of the machine, the pitch angle of the machine, the three-dimensional hard earth power map, and the soft earth calibration factor as the machine moves along the work material. 
     In another aspect, a controller-implemented method for determining a state of compaction of a work material during a compaction operation includes moving a machine along a along a hard earth calibration surface at plurality of different speeds and a plurality of different pitch angles, determining a plurality of hard earth calibration data points based upon a speed of the machine, a pitch angle of the machine, and a power loss of the machine as the machine moves along the hard earth calibration surface with the plurality of hard earth calibration data points corresponding to the plurality of different speeds and the plurality of different pitch angles and determining a three-dimensional hard earth power map based upon the plurality of hard earth calibration data points. The method further includes moving the machine along a soft earth calibration surface, determining at least one soft earth calibration data point based upon the speed of the machine, the pitch angle of the machine, and the power loss of the machine as the machine moves along a soft earth calibration surface, and determining a soft earth calibration factor based upon the at least one soft earth calibration data point. The method also includes moving the machine along the work material and determining the state of compaction of the work material based upon the speed of the machine, the pitch angle of the machine, the three-dimensional hard earth power map, and the soft earth calibration factor as the machine moves along the work material. 
     In still another aspect, a machine includes a prime mover and a roller operatively connected to the prime mover, a roller associated with a machine and configured to engage and compact the work material, a speed sensor associated with the machine operative to determine a speed of the machine, a pitch angle sensor associated with the machine operative to determine a pitch angle of the machine, and a power loss sensor associated with the machine operative to determine a power loss of the machine. A controller is configured to determine a plurality of hard earth calibration data points based upon the speed of the machine, the pitch angle of the machine, and the power loss of the machine as the machine moves along a hard earth calibration surface with the plurality of hard earth calibration data points corresponding to a plurality of different speeds and a plurality of different pitch angles. The controller is further configured to determine a three-dimensional hard earth power map based upon the plurality of hard earth calibration data points, determine at least one soft earth calibration data point based upon the speed of the machine, the pitch angle of the machine, and the power loss of the machine as the machine moves along a soft earth calibration surface, determine a soft earth calibration factor based upon the at least one soft earth calibration data point, and determine the state of compaction of the work material based upon the speed of the machine, the pitch angle of the machine, the three-dimensional hard earth power map, and the soft earth calibration factor as the machine moves along the work material. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  depicts a diagrammatic view of a machine in accordance with the disclosure; 
         FIG. 2  depicts a schematic view of an exemplary drive system and an operator station for use with the machine of  FIG. 1 ; 
         FIG. 3  depicts a graph of gross drive power as a function of slope for two work surfaces having different levels of compaction; 
         FIG. 4  depicts a block diagram of a state of compaction system; 
         FIG. 5  depicts a flowchart of a process for determining the state of compaction of a work surface during a compaction operation; 
         FIG. 6  depicts a flowchart of a hard earth calibration process of  FIG. 5 ; 
         FIG. 7  depicts a three-dimensional power map of a hard earth calibration surface as a function of the speed and pitch angle of the machine; and 
         FIG. 8  is similar to  FIG. 7  but also includes a second three-dimensional power map based upon a soft earth surface; 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  depicts a diagrammatic illustration of a machine  10  such as a self-propelled single drum compactor with a single cylindrical drum or roller  11  for compacting a work material  101  at work site  100 . The machine  10  includes a frame  12  and a prime mover such as an engine  13 . Engine  13  is a part of a drive system  14  ( FIG. 2 ) that propels the machine  10  as desired. The systems and methods of this disclosure may be used with any machine propulsion and drivetrain mechanisms applicable in the art including hydrostatic, electric, or mechanical drives. The drive system  14  may operate to drive roller  11  and/or one or more deflectable tires  15 . In other embodiments, other types of work material engaging members may be used such as replacing the deflectable tires  15  with another roller. 
     In one embodiment depicted in  FIG. 2 , drive system  14  may be a hydrostatic system in which engine  13  is operatively connected to first pump  16  and second pump  17 . Each of the first pump  16  and the second pump  17  may be operatively hydraulically connected to power first motor  20  and second motor  21 , respectively, via a first hydraulic line  22  and a second hydraulic line  23 . First motor  20  may be driven by pressurized hydraulic fluid from first pump  16  to rotate roller  11  and second motor  21  may be driven by pressurized hydraulic fluid from second pump  17  to rotate deflectable tires  15 . 
     Each of first pump  16  and second pump  17  may be a variable displacement pump with the displacement controlled by controller  31 . First pump  16  and second pump  17  may each direct pressurized hydraulic fluid to and from their respective motors in two different directions to operate the motors in forward and reverse directions. First pump  16  and second pump  17  may each include a stroke-adjusting mechanism, for example a swashplate, the position of which is hydro- or electro-mechanically adjusted to vary the output (e.g., a discharge pressure or rate) of the pump. The displacement of each of the first pump  16  and the second pump  17  may be adjusted so the flow is either into its first hydraulic line  22  or its second hydraulic line  23  so that the pump may drive its respective motor in either forward and reverse directions, depending on the direction of fluid flow. Each of the first pump  16  and the second pump  17  may be operatively connected to engine  13  of machine  10  by, for example, a shaft  24 , a belt, or in any other suitable manner. 
     Each of first motor  20  and second motor  21  may be driven to rotate by a fluid pressure differential generated by its respective pump and supplied through first hydraulic line  22  and second hydraulic line  23 . The flow rate of fluid into and out of the motor may determine an output velocity while a pressure differential across the pumping mechanism of the motor may determine an output torque. Each of first motor  20  and second motor  21  may be a variable displacement motor with the displacement controlled by controller  31 . In another embodiment, each of first motor  20  and second motor  21  may be a fixed and/or a multi-speed motor. 
     Machine  10  may include an operator station  25  from which an operator may control the machine  10 . Operator station  25  may include an operator interface  26  ( FIG. 2 ) proximate an operator seat  27  through which the operator may issue commands to control propulsion and steering systems of the machine  10  as well as operate other systems and implements associated with the machine. Operator interface  26  may include a plurality of input devices  28  such as a joystick, a pedal, a push-button, a knob, a switch, or another device. The operator may manipulate an input device to affect corresponding operations of machine  10 . Operator interface  26  may further include a display  29  on which various types of information useful or necessary for the operation of the machine  10  may be displayed. 
     Machine  10  may include a control system  30  as shown generally by an arrow in  FIG. 1  indicating association with the machine  10 . The control system  30  may include an electronic control module or controller  31 , various input devices to control the machine  10 , and a plurality of sensors associated with the machine  10  that provide data and input signals representative of various operating parameters of the machine  10 . The term “sensor” is meant to be used in its broadest sense to include one or more sensors and related components that may be associated with the machine  10  and that may cooperate to sense various functions, operations, and operating characteristics of the machine. 
     The controller  31  may be an electronic controller that operates in a logical fashion to perform operations, execute control algorithms, store and retrieve data and other desired operations. The controller  31  may include or access memory, secondary storage devices, processors, and any other components for running an application. The memory and secondary storage devices may be in the form of read-only memory (ROM) or random access memory (RAM) or integrated circuitry that is accessible by the controller. Various other circuits may be associated with the controller  31  such as power supply circuitry, signal conditioning circuitry, driver circuitry, and other types of circuitry. 
     The controller  31  may be a single controller or may include more than one controller disposed to control various functions and/or features of the machine  10 . The term “controller” is meant to be used in its broadest sense to include one or more controllers and/or microprocessors that may be associated with the machine  10  and that may cooperate in controlling various functions and operations of the machine. The functionality of the controller  31  may be implemented in hardware and/or software without regard to the functionality. The controller  31  may rely on one or more data maps relating to the operating conditions of the machine  10  that may be stored in the memory of controller. Each of these data maps may include a collection of data in the form of tables, graphs, and/or equations. 
     The control system  30  may be located on the machine  10  and may also include components located remotely from the machine such as at a command center  103 . The functionality of control system  30  may be distributed so that certain functions are performed at machine  10  and other functions are performed remotely. In such case, the control system  30  may include a communications system such as wireless network system  104  for transmitting signals between the machine  10  and a system located remote from the machine. 
     A position sensing system  32 , as shown generally by an arrow in  FIG. 1  indicating association with the machine  10 , may include a position sensor  33  that operates to sense a position of the machine relative to the work site  100 . The position sensor  33  may include a plurality of individual sensors that cooperate to provide position signals to controller  31  to indicate the position of the machine  10 . In one example, the position sensor  33  may include one or more sensors that interact with a positioning system such as a global navigation satellite system or a global positioning system to operate as a position sensor. The controller  31  may determine the position of the machine  10  within work site  100  as well as the orientation of the machine such as its heading, pitch and roll. In other examples, the position sensor  33  may be an odometer or another wheel rotation sensing sensor, a perception based system, or may use other systems such as lasers, sonar, or radar to determine the position of the machine  10 . 
     Machine  10  may also include a drive speed sensing system  34 , as shown generally by an arrow in  FIG. 1  indicating association with the machine  10 , that operates to sense a speed of the machine. The drive speed sensing system  34  may include a speed sensor  35  ( FIG. 2 ) for generating speed signals indicative of the speed of the machine  10 . Controller  31  may utilize the speed signals to determine the speed of the machine  10  relative to work surface  102 . In one example, the speed sensor  35  may be a magnetic sensor associated with second motor  21 , which is used to drive the deflectable tires  15 . In another embodiment, controller  31  may utilize data from the position sensing system  32  to determine the speed of the machine. 
     Machine  10  may also include an inclination sensing system  36 , as shown generally by an arrow in  FIG. 1  indicating association with the machine  10 , for determining the inclination or pitch angle of the machine relative to a level ground reference (i.e., perpendicular to the direction of gravity). The inclination sensing system may include an inclination or pitch angle sensor  37  for generating pitch angle signals that are used by controller  31  to determine the inclination or pitch angle of machine  10 . In some embodiments, the inclination sensing system  36  may use a pitch rate sensor  38  in addition to or instead of the pitch angle sensor  37  to determine the pitch angle of the machine  10 . 
     Machine  10  may also include various sensors associated with the drive system  14 . For example, the machine  10  may include a power loss measurement system  40  for determining the amount of power lost or used during a compaction operation of the machine. The power loss measurement system  40  may include a power loss sensor  41  for generating signals indicative of power loss of the machine during a compaction operation. In one embodiment, the power loss sensor  41  may embody motor hydraulic sensors  42  ( FIG. 2 ) to measure the difference between the hydraulic pressure within the first hydraulic line  22  and second hydraulic line  23  at the input and output of each of the first motor  20  and the second motor  21 . The amount of power used to compact the work material  101  may be calculated based upon the change in hydraulic pressure between the input and the output of each of the first motor  20  and the second motor  21  together with the flow rate of the hydraulic fluid. In one example, the flow rate of hydraulic fluid through the first motor  20  and the second motor  21  may be determined by using speed sensor  35  to determine the speed of the machine  10  and determine the flow rate through the first motor  20  and the second motor  21  based upon the speed of the machine. 
     In another embodiment, the drive system  14  may include a mechanical drive with a torque converter (not shown). In such case, the power loss sensor  41  may include sensors that are used to determine the input speed of the torque converter (or the output speed of engine  13 ) and the output speed of the torque converter. The amount of power used to compact the work material  101  may be calculated based upon the change in speed between the input and the output of the torque converter. 
     Control system  30  may include a state of compaction system  45  for determining the level or state of compaction of work material  101  as machine  10  moves over the work surface  102 . As the machine  10  moves along the work surface  102 , power is used to compact the work material  101 , to move the machine, and to overcome friction losses of the machine, and power is gained or lost depending on whether the machine is traveling down or up a grade. The state of compaction system  45  generally operates based upon the concept that less power is required to move a machine across a harder or more compacted work material  101  as compared to a softer or less compacted work material. By determining the actual drive power (P Actual ) used by the machine  10  as it moves along the work surface  102  and compacts the work material  101 , a relative state of compaction of the work material may be determined. As a result, the actual drive power P Actual ) is directly proportional to the softness or state of compaction of the work surface  102 . 
     The actual drive power (P Actual ) may be generally represented by the equation: 
         P   Actual   =P   Gross   −P   Grade   −P   Friction   (1)
 
     where P Gross  is gross amount of power used to propel the machine  10  along the work surface  102 , P Grade  is the change in power due to the change in elevation or grade of the machine, and P Friction  is the power lost due to friction and other losses associated with the machine as it moves. The change in power due to a change in elevation (P Grade ) will increase as the slope upon which the machine  10  is traveling increases and will decrease as the slope decreases. In general, the friction power loss (P Friction ) will increase as the speed of the machine  10  increases. 
     In some instances, the change in power due to a change in elevation (P Grade ) and the friction power loss (P Friction ) may be combined to define a lumped or summed power change (P Lumped ). As a result, Equation (1) may be re-written as: 
         P   Actual   =P   Gross   −P   Lumped   (2)
 
     Operation of the machine  10  on a soft work surface  102  may be equated to or modeled after the operation of the machine on a hard work surface but with the machine moving up or climbing a slope or angle. Referring to  FIG. 3 , a first curve  105  depicts an example of the gross amount of power (P Gross ) used to propel the machine  10  along a constant density or hardness hard work surface as a function of the slope or pitch angle and at a constant speed. A second curve  107  depicts an example of the gross amount of power (P Gross ) used to propel the machine  10  along a constant density or hardness soft work surface as a function of the slope or pitch angle and at the same constant speed. In this example, it may be seen that the gross amount of power required to move the machine  10  on a hard surface at a six degree slope as indicated at  106  is approximately equal to the gross amount of power required to move the machine  10  on a two degree slope as indicated at  108 . As a result, the operation of the machine  10  on the soft surface as specified in  FIG. 3  may be approximated to the operation of the machine on a hard surface by adding a slope of four degrees to the analysis. 
     In an alternative model or explanation of the relationship between first curve  105  and second  107 , the power to operate on any surface at a fixed speed and angle will vary depending on the hardness or density of the material. More specifically, the power will be at a minimum power on a hard work surface corresponding to first curve  105  and increase along a vertical axis as the work surface becomes softer. For example, axis  115  depicts the gross amount of power (P Gross ) used to propel the machine  10  along the work surface for a fixed speed and angle. The gross amount of power (P Gross ) used to propel the machine  10  is at a minimum on the hard work surface corresponding to first curve  105  such as at point  106  and increases along axis  115  such that the gross amount of power is higher as one moves up axis  115  and the work surface becomes softer. Thus, the gross amount of power (P Gross ) used to propel the machine  10  along the work surface corresponding to curve  107  such as at point  116  is thus higher than that at point  106 . 
     The alternative model provides a density correlation between net power or actual drive power (P Actual ) and the gross amount of power (P Gross ) at a given speed and angle. For example, a work surface  102  having an actual drive power (P Actual ) halfway between first curve  105  and second curve  107  is depicted in phantom at  117 . The density or hardness of the work surface  102  along axis  115  for the same speed and angle is halfway between density of first curve  105  and second curve  107  as well. For each different speed and angle, the ratiometric relationship still holds but the axis  115  will be shifted and extends upward from the new speed and angle coordinate point. 
     It has been determined by empirical data that the change in the gross amount of power (P Gross ) required or used as the machine moves along the work surface is, in general, directly proportional to the change in actual drive power (P Actual ) due to the compaction of the work surface when operating at the same slope and speed. In other words, when operating at a specified slope and speed, a change in the gross amount of power (P Gross ) used will result in a proportional change in actual drive power (P Actual ). As set forth in more detail below, by monitoring the gross amount of power (P Gross ) used to propel the machine  10 , the actual drive power (P Actual ) attributable to the compaction of the work surface  102  may be determined for a particular portion of the work site  100 . 
     As depicted in  FIG. 4 , the controller  31  receives information from various sensors and processes this information. Controller  31  may receive, at a first input node  50  position signals from position sensor  33 , speed signals from speed sensor  35  at a second input node  51 , and inclination signals from the pitch angle sensor  37  at a third input node  52 . If a pitch rate sensor  38  is included, the controller  31  may receive pitch rate signals from the pitch rate sensor at a fourth input node  53 . At a fifth input node  54 , the controller  31  may receive signals from power loss sensor  41  indicative of power loss that occurs during a compacting operation. 
     Controller  31  may generate various output signals based upon the operation of the state of compaction system  45 . For example, at a first output node  55 , the controller  31  may generate signals indicative of the gross amount of power (P Gross ) used to propel the machine  10  along the work surface  102 . At a second output node  56 , the controller  31  may use the gross amount of power (P Gross ) used and, the speed and pitch angle of the machine  10  to generate signals indicative of the actual drive power (P Actual ) used for compaction and thus determine and display the state of compaction of the work material  101 . 
       FIG. 5  depicts a flowchart of the operation of the state of compaction system  45  in conjunction with the operation of machine  10 . At stage  60 , a hard earth calibration may be performed to determine a baseline for the gross power loss characteristics of the machine  10 . Referring to  FIG. 6 , a flowchart of the hard earth calibration process is depicted. At stage  80 , the machine  10  is positioned on a hard earth calibration surface at a first location. The hard earth calibration surface is a surface that does not deflect or compact under the weight of the machine as would occur with a compactable work material. As a result, the power required to move the machine  10  along such a calibration surface does not include any energy used to compact the work material. The power used as the machine  10  moves along the calibration surface thus accurately reflects the lumped power change (P Lumped ) including the friction losses of the machine required to move the machine such as the rolling resistance and other losses together with power losses or gains as the machine moves uphill or downhill during the calibration process. 
     An initial calibration speed may be set or stored within controller  31  at stage  81 . The machine  10  may be moved along the hard earth calibration surface  102  at stage  82  at a constant speed equal to the initial calibration speed and at a constant slope. In one example, the machine  10  may be moved in forward and then in reverse to obtain data with the machine moving in opposite directions. 
     At stage  83 , the controller  31  may receive data from the various sensors of the machine. The controller  31  may determine at stage  84  hard earth calibration data such as the speed of the machine  10 , the pitch angle of the machine, and the gross amount of power (P Gross ) used to propel the machine along the calibration surface. At decision stage  85 , the controller  31  may determine whether the machine  10  has been moved along the hard earth calibration surface at a threshold number of different speeds for the pitch angle or slope on which the machine is moving. If the machine  10  has not been moved along the hard earth calibration surface at a sufficient number of speeds, the controller  31  may at stage  86  change the speed of the machine and the process of stages  82 - 85  repeated. In one example, the power losses may be determined by operating the machine  10  at a series of different speeds (e.g., 1 kph, 2 kph, 3 kph, 4 kph, etc.) while using the power loss measurement system  40  to determine the amount of power required to move the machine at each of those speeds. 
     If the machine  10  has been moved along the hard earth calibration surface at a sufficient number of speeds, the controller  31  may at decision stage  87  determine whether has been moved along the hard earth calibration surface at a threshold number of different pitch angles or slopes. If the machine  10  has not been moved along the hard earth calibration surface at a sufficient number of pitch angles, the controller  31  may at stage  88  move the machine to a new location with a hard earth calibration surface having a different pitch angle and the process of stages  81 - 87  repeated. 
     It should be noted that, in some instances, the hard earth calibration location may not permit the machine  10  to be moved at a constant angle but the system disclosed herein may still be used to perform the hard earth calibration process. To do so, the machine  10  may be moved about the hard earth calibration surface at the hard earth calibration location and the controller may record the pitch angle, the speed, and the gross amount of power (P Gross ) used to propel the machine as the machine moves along the hard earth calibration surface. 
     Referring back to  FIG. 5 , after the machine  10  has been moved along the hard earth calibration surface at a sufficient number of pitch angles and at a sufficient number of speeds, the controller  31  may at stage  61  generate a three-dimensional hard earth power map  110  ( FIG. 7 ) based upon the hard earth calibration data generated in accordance with  FIG. 6  as the machine  10  is moved along the hard earth calibration surface. More specifically, as the machine  10  is moved along the hard earth calibration surface, the speed and pitch angle of the machine together with the gross amount of power (P Gross ) used to propel the machine define a hard earth calibration data point  111 . As the machine  10  is moved at different speeds and different pitch angles, additional hard earth calibration data points  111  are defined to create a set or plurality of hard earth calibration data points  111 . 
     Controller  31  may use any desired process to form the three-dimensional hard earth power map  110  that maps the gross amount of power (P Gross ) used as the machine moves along the work surface  102  as a function of the slope upon which the machine  10  is moving and the speed of the machine. In one example, a least squares method may be used to determine the three-dimensional hard earth power map. In doing so, the three-dimensional hard earth power map  110  may take the form of: 
         P   Gross   =C   1   +C   2   *Spd+C   3   *PA+C   4   *Spd   2   +C   5   *Spd*PA   (3)
 
     where C 1 -C 5  are constants, Spd is the speed of the machine  10 , and PA is the pitch angle of the machine. 
     At stage  62 , a soft earth calibration may be performed to determine a soft earth calibration factor (SECF) that may be subsequently used to determine the actual drive power (P Actual ) at any location at the work site  100  and thus estimate the state of compaction of the work surface  102 . To perform the soft earth calibration process, the machine  10  may be moved to a soft earth calibration surface of the work site  100  at which the state of compaction of the work material  101  or the actual drive power (P Actual ) is known. In some instances, the machine operator or other personnel may prepare or condition the work material in a desired manner and then perform one or more tests to determine the actual drive power (P Actual ) setting or reading for the work material  101  at the soft earth calibration surface. 
     As the machine  10  moves over the area of known compaction, controller  31  may determine the gross amount of power (P Gross ) used to propel the machine together with the speed and pitch angle of the machine. Each of these values together with the actual drive power (P Actual ) may be stored as a soft earth calibration data point. 
     If desired, more than one soft earth calibration data point may be generated as the machines move along the area of known compaction. In such case, the controller  31  may generate an average of the soft earth calibration data points, select a data point that is most representative of the soft earth calibration process, or use another method to generate a soft earth calibration data point. 
     At stage  63 , a three-dimensional soft earth power map  112  ( FIG. 8 ) may be created that generally follows the three-dimensional hard earth power map  110  but is shifted by an angle to approximate the machine  10  moving up a slope. The controller  31  may calculate the gross amount of power (P Advanced ) required to move the machine along the work surface  102  based upon the three-dimensional soft earth power map  112  but at the slope and speed corresponding to the soft earth calibration data point. 
     As stated above, the change in the gross amount of power (P Gross ) required or used as the machine moves along the work surface is, in general, directly proportional to the change in actual drive power (P Actual ) due to the compaction of the work surface when operating at the same slope and speed. Accordingly, to determine the shift in pitch angle necessary to compensate for soft material, a soft earth calibration factor (SECF) may be generated at stage  64  that may be subsequently used to determine the actual drive power (P Actual ) at any location on the work surface  102 . To do so, the ratio of the gross powers and actual drive powers may be written in terms of the actual drive power P Gross(Advanced)  determined by the three-dimensional soft earth power map  112  at the slope and speed corresponding to the soft earth calibration point as follows: 
     
       
         
           
             
               
                 
                   
                     P 
                     
                       Actual 
                        
                       
                         ( 
                         Advanced 
                         ) 
                       
                     
                   
                   = 
                   
                     
                       P 
                       
                         Actual 
                          
                         
                           ( 
                           Hard 
                           ) 
                         
                       
                     
                     - 
                     
                         
                       
                         [ 
                         
                           
                             ( 
                             
                               
                                 P 
                                 
                                   Actual 
                                    
                                   
                                     ( 
                                     Hard 
                                     ) 
                                   
                                 
                               
                               - 
                               
                                 P 
                                 
                                   Actual 
                                    
                                   
                                     ( 
                                     Soft 
                                     ) 
                                   
                                 
                               
                             
                             ) 
                           
                            
                           
                             
                               
                                 P 
                                 
                                   Gross 
                                    
                                   
                                     ( 
                                     Advanced 
                                     ) 
                                   
                                 
                               
                               - 
                               
                                 P 
                                 
                                   Gross 
                                    
                                   
                                     ( 
                                     Hard 
                                     ) 
                                   
                                 
                               
                             
                             
                               P 
                               
                                 
                                   Gross 
                                    
                                   
                                     ( 
                                     Soft 
                                     ) 
                                   
                                 
                                 - 
                                 
                                   P 
                                   
                                     Gross 
                                      
                                     
                                       ( 
                                       Hard 
                                       ) 
                                     
                                   
                                 
                               
                             
                           
                         
                         ] 
                       
                     
                   
                 
               
               
                 
                   ( 
                   4 
                   ) 
                 
               
             
           
         
       
     
     where P Actual(Hard)  is the actual drive power at the hard earth calibration location, P Actual(Soft)  is the actual drive power at the soft earth calibration location, P Advanced  is the gross amount of power used to move the machine along the work surface  102  based upon the three-dimensional soft earth power map  112  at the slope and speed corresponding to the soft earth calibration data point, P Gross(Hard)  is the gross amount of power used to move the machine along the work surface  102  during the hard earth calibration process at the slope and speed corresponding to the soft earth calibration data point as determined from the three-dimensional hard earth power map  110 , and P Gross(Soft)  is the gross amount of power used to move the machine along the work surface  102  during the soft earth calibration process at the slope and speed corresponding to the soft earth calibration data point. 
     The actual drive power (P Actual (Advanced) ) determined by the three-dimensional soft earth power map  112  at the slope and speed corresponding to the soft earth calibration data point may then be set as the soft earth calibration factor (SECF). The soft earth calibration factor (SECF), establishes a relationship between the state of compaction or actual drive power required due to the compaction of the work surface  102  along the three-dimensional soft earth power map  112  and the three-dimensional hard earth power map  110 . The soft earth calibration factor (SECF) may be used to determine the state of compaction or actual drive power (P Actual(Current) ) required due to the compaction of the work surface  102  at any location at the work site  100 . More specifically, the proportionality of the change in the gross amount of power (P Gross ) required or used as the machine moves along the work surface to the change in actual drive power (P Actual)  due to the compaction of the work surface when operating at the same slope and speed may be used to generate an equation for the state of compaction or actual drive power P Actual (Current)  as follows: 
     
       
         
           
             
               
                 
                   
                     P 
                     
                       Actual 
                        
                       
                         ( 
                         Current 
                         ) 
                       
                     
                   
                   = 
                   
                     
                       P 
                       
                         Actual 
                          
                         
                           ( 
                           Hard 
                           ) 
                         
                       
                     
                     + 
                     
                       [ 
                       
                         
                           ( 
                           
                             
                               S 
                                
                               
                                   
                               
                                
                               E 
                                
                               
                                   
                               
                                
                               C 
                                
                               
                                   
                               
                                
                               F 
                             
                             - 
                             
                               P 
                               
                                 Actual 
                                  
                                 
                                   ( 
                                   Hard 
                                   ) 
                                 
                               
                             
                           
                           ) 
                         
                          
                         
                           
                             
                               P 
                               
                                 Gross 
                                  
                                 
                                   ( 
                                   Current 
                                   ) 
                                 
                               
                             
                             - 
                             
                               P 
                               
                                 Gross 
                                  
                                 
                                   ( 
                                   Hard 
                                   ) 
                                 
                               
                             
                           
                           
                             P 
                             
                               
                                 Gross 
                                  
                                 
                                   ( 
                                   Advanced 
                                   ) 
                                 
                               
                               - 
                               
                                 P 
                                 
                                   Gross 
                                    
                                   
                                     ( 
                                     Hard 
                                     ) 
                                   
                                 
                               
                             
                           
                         
                       
                       ] 
                     
                   
                 
               
               
                 
                   ( 
                   5 
                   ) 
                 
               
             
           
         
       
     
     where P Actual(Current)  is the actual drive power required due to the compaction of the work surface at the current location of the machine  10 , P Actual(Hard)  is the actual drive power at the hard earth calibration location, SECF is the soft earth calibration factor, P Gross(Current)  is the gross amount of power used to move the machine along the work surface  102  at the current location of the machine, P Gross(Hard)  is the hard earth gross amount of power used to move the machine along the work surface  102  at the slope and speed corresponding to the current location as determined from the three-dimensional hard earth power map  110 , and P Gross(Advanced)  is the soft earth gross amount of power used to move the machine along the work surface  102  at the slope and speed corresponding to the current location as determined from the three-dimensional soft earth power map  112 . 
     At stage  65 , the machine  10  may be moved to another location at the work site  100  and the compaction operation begun. As the machine  10  operates, the controller  31  may receive data from the various sensors at stage  66 . At stage  67 , the controller  31  may determine the state of the machine  10 . More specifically, the controller  31  may determine the position of the machine  10  based upon position signals from the position sensing system  32  and determine the speed at which the machine is operating based upon speed signals from the drive speed sensing system  34 . In addition, the controller  31  may also determine the pitch angle or inclination of the machine  10  based upon inclination signals from the inclination sensing system  36 . 
     At stage  68 , the controller  31  may determine the gross amount of power (P Gross ) used to propel the machine  10  along the work surface  102  as the machine  10  moves about the work site  100 . In doing so, the controller  31  may utilize the power loss measurement system  40  as described above. In still another embodiment, the power loss measurement system  40  may measure the difference between the input and the output of a torque converter used to drive the machine  10 . 
     At stage  69 , the controller  31  may determine power losses based upon the three-dimensional hard earth power map  110  and the three-dimensional soft earth power map  112 . More specifically, the controller  31  may determine the gross amount of power (P Gross(Hard) ) used to move the machine  10  along the work surface  102  at the slope and speed corresponding to the current location as determined from the three-dimensional hard earth power map  110 . The controller  31  may also determine the gross amount of power (P Gross(Advanced) ) used to move the machine along the work surface  102  at the slope and speed corresponding to the current location as determined from the three-dimensional soft earth power map  112 . 
     At stage  70 , the controller  31  may determine the actual drive power (P Actual ) according to equation (5) for the current location of the machine  10  where the actual drive power (P Actual(Hard) ) at the hard earth calibration location is determined at stage  60 , the soft earth calibration factor (SECF) is determined at stage  64 , the gross amount of power (P Gross (Current) ) used to move the machine at the current location is determined at stage  68 , the gross amount of power (P Gross(Hard) ) used to move the machine as determined from the three-dimensional hard earth power map  110  is determined at stage  69 , and the gross amount of power (P Gross(Advanced) ) used to move the machine as determined from the three-dimensional soft earth power map  112  is also determined at stage  69 . 
     The actual drive power (P Actual(Current) ) at the current location may be stored at stage  71  and displayed on display  29  at stage  72 . At decision stage  73 , the controller  31  may determine whether the actual drive power (P Actual(Current) ) is equal to a desired drive power. If the actual drive power (P Actual(Current) ) is not equal the desired drive power, the operator may continue to operate machine  10  and the process of stages  65 - 73  repeated. If the actual drive power (P Actual(Current) ) does equal the desired drive power at decision stage  73 , the operator may move the machine  10  to a new location and begin a new compacting process, if desired. 
     INDUSTRIAL APPLICABILITY 
     The industrial applicability of the system described herein will be readily appreciated from the forgoing discussion. The foregoing discussion is applicable to machines  10  such as compactors that engage the work surface  102  above a work material  101  to compact the material to prepare it for a subsequent use or otherwise reduce its volume. Such system may be used at a construction site, a roadwork site, a mining site, a landfill, or any other area in which compaction of work material  101  is desired. Work material  101  may include any material such as asphalt, gravel, soil, sand, landfill trash, and other types of material. 
     When compacting a work material  101 , it may be desirable to determine the state of compaction of the work material. The state of compaction system  45  is operative to utilize data from the sensors as well as the characteristics of the machine  10  to determine the state of compaction of the work material  101 . The state of compaction system  45  may be used by performing a hard earth calibration process on a plurality of slopes and at a plurality of speeds. The gross amount of power (P Gross ) used during the hard earth calibration process may be recorded within controller  31  together with the corresponding slopes and speeds. The controller  31  may generate a three-dimensional hard earth power map  110  based upon the gross amount of power (P Gross ) used during the hard earth calibration process and the corresponding slopes and speeds. 
     In addition to performing the hard earth calibration process, the state of compaction system  45  may also use a soft earth calibration process. The gross amount of power (P Gross ) used as the machine  10  moves along an area of soft earth having a known level or extent of compaction may be recorded within controller  31  together with the slope and speed of the machine. The soft earth calibration process may be performed based upon one or more sets of date points. The soft earth calibration process may be used to generate a soft earth calibration factor that may then be used with the three-dimensional hard earth power map  110  to determine the state of compaction for any location at the work site  100 . An electronic map of the work site  100  including the state of compaction may be generated and stored within controller  31  and/or at a remote location. 
     It will be appreciated that the foregoing description provides examples of the disclosed system and technique. All references to the disclosure or examples thereof are intended to reference the particular example being discussed at that point and are not intended to imply any limitation as to the scope of the disclosure more generally. All language of distinction and disparagement with respect to certain features is intended to indicate a lack of preference for those features, but not to exclude such from the scope of the disclosure entirely unless otherwise indicated. 
     Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. 
     Accordingly, this disclosure includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the disclosure unless otherwise indicated herein or otherwise clearly contradicted by context.