Patent Publication Number: US-11384509-B2

Title: Work machine

Description:
TECHNICAL FIELD 
     The present invention relates to a work machine such as a hydraulic excavator. 
     BACKGROUND ART 
     As a technology for improving the work efficiency of a work machine (for example, a hydraulic excavator) that includes a work implement such as, for example, a front work implement driven by a hydraulic actuator, a machine control (MC) is available. The MC is a technology for performing, in the case where an operation device is operated by an operator, operation support for the operator by executing semiautomatic control of controlling a work implement to act in accordance with a condition determined in advance. 
     As the MC for a hydraulic excavator that is one form of a work machine, semiautomatic excavation shaping control is known which controls a front work implement such that a control point of the front work implement (a bucket toe) is prevented from entering a target surface also called design surface (Such semiautomatic excavation shaping control is sometimes called “area limiting control” in the sense of control of limiting the area of movement of the front work implement to an area above a target surface). For example, in a work machine control system of Patent Document 1, in the case where an operation signal outputted in response to an operation of a front work implement by an operator includes an arm operation signal, it is decided that it is tried to perform a shaping work in which the bucket is moved along the target surface. Then, the boom is automatically caused to act such that the speed of the distal end of the bucket that appears in a direction perpendicular to the target surface is cancelled by an arm action thereby to implement a work for moving the bucket semiautomatically along the target surface. The speed of the distal end of the bucket described above is hereinafter referred to as perpendicular speed. 
     The work described above makes it possible, in a leveling work of moving the bucket along the target surface, to excavate and shape the target surface only if the operator operates the arm. Further, since the operator can adjust the bucket distal end speed (which is hereinafter referred to as excavation speed), caused in a parallel direction to the target surface by the operation amount of the arm, the operator can perform the leveling operation at an intended speed. This is because, since the excavation speed by an arm action has a tendency that it is higher than the perpendicular speed and the excavation speed by a boom action has a tendency that it is lower than the perpendicular speed, the excavation speed fluctuates mainly in accordance with the arm action speed. 
     PRIOR ART DOCUMENT 
     Patent Document 
     Patent Document 1: PCT Patent Publication No. WO 2012/127912 
     SUMMARY OF THE INVENTION 
     Problems to be Solved by the Invention 
     However, according to a work machine that uses the work implement control system disclosed in Patent Document 1, depending on the excavation speed, it is difficult to move the bucket stably along the target surface, resulting in the possibility that the shaping accuracy of the target surface may be lost. In the case where a leveling work is performed utilizing the semiautomatic excavation shaping control, the arm performs a crowding action (leveling action) in accordance with the operation of the operator and the boom automatically performs a raising action such that the perpendicular speed caused by the arm action is cancelled. If the bucket distal end enters below the target surface by an influence of disturbance such as the soil quality, then the boom raising speed increases such that the bucket tip does not enter the target surface any more. If the bucket distal end thereafter reaches the target surface, then the boom raising speed is suppressed and tends to hold the bucket distal end on the target surface. 
     However, at this time, if the excavation speed is somewhat high, then the increase of the boom raising speed may not be made in time, resulting in the possibility that the bucket distal end may move over a long distance in the horizontal direction while it remains positioned below the target surface. Alternatively, suppression of the boom raising speed when the bucket distal end reaches the target surface may not be made in time, resulting in the possibility that the bucket distal end may lift up from the target surface. In other words, if the arm action is performed at a high speed, then it is difficult to perform stable semiautomatic excavation shaping control, resulting in the possibility that the excavation shaping accuracy may be lost. This occurs because the inertial load of the boom is higher than that of the arm and the delay of an actual speed change of the boom cylinder with respect to a speed change thereof required by the control system is large. 
     The present invention has been made in view of such a subject as described above and contemplates provision of a work machine that can perform semiautomatic excavation shaping control with higher accuracy even where the excavation speed is high. 
     Means for Solving the Problems 
     In order to achieve the object described above, according to the present invention, there is provided a work machine including a work implement having a plurality of front members, a plurality of hydraulic actuators configured to drive the plurality of front members, an operation device configured to instruct an action for each of the plurality of hydraulic actuators in response to an operation by an operator, and a controller including a target speed calculation section configured to calculate target speeds individually for the plurality of front members such that, when the operation device is operated, the work implement is limited so as to be positioned above a predetermined target surface, in which the controller includes a signal separation section configured to separate each of signals of the target speeds for the plurality of front members into a low frequency component having a frequency lower than a predetermined threshold value and a high frequency component having a frequency higher than the threshold value, a high fluctuation target speed calculation section configured to allocate the high frequency component separated by the signal separation section preferentially to one of the front members, the one front member having a relatively small inertial load, from among the plurality of front members to calculate high fluctuation target speeds individually for the plurality of front members, a high fluctuation target actuator speed calculation section configured to calculate the high fluctuation target speeds individually for the plurality of actuators, based on the high fluctuation target speeds for the plurality of front members calculated by the high fluctuation target speed calculation section and posture data of the plurality of front members, a low fluctuation target actuator speed calculation section configured to calculate low fluctuation target speeds individually for the plurality of actuators, based on the low frequency component separated by the signal separation section and the posture data of the plurality of front members, and an actuator controller configured to control the plurality of actuators individually, based on values obtained by adding results of the calculation of the high fluctuation target actuator speed calculation section and results of the calculation of the low fluctuation target actuator speed calculation section individually for the plurality of actuators. 
     Advantage of the Invention 
     According to the present invention, even in the case where the excavation speed is high, semiautomatic excavation shaping control can be performed with high accuracy. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side elevational view of a hydraulic excavator  1  that is an example of a work machine according to an embodiment of the present invention. 
         FIG. 2  is a side elevational view of the hydraulic excavator  1  in a global coordinate system and a local coordinate system. 
         FIG. 3  is a block diagram of a machine body control system  23  of the hydraulic excavator  1 . 
         FIG. 4  is a schematic view of a hardware configuration of a controller  25 . 
         FIG. 5  is a schematic view of a hydraulic circuit  27  of the hydraulic excavator  1 . 
         FIG. 6  is a functional block diagram of the controller  25  according to a first embodiment. 
         FIG. 7  is a functional block diagram of a target actuator speed calculation section  100  according to the first embodiment. 
         FIG. 8  is a graph illustrating a relationship between a distance D between a bucket distal end P 4  and a target surface  60  and a speed correction coefficient k. 
         FIG. 9  is a schematic view representing speed vectors before and after correction according to the distance D of the bucket distal end P 4 . 
         FIG. 10  is a functional block diagram of a correction speed calculation section  140  in the first embodiment. 
         FIG. 11  is a view depicting an example of target speed signals for front members and target actuator speeds in an overlapping relationship on  FIG. 10 . 
         FIG. 12  is a flow chart representative of a control flow by the controller  25  according to the first embodiment. 
         FIG. 13  is a functional block diagram of the correction speed calculation section  140  in a second embodiment. 
         FIG. 14  is a functional block diagram of the correction speed calculation section  140  in a third embodiment. 
         FIG. 15  is an explanatory view of a situation in which a bucket  10  takes a singular posture. 
         FIG. 16  is an explanatory view of a situation in which an arm  9  takes a singular posture. 
         FIG. 17  is a functional block diagram of the correction speed calculation section  140  in a fourth embodiment. 
         FIG. 18  is a functional block diagram of the correction speed calculation section  140  in a fifth embodiment. 
     
    
    
     MODES FOR CARRYING OUT THE INVENTION 
     In the following, work machines according to embodiments of the present invention are described with reference to the drawings. Although a hydraulic excavator including a bucket  10  as a work tool (attachment) at the distal end of a work implement is exemplified in the following description, the present invention may be applied to a work machine that includes an attachment other than the bucket. The present invention can be applied also to a work machine other than a hydraulic excavator if the work machine has a work implement of an articulated type configured from a plurality of front members (which are an attachment, an arm, a boom and so forth), connected to each other. 
     Further, in regard to the meaning of such terms as “on”, “above” and “below” that are used herein together with a term that represents a certain shape (for example, a target surface, a design surface or the like), “on” signifies the “surface of the certain shape”; “above” signifies a “position higher than the surface” of the certain shape; and “below” signifies a “position lower than the surface” of the certain shape. Further, in the following description, in the case where a plurality of same components exist, although an alphabetical character is sometimes added to the tail end of a reference character (numeral), the plurality of components are sometimes represented collectively with such alphabetical characters omitted. For example, where two pumps  2   a  and  2   b  exist, they are sometimes represented collectively as pumps  2 . 
     First Embodiment 
       FIG. 1  is a side elevational view of a hydraulic excavator  1  that is an example of a work machine according to the embodiment of the present invention. The hydraulic excavator  1  includes a track structure (lower track structure  2 ) that travels by driving a crawler belt provided on each of left and right sides by a hydraulic motor (not depicted), and a swing structure (upper swing structure  3 ) provided for swing motion on the track structure  2 . 
     The swing structure  3  includes an operation room  4 , a machine room  5  and a counterweight  6 . The operation room  4  is provided at a left side portion of a front portion of the swing structure  3 . The machine room  5  is provided behind the operation room  4 . The counterweight is provided behind the machine room  5 , namely, at a rear end of the swing structure  3 . 
     The swing structure  3  further includes a work implement (front work implement  7 ) of the articulated type. The work implement  7  is provided on the right side of the operation room  4  at a front portion of the swing structure  3 , namely, at a substantially central portion of a front portion of the swing structure  3 . The work implement  7  includes a boom  8 , an arm  9 , a bucket (work tool)  10 , a boom cylinder  11 , an arm cylinder  12  and a bucket cylinder  13 . The boom  8  is attached at a proximal end portion thereof for pivotal motion to a front portion of the swing structure  3  through a boom pin P 1  (depicted in  FIG. 2 ). The arm  9  is attached at a proximal end portion thereof to a distal end portion of the boom  8  for pivotal motion through an arm pin P 2  (depicted in  FIG. 2 ). The bucket  10  is attached at a proximal end portion thereof to a distal end portion of the arm  9  for pivotal motion through a bucket pin P 3  (depicted in  FIG. 2 ). The boom cylinder  11 , arm cylinder  12  and bucket cylinder  13  are hydraulic cylinders individually driven by hydraulic working fluid. The boom cylinder  11  expands and contracts to drive the boom  8 ; the arm cylinder  12  expands and contracts to drive the arm  9 ; and the bucket cylinder  13  expands and contracts to drive the bucket  10 . It is to be noted that, in the following description, each of the boom  8 , arm  9  and bucket (work tool)  10  is sometimes referred to as front member. 
     Installed in the inside of the machine room  5  are a first hydraulic pump  14  and a second hydraulic pump  15  of the variable displacement type (depicted in  FIG. 3 ) and an engine (prime mover)  16  (depicted in  FIG. 3 ) for driving the first hydraulic pump  14  and the second hydraulic pump  15 . 
     A machine body tilt sensor  17  is attached in the inside of the operation room  4 ; a boom tilt sensor  18  is attached to the boom  8 ; an arm tilt sensor  19  is attached to the arm  9 ; and a bucket tilt sensor  20  is attached to the bucket  10 . For example, the machine body tilt sensor  17 , boom tilt sensor  18 , arm tilt sensor  19  and bucket tilt sensor  20  are IMUs (Inertial Measurement Units): inertial measurement devices. The machine body tilt sensor  17  measures an angle (ground angle) of the swing structure (machine body)  3  with respect to a horizontal plane; the boom tilt sensor  18  measures the ground angle of the boom; the arm tilt sensor  19  measures the ground angle of the arm  9 ; and the bucket tilt sensor  20  measures the ground angle of the bucket  10 . 
     A first GNSS antenna  21  and a second GNSS antenna  22  are attached to left and right portions of a rear portion of the swing structure  3 , respectively. The GNSS is an abbreviation of Global Navigation Satellite System. Each of the first GNSS antenna  21  and the second GNSS antenna  22  can calculate position data of predetermined two points (for example, positions of the proximal ends of the GNSS antennae  21  and  22 ), in a global coordinate system from navigation signals received from a plurality of navigation satellites (preferably from four or more navigation satellites). Then, from the calculated position data (coordinate values), of the two points in the global coordinate system, coordinate values of the origin P 0  (depicted in  FIG. 2 ) of a local coordinate system in which the hydraulic excavator  1  is installed, namely, in a machine body reference coordinate system, and postures of the three axes configuring the local coordinate system in the global coordinate system can be calculated. In the example of  FIG. 2 , the postures of the three axes are postures and orientations of the track structure  2  and the swing structure  3 . A calculation process of various positions based on such navigation signals can be performed by a controller  25  hereinafter described. 
       FIG. 2  is a side elevational view of the hydraulic excavator  1 . As depicted in  FIG. 2 , the length of the boom  8 , namely, the length from the boom pin P 1  to the arm pin P 2 , is represented by L 1 . Meanwhile, the length of the arm  9 , namely, the length from the arm pin P 2  to the bucket pin P 3 , is represented by L 2 . Further, the length of the bucket  10 , namely, the length from the bucket pin P 3  to a bucket distal end P 4  (a toe of the bucket  10 ), is represented by L 3 . Further, the inclination of the swing structure  3  with respect to the global coordinate system, namely, the angle defined by the vertical direction to the horizontal plane (the direction perpendicular to the horizontal plane), and the machine body vertical direction (the direction of the center axis of swing motion of the swing structure  3 ), is represented by θ 4 . The angle just described is hereinafter referred to as machine body front-back tilt angle θ 4 . The angle defined by a line segment interconnecting the boom pin P 1  and the arm pin P 2  and the machine body vertical direction is represented by θ 1 , and the angle is hereinafter referred to as boom angle θ 1 . The angle defined by a line segment interconnecting the arm pin P 2  and the bucket pin P 3  and a straight line including the boom pin P 1  and the arm pin P 2  is represented by θ 2 , and the angle is hereinafter referred to as arm angle θ 2 . The angle defined by a line segment interconnecting the bucket pin P 3  and the bucket distal end P 4  and a straight line interconnecting the arm pin P 2  and the bucket pin P 3  is represented by θ 3 , and the angle is hereinafter referred to as bucket angle θ 3 . 
       FIG. 3  is a block diagram of the machine body control system  23  of the hydraulic excavator  1 . The machine body control system  23  includes an operation device  24  for operating the work implement  7 , an engine  16  for driving the first and second hydraulic pumps  14  and  15 , a flow control valve device  26  for controlling the flow rate and the direction of hydraulic working fluid to be supplied from the first and second hydraulic pumps  14  and  15  to the boom cylinder  11 , arm cylinder  12  and bucket cylinder  13 , and a controller  25  that is a controller for controlling the flow control valve device  26 . 
     The operation device  24  includes a boom operation lever  24   a  for operating the boom  8  (boom cylinder  11 ), an arm operation lever  24   b  for operating the arm  9  (arm cylinder  12 ), and a bucket operation lever  24   c  for operating the bucket  10  (bucket cylinder  13 ). For example, each of the operation levers  24   a ,  24   b  and  24   c  is an electric lever and outputs a voltage value according to a tilt angle (operation amount) and a tilt direction (operation direction) of the lever to the controller  25 . The boom operation lever  24   a  outputs a target action amount for the boom cylinder  11  as a voltage value according to the operation amount of the boom operation lever  24   a  (which is hereinafter referred to as boom operation amount). The arm operation lever  24   b  outputs a target action amount for the arm cylinder  12  as a voltage value according to the operation amount of the arm operation lever  24   b  (which is hereinafter referred to as arm operation amount). The bucket operation lever  24   c  outputs a target action amount for the bucket cylinder  13  as a voltage value according to the bucket operation lever  24   c  (which is hereinafter referred to as bucket operation amount). As an alternative, each of the operation levers  24   a ,  24   b  and  24   c  may be formed as a hydraulic pilot lever such that a pilot pressure generated in response to a tilt amount of the lever is converted into a voltage value by a pressure sensor (not depicted) and outputted to the controller  25  to detect the operation amount of the lever. 
     The controller  25  calculates a control command on the basis of an operation amount outputted from the operation device  24 , position data of the bucket distal end P 4  that is a predetermined control point set in advance to the work implement  7  (control point position data), and position data of the target surface  60  (depicted in  FIG. 2 ) (target surface data), stored in advance in the controller  25 , and outputs the control command to the flow control valve device  26 . The controller  25  in the present embodiment calculates the target speeds for the hydraulic cylinders  11 ,  12  and  13  in response to the distance D between the bucket distal end P 4  that is the control point and the target surface  60 , namely, to the target surface distance D (depicted in  FIG. 2 ), such that, at the time of operation of the operation device  24 , the range of action of the work implement  7  is limited to a position on or above the target surface  60 . It is to be noted that, although the bucket distal end P 4  (the control point of the bucket  10 ), is set as the control point of the work implement  7  in the present embodiment, an arbitrary point on the work implement  7  can be set as the control point, and, for example, a point on the work implement  7  nearest to the target surface  60  at the distal end side with respect to the arm  9  may be set as the control point. 
       FIG. 4  is a schematic view of a hardware configuration of the controller  25 . Referring to  FIG. 4 , the controller  25  includes an input interface  91 , a central processing unit (CPU)  92  that is a processor, a read only memory (ROM)  93  and a random access memory (RAM)  94  that are storage devices, and an output interface  95 . 
     Inputted to the input interface  91 , signals from the tilt sensors  17 ,  18 ,  19  and  20 , voltage values (operation signals) from the operation device  24 , a signal from a target surface setting device  51 , and signals from an inertia information setting device  41 . The tilt sensors  17 ,  18 ,  19  and  20  configure a work implement posture sensor  50  that detects the posture of the work implement  7 . The voltage values or operation signals from the operation device  24  indicate operation amounts and operation directions of the operation levers  24   a ,  24   b  and  24   c . The target surface setting device  51  is a device for setting a target surface  60  that becomes a reference to an excavation work or a fill work by the work implement  7 . The inertia information setting device  41  is a device for setting inertia data such as the mass, inertial moment and so forth of the boom  8 , arm  9  and bucket  10 . The inertia information setting device  41  converts the inputted signals such that the CPU  92  can perform calculation with the signals. 
     The ROM  93  is a recording medium in which control programs for allowing the controller  25  to execute various control processes including processes hereinafter described with reference to a flow chart and various kinds of data and so forth necessary for execution of the control processes. The CPU  92  performs a predetermined calculation process for signals fetched thereto from the input interface  91 , ROM  93  and RAM  94  in accordance with the control programs stored in the ROM  93 . The output interface  95  generates and outputs a signal for outputting according to a result of the calculation by the CPU  92 . As the signal for outputting of the output interface  95 , control commands for the solenoid valves  32 ,  33 ,  34  and  35  (depicted in  FIG. 5  are available, and the solenoid valves  32 ,  33 ,  34  and  35  act on the basis of the control commands to control the hydraulic cylinders  11 ,  12  and  13 . It is to be noted that, although the controller  25  of  FIG. 4  includes semiconductor memories including the ROM  93  and RAM  94  as the storage devices, they can be replaced particularly by any storage device, and the controller  25  may include a magnetic storage device such as, for example, a hard disk drive. 
     The flow control valve device  26  includes a plurality of electromagnetically drivable spools and drives a plurality of hydraulic actuators incorporated in the hydraulic excavator  1  and including the hydraulic cylinders  11 ,  12  and  13  by changing the opening area (the restrictor opening), of each spool on the basis of a control command outputted from the controller  25 . 
       FIG. 5  is a schematic view of the hydraulic circuit  27  of the hydraulic excavator  1 . The hydraulic circuit  27  includes a first hydraulic pump  14 , a second hydraulic pump  15 , a flow control valve device  26 , and hydraulic working fluid tanks  36   a  and  36   b.    
     The flow control valve device  26  includes a first arm spool  28 , a second arm spool  29 , a bucket spool  30 , a boom spool  31 , first arm spool driving solenoid valves  32   a  and  32   b , second arm spool driving solenoid valves  33   a  and  33   b , bucket spool driving solenoid valves  34   a  and  34   b , and boom spool driving solenoid valves  35   a  and  35   b . The first arm spool  28  is a first flow control valve for controlling the flow rate of hydraulic working fluid to be supplied from the first hydraulic pump  14  to the arm cylinder  12 . The second arm spool  29  is a third flow control valve that controls the flow rate of hydraulic working fluid to be supplied from the second pump  15  to the arm cylinder  12 . The bucket spool  30  controls the flow rate of hydraulic working fluid to be supplied from the first hydraulic pump  14  to the bucket cylinder  13 . The boom spool (first boom spool)  31  is a second flow control valve for controlling the flow rate of hydraulic working fluid to be supplied from the second hydraulic pump  15  to the boom cylinder  11 . The first arm spool driving solenoid valves  32   a  and  32   b  generate a pilot pressure for driving the first arm spool  28 . The second arm spool driving solenoid valves  33   a  and  33   b  generate a pilot pressure for driving the second arm spool  29 . The bucket spool driving solenoid valves  34   a  and  34   b  generate a pilot pressure for driving the bucket spool  30 . The boom spool driving solenoid valves (first boom spool driving solenoid valves)  35   a  and  35   b  generate a pilot pressure for driving the boom spool  31 . 
     The first arm spool  28  and the bucket spool  30  are connected in parallel to the first hydraulic pump  14 , and the second arm spool  29  and the boom spool  31  are connected in parallel to the second hydraulic pump  15 . 
     The flow control valve device  26  is a device of an open center type (a center bypass type). The spools  28 ,  29 ,  30  and  31  have center bypass portions  28   a ,  29   a ,  30   a  and  31   a , respectively, which are flow paths for guiding hydraulic working fluid discharged from the first and second hydraulic pumps  14  and  15  to the hydraulic working fluid tanks  36   a  and  36   b , respectively, until a predetermined spool position is reached from a neutral position. In the present embodiment, the first hydraulic pump  14 , center bypass portion  28   a  of the first arm spool  28 , center bypass portion  30   a  of the bucket spool  30  and tank  36   a  are connected in series in this order, and the center bypass portion  28   a  and the center bypass portion  30   a  configure a center bypass flow path for guiding hydraulic working fluid discharged from the first hydraulic pump  14  to the tank  36   a . Meanwhile, the second hydraulic pump  15 , center bypass portion  29   a  of the second arm spool  29 , center bypass portion  31   a  of the boom spool  31  and the tank  36   b  are connected in series in this order, and the center bypass portion  29   a  and the center bypass portion  31   a  configure a center bypass flow path for guiding hydraulic working fluid discharged from the second hydraulic pump  15  to the tank  36   b.    
     To the solenoid valves  32 ,  33 ,  34  and  35 , pressurized fluid discharged from a pilot pump (not depicted) that is driven by the engine  16  is guided. The solenoid valves  32 ,  33 ,  34  and  35  suitably act on the basis of a control command from the controller  25  to cause the pressurized fluid, which is a pilot pressure, from the pilot pump to act upon driving portions of the spools  28 ,  29 ,  30  and  31  thereby to drive the spools  28 ,  29 ,  30  and  31  to operate the hydraulic cylinders  11 ,  12  and  13 . 
     For example, in the case where a command is issued from the controller  25  to operate the arm cylinder  12  in its extension direction, the command is outputted to the first arm spool driving solenoid valve  32   a  and the second arm spool driving solenoid valve  33   a . In the case where a command is issued to operate the arm cylinder  12  in its contraction direction, the command is outputted to the first arm spool driving solenoid valve  32   b  and the second arm spool driving solenoid valve  33   b . In the case where a command is issued to operate the bucket cylinder  13  in its extension direction, the command is outputted to the bucket spool driving solenoid valve  34   a , but in the case where a command is issued to operate the bucket cylinder  13  in its contraction direction, the command is outputted to the bucket spool driving solenoid valve  34   b . In the case where a command is outputted to operate the boom cylinder  11  in its extension direction, the command is outputted to the boom spool driving solenoid valve  35   a , and in the case where a command is issued to the boom cylinder  11  to operate in its contraction direction, the command is outputted to the boom spool driving solenoid valve  35   b.    
       FIG. 6  depicts a functional block diagram in which processes executed by the controller  25  according to the present embodiment are classified and summarized into a plurality of blocks from the functional aspect. As depicted in  FIG. 6 , the controller  25  functions as a target actuator speed calculation section  100  that calculates a target speed (a target actuator speed), for each of the hydraulic cylinders  11 ,  12  and  13 , and an actuator controller  200  that calculates a solenoid valve driving signal on the basis of the target actuator speed and outputs the solenoid valve driving signal to the applicable one of the solenoid valves  32 ,  33 ,  34  and  35 . 
     The target actuator speed calculation section  100  calculates target speeds for the boom cylinder  11 , arm cylinder  12  and bucket cylinder  13  as target actuator speeds on the basis of operation amount data obtained from the operation signals (voltage values) of the operation devices  24   a  to  24   c , posture data of the work implement  7  (which includes the front members  8 ,  9  and  10 ), and the swing structure  3  obtained from detection signals of the tilt sensors  13   a  to  13   d  as the work implement posture sensor  50 , position data of the target surface  60  (target surface data), defined on the basis of an input from the target surface setting device  51 , and inertia data of the front members  8 ,  9  and  10  defined on the basis of an input from the inertia information setting device  41 . 
       FIG. 7  is a functional block diagram of the target actuator speed calculation section  100 . The target actuator speed calculation section  100  includes a control point position calculation section  53 , a target surface storage section  54 , a distance calculation section  37 , a target speed calculation section  38 , an actuator speed calculation section  130  and a correction speed calculation section  140 . 
     The control point position calculation section  53  calculates the position of the bucket distal end P 4  that is a control point of the present embodiment in the global coordinate system and the posture of each of the front members  8 ,  9  and  10  of the work implement  7  in the global coordinate system. Although it is sufficient if the calculation is based on a known method, for example, from navigation signals received by the GNSS antennae  21  and  22 , coordinate values of the origin P 0  (depicted in  FIG. 2 ) of the local coordinate system (of the machine body reference coordinate system), in the global coordinate system and the posture data-orientation data of the track structure  2  and the swing structure  3  in the global coordinate system are calculated first. Then, utilizing results of this calculation, data of the inclination angles θ 1 , θ 2 , θ 3  and θ 4  from the work implement posture sensor  50 , coordinate values of the boom foot pin P 1  in the local coordinate system, and a boom length L 1 , an arm length L 2  and a bucket length L 3 , the position of the bucket distal end P 4  that is the control point of the present embodiment in the global coordinate system and the postures of the front members  8 ,  9  and  10  of the work implement  7  in the global coordinate system are calculated. It is to be noted that the coordinate values of the control point of the work implement  7  may be measured by an external measurement instrument such as a laser surveying meter and acquired by communication with the external measurement instrument. 
     The target surface storage section  54  has stored therein position data (target surface data), of the target surface  60 , which is calculated on the basis of data from the target surface setting device  51  located in the operation room  4 , in the global coordinate system. In the present embodiment, as depicted in  FIG. 2 , a cross sectional shape when three-dimensional data of the target surface is cut along the plane in which each of the front members  8 ,  9  and  10  of the work implement  7  acts (along the action plane of the work machine), is utilized as the target surface  60  (which is a two-dimensional target surface). It is to be noted that, although the number of such target surfaces  60  in the example of  FIG. 2  is one, a plurality of target planes may exist. In the case where a plurality of target surfaces exist, for example, a method that sets a surface having the shortest distance from the control point of the work implement  7  as the target surface, another method that sets a surface positioned vertically below the bucket distal end P 4  as the target surface, a further method that sets an arbitrarily selected surface as the target surface and so forth are available. Further, as the position data of the target surface  60 , position data of a target surface  60  around the hydraulic excavator  1  may be acquired by communication from an external server on the basis of position data of the control point of the work implement  7  in the global coordinate system and stored into the target surface storage section  54 . 
     The distance calculation section  37  calculates the distance D (depicted in  FIG. 2 ) between the control point of the work implement  7  and the target surface  60  from the position data of the control point of the work implement  7  calculated by the control point position calculation section  53  and the position data of the target surface  60  acquired from the target surface storage section  54 . 
     The target speed calculation section  38  is an element that calculates the target speeds for the front members  8 ,  9  and  10  (the boom target speed, arm target speed and bucket target speed), in response to the distance D such that, at the time of operation of the operation device  24 , the range of action of the work implement  7  is limited to a position on or above the target surface  60 . In the present embodiment, the target speed calculation section  38  performs the following calculations. 
     First, the target speed calculation section  38  calculates a demanded speed to the boom cylinder  11  (a boom cylinder demanded speed), from a voltage value (which is a boom operation amount), inputted from the boom operation lever  24   a ; calculates a demanded speed to the arm cylinder  12  (an arm cylinder demanded speed), from a voltage value (which is an arm cylinder demanded speed), inputted from the arm operation lever  24   b ; and calculates a demanded speed to the bucket cylinder  13  (a bucket cylinder demanded speed), from a voltage value) which is a bucket operation amount), inputted from the bucket operation lever  24   c . The target speed calculation section  38  calculates three speed vectors to be generated at the bucket distal end P 4  by the three cylinder demanded speeds from the calculated three cylinder demanded speeds and the postures of the front members  8 ,  9  and  10  of the work implement  7  calculated by the control point position calculation section  53 . Then, the target speed calculation section  38  determines the sum of the three speed vectors as a speed vector V 0 , namely, as a demanded speed vector, of the work implement  7  at the bucket distal end P 4 . Then, the target speed calculation section  38  calculates also a speed component V 0   z  in the target surface vertical direction and a speed component V 0   x  in the target surface horizontal direction of the speed vector V 0 . 
     Then, the target speed calculation section  38  calculates a correction coefficient k that is determined in response to the distance D.  FIG. 8  is a graph representative of a relationship between the distance D between the bucket distal end P 4  and the target surface  60  and the speed correction coefficient k. A distance when the bucket distal end P 4 , namely (the control point of the work implement  7 ), is positioned above the target surface  60  is made positive and a distance when the bucket distal end P 4  is positioned below the target surface  60  is made negative, and when the distance D is in the positive, the target speed calculation section  38  outputs a positive correction coefficient, but when the distance D is in the negative, the target speed calculation section  38  outputs a negative correction coefficient, as a value equal to or lower than 1. It is to be noted that, in regard to the speed vector, the direction in which the target surface  60  is approached from above the target surface  60  is made positive. 
     Then, the target speed calculation section  38  multiplies the speed component V 0   z  of the speed vector V 0  in the target surface vertical direction by the correction coefficient k determined in response to the distance D to calculate a speed component V 1   z . The target speed calculation section  38  synthesizes the speed component V 1   z  and the speed component V 0   x  of the speed vector V 0  in the target surface horizontal direction to calculate a synthetic speed vector (a target speed vector) V 1 . Then, in order to allow the actions of the three hydraulic cylinders  11 ,  12  and  13  to generate the synthetic speed vector V 1  at the bucket distal end P 4 , the target speed calculation section  38  calculates speed vectors, which are to be generated at the bucket distal end P 4  by the three hydraulic cylinders  11 ,  12  and  13 , as target speeds for the front members  8 ,  9  and  10  corresponding to the three hydraulic cylinders. The target speeds for the front members  8 ,  9  and  10  are speed vectors having start points at the bucket distal end P 4  and particularly include a target speed (boom target speed) for the speed that is generated at the bucket distal end P 4  by action of the boom  8  driven by the boom cylinder  11  (for the bucket distal end speed), a target speed (arm target speed) that is generated at the bucket distal end P 4  by action of the arm  9  driven by the arm cylinder  12 , and a target speed (bucket target speed) that is generated at the bucket distal end P 4  by the bucket  10  driven by the bucket cylinder  13 . The target speed calculation section  38  calculates the boom target speed, arm target speed and bucket target speed every moment and outputs a set of the three times series as target speed signals for the front members  8 ,  9  and  10  to the actuator speed calculation section  130  and the correction speed calculation section  140 . 
       FIG. 9  is a schematic view representing speed vectors at the bucket distal end P 4  before and after correction according to the distance D. By multiplying the component V 0   z  (depicted in the left figure of  FIG. 9 ), of the demanded speed vector V 0  in the target surface vertical direction by the speed correction coefficient k, the speed vector V 1   z  in the target surface vertical direction equal to or less than V 0   z  (depicted in the right figure of  FIG. 9 ) is obtained. A synthetic speed component V 1  of V 1   z  and V 0   x  that is a component of the speed vector V 0  in the target surface horizontal direction is calculated, and an arm target speed, a boom target speed and a bucket target speed with which V 1  can be outputted are calculated. 
     As one of methods for calculating the target speeds for the front members  8 ,  9  and  10  (the boom target speed, arm target speed and bucket target speed), from the synthetic speed vector V 1 , a method is available which determines speed vectors to be generated at the bucket distal end P 4  by an arm cylinder demanded speed and a bucket cylinder demanded speed as an arm target speed and a bucket target speed, respectively, subtracts the sum of the arm target speed and the bucket target speed from the synthetic speed vector V 1  and determines a speed vector obtained by the subtraction as a boom target speed. However, this calculation is nothing but a mere example, and any other calculation method may be used if a synthetic speed vector V 1  is obtained by the calculation method. 
     The actuator speed calculation section  130  geometrically calculates and outputs the speeds of the hydraulic cylinders  11 ,  12  and  13 , namely, (the boom cylinder speed, arm cylinder speed and bucket cylinder speed (actuator speeds)), necessary to generate target speeds for the front members  8 ,  9  and  10  on the basis of the target speeds for the front members  8 ,  9  and  10  (the boom target speed, arm target speed and bucket target speed), inputted from the target speed calculation section  38  and the posture data from the work implement posture sensor  50 . 
     The correction speed calculation section  140  calculates correction speeds for correcting the speeds of the hydraulic cylinders  11 ,  12  and  13  (which are the boom cylinder speed, arm cylinder speed and bucket cylinder speed), calculated by the actuator speed calculation section  130  (a boom cylinder correction speed, an arm cylinder correction speed and a bucket cylinder correction speed), on the basis of the posture data from the work implement posture sensor  50 , data of the target speeds for the front members  8 ,  9  and  10  from the target speed calculation section  38  and inertia data from the inertia data setting device  41 . Although, in the present embodiment, the target actuator speeds are calculated by adding correction speeds to the speeds of the hydraulic cylinders  11 ,  12  and  13  calculated by the actuator speed calculation section  130 , the method for correction is not limited to this. Now, details of the correction speed calculation section  140  are described with reference to  FIG. 14 . 
       FIG. 10  is a functional block diagram of the correction speed calculation section  140 . As depicted in  FIG. 10 , the correction speed calculation section  140  includes a signal separation section  150 , a high fluctuation target speed calculation section  143 , a pre-correction target actuator speed calculation section  141   a , a low fluctuation target actuator speed calculation section  141   b  and a high fluctuation target actuator speed calculation section  141   c.    
     In  FIG. 11 , an example of A) signals of target speeds for the three front members  8 ,  9  and  10  inputted from the target speed calculation section  38 , B) low frequency components of target speed signals for the front members  8 ,  9  and  10  outputted from the signal separation section  150 , C) high frequency components of the target speed signals for the front members  8 ,  9  and  10  outputted from the signal separation section  150 , D) a high frequency component of the target speed signal for the bucket  10  outputted from the high fluctuation target speed calculation section  143 , E) a low frequency component of the target speed signal (which is a target speed signal after correction), for the boom cylinder  11  outputted from the low fluctuation target actuator speed calculation section  141   b , F) a low frequency component of the target speed signal (which is a target speed signal after correction), for the arm cylinder  12  outputted from the low fluctuation target actuator speed calculation section  141   b , G) a low frequency component of the target speed signal for the bucket cylinder  13  outputted from the low fluctuation target actuator speed calculation section  141   b , H) a high frequency component of the target speed signal for the bucket cylinder  13  outputted form the high fluctuation target actuator speed calculation section  141   c  and I) the target speed signal (which is a target speed signal after correction), for the bucket cylinder  13  is represented in an overlapping relationship. The alphabetical capital letters coincide with those indicated in balloons in  FIG. 11 . 
     The signal separation section  150  is an element that separates each of signals (depicted in a balloon A of  FIG. 11 ), of the target speeds for the three front members  8 ,  9  and  10  (the boom target speed, arm target speed and bucket target speed), inputted from the target speed calculation section  38 , into a low frequency component (depicted in a balloon B of  FIG. 11 ), of a frequency lower than a predetermined threshold value (which is a shield frequency), and a high frequency component (depicted in a balloon C of  FIG. 11 ), having a frequency higher than the threshold value. The signal separation section  150  in the present embodiment includes a low pass filter section  142  for separating a low frequency component from a target speed and a frequency component separation section (high pass filter section)  151  that separates a high frequency component from the target speed. The shielding frequency can be determined taking the limit of the responsiveness of the boom  8  or the arm  9  having a relatively high inertial load into consideration. 
     The low pass filter section  142  passes components of lower frequencies than a predetermined threshold value (shielding frequency), namely, (low frequency components), from within signals of the target speeds for the front members  8 ,  9  and  10  but reduces components of frequencies higher than the threshold value to separate the low frequency components (depicted in the balloon B of  FIG. 11 ) from the target speed signals. Consequently, in the case where a change of a target speed signal per time is large, the target speed signal is attenuated in response to the shielding frequency. The low frequency components separated by the low pass filter section  142  exist for each of the front members  8 ,  9  and  10  similarly to the target speeds and are outputted to the frequency component separation section  151  and the low fluctuation target actuator speed calculation section  141   b.    
     The frequency component separation section  151  subtracts the low frequency components from the low pass filter section  142  from the target speed signals for the three front members  8 ,  9  and  10  inputted from the target speed calculation section  38  and outputs the remaining target speed signals for the front members  8 ,  9  and  10  as high frequency components (depicted in the balloon C of  FIG. 11 ). The high frequency components are outputted to the high fluctuation target speed calculation section  143 . It is to be noted that the frequency component separation section  151  may otherwise be configured from a high pass filter that passes components of frequencies higher than the threshold value (shielding frequency) of the low pass filter section  142  (high frequency components), from within the target speed signals for the front members  8 ,  9  and  10  but reduces components of frequencies lower than the threshold value to separate the high frequency components from the target speed signals. However, if a target speed component obtained by subtracting a low frequency component outputted from the low pass filter section  142  from a target speed component outputted from the target speed calculation section  38  is determined as a high frequency component as in the present embodiment, then since the sum of the low frequency component and the high frequency component outputted from the signal separation section  150  can be kept to the original target speed, the target speed can be prevented from changing before and after it passes the signal separation section  150 . 
     The high fluctuation target speed calculation section  143  refers to the inertia data obtained from the inertia information setting device  41  to allocate the high frequency components separated by the signal separation section  150  preferentially to a front member or members whose inertial load is relatively small from among the three front members  8 ,  9  and  10  to calculate high fluctuation target speeds for the three front members. In the present embodiment, all frequency components are allocated to the bucket  10  whose inertial load is smallest from among the three front members  8 ,  9  and  10  (as depicted in a balloon D of  FIG. 11 ), and the high fluctuation target speed for the boom  8  and the arm  9  is zero. Especially in the present embodiment, speed components perpendicular to the target surface  60  of the target speeds defined by the high frequency components of the three front members  8 ,  9  and  10  separated by the signal separation section  150  are calculated, and the sum of the three perpendicular speed components is determined as the high fluctuation target speed for the bucket  10 . If the high fluctuation target speed for the bucket  10  is restricted to the perpendicular component in this manner, then the perpendicular component V 1   z  (depicted on the right side in  FIG. 9 ) is maintained although there is the possibility that the horizontal component V 0   x  (depicted on the right side in  FIG. 9 ), of the synthetic speed vector V 1  may be changed by the speed correction of the correction speed calculation section  140 . Therefore, while entering of the packet distal end P 4  to a position below the target surface  60  is prevented, geometric transformation of a speed vector is facilitated. 
     The pre-correction target actuator speed calculation section  141   a  calculates the speeds of the boom cylinder  11 , arm cylinder  12  and bucket cylinder  13  (the actuator speeds), necessary to generate the three target speeds (bucket distal end speed) and hence the packet distal end speed, utilizing geometric transformation from the signals of the target speeds for the three front members  8 ,  9  and  10  (the boom target speed, arm target speed and bucket target speed), inputted from the target speed calculation section  38  and the posture data at the time. The actuator speeds have values equal to those outputted from the actuator speed calculation section  130  and are sometimes referred to each as “pre-correction target actuator speed.” 
     The low fluctuation target actuator speed calculation section  141   b  calculates, from the low frequency components of the target speed signals for the three front members  8 ,  9  and  10  inputted from the signal separation section  150  and the posture data at the time, the actuator speeds necessary to generate the three low frequency components, namely, the speed of the boom cylinder  11  (depicted in a balloon E of  FIG. 11 ), the speed of the arm cylinder  12  (depicted in a balloon F of  FIG. 11 ) and the speed of the bucket cylinder  13  (depicted in a balloon G of  FIG. 11 ), utilizing geometric transformation. Each of the actuator speeds is sometimes referred to as “low fluctuation target actuator speed.” 
     The high fluctuation target actuator speed calculation section  141   c  calculates, from the high frequency components of the target speed signals for the three front members  8 ,  9  and  10  inputted from the high fluctuation target speed calculation section  143  and the posture data at the time, the speeds of the boom cylinder  11 , arm cylinder  12  and bucket cylinder  13  necessary to generate the three high frequency components (the actuator speeds), utilizing geometric transformation. Each of the actuator speeds is sometimes referred to as “high fluctuation target actuator speed.” It is to be noted that, since the high frequency components of the target speed signals for the boom  8  and the arm  9  inputted from the high fluctuation target speed calculation section  143  in the present embodiment is zero as described hereinabove, this results in calculation only of the speed of the bucket cylinder  13  (as depicted in a balloon H of  FIG. 11 ). 
     According to the configuration described above, the correction speed calculation section  140  outputs the correction speeds individually of the hydraulic cylinders  11 ,  12  and  13 . As the boom cylinder correction speed and the arm cylinder correction speed, the difference of the pre-correction target actuator speeds calculated by the pre-correction target actuator speed calculation section  141   a  from the low fluctuation target actuator speeds calculated by the low fluctuation target actuator speed calculation section  141   b  are outputted. As the bucket cylinder correction speed, the difference of the pre-correction target actuator speed calculated by the pre-correction target actuator speed calculation section  141   a  from the sum of the low fluctuation target actuator speed calculated by the low fluctuation target actuator speed calculation section  141   b  and the high fluctuation target actuator speed calculated by the high fluctuation target actuator speed calculation section  141   c  is outputted. 
     The correction speeds of the actuators obtained in this manner are added to the speeds of the hydraulic cylinders  11 ,  12  and  13  outputted from the actuator speed calculation section  130  depicted in  FIG. 7  and are outputted as target actuator speeds (as a target boom cylinder speed, a target arm cylinder speed and a target bucket cylinder speed), from the target actuator speed calculation section  100  to the actuator controller  200  (depicted in  FIG. 6 ). The calculation values of the actuator speed calculation section  130  and the pre-correction target actuator speed calculation section  141   a  are equal to each other, and as a result, the target boom cylinder speed outputted form the target actuator speed calculation section  100  becomes the low fluctuation target actuator speed (depicted in the balloon E of  FIG. 11 ); the target arm cylinder speed becomes the low fluctuation target actuator speed (depicted in the balloon F of  FIG. 11 ); and the target bucket cylinder speed becomes the speed of the sum of the low fluctuation target actuator speed and the high fluctuation target actuator speed (as depicted in a balloon I of  FIG. 11 ). 
     Referring back to  FIG. 6 , upon calculation of solenoid valve driving signals for the solenoid valves  32 ,  33 ,  34  and  35 , the actuator controller  200  utilizes a table in which target speeds for the hydraulic cylinders  11 ,  12  and  13  (target boom cylinder speeds, target arm cylinder speeds and target bucket cylinder speeds), and solenoid valve driving signals for the spool driving solenoid valves  35   a ,  35   b ,  32   a ,  32   b ,  33   a ,  33   b ,  34   a  and  34   b  for operating the spools  31 ,  28 ,  29  and  30  corresponding to the hydraulic cylinders  11 ,  12  and  13  are defined in a one-to-one correlation. 
     As this table, a table for the boom spool driving solenoid valve  35   a  that is utilized in the case where the boom cylinder  11  is to be extended and a table for the boom spool driving solenoid valve  35   b  that is utilized in the case where the arm cylinder  12  is to be contracted are available. Further, as two tables that are utilized in the case where the arm cylinder  12  is to be extended, a table of the first arm spool driving solenoid valve  32   a  and a table for the second arm spool driving solenoid valve  33   a  are available. Further, as two tables that are utilized in the case where the arm cylinder  12  is to be contracted, a table of the first arm spool driving solenoid valve  32   b  and a table for the second arm spool driving solenoid valve  33   b  are available. Furthermore, a table for the bucket spool driving solenoid valve  34   a  that is utilized in the case where the bucket cylinder  13  is to be extended and a table for the bucket spool driving solenoid valve  34   b  that is utilized in the case where the bucket cylinder  13  is to be contracted are available. In those eight tables, a correlation between a target speed and a current value is defined such that the current values to the solenoid valves  35   a ,  35   b ,  32   a ,  32   b ,  33   a ,  33   b ,  34   a  and  34   b  increase monotonously together with increase in magnitude of the target speeds for the hydraulic cylinders  11 ,  12  and  13  (the target actuator speeds), on the basis of a relationship between the current values to the solenoid valves  35   a ,  35   b ,  32   a ,  32   b ,  33   a ,  33   b ,  34   a  and  34   b  and the actual speeds of the hydraulic cylinders  11 ,  12  and  13  determined by an experiment or a simulation in advance. 
     For example, when a command of a target arm cylinder speed and a target boom cylinder speed are applicable, the actuator controller  200  generates control commands for the solenoid valves  32 ,  33  and  35  to drive the first arm spool  28 , second arm spool  29  and boom spool  31 . Consequently, the arm cylinder  12  and the boom cylinder  11  act on the basis of the target arm cylinder speed and the target boom cylinder speed, respectively. 
       FIG. 12  is a flow chart representative of a control flow by the controller  25 . The controller  25  starts processing of  FIG. 12  when the operation device  24  is operated by an operator, and the control point position calculation section  53  calculates position data of the bucket distal end P 4  (which is the control point), in the global coordinate system on the basis of data of the inclination angles θ 1 , θ 2 , θ 3  and θ 4 , position data, posture data (angle data) and orientation data of the hydraulic excavator  1  calculated from navigation signals of the GNSS antennae  21  and  22 , the dimension data L 1 , L 2  and L 3  of the front members stored in advance and so forth (procedure S 1 ). 
     In procedure S 2 , the distance calculation section  37  extracts and acquires position data of target surfaces (target surface data), included in a predetermined range with reference to the position data of the bucket distal end P 4  in the global coordinate system calculated by the control point position calculation section  53  from the target surface storage section  54  (in this case, position data of the hydraulic excavator  1  may be utilized) in place of the position data of the bucket distal end P 4 . Then, a target surface positioned nearest to the bucket distal end P 4  from among the target surfaces is set as a target surface  60  of a control target, namely, as a target surface  60  with reference to which the distance D is to be calculated. 
     In procedure S 3 , the distance calculation section  37  calculates the distance D on the basis of the position data of the bucket distal end P 4  calculated in procedure S 1  and the position data of the target surface  60  set in procedure S 2 . 
     In procedure S 4 , the target speed calculation section  38  calculates, on the basis of the distance D calculated in procedure S 3  and operation amounts (voltage values) of the operation levels inputted from the operation device  24 , target speeds for the front members  8 ,  9  and  10  such that the bucket distal end P 4  is kept on or above the target surface  60  even if the work implement  7  acts. 
     In procedure S 5 , the actuator speed calculation section  130  calculates, on the basis of the target speeds for the front members  8 ,  9  and  10  calculated in procedure S 4  and the position data of the work implement  7  obtained from the work implement posture sensor  50 , speeds of the boom cylinder  11 , arm cylinder  12  and bucket cylinder  13  (actuator speeds), necessary to generate the target speeds for the front members  8 ,  9  and  10  calculated in procedure S 4 . 
     In procedure S 6 , the pre-correction target actuator speed calculation section  141   a  calculates, on the basis of the target speeds for the front members  8 ,  9  and  10  calculated in procedure S 4  and the posture data of the work implement  7  obtained from the work implement posture sensor  50 , speeds of the boom cylinder  11 , arm cylinder  12  and bucket cylinder  13  (pre-correction target actuator speeds), necessary to generate the target speeds for the front members  8 ,  9  and  10  calculated in procedure S 4 . It is to be noted that the pre-correction target actuator speeds calculated here have values equal to the actuator speeds calculated in procedure S 5 . 
     In procedure S 7 , the signal separation section  150  separates each of signals of the target speeds for the front members  8 ,  9  and  10  calculated in procedure S 4  into a high frequency component and a low frequency component. Consequently, for example, as depicted in  FIG. 11 , the target speed in the balloon A is separated into a low frequency component (low fluctuation component) of the balloon B, which indicates a relatively small speed fluctuation per time, and a high frequency component (high fluctuation component) of the balloon C, which indicates a relatively large speed fluctuation per unit time. 
     In procedure S 8 , the low fluctuation target actuator speed calculation section  141   b  calculates, on the basis of the low frequency components of the target speed signals for the front members  8 ,  9  and  10  separated in procedure S 7  and the posture data of the work implement  7  obtained from the work implement posture sensor  50 , speeds of the boom cylinder  11 , arm cylinder  12  and bucket cylinder  13  necessary to generate the low frequency components of the target speed signals for the front members  8 ,  9  and  10  separated in procedure S 7  (low fluctuation target actuator speeds). 
     In procedure S 9 , the high fluctuation target speed calculation section  143  calculates components perpendicular to the target surface  60  from within the high frequency components of the target speed signals for the front members  8 ,  9  and  10  separated in procedure S 7  and outputs the sum of all of the calculated perpendicular components as a high frequency component of the target speed signal for the bucket  10  to the high fluctuation target actuator speed calculation section  141   c.    
     In procedure S 10 , the high fluctuation target actuator speed calculation section  141   c  calculates, on the basis of the high frequency component of the target speed signal for the bucket  10  calculated in procedure S 9  and the posture data of the work implement  7  obtained from the work implement posture sensor  50 , a speed of the bucket cylinder  13  necessary to generate the high frequency component of the target speed signal for the bucket  10  calculated in procedure S 9  (a high fluctuation target actuator speed). 
     In procedure S 11 , the correction speed calculation section  140  calculates correction speeds for the actuators  11 ,  12  and  13 . In the present embodiment, the correction speed for each of the actuators  11 ,  12  and  13  is the difference of the pre-correction target actuator speed (procedure S 6 ) from the sum of the low fluctuation target actuator speed (procedure S 8 ) and the high fluctuation target actuator speed (procedure S 9 ) as depicted in  FIG. 12 . Such difference is calculated for each of the actuators  11 ,  12  and  13  and determined as a correction speed. In particular, the correction speed calculation section  140  outputs the difference of the boom cylinder speed (procedure S 8 ) calculated by the pre-correction target actuator speed calculation section  141   a  from the boom cylinder speed (procedure S 8 ) calculated by the low fluctuation target actuator speed calculation section  141   b  as a boom cylinder correction speed. Further, the correction speed calculation section  140  outputs the difference of the arm cylinder speed (procedure S 6 ) calculated by the pre-correction target actuator speed calculation section  141   a  from the arm cylinder speed (procedure S 8 ) calculated by the low fluctuation target actuator speed calculation section  141   b  as an arm cylinder correction speed. Furthermore, the correction speed calculation section  140  outputs the difference of the bucket cylinder speed (procedure S 6 ) calculated by the pre-correction target actuator speed calculation section  141   a  from the sum of the bucket cylinder speed (procedure S 8 ) calculated by the low fluctuation target actuator speed calculation section  141   b  and the bucket cylinder speed (procedure S 9 ) calculated by the high fluctuation target actuator speed calculation section  141   c  as a bucket cylinder correction speed. 
     In procedure S 12 , the target actuator speed calculation section  100  calculates a target speed for each of the actuators  11 ,  12  and  13  (a target actuator speed). In the present embodiment, the target speeds for the actuators  11 ,  12  and  13  are the sums of the speeds of the actuators  11 ,  12  and  13  calculated in procedure S 5  and the correction speeds for the actuators  11 ,  12  and  13  calculated in procedure S 5  as depicted in  FIG. 12 . Since the speeds of the actuators  11 ,  12  and  13  calculated in procedure S 5  have values equal to those of the pre-correction target actuator speeds calculated in procedure S 6 , the target speed for each of the actuators  11 ,  12  and  13  becomes the sum of the low fluctuation target actuator speed (procedure S 8 ) calculated by the low fluctuation target actuator speed calculation section  141   b  and the high fluctuation target actuator speed (procedure S 9 ) calculated by the high fluctuation target actuator speed calculation section  141   c . In particular, the target actuator speed calculation section  100  outputs the boom cylinder speed (procedure S 8 ) calculated by the low fluctuation target actuator speed calculation section  141   b  as a boom cylinder target speed. Further, the target actuator speed calculation section  100  outputs the arm cylinder speed (procedure S 8 ) calculated by the low fluctuation target actuator speed calculation section  141   b  as an arm cylinder target speed. Furthermore, the target actuator speed calculation section  100  outputs the sum of the bucket cylinder speed (procedure S 8 ) calculated by the low fluctuation target actuator speed calculation section  141   b  and the bucket cylinder speed (procedure S 9 ) calculated by the high fluctuation target actuator speed calculation section  141   c  as a bucket cylinder target speed. 
     In procedure S 13 , the actuator controller  200  calculates a signal for driving the second flow rate control valve (boom spool)  31  on the basis of the boom cylinder target speed and outputs the signal to the solenoid valve  31   a  or the solenoid valve  31   b . Similarly, the actuator controller  200  calculates signals for driving the first flow control valve (first arm spool)  28  and the third flow control valve (second arm spool)  29  on the basis of the arm cylinder target speed and outputs the signals the solenoid valve  32   a  and the solenoid valve  33   a  or the solenoid valve  32   b  and the solenoid valve  33   b . Furthermore, the actuator controller  200  calculates a signal for driving the bucket spool (bucket spool)  30  on the basis of the bucket cylinder target speed and outputs the signal to the solenoid valve  34   a  or the solenoid valve  34   b . Consequently, the actuators  11 ,  12  and  13  are driven on the basis of the target speeds therefor, namely (of the target actuator speeds therefor), to operate the front members  8 ,  9  and  10 , respectively. 
     After the process in procedure S 13  ends, it is confirmed that the operation of the operation device  24  continues and the processing returns to the top of the flow and repeats the processes in the procedures beginning with procedure S 1 . It is to be noted that, if the operation of the operation device  24  ends even in the middle of the flow of  FIG. 12 , the processing is encoded and it is waited that operation of the operation device  24  is started next. 
     In the hydraulic excavator  1  configured in such a manner as described above, the boom  8  and the arm  9  operate in accordance with target speed signals whose fluctuation per time is small (with low frequency components in the balloon B of  FIG. 11 ) while a target speed signal that is excluded from the target speed signals for the boom  8  and the arm  9  and whose fluctuation per time is large (a high frequency component depicted in the balloon C of  FIG. 11 ) is added to the target speed signal for the bucket  10  such that it is converted into action of the bucket  10 . Since the bucket  10  has a relatively low inertial load in comparison with the boom  8  or the arm  9 , it can respond rapidly also to a target speed signal whose fluctuation per time is large. In particular, even in a case in which the change of the target speed signal for any of the front members  8 ,  9  and  10  per time is so large that it exceeds the responsiveness of the boom  8  or the arm  9  whose inertial load is relatively large like, for example, a case in which, in a state in which the bucket distal end P 4  is on the target surface  60  during finishing work of the target surface  60 , the operator inputs a quick arm crowding operation in error, such exceeding amount is compensated for by action of the bucket  10  whose inertial load is relatively small. Since this makes it possible to make at least the perpendicular component of the actual speed vector of the packet distal end coincide with the target speed, stable semiautomatic excavation shaping control of high accuracy can be achieved. 
     Second Embodiment 
     Although, in the first embodiment described hereinabove, a frequency component of a target speed signal separated by the signal separation section  150  is allocated only to the bucket  10 , it may otherwise be allocated only to the arm  9  in place of the bucket  10 . Here, this case is described as a second embodiment of the present invention. It is to be noted that description of like elements to those of the embodiment described above is omitted (This similarly applies also to the succeeding embodiments). 
       FIG. 13  is a functional block diagram of the correction speed calculation section  140  in the second embodiment. As depicted in  FIG. 13 , the correction speed calculation section  140  has a configuration similar to that in the first embodiment. However, in the present embodiment, the high fluctuation target speed calculation section  143  allocates all high frequency components to the arm  9  from among the three front members  8 ,  9  and  10  while the high fluctuation target speed for the boom  8  and the bucket  10  is zero. It is to be noted that, also in the present embodiment, speed components, which are perpendicular to the target surface  60 , of the target speeds defined by the high frequency components of the three front members  8 ,  9  and  10  separated by the signal separation section  150  are calculated, and the sum of the three perpendicular speed components is determined as the high fluctuation target speed for the arm  9 . 
     In the first embodiment, even in the case where the operator does not operate the bucket  10 , in the case where a high frequency component is generated in a target speed signal, there is the possibility that the bucket  10  may act to provide a discomfort feeling to the operator by semiautomatic excavation control. However, in the present embodiment configured in such a manner as described above, since a high frequency component generated in a target speed signal is allocated to the arm  9 , the bucket  10  does not act unless an operation for the bucket  10  is performed. Therefore, the front member that is not operated by the operator (the bucket  10 ), is prevented from acting by semiautomatic excavation control, and the disagreeable feeling that may be provided to the operator can be moderated. Further, since the arm  9  has a small inertial load in comparison with the boom  8 , even in the case where the number of times of fluctuation of a target speed signal per time is large, stable semiautomatic excavation control can be performed with high accuracy. 
     Third Embodiment 
     In the two embodiments described above, a high frequency component of a target speed signal separated by the signal separation section  150  is allocated to one of the bucket  10  and the arm  9 . However, in the present embodiment, a high frequency component of a target speed signal is distributed to the front members  8 ,  9  and  10  at an appropriate ratio (at an appropriate distribution ratio), which is determined taking the inertial loads of the front members  8 ,  9  and  10  into consideration, so as to be added to low fluctuation target actuator speeds of the boom  8 , arm  9  and bucket  10 . 
       FIG. 14  is a functional block diagram of the correction speed calculation section  140  in the third embodiment. The high fluctuation target speed calculation section  143  in the present embodiment allocates high frequency components separated by the signal separation section  150  preferentially to a front member whose inertial load is relatively small from among the three front members  8 ,  9  and  10  to calculate high fluctuation target speeds for the three front members  8 ,  9  and  10 . In the present embodiment, the high frequency components of the target speed signals are distributed to the front members  8 ,  9  and  10  at a ratio determined taking the inertial loads of the front members  8 ,  9  and  10  into consideration. Since generally the inertial load of the boom  8 , arm  9  and bucket  10  decreases in this order, from the point of view of the assurance of the responsiveness, it is preferable to increase the distribution rate in this order. For example, although the distribution ratio can be a ratio of reciprocals (namely, an inverse ratio), of numerical values obtained by quantifying the inertial loads of the boom  8 , arm  9  and bucket  10  on the basis of the inertia data, some other ratio may be used. In addition, such a configuration that the distribution ratio is corrected in response to the posture data of the front members  8 ,  9  and  10  may be used. 
     As depicted in  FIG. 14 , in the present embodiment, outputs of the high fluctuation target actuator speed calculation section  141   c  are added to all of the three outputs from the low fluctuation target actuator speed calculation section  141   b . In other words, all of the three outputs of the correction speed calculation section  140  are differences of the outputs of the pre-correction target actuator speed calculation section  141   a  from the sums of the outputs of the low fluctuation target actuator speed calculation section  141   b  and the outputs of the high fluctuation target actuator speed calculation section  141   c.    
     According to the present embodiment configured in this manner, since the high fluctuation target actuator speed is distributed not only to the bucket  10  or the arm  9  but to the front members  8 ,  9  and  10  in accordance with a distribution ratio determined on the basis of inertia data, for example, in the case where the high fluctuation target speed is excessively high and exceeds a maximum action speed of the bucket  10 , this can be coped with by allocating the remaining part of the high fluctuation target speed to the arm  9 . Then, if the remaining part cannot be covered even if it is distributed to the bucket  10  and the arm  9 , it is possible to cause to the boom  8  to bear part of the remaining part. This makes it possible to achieve stable semiautomatic excavation of high accuracy even in the case where the high fluctuation target speed is excessively high. 
     Fourth Embodiment 
     There is the possibility that, from among the three front members  8 ,  9  and  10 , the arm  9  or the bucket  10  may take such a posture that a straight line interconnecting the axis of pivotal motion of the same and the bucket distal end P 4  is perpendicular to the target surface  60 . (The posture just described is hereinafter referred to as “singular posture.”)  FIG. 15  is an explanatory view of a situation that the bucket  10  takes its singular posture, and  FIG. 16  is an explanatory view of a situation that the arm  9  takes its singular posture. In the case where the arm  9  or the bucket  10  takes its singular posture, even if the hydraulic cylinder  12  or  13  for the arm  9  or the bucket  10  acts, a perpendicular speed component cannot be generated at the bucket distal end P 4 . If a high fluctuation speed is allocated to the front member  9  or  10  that is in such a situation as just described, then a command for an impossible action is provided to the hydraulic cylinder  12  or  13  and unstable action may be caused. Therefore, in the present embodiment, at least one of the arm  9  and the bucket  10  takes its singular posture, carrying out of the distribution of a target speed is aborted. 
       FIG. 17  is a functional block diagram of the correction speed calculation section  140  in the fourth embodiment. The present embodiment is equivalent to the third embodiment in which a posture decision section  144  is additionally provided such that an output of the same is inputted to the low pass filter section  142 . 
     The posture decision section  144  decides, on the basis of posture data of the work implement  7  and position data of the target surface, whether or not a first straight line L 1  (depicted in  FIG. 16 ) which interconnects the packet distal end and the center of pivotal motion of the arm  9  on an action plane of the work implement  7  is orthogonal to the target surface  60  and whether or not a second straight line L 2  (depicted in  FIG. 15 ) which interconnects the packet distal end and the center of pivotal motion of the bucket  10  is similarly orthogonal to the target surface  60  on the action plane of the work implement  7 . Then, the posture decision section  144  outputs a result of the decision to the low pass filter section  142 . In particular, in the case where the posture decision section  144  decides that one of the first straight line L 1  and the second straight line L 2  is orthogonal to the target surface  60 , it outputs a reset signal. 
     In the case where it is decided by the posture decision section  144  that one of the first straight line L 1  and the second straight line L 2  is orthogonal to the target surface  60  (namely, in the case where a reset signal is outputted), the low pass filter section  142  (the signal separation section  150 ), does not execute the process for separating each of signals of target speeds for the three front members  8 ,  9  and  10  into a low frequency component having a frequency lower than the threshold value (shielding frequency) and a high frequency component having a frequency higher than the threshold value, but outputs the signals of the target speeds for the three front members  8 ,  9  and  10  as they are to the low fluctuation target actuator speed calculation section  141   b . In particular, if a reset signal is inputted from the posture decision section  144 , then the low pass filter section  142  temporarily stops its filter function and outputs the target speed signals for the front members  8 ,  9  and  10  inputted from the target speed calculation section  38  as they are. 
     If the correction speed calculation section  140  is configured in this manner, then in the case where one of the arm  9  and the bucket  10  takes its singular posture, the high frequency component outputted from the signal separation section  150  to the high fluctuation target speed calculation section  143  decreases zero without fail and the output of the pre-correction target actuator speed calculation section  141   a  and the output of the low fluctuation target actuator speed calculation section  141   b  coincide with each other without fail. As a result, all of the correction speeds outputted from the correction speed calculation section  140  are zero. In other words, conventional semiautomatic excavation control only with outputs of the actuator speed calculation section  130  is performed. Accordingly, according to the present embodiment, in the case where one of the arm  9  and the bucket  10  takes its singular posture, semiautomatic excavation control can be prevented from suffering from occurrence of unstable action. 
     Fifth Embodiment 
       FIG. 18  is a functional block diagram of the correction speed calculation section  140  in the fifth embodiment. The present embodiment is equivalent to the third embodiment in which the posture decision section  144  is additionally provided such that an outputs thereof is inputted to the high fluctuation target speed calculation section  143 . 
     The posture decision section  144  performs decision same as that in the fourth embodiment and outputs a result of the decision to the low pass filter section  142 . In particular, in the case where it is decided that one of the first straight line L 1  and the second straight line L 2  is orthogonal to the target surface  60 , the posture decision section  144  outputs a reset signal. However, the reset signal in the present embodiment includes data indicating whether the front member that takes a singular posture is the arm  9  or the bucket  10 . 
     In the case where it is decided by the posture decision section  144  that the first straight line L 1  is orthogonal to the target surface  60 , the high fluctuation target speed calculation section  143  distributes high frequency components of target speed signals for the boom  8 , arm  9  and bucket  10  separated by the signal separation section  150  to the front members except the arm  9  from among the boom  8 , arm  9  and bucket  10  (namely, to the boom  8  and the bucket  10 ), and calculates high fluctuation target speeds for the arm  9  and the bucket  10 . On the other hand, in the case where it is decided by the posture decision section  144  that the second straight line L 2  is orthogonal to the target surface  60 , the high fluctuation target speed calculation section  143  distributes high frequency components of target speed signals for the boom  8 , arm  9  and bucket  10  separated by the signal separation section  150  to the front members except the bucket  10  from among the boom  8 , arm  9  and bucket  10  (namely, to the boom  8  and the arm  9 ), and calculates high fluctuation target speeds for the arm  9  and the bucket  10 . However, in both cases, from a point of view of inertial loads, the distribution rate to the boom  8  may be set to zero. It is to be noted that, in the case where both of the first straight line L 1  and the second straight line L 2  are orthogonal to the target surface  60 , the high frequency components are distributed only to the boom  8  to calculate a high fluctuation target speed. 
     If the correction speed calculation section  140  is configured in such a manner as described above, then in the case where the arm  9  or the bucket  10  takes its singular posture, the high fluctuation target speed for the front member that takes the singular posture becomes zero without fail, and the output of the pre-correction target actuator speed calculation section  141   a  and the output of the low fluctuation target actuator speed calculation section  141   b  coincide with each other without fail. As a result, the correction speed for the actuator of the front member outputted from the correction speed calculation section  140  becomes zero. In other words, for the front member that takes its singular posture, conventional semiautomatic excavation control with an output only of the actuator speed calculation section  130  is performed. Accordingly, according to the present embodiment, in the case where the arm  9  or the bucket  10  takes the singular posture, semiautomatic excavation control can be prevented from suffering from occurrence of unstable action. It is to be noted that, different from the fourth embodiment in which, in the case where a reset signal is outputted, the high fluctuation target actuator speeds for all front members are set to zero, in the present embodiment, a high fluctuation target actuator speed can be generated for any front member that does not take its singular posture. Therefore, semiautomatic excavation that is higher in accuracy than that in the fourth embodiment can be performed stably. 
     &lt;Others&gt; 
     The present invention is not limited to the embodiments described above and includes various modifications without departing from the subject matter of the same. For example, the present invention is not limited to configurations that include all components described in connection with the embodiments described above but includes configurations from which the components are partly omitted. Further, it is possible to add or replace part of the components of a certain embodiment to or with the components of a different embodiment. 
     Although, in the embodiments described hereinabove, the actuator speed calculation section  130  and the correction speed calculation section  140  are different calculation elements from each other, they may otherwise be integrated into a single calculation element having equivalent functions. 
     While, in the embodiments described hereinabove, the actuator speed calculation section  130  and the pre-correction target actuator speed calculation section  141   a  are provided, each of the target speeds for the actuators  11 ,  12  and  13  is the sum of a low fluctuation target actuator speed and a high fluctuation target actuator speed as demonstrated by procedure S 12  of  FIG. 12 . Therefore, the controller  25  may be configured such that the actuator speed calculation section  130  and the pre-correction target actuator speed calculation section  141   a  are omitted and the sum of the output of the low fluctuation target actuator speed calculation section  141   b  and the output of the high fluctuation target actuator speed calculation section  141   c  is outputted as a target actuator speed to the actuator controller  200 . 
     The components of the controller  25  and functions, execution processes and so forth of the components may be implemented partly or entirely by hardware such that (for example, logics that execute the functions are designed as an integrated circuit or circuits). Further, the components of the controller  25  described above may be given as a program (software) that implements the functions of the components of the controller  25  by being read out and executed by an arithmetic processing unit (for example, a CPU). Data relating to the program can be stored, for example, in a semiconductor memory (a flash memory or an SSD), a magnetic storage device (a hard disk drive), a recording medium (such as a magnetic disk or an optical disk) or the like. 
     DESCRIPTION OF REFERENCE CHARACTERS 
     
         
           1 : Hydraulic excavator (work machine) 
           2 : Track structure 
           3 : Swing structure 
           4 : Operation room 
           5 : Machine room 
           6 : Counterweight 
           7 : Work implement 
           8 : Boom 
           9 : Arm 
           10 : Bucket 
           11 : Boom cylinder 
           12 : Arm cylinder 
           13 : Bucket cylinder 
           14 : First hydraulic pump 
           15 : Second hydraulic pump 
           16 : Engine (prime mover) 
           17 : Machine body tilt sensor 
           18 : Boom tilt sensor 
           19 : Arm tilt sensor 
           20 : Bucket tilt sensor 
           21 : First GNSS antenna 
           22 : Second GNSS antenna 
           23 : Machine body control system 
           24 : Operation device 
           25 : Controller 
           26 : Flow control valve device 
           27 : Hydraulic circuit 
           28 : First arm spool (first flow control valve) 
           29 : Second arm spool (third flow control valve) 
           30 : Bucket spool 
           31 : Boom spool (second flow control valve) 
           32   a ,  32   b : First arm spool driving solenoid valve 
           33   a ,  33   b : Second arm spool driving solenoid valve 
           34   a ,  34   b : Bucket spool driving solenoid valve 
           35   a ,  35   b : Boom spool driving solenoid valve 
           36   a ,  36   b : Hydraulic working fluid tank 
           37 : Distance calculation section 
           38 : Target speed calculation section 
           41 : Inertia information setting device 
           42 : Second boom spool (fourth flow control valve) 
           43   a ,  43   b : Second boom spool driving solenoid valve) 
           44 : Hydraulic fluid tank 
           50 : Work implement posture sensor 
           51 : Target surface setting device 
           53 : Control point position calculation section 
           54 : Target surface storage section 
           60 : Target surface 
           100 : Target actuator speed calculation section 
           130 : Actuator speed calculation section 
           140 : Correction speed calculation section 
           141   a : Pre-correction target actuator speed calculation section 
           141   b : Low fluctuation target actuator speed calculation section 
           141   c : High fluctuation target actuator speed calculation section 
           142 : Low pass filter section 
           143 : High fluctuation target speed calculation section 
           144 : Posture decision section 
           15 −: Signal separation section 
           151 : Frequency component separation section 
           200 : Actuator controller