Patent Publication Number: US-9410305-B2

Title: Excavation control system for hydraulic excavator

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 14/238,059, filed on Feb. 10, 2014, which is a U.S. National stage application of International Application No. PCT/JP2013/057211, filed on Mar. 14, 2013. This U.S. National stage application claims priority under 35 U.S.C. §119(a) to Japanese Patent Application No. 2012-090034, filed in Japan on Apr. 11, 2012. The entire contents of U.S. patent application Ser. No. 14/238,059 and Japanese Patent Application No. 2012-090034 are hereby incorporated herein by reference. 
    
    
     BACKGROUND 
     1. Field of the Invention 
     The present invention relates to an excavation control system for a hydraulic excavator. 
     2. Background Information 
     The conventional art proposes, for a construction machine provided with a front device including a bucket, an excavation region limit control that moves the bucket along a boundary face indicating a target shape for an excavation object (for example, refer to International Publication No. WO95/30059). 
     Further, the conventional art discloses a method for calculating designed surface data in a computer located in a hydraulic excavator, based on dimensions and gradient data sent from a computer located at an office (refer Japanese Patent Laid-open No. 2006-26594). 
     SUMMARY 
     However, in the invention disclosed in Japanese Patent Laid-open No. 2006-26594, the computer at the hydraulic excavator side calculates designed surface data regardless of whether or not the bucket of the hydraulic excavator is positioned in a range in which excavation is possible. For this reason the processing load on the computer at the hydraulic excavator side becomes large, moreover there are cases in which the calculated designed surface data must be discarded without being used. 
     In light of the above described problems, a purpose of the present invention is to provide an excavation control system for a hydraulic excavator capable of simply acquiring the desired designed surface data. A hydraulic excavator excavation control system according to an aspect of the present invention is provided with a vehicle main body, a working unit, a designed landform data storage part, a bucket position data generation part, a designed surface data generation part and an excavation limit control part. The working unit has a boom, an arm and a bucket. The boom is attached to the vehicle main body. The arm is attached to the boom. The bucket is attached to the arm. The designed landform data storage part is configured to store designed landform data indicating a target shape for an excavation object. The bucket position data generation part is configured to generate bucket position data indicating a current position of the bucket. The designed surface data generation part is configured to generate superior designed surface data and subordinate designed surface data based on the designed landform data and the bucket position data. The superior designed surface data indicates a superior designed surface corresponding to a position of the bucket. The subordinate designed surface data indicates a first subordinate designed surface linked to the superior designed surface. The designed surface data generation part is configured to generate shape data indicating shapes of the superior designed surface and the first subordinate designed surface. The excavation limit control part is configured to automatically adjust a position of the bucket in relation to the superior designed surface and the first subordinate designed surface based on the shape data and the bucket position data. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a perspective view of the hydraulic excavator; 
         FIG. 2A  is a side view of the hydraulic excavator  100 ; 
         FIG. 2B  is a rear view of the hydraulic excavator  100 ; 
         FIG. 3  is a block diagram showing the functional configuration of the excavation control system for the hydraulic excavator; 
         FIG. 4  is a block diagram showing the configuration of the display controller; 
         FIG. 5  is a schematic diagram showing a prospective surfaces; 
         FIG. 6  is a schematic diagram showing designed surfaces; 
         FIG. 7  is a block diagram showing the configuration of the working unit controller; 
         FIG. 8  is a schematic diagram showing the positional relationship between the bucket and the designed surface S; 
         FIG. 9  is a graph showing the relationship between limit speed and distance; and 
         FIG. 10  is a schematic diagram explaining operation of the bucket. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENT(S) 
     An embodiment of the present invention will now be described with reference to the drawings. 
     Entire Configuration of the Hydraulic Excavator  100   
       FIG. 1  is a perspective view of the hydraulic excavator  100  related to this embodiment of the present invention. The hydraulic excavator  100  has a vehicle main body  1 , and a working unit  2 . Further, an excavation control system  200  is installed to the hydraulic excavator  100 . The configuration and operation of the excavation control system  200  is described subsequently. 
     The vehicle main body  1  has a revolving body  3 , a cab  4 , and a drive unit  5 . The revolving body  3  is arranged above the drive unit  5 , and is capable of turning centered around a pivotal axis following the upward-downward direction. The revolving body  3  houses a hydraulic pump and an engine etc., not shown in the drawing. 
     A first Global Navigation Satellite Systems (GNSS) antenna  21  and a second GNSS antenna  22  are arranged over the rear end portion of the revolving body  3 . The first GNSS antenna  21  and the second GNSS antenna  22  are RTK-GNSS (Real-Time Kinematic Global Navigation Satellite Systems, GNSS means satellite systems covering the entire globe) antennas. 
     The cab  4  is arranged over the front portion of the revolving body  3 . Different kinds of operating devices are arranged in the cab  4 . The traveling device  5  has a pair of crawler belt  5   a  and  5   b,  and the hydraulic excavator  100  is caused to travel by the rotations of each of the crawler belt  5   a  and  5   b.    
     The working unit  2  is installed on the revolving body  3 . The working unit  2  has a boom  6 , an arm  7 , a bucket  8 , a boom cylinder  10 , an arm cylinder  11 , and a bucket cylinder  12 . 
     The base end portion of the boom  6  is attached so as to be capable of swinging, to the front portion of the revolving body  3  via a boom pin  13 . The base end portion of the arm  7  is attached, so as to be capable of swinging, to the leading end portion of the boom  6  via an arm pin  14 . The bucket  8  is attached, so as to be capable of swinging, at the leading end portion of the arm  7  via a bucket pin  15 . The boom cylinder  10 , the arm cylinder II, and the bucket cylinder  12  are each driven by hydraulic fluid. The boom cylinder  10  drives the boom  6 . The arm cylinder  11  drives the arm  7 . The bucket cylinder  12  drives the bucket  8 . 
     Here,  FIG. 2A  is a side view of the hydraulic excavator  100 , and  FIG. 2B  is a rear view of the shovel  100 . As shown in  FIG. 2A , the length of the boom  6 , that is to say, the length from the boom pin  13  to the arm pin  14  is L1. The length of the arm  7 , that is to say, the length from the arm pin  14  to the bucket pin  15  is L2. The length of the bucket  8 , that is to say, the length from the bucket pin  15  to the tip end of the tooth of the bucket  8  (hereinafter referred to as “the cutting edge  8   a ”), is L3. 
     Further, as shown in  FIG. 2A , the first, second, and third stroke sensors  16 ,  17 , and  18  are installed to, respectively, the boom cylinder  10 , the arm cylinder  11 , and the bucket cylinder  12 . The first stroke sensor  16  detects the length of the stroke of the boom cylinder  10  (hereinafter referred to as “boom cylinder length N 1 ”). A display controller  28  described subsequently, (refer  FIG. 4 ), calculates the angle of inclination θ1 of the boom  6  in relation to the perpendicular direction of the vehicle main body coordinate system, from the boom cylinder length N 1  as detected by the first stroke sensor  16 . 
     The second stroke sensor  17  detects the length of the stroke of the arm cylinder  11  (hereinafter referred to as the “arm cylinder length N 2 ”). The display controller  28  detects the angle of inclination θ2 of the arm  7  in relation to the boom  6  from the arm cylinder length N 2  as detected by the second stroke sensor  17 . 
     The third stroke sensor  18  detects the length of the stroke of the bucket cylinder  12  (hereinafter referred to as the “bucket cylinder length N 3 ”). The display controller  28  calculates the angle of inclination θ3 of the cutting edge  8   a  of the bucket  8  in relation to the arm  7  from the bucket cylinder length N 3  as detected by the third stroke sensor  18 . 
     As shown in  FIG. 2A  the vehicle main body  1  is provided with position detection part  19 . The position detection part  19  detects the current position of the hydraulic excavator  100 . The position detection part  19  has the above described first and second GNSS antennas  21  and  22 , a global coordinate computing unit  23 , and an Inertial Measurement Unit (IMU). 
     The first and second GNSS antennas  21  and  22  are mutually separated in the vehicle widthwise direction. A signal coordinated to the GNSS radio waves received by the first and second GNSS antennas  21  and  22  is input to the global coordinate computing unit  23 . 
     The global coordinate computing unit  23  detects the position of the first and second GNSS antennas  21  and  22 . The IMU  24  detects the angle of inclination θ4 in the vehicle widthwise direction of the vehicle main body  1  in relation to the direction of gravitational force (the vertical line) (refer  FIG. 2B ), and the angle of inclination θ5 in the forward-rearward direction of the vehicle main body  1  (refer  FIG. 2A ). 
     The global coordinate computing unit  23  updates the current positional information of the first and second GNSS antennas  21  and  22  in connection with the revolutions and movement and the like of the hydraulic excavator  100 . 
     Configuration of the Excavation Control System  200   
       FIG. 3  is a block diagram showing the functional configuration of the excavation control system  200 . The excavation control system  200  is provided with an operating device  25 , a working unit controller  26 , a proportional control valve  27 , a display controller  28 , and a display  29 . 
     The operating device  25  receives the operations of the operator driving the working unit  2 , and outputs an operation signal in conformance with the operation of the operator. Basically, the operating device  25  has a boom operating tool  31 , an arm operating tool  32 , and a bucket operating tool  33 . 
     The boom operating tool  31  includes a boom operating lever  31   a,  and boom operation detection part  31   b . The boom operating lever  31  a receives operation of the boom  6  by the operator. The boom operation detection part  31   b  outputs a boom operation signal M 1  in conformance with operation of the boom operating lever  31   a.    
     An arm operating lever  32   a  receives operation of the arm  7  by the operator. Arm operation detection part  32   b  outputs an arm operation signal M 2  in conformance with operation of the arm operating lever  32   a.    
     The bucket operating tool  33  includes a bucket operating lever  33   a,  and bucket operation detection part  33   b.  The bucket operating lever  33   a  receives operation of the bucket  8  by the operator. The bucket operation detection part  33   b  outputs a bucket operation signal M 3  in conformance with operation of the bucket operating lever  33   a.    
     The working unit controller  26  acquires the boom operation signal M 1 , the arm operation signal M 2 , and the bucket operation signal M 3  from the operating device  25  (hereinafter these signals being referred to jointly as “operation signals M”). Further, the working unit controller  26  acquires the boom cylinder length N 1 , the arm cylinder length N 2 , and the bucket cylinder length N 3  from, respectively, the first, second and third stroke sensors,  16 ,  17  and  18 , and based on this information, the working unit controller  26  drives the working unit  2  by outputting control signals to the proportional control valve  27 . The function of the working unit controller  26  is described subsequently. 
     The proportional control valve  27  is arranged between a hydraulic pump (not shown) and the cylinders (the boom cylinder  10 , the arm cylinder  11  and the bucket cylinder  12 ). The proportional control valve  27  supplies hydraulic fluid to each of the boom cylinder  10 , the arm cylinder  11 , and the bucket cylinder  12 , while adjusting the degree of opening of the valve in conformance with a control signal from the working unit controller  26 . 
     The display controller  28  acquires the boom cylinder length N 1 , the arm cylinder length N 2  and the bucket cylinder length N 3  from, respectively, the first, second, and third stroke sensors  16 ,  17  and  18 . Further, the display controller  28  acquires the angle of inclination θ4 from the IMU  24 , and acquires from the global coordinate computing unit  23 , the locations of the first and second GNSS antennas  22  (shown as the antenna location in  FIG. 3 ). 
     Then, the display controller  28 , based on the current position of the bucket  8  as calculated from this information and the designed landform that is a target shape for an excavation object, generates the described prospective surfaces S 0  (refer  FIG. 5 ) and the first through fifth designed surfaces S 1 -S 5  (refer  FIG. 6 ). The display controller  28  causes the prospective surfaces S 0  to be displayed on the display  29 , and sends the first through fifth designed surfaces S 1 -S 5  to the working unit controller  26 . The functions of the display controller  28  are described subsequently. 
     Configuration of the Display Controller  28   
       FIG. 4  is a block diagram showing the configuration of the display controller  28 .  FIG. 5  is a schematic diagram showing an example of a prospective surfaces S 0 , and  FIG. 6  is a schematic diagram showing an example of the first through fifth designed surfaces S 1 -S 5 . 
     The display controller  28  is provided with designed landform data storage part  281 , bucket position data generation part  282 , prospective surfaces data generation part  283 , and designed surface data storage part  284 . 
     1. The Designed Landform Data Storage Part  281   
     The designed landform data storage part  281  stores designed landform data Dg indicating the target shape for the excavation object in the working range (hereinafter referred to as “designed landform”). It is suitable for the designed landform data Dg to include angle data or coordinates data necessary for generating three-dimensional shapes for the first through fifth designed surfaces S 1 -S 5  and the prospective surfaces S 0 . 
     2. The Bucket Position Data Generation Part  282   
     The bucket position data generation part  282  acquires the boom cylinder length N 1 , the arm cylinder length N 2  and the bucket cylinder length N 3  from respectively, the first, second, and third stroke sensors  16 ,  17 , and  18 , acquires the angle of inclination θ4 from the IMU  24 , and acquires the positions of the first and second GNSS antennas  21 ,  22 , from the global coordinate computing unit  23 . The bucket position data generation part  282  calculates the angles of inclination θ1-θ3 based on the boom cylinder length N 1 , the arm cylinder length N 2 , and the bucket cylinder length N 3 . 
     Then, the bucket position data generation part  282  generates bucket position data Dp indicating the current position of the bucket  8 , based on the positions of the first and second GNSS antennas  21 ,  22  and the angles of inclination θ1-θ4. The bucket position data generation part  282  sends the bucket position data Dp thus generated to the working unit controller  26 . 
     Further, the bucket position data generation part  282  intermittently updates the bucket position data Dp, in conformance with the updating of the information indicating the current position of the first and second GNSS antennas  21 ,  22  from the global coordinate computing unit  23 . 
     3. The Prospective Surfaces Data Generation Part  283   
     The prospective surfaces data generation part  283  acquires the designed landform data Dg stored in the designed landform data storage part  281 , and the bucket position data Dp generated by the bucket position data generation part  282 . The prospective surfaces data generation part  283  acquires the designed landform in the vicinity of the bucket indicating the area in the vicinity of the cutting edge  8   a  from among the designed landform, based on the designed landform data Dg and the bucket position data Dp. 
     Next, the prospective surfaces data generation part  283  determines the prospective surfaces S 0  that becomes the prospective designed surface for the intersection of the designed landform in the vicinity of the bucket and the working plane of the working unit  2  (that is to say, the plane passing through the center of the working unit  2  in the vehicle width wise direction), and generates prospective surfaces data D S2 -D S0  indicating the prospective surfaces S 0 . 
     The prospective surfaces data generation part  283  sends the prospective surfaces data D S0  to the display  29 , causing the prospective surfaces S 0  to be displayed to the operator. Further, the prospective surfaces data generation part  283  sends the prospective surfaces data D S0  to the designed surface data storage part  284 . 
     Note that the prospective surfaces data generation part  283  intermittently updates the prospective surfaces data D S0 , in conformance with the updating of the bucket position data Dp from the bucket position data generation part  282 . 
     4. The Designed Surface Data Storage Part  284   
     The designed surface data storage part  284  requires the bucket position data Dp generated by the bucket position data generation part  282 , and the prospective surfaces data D S0  generated by the prospective surfaces data generation part  283 . 
     The designed surface data storage part  284 , as shown in  FIG. 6 , determines the surface to which the bucket  8  is closest as the first designed surface S 1  from among the prospective surfaces S 0 , based on the bucket position data Dp and the prospective surfaces data D S0 , and generates the first designed surface data D S1  indicating the first designed surface S 1 . 
     Further, the designed surface data storage part  284  generates the second through fifth designed surface data D S2 -D S5  indicating the second through fifth designed surfaces S 2 -S 5  linked to the first designed surface S 1 . 
     Specifically, the designed surface data storage part  284  sets the second designed surface S 2  connected to the vehicle main body  1  side end portion of the first designed surface S 1 , and the third designed surface S 3  further linked to the vehicle main body  1  side end portion of the second designed surface S 2 . Further, the designed surface data storage part  284  sets the fourth designed surface S 4  linked to the opposite side of the vehicle main body  1  end portion of the first designed surface S 1 , and the fifth designed surface S 5  further linked to the opposite side of the vehicle main body  1  end portion of the fourth designed surface S 4 . 
     Note that, in this embodiment, the first designed surface S 1  is an example of a “superior designed surface” and the second through fifth designed surfaces S 2 -S 5  are an example of a “plurality of subordinate designed surfaces”. Further, the first designed surface data D S1  indicating the first designed surface S 1  is an example of “superior designed surface data”, and the second through fifth designed surface data D S2 -D S5  indicating the second through fifth designed surfaces S 2 -S 5 , are examples of “subordinate designed surface data”. 
     Further, the designed surface data storage part  284 , based on the first through fifth designed surface data D S1 -D S5  is generated, generates shaped data Df indicating the shape of the first through fifth designed surfaces S 1 -S 5 . 
     As shown in  FIG. 6 , the first designed surface data D S1  includes the coordinates data P 1 , the coordinates data P 2 , and the angle data θ1, the first designed surface S 1  being prescribed by these items of information. Basically, the dimensions of the first designed surface S 1  are prescribed by the coordinates data P 1  and the coordinates data P 2 , and the gradient of the first designed surface S 1  in relation to the horizontal line is prescribed by the angle data θ1. 
     Further, the second designed surface data D S2  includes the coordinates data P 3 , and the angle data θ2, the second designed surface S 2  being prescribed by these items of information. Basically, the dimensions of the second designed surface S 2  are prescribed by the coordinates data P 1  and the coordinates data P 3 , while the gradient of the second designed surface S 2  in relation to the horizontal line is prescribed by the angle data θ2. 
     Again, the third designed surface data D S3  includes the angle data θ3 (in the example in  FIG. 6 , θ3=0°, the third designed surface S 3  being prescribed by this information. Basically, the gradient, in relation to the horizontal line, of the third designed surface S 3 , the starting point of which is the coordinate data P 3 , is prescribed by the angle data θ3. Note that it is suitable for the dimensions of the third designed surface S 3  to not be prescribed. 
     Further, the fourth designed surface data D S4  includes the coordinates data P 4 , and the angle data θ4. Basically, the dimensions of the fourth designed surface S 4  are prescribed by the coordinates data P 4  and the coordinates data P 2 , while the gradient of the fourth designed surface S 4  in relation to the horizontal line is prescribed by the angle θ4. 
     Again, the fifth designed surface data D S5  includes the angle data θ5, the fifth designed surface S 5  being prescribed by this information. Basically, the gradient, in relation to the horizontal line, of the fifth designed surface S 5  the starting point of which is the coordinates data P 4 , is prescribed by the angle data θ5. Note that it is suitable for the dimensions of the fifth designed surface S 5  to not be prescribed. 
     The designed surface data storage part  284  sends to the working unit controller  26  the shape data Df indicating the first through fifth designed surfaces S 1 -S 5  generated as described above. Further, the designed surface data storage part  284  updates the first through fifth designed surfaces D S1 -D S5  and the shape data Df in conformance with the updating of the bucket position data Dp from the bucket position data generation part  282  or the updating of the prospective surfaces data D S0  by the prospective surfaces data generation part  283 . 
     The Configuration of the Working Unit Controller  26   
       FIG. 7  is a block diagram showing the configuration of the working unit controller  26 .  FIG. 8  is a schematic diagram showing the positional relationship between the bucket  8  and the designed surface S (including the first through fifth designed surfaces S 1 -S 5 ). 
     As shown in  FIG. 7 , the working unit controller  26  is provided with relative distance acquisition part  261 , limit speed determination part  262 , relative speed acquisition part  263 , and excavation limit control part  264 . 
     1. The Relative Distance Acquisition Part  261   
     The relative distance acquisition part  261  acquires the bucket position data Dp from the bucket position data generation part  282  and the shape data Df for the first through fifth designed surfaces S 1 -S 5  from the designed surface data storage part  284 . 
     The relative distance acquisition part  261 , based on the bucket position data Dp and the shape data Df, acquires the distance d between the first designed surface S 1  and the cutting edge  8   a  in the direction perpendicular to the first designed surface S 1 . The relative distance acquisition part  261  outputs the distance d to the limit speed determination part  262 . 
     In the example shown in  FIG. 8 , the distance d is less than the line distance h to the excavation limit control intervention line C, and the cutting edge  8   a  intrudes into the inner side of the excavation limit control intervention line C. It is suitable for the excavation limit control intervention line C to be set at a discretionary distance from the first designed surface S 1  as deemed appropriate. 
     2. The Limit Speed Determination Part  262   
     The limit speed determination part  262  acquires the limit speed V in conformance with the distance d. The limit speed determination part  262  compares the distance d and the line distance h, and in the case of a determination that the cutting edge  8   a  exceeds the excavation limit control intervention line C, acquires the limit speed V of the relative speed Q 1  in relation to the designed surface S of the cutting edge  8   a.    
     Here,  FIG. 9  is a graph showing the relationship between limit speed V of the relative speed Q 1  and the distance d. As shown in  FIG. 9 , the limit speed V reaches maximum where the distance d is greater than or equal to the line distance h, and slows down to the extent that the distance d becomes less than the line distance h. Thus when the distance d is “0”, the limit speed V also becomes “0”. The limit speed determination part  262  outputs the limit speed V to the excavation limit control part  264 . 
     3. The Relative Speed Acquisition Part  263   
     The relative speed acquisition part  263  calculates the speed Q of the cutting edge  8   a  based on the operation signals M acquired from the operating device  25 . Further, the relative speed acquisition part  263 , based on the speed Q, acquires the relative speed Q 1  in relation to the designed surface S of the cutting edge  8   a  (refer  FIG. 8 ). 
     The relative speed acquisition part  263  outputs the relative speed Q 1  to the excavation limit control part  264 . In the example shown in  FIG. 8 , the relative speed Q 1  is greater than the limit speed V. 
     4. The Excavation Limit Control Part  264   
     The excavation limit control part  264  determines whether or not the relative speed Q 1  in relation to the designed surface S of the cutting edge  8   a,  has exceeded the limit speed V. 
     In the case the excavation limit control part  264  determines that the relative speed Q 1  has exceeded the limit speed V, the excavation limit control part  264  implements excavation limit control by bringing the relative speed Q 1  down to the limit speed V in order to automatically adjust the position of the cutting edge  8   a  in relation to the designed surface S. 
     On the other hand, when the excavation limit control part  264  determines that the relative speed Q 1  has not exceeded the limit speed V, the excavation limit control part  264  causes the working unit  2  to drive in accordance with the instructions of the operator by outputting the output to the proportional control valve  27  as it is with no corrections. 
     Actions and Effects 
     (1) The excavation control system  200  related to this embodiment of the present invention, based on the bucket position data Dp and the prospective surfaces data D S0 , generates the first designed surface data D S1  indicating the first designed surface S 1  that is closest to the bucket  8 , and the second through fifth designed surface data D S2 -D S5  indicating the second through fifth designed surfaces S 2 -S 5  linked to the first designed surface S 1 , and generates, based on the first through fifth designed surface data D S1 -D S5 , the shape data Df indicating the shape of the first through fifth designed surfaces S 1 -S 5 . 
     In this way, as the first designed surface S 1  is set with the position of the bucket  8  as reference, the designed surface data DS (including the first through fifth designed surface data D S1 -D S5 ) desired as being necessary for the excavation work can be acquired simply. Accordingly, the processing load for generating the designed surface data DS can be lowered and generation of designed surface data DS not required for the excavation work can be suppressed. 
     Further, as shown in  FIG. 6 , as the second through fifth designed surfaces S 2 -S 5  are set with the first designed surface S 1  as reference, in comparison to the case in which for example, only the second and fourth designed surfaces S 2  and S 4  are set with the first designed surface S 1  as reference, the operator is able to control the bucket  8  not to be driven in a direction unintended by the operator. 
     Specifically, in the case in which only the second and fourth designed surfaces S 2  and S 4  are set, excavation operation would be as follows when the second designed surface S 2  is excavated after the first designed surface S 1  has been excavated. Firstly, if data for the third designed surface S 3  was acquired prior to completion of excavation of the second designed surface S 2 , the working unit controller  26  would recognize that the second designed surface S 2  would be extended, and the bucket  8  is driven upward straight out of the second designed surface S 2  as shown in  FIG. 10 . Then there is the concern that excavation following the target shape would not be able to be performed because the bucket  8  would be guided to the third designed surface S 3  at that point in time at which the data for the third designed surface S 3  is acquired. 
     In the meantime, according to this embodiment of the present invention, because the second through fifth designed surfaces S 2 -S 5  are set taking the first designed surface S 1  as reference, when excavation moves from the first designed surface S 1  to the second designed surface S 2  the third designed surface has already been set, therefore the bucket  8  can be guided from the second designed surface S 2  to the third designed surface S 3 . 
     (2) The designed surface data storage part  284  updates the first through fifth designed surface data D S1 -D S5  and the shape data Df in conformance with the updating of the bucket position data Dp by the bucket position data generation part  282 . 
     Accordingly, when for example excavation moves from the excavation of the first designed surface S 1  to excavation of the second designed surface S 2 , the second designed surface S 2  is promptly updated to the first designed surface, moreover the other designed surface linked to the third designed surface S 3  is set anew. Accordingly, the phenomena of the bucket being driven in an unintended direction can be suppressed. 
     (3) The designed surface data storage part  284  sets the second and third designed surfaces S 1 , S 2  so as to link sequentially to the side of the first designed surface S 1  facing the vehicle main body  1 , and sets the fourth and fifth designed surfaces S 4  and S 5  so as to link sequentially to the side of the first designed surface S 1  facing the opposite side to the vehicle main body  1 . 
     In this way, because two designed surfaces are set on either side of the first designed surface S 1 , when earth excavated from a trench is deposited on either the front side of the trench or the rear side of the trench, it is possible to suppress the effect of the bucket being driven in an unintended direction. 
     Specifically, as the first designed surface S 1  is the bottom surface of the trench, the two designed surfaces S 2  and S 4  linked to the respective ends of the first designed surface S 1  are the respective wall surfaces of the trench and the two designed surfaces are positioned in a range of movement of the working unit  2 , the operator determines in the circumstances whether to deposit soil on the front side of the trench or the rear side of the trench. Thus, by setting two designed surfaces on either side of the first designed surface S 1  in advance, the operation can be coordinated to the case of depositing excavation object on either the front side or the rear side of the trench. 
     Other Embodiments 
     In the foregoing, the present invention is described with respect to an embodiment thereof, however the invention is not limited to the embodiment described above. It is therefore understood that numerous modifications and variations can be devised without departing from the scope of the invention. 
     (A) In the above-described embodiment, the display controller  28 , based on the first through fifth designed surface data D S1 -D S5 , generates the shape data Df indicating the shape of the first through fifth designed surfaces S 1 -S 5 , however this is illustrative and not restrictive. It is also suitable for the display controller  28  to generate, based on six or more designed surface data DS, shape data Df indicating the shape of six or more designed surfaces S. 
     In the case in which the area indicated by the designed landform data Dg is narrow, there may be cases in which only four or less designed surfaces are set. In such a case, it is suitable for the display controller  28  to generate shape data Df indicating the shape of four or less designed surfaces S, based on four or less designed surface data DS. 
     (B) In the above-described embodiment, the controller  28  sets the second and third designed surfaces S 1 , S 2  so as to be sequentially linked to one side of the first designed surface S 1 , and sets the fourth and fifth designed surfaces S 4  and S 5  so as to be sequentially linked to the other side of the first designed surface S 1 , however this is illustrative and not restrictive. For example, it is suitable for the display controller  28  to set the second through fifth designed surfaces S 2 -S 5  so as to be sequentially linked to one side of the first designed surface S 1 . Again, it is suitable for the display controller  28  to set the second through fourth designed surfaces S 2 -S 4  so as to be sequentially linked to one side of the first designed surface S 1 , moreover, to set the fifth designed surface S 5  so as to be sequentially linked to the other side of the first designed surface S 1 . 
     (C) In the above-described embodiment, although not mentioned specifically, it is suitable for the display controller  28  to generate shape data Df indicating a designed surface included within the range of movement of the bucket  8 . This case enables a reduction in the processing load of the display controller  28 , which is not required to set a designed surface S for which the bucket  8  will obviously not perform an excavation operation. 
     (D) In the above-described embodiment, the working unit controller  26 , based on the position of the cutting edge  8   a  of bucket  8 , implements a speed limit, however this is illustrative and not restrictive. The working unit controller  26  can implement a speed limit based on the arbitrary position of the bucket  8  (for example, the lowest point of the bucket  8 ). 
     (E) In the above-described embodiment, the predetermined position at which the cutting edge  8   a  stops is set as being above the designed surface S, however this is illustrative and not restrictive. It is also suitable for the predetermined position to be set as a discretionary position separate from the designed surface S to the hydraulic excavator  100  side. 
     (F) Although not mentioned specifically in the above-described embodiment, it is suitable for the excavation control system  200  to restrict the relative speed Q 1  to the limit speed V only through reducing the rotation speed of the boom  6 , and suitable to restrict the relative speed Q 1  to the limit speed V by adjusting the rotation speed of not only the boom  6 , but that of the arm  7  and the bucket  8 . 
     (G) In the above-described embodiment, the excavation control system  200 , based on the operation signals M acquired from the operating device  25 , calculates the speed Q of the cutting edge  8   a,  however this is illustrative and not restrictive. It is also suitable for the excavation control system  200  to calculate the speed Q based on the degree of change per time unit of each of the cylinder lengths N 1 -N 3  acquired from the first through third stroke sensors  16 ,  17 , and  18 . In this case, a more accurate calculation of the speed Q can be realized in comparison to the case of calculating speed Q based on the operation signals M. 
     (H) In the above-described embodiment, as shown in  FIG. 9 , the limit speed and the vertical distance are in a linear relationship, however this configuration is illustrative and not restrictive. The limit speed and the vertical distance can be in a relationship set as appropriate, this need not be a linear relationship, and need not pass through a point of origin. 
     (I) In the above-described embodiment, as shown in  FIG. 6 , the first designed surface data D S1  includes the coordinates data P 1 , the coordinates data P 2 , and the angle data θ1, however it is also suitable for the angle data θ1 to not be included in the first designed surface data D S1 . In this case, it is possible for the first designed surface S 1  to be prescribed by the coordinates data P 1  and the coordinates data P 2 . 
     (J) In the above-described embodiment, the excavation control system  200  determines the first designed surface S 1  as that surface to which the bucket  8  is closest among the prospective surfaces S 0 , however this is illustrative and not restrictive. The first designed surface S 1  can be determined based on a position prescribed above the bucket  8 . Accordingly, the excavation control system  200  may determine a surface positioned beneath the bucket  8  in the vertical direction as the first designed surface Si from the prospective surfaces S 0 . 
     The present invention can be used in a hydraulic excavator.