Patent Publication Number: US-11391011-B2

Title: Hydraulic excavator

Description:
TECHNICAL FIELD 
     The present invention relates to a work machine. 
     BACKGROUND ART 
     In a hydraulic excavator, a boom, an arm, a bucket, and the like of a work implement (hereinafter, also referred to as “front work implement”) are rotatably supported, so that a tip end of the bucket traces out a circular arc locus when the bucket is moved solely. Owing to this, in a case of forming a linear finished surface by the tip end of the bucket by, for example, an arm crowding action, then an operator needs to drive the boom, the arm, and the bucket in a combined fashion so that the tip end of the bucket traces out a linear locus; thus, the operator is required to have expertise. 
     To address this challenge, there is a technique for applying a function to control actuators to be driven either automatically or semiautomatically by a computer (controller) (hereinafter, referred to as machine control) to control the excavation work, and moving the tip end of the bucket along a design surface (hereinafter, also referred to as “target excavation surface”) during an excavation action (arm or bucket action). As the technique of this type, there is known one for automatically controlling a boom cylinder during the excavation action by operator&#39;s operation to add a boom raising action as appropriate, and limiting a tip end position of the bucket onto the design surface. 
     However, in a case of conducting work for laying earth on a flat or recessed geographical feature to raise a ground level (hereinafter, referred to as “filling work”), a filled upper surface after completion serves as the design surface. The tip end of the bucket is often located below the design surface during the filling work. Owing to this, when the arm crowding action is performed in a state in which the tip end of the bucket is located below the design surface (that is, within a filling range), the machine control to limit the tip end position of the bucket onto the design surface is executed, which possibly results in sudden start of the boom raising action. 
     To address the problem, Patent Document 1, for example, describes a work vehicle that includes: a design surface information acquiring section acquiring data about a design surface indicative of a target shape of a work object by a work implement; a cutting edge position computing section computing a position of a cutting edge of a bucket; and an action limiting section executing action limiting control by which a boom is forcibly raised in accordance with a relative position of the cutting edge of the bucket to the design surface, and the position of the cutting edge is limited to a region above the design surface, and Patent Document 1 describes that, in a state in which the cutting edge is located away from the design surface vertically below by a predetermined distance or longer, the action limiting section does not execute the action limiting control. 
     PRIOR ART DOCUMENT 
     Patent Document 
     Patent Document 1: JP 5706050 B1 
     SUMMARY OF THE INVENTION 
     Problem to be Solved by the Invention 
     According to the work vehicle described in Patent Document 1, the action limiting section does not execute the action limiting control in the state in which the cutting edge of the bucket (tip end of the bucket) is located away from the target excavation surface (design surface) vertically below by a predetermined distance or longer. Owing to this, when the action limiting control (forced boom raising action) is suddenly executed (hereinafter, such a boom action is often referred to as “sudden action”) irrespectively of operator&#39;s intention in a case of changing the distance of the cutting edge to the target excavation surface from the state of being equal to or larger than the predetermined distance to a state of being smaller than the predetermined distance. As a result, the occurrence of the sudden boom raising action causes the operator who does not desire or expect the boom raising action to feel heavy discomfort. In addition, in a case of the presence of the cutting edge of the bucket near the predetermined distance, the boom raising action under the action limiting control is executed or not executed. In this way, the changeover between on and off of the control irrespective of operator&#39;s intention possibly, frequently occurs. Owing to this, there is a concern of increasing operator&#39;s discomfort. 
     An object of the present invention is, therefore, to provide a work machine capable of suppressing sudden occurrence of a boom raising action (occurrence of a sudden action) while a tip end of a work implement is located below a target excavation surface. 
     Means for Solving the Problem 
     While the present application includes a plurality of means for solving the problems. As an example, there is provided a multijoint work machine including: a travel structure; a swing structure swingably attached onto the travel structure; a multijoint work implement that is attached to the swing structure and that includes a boom, an arm, and a bucket; an operation device that outputs an action direction to each of the travel structure, the swing structure, the boom, the arm, and the bucket in response to an operator&#39;s operation; and a controller that executes region limiting control to forcibly raise the boom in such a manner that a position of a tip end of the work implement is kept on a target excavation surface and within a region above the target excavation surface if the operation device issues the action direction to the arm or the bucket. The controller includes a target action determination section that determines which is selected as a control mode over a raising speed of the boom at a time of executing the region limiting control, a first mode or a second mode specified by a raising speed lower than a raising speed of the first mode if the tip end of the work implement is located below the target excavation surface, and controls the raising speed of the boom during the region limiting control on the basis of a result of determination. 
     Effect of the Invention 
     According to the present invention, it is possible to suppress sudden occurrence of a boom raising action if a tip end of a work implement is located below a target excavation surface; thus, it is possible to suppress an operator from feeling discomfort. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a configuration diagram of a hydraulic excavator. 
         FIG. 2  is a diagram illustrating a controller together with a hydraulic drive system in the hydraulic excavator according to an embodiment of the present invention. 
         FIG. 3  is a hardware configuration diagram of the controller. 
         FIG. 4  is a diagram illustrating a coordinate system in the hydraulic excavator. 
         FIG. 5  is a configuration diagram of a control system according to the present invention. 
         FIG. 6  is a conceptual diagram of excavation work. 
         FIG. 7  is a control flowchart according to a first embodiment of the present invention. 
         FIG. 8  is a diagram illustrating a relationship between the hydraulic excavator and a target excavation surface. 
         FIG. 9  is a control flowchart according to a second embodiment of the present invention. 
         FIG. 10  is a control flowchart according to a third embodiment of the present invention. 
         FIG. 11  is a diagram of an example of control modes over a boom raising speed. 
         FIG. 12  is a diagram of another example of control modes over the boom raising speed. 
     
    
    
     MODES FOR CARRYING OUT THE INVENTION 
     Embodiments of the present invention will be described hereinafter with reference to the drawings. While an example of a hydraulic excavator provided with a bucket  10  as an attachment on a tip end of a work implement is described below, the present invention may be applied to a hydraulic excavator provided with an attachment other than the bucket. In the following description, when a plurality of same constituent elements are present, alphabets are often added to reference characters (numbers). However, the plurality of constituent elements are often denoted generically by omitting the alphabets. For example, when three pumps  300   a ,  300   b , and  300   c  are present, these are often denoted generically by pumps  300 . 
     First Embodiment 
       FIG. 1  is a configuration diagram of a hydraulic excavator according to a first embodiment of the present invention, and  FIG. 2  is a diagram illustrating a controller together with a hydraulic drive system in the hydraulic excavator according to the first embodiment of the present invention. In  FIG. 1 , a hydraulic excavator  1  is configured with a front work implement  1 A and a machine body  1 B. The machine body  1 B is configured with a lower travel structure  11  and an upper swing structure  12  swingably attached onto the lower travel structure  11 . The front work implement  1 A is configured by coupling a plurality of driven members (a boom  8 , an arm  9 , and a bucket  10 ) each rotating in a perpendicular direction, and a base end of the boom  8  of the front work implement  1 A is supported by a front portion of the upper swing structure  12 . 
     The boom  8 , the arm  9 , the bucket  10 , the upper swing structure  12 , and the lower travel structure  11  configure driven members that are driven by a boom cylinder  5 , an arm cylinder  6 , a bucket cylinder  7 , a swing hydraulic motor  4 , and left and right travel motors  3   a  and  3   b , respectively. Action directions to these driven members  8 ,  9 ,  10 ,  12 , and  11  are output in response to operator&#39;s operations on a travel right lever  23   a , a travel left lever  23   b , an operation right lever  1   a , and an operation left lever  1   b  (which are often generically referred to as operation levers  1 ,  23 ) mounted in an operation room on the upper swing structure  12 . 
     An operation device  47   a  (refer to  FIG. 2 ) having the travel right lever  23   a , an operation device  47   b  (refer to  FIG. 2 ) having the travel left lever  23   b , operation devices  45   a  and  46   a  having the operation right lever  1   a , and operation devices  45   b  and  46   b  having the operation left lever  1   b  are installed in the operation room. The operation devices  45  to  47 , which are hydraulic pilot operation devices, supply, as control signals, pilot pressures (often referred to as operating pressures) in response to operation amounts (for example, lever strokes) and operation directions of the operation levers  1 ,  23  operated by an operator to hydraulic drive sections  150   a  to  155   b  of flow control valves  15   a  to  15   f  (refer to  FIG. 2 ) via pilot lines  144   a  to  149   b  (refer to  FIG. 2 ) to drive these flow control valves  15   a  to  15   f.    
     A hydraulic fluid delivered from a hydraulic pump  2  is supplied to the travel right hydraulic motor  3   a , the travel left hydraulic motor  3   b , the swing hydraulic motor  4 , the boom cylinder  5 , the arm cylinder  6 , and the bucket cylinder  7  via the flow control valves  15   a ,  15   b ,  15   c ,  15   d ,  15   e , and  15   f  (refer to  FIG. 2 ) within a control valve unit  20 . The boom cylinder  5 , the arm cylinder  6 , and the bucket cylinder  7  expand and contract by the supplied hydraulic fluid, whereby the boom  8 , the arm  9 , and the bucket  10  rotate and a position and a posture of the bucket  10  change. Furthermore, the swing hydraulic motor  4  rotates by the supplied hydraulic fluid, whereby the upper swing structure  12  swings with respect to the lower travel structure  11 . Moreover, the travel right hydraulic motor  3   a  and the travel left hydraulic motor  3   b  rotate by the supplied hydraulic fluid, whereby the lower travel structure  11  travels. 
     Meanwhile, a boom angle sensor  30 , an arm angle sensor  31 , and a bucket angle sensor  32  are attached to a boom pin, an arm pin, and a bucket link  13  so that rotation angles α, β, γ (refer to  FIG. 4 ) of the boom  8 , the arm  9 , and the bucket  10  can be measured, respectively, and a machine body tilt angle sensor  33  that detects a longitudinal tilt angle θ of the upper swing structure  12  (machine body  1 B) with respect to a reference plane (for example, horizontal plane) is attached to the upper swing structure  12 . 
     As illustrated in  FIG. 2 , the hydraulic excavator  1  of  FIG. 1  has the hydraulic pump  2 , a plurality of hydraulic actuators, which includes the boom cylinder  5 , the arm cylinder  6 , the bucket cylinder  7 , the swing hydraulic motor  4 , and the left and right travel motors  3   a  and  3   b  driven by the hydraulic fluid supplied from this hydraulic pump  2 , the travel right lever  23   a , the travel left lever  23   b , the operation right lever  1   a , and the operation left lever  1   b  provided to correspond to these hydraulic actuators  3  to  7 , respectively, the plurality of flow control valves  15   a  to  15   f , which are connected between the hydraulic pump  2  and the plurality of hydraulic actuators  3  to  7 , which are controlled by the control signals output from the operation devices  45   a ,  45   b ,  46   a ,  46   b ,  47   a , and  47   b  in response to the operation amounts and the operation directions of the operation levers  1 ,  23 , and which control flow rates and directions of the hydraulic fluid supplied to the hydraulic actuators  4  to  7 , and a relief valve  16  opened if a pressure between the hydraulic pump  2  and the flow control valves  15   a  to  15   f  is equal to or higher than a set value. These elements configure the hydraulic drive system that drives the driven members of the hydraulic excavator  1 . 
     The hydraulic excavator of the present embodiment is provided with a control system assisting an operator&#39;s excavation operation. Specifically, the hydraulic excavator  1  is provided with an excavation control system that exercises control to forcibly raise the boom  8  (often referred to as “region limiting control”) on the basis of a position relationship between the target excavation surface and the tip end of the work implement  1 A such that a position of a tip end of the work implement  1 A (claw tip of the bucket  10 ) is kept on the target excavation surface and within a region above the target excavation surface in a case of the presence of the action direction issued to the arm  9  or the bucket  10  from the operation device  45   b  or  46   a . The excavation control system that can execute this region limiting control includes a limiting control switch  17  that is installed at a position at which the limiting control switch  17  does not obstruct an operator&#39;s view such as a position above an operation panel within the operation room and that changes over between validation and invalidation of the region limiting control, pressure sensors  70   a  and  70   b  that are provided in pilot lines  144   a  and  144   b  of the operation device  45   a  for the boom  8  and that detect a pilot pressure (control signal) as the operation amount of the operation lever  1   a , pressure sensors  71   a  and  71   b  that are provided in pilot lines  145   a  and  145   b  of the operation device  45   b  for the arm  9  and that detect a pilot pressure (control signal) as the operation amount of the operation lever  1   b , a solenoid proportional valve  54   a  that has a primary port side connected to a pilot pump  48  and that reduces a pilot pressure from the pilot pump  48  to output the reduced pilot pressure, a shuttle valve  82  that is connected to a secondary port side of the solenoid proportional valve  54   a  in the pilot line  144   a  of the operation device  45   a  for the boom  8 , that selects a higher pressure from between the pilot pressure in the pilot line  144   a  and the control pressure output from the solenoid proportional valve  54   a , and that guides the selected higher pressure to the hydraulic drive section  150   a  of the flow control valve  15   a , a solenoid proportional valve  54   b  that is installed in the pilot line  144   b  of the operation device  45   a  for the boom  8  and that reduces the pilot pressure in the pilot line  144   b  in response to an electrical signal to output the reduced pilot pressure, and a controller  40  that is a computer capable of executing the region limiting control. 
     The pilot lines  145   a  and  145   b  for the arm  9  are provided with the pressure sensors  71   a  and  71   b  each detecting the pilot pressure and outputting the pilot pressure to the controller  40  and solenoid proportional valves  55   a  and  55   b  each reducing the pilot pressure on the basis of a control signal from the controller  40  and outputting the reduced pilot pressure. The pilot lines  146   a  and  146   b  for the bucket  10  are provided with pressure sensors  72   a  and  72   b  each detecting the pilot pressure and outputting the pilot pressure to the controller  40 , and solenoid proportional valves  56   a  and  56   b  each reducing the pilot pressure on the basis of a control signal from the controller  40  and outputting the pilot pressure. It is noted that connection lines among the pressure sensors  71  and  72 , the solenoid proportional valves  55  and  56 , and the controller  40  are not depicted in  FIG. 2  because of space limitations. 
     Shape information and position information about the target excavation surface stored in a ROM  93  or RAM  94  to be described later, detection signals of the angle sensor  30  to  32  and the tilt angle sensor  33 , and detection signals of the pressure sensors  70  to  72  are input to the controller  40 . Furthermore, the controller  40  outputs electrical signals for correcting the control signals (pilot pressures) for exercising excavation control (region limiting control) to limit a region to the solenoid proportional valves  54  to  56 . 
       FIG. 3  illustrates a hardware configuration of the controller  40 . The controller  40  has an input section  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 section  95 . The signals from the operation devices  45  to  47 , a signal from a setting device  51  that sets the target excavation surface, and the signals from the angle sensors  30  to  32  and the tilt angle sensor  33  are input to the input section  91 , and the input section  91  performs A/D conversion. The ROM  93  is a recording medium that records a control program for executing flowcharts of  FIGS. 8 and 9  to be described later, various information necessary to execute the flowcharts, and the like, and the CPU  92  performs a predetermined computing process on the signals imported from the input section  91  and the memories  93  and  94  in accordance with the control program stored in the ROM  93 . The output section  95  generates to-be-output signals in response to a computation result of the CPU  92 , and outputs the signals to the solenoid proportional valves  54  to  56  and an informing device  53 , thereby driving/controlling the hydraulic actuators  4  to  7  and displaying images of the machine body  1 B, the bucket  10 , the target excavation surface, and the like on a display screen of a monitor that is the informing device  53 . While the controller  40  of  FIG. 3  includes semiconductor memories that are the ROM  93  and the RAM  94  as the storage devices, another storage device can be provided as an alternative to the semiconductor memories, and the controller  40  may be provided with, for example, a magnetic storage device such as a hard disk drive. 
       FIG. 5  is a functional block diagram of the controller  40  according to the embodiment of the present invention. The controller  40  is provided with a work implement posture computing section  41 , a target excavation surface computing section  42 , a target action computing section  43 , a solenoid proportional valve control section  44 , and a target action determination section  49 . In addition, a work implement posture sensor  50 , a target excavation surface setting device  51 , an operator&#39;s operation sensor  52 , the informing device  53 , and the solenoid proportional valves  54  to  56  are connected to the controller  40 . 
     The work implement posture sensor  50  is configured with the boom angle sensor  30 , the arm angle sensor  31 , the bucket angle sensor  32 , and the machine body tilt angle sensor  33 . The target excavation surface setting device  51  is an interface to which information about the target excavation surface (including position information about the target excavation surface) can be input. The information may be input to the target excavation surface setting device  51  either by operator&#39;s manually inputting the information or by importing the information from outside via a network or the like. Furthermore, a satellite communication antenna is connected to the target excavation surface setting device  51 , and the target excavation surface setting device  51  may compute excavator global coordinates. The operator&#39;s operation sensor  52  is configured with the pressure sensors  70   a ,  70   b ,  71   a ,  71   b ,  72   a , and  72   b  that acquire the operating pressures generated by operator&#39;s operating the operation levers  1 . The informing device  53  is configured with at least one of a display (display device) that displays the position relationship between the target excavation surface and the work implement  1 A for the operator and a loudspeaker that informs the operator of the position relationship between the target excavation surface and the work implement  1 A by a sound (including a voice). The solenoid proportional valves  54  to  56  are provided in the pilot pressure (operating pressure) hydraulic lines described with reference to  FIG. 2  and can increase/decrease downstream the operating pressures generated by operator&#39;s lever operation. Alternatively, the operating pressures can be generated without the operator&#39;s lever operation. 
       FIG. 6  illustrates an example of a horizontal excavation action under machine control that is a function to control the work implement  1 A either automatically or semiautomatically and to shape the target excavation surface. In a case of conducting horizontal excavation by operator&#39;s operating the operation levers  1  and an action of crowding the arm  9  in an arrow A direction, a boom raising command is output as appropriate so that the tip end (claw tip) of the bucket  10  does not penetrate a region below the target excavation surface  60 , and the solenoid proportional valve  54   a  is controlled such that an action of raising the boom  8  is automatically carried out. In addition, the solenoid proportional valves  55  are controlled to carry out the action of crowding the arm  9  so as to realize an excavation speed or excavation accuracy demanded by the operator. At this time, a speed of the arm  9  may be reduced by the solenoid proportional valves  55  as needed for improvement of the excavation accuracy. Furthermore, the solenoid proportional valves  56  may be controlled to cause the bucket  10  to automatically rotate in an arrow C direction (dumping direction) so that an angle B of a back surface of the bucket  10  with respect to the target excavation surface  60  becomes a constant value and leveling work can be easily conducted. In this way, the function to control the actuators either automatically or semiautomatically with respect to the operation amounts of the operation levers  1  by the operator, and to actuate the constituent elements of the work implement such as the boom  8 , the arm  9 , the bucket  10 , and the upper swing structure  12  is referred to as “machine control.” The region limiting control is one type of machine control. 
     The work implement posture computing section  41  computes a posture of the work implement  1 A on the basis of information from the work implement posture sensor  50 . The posture of the work implement  1 A can be defined on the basis of excavator reference coordinates of  FIG. 4 . The excavator reference coordinates of  FIG. 4  are coordinates set to the upper swing structure  12 , a base of the boom  8  rotatably supported by the upper swing structure  12  is assumed as an origin, and Z-axis is set in a vertical direction of the upper swing structure  12  and an X-axis is set in a horizontal direction thereof. It is assumed that a tilt angle of the boom  8  with respect to the X-axis is a boom angle α, a tilt angle of the arm  9  with respect to the boom is an arm angle β, and a tilt angle of the claw tip of the bucket with respect to the arm is a bucket angle γ. It is also assumed that a tilt angle of the machine body  1 B (upper swing structure  12 ) with respect to the horizontal plane (reference plane) is a tilt angle θ. The boom angle α is detected by the boom angle sensor  30 , the arm angle β is detected by the arm angle sensor  31 , the bucket angle γ is detected by the bucket angle sensor  32 , and the tilt angle θ is detected by the machine body tilt angle sensor  33 . The boom angle α becomes maximum when the boom  8  is raised to a maximum level (highest level) (when the boom cylinder  5  is at a stroke end in a raising direction, that is, when a boom cylinder length is the largest), and becomes minimum when the boom  8  is lowered to a minimum level (lowest level) (when the boom cylinder  5  is at a stroke end in a lowering direction, that is, when the boom cylinder length is the smallest). The arm angle β becomes minimum when an arm cylinder length is the smallest, and becomes maximum when the arm cylinder length is the largest. The bucket angle γ becomes minimum when a bucket cylinder length is the smallest (as depicted in  FIG. 4 ), and becomes maximum when the bucket cylinder length is the largest. 
     The target excavation surface computing section  42  computes the target excavation surface  60  on the basis of information from the target excavation surface setting device  51 . The target action computing section  43  computes a target action of the work implement  1 A so that the bucket  10  moves on the target excavation surface and within the region above the target excavation surface, on the basis of information from the work implement posture computing section  41 , the target excavation surface computing section  42 , the target action determination section  49 , and the operator&#39;s operation sensor  52 . The solenoid proportional valve control section  44  computes commands to the solenoid proportional valves  54  to  56  on the basis of commands from the target action computing section  43 . The solenoid proportional valves  54  to  56  are controlled on the basis of the commands from the solenoid proportional valve control section  44 . Furthermore, the informing device  53  informs the operator of various information related to the machine control on the basis of information from the target action computing section  43 . 
     The commands output from the target action computing section  43  to the solenoid proportional valve control section  44  include a boom raising command. The boom raising command is a command output to the solenoid proportional valve control section  44  at a time of forcibly raising the boom  8  so that the position of the tip end of the bucket  10  is kept on the target excavation surface  60  and within the region above the target excavation surface  60  at a time of executing the region limiting control. When the boom raising command is input to the solenoid proportional valve control section  44 , then the solenoid proportional valve control section  44  outputs a valve opening command (command current) to the solenoid proportional valve  54   a , and a hydraulic fluid (hereinafter, referred to as secondary pressure) generated in the solenoid proportional valve  54   a  is supplied to the hydraulic drive section  150   a  to drive the control valve  15   a . The hydraulic operating fluid is thereby guided into a bottom-side hydraulic chamber of the boom cylinder  5  from the hydraulic pump  2  to raise the boom  8 . A raising speed of the boom  8  (boom raising speed) at that time is controllable by a value of a secondary pressure of the solenoid proportional valve  54   a , that is, a command from the solenoid proportional valve control section  44  to the solenoid proportional valve  54   a.    
     The target action determination section  49  determines which is more preferably selected, a first mode (normal boom raising control) or a second mode (deceleration boom raising slow action control) as a control mode over the raising speed of the boom  8  during execution of the region limiting control if the tip end of the work implement  1 A is located below the target excavation surface, and outputs a result of determination to the target action computing section  43 . The target action computing section  43  outputs a command computed on the basis of this result of the determination to the solenoid proportional valve control section  44 . The solenoid proportional valve control section  44  outputs the command to the solenoid proportional valve  54   a  on the basis of this command, and the boom raising speed is finally controlled in the control mode selected by the target action determination section  49 . 
     In the present embodiment, the target action determination section  49  makes the determination on the basis of a downward penetration amount of the tip end of the work implement  1 A (claw tip of the bucket  10 ) into the target excavation surface  60 , selects the second mode (deceleration boom raising slow action control) if the penetration amount is equal to or higher than a predetermined value, and selects the first mode (normal boom raising control) if the penetration amount is lower than the predetermined value. Details of the target action determination section  49  will be described with reference to  FIG. 7 . 
       FIG. 7  illustrates a control flowchart by the target action determination section  49  of the present embodiment. First, in Step  100 , the target action determination section  49  computes the distance between the target excavation surface  60  and the tip end of the bucket  10  on the basis of the position of the tip end of the bucket  10  in the excavator reference coordinates input from the work implement posture computing section  41  and the position of the target excavation surface (abbreviated as “target surface” in  FIG. 7 )  60  in the excavator reference coordinates input from the target excavation surface computing section  42 . In addition, it is assumed that the distance is a penetration amount D of the work implement  1 A into the target excavation surface  60  and the penetration amount D of the work implement  1 A is the penetration amount D of the tip end of the bucket  10  in a case in which the tip end of the bucket  10  is located below the target excavation surface  60 . If the penetration amount D is equal to or higher than a predetermined value D 1  (for example, 300 mm), a process goes to Step  101 . 
     In Step  101 , the target action determination section  49  determines whether the operator causes the operation device  45   b  or  46   b  to issue the action direction to the arm  9  or the bucket  10 , that is, whether the operation input is performed on the operation lever  1   b  or  1   a  on the basis of an output from the operator&#39;s operation sensor  52 . If determining in Step  101  that the operation input is performed on the arm  9  or the bucket  10 , the target action determination section  49  selects the deceleration boom raising slow action control as the control mode in Step  104 . The target action determination section  49  thereby outputs a control mode command in the second mode to the target action computing section  43 , and the boom raising speed during the boom raising control is controlled in the second mode by the solenoid proportional valve  54   a.    
     Now, the normal boom raising control (first mode) and the deceleration boom raising slow action control (second mode) will be described. Normally, when the region limiting control described above is executed, then the boom raising command is output from the target action computing section  43 , and the boom raising action is controlled in such a manner that the tip end of the bucket does not penetrate the target excavation surface  60  on the basis of the command. It is assumed that the control mode over the boom raising speed at this time is the normal boom raising control (first mode). On the other hand, the deceleration boom raising slow action control (second mode) is a control mode that is not intended to prevent the penetration of the tip end of the bucket into the target excavation surface  60  but that is selected to mitigate operator&#39;s discomfort, and the boom raising speed at that time is always set lower than the speed during the normal boom raising control in the same condition. For example, the speed in the second mode can be set to a value obtained by multiplying the speed in the first mode by a predetermined rate (for example, 20%). The speed in the second mode can be kept to a predetermined value in such a manner that the speed in the second mode is always controlled to be equal to or lower than the speed in the first mode. As the predetermined value in this case, a minimum value of the boom raising speed, that is, the boom raising speed while a minimum pilot pressure that enables the control valve  15   a  to move from a neutral position is acting on the hydraulic drive section  150   a  can be selected. 
     The boom speed control based on the deceleration boom raising slow action control can be exercised continuously until the bucket tip end is located above the target excavation surface  60 . In other words, in this case, once the deceleration boom raising slow action control is selected, the deceleration boom raising slow action control is continuously selected while the bucket tip end is penetrating into the target excavation surface  60  even if the penetration amount of the bucket tip end into the target excavation surface  60  becomes lower than the predetermined value. It is noted that this is also applicable to other embodiments. 
     Furthermore, if the deceleration boom raising slow action control is selected in Step  104 , the target action determination section  49  issues a command to the informing device  53  to inform the operator of the selection of the deceleration boom raising slow action control in Step  105 . At this time, operator&#39;s changing over the limiting control switch  17  to a region limiting control invalid position stops the selection of the deceleration boom raising slow action control and the execution of the region limiting control. 
     On the other hand, if determining in Step  101  that the operation input is not performed on the arm  9  or the bucket  10 , the target action determination section  49  does not execute the boom raising control (Step  107 ). 
     Moreover, if determining in Step  100  that the penetration amount of the bucket tip end into the target excavation surface is equal to or lower than the predetermined value, the process goes to Step  102 . In and after Step  102 , the target action determination section  49  executes the normal region limiting control. First, if the target action determination section  49  determines that the arm  9  or the bucket  10  is operated on the basis of an output from the operator&#39;s operation sensor  52  in Step  102 , the process goes to Step  103 . 
     In Step  103 , the target action determination section  49  determines whether the boom raising command is issued from the target action computing section  43  on the basis of an input signal from the target action computing section  43 . If determining in Step  103  that the boom raising command is issued, the target action determination section  49  selects the normal boom raising control to execute boom raising in Step  106 . In other words, the target action determination section  49  issues a control mode command in the first mode to the target action computing section  43 , and the boom raising speed during the boom raising control is controlled in the first mode by the solenoid proportional valve  54   a.    
     If determining in Step  103  that the boom raising command is not output, or determining in Step  102  that the operation input is not performed on the arm  9  or the bucket  10 , the target action determination section  49  does not execute the boom raising control. 
     After the process goes up to “RETURN” in the flowchart, the process returns to Step  100  and the target action determination section  49  repeats the process described above. 
     Effects by the present configuration will be described with reference to  FIG. 8 .  FIG. 8  illustrates a position relationship between the hydraulic excavator and the target excavation surface  60 . The hydraulic excavator can travel on a ground  600  in a current geographical feature. The target excavation surface  60  is indicated by a broken line and this indicates a surface that is now subjected to the filling work and to be finally shaped. 
     As indicated by an arrow E, it is assumed herein that the hydraulic excavator travels on the ground  600  from left to right and that the tip end of the bucket  10  penetrates into a region below the target excavation surface  60 . The hydraulic excavator normally travels without operating the front work implement  1 A (front operation). In other words, the boom raising control is not executed by presence of Step  101  or  102  of  FIG. 7  because of no operation on the arm  9  or the bucket  10 , and the tip end of the bucket  10  penetrates into the region below the target excavation surface  60  as the hydraulic excavator travels. A reference character D denotes the distance between the target excavation surface  60  and the tip end of the bucket  10  (penetration amount), and reference character D 1  denotes the predetermined value in Step  100 . 
     As disclosed in Japanese Patent No. 5706050, in a case of configuring the hydraulic excavator in such a manner that the region limiting control is not executed when the penetration amount D is equal to or higher than the predetermined value (which is assumed as D 1  similarly to the present embodiment), the boom raising control is not executed while the work is conducted in a range in which the penetration amount D is equal to or higher than D 1  even with the operator&#39;s operating the arm  9  in a state of the hydraulic excavator on a right side of  FIG. 8 . Owing to this, a probability increases that the operator forgets the execution of the region limiting control when the penetration amount D is lower than D 1  or falsely understand that the region limiting control does not work at all irrespectively of the penetration amount D. In addition, if the filling work then proceeds to reduce the penetration amount D and the tip end of the bucket  10  reaches D 1 , the boom raising control is suddenly executed at the normal speed specified in the first mode. The occurrence of this sudden action causes the operator who does not expect or desire the boom raising action to feel heavy discomfort. Furthermore, in the work in circumstances where the penetration amount D continues to be a value near D 1 , the changeover between on and off of the boom raising control frequently occurs in response to a change in the penetration amount D; thus, there is a concern that the operator desired action cannot be smoothly carried out to disturb the progress of the work. 
     In the present embodiment configured as described above, by contrast, when the arm  9  is operated in the state of the hydraulic excavator on the right side of  FIG. 8 , the boom raising control is executed at the low speed specified in the second mode. The boom raising speed at this time is lower than the normal speed (that is, lower than that when the penetration amount D is lower than D 1 ); thus, it is possible to suppress anxiety of the operator about the sudden boom raising action by the machine control. Furthermore, the forgetting or misunderstanding described above does not occur since the operator can perceive that the region limiting control functions by expression of the boom raising action. Moreover, the operator spontaneously suspends the region limiting control by the region limiting control switch  17  on an occasion of a case in which the region limiting control is unnecessary; thus, it is possible to prevent the execution of the operator unintended machine control. Therefore, according to the present embodiment, if the tip end of the work implement is located below the target excavation surface, it is possible to suppress the sudden occurrence of the boom raising action and, therefore, possible to suppress the operator from feeling discomfort. 
     Moreover, in the embodiment described above, if the second mode is selected, the controller  40  is configured to inform the operator of the selection through the informing device. This can further accelerate the operator&#39;s recognition of the region limiting control, so that it is possible to further suppress the occurrence of the forgetting or misunderstanding described above. 
     Furthermore, as mentioned above, in a case of configuring the controller  40  in such a manner that the boom speed control based on the deceleration boom raising slow action control (second mode) is continuously carried out until the tip end of the bucket is located above the target excavation surface  60 , the boom raising control based on the deceleration boom raising slow action control is carried out while the bucket tip end is penetrating into the target excavation surface  60  even if the penetration amount D of the bucket tip end into the target excavation surface  60  is lower than the predetermined value D 1 . Owing to this, the speed of automatic boom raising does not suddenly change until the bucket tip end reaches the target excavation surface  60 ; thus, it is possible to mitigate operator&#39;s discomfort. 
     Second Embodiment 
     A second embodiment of the present invention will next be described. It is noted that a hardware configuration of a hydraulic excavator in the present embodiment is the same as that in the first embodiment and, therefore, not described and that functions overlapping those in the first embodiment are not sometimes described. 
     In the present embodiment, “determination” by the target action determination section  49  differs from that in the first embodiment, and the target action determination section  49  is configured to change the control mode over the boom raising speed during the boom raising control in the light of a reason for penetration into the target excavation surface. In other words, the target action determination section  49  changes the control mode over the boom raising speed, depending on the reason for the penetration into the target excavation surface such as the penetration due to travel or swing, the penetration due to a forward posture of the excavator, and the penetration due to other unexpected reasons (for example, the penetration due to deteriorated control accuracy during excavation). 
     Specifically, the target action determination section  49  determines which is preferably selected to control the boom speed during the boom raising control, the first mode or the second mode, on the basis of the action direction to the lower travel structure  11  or the upper swing structure  12  from the operation devices  46   b ,  47   a , and  47   b  (operation levers  1   b ,  23   a , and  23   b ) and the position relationship between the target excavation surface  60  and the tip end of the work implement  1 A. In addition, the target action determination section  49  selects the second mode (deceleration boom raising slow action control) if the tip end of the work implement  1 A moves below the target excavation surface  60  by the action direction to the lower travel structure  11  or the upper swing structure  12  from the operation devices  46   b ,  47   a , and  47   b  (operation levers  1   b ,  23   a , and  23   b ), and selects the first mode (normal boom raising control) if the action direction to the lower travel structure  11  or the upper swing structure  12  from the operation devices  47   a  and  47   b  or the operation device  46   b  is not present and if the tip end of the work implement  1 A is located above the target excavation surface  60 . Details of the target action determination section  49  will be described with reference to  FIG. 9 . 
       FIG. 9  is a control flowchart by the target action determination section  49  in the present embodiment. It is noted that the present flowchart is carried out per control cycle. 
     First, in Step  200 , the target action determination section  49  determines whether the penetration of the bucket tip end into the target excavation surface  60  was present in a control cycle just before a current control cycle. If determining that the penetration of the bucket tip end into the target excavation surface  60  was not present, the target action determination section  49  regards the current bucket tip end as being located above the target excavation surface  60  and a process goes to Step  201 . 
     In Step  201 , the target action determination section  49  determines whether a travel operation or a swing operation is present via the operation levers  23   a  and  23   b  or the operation lever  1   b . If the target action determination section  49  determines herein that the travel operation or the swing operation is present, the process goes to Step  202 . 
     In Step  202 , the target action determination section  49  determines whether the penetration of the bucket tip end into the target excavation surface  60  is present on the basis of the position of the tip end of the bucket  10  input from the work implement posture computing section  41  and the position of the target excavation surface  60  input from the target excavation surface computing section  42 . If determining in Step  202  that the penetration into the target excavation surface  60  is present, then the target action determination section  49  determines that a cause for the penetration is the travel or swing operation, and the process goes to Step  203 . 
     In Step  203 , the target action determination section  49  determines whether an operation input is performed on the arm  9  or the bucket  10  from the operation lever  1   b  or  1   a . If determining herein that the operation input is performed on the arm  9  or the bucket  10 , the target action determination section  49  selects the deceleration boom raising slow action control (second mode) as the control mode over the boom raising speed in Step  209 . In addition, in Step  210 , the target action determination section  49  issues a command to the informing device  53  to inform the operator of the selection of the deceleration boom raising slow action control due to the presence of the swing or travel. It is noted that the deceleration boom raising slow action control may be executed until the work implement  1 A is located above the target excavation surface  60  similarly to the first embodiment. 
     If the target action determination section  49  determines in Step  201  that the travel operation or the swing operation is not present, the process goes to Step  204 . 
     In Step  204 , the target action determination section  49  determines whether the machine body tilt angle θ is greater than a predetermined angle θ 1  in a forward tilting direction, on the basis of an output from the machine body tilt angle sensor  33 . If the target action determination section  49  determines in Step  204  that the machine body tilt angle θ is greater than the predetermined angle θ 1 , the process goes to Step  215 . 
     In Step  215 , the target action determination section  49  determines whether the penetration of the bucket tip end into the target excavation surface  60  is present on the basis of the position of the tip end of the bucket  10  input from the work implement posture computing section  41  and the position of the target excavation surface  60  input from the target excavation surface computing section  42 . If determining in Step  215  that the penetration into the target excavation surface  60  is present, then the target action determination section  49  determines that a cause for the penetration is a forward tilt posture of the machine body, and the process goes to Step  205 . 
     In Step  205 , the target action determination section  49  determines whether the operation input is performed on the arm  9  or the bucket  10 . If the target action determination section  49  determines in Step  205  that the operation input is performed on the arm  9  or the bucket  10 , the process goes to Step  206 . 
     In Step  206 , similarly to Step  103  of  FIG. 7 , the target action determination section  49  determines whether the boom raising command is issued. If determining in Step  206  that the boom raising command is issued, the target action determination section  49  determines not to execute the boom raising control (that is, cancels the boom raising command in Step  206 ) since the machine body tilt angle θ is great, and issues a command to the informing device  53  to inform the operator that the boom raising control is not executed in Step  212 . 
     If the target action determination section  49  determines that the penetration was present in Step  200 , if the target action determination section  49  determines that the penetration into the target excavation surface  60  is not present in Step  202  or  215 , or if the target action determination section  49  determines that the machine body tilt angle θ is equal to or less than a predetermined angle θ 1  in Step  204 , the process goes to Step  207 . It is noted that cases of going to Step  207  include a case in which the penetration is not due to the travel, the swing, or the forward tilt posture but for some reason during the excavation work (for example, the deteriorated control accuracy during excavation). 
     The target action determination section  49  selects the normal boom raising control (first mode) in Step  213  if determining that the arm  9  or the bucket  10  is operated and the boom raising command is issued at that time in Steps  207  and  208 . In addition, it is assumed that the target action determination section  49  does not execute the boom raising control in Step  211  if determining that the arm or bucket operation is not present in Step  203 ,  205 , or  207  or if the boom raising command is not output in Step  206  or  208 . 
     Effects of the present embodiment will be described. A case in which the tip end of the work implement  1 A moves below the target excavation surface  60  due to the travel of the lower travel structure  11  or the swing of the upper swing structure  12  does not necessarily indicate that the bucket tip end penetrates into the target excavation surface  60  during the excavation work. In the present embodiment, therefore, the boom raising control is executed in the second mode lower in speed than the first mode in such a case, and the operator is informed that the control different from normal control is functioning. By doing so, if the boom raising action at the low speed occurs after the travel or the swing, it is possible to cause the operator to easily recognize that movement of the bucket tip end below the target excavation surface  60  is due to the travel or the swing. Therefore, if the operator does not desire to execute the region limiting control (boom raising control), the operator can easily and spontaneously suspend the region limiting control by the region limiting control switch  17 . 
     Furthermore, if the bucket tip end penetrates into the target excavation surface  60  due to the bad geographical features and the tilting of the machine body, then the excavator has an unstable posture in many cases, and there is a concern of the deteriorated excavation accuracy under such circumstances. In the present embodiment, therefore, even with the penetration into the target excavation surface  60  without the action direction to the lower travel structure  11  or the upper swing structure  12 , the target action determination section  49  is configured to regard the tilting of the machine body as the cause for the penetration and to suspend the boom raising control (region limiting control) if the machine body tilt angle θ is greater than the predetermined angle θ 1  in the forward tilting direction. With this configuration, it is possible to avoid execution of the boom raising control with the excavator in the unstable posture and continue stable work. 
     Furthermore, in the present embodiment, the target action determination section  49  is configured to execute Step  207  if a determination result is NO in Steps  201  and  204 ; thus, even if the bucket tip end penetrates into the target excavation surface  60  for the cause other than the above causes (the travel, the swing, and the tilting of the machine body), the target action determination section  49  can control the boom speed in the first mode. With this configuration, if the bucket tip end penetrates into the region below the target excavation surface  60  for some cause (for example, the deteriorated control accuracy over the bucket tip end) during the excavation work, the bucket tip end can be promptly moved back to the target excavation surface  60 ; thus, it is possible to prevent deterioration of work efficiency for the excavation work. 
     Therefore, according to the present embodiment, it is possible to carry out appropriate boom raising control, depending on the various circumstances described above. 
     Third Embodiment 
     A third embodiment of the present invention will next be described. The present embodiment is a modification of the first embodiment. It is noted that a hardware configuration of a hydraulic excavator in the present embodiment is the same as that in the first embodiment and, therefore, not described and that functions overlapping those in the first and second embodiments are not described. 
       FIG. 10  is a flowchart by the target action determination section  49  in the third embodiment. As obvious from this figure, the target action determination section  49  makes determination on the basis of the machine body tilt angle θ of the excavator in Step  204 . In addition, the target action determination section  49  (1) selects the second mode if the penetration amount D is equal to or higher than the predetermined value D 1  (if the process passes through Step  104 ), (2) suspends the region limiting control if the penetration amount D is lower than the predetermined value D 1  and the machine body tilt angle θ is equal to or greater than the predetermined angle θ 1  (if the process passes through Step  212 ), and (3) selects the first mode if the penetration amount D is lower than the predetermined value D 1  and the machine body tilt angle θ is less than the predetermined angle θ 1  (if the process passes through Step  105 ). 
     In the present embodiment configured as described so far, similarly to the second embodiment, it is possible to avoid execution of the boom raising control with the excavator in the unstable posture and continue stable work. 
     &lt;Note&gt; 
     Examples of the first mode and the second mode that are the control modes over the boom raising speed during the execution of the region limiting control will be described with reference to  FIGS. 11 and 12 . 
     In  FIG. 11 , a boom raising speed VB in the first mode is specified by a straight line and a speed VB in the second mode is specified by a curve. If the first mode and the second mode are smoothly connected at the predetermined value D 1  and the penetration amount D changes from a state of being equal to or higher than D 1  to a state of being lower than D 1 , a case of changing over between the modes before and after the predetermined value D 1  is supposed. It is noted that the first mode may be similarly specified by a curve or the second mode may be similarly specified by a straight line. 
     In  FIG. 12 , the speed VB in the second mode is specified by a constant value irrespective of the penetration amount D. In  FIG. 12 , if the penetration amount D changes from the state of being equal to or higher than D 1  to the state of being lower than D 1 , a case of keeping the second mode until the penetration amount D becomes zero without changeover of the mode even with the penetration amount D reaching the predetermined value D 1  (a case of continuously executing the boom speed control based on the second mode until the bucket tip end is located above the target excavation surface  60 ) is supposed. 
     While the penetration amount D is associated with the boom raising speed VB for the brevity of description in the examples of  FIGS. 11 and 12 , the boom raising speed VB in each mode can be made independent of the penetration amount. Any pattern of the first mode and the second mode is applicable to cases other than the examples of  FIGS. 11 and 12  as long as the speed in the second mode takes on a value equal to or lower than the speed in the first mode with the same penetration amount. 
     Meanwhile, while the penetration of the work implement  1 A into the target excavation surface  60  has been described while taking the penetration amount of the bucket tip end by way of example in each of the embodiments described above, an object to be controlled is not limited to the bucket tip end. For example, not the bucket tip end but an arbitrary point on the bucket such as the back surface of the bucket may be set as the object to be controlled. 
     While the angle sensors are used for detecting the angles of the boom, the arm, and the bucket for information about the posture, stroke sensors detecting stroke lengths of the boom cylinder, the arm cylinder, and the bucket cylinder may be used to calculate the information about the posture of the excavator as an alternative to the angle sensors. 
     In the flowcharts of  FIGS. 7, 9, and 10 , Steps  101 ,  102 ,  103 ,  203 ,  205 ,  206 ,  207 , and  208  can be omitted. 
     While various types of control is exercised by setting the bucket tip end and the target excavation surface to a two-dimensional coordinate system (excavator coordinate system) set to the hydraulic excavator, the bucket tip end and the target excavation surface may be set to a three-dimensional coordinate system (world coordinate system) set to the ground (Earth) as an alternative to the two-dimensional coordinate system. 
     In the first embodiment, if a determination result is YES in Step  101 , then the same determination (determination whether the boom raising command is output) as that in Step  103  may be additionally executed, and the process may go to Step  104  if a determination result is YES in the additional step and go to Step  107  if the determination result is NO in the additional step. 
     In the second embodiment, if a determination result is NO in Step  201  (travel operation/swing operation is not present), the process may go not to Step  204  but to Step  207 . In other words, Steps  204 ,  205 ,  206 , and  212  can be omitted. 
     While it is determined whether the travel or swing operation is present in Step  201 , determination may be made only on the basis of the presence of the travel operation. Furthermore, if the bucket tip end is to penetrate into the target excavation surface by the swing on the assumption that the machine control is executed with objects to be controlled including the swing, the swing may be controlled or interrupted. 
     Moreover, while a determination condition of Step  204  is that the machine body tilt angle θ is equal to or greater than the predetermined angle θ 1  in the forward tilting direction, the determination condition is not necessarily limited to the forward tilting direction. For example, the determination condition according to a backward tilting direction or a roll tilting (roll angle) may be used. 
     Various patterns are available for determination of the penetration into the target excavation surface due to the travel or the swing. For example, as an alternative to the above example, the target action determination section  49  may be configured to monitor the position relationship between the bucket tip end and the target surface during the travel operation or swing operation, and to execute the process of Step  203  upon confirmation of the movement of the bucket tip end from above the target excavation surface to below the target excavation surface. 
     While the case of suspending the boom raising control if the machine body tilt angle θ exceeds θ 1  has been described in the second and third embodiments, the system may be configured such that the boom raising control is exercised in the second mode as an alternative to this case. 
     DESCRIPTION OF REFERENCE CHARACTERS 
     
         
           1 A: Front work implement 
           8 : Boom 
           9 : Arm 
           10 : Bucket 
           11 : Lower travel structure 
           12 : Upper swing structure 
           30 : Boom angle sensor 
           31 : Arm angle sensor 
           32 : Bucket angle sensor 
           40 : Controller 
           41 : Work implement posture computing section 
           42 : Target excavation surface computing section 
           43 : Target action computing section 
           44 : Solenoid proportional valve control section 
           45 : Operation device (boom, arm) 
           46 : Operation device (bucket, swing) 
           47 : Operation device (travel) 
           49 : Target action determination section 
           53 : Informing device 
           54 ,  55 ,  56 : Solenoid proportional valve