Abstract:
A control system for a mobile excavation machine is disclosed. The control system may have a ground engaging work tool, a sensor, and a controller. The sensor may be configured to sense a parameter indicative of a current travel speed of the mobile excavation machine and generate a speed signal in response thereto. The controller may be in communication with the ground engaging work tool and the sensor, and configured to receive the signal. The controller may also be configured to determine an amount of material currently being moved by the work tool and calculate a current productivity value associated with removal of the material based on the speed signal and the determined amount of material currently being moved. The controller may be further configured to control the ground engaging work tool to vary the amount of material currently being moved in response to the current productivity value.

Description:
TECHNICAL FIELD 
     The present disclosure relates generally to an automated machine control system and, more particularly, to a system for automatically calculating instantaneous productivity and controlling a machine&#39;s excavation in response thereto. 
     BACKGROUND 
     Machines such as, for example, dozers, motor graders, wheel loaders, and other types of heavy equipment are used to perform a variety of earth-moving tasks. Some of these tasks requiring removal of large amounts of material can be difficult for an unskilled or inexperienced operator to achieve efficiently. For example, an unskilled operator may attempt to remove a maximum amount of material during each excavation pass, but may only be able to do so at a very slow speed. Another unskilled operator may attempt to travel quickly, but may only be able to move a very small amount of material during each excavation pass at that speed. Finding the most productive combination of load and travel speed can be complicated, especially when manually performed by an inexperienced operator. Poor productivity and low efficiency can be costly to a machine owner. Because of these factors, the completion of some tasks by a completely operator-controlled machine can be expensive, labor intensive, time consuming, and inefficient. 
     One method of improving the operation of a machine under such conditions is described in U.S. Pat. No. 4,423,785 (the &#39;785 patent) issued to Kurihara et al. on Jan. 3, 1984. The &#39;785 patent describes a load control device for a working tool of a construction vehicle. The load control device is programmed with an effective traction power versus vehicle speed curve that is associated with the particular construction vehicle and working tool. From this curve, the load control device selects a maximum productivity point having a corresponding travel speed and drive force. The travel speed and drive force are then made desired values used to automatically control operation of the construction machine. As the construction vehicle moves about a worksite and is exposed to accelerations and decelerations associated with changes in terrain, the desired values are modified. By targeting the maximum productivity point, operation of the construction machine may be improved. 
     Although the construction machine of the &#39;785 patent may be capable of improving machine productivity, its use may be limited. That is, because control of the construction machine is based on a predefined curve associated with only one new machine and a single work tool configuration for that machine, the curve&#39;s accuracy may hinge on the machine&#39;s configuration and capacity remaining unchanged. And, for the same reason, the control strategy may be inapplicable to other machines or other work tool configurations having a different output capacity or to an older machine with diminished capacity. 
     The disclosed system is directed to overcoming one or more of the problems set forth above. 
     SUMMARY OF THE INVENTION 
     In one aspect, the present disclosure is directed to a control system for a mobile excavation machine. The control system may include a ground engaging work tool, a sensor, and a controller. The sensor may be configured to sense a parameter indicative of a current travel speed of the mobile excavation machine and generate a speed signal in response thereto. The controller may be in communication with the ground engaging work tool and the sensor, and configured to receive the signal. The controller may also be configured to determine an amount of material currently being moved by the work tool and calculate a current productivity value associated with removal of the material based on the speed signal and the determined amount of material currently being moved. The controller may be further configured to control the ground engaging work tool to vary the amount of material currently being moved in response to the current productivity value. 
     In yet another aspect, the present disclosure is directed to a method of controlling machine operation. The method may include determining a current machine travel speed, and determining an amount of material currently being excavated. The method may also include calculating a current productivity value based on the current machine travel speed and the determined amount of material currently being excavated. The method may further include varying the amount of material currently being excavated in response to the current productivity value. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a pictorial illustration of an exemplary disclosed machine operating at a worksite; 
         FIG. 2  is a diagrammatic illustration of an exemplary disclosed control system for use with the machine of  FIG. 1 ; 
         FIG. 3  is a graph of travel speed of the machine of  FIG. 1  versus productivity; and 
         FIG. 4  is a flowchart depicting an exemplary method performed by the control system of  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  illustrates a worksite  10  with an exemplary machine  12  performing a predetermined task. Worksite  10  may include, for example, a mine site, a landfill, a quarry, a construction site, or any other type of worksite. The predetermined task may be associated with altering the current geography at worksite  10  and may include, for example, a grading operation, a scraping operation, a leveling operation, a bulk material removal operation, or any other type of geography altering operation at worksite  10 . 
     Machine  12  may embody a mobile machine that performs some type of operation associated with an industry such as mining, construction, farming, or any other industry. For example, machine  12  may be an earth moving machine such as a dozer having a blade or other work implement  18  movable by way of one or more motors or cylinders  20 . Machine  12  may also include one more traction devices  22 , which may function to steer and/or propel machine  12 . 
     As best illustrated in  FIG. 2 , machine  12  may include a control system  16  in communication with components of machine  12  to affect the operation of machine  12 . In particular, control system  16  may include a power source  24 , a means  26  for driving cylinders  20  and traction device  22 , a travel speed sensor  28 , load sensor  29 , and a controller  30 . Controller  30  may be in communication with power source  24 , driving means  26 , cylinders  20 , traction device  22 , and travel speed sensor  28  via multiple communication links  32 ,  34 ,  36   a - c,    38 , and  40 , respectively. 
     Power source  24  may embody an internal combustion engine such as, for example, a diesel engine, a gasoline engine, a gaseous fuel powered engine, or any other type of engine apparent to one skilled in the art. Power source  24  may alternatively or additionally include a non-combustion source of power such as a fuel cell, a power storage device, an electric motor, or other similar mechanism. Power source  24  may be connected to driving means  26  via a direct mechanical coupling, an electric circuit, or in any other suitable manner. 
     Driving means  26  may include a pump such as a variable or fixed displacement hydraulic pump drivably connected to power source  24 . Driving means  26  may produce a stream of pressurized fluid directed to cylinders  20  and/or to a motor associated with traction device  22  to drive the motion thereof. Alternatively or additionally, driving means  26  could include a generator configured to produce an electrical current used to drive any one or all of cylinders  20  and traction device  22 , a mechanical transmission device, or any other appropriate means known in the art. 
     Speed sensor  28  may be associated with machine  12  to determine a travel speed of machine  12  relative to the work site  10 . For example, speed sensor  28  may embody an electronic receiver configured to communicate with one or more satellites (not shown) or a local radio or laser transmitting system to determine a relative location and speed of itself. Speed sensor  28  may receive and analyze high-frequency, low power radio or laser signals from multiple locations to triangulate a relative 3-D position and speed. Speed sensor  28  may also include a ground-sensing radar system to determine the travel speed of machine  12  relative to the work site  10 . Alternatively, speed sensor  28  may embody an Inertial Reference Unit (IRU) or a position sensor associated with traction device  22 , or any other known locating and speed sensing device operable to receive or determine positional information associated with machine  12 . A signal indicative of this position and speed may then be communicated from speed sensor  28  to controller  30  via communication link  40 . 
     Load sensor  29  may measure external loads applied to the work implement  18 . In particular, load sensor  29  may measure load data such as hydraulic pressure or electrical current data and relay the load data to controller  30  via communication link  41   a,    41   b,  or  41   c.  Load sensor  29  may embody, for example, a strain gauge associated with the work implement  18 . 
     Controller  30  may include means for monitoring, recording, storing, indexing, processing, determining, and/or communicating the location and speed of machine  12 , the load on cylinders  20 , and the productivity of machine  12  and for automatically controlling operations of machine  12  in response to a maximum productivity. These means may include, for example, a memory, one or more data storage devices, a central processing unit, or any other components that may be used to run the disclosed application. Furthermore, although aspects of the present disclosure may be described generally as being stored in memory, one skilled in the art will appreciate that these aspects can be stored on or read from different types of computer program products or computer-readable media such as computer chips and secondary storage devices, including hard disks, floppy disks, optical media, CD-ROM, or other forms of RAM or ROM. 
     Controller  30  may determine productivity based on one or more inputs associated with the operational characteristics of machine  12 . Specifically, productivity may be a function of the load measured by load sensors  29  and speed measured by speed sensor  28 . Productivity may be a measure of, for example, the amount of material that work machine  12  moves in a given interval of time (i.e., volume per time). Alternatively, productivity may be a measure of forces (i.e., power to the ground) with respect to work implement  18  position and speed. It is also contemplated that the productivity may be determined by other methods of calculating or approximating the work performed by the machine  12  within a time period. 
     Controller  30  may record and/or compare data relating to the productivity of machine  12  at different machine speeds. In this way, controller  30  may further determine a change in productivity with respect to the speed of machine  12 . To maximize an instantaneous productivity of machine  12 , controller  30  may evaluate the time derivative of the productivity and determine a point of maximum productivity. The point of maximum productivity may indicate a speed at which machine  12  may move the maximum amount of material given the current mechanical and terrain characteristics. Since the data used to determine productivity may be created and stored by controller  30  on the fly and continuously or periodically updated according to various input parameters from speed sensor  28 , load sensor  29 , and any other available input device, the determination of maximum productivity may not be limited to a single machine  12 , a single work implement  18  configuration, or a single type of worksite  10 . Controller  30  and the associated automated excavation control may be utilized with different types of machine  12 , different work implement  18  configurations and different worksites  10 , each time creating a job-specific productivity map and maximizing instantaneous productivity based on that map. 
       FIG. 3  illustrates an exemplary curve of machine speed versus the productivity of machine  12 . At low speeds, machine  12  may be operating suboptimally (relative to productivity) because of the extra time needed to complete a given task at a low speed. Point  301  of  FIG. 3  may depict such a suboptimal productivity due to low speed. Even though the machine may be able to lower work implement  18  to a blade depth deeper than what may be possible at higher speeds (i.e., may move more material in a single pass), the increased volume of moved material may still be insufficient to compensate for the slower speed and a less than maximum productivity may be obtained. Further, at excessive speeds, machine  12  may operate suboptimally because the blade depth of work implement  18  may be quite shallow (i.e. the volume of material moved in a single pass may be little) such that the power produced by the machine  12  may be directed to maintain the high speeds. Point  302  of  FIG. 3  may depict such a suboptimal productivity due to excessive speed. Though the machine may be operating at a high speed, many trips across or through worksite  10  may be required to move the desired amount of material. The higher speed may be insufficient to compensate for the shallow blade depth of work implement  18 , and a less than maximum productivity may be obtained. Point  300  of  FIG. 3  may depict a maximum attainable productivity for a given machine  12  and work implement  18  configuration. This point  300  may depict a most productive combination of load and travel speed. 
     Controller  30  may control cylinders  20  and/or traction devices  22  to automatically alter the geography of worksite  10 . In particular, controller  30  may automatically control operations of machine  12  to engage work implement  18  with the terrain of worksite  10 . Controller  30  may be in communication with the actuation components of cylinders  20  to raise, lower, or maintain the position of work implement  18 . Controller  30  may further be in communication with traction device  22  to raise, lower, or maintain the current speed of machine  12 . In this manner, controller  30  may provide for partial or full automatic control of machine  12 . 
     Controller  30  may control cylinder  20  to achieve maximum productivity. Specifically, controller  30  may increase the depth of work implement  18  to slow the machine  12  or decrease the depth of work implement  18  to increase the speed of machine  12 . Controller  30  may manipulate the depth of work implement  18  to find the optimal operational condition where the rate of change of productivity with respect to machine speed is zero. It is contemplated that controller  30  may alternatively only determine whether the machine  12  is currently operating at a maximum productivity, and then relinquish control of machine  12  to an operator with information regarding the productivity, if desired. 
       FIG. 4  is flow chart depicting an exemplary method performed by the control system of  FIG. 2 .  FIG. 4  will be discussed in more detail in the following section to further illustrate the disclosed control system and its operation. 
     INDUSTRIAL APPLICABILITY 
     The disclosed control system may be applicable to machines performing material moving operations where productivity is important. In particular, the disclosed control system may determine a machine&#39;s current productivity and automatically control an operating condition (such as blade height) to maximize removal of earthen material in a minimum amount of time. Because the control system may only be based on currently determined productivity, the control system may be applicable to nearly any machine  12  in any condition with any configuration of work implement  18  operating at any worksite  10 . The operation of control system  16  will now be described. 
       FIG. 4  illustrates the operation of control system  16 . Controller  30  may receive a request to begin an automatic digging (autodig) function (step  410 ). This request may be made by the operator currently in control of the machine. The request may be made via a single switch (not shown). It is contemplated that the single switch may trigger a series of machine  12  events simultaneously or in a predetermined sequence. For example, operator manipulation of the single switch may begin an autodig function, which will be described in detail below. Further, the single switch may be programmed to allow controller  30  to automate complicated sequences of machine  12  events, such as downshifting, upshifting, or changing machine direction while simultaneously lowering or raising work implement  18 . It is also contemplated that the request to begin an autodig function may be initiated using any other method known in the art for communicating a request to controller  30 . 
     Upon receiving a request to initiate the autodig function, controller  30  may increase the speed of machine  12  to a maximum speed (step  420 ). The maximum speed may be a limit of the machine  12  or may, alternatively, be a limit set by an operator. Controller  30  may increase machine travel speed by regulating the output of driving means  26  and/or power source  24 . Once this maximum speed is attained, controller  30  may lower work implement  18  of machine  12  into the work surface (step  430 ). Work implement  18  may be moved by regulating, for example, a pressure of fluid supplied to cylinders  20 . Once work implement  18  engages worksite  10 , the maximum speed of machine  12  will begin to decrease as a result of the increasing load on cylinders  20  and machine  12 . In fact, there may exist a point at which machine  12  stops (i.e., completely stalls) due to an excessive load. Similarly, as work implement  18  is retracted from worksite  10 , machine  12  may increase speed due to a decreasing load on cylinders  20 . As the work implement  18  is completely retracted and blade depth is zero, machine  12  may return to the maximum speed attained before work implement  18  engaged worksite  10 . At a point between the maximum ground speed and the stalled condition, the work implement may attain a maximum productivity depth. This depth may indicate a situation where the greatest amount of material is being removed in the least amount of time. From this work implement  18  depth, an increase or decrease in depth may result in less productivity (i.e. the slope of the productivity versus speed is zero). Further, the maximum productivity depth of work implement  18  may be unique to machine  12 , the configuration and condition of work implement  18 , and current worksite  10  conditions. 
     As machine  12  is maintaining a positive speed and load sensors  29  detect a load on the work implement  18  of machine  12 , controller  30  may continuously monitor one or more inputs from speed sensor  28  and load sensor  29  to determine an instantaneous productivity of machine  10  with respect to the current speed of machine  10  (step  440 ). If controller  30  determines that the current rate of change of productivity with respect to the current speed is nonzero (i.e. increasing or decreasing) or exceeds zero by a certain amount (step  450 ; no), then controller  30  may continue to manipulate tool depth and, subsequently the machine speed, to maximize productivity (step  460 ) while continuously determining the instantaneous productivity of machine  12  (step  440 ). For example, when the current rate of change of productivity is nonzero and an increase in work implement  18  depth will increase productivity even though machine speed may decrease, controller  30  may regulate work implement  18  to an increased depth. Likewise, if the current rate of change of productivity is nonzero and a decrease of work implement  18  depth will increase productivity even though less material may be moved in a single pass, controller  30  may regulate work implement  18  to a decreased depth. 
     When controller  30  determines that the current rate of change of productivity with respect to the current speed is about zero (i.e., machine  12  has reached a maximum attainable productivity and any change in tool depth results in less productivity) (step  450 ; yes), then controller  30  may maintain the current depth of work implement  18 , while continuously monitoring the rate of change of productivity (step  440 ). If, at some future time, controller  30  determines that the rate of change of productivity with respect to the current speed is no longer about zero (step  450 ; no) (i.e., no longer at a maximum productivity), then controller  30  once again may manipulate work implement  18  depth and, indirectly, machine speed (step  460 ), while continuing to monitor the rate of change of productivity (step  440 ). 
     Alternatively, it is contemplated that instead of always creating and updating a curve similar to  FIG. 4 , controller  30  may create a curve similar to  FIG. 4  and, from that created curve, determine a target speed which may cause machine  12  to operate at a maximum productivity given the current machine and terrain characteristics. Controller  30  may then manipulate cylinders  20  and work implement  18  to obtain that target speed, without continuously updating and creating a new productivity curve similar to  FIG. 4 . The curve similar to  FIG. 4  produced by controller  30  may be stored temporarily in the memory of controller  30  and periodically updated (i.e., every day), or it may be updated in response to a change in configuration of machine  12  or worksite  10  (i.e., changing work implement  18 ). Alternatively, the curve created by controller  30  may be updated only upon request from the operator of machine  12 . 
     Because controller  30  may be used with a variety of machines and work implement configurations, it&#39;s accuracy may be substantially unaffected by a change in the machine, work implement configuration, or capacity. Also, because controller  30  may be independent of machine, or limited to pre-programmed specific control maps, it may be applicable to and utilized in other machines or work implement configurations having a different output capacity, and to an older machine with diminished capacity. 
     It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed control system. Other embodiments will be apparent to those skilled in the art from consideration of the specification and practice of the disclosed control system. It is intended that the specification and examples be considered as exemplary only, with a true scope being indicated by the following claims and their equivalents.