Patent Publication Number: US-10774505-B2

Title: Work machine control system, work machine, and work machine control method

Description:
FIELD 
     The present invention relates to a work machine control system, a work machine, and a work machine control method. 
     BACKGROUND 
     Recently, an information and communication technology (ICT) is increasingly applied in a work machine such as a bulldozer. For example, there is a work machine or the like mounted with a global navigation satellite systems (GNSS) and the like and adapted to: detect own position; compare such positional information with current topographical data indicating a current topography of a work site; and find a position, a posture, or the like of a work unit by performing arithmetic processing (refer to Patent Literature 1, for example). The current topographical data is managed by, for example, an external server and the like, and transmitted to the work machine from such a server. The work machine receives one kind of current topographical data transmitted from the server, and performs arithmetic processing and the like. 
     CITATION LIST 
     Patent Literature 
     Patent Literature 1: Japanese Laid-open Patent Publication No. 2014-205955 
     SUMMARY 
     Technical Problem 
     Recently, in such a work machine, it is requested to accurately perform automatic control for a work unit by using, for example, current topographical data. In this case, it may be difficult to accurately perform automatic control for a work unit depending on accuracy of current topographical data transmitted from a management device. Therefore, estimating accuracy of the current topographical data is required. 
     The present invention is made considering the above-described situation, and an object of the present invention is to provide a work machine control system, a work machine, and a work machine control method capable of estimating accuracy of current topographical data. 
     Solution to Problem 
     According to an aspect of the present invention, a work machine control system comprises: an acquisition unit configured to acquire a plurality of pieces of current topographical data of a work site where a work machine including a work unit performs work; a setting unit configured to set predetermined first current topographical data and second current topographical data from the plurality of pieces of current topographical data acquired by the acquisition unit; and an arithmetic unit configured to calculate a difference between the first current topographical data and the second current topographical data, and obtain revision data to revise the first current topographical data based on the difference and parameter information related to a current topography of the work site. 
     Advantageous Effects of Invention 
     According to an embodiment of the present invention, accuracy of the current topographical data can be estimated. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a view illustrating an exemplary work machine according to the present embodiment. 
         FIG. 2  is a block diagram illustrating an exemplary control system that is a work machine control system according to the present embodiment. 
         FIG. 3  is a block diagram illustrating an exemplary display controller. 
         FIG. 4  is a diagram illustrating exemplary current topographical data. 
         FIG. 5  is a schematic diagram illustrating a state of calculating an inclination angle. 
         FIG. 6  is a table illustrating a correspondence relation between an angle group and an estimated error amount. 
         FIG. 7  is a histogram illustrating an exemplary estimated error function. 
         FIG. 8  is a diagram schematically illustrating processing to find an estimated error amount for each grid area. 
         FIG. 9  is a graph schematically illustrating processing to adjust an estimated error amount. 
         FIG. 10  is a flowchart illustrating an exemplary work machine control method according to the present embodiment. 
         FIG. 11  is a graph illustrating an estimated error function according to a modified example. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     An embodiment of a work machine control system, a work machine, and a work machine control method according to the present invention will be described based on the drawings. Note that the present invention is not limited by the embodiment. Furthermore, note that components in the following embodiment include a component readily replaceable by a man skilled in the art or a component substantially identical thereto. 
       FIG. 1  is a view illustrating an exemplary work machine according to the present embodiment. In the present embodiment, a description will be provided by exemplifying a bulldozer  100  as a work machine. The bulldozer  100  includes a vehicle body  10  and a work unit  20 . In the present embodiment, the bulldozer  100  is used in a work site such as a mine. 
     An X-axis, a Y-axis, a Z-axis illustrated in  FIG. 1  represent an X-axis, a Y-axis, a Z-axis in a global coordinate system. In the present embodiment, a direction in which the work unit  20  is located relative to the vehicle body  10  is defined as a frontward direction. Therefore, a direction in which the vehicle body  10  is located relative to the work unit  20  is defined as a backward direction. In the present embodiment, a direction in which the vehicle body  10  is located relative to a ground contact surface where a crawler  11   a  contacts the ground is defined as an upward direction, and a direction directed from the vehicle body  10  to the ground contact surface, in other words, a gravity direction is defined as a downward direction. Note that, in  FIG. 1 , the bulldozer  100  is disposed in a state in which a front-back direction is made to coincide with the X-direction, a vehicle width direction is made to coincide with the Y-direction, and a vertical direction is made coincide with the Z-direction. 
     The vehicle body  10  includes a travel device  11  as a travel unit. The travel device  11  includes the crawler  11   a . The crawler  11   a  is disposed on each of right and left sides of the vehicle body  10 . The travel device  11  makes the bulldozer  100  travel by rotating the crawler  11   a  by a hydraulic motor not illustrated. 
     The vehicle body  10  includes an antenna  12 . The antenna  12  is used to detect a current position of the bulldozer  100 . The antenna  12  is electrically connected to a global coordinate arithmetic device  15 . The global coordinate arithmetic device  15  is a position detector adapted to detect a position of the bulldozer  100 . The global coordinate arithmetic device  15  detects the current position of the bulldozer  100  by utilizing global navigation satellite systems (GNSS represents global navigation satellite systems). In the following description, the antenna  12  will be suitably referred to as a GNSS antenna  12 . A signal in accordance with GNSS radio waves received by the GNSS antenna  12  is received in the global coordinate arithmetic device  15 . The global coordinate arithmetic device  15  finds a setting position of the GNSS antenna  12  in the global coordinate system (X, Y, Z) illustrated in  FIG. 1 . A global positioning system (GPS) can be exemplified as an example of the global navigation satellite system, but the global navigation satellite system is not limited thereto. It is preferable that the GNSS antenna  12  be set at an upper end of an operation room  13 , for example. 
     The vehicle body  10  includes the operation room  13  provided with an operation seat to be seated by an operator. In the operation room  13 , various kinds of operating devices and a display unit  14  to display image data are disposed. The display unit  14  is, for example, a liquid crystal device or the like, but not limited thereto. For the display unit  14 , a touch panel integrating an input unit with a display unit can be used, for example. Additionally, an operating device not illustrated is provided in the operation room  13 . The operating device is a device to operate at least one of the work unit  20  and the travel device  11 . 
     The work unit  20  includes a blade  21  that is a working tool, a lift frame  22  to support the blade  21 , and a lift cylinder  23  to drive the lift frame. The blade  21  includes a blade edge  21   p . The blade edge  21   p  is disposed at a lower end portion of the blade  21 . The blade edge  21   p  contacts the ground during work such as land grading work or excavation work. The blade  21  is supported by the vehicle body  10  via the lift frame  22 . The lift cylinder  23  connects the vehicle body  10  to the lift frame  22 . The lift cylinder  23  drives the lift frame  22  and vertically moves the blade  21 . The work unit  20  includes a lift cylinder sensor  23   a . The lift cylinder sensor  23   a  detects lift cylinder length data La representing a stoke length of the lift cylinder  23 . 
       FIG. 2  is a block diagram illustrating an exemplary control system  200  that is a work machine control system according to the present embodiment. As illustrated in  FIG. 2 , the control system  200  includes: the global coordinate arithmetic device  15 ; an inertial measurement unit (IMU)  16  that is a state detector to detect an angular speed and an acceleration speed; a navigation controller  40 ; a display controller  30 ; and a work unit controller  50 . 
     The global coordinate arithmetic device  15  acquires reference positional data P 1  that is positional data of the antenna  12  indicated by the global coordinate system. The global coordinate arithmetic device  15  includes: a processing unit that is a processor such as a central processing unit (CPU); and a storage unit that is a storage device such as a random access memory (RAM) and a read only memory (ROM). 
     The global coordinate arithmetic device  15  generates positional data P indicating a position of the vehicle body  10  based on the reference positional data P 1 . The positional data P indicates a position in the global coordinate system (X, Y, Z). The global coordinate arithmetic device  15  outputs the generated positional data P to the navigation controller  40  and display controller  30 . 
     The IMU  16  is the state detector to detect operational information of the bulldozer  100 . In the embodiment, the operational information may include information indicating a posture of the bulldozer  100 . Exemplary information indicating the posture of the bulldozer  100  may include a roll angle, a pitch angle, and an orientation angle of the bulldozer  100 . The IMU  16  is mounted on the vehicle body  10 . The IMU  16  may be installed at a lower portion of the operation room  13 , for example. 
     The IMU  16  detects an angular speed and an acceleration speed of the bulldozer  100 . With operation of the bulldozer  100 , various kinds of acceleration speeds such as an acceleration speed generated during travel, an angular acceleration speed during swing, and a gravitational acceleration speed are generated in the bulldozer  100 , and the IMU  16  detects and outputs at least the gravitational acceleration speed. Here the gravitational acceleration speed is an acceleration speed corresponding to resistance against gravity. The IMU  16  detects, for example, acceleration speeds in the X-axis direction, Y-axis direction, and Z-axis direction and angular speeds (rotation angular speeds) around the X-axis, Y-axis, and Z-axis in the global coordinate system (X, Y, Z). 
     The display controller  30  displays an image such as a guidance screen on the display unit  14 . The display controller  30  includes a communication unit  32 . The communication unit  32  can communicate with an external communication apparatus. The communication unit  32  receives, for example, current topographical data  70  and design topographical data  80  of a work site from a management server  300  and the like. The communication unit  32  may also receive the current topographical data  70  and design topographical data  80  of the work site from an external storage device such as a USB memory, a PC, a portable terminal, and so on. 
     The navigation controller  40  includes: a processing unit that is a processor such as a CPU; and a storage unit that is a storage device such as a RAM and a ROM. The navigation controller  40  receives a detection value of the global coordinate arithmetic device  15 , a detection value of the IMU  16 , and an output value from the work unit controller  50  described later. The navigation controller  40  finds positional information related to a position of the bulldozer  100  from the detection value of the global coordinate arithmetic device  15  and the detection value of the IMU  16 , and outputs the same to the display controller  30 . The navigation controller  40  receives blade edge positional data from the work unit controller  50 . The blade edge positional data is data indicating a blade edge position that is a three-dimensional position of the blade edge  21   p . The navigation controller  40  generates target blade edge positional data indicating a target blade edge position based on the blade edge positional data. The navigation controller  40  uses current topographical data indicating a current topography of a work site at the time of generating the target blade edge positional data. The navigation controller  40  generates, for example, a virtual target ground surface on which the current topography indicated by the current topographical data is offset downward by a predetermined distance, and generates the target blade edge positional data such that the blade edge  21   p  conforms to the virtual target ground surface. 
     The work unit controller (work unit control unit)  50  includes: a processing unit that is a processor such as a CPU; and a storage unit that is a storage device such as a RAM and a ROM. The work unit controller  50  detects the blade edge positional data by using positional information of the blade  21  and outputs the same to the navigation controller  40 . The work unit controller  50  receives the target blade edge positional data from the navigation controller  40 . The work unit controller  50  generates and outputs a work unit command value adapted to control operation of the work unit  20  based on the target blade edge positional data. 
       FIG. 4  is a diagram illustrating exemplary current topographical data. As illustrated in  FIG. 4 , current topographical data  70  is data related to a height position (Z-coordinate) in each grid area G in the case of sectioning the work site into a plurality of grid areas G in the X-direction and Y-direction of the global coordinate system. Meanwhile, the current topographical data  70  is only needed to be the data related to height data of any position in a grid area G, and for example, may be height data at a center position of a grid area G or may also be height data at four corners of a grid area G. The grid area G is set to have a square shape, for example, but not limited thereto, and may have other shapes such as a rectangle, a parallelogram, and a triangle. 
     In the present embodiment, the current topographical data  70  is generated by, for example, measuring a current topography of a work site by using various kinds of measuring methods. The current topographical data  70  includes, for example, multiple kinds of current topographical data obtained by different measuring methods. Exemplary measuring methods adapted to generate the current topographical data  70  may include: a method of measuring a current topography by using positional information of a vehicle which travels in a work site; a method of measuring a current topography by using positional information of a work machine such as the bulldozer  100  which travels in a work site, a method of surveying a current topography by making a surveying vehicle travel; a method of surveying a current topography by using a stationary surveying instrument; a method of measuring a current topography by a stereo camera; and a method of measuring a current topography by an unmanned air vehicle such as a drone. Meanwhile, measurement by a drone and the like may be a method in which a current topography is photographed by using, for example, a camera and the like and current topographical data is measured based on this photographing result, or the current topographical data may be measured by using a laser scanner. Identifying information may also be assigned to the current topographical data  70  in order to identify a measuring method and the like. 
       FIG. 3  is a block diagram illustrating an exemplary navigation controller  40 . As illustrated in  FIG. 3 , the navigation controller  40  includes a processing unit  44  and a storage unit  45 . The navigation controller  40  has the processing unit  44  and the storage unit  45  connected via a signal line such as a bus line  46 . 
     The processing unit  44  is a processor such as a CPU. The processing unit  44  includes a current topographical data calculation unit  61 , an acquisition unit  62 , a setting unit  63 , and an arithmetic unit  64 , a correction unit  65 , and an adjustment unit  66 . 
     The current topographical data calculation unit  61  calculates current topographical data  70  indicating a current topography for a region of the work site where, for example, the bulldozer  100  has passed. The current topographical data calculation unit  61  calculates the current topographical data  70  based on, for example, positional information output from the global coordinate arithmetic device  15 . In this case, the current topographical data calculation unit  61  calculates, for example, a Z-coordinate in each of grid areas G corresponding to the region where the bulldozer  100  has passed. 
     The acquisition unit  62  acquires a plurality of pieces of the current topographical data  70  indicating a current topography of the work site. The current topographical data  70  acquired by the acquisition unit  62  includes, for example, current topographical data  70  received from a management server  300  and the current topographical data  70  generated in the current topographical data calculation unit  61 . 
     Accuracy, a range including data, and the like of the plurality of pieces of current topographical data  70  acquired by the acquisition unit  62  may be varied by a measuring method and the like. For example, current topographical data  70  acquired by performing measurement by making a vehicle travel in the work site has low measurement accuracy because a travel speed during the measurement is fast. On the other hand, the number of grid areas G including data can be increased by measuring the current topographical data  70  by making the vehicle travel across a wide region of the work site. 
     Additionally, the bulldozer  100  travels at a speed slower than the above vehicle, and therefore, current topographical data  70  acquired by making the bulldozer  100  travel has high measurement accuracy because of the slow travel speed. On the other hand, since the bulldozer  100  mainly travels, for example, at places of the work site in order that the bulldozer  100  may perform work and move for the work, the number of grid areas G including data is limited. 
     Therefore, the acquisition unit  62  may acquire, for example, current topographical data  70  which is highly accurate and includes a small number of grid areas G and current topographical data  70  which is low accurate and includes a large number of grid areas G, in other words, the acquisition unit  62  may acquire the plurality of pieces of current topographical data  70  having different accuracy in a mixed manner. In this case, as for a grid area G including highly-accurate current topographical data  70 , the processing can be performed by using this highly-accurate current topographical data  70 . On the other hand, as for a grid area G not including such highly-accurate current topographical data  70 , the processing is performed by using low-accurate current topographical data  70 . In the present embodiment, in this case, the low-accurate current topographical data  70  is revised by using the highly-accurate current topographical data  70 , thereby improving accuracy of the low-accurate current topographical data  70 . In the following, the relatively low-accurate current topographical data  70  is defined as first current topographical data  71 , and the highly-accurate current topographical data  70  is defined as second current topographical data  72 . 
     The setting unit  63  sets the first current topographical data  71  and the second current topographical data  72  based on the plurality of pieces of current topographical data  70  acquired by the acquisition unit  62 . The setting unit  63  may set the first current topographical data  71  and the second current topographical data  72  by any method. In the following, a description will be provided by exemplifying a case where a measuring method for current topographical data  70  set as the first current topographical data  71  and a measuring method for the current topographical data  72  set as the second current topographical data  72  are preliminarily determined, and the setting unit  63  sets the first current topographical data  71  and the second current topographical data  72  based on the methods by which the current topographical data  70  is measured. 
     The arithmetic unit  64  calculates, for each of the grid areas G, a height data difference between the first current topographical data  71  and the second current topographical data  72  at the same position in a grid area G. A plurality of height data differences calculated for each of the grid areas G is stored in the storage unit  45  as difference data  82 . 
     Furthermore, the arithmetic unit  64  finds an estimated error function in order to revise the first current topographical data  71  based on the plurality of differences calculated for each of the grid areas G and later-described parameter information related to a current topography of a work site. The estimated error function is an example of revision data. The inventor of the present invention has discovered correlation that, for example, the larger an inclination angle relative to a horizontal plane a grid area G has, the larger height data difference is in the current topographical data  70 . Therefore, in the present embodiment, a description will be provided by exemplifying an inclination angle relative to the horizontal plane in each of the grid areas G as the parameter information. In this case, the arithmetic unit  64  calculates, for each grid area G, an inclination angle relative to the horizontal plane, categorizes each grid areas G as one of a plurality of groups based on an angle size of the calculated inclination angle, and sets the group as the parameter information. In the following, a procedure by which the arithmetic unit  64  sets the parameter information will be described. 
       FIG. 5  is a schematic diagram illustrating a state of calculating an inclination angle. As illustrated in  FIG. 5 , in the case of finding an inclination angle in one grid area Gt, the arithmetic unit  64  finds a height position difference between the grid area Gt and peripheral grid areas. In the present embodiment, four grid areas Gn, Gs, Ge, Gw which share respective sides of the grid area Gt are included as the peripheral grid areas of the grid area Gt. Meanwhile, the peripheral grid areas of the grid area Gt may also include grid areas G obliquely adjacent to the grid area Gt instead of the above four grid areas Gn, Gs, Ge, Gw or in addition to the above four grid areas Gn, Gs, Ge, Gw. 
     In  FIG. 5 , a height position difference h between the grid area Gt and the grid area Ge is illustrated as an example. The arithmetic unit  64  calculates such a height position difference between the grid area Gt and each of the grid areas Gn, Gs, Ge, Gw. The arithmetic unit  64  calculates an angle α based on the calculated height position difference and a pitch d of a grid area. In this case, the angle α is an angle between the horizontal plane and each of straight lines connecting a center point Ot of the grid area Gt to each of center points of the grid areas Gn, Gs, Ge, Gw (center point Oe is illustrated in  FIG. 5 ). The arithmetic unit  64  adopts, for example, a largest value among the calculated four angles α as the inclination angle of the grid area Gt. Meanwhile, the arithmetic unit  64  may also adopt an average value of the calculated four angles α as the inclination angle of the grid area Gt. 
     In the case of calculating the inclination angle, the arithmetic unit  64  categorizes the calculated inclination angle as one of the plurality of angle groups (groups) based on angle size.  FIG. 6  is a table illustrating a correspondence relation between an angle group and an estimated error amount. As illustrated in  FIG. 6 , the arithmetic unit  64  categorizes an inclination angle into one of, for example, seven groups including first to seventh groups based on the angle size of the inclination angle. 
     For example, in the case where angles α1, α2, α3, α4, α5, α6 satisfy a relation of α1&lt;α2&lt;α3&lt;α4&lt;α5&lt;α6, the first group is a group which a grid area G having an inclination angle of 0° or more and less than α1° belongs to. The second group is a group which a grid area G having an inclination angle of α1° or more and less than α2° belongs to. The third group is a group which a grid area G having an inclination angle of α2° or more and less than α3° belongs to. The fourth group is a group which a grid area G having an inclination angle of α3° or more and less than α4° belongs to. The fifth group is a group which a grid area G having an inclination angle of α4° or more and less than α5° belongs to. The sixth group is a group which a grid area G having an inclination angle of α5° or more and less than α6° belongs to. The seventh group is a group which a grid area G having an inclination angle of α6° or more belongs to. Thus, the arithmetic unit  64  sets the parameter information by setting the plurality of angle groups (groups). 
     The arithmetic unit  64  finds an estimated error function in order to revise the first current topographical data  71  based on the calculated plurality of differences and the parameter information. In the following, a procedure by which the arithmetic unit  64  finds an estimated error function will be described. In the present embodiment, the arithmetic unit  64  finds an estimated error amount for each angle group that is the parameter information. Specifically, the arithmetic unit  64  finds a height data difference between the first current topographical data  71  and the second current topographical data  72  at the same position in a grid area G for each of the plurality of grid areas G belonging to the respective angle groups, and calculates an average value or a center value of the differences, for example. The calculated result is an estimated error amount in the angle group. As illustrated in  FIG. 6 , estimated error amounts (E 1  to E 7 ) are found for the respective groups formed of the first to seventh groups. Thus, the arithmetic unit  64  correlates the angle group (angle information) that is the parameter information to the estimated error amount, thereby finding an estimated error function F 1  indicating a relation between the angle group and the estimated error amount. In the present embodiment, the estimated error function F 1  includes all of relations between the respective angle groups from first to seventh groups and the estimated error amounts (E 1  to E 7 ) of the respective angle groups. In the present embodiment, the arithmetic unit  64  may create, for example, a histogram in which an angle group is correlated to an error estimated amount on a one-to-one basis as a style of the estimated error function F 1 . 
       FIG. 7  is a histogram illustrating an estimated error function, and specifically illustrates a relation between an angle group to which a grid area G belongs and an estimated error amount. A horizontal axis in  FIG. 7  represents the angle group, and a vertical axis in  FIG. 7  represents the estimated error amount (unit: m). As illustrated in  FIG. 7 , the estimated error amounts satisfy a relation of E 1 &lt;E 2 &lt;E 3 &lt;E 4 &lt;E 5 &lt;E 6 &lt;E 7 . As understood from  FIG. 7 , a grid area G belonging to an angle group having a larger inclination angle has a larger estimated error amount in the grid area G. 
     Additionally,  FIG. 8  is a diagram schematically illustrating processing to find an estimated error amount for each grid area G. Based on the estimated error function F 1 , the arithmetic unit  64  finds, for each grid area G, an estimated error amount corresponding to an angle group which the grid area G belongs to. 
     The correction unit  65  corrects the first current topographical data  71  based on the estimated error function F 1  found in the arithmetic unit  64 . Meanwhile, the correction unit  65  may also correct the first current topographical data  71  only in the case where a value of the first current topographical data  71  becomes smaller before and after correction. In this case, the value of the current topographical data  71  can be prevented from becoming larger than an actual current topography. Therefore, the blade edge  21   p  of the blade  21  can be prevented from separating from the ground at the time of automatically controlling the work unit  20 . For example, in the case of automatically controlling the work unit  20  based on the first current topographical data  71  in a grid area G including no second current topographical data  72  and including only the first current topographical data  71 , the correction unit  65  revises height data of the first current topographical data  71  by an estimated error amount. As a result, the ground of a work site can be surely excavated and so-called missed swing of the blade  21  can be avoided. 
     In the case of newly obtaining difference data  82  between the second current topographical data  72  and the first current topographical data  71  in a state in which the estimated error amounts E 1 , E 2 , E 3 , E 4 , E 5 , E 6 , E 7  have been found, the adjustment unit  66  updates the estimated error amounts by using new difference data  82 . For example, in the case where the bulldozer  100  newly travels in a grid area G not including so far highly-accurate second current topographical data  72  and including only the relatively low-accurate first current topographical data  71  and then second current topographical data  72  is newly generated for this grid area G, an estimated error amount that has been already calculated can be updated by using difference data  82  in this grid area G to calculate an estimated error amount. 
     In this case, the adjustment unit  66  calculates differences for a plurality of grid areas G belonging to the respective angle groups in a similar manner as the arithmetic unit  64  does, and calculates an average value or a center value of the differences, for example.  FIG. 9  is a graph schematically illustrating processing to adjust an estimated error amount, in which a horizontal axis represents the angle group, and a vertical axis represents the estimated error amount in a similar manner as  FIG. 7 . 
     For example, as for a plurality of grid areas G belonging to the third group, an estimated error amount of the third group is, for example, E 3  before adjustment processing by the adjustment unit  66 . In the case where the estimated error amount becomes E 3   a  as a result of adjustment processing by the adjustment unit  66 , in other words, as a result of re-calculation of an estimated error amount by using newly-added second current topographical data  72 , the adjustment unit  66  changes the estimated error amount of the third group from E 3  to E 3   a  as illustrated in  FIG. 9 . 
     Additionally, the storage unit  45  stores current topographical data  70 , design topographical data  80 , difference data  82 , and an estimated error function F 1 . Furthermore, the storage unit  45  stores programs, data, and the like in order to execute various kinds of processing in the processing unit  44 . 
       FIG. 10  is a flowchart illustrating an exemplary work machine control method according to the present embodiment. In Step ST 10 , the acquisition unit  62  of the navigation controller  40  acquires current topographical data  70 . Examples of the current topographical data  70  may include current topographical data  70  received from the management server  300  and current topographical data  70  generated in the current topographical data calculation unit  61 . 
     Next, the setting unit  63  sets first current topographical data  71  and second current topographical data  72  based on a plurality of pieces of current topographical data  70  acquired by the acquisition unit  62  (Step ST 20 ). In Step ST 20 , the setting unit  63  sets data close to an actual current topography, namely, highly-accurate data as the second current topographical data  72  so as to use the second current topographical data  72  as teaching data (reference data for revision) in order to revise the first current topographical data  71 . Additionally, in Step ST 20 , the setting unit  63  may set the first current topographical data  71  and the second current topographical data  72  by any method, but in the present embodiment, for example, a measuring method for the current topographical data  70  set as the first current topographical data  71  and a measuring method for the current topographical data  70  set as the second current topographical data  72  are preliminarily determined, and the setting unit  63  sets the first current topographical data  71  and the second current topographical data  72  based on the methods by which the current topographical data  70  is measured. 
     Next, the arithmetic unit  64  calculates, for each grid area G, a difference of height data of the first current topographical data  71  from the second current topographical data  72  at the same position in the grid area G (Step ST 30 ). Subsequently, the arithmetic unit  64  sets parameter information for each grid area G (Step ST 40 ). In Step ST 40 , the arithmetic unit  64  can set various kinds of information as the parameter information. In the present embodiment, for example, the arithmetic unit  64  calculates, for each grid area G, an inclination angle relative to a horizontal plane, categorizes each grid area G as one of a plurality of groups based on an angle size of the calculated inclination angle, and sets the group as the parameter information. In Step ST 40 , the arithmetic unit  64  sets the parameter information by setting, for example, the angle groups from a first group to a seventh group based on the angle sizes of the inclination angles. 
     Next, the arithmetic unit  64  derives an estimated error function F 1  based on the calculated differences and the parameter information (Step ST 50 ). In Step ST 50 , the arithmetic unit  64  finds, for example, estimated error amounts (E 1  to E 7 ) for the respective angle groups, and derives the estimated error function F 1  by correlating the angle groups to the estimated error amounts. 
     After that, for example, in the case of automatically controlling the work unit  20  based on the first current topographical data  71  in a grid area G not including the second current topographical data  72  and only including the first current topographical data  71 , the correction unit  65  corrects the first current topographical data  71  based on the derived estimated error function F 1  (Step ST 60 ). After that, the navigation controller  40  and the work unit controller  50  may also control the work unit  20  based on the corrected first current topographical data  71  as the current topographical data  70 . In this case, since the work unit  20  is controlled based on the first current topographical data  71  having more improved accuracy, the work unit  20  can be controlled accurately. Furthermore, since the work unit  20  can surely excavate the ground of a work site, so-called missed swing of the blade  21  can be avoided. 
     Meanwhile, after Step ST 50  or Step ST 60 , the bulldozer  100  newly travels in a grid area G not including so far highly-accurate second current topographical data  72  and including only relatively low-accurate first current topographical data  71  and then new second current topographical data  72  is generated for this grid area G, the adjustment unit  66  may perform processing to update the estimated error function F 1 . In this case, the adjustment unit  66  updates the estimated error amount based on the difference data  82  of the first current topographical data  71  from the second current topographical data  72 . 
     As described above, the work machine control system  200  according to the present embodiment includes: the acquisition unit  62  adapted to acquire the plurality of pieces of current topographical data  70  for the work site where the bulldozer  100  performs work; the setting unit  63  adapted to set the first current topographical data  71  and the second current topographical data  72  from the plurality of pieces of current topographical data  70  acquired by the acquisition unit  62 ; and the arithmetic unit  64  adapted to calculate a difference between the first current topographical data  71  and the second current topographical data  72 , and find an estimated error function F 1  that is revision data to revise the first current topographical data  71  based on the difference and the parameter information related to the current topography of the work site. 
     Furthermore, the work machine control system  200  according to the present embodiment finds, for each grid area G, an inclination angle relative to a horizontal plane as parameter information and categorizes the found inclination angle as one of a plurality of angle groups based on the angle size. Therefore, even when the number of grid areas G for which inclination angles are found is increased, the number of parameter information is not increased and kept constant. Therefore, a large amount of information can be efficiently processed. 
     According to this configuration, the first current topographical data  71  and the second current topographical data  72  are set from among the acquired plurality of pieces of current topographical data  70 , the estimated error function F 1  of the first current topographical data  71  is calculated by using the second current topographical data  72  as the teaching data, and the first current topographical data  71  can be revised based on the estimated error function F 1 . Therefore, accuracy of the first current topographical data  71  can be improved. 
     While the embodiment has been described above, note that the embodiment is not limited by the described content. Further, the components described above may include a component readily conceivable by those skilled in the art, a component substantially identical, and a component in a so-called equivalent range. Further, the components described above can be suitably combined. Furthermore, at least one of various kinds of omission, replacement, and modification can be made for the components in the scope without departing from the gist of the embodiment. For example, the respective processing executed by the navigation controller  40  may also be executed by the display controller  30 , work unit controller  50 , or a controller other than these. 
     Furthermore, in the above embodiment, the description has been provided by exemplifying the bulldozer  100  as a work machine, but not limited thereto, a different work machine such as an excavator or a wheel loader may also be used. Additionally, the control system  200  of the above embodiment may be provided in a work machine such as the bulldozer  100 , may also be provided in the management server  300  and the like, or may also be shared by a work machine and a management server. 
     Moreover, in the above embodiment, the description has been provided by exemplifying the case where the measuring method for the current topographical data  70  set as the first current topographical data  71  and the measuring method for the current topographical data  70  set as the second current topographical data  72  are preliminarily determined, and the setting unit  63  sets the first current topographical data  71  and the second current topographical data  72  based on the methods by which the current topographical data  70  is measured, but not limited thereto. For example, the setting unit  63  may set the first current topographical data  71  and the second current topographical data  72  based on a command or input by an operator. In addition, the setting unit  63  may preliminarily set, for example, priority order or quantified accuracy information in accordance with each measuring method for current topographical data  70 , and may set the first current topographical data  71  and the second current topographical data  72  based on the priority order or the accuracy information. Moreover, for example, the setting unit  63  may compare the plurality of pieces of current topographical data  70  acquired by the acquisition unit  62  with correct current topographical data preliminarily measured by a surveying instrument such as a laser scanner, and may set current topographical data  70  having a large difference as the first current topographical data  71  and set current topographical data  70  having a small difference as the second current topographical data  72 . 
     Meanwhile, in the above embodiment, the setting unit  63  sets, as the first current topographical data  71 , current topographical data  70  in the case of measuring a current topography by using positional information of a vehicle which travels in a work site, and sets, as the second current topographical data  72 , current topographical data  70  in the case of measuring a current topography by using positional information of a work machine such as the bulldozer  100  which travels in the work site, but not limited thereto. For example, in the case of measuring the current topography by using positional information of a vehicle or the like, accuracy may be varied by accuracy and a calculation algorithm of each kind of a sensor. Therefore, the current topographical data  70  in the case of measuring a current topography by using the positional information of the vehicle may be set as the second current topographical data  72 , and the current topographical data  70  in the case of measuring the current topography by using the positional information of the work machine may be set as the first current topographical data  71 . 
     Additionally, in the above embodiment, an inclination angle relative to a horizontal plane is found for a grid area G as parameter information, and the inclination angle is categorized as one of the plurality of angle groups based on the angle size, but not limited thereto.  FIG. 11  is a graph illustrating an estimated error function according to a modified example. 
     For example, in the case of using the inclination angle relative to the horizontal plane for a grid area G as the parameter information, the arithmetic unit  64  may find, for each of the grid areas G, a relation between an inclination angle and an estimated error amount, derive an approximate curve based on respective values, and set the approximate curve as an estimated error function F 2  as illustrated in  FIG. 11 . The approximate curve can be found by an approximation method such as a least-square method. Furthermore, the approximate curve can be a curve determined by a quadratic function, or a cubic or higher function. In this case, the correction unit  65  corrects the first current topographical data  71  based on the estimated error function F 2 . The estimated error function F 2  is an example of revision data. 
     Furthermore, the revision data is not limited to the above-described estimated error function F 1  and estimated error function F 2 , and any type of data may be applied. 
     Furthermore, in the above-described embodiment, the description has been provided for the case of using, as the parameter information, the inclination angle relative to the horizontal plane related to the grid area G, but not limited thereto. For example, as the time of receiving GNSS radio waves, the antenna  12  also receives accuracy information in addition to positional information. In this case, the navigation controller  40  stores, in the storage unit  45 , the received accuracy information in a manner correlated to the positional information as the data for each grid area G. For example, in the case where the current topographical data  70  is generated in the current topographical data calculation unit  61  and the like based on positional information included in the GNSS radio waves, the arithmetic unit  64  may use the accuracy information included in the GNSS radio waves as the parameter information of the first current topographical data  71 . 
     Furthermore, for example, water content of earth and sand to be working targets in a work site, and geological information such as compositions of soil or rocks may also be used as the parameter information. In this case, the navigation controller  40  stores, in the storage unit  45 , for example, the geological information measured by a measuring instrument and the like as the data for each grid area G in a manner correlated to the positional information. Consequently, the arithmetic unit  64  can use, for example, the geological information measured by a measuring device and the like as the parameter information. 
     Furthermore, for example, a time when the current topographical data  70  is generated or a time when the acquisition unit  62  acquires the current topographical data  70  may be written in the current topographical data  70  as time information, and such time information may also be used as the parameter information. In this case, it can be estimated, for example, that the older time current topographical data  70  is acquired, the larger an error is. 
     Additionally, for example, the navigation controller  40  may store, in the storage unit  45 , measuring method data indicating measuring methods at the time of generating current topographical data  70  in a manner correlated to the current topographical data  70  or as data for each grid area G. In this case, the setting unit  63  sets the first current topographical data  71  and the second current topographical data  72  based on the measuring methods for the current topographical data  70 . Furthermore, the arithmetic unit  64  may preliminarily set a revision amount of the first current topographical data  71  based on a difference of the measuring method between the first current topographical data  71  and the second current topographical data  72 , and may uniformly revise the first current topographical data  71  based on the revision amount. 
     REFERENCE SIGNS LIST 
     α Angle 
     E 1 , E 2 , E 3 , E 4 , E 5 , E 6 , E 7  Estimated error amount 
     F 1 , F 2  Estimated error function 
     G, Ge, Gn, Gs, Gt, Gw Grid area 
       10  Vehicle body 
       11  Travel device 
       11   a  Crawler 
       20  Work unit 
       21  Blade 
       21   p  Blade edge 
       30  Display controller 
       31  Input unit 
       32  Communication unit 
       33  Output unit 
       34  Processing unit 
       35  Storage unit 
       40  Navigation controller 
       50  Work unit controller 
       61  Current topographical data calculation unit 
       62  Acquisition unit 
       63  Setting unit 
       64  Arithmetic unit 
       65  Correction unit 
       66  Adjustment unit 
       67  Display control unit 
       70  Current topographical data 
       71  First current topographical data 
       72  Second current topographical data 
       80  Design topographical data 
       81  Virtual design data 
       82  Difference data 
       100  Bulldozer 
       200  Control system 
       300  Management server