Patent Publication Number: US-2021164194-A1

Title: Shovel

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation application filed under 35 U.S.C. 111(a) claiming benefit under 35 U.S.C. 120 and 365(c) of PCT International Application No. PCT/JP2019/031706, filed on Aug. 9, 2019 and designating the U.S., which claims priority to Japanese patent application No. 2018-151853, filed on Aug. 10, 2018. The entire contents of the foregoing applications are incorporated herein by reference. 
    
    
     BACKGROUND 
     Technical Field 
     The present disclosure relates to shovels. 
     Description of Related Art 
     A shovel whose movements are operated by an operator or the like is known. 
     SUMMARY 
     According to an aspect of the present invention, a shovel includes an operating element and circuitry. The circuitry is configured to recognize a worker in an area surrounding the shovel and recognize a predetermined gesture made by the recognized worker. The circuitry is further configured to perform operation control on the operating element in response to the predetermined gesture made by the worker recognized by the recognition part. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side view of a shovel; 
         FIG. 2  is a plan view of the shovel; 
         FIG. 3  is a diagram illustrating an example configuration of a hydraulic system of the shovel; 
         FIG. 4A  is a diagram illustrating an example of a constituent part of an arm-related operation system in the hydraulic system of the shovel; 
         FIG. 4B  is a diagram illustrating an example of a constituent part of a boom-related operation system in the hydraulic system of the shovel; 
         FIG. 4C  is a diagram illustrating an example of a constituent part of a bucket-related operation system in the hydraulic system of the shovel; 
         FIG. 4D  is a diagram illustrating an example of a constituent part of an upper swing structure-related operation system in the hydraulic system of the shovel; 
         FIG. 5A  is a diagram illustrating an example of a constituent part of a lower traveling structure-related operation system in the hydraulic system of the shovel; 
         FIG. 5B  is a diagram illustrating an example of a constituent part of the lower traveling structure-related operation system in the hydraulic system of the shovel; 
         FIG. 6  is a diagram illustrating another example of an operating device; 
         FIG. 7  is a functional block diagram illustrating a first example of a configuration associated with a gesture operation function of the shovel; 
         FIG. 8  is a diagram illustrating an example of a correspondence between recognition target gestures and the operation details of operating elements; 
         FIG. 9  is a flowchart schematically illustrating an example of a gesture operation control process executed by a controller of the shovel; 
         FIG. 10  is a schematic diagram illustrating an example configuration of a remote control system including the shovel; 
         FIG. 11  is a functional block diagram illustrating a second example of the configuration associated with the gesture operation function of the shovel; 
         FIG. 12A  is a functional block diagram illustrating a third example of the configuration associated with the gesture operation function of the shovel; 
         FIG. 12B  is a functional block diagram illustrating the third example of the configuration associated with the gesture operation function of the shovel; and 
         FIG. 13  is a functional block diagram illustrating a fourth example of the configuration associated with the gesture operation function of the shovel. 
     
    
    
     DETAILED DESCRIPTION 
     As noted above, a shovel whose movements are operated by an operator or the like is known. The shovel, however, does not move unless operated from inside the cabin by the operator or the like. Therefore, there is a demand for a shovel operable by a worker or the like around. 
     According to an aspect of the present invention, it is possible to provide a shovel operable by a worker or the like around. 
     An embodiment of the present invention is described below with reference to the drawings. 
     [Shovel Overview] 
     First, an overview of a shovel  100  according to this embodiment is given with reference to  FIGS. 1 and 2 . 
       FIG. 1  is a side view of the shovel  100  according to this embodiment.  FIG. 2  is a plan view of the shovel  100  according to this embodiment. 
     The shovel  100  according to this embodiment includes a lower traveling structure  1 ; an upper swing structure  3  swingably mounted on the lower traveling structure  1  via a swing mechanism  2 ; a boom  4 , an arm  5  and a bucket  6  constituting an attachment AT; and a cabin  10 . 
     The lower traveling structure  1  includes a pair of right and left crawlers  10 , specifically, a left crawler  1 CL and a right crawler  1 CR. The left crawler  1 CL and the right crawler  1 CR are hydraulically driven by travel hydraulic motors  2 M (specifically, travel hydraulic motors  2 ML and  2 MR), so that the lower traveling structure  1  causes the shovel  100  to travel. 
     The upper swing structure  3  is driven by a swing hydraulic motor  2 A to swing relative to the lower traveling structure  1 . 
     The boom  4  is pivotably attached to the front center of the upper swing structure  3  to be movable upward and downward. The arm  5  is pivotably attached to the distal end of the boom  4  to be pivotable upward and downward. The bucket  6  is pivotably attached to the distal end of the arm  5  to be pivotable upward and downward. The boom  4 , the arm  5 , and the bucket  6  are hydraulically driven by a boom cylinder  7 , an arm cylinder  8 , and a bucket cylinder  9 , respectively, which serve as hydraulic actuators. 
     The cabin  10  is a cab in which an operator rides, and is mounted on the front left of the upper swing structure  3 . 
     The shovel  100  operates operating elements (driven elements) such as the lower traveling structure  1 , the upper swing structure  3 , the boom  4 , the arm  5 , and the bucket  6  in response to operations of the operator riding in the cabin  10  (hereinafter “riding operator” for convenience) or remote control signals received from a predetermined external device (for example, a management apparatus  200  as described below) 
     Furthermore, the shovel  100  automatically operates hydraulic actuators independent of operations of the riding operator of the cabin  10  or the details of the remote control of an operator of the externa device (hereinafter “remote operator” for convenience). According to this, the shovel  100  implements the function of automatically operating at least one or more of operating elements (driven elements) such as the lower traveling structure  1 , the upper swing structure  3 , the boom  4 , the arm  5 , and the bucket  6  (hereinafter “automatic operation function”). For example, as describe below, the shovel  100  implements a gesture operation function using the automatic operation function, which is described in detail below. The automatic operation function may include the function of automatically operating an operating element (hydraulic actuator) other than an operating element (hydraulic actuator) to be operated in response to the riding operator&#39;s operation or the remote control of the remote operator (so-called “semi-automatic operation function”). Furthermore, the automatic operation function may also include the function of automatically operating at least one or more of operating elements (hydraulic actuators) without the riding operator&#39;s operation or the remote control of the remote operator (so-called “fully automatic operation function”). Furthermore, the automatic operation function may include the function of the shovel  100  recognizing the gesture of a person such as a worker around the shovel  100  and automatically operating one or more of operating elements (hydraulic actuators) according to the details of the recognized gesture (below-described “gesture operation function”). Furthermore, the semi-automatic operation function, the fully automatic operation function, and the gesture operation function may include not only a mode in which the operation details of an operating element (hydraulic actuator) to be automatically operated are automatically determined according to predetermined rules but also a mode in which the shovel  100  autonomously performs various determinations and the operation details of an operating element (hydraulic actuator) to be automatically operated are autonomously determined along the determination results to cause the operating element to automatically operate (so-called “autonomous operation function”). 
     [Shovel Configuration] 
     Next, a configuration of the shovel  100  is described with reference to  FIG. 3 ,  FIGS. 4A through 4D ,  FIGS. 5A and 5B , and  FIG. 6  in addition to  FIGS. 1 and 2 . 
       FIG. 3  is a diagram illustrating an example configuration of the hydraulic system of the shovel  100 . 
       FIGS. 4A through 4D  are diagrams illustrating examples of constituent parts of operation systems associated with the arm  5 , the boom  4 , the bucket  6 , and the upper swing structure  3 , respectively, in the hydraulic system of the shovel  100 . 
       FIGS. 5A and 5B  are diagrams illustrating examples of constituent parts of an operation system associated with the lower traveling structure  1  in the hydraulic system of the shovel  100 . Specifically,  FIGS. 5A and 5B  are diagrams illustrating examples of constituent parts of operation systems associated with the left crawler  1 CL and the right crawler  1 CR, respectively, in the hydraulic system of the shovel  100 . 
       FIG. 6  is a diagram illustrating another example of an operating device  26 . Specifically,  FIG. 6  is a diagram illustrating another example configuration of a pilot circuit that causes a pilot pressure to act on a control valve  17  (control valves  171 ,  172 ,  173 ,  174 ,  175 L,  175 R,  176 L and  176 R) that hydraulically controls hydraulic actuators. As an example,  FIG. 6  illustrates a pilot circuit that causes a pilot pressure to act on the control valve  17  (the control valves  175 L and  175 R) that hydraulically controls the boom cylinder  7 . 
     Individual pilot circuits that hydraulically controls the travel hydraulic motors  2 ML and  2 MR, the swing hydraulic motor  2 A, the arm cylinder  8 , and the bucket cylinder  9  are expressed the same as the pilot circuit of  FIG. 6  that hydraulically controls the boom cylinder  7 . Therefore, a graphical representation of these pilot circuits is omitted. 
     First, a configuration of the hydraulic system of the shovel  100  is described. 
     The hydraulic system of the shovel  100  according to this embodiment includes an engine  11 , a regulator  13 , a main pump  14 , a pilot pump  15 , the control valve  17 , the operating device  26 , discharge pressure sensors  28 L and  28 R, operating pressure sensors  29 LA,  29 LB,  29 RA,  29 RB,  29 DL, and  29 DR, and a controller  30 . Hereinafter, the operating pressure sensors  29 LA,  29 LB,  29 RA,  29 RB,  29 DL, and  29 DR may be collectively or individually referred to as “operating pressure sensor  29 .” Furthermore, as described above, the hydraulic system of the shovel  100  according to this embodiment includes hydraulic actuators such as the travel hydraulic motors  2 ML and  2 MR, the swing hydraulic motor  2 A, the boom cylinder  7 , the arm cylinder  8 , and the bucket cylinder  9  that hydraulically drive driven elements (operating elements) such as the lower traveling structure  1 , the upper swing structure  3 , the boom  4 , the arm  5 , and the bucket  6 . 
     The engine  11  is the main power source of the hydraulic system and is mounted on the back of the upper swing structure  3 , for example. Specifically, the engine  11  rotates constantly at a preset target rotational speed under the direct or indirect control of the controller  30  to drive the main pump  14  and the pilot pump  15 . The engine  11  is, for example, a diesel engine fueled with diesel fuel. 
     Regulators  13 L and  13 R control the discharge quantities of main pumps  14 L and  14 R. For example, the regulators  13 L and  13 R adjust the angles (tilt angles) of the swash plates of the main pumps  14 L and  14 R in response to a control command from the controller  30 . The regulators  13 L and  13 R correspond to the main pumps  14 L and  14 R, respectively. 
     The main pump  14 L and  14 R are, for example, mounted on the back of the upper swing structure  3  the same as the engine  11 , and as described above, are driven by the engine  11  to supply hydraulic oil to the control valve  17  through a high-pressure hydraulic line. The main pumps  14 L and  14 R are, for example, variable displacement hydraulic pumps, and their discharge flow rates (discharge pressures) are controlled by the regulators  13 L and  13 R adjusting the tilt angles of the swash plates to adjust piston stroke lengths under the control of the controller  30  as described above. 
     The pilot pump  15  is, for example, mounted on the back of the upper swing structure  3  and supplies a pilot pressure to the operating device  26  via a pilot line. The pilot pump  15  is, for example, a fixed displacement hydraulic pump and is driven by the engine  11  as described above. 
     The control valve  17  is a hydraulic control device that is mounted in the center of the upper swing structure  3  and controls a hydraulic drive system according to the operator&#39;s operation on the operating device  26 , for example. As described above, the control valve  17  is connected to the main pump  14  via a high-pressure hydraulic line, and selectively supplies hydraulic oil supplied from the main pump  14  to the hydraulic actuators (the travel hydraulic motors  2 ML and  2 MR, the swing hydraulic motor  2 A, the boom cylinder  7 , the arm cylinder  8 , and the bucket cylinder  9 ) in accordance with the operating state of the operating device  26  or in response to a control command according to the automatic operation function of the shovel  100 . Specifically, the control valve  17  includes the control valves  171  through  174 ,  175 L,  175 R,  176 L and  176 R that control the flow rate and flow direction of hydraulic oil supplied from the main pump  14  to the individual hydraulic actuators. 
     The control valve  171  corresponds to the travel hydraulic motor  2 ML. The control valve  172  corresponds to the travel hydraulic motor  2 MR. The control valve  173  corresponds to the swing hydraulic motor  2 A. The control valve  174  corresponds to the bucket cylinder  9 . The control valves  175 L and  175 R correspond to the boom cylinder  7 . Hereinafter, the control valves  175 L and  175 R may be collectively or individually referred to as “control valve  175 .” The control valves  176 L and  176 R correspond to the arm cylinder  8 . Hereinafter, the control valves  176 L and  176 R may be collectively or individually referred to as “control valve  176 .” 
     The operating device  26  is provided near the operator seat of the cabin  10  and serves as an operation inputting part for the operator operating various operating elements (driven elements such as the lower traveling structure  1 , the upper swing structure  3 , the boom  4 , the arm  5 , and the bucket  6 ). In other words, the operating device  26  is an operation inputting part for the operator operating hydraulic actuators (namely, the travel hydraulic motors  2 ML and  2 MR, the swing hydraulic motor  2 A, the boom cylinder  7 , the arm cylinder  8 , the bucket cylinder  9 , etc.) that drive corresponding operating elements (driven elements). 
     As illustrated in  FIGS. 4A through 4D, 5A, and 5B , the operating device  26  is, for example, of a hydraulic pilot type to output a pilot pressure commensurate with its operating state. The operating device  26  is connected to the control valve  17  via a below-described shuttle valve  32  provided in a hydraulic line on its secondary side. This allows pilot pressures commensurate with the operating states of the lower traveling structure  1 , the upper swing structure  3 , the boom  4 , the arm  5 , the bucket  6 , etc., in the operating device  26  to be input to the control valve  17 . Therefore, the control valve  17  can drive hydraulic actuators in accordance with the operating states in the operating device  26 . 
     The operating device  26  includes a left operating lever  26 L and a right operating lever  26 R for operating the attachment AT, namely, the boom  4  (the boom cylinder  7 ), the arm  5  (the arm cylinder  8 ), the bucket  6  (the bucket cylinder  9 ), and the upper swing structure  3  (the swing hydraulic motor  2 A). Furthermore, the operating device  26  includes travel levers  26 D for operating the lower traveling structure  1 , and the travel levers  26 D include a left travel lever  26 DL for operating the left crawler  1 CL (the travel hydraulic motor  2 ML) and a right travel lever  26 DR for operating the right crawler  1 CR (the travel hydraulic motor  2 MR). 
     The left operating lever  26 L is used to swing the upper swing structure  3  and operate the arm  5 . The left operating lever  26 L is operated in a forward or a backward direction relative to the operator in the cabin  10  (namely, the forward or the backward direction of the upper swing structure  3 ) to output a control pressure commensurate with the amount of lever operation (pilot pressure) to secondary-side pilot lines connected to pilot ports of the control valves  176 L and  176 R, using hydraulic oil discharged from the pilot pump  15 . Furthermore, the left operating lever  26 L is operated in a rightward or a leftward direction relative to the operator in the cabin  10  (namely, the rightward or the leftward direction of the upper swing structure  3 ) to output a control pressure commensurate with the amount of lever operation (pilot pressure) to a secondary-side pilot line connected to a pilot port of the control valve  173 , using hydraulic oil discharged from the pilot pump  15 . 
     The right operating lever  26 R is used to operate the boom  4  and operate the bucket  6 . The right operating lever  26 R is operated in the forward or the backward direction relative to the operator in the cabin  10  to output a control pressure commensurate with the amount of lever operation (pilot pressure) to secondary-side pilot lines connected to pilot ports of the control valves  175 L and  175 R, using hydraulic oil discharged from the pilot pump  15 . Furthermore, the right operating lever  26 R is operated in the rightward or the leftward direction relative to the operator in the cabin  10  to output a control pressure commensurate with the amount of lever operation (pilot pressure) to a secondary-side pilot line connected to the control valve  174 , using hydraulic oil discharged from the pilot pump  15 . 
     As described above, the left travel lever  26 DL is used to operate the left crawler  1 CL, and may be configured to work together with an undepicted left travel pedal. The left travel lever  26 DL is operated in the forward or the backward direction relative to the operator in the cabin  10  to output a control pressure commensurate with the amount of lever operation (pilot pressure) to a secondary-side pilot line connected to the control valve  171 , using hydraulic oil discharged from the pilot pump  15 . 
     As described above, the right travel lever  26 DR is used to operate the right crawler  1 CR, and may be configured to work together with an undepicted right travel pedal. The right travel lever  26 DR is operated in the forward or the backward direction relative to the operator in the cabin  10  to output a control pressure commensurate with the amount of lever operation (pilot pressure) to a secondary-side pilot line connected to the control valve  172 , using hydraulic oil discharged from the pilot pump  15 . 
     Furthermore, as illustrated in  FIG. 6 , the operating device  26  (the left operating lever  26 L, the right operating lever  26 R, the left travel lever  26 DL, and the right travel lever  26 DR) may be of an electric type that outputs an electrical signal instead of a hydraulic pilot type that outputs a pilot pressure. In this case, the control valves  171  through  174 ,  175 L,  175 R,  176 L and  176 R in the control valve  17  may be of an electromagnetic solenoid type that operates with an electrical signal commensurate with the operation details of the operating device  26  output from the operating device  26  or the controller  30 . 
     As illustrated in  FIG. 6 , a pilot circuit according to the example includes a solenoid valve  60  for boom raising operation and a solenoid valve  62  for boom lowering operation. 
     The solenoid valve  60  is configured to be able to control the pressure of hydraulic oil in an oil conduit (pilot line) connecting the pilot pump  15  and the boom-raising-side pilot port of the control valve  17  of a pilot pressure-operated type (specifically, the control valves  175 L and  175 R). 
     The solenoid valve  62  is configured to be able to control the pressure of hydraulic oil in an oil conduit (pilot line) connecting the pilot pump  15  and the boom-lowering-side pilot port of the control valve  17  (the control valves  175 L and  175 R). 
     When the boom  4  (the boom cylinder  7 ) is manually operated, the controller  30  generates a boom raising operation signal (electrical signal) or a boom lowering operation signal (electrical signal) in response to an operation signal (electrical signal) commensurate with the details of a forward or a backward operation output by the right operating lever  26 R (an operation signal generating part  26 Ra). The operation signal (electrical signal) output from the right operating lever  26 R represents the details (for example, the amount of operation and the direction of operation) of the forward or the backward operation. The boom raising operation signal (electrical signal) and the boom lowering operation signal (electrical signal) output by the controller  30  change according to the details (the amount of operation and the direction of operation) of the forward and the backward operation of the right operating lever  26 R. 
     Specifically, when the right operating lever  26 R is operated in a boom raising direction, the controller  30  outputs a boom raising operation signal (electrical signal) commensurate with the amount of operation to the solenoid valve  60 . The solenoid valve  60  operates in response to the boom raising operation signal (electrical signal) to control a pilot pressure acting on the boom-raising-side pilot ports of the control valves  175 L and  175 R, namely, a boom raising operation signal (pressure signal). Likewise, when the right operating lever  26 R is operated in a boom lowering direction, the controller  30  outputs a boom lowering operation signal (electrical signal) commensurate with the amount of operation to the solenoid valve  62 . The solenoid valve  62  operates in response to the boom lowering operation signal (electrical signal) to control a pilot pressure acting on the boom-lowering-side pilot ports of the control valves  175 L and  175 R, namely, a boom lowering operation signal (pressure signal). This enables the control valve  17  to cause the boom cylinder  7  (the boom  4 ) to operate according to the details of the forward and the backward operation of the right operating lever  26 R. 
     When the boom  4  (the boom cylinder  7 ) automatically operates, the controller  30 , for example, generates a boom raising operating signal (electrical signal) or a boom lowering operation signal (electrical signal) according to a correcting operation signal (electrical signal) without depending on the operation signal (electrical signal) output by the operation signal generating part  26 Ra of the right operating lever  26 R. The correcting operation signal may be either an electrical signal generated by the controller  30  or an electrical signal generated by a control device other than the controller  30 , or the like. This enables the control valve  17  to implement the function of automatically operating the boom  4  (the boom cylinder  7 ) according to the correcting operation signal (electrical signal). 
     The arm  5  (the arm cylinder  8 ), the bucket  6  (the bucket cylinder  9 ), the upper swing structure  3  (the swing hydraulic motor  2 A), and the lower traveling structure  1  (the travel hydraulic motors  2 ML and  2 MR), whose operations are based on similar pilot circuits, operate the same as the boom  4  (the boom cylinder  7 ). 
     Thus, the automatic operation function of the shovel  100  can be executed more easily when the operating device  26  of an electric type is adopted than when the operating device  26  of a hydraulic pilot type is adopted. 
     The discharge pressure sensors  28 L and  28 R detect the discharge pressures of the main pumps  14 L and  14 R, respectively. Detection signals corresponding to the discharge pressures detected by the discharge pressure sensors  28 L and  28 R are fed into the controller  30 . 
     The operating pressure sensor  29  detects the secondary-side pilot pressure of the operating device  26 , namely, pilot pressures commensurate with the operating states of operating elements (namely, hydraulic actuators) in the operating device  26 . The detection signals of pilot pressures commensurate with the operating states of the lower traveling structure  1 , the upper swing structure  3 , the boom  4 , the arm  5 , the bucket  6 , etc., in the operating device  26  generated by the operating pressure sensor  29  are fed into the controller  30 . 
     The operating pressure sensor  29 LA detects the details (for example, the direction of operation and the amount of operation) of the operator&#39;s forward or backward operation of the left operating lever  26 L in the form of the pressure of hydraulic oil (hereinafter “operating pressure”) in corresponding secondary-side pilot lines of the left operating lever  26 L. 
     The operating pressure sensor  29 LB detects the details (for example, the direction of operation and the amount of operation) of the operator&#39;s rightward or leftward operation of the left operating lever  26 L in the form of the operating pressure of a corresponding secondary-side pilot line of the left operating lever  26 L. 
     The operating pressure sensor  29 RA detects the details (for example, the direction of operation and the amount of operation) of the operator&#39;s forward or backward operation of the right operating lever  26 R in the form of the operating pressure of corresponding secondary-side pilot lines of the right operating lever  26 R. 
     The operating pressure sensor  29 RB detects the details (for example, the direction of operation and the amount of operation) of the operator&#39;s rightward or leftward operation of the right operating lever  26 R in the form of the operating pressure of a corresponding secondary-side pilot line of the right operating lever  26 R. 
     The operating pressure sensor  29 DL detects the details (for example, the direction of operation and the amount of operation) of the operator&#39;s forward or backward operation of the left travel lever  26 DL in the form of the operating pressure of a corresponding secondary-side pilot line of the left travel lever  26 DL. 
     The operating pressure sensor  29 DR detects the details (for example, the direction of operation and the amount of operation) of the operator&#39;s forward or backward operation of the right travel lever  26 DR in the form of the operating pressure of a corresponding secondary-side pilot line of the right travel lever  26 DR. 
     The operation details of the operating device  26  (the left operating lever  26 L, the right operating lever  26 R, the left travel lever  26 DL, and the right travel lever  26 DR) may also be detected by sensors other than the operating pressure sensor  29  (for example, potentiometers or the like attached to the left operating lever  26 L, the right operating lever  26 R, the left travel lever  26 DL, and the right travel lever  26 DR). Furthermore, when the operating device  26  is of an electric type, the operating pressure sensor  29  is omitted. This is because an electrical signal (operation signal) corresponding to the operating state of the electric operating device  26  is input to the controller  30 , so that the controller  30  can determine the operating state from the operation signal. 
     The controller  30  is, for example, provided in the cabin  10 , and controls the driving of the shovel  100 . The functions of the controller  30  may be implemented by desired hardware, desired software, or their combination. For example, the controller  30  includes circuitry constituted mainly of a microcomputer that includes a CPU (Central Processing Unit), a memory unit such as a RAM (Random Access Memory), a non-volatile secondary storage such as a ROM (Read Only Memory), and various input/output interfaces. The controller  30  implements various functions by executing, on the CPU, various programs stored in the secondary storage, for example. 
     One or more of the functions of the controller  30  may be implemented by another controller (control device). That is, the functions of the controller  30  may be distributed among and implemented by multiple controllers. 
     Here, as illustrated in  FIG. 3 , in the hydraulic system of the shovel  100 , the part of the hydraulic system of a drive system that drives hydraulic actuators circulates hydraulic oil from each of the main pumps  14 L and  14 R driven by the engine  11  to a hydraulic oil tank by way of center bypass oil conduits C 1 L and C 1 R or parallel oil conduits C 2 L and C 2 R. 
     The center bypass oil conduit C 1 L starts at the main pump  14 L and ends at the hydraulic oil tank, passing through the control valves  171 ,  173 ,  175 L and  176 L in this order in the control valve  17 . 
     The center bypass oil conduit C 1 R starts at the main pump  14 R and ends at the hydraulic oil tank, passing through the control valves  172 ,  174 ,  175 R and  176 R in this order in the control valve  17 . 
     The control valve  171  is a spool valve that supplies hydraulic oil discharged from the main pump  14 L to the travel hydraulic motor  2 ML and discharges hydraulic oil discharged by the travel hydraulic motor  2 ML to the hydraulic oil tank. 
     The control valve  172  is a spool valve that supplies hydraulic oil discharged from the main pump  14 R to the travel hydraulic motor  2 MR and discharges hydraulic oil discharged by the travel hydraulic motor  2 MR to the hydraulic oil tank. 
     The control valve  173  is a spool valve that supplies hydraulic oil discharged from the main pump  14 L to the swing hydraulic motor  2 A and discharges hydraulic oil discharged by the swing hydraulic motor  2 A to the hydraulic oil tank. 
     The control valve  174  is a spool valve that supplies hydraulic oil discharged from the main pump  14 R to the bucket cylinder  9  and discharges hydraulic oil in the bucket cylinder  9  to the hydraulic oil tank. 
     The control valves  175 L and  175 R are spool valves that supply hydraulic oil discharged by the main pumps  14 L and  14 R, respectively, to the boom cylinder  7  and discharge hydraulic oil in the boom cylinder  7  to the hydraulic oil tank. 
     The control valves  176 L and  176 R are spool valves that supply hydraulic oil discharged by the main pumps  14 L and  14 R, respectively, to the arm cylinder  8  and discharge hydraulic oil in the arm cylinder  8  to the hydraulic oil tank. 
     Each of the control valves  171  through  174 ,  175 L,  175 R,  176 L and  176 R controls the flow rate of hydraulic oil discharged from or supplied to a hydraulic actuator according to a pilot pressure acting on its pilot port. Furthermore, each of the control valves  171  through  174 ,  175 L,  175 R,  176 L and  176 R switches the direction of flow of hydraulic oil discharged from or supplied to a hydraulic actuator according to on which one of the two pilot ports a pilot pressure is acting. 
     The parallel oil conduit C 2 L supplies hydraulic oil from the main pump  14 L to the control valves  173 ,  175 L and  176 L in parallel with the center bypass oil conduit C 1 L. Specifically, the parallel oil conduit C 2 L is configured to diverge from the center bypass oil conduit C 1 L upstream of the control valve  171  to make it possible to supply hydraulic oil from the main pump  14 L to the control valves  171 ,  173 ,  175 L and  176 L in parallel. This enables the parallel oil conduit C 2 L to supply hydraulic oil to a control valve further downstream when the flow of hydraulic oil through the center bypass oil conduit C 1 L is restricted or blocked by any of the control valves  171 ,  173  and  175 L. 
     The parallel oil conduit C 2 R supplies hydraulic oil from the main pump  14 R to the control valves  174 ,  175 R and  176 R in parallel with the center bypass oil conduit C 1 R. Specifically, the parallel oil conduit C 2 R is configured to diverge from the center bypass oil conduit C 1 R upstream of the control valve  172  to make it possible to supply hydraulic oil from the main pump  14 R to the control valves  172 ,  174 ,  175 R and  176 R in parallel. This enables the parallel oil conduit C 2 L to supply hydraulic oil to a control valve further downstream when the flow of hydraulic oil through the center bypass oil conduit C 1 R is restricted or blocked by any of the control valves  172 ,  174  and  175 R. 
     The regulators  13 L and  13 R control the discharge quantities of the main pumps  14 L and  14 R by adjusting the tilt angles of the swash plates of the main pumps  14 L and  14 R, respectively, under the control of the controller  30 . The discharge pressure sensor  28 L detects the discharge pressure of the main pump  14 L, and a detection signal corresponding to the detected discharge pressure is fed into the controller  30 . The same is true for the discharge pressure sensor  28 R. This enables the controller  30  to control the regulators  13 L and  13 R according to the discharge pressures of the main pump  14 L and  14 R. 
     Negative control throttles (hereinafter “NC throttles”)  18 L and  18 R are provided between the most downstream control valves  176 L and  176 R and the hydraulic oil tank in the center bypass oil conduits C 1 L and C 1 R, respectively. As a result, the flow of hydraulic oil discharged by the main pumps  14 L and  14 R is restricted by the NC throttles  18 L and  18 R. The NC throttles  18 L and  18 R generate control pressures for controlling the regulators  13 L and  13 R (hereinafter “NC pressures”). 
     NC pressure sensors  19 L and  19 R detect the NC pressures of the NC throttles  18 L and  18 R, respectively, and detection signals corresponding to the detected NC pressures are fed into the controller  30 . 
     The controller  30  may control the regulators  13 L and  13 R and control the discharge quantities of the main pumps  14 L and  14 R according to the discharge pressures of the main pumps  14 L and  14 R detected by the discharge pressure sensors  28 L and  28 R. For example, according as the discharge pressure of the main pump  14 L increases, the controller  30  may reduce the discharge quantity by adjusting the swash plate tilt angle of the main pump  14 L by controlling the regulator  13 L. The same is true for the regulator  13 R. This enables the controller  30  to perform full power control on the main pumps  14 L and  14 R such that the absorbed power of the main pumps  14 L and  14 R expressed as the product of discharge pressure and discharge quantity is prevented from exceeding the output power of the engine  11 . 
     Furthermore, the controller  30  may control the discharge quantities of the main pumps  14 L and  14 R by controlling the regulators  13 L and  13 R according to the NC pressures detected by the NC pressure sensors  19 L and  19 R. 
     For example, the controller reduces the discharge quantities of the main pumps  14 L and  14 R as the NC pressures increase and increases the discharge quantities of the main pumps  14 L and  14 R as the NC pressures decrease. Specifically, in a standby state where none of the hydraulic actuators is operated in the shovel  100  (the state illustrated in  FIG. 3 ), hydraulic oil discharged from the main pumps  14 L and  14 R arrive at the NC throttles  18 L and  18 R through the center bypass oil conduits C 1 L and C 1 R. The flow of hydraulic oil discharged from the main pumps  14 L and  14 R increase the NC pressures generated upstream of the NC throttles  18 L and  18 R. As a result, the controller  30  decreases the discharge quantities of the main pumps  14 L and  14 R to a minimum allowable discharge quantity to reduce pressure loss (pumping loss) during the passage of the discharged hydraulic oil through the center bypass oil conduits C 1 L and C 1 R. 
     In contrast, when any of the hydraulic actuators is operated, hydraulic oil discharged from the main pump  14 L or  14 R flows into the operated hydraulic actuator via a control valve corresponding to the operated hydraulic actuator. The flow of hydraulic oil discharged from the main pump  14 L or  14 R that arrives at the NC throttle  18 L or  18 R is reduced in amount or lost, so that the control pressure generated upstream of the NC throttle  18 L or  18 R is reduced. As a result, the controller  30  can increase the discharge quantity of the main pump  14 L or  14 R to circulate sufficient hydraulic oil to the operated hydraulic actuator to ensure driving of the operated hydraulic actuator. 
     Furthermore, as illustrated in  FIGS. 4A through 4D  and  FIGS. 5A and 5B , in the hydraulic system of the shovel  100 , the part of the hydraulic system of an operation system includes the pilot pump  15 , the operating device  26  (the left operating lever  26 L, the right operating lever  26 R, the left travel lever  26 DL, and the right travel lever  26 DR), proportional valves  31 AL,  31 AR,  31 BL,  31 BR,  31 CL,  31 CR,  31 DL,  31 DR,  31 EL,  31 ER,  31 FL and  31 FR, shuttle valves  32 AL,  32 AR,  32 BL,  32 BR,  32 CL,  32 CR,  32 DL,  32 DR,  32 EL,  32 ER,  32 FL and  32 FR, and pressure reducing proportional valves  33 AL,  33 AR,  33 BL,  33 BR,  33 CL,  33 CR,  33 DL,  33 DR,  33 EL,  33 ER,  33 FL and  33 FR. Hereinafter, the proportional valves  31 AL,  31 AR,  31 BL,  31 BR,  31 CL,  31 CR,  31 DL,  31 DR,  31 EL,  31 ER,  31 FL and  31 FR may be collectively or individually referred to as “proportional valve  31 .” Furthermore, the shuttle valves  32 AL,  32 AR,  32 BL,  32 BR,  32 CL,  32 CR,  32 DL,  32 DR,  32 EL,  32 ER,  32 FL and  32 FR may be collectively or individually referred to as “shuttle valve  32 .” Furthermore, the pressure reducing proportional valves  33 AL,  33 AR,  33 BL,  33 BR,  33 CL,  33 CR,  33 DL,  33 DR,  33 EL,  33 ER,  33 FL and  33 FR may be collectively or individually referred to as “pressure reducing proportional valve  33 .” 
     The proportional valve  31  is provided in a pilot line connecting the pilot pump  15  and the shuttle valve  32 , and is configured to be able to change its flow area (a cross-sectional area through which hydraulic oil can pass). The proportional valve  31  operates in response to a control command input from the controller  30 . This enables the controller  30  to supply hydraulic oil discharged from the pilot pump  15  to a pilot port of a corresponding control valve in the control valve  17  via the proportional valve  31  and the shuttle valve  32  even when the operating device  26  (specifically, the left operating lever  26 L, the right operating lever  26 R, the left travel lever  26 DL, or the right travel lever  26 DR) is not operated by the operator. 
     The shuttle valve  32  includes two inlet ports and one outlet port, and outputs hydraulic oil having the higher one of the pilot pressures input to the two inlet ports to the outlet port. Of the two inlet ports of the shuttle valve  32 , one is connected to the operating device  26  via the pressure reducing proportional valve  33 , and the other is connected to the proportional valve  31 . The outlet port of the shuttle valve  32  is connected to a pilot port of a corresponding control valve in the control valve  17  through a pilot line. Therefore, the shuttle valve  32  can cause the higher one of the pilot pressure generated by the pressure reducing proportional valve  33  using a pilot pressure output from the operating device  26  as a source pressure and the pilot pressure generated by the proportional valve  31 , to act on a pilot port of a corresponding control valve. The controller  30 , for example, controls the proportional valve  31  and the pressure reducing proportional valve  33  to cause a pilot pressure higher than a pilot pressure input to the shuttle valve  32  from a secondary-side pilot line of the operating device  26  by way of the pressure reducing proportional valve  33  to be output from the proportional valve  31 . This enables the controller  30  to control the operations of the lower traveling structure  1 , the upper swing structure  3 , and the attachment AT by controlling corresponding control valves independent of the operator&#39;s operation of the operating device  26 . Therefore, the controller  30  can implement the automatic operation function of the shovel  100  using the proportional valve  31  and the pressure reducing proportional valve  33 . 
     The pressure reducing proportional valve  33  is provided in a pilot line connecting the operating device  26  and the shuttle valve  32 , and is configured to be able to change its flow area. The pressure reducing proportional valve  33  operates in response to a control command input from the controller  30 . This enables the controller  30  to force reduction of the pilot pressure output from the operating device  26  when the operating device  26  (specifically, the left operating lever  26 L, the right operating lever  26 R, the left travel lever  26 DL, or the right travel lever  26 DR) is operated by the operator. Therefore, even during the operation of the operating device  26 , the controller  30  can forcibly control or stop the operation of a hydraulic actuator corresponding to the operation of the operating device  26 . Furthermore, for example, even during the operation of the operating device  26 , the controller  30  can reduce the pilot pressure output from the operating device  26  to cause the pilot pressure output from the operating device  26  to be lower than the pilot pressure output from the proportional valve  31 . Therefore, by controlling the proportional valve  31  and the pressure reducing proportional valve  33 , the controller  30  can ensure that a desire pilot pressure acts on a pilot port of a control valve in the control valve  17  irrespective of the operation details of the operating device  26 . 
     As illustrated in  FIG. 4A , the left operating lever  26 L is used to operate the arm cylinder  8  corresponding to the arm  5  in a manner in which the left operating lever  26 L is tilted forward or backward by the operator. That is, when the left operating lever  26 L is tilted forward or backward, the target of operation of the left operating lever  26 L is the operation of the arm  5 . The left operating lever  26 L outputs a pilot pressure commensurate with the details of the forward or the backward operation to the secondary side, using hydraulic oil discharged from the pilot pump  15 . 
     The shuttle valve  32 AL has two inlet ports, one connected to a secondary-side pilot line of the left operating lever  26 L corresponding to an operation in a direction to close the arm  5  (hereinafter “arm closing operation”) and the other connected to the secondary-side pilot line of the proportional valve  31 AL, and has an outlet port connected to the right pilot port of the control valve  176 L and the left pilot port of the control valve  176 R. 
     The shuttle valve  32 AR has two inlet ports, one connected to a secondary-side pilot line of the left operating lever  26 L corresponding to an operation in a direction to open the arm  5  (hereinafter “arm opening operation”) and the other connected to the secondary-side pilot line of the proportional valve  31 AR, and has an outlet port connected to the left pilot port of the control valve  176 L and the right pilot port of the control valve  176 R. 
     That is, the left operating lever  26 L causes a pilot pressure commensurate with the details of the forward or the backward operation to act on pilot ports of the control valves  176 L and  176 R through the shuttle valve  32 AL or  32 AR. Specifically, in response to the arm closing operation, the left operating lever  26 L outputs a pilot pressure commensurate with the amount of operation to one inlet port of the shuttle valve  32 AL and causes the pilot pressure to act on the right pilot port of the control valve  176 L and the left pilot port of the control valve  176 R via the shuttle valve  32 AL. Furthermore, in response to the atm opening operation, the left operating lever  26 L outputs a pilot pressure commensurate with the amount of operation to one inlet port of the shuttle valve  32 AR and causes the pilot pressure to act on the left pilot port of the control valve  176 L and the right pilot port of the control valve  176 R via the shuttle valve  32 AR. 
     The proportional valve  31 AL operates in response to a control current input from the controller  30 . Specifically, the proportional valve  31 AL outputs a pilot pressure commensurate with a control current input from the controller  30  to the other inlet port of the shuttle valve  32 AL, using hydraulic oil discharged from the pilot pump  15 . This enables the proportional valve  31 AL to control a pilot pressure acting on the right pilot port of the control valve  176 L and the left pilot port of the control valve  176 R via the shuttle valve  32 AL. 
     The proportional valve  31 AR operates in response to a control current input from the controller  30 . Specifically, the proportional valve  31 AR outputs a pilot pressure commensurate with a control current input from the controller  30  to the other inlet port of the shuttle valve  32 AR, using hydraulic oil discharged from the pilot pump  15 . This enables the proportional valve  31 AR to control a pilot pressure acting on the left pilot port of the control valve  176 L and the right pilot port of the control valve  176 R via the shuttle valve  32 AR. 
     That is, the proportional valves  31 AL and  31 AR can control a pilot pressure output to the secondary side such that the control valves  176 L and  176 R can stop at a desired valve position independent of the forward or the backward operating state of the left operating lever  26 L. Hereinafter, the proportional valves  31 AL and  31 AR may be collectively or individually referred to as “arm proportional valve  31 A.” 
     The pressure reducing proportional valve  33 AL operates in response to a control current input from the controller  30 . Specifically, when no control current is input from the controller  30 , the pressure reducing proportional valve  33 AL outputs a pilot pressure commensurate with the arm closing operation of the left operating lever  26 L directly to the secondary side. In contrast, when a control current is input from the controller  30 , the pressure reducing proportional valve  33 AL reduces the pilot pressure of a secondary-side pilot line corresponding to the arm closing operation of the left operating lever  26 L to an extent corresponding to the control current, and outputs the reduced pilot pressure to the one inlet port of the shuttle valve  32 AL. This enables the pressure reducing proportional valve  33 AL to forcibly control or stop the operation of the arm cylinder  8  corresponding to the arm closing operation on an as-needed basis even during the arm closing operation of the left operating lever  26 L. Furthermore, the pressure reducing proportional valve  33 AL can cause the pilot pressure acting on the one inlet port of the shuttle valve  32 AL to be lower than the pilot pressure acting on the other inlet port of the shuttle valve  32 AL from the proportional valve  31 AL even during the arm closing operation of the left operating lever  26 L. Therefore, the controller  30  can ensure that a desire pilot pressure acts on the am-closing-side pilot ports of the control valves  176 L and  176 R by controlling the proportional valve  31 AL and the pressure reducing proportional valve  33 AL. 
     The pressure reducing proportional valve  33 AR operates in response to a control current input from the controller  30 . Specifically, when no control current is input from the controller  30 , the pressure reducing proportional valve  33 AR outputs a pilot pressure commensurate with the arm opening operation of the left operating lever  26 L directly to the secondary side. In contrast, when a control current is input from the controller  30 , the pressure reducing proportional valve  33 AR reduces the pilot pressure of a secondary-side pilot line corresponding to the arm opening operation of the left operating lever  26 L to an extent corresponding to the control current, and outputs the reduced pilot pressure to the one inlet port of the shuttle valve  32 AR. This enables the pressure reducing proportional valve  33 AR to forcibly control or stop the operation of the arm cylinder  8  corresponding to the arm opening operation on an as-needed basis even during the arm opening operation of the left operating lever  26 L. Furthermore, the pressure reducing proportional valve  33 AR can cause the pilot pressure acting on the one inlet port of the shuttle valve  32 AR to be lower than the pilot pressure acting on the other inlet port of the shuttle valve  32 AR from the proportional valve  31 AR even during the arm opening operation of the left operating lever  26 L. Therefore, the controller  30  can ensure that a desire pilot pressure acts on the arm-opening-side pilot ports of the control valves  176 L and  176 R by controlling the proportional valve  31 AR and the pressure reducing proportional valve  33 AR. 
     Thus, the pressure reducing proportional valves  33 AL and  33 AR can forcibly control or stop the operations of the arm cylinder  8  corresponding to the forward and the backward operating state of the left operating lever  26 L. Furthermore, the pressure reducing proportional valves  33 AL and  33 AR can assist in ensuring that the pilot pressures of the proportional valves  31 AL and  31 AR act on the pilot ports of the control valves  176 L and  176 R through the shuttle valves  32 AL and  32 AR by reducing pilot pressures acting on the one inlet ports of the shuttle valves  32 AL and  32 AR. 
     The controller  30  may forcibly control or stop the operation of the arm cylinder  8  corresponding to the arm closing operation of the left operating lever  26 L by controlling the proportional valve  31 AR instead of controlling the pressure reducing proportional valve  33 AL. For example, in the case of performing the arm closing operation with the left operating lever  26 L, the controller  30  may control the proportional valve  31 AR to act on the arm-opening-side pilot ports of the control valves  176 L and  176 R from the proportional valve  31 AR via the shuttle valve  32 AR. This causes a pilot pressure to act on the arm-opening-side pilot ports of the control valves  176 L and  176 R against a pilot pressure acting on the arm-closing-side pilot ports of the control valves  176 L and  176 R from the left operating lever  26 L via the shuttle valve  32 AL. Therefore, the controller  30  can forcibly move the control valves  176 L and  176 R toward a neutral position to forcibly control or stop the operation of the arm cylinder  8  corresponding to the arm closing operation of the left operating lever  26 L. Likewise, the controller  30  may forcibly control or stop the operation of the arm cylinder  8  corresponding to the arm opening operation of the left operating lever  26 L by controlling the proportional valve  31 AL instead of controlling the pressure reducing proportional valve  33 AR. 
     The operating pressure sensor  29 LA detects the details of the operator&#39;s forward or the backward operation of the left operating lever  26 L in the form of pressure (operating pressure), and a detection signal corresponding to the detected pressure is fed into the controller  30 . This enables the controller  30  to determine the details of the forward or the backward operation of the left operating lever  26 L. Examples of the details of the forward and the backward operation of the left operating lever  26 L to be detected may include the direction of operation and the amount of operation (the angle of operation). Hereinafter, the same applies to the rightward and the leftward operation of the left operating lever  26 L and the forward and the backward operation and the rightward and the leftward operation of the right operating lever  26 R. 
     The controller  30  can cause hydraulic oil discharged from the pilot pump  15  to be supplied to the right pilot port of the control valve  176 L and the left pilot port of the control valve  176 R via the proportional valve  31 AL and the shuttle valve  32 AL, independent of the operator&#39;s arm closing operation on the left operating lever  26 L. Furthermore, the controller  30  can cause hydraulic oil discharged from the pilot pump  15  to be supplied to the left pilot port of the control valve  176 L and the right pilot port of the control valve  176 R via the proportional valve  31 AR and the shuttle valve  32 AR, independent of the operator&#39;s arm opening operation on the left operating lever  26 L. That is, the controller  30  can automatically control the opening and closing operation of the arm  5 . 
     Furthermore, for example, as illustrated in  FIG. 4B , the right operating lever  26 R is used to operate the boom cylinder  7  corresponding to the boom  4  in a manner in which the right operating lever  26 R is tilted forward or backward by the operator. That is, when the right operating lever  26 R is tilted forward or backward, the target of operation of the right operating lever  26 R is the operation of the boom  4 . The right operating lever  26 R outputs a pilot pressure commensurate with the details of the forward or the backward operation to the secondary side, using hydraulic oil discharged from the pilot pump  15 . 
     The shuttle valve  32 BL has two inlet ports, one connected to a secondary-side pilot line of the right operating lever  26 R corresponding to an operation in a direction to raise the boom  4  (hereinafter “boom raising operation”) and the other connected to the secondary-side pilot line of the proportional valve  31 BL, and has an outlet port connected to the right pilot port of the control valve  175 L and the left pilot port of the control valve  175 R. 
     The shuttle valve  32 BR has two inlet ports, one connected to a secondary-side pilot line of the right operating lever  26 R corresponding to an operation in a direction to lower the boom  4  (hereinafter “boom lowering operation”) and the other connected to the secondary-side pilot line of the proportional valve  31 BR, and has an outlet port connected to the right pilot port of the control valve  175 R. 
     That is, the right operating lever  26 R causes a pilot pressure commensurate with the details of the forward or the backward operation to act on pilot ports of the control valves  175 L and  175 R through the shuttle valve  32 BL or  32 BR. Specifically, in response to the boom raising operation, the right operating lever  26 R outputs a pilot pressure commensurate with the amount of operation to one inlet port of the shuttle valve  32 BL and causes the pilot pressure to act on the right pilot port of the control valve  175 L and the left pilot port of the control valve  175 R via the shuttle valve  32 BL. Furthermore, in response to the boom lowering operation, the right operating lever  26 R outputs a pilot pressure commensurate with the amount of operation to one inlet port of the shuttle valve  32 BR and causes the pilot pressure to act on the right pilot port of the control valve  175 R via the shuttle valve  32 BR. 
     The proportional valve  31 BL operates in response to a control current input from the controller  30 . Specifically, the proportional valve  31 BL outputs a pilot pressure commensurate with a control current input from the controller  30  to the other inlet port of the shuttle valve  32 BL, using hydraulic oil discharged from the pilot pump  15 . This enables the proportional valve  31 BL to control a pilot pressure acting on the right pilot port of the control valve  175 L and the left pilot port of the control valve  175 R via the shuttle valve  32 BL. 
     The proportional valve  31 BR operates in response to a control current input from the controller  30 . Specifically, the proportional valve  31 BR outputs a pilot pressure commensurate with a control current input from the controller  30  to the other pilot port of the shuttle valve  32 BR, using hydraulic oil discharged from the pilot pump  15 . This enables the proportional valve  31 BR to control a pilot pressure acting on the right pilot port of the control valve  175 R via the shuttle valve  32 BR. 
     That is, the proportional valves  31 BL and  31 BR can control a pilot pressure output to the secondary side such that the control valves  175 L and  175 R can stop at a desired valve position independent of the forward or the backward operating state of the right operating lever  26 R. Hereinafter, the proportional valves  31 BL and  31 BR may be collectively or individually referred to as “boom proportional valve  31 B.” 
     The pressure reducing proportional valve  33 BL operates in response to a control current input from the controller  30 . Specifically, when no control current is input from the controller  30 , the pressure reducing proportional valve  33 BL outputs a pilot pressure commensurate with the boom raising operation of the right operating lever  26 R directly to the secondary side. In contrast, when a control current is input from the controller  30 , the pressure reducing proportional valve  33 BL reduces the pilot pressure of a secondary-side pilot line corresponding to the boom raising operation of the right operating lever  26 R to an extent corresponding to the control current, and outputs the reduced pilot pressure to the one inlet port of the shuttle valve  32 BL. This enables the pressure reducing proportional valve  33 BL to forcibly control or stop the operation of the boom cylinder  7  corresponding to the boom raising operation on an as-needed basis even during the boom raising operation of the right operating lever  26 R. Furthermore, the pressure reducing proportional valve  33 BL can cause the pilot pressure acting on the one inlet port of the shuttle valve  32 BL to be lower than the pilot pressure acting on the other inlet port of the shuttle valve  32 BL from the proportional valve  31 BL even during the boom raising operation of the right operating lever  26 R. Therefore, the controller  30  can ensure that a desire pilot pressure acts on the boom-raising-side pilot ports of the control valves  175 L and  175 R by controlling the proportional valve  31 BL and the pressure reducing proportional valve  33 BL. 
     The pressure reducing proportional valve  33 BR operates in response to a control current input from the controller  30 . Specifically, when no control current is input from the controller  30 , the pressure reducing proportional valve  33 BR outputs a pilot pressure commensurate with the boom lowering operation of the right operating lever  26 R directly to the secondary side. In contrast, when a control current is input from the controller  30 , the pressure reducing proportional valve  33 BR reduces the pilot pressure of a secondary-side pilot line corresponding to the boom lowering operation of the right operating lever  26 R to an extent corresponding to the control current, and outputs the reduced pilot pressure to the one inlet port of the shuttle valve  32 BR. This enables the pressure reducing proportional valve  33 BR to forcibly control or stop the operation of the boom cylinder  7  corresponding to the boom lowering operation on an as-needed basis even during the boom lowering operation of the right operating lever  26 R. Furthermore, the pressure reducing proportional valve  33 BR can cause the pilot pressure acting on the one inlet port of the shuttle valve  32 BR to be lower than the pilot pressure acting on the other inlet port of the shuttle valve  32 BR from the proportional valve  31 BR even during the boom lowering operation of the right operating lever  26 R. Therefore, the controller  30  can ensure that a desire pilot pressure acts on the boom-lowering-side pilot ports of the control valves  175 L and  175 R by controlling the proportional valve  31 BR and the pressure reducing proportional valve  33 BR. 
     Thus, the pressure reducing proportional valves  33 BL and  33 BR can forcibly control or stop the operations of the boom cylinder  7  corresponding to the forward and the backward operating state of the right operating lever  26 R. Furthermore, the pressure reducing proportional valves  33 BL and  33 BR can assist in ensuring that the pilot pressures of the proportional valves  31 BL and  31 BR act on the pilot ports of the control valves  175 L and  175 R through the shuttle valves  32 BL and  32 BR by reducing pilot pressures acting on the one inlet ports of the shuttle valves  32 BL and  32 BR. 
     The controller  30  may forcibly control or stop the operation of the boom cylinder  7  corresponding to the boom raising operation of the right operating lever  26 R by controlling the proportional valve  31 BR instead of controlling the pressure reducing proportional valve  33 BL. For example, in the case of performing the boom raising operation with the right operating lever  26 R, the controller  30  may control the proportional valve  31 BR to act on the boom-lowering-side pilot ports of the control valves  175 L and  175 R from the proportional valve  31 BR via the shuttle valve  32 BR. This causes a pilot pressure to act on the boom-lowering-side pilot ports of the control valves  175 L and  175 R against a pilot pressure acting on the boom-raising-side pilot ports of the control valves  175 L and  175 R from the right operating lever  26 R via the shuttle valve  32 BL. Therefore, the controller  30  can forcibly move the control valves  175 L and  175 R toward a neutral position to forcibly control or stop the operation of the boom cylinder  7  corresponding to the boom raising operation of the right operating lever  26 R. Likewise, the controller  30  may forcibly control or stop the operation of the boom cylinder  7  corresponding to the boom lowering operation of the right operating lever  26 R by controlling the proportional valve  31 BL instead of controlling the pressure reducing proportional valve  33 BR. 
     The operating pressure sensor  29 RA detects the details of the operator&#39;s forward or the backward operation of the right operating lever  26 R in the form of pressure (operating pressure), and a detection signal corresponding to the detected pressure is fed into the controller  30 . This enables the controller  30  to determine the details of the forward or the backward operation of the right operating lever  26 R. 
     The controller  30  can cause hydraulic oil discharged from the pilot pump  15  to be supplied to the right pilot port of the control valve  175 L and the left pilot port of the control valve  175 R via the proportional valve  31 BL and the shuttle valve  32 BL, independent of the operator&#39;s boom raising operation on the right operating lever  26 R. Furthermore, the controller  30  can cause hydraulic oil discharged from the pilot pump  15  to be supplied to the right pilot port of the control valve  175 R via the proportional valve  31 BR and the shuttle valve  32 BR, independent of the operator&#39;s boom lowering operation on the right operating lever  26 R. That is, the controller  30  can automatically control the raising and lowering operation of the boom  4 . 
     As illustrated in  FIG. 4C , the right operating lever  26 R is used to operate the bucket cylinder  9  corresponding to the bucket  6  in a manner in which the right operating lever  26 R is tilted rightward or leftward by the operator. That is, when the right operating lever  26 R is tilted rightward or leftward, the target of operation of the right operating lever  26 R is the operation of the bucket  6 . The right operating lever  26 R outputs a pilot pressure commensurate with the details of the rightward or the leftward operation to the secondary side, using hydraulic oil discharged from the pilot pump  15 . 
     The shuttle valve  32 CL has two inlet ports, one connected to a secondary-side pilot line of the right operating lever  26 R corresponding to an operation in a direction to close the bucket  6  (hereinafter “bucket closing operation”) and the other connected to the secondary-side pilot line of the proportional valve  31 CL, and has an outlet port connected to the left pilot port of the control valve  174 . 
     The shuttle valve  32 CR has two inlet ports, one connected to a secondary-side pilot line of the right operating lever  26 R corresponding to an operation in a direction to open the bucket (hereinafter “bucket opening operation”) and the other connected to the secondary-side pilot line of the proportional valve  31 CR, and has an outlet port connected to the right pilot port of the control valve  174 . 
     That is, the right operating lever  26 R causes a pilot pressure commensurate with the details of the rightward or the leftward operation to act on a pilot port of the control valve  174  through the shuttle valve  32 CL or  32 CR. Specifically, in response to the bucket closing operation, the right operating lever  26 R outputs a pilot pressure commensurate with the amount of operation to one inlet port of the shuttle valve  32 CL and causes the pilot pressure to act on the left pilot port of the control valve  174  via the shuttle valve  32 CL. Furthermore, in response to the bucket opening operation, the right operating lever  26 R outputs a pilot pressure commensurate with the amount of operation to one inlet port of the shuttle valve  32 CR and causes the pilot pressure to act on the right pilot port of the control valve  174  via the shuttle valve  32 CR. The proportional valve  31 CL operates in response to a control current input from the controller  30 . Specifically, the proportional valve  31 CL outputs a pilot pressure commensurate with a control current input from the controller  30  to the other inlet port of the shuttle valve  32 CL, using hydraulic oil discharged from the pilot pump  15 . This enables the proportional valve  31 CL to control a pilot pressure acting on the left pilot port of the control valve  174  via the shuttle valve  32 CL. 
     The proportional valve  31 CR operates in response to a control current input from the controller  30 . Specifically, the proportional valve  31 CR outputs a pilot pressure commensurate with a control current input from the controller  30  to the other pilot port of the shuttle valve  32 CR, using hydraulic oil discharged from the pilot pump  15 . This enables the proportional valve  31 CR to control a pilot pressure acting on the right pilot port of the control valve  174  via the shuttle valve  32 CR. 
     That is, the proportional valves  31 CL and  31 CR can control a pilot pressure output to the secondary side such that the control valve  174  can stop at a desired valve position independent of the rightward or the leftward operating state of the right operating lever  26 R. Hereinafter, the proportional valves  31 CL and  31 CR may be collectively or individually referred to as “bucket proportional valve  31 C.” 
     The pressure reducing proportional valve  33 CL operates in response to a control current input from the controller  30 . Specifically, when no control current is input from the controller  30 , the pressure reducing proportional valve  33 CL outputs a pilot pressure commensurate with the bucket closing operation of the right operating lever  26 R directly to the secondary side. In contrast, when a control current is input from the controller  30 , the pressure reducing proportional valve  33 CL reduces the pilot pressure of a secondary-side pilot line corresponding to the bucket closing operation of the right operating lever  26 R to an extent corresponding to the control current, and outputs the reduced pilot pressure to the one inlet port of the shuttle valve  32 CL. This enables the pressure reducing proportional valve  33 CL to forcibly control or stop the operation of the bucket cylinder  9  corresponding to the bucket closing operation on an as-needed basis even during the bucket closing operation of the right operating lever  26 R. Furthermore, the pressure reducing proportional valve  33 CL can cause the pilot pressure acting on the one inlet port of the shuttle valve  32 CL to be lower than the pilot pressure acting on the other inlet port of the shuttle valve  32 CL from the proportional valve  31 CL even during the bucket closing operation of the right operating lever  26 R. Therefore, the controller  30  can ensure that a desire pilot pressure acts on the bucket-closing-side pilot port of the control valve  174  by controlling the proportional valve  31 CL and the pressure reducing proportional valve  33 CL. 
     The pressure reducing proportional valve  33 CR operates in response to a control current input from the controller  30 . Specifically, when no control current is input from the controller  30 , the pressure reducing proportional valve  33 CR outputs a pilot pressure commensurate with the bucket opening operation of the right operating lever  26 R directly to the secondary side. In contrast, when a control current is input from the controller  30 , the pressure reducing proportional valve  33 CR reduces the pilot pressure of a secondary-side pilot line corresponding to the bucket opening operation of the right operating lever  26 R to an extent corresponding to the control current, and outputs the reduced pilot pressure to the one inlet port of the shuttle valve  32 CR. This enables the pressure reducing proportional valve  33 CR to forcibly control or stop the operation of the bucket cylinder  9  corresponding to the bucket opening operation on an as-needed basis even during the bucket opening operation of the right operating lever  26 R. Furthermore, the pressure reducing proportional valve  33 CR can cause the pilot pressure acting on the one inlet port of the shuttle valve  32 CR to be lower than the pilot pressure acting on the other inlet port of the shuttle valve  32 CR from the proportional valve  31 CR even during the bucket opening operation of the right operating lever  26 R. Therefore, the controller  30  can ensure that a desire pilot pressure acts on the bucket-opening-side pilot port of the control valve  174  by controlling the proportional valve  31 CR and the pressure reducing proportional valve  33 CR. 
     Thus, the pressure reducing proportional valves  33 CL and  33 CR can forcibly control or stop the operations of the bucket cylinder  9  corresponding to the rightward and the leftward operating state of the right operating lever  26 R. Furthermore, the pressure reducing proportional valves  33 CL and  33 CR can assist in ensuring that the pilot pressures of the proportional valves  31 CL and  31 CR act on the pilot ports of the control valve  174  through the shuttle valves  32 CL and  32 CR by reducing pilot pressures acting on the one inlet ports of the shuttle valves  32 CL and  32 CR. 
     The controller  30  may forcibly control or stop the operation of the bucket cylinder  9  corresponding to the bucket closing operation of the right operating lever  26 R by controlling the proportional valve  31 CR instead of controlling the pressure reducing proportional valve  33 CL. For example, in the case of performing the bucket closing operation with the right operating lever  26 R, the controller  30  may control the proportional valve  31 CR to act on the bucket-opening-side pilot port of the control valve  174  from the proportional valve  31 CR via the shuttle valve  32 CR. This causes a pilot pressure to act on the bucket-opening-side pilot port of the control valve  174  against a pilot pressure acting on the bucket-closing-side pilot port of the control valve  174  from the right operating lever  26 R via the shuttle valve  32 CL. Therefore, the controller  30  can forcibly move the control valve  174  toward a neutral position to forcibly control or stop the operation of the bucket cylinder  9  corresponding to the bucket closing operation of the right operating lever  26 R. Likewise, the controller  30  may forcibly control or stop the operation of the bucket cylinder  9  corresponding to the bucket opening operation of the right operating lever  26 R by controlling the proportional valve  31 CL instead of controlling the pressure reducing proportional valve  33 CR. The operating pressure sensor  29 RB detects the details of the operator&#39;s rightward or the leftward operation of the right operating lever  26 R in the form of pressure (operating pressure), and a detection signal corresponding to the detected pressure is fed into the controller  30 . This enables the controller  30  to determine the details of the rightward or the leftward operation of the right operating lever  26 R. 
     The controller  30  can cause hydraulic oil discharged from the pilot pump  15  to be supplied to the left pilot port of the control valve  174  via the proportional valve  31 CL and the shuttle valve  32 CL, independent of the operator&#39;s bucket closing operation on the right operating lever  26 R. Furthermore, the controller  30  can cause hydraulic oil discharged from the pilot pump  15  to be supplied to the right pilot port of the control valve  174  via the proportional valve  31 CR and the shuttle valve  32 CR, independent of the operator&#39;s bucket opening operation on the right operating lever  26 R. That is, the controller  30  can automatically control the opening and closing operation of the bucket  6 . 
     Furthermore, for example, as illustrated in  FIG. 4D , the left operating lever  26 L is used to operate the swing hydraulic motor  2 A corresponding to the upper swing structure  3  (the swing mechanism  2 ) in a manner in which the left operating lever  26 L is tilted rightward or leftward by the operator. That is, when the left operating lever  26 L is tilted rightward or leftward, the target of operation of the left operating lever  26 L is the operation of the upper swing structure  3 . The left operating lever  26 L outputs a pilot pressure commensurate with the details of the rightward or the leftward operation to the secondary side, using hydraulic oil discharged from the pilot pump  15 . 
     The shuttle valve  32 DL has two inlet ports, one connected to a secondary-side pilot line of the left operating lever  26 L corresponding to an operation to swing the Upper swing structure  3  counterclockwise (hereinafter “counterclockwise swing operation”) and the other connected to the secondary-side pilot line of the proportional valve  31 DL, and has an outlet port connected to the left pilot port of the control valve  173 . 
     The shuttle valve  32 DR has two inlet ports, one connected to a secondary-side pilot line of the left operating lever  26 L corresponding to an operation to swing the upper swing structure  3  clockwise (hereinafter “clockwise swing operation”) and the other connected to the secondary-side pilot line of the proportional valve  31 DR, and has an outlet port connected to the right pilot port of the control valve  173 . 
     That is, the left operating lever  26 L causes a pilot pressure commensurate with the details of the clockwise or the counterclockwise swing operation to act on a pilot port of the control valve  173  through the shuttle valve  32 DL or  32 DR. Specifically, in response to the counterclockwise swing operation, the left operating lever  26 L outputs a pilot pressure commensurate with the amount of operation to one inlet port of the shuttle valve  32 DL and causes the pilot pressure to act on the left pilot port of the control valve  173  via the shuttle valve  32 DL. Furthermore, in response to the clockwise swing operation, the left operating lever  26 L outputs a pilot pressure commensurate with the amount of operation to one inlet port of the shuttle valve  32 DR and causes the pilot pressure to act on the right pilot port of the control valve  173  via the shuttle valve  32 DR. 
     The proportional valve  31 DL operates in response to a control current input from the controller  30 . Specifically, the proportional valve  31 DL outputs a pilot pressure commensurate with a control current input from the controller  30  to the other pilot port of the shuttle valve  32 DL, using hydraulic oil discharged from the pilot pump  15 . This enables the proportional valve  31 DL to control a pilot pressure acting on the left pilot port of the control valve  173  via the shuttle valve  32 DL. 
     The proportional valve  31 DR operates in response to a control current input from the controller  30 . Specifically, the proportional valve  31 DR outputs a pilot pressure commensurate with a control current input from the controller  30  to the other pilot port of the shuttle valve  32 DR, using hydraulic oil discharged from the pilot pump  15 . This enables the proportional valve  31 DR to control a pilot pressure acting on the right pilot port of the control valve  173  via the shuttle valve  32 DR. 
     That is, the proportional valves  31 DL and  31 DR can control a pilot pressure output to the secondary side such that the control valve  173  can stop at a desired valve position independent of the rightward or the leftward operating state of the left operating lever  26 L. Hereinafter, the proportional valves  31 DL and  31 DR may be collectively or individually referred to as “swing proportional valve  31 D.” 
     The pressure reducing proportional valve  33 DL operates in response to a control current input from the controller  30 . Specifically, when no control current is input from the controller  30 , the pressure reducing proportional valve  33 DL outputs a pilot pressure commensurate with the counterclockwise swing operation of the left operating lever  26 L directly to the secondary side. In contrast, when a control current is input from the controller  30 , the pressure reducing proportional valve  33 DL reduces the pilot pressure of a secondary-side pilot line corresponding to the counterclockwise swing operation of the left operating lever  26 L to an extent corresponding to the control current, and outputs the reduced pilot pressure to the one inlet port of the shuttle valve  32 DL. This enables the pressure reducing proportional valve  33 DL to forcibly control or stop the operation of the swing hydraulic motor  2 A corresponding to the counterclockwise swing operation on an as-needed basis even during the counterclockwise swing operation of the left operating lever  26 L. Furthermore, the pressure reducing proportional valve  33 DL can cause the pilot pressure acting on the one inlet port of the shuttle valve  32 DL to be lower than the pilot pressure acting on the other inlet port of the shuttle valve  32 DL from the proportional valve  31 DL even during the counterclockwise swing operation of the left operating lever  26 L. Therefore, the controller  30  can ensure that a desire pilot pressure acts on the counterclockwise-swing-side pilot port of the control valve  173  by controlling the proportional valve  31 DL and the pressure reducing proportional valve  33 DL. 
     The pressure reducing proportional valve  33 DR operates in response to a control current input from the controller  30 . Specifically, when no control current is input from the controller  30 , the pressure reducing proportional valve  33 DR outputs a pilot pressure commensurate with the clockwise swing operation of the left operating lever  26 L directly to the secondary side. In contrast, when a control current is input from the controller  30 , the pressure reducing proportional valve  33 DR reduces the pilot pressure of a secondary-side pilot line corresponding to the clockwise swing operation of the left operating lever  26 L to an extent corresponding to the control current, and outputs the reduced pilot pressure to the one inlet port of the shuttle valve  32 DR. This enables the pressure reducing proportional valve  33 DR to forcibly control or stop the operation of the swing hydraulic motor  2 A corresponding to the clockwise swing operation on an as-needed basis even during the clockwise swing operation of the left operating lever  26 L. Furthermore, the pressure reducing proportional valve  33 DR can cause the pilot pressure acting on the one inlet port of the shuttle valve  32 DR to be lower than the pilot pressure acting on the other inlet port of the shuttle valve  32 DR from the proportional valve  31 DR even during the clockwise swing operation of the left operating lever  26 L. Therefore, the controller  30  can ensure that a desire pilot pressure acts on the clockwise-swing-side pilot port of the control valve  173  by controlling the proportional valve  31 DR and the pressure reducing proportional valve  33 DR. 
     Thus, the pressure reducing proportional valves  33 DL and  33 DR can forcibly control or stop the operations of the swing hydraulic motor  2 A corresponding to the rightward and the leftward operating state of the left operating lever  26 L. Furthermore, the pressure reducing proportional valves  33 DL and  33 DR can assist in ensuring that the pilot pressures of the proportional valves  31 DL and  31 DR act on the pilot ports of the control valve  173  through the shuttle valves  32 DL and  32 DR by reducing pilot pressures acting on the one inlet ports of the shuttle valves  32 DL and  32 DR. 
     The controller  30  may forcibly control or stop the operation of the swing hydraulic motor  2 A corresponding to the counterclockwise swing operation of the left operating lever  26 L by controlling the proportional valve  31 DR instead of controlling the pressure reducing proportional valve  33 DL. For example, in the case of performing the counterclockwise swing operation with the left operating lever  26 L, the controller  30  may control the proportional valve  31 DR to act on the clockwise-swing-side pilot port of the control valve  173  from the proportional valve  31 DR via the shuttle valve  32 DR. This causes a pilot pressure to act on the clockwise-swing-side pilot port of the control valve  173  against a pilot pressure acting on the counterclockwise-swing-side pilot port of the control valve  173  from the left operating lever  26 L via the shuttle valve  32 DL. Therefore, the controller  30  can forcibly move the control valve  173  toward a neutral position to forcibly control or stop the operation of the swing hydraulic motor  2 A corresponding to the counterclockwise swing operation of the left operating lever  26 L. Likewise, the controller  30  may forcibly control or stop the operation of the swing hydraulic motor  2 A corresponding to the clockwise swing operation of the left operating lever  26 L by controlling the proportional valve  31 DL instead of controlling the pressure reducing proportional valve  33 DR. 
     The operating pressure sensor  29 LB detects the state of the operator&#39;s operation of the left operating lever  26 L in the form of pressure, and a detection signal corresponding to the detected pressure is fed into the controller  30 . This enables the controller  30  to determine the details of the rightward or the leftward operation of the left operating lever  26 L. 
     The controller  30  can cause hydraulic oil discharged from the pilot pump  15  to be supplied to the left pilot port of the control valve  173  via the proportional valve  31 DL and the shuttle valve  32 DL, independent of the operator&#39;s counterclockwise swing operation on the left operating lever  26 L. Furthermore, the controller  30  can cause hydraulic oil discharged from the pilot pump  15  to be supplied to the right pilot port of the control valve  173  via the proportional valve  31 DR and the shuttle valve  32 DR, independent of the operator&#39;s clockwise swing operation on the left operating lever  26 L. That is, the controller  30  can automatically control the clockwise and counterclockwise operation of the upper swing structure  3 . 
     Furthermore, for example, as illustrated in  FIG. 5A , the left travel lever  26 DL is used to operate the travel hydraulic motor  2 ML corresponding to the left crawler  1 CL. That is, the target of operation of the left travel lever  26 DL is the travel operation of the left crawler  1 CL. The left travel lever  26 DL outputs a pilot pressure commensurate with the details of the forward or the backward operation to the secondary side, using hydraulic oil discharged from the pilot pump  15 . 
     The shuttle valve  32 EL has two inlet ports, one connected to a secondary-side pilot line of the left travel lever  26 DL corresponding to an operation in a forward direction corresponding to the forward travel direction of the left crawler  1 CL (hereinafter “forward travel operation”) and the other connected to the secondary-side pilot line of the proportional valve  31 EL, and has an outlet port connected to the left pilot port of the control valve  171 . 
     The shuttle valve  32 ER has two inlet ports, one connected to a secondary-side pilot line of the left travel lever  26 DL corresponding to an operation in a backward direction corresponding to the backward travel direction of the left crawler  1 CL (hereinafter “backward travel operation”) and the other connected to the secondary-side pilot line of the proportional valve  31 ER, and has an outlet port connected to the right pilot port of the control valve  171 . 
     That is, the left travel lever  26 DL causes a pilot pressure commensurate with the details of the forward or the backward operation to act on a pilot port of the control valve  171  through the shuttle valve  32 EL or  32 ER. Specifically, in response to the forward travel operation, the left travel lever  26 DL outputs a pilot pressure commensurate with the amount of operation to one inlet port of the shuttle valve  32 EL and causes the pilot pressure to act on the left pilot port of the control valve  171  via the shuttle valve  32 EL. Furthermore, in response to the backward travel operation, the left travel lever  26 DL outputs a pilot pressure commensurate with the amount of operation to one inlet port of the shuttle valve  32 ER and causes the pilot pressure to act on the right pilot port of the control valve  171  via the shuttle valve  32 ER. 
     The proportional valve  31 EL operates in response to a control current input from the controller  30 . Specifically, the proportional valve  31 EL outputs a pilot pressure commensurate with a control current input from the controller  30  to the other pilot port of the shuttle valve  32 EL, using hydraulic oil discharged from the pilot pump  15 . This enables the proportional valve  31 EL to control a pilot pressure acting on the left pilot port of the control valve  171  via the shuttle valve  32 EL. 
     The proportional valve  31 ER operates in response to a control current input from the controller  30 . Specifically, the proportional valve  31 ER outputs a pilot pressure commensurate with a control current input from the controller  30  to the other pilot port of the shuttle valve  32 ER, using hydraulic oil discharged from the pilot pump  15 . This enables the proportional valve  31 ER to control a pilot pressure acting on the right pilot port of the control valve  171  via the shuttle valve  32 ER. 
     That is, the proportional valves  31 EL and  31 ER can control a pilot pressure output to the secondary side such that the control valve  171  can stop at a desired valve position independent of the operating state of the left travel lever  26 DL. 
     The pressure reducing proportional valve  33 EL operates in response to a control current input from the controller  30 . Specifically, when no control current is input from the controller  30 , the pressure reducing proportional valve  33 EL outputs a pilot pressure commensurate with the forward travel operation of the left travel lever  26 DL directly to the secondary side. In contrast, when a control current is input from the controller  30 , the pressure reducing proportional valve  33 EL reduces the pilot pressure of a secondary-side pilot line corresponding to the forward travel operation of the left travel lever  26 DL to an extent corresponding to the control current, and outputs the reduced pilot pressure to the one inlet port of the shuttle valve  32 EL. This enables the pressure reducing proportional valve  33 EL to forcibly control or stop the operation of the travel hydraulic motor  2 ML corresponding to the forward travel operation on an as-needed basis even during the forward travel operation of the left travel lever  26 DL. Furthermore, the pressure reducing proportional valve  33 EL can cause the pilot pressure acting on the one inlet port of the shuttle valve  32 EL to be lower than the pilot pressure acting on the other inlet port of the shuttle valve  32 EL from the proportional valve  31 EL even during the forward travel operation of the left travel lever  26 DL. Therefore, the controller  30  can ensure that a desire pilot pressure acts on the forward-travel-side pilot port of the control valve  171  by controlling the proportional valve  31 EL and the pressure reducing proportional valve  33 EL. 
     The pressure reducing proportional valve  33 ER operates in response to a control current input from the controller  30 . Specifically, when no control current is input from the controller  30 , the pressure reducing proportional valve  33 ER outputs a pilot pressure commensurate with the backward travel operation of the left travel lever  26 DL directly to the secondary side. In contrast, when a control current is input from the controller  30 , the pressure reducing proportional valve  33 ER reduces the pilot pressure of a secondary-side pilot line corresponding to the backward travel operation of the left travel lever  26 DL to an extent corresponding to the control current, and outputs the reduced pilot pressure to the one inlet port of the shuttle valve  32 ER. This enables the pressure reducing proportional valve  33 ER to forcibly control or stop the operation of the travel hydraulic motor  2 ML corresponding to the backward travel operation on an as-needed basis even during the backward travel operation of the left travel lever  26 DL. Furthermore, the pressure reducing proportional valve  33 ER can cause the pilot pressure acting on the one inlet port of the shuttle valve  32 ER to be lower than the pilot pressure acting on the other inlet port of the shuttle valve  32 ER from the proportional valve  31 ER even during the backward travel operation of the left travel lever  26 DL. Therefore, the controller  30  can ensure that a desire pilot pressure acts on the backward-travel-side pilot port of the control valve  171  by controlling the proportional valve  31 ER and the pressure reducing proportional valve  33 ER. 
     Thus, the pressure reducing proportional valves  33 EL and  33 ER can forcibly control or stop the operations of the travel hydraulic motor  2 ML corresponding to the forward and the backward operating state of the left travel lever  26 DL. Furthermore, the pressure reducing proportional valves  33 EL and  33 ER can assist in ensuring that the pilot pressures of the proportional valves  31 EL and  31 ER act on the pilot ports of the control valve  171  through the shuttle valves  32 EL and  32 ER by reducing pilot pressures acting on the one inlet ports of the shuttle valves  32 EL and  32 ER. 
     The controller  30  may forcibly control or stop the operation of the travel hydraulic motor  2 ML corresponding to the forward travel operation of the left travel lever  26 DL by controlling the proportional valve  31 ER instead of controlling the pressure reducing proportional valve  33 EL. For example, in the case of performing the forward travel operation with the left travel lever  26 DL, the controller  30  may control the proportional valve  31 ER to act on the backward-travel-side pilot port of the control valve  171  from the proportional valve  31 ER via the shuttle valve  32 ER. This causes a pilot pressure to act on the backward-travel-side pilot port of the control valve  171  against a pilot pressure acting on the forward-travel-side pilot port of the control valve  171  from the left travel lever  26 DL via the shuttle valve  32 EL. Therefore, the controller  30  can forcibly move the control valve  171  toward a neutral position to forcibly control or stop the operation of the travel hydraulic motor  2 ML corresponding to the forward travel operation of the left travel lever  26 DL. Likewise, the controller  30  may forcibly control or stop the operation of the travel hydraulic motor  2 ML corresponding to the backward travel operation of the left travel lever  26 DL by controlling the proportional valve  31 EL instead of controlling the pressure reducing proportional valve  33 ER. 
     The operating pressure sensor  29 DL detects the details of the operator&#39;s forward or the backward operation of the left travel lever  26 DL in the form of pressure, and a detection signal corresponding to the detected pressure is fed into the controller  30 . This enables the controller  30  to determine the details of the forward or the backward operation of the left travel lever  26 DL. 
     The controller  30  can cause hydraulic oil discharged from the pilot pump  15  to be supplied to the left pilot port of the control valve  171  via the proportional valve  31 EL and the shuttle valve  32 EL, independent of the operator&#39;s forward travel operation on the left travel lever  26 DL. Furthermore, the controller  30  can cause hydraulic oil discharged from the pilot pump  15  to be supplied to the right pilot port of the control valve  171  via the proportional valve  31 ER and the shuttle valve  32 ER, independent of the operator&#39;s backward travel operation on the left travel lever  26 DL. That is, the controller  30  can automatically control the forward and backward operation of the left crawler  1 CL. 
     Furthermore, for example, as illustrated in  FIG. 5B , the right travel lever  26 DR is used to operate the travel hydraulic motor  2 MR corresponding to the right crawler  1 CR. That is, the target of operation of the right travel lever  26 DR is the travel operation of the right crawler  1 CR. The right travel lever  26 DR outputs a pilot pressure commensurate with the details of the forward or the backward operation to the secondary side, using hydraulic oil discharged from the pilot pump  15 . 
     The shuttle valve  32 FR has two inlet ports, one connected to a secondary-side pilot line of the right travel lever  26 DR corresponding to an operation in a forward direction corresponding to the forward travel direction of the right crawler  1 CR (hereinafter “forward travel operation”) and the other connected to the secondary-side pilot line of the proportional valve  31 FR, and has an outlet port connected to the right pilot port of the control valve  172 . 
     The shuttle valve  32 FL has two inlet ports, one connected to a secondary-side pilot line of the right travel lever  26 DR corresponding to an operation in a backward direction corresponding to the backward travel direction of the right crawler  1 CR (hereinafter “backward travel operation”) and the other connected to the secondary-side pilot line of the proportional valve  31 FL, and has an outlet port connected to the left pilot port of the control valve  172 . 
     That is, the right travel lever  26 DR causes a pilot pressure commensurate with the details of the forward or the backward operation to act on a pilot port of the control valve  172  through the shuttle valve  32 FL or  32 FR. Specifically, in response to the forward travel operation, the right travel lever  26 DR outputs a pilot pressure commensurate with the amount of operation to one inlet port of the shuttle valve  32 FR and causes the pilot pressure to act on the right pilot port of the control valve  172  via the shuttle valve  32 FR. Furthermore, in response to the backward travel operation, the right travel lever  26 DR outputs a pilot pressure commensurate with the amount of operation to one inlet port of the shuttle valve  32 FL and causes the pilot pressure to act on the left pilot port of the control valve  172  via the shuttle valve  32 FL. 
     The proportional valve  31 FL operates in response to a control current input from the controller  30 . Specifically, the proportional valve  31 FL outputs a pilot pressure commensurate with a control current input from the controller  30  to the other pilot port of the shuttle valve  32 FL, using hydraulic oil discharged from the pilot pump  15 . This enables the proportional valve  31 FL to control a pilot pressure acting on the left pilot port of the control valve  172  via the shuttle valve  32 FL. 
     The proportional valve  31 FR operates in response to a control current input from the controller  30 . Specifically, the proportional valve  31 FR outputs a pilot pressure commensurate with a control current input from the controller  30  to the other pilot port of the shuttle valve  32 FR, using hydraulic oil discharged from the pilot pump  15 . This enables the proportional valve  31 FR to control a pilot pressure acting on the right pilot port of the control valve  172  via the shuttle valve  32 FR. 
     That is, the proportional valves  31 FL and  31 FR can control a pilot pressure output to the secondary side such that the control valve  172  can stop at a desired valve position independent of the operating state of the right travel lever  26 DR. 
     The pressure reducing proportional valve  33 FL operates in response to a control current input from the controller  30 . Specifically, when no control current is input from the controller  30 , the pressure reducing proportional valve  33 FL outputs a pilot pressure commensurate with the backward travel operation of the right travel lever  26 DR directly to the secondary side. In contrast, when a control current is input from the controller  30 , the pressure reducing proportional valve  33 FL reduces the pilot pressure of a secondary-side pilot line corresponding to the backward travel operation of the right travel lever  26 DR to an extent corresponding to the control current, and outputs the reduced pilot pressure to the one inlet port of the shuttle valve  32 FL. This enables the pressure reducing proportional valve  33 FL to forcibly control or stop the operation of the travel hydraulic motor  2 MR corresponding to the backward travel operation on an as-needed basis even during the backward travel operation of the right travel lever  26 DR. Furthermore, the pressure reducing proportional valve  33 FL can cause the pilot pressure acting on the one inlet port of the shuttle valve  32 FL to be lower than the pilot pressure acting on the other inlet port of the shuttle valve  32 FL from the proportional valve  31 FL even during the backward travel operation of the right travel lever  26 DR. Therefore, the controller  30  can ensure that a desire pilot pressure acts on the backward-travel-side pilot port of the control valve  172  by controlling the proportional valve  31 FL and the pressure reducing proportional valve  33 FL. 
     The pressure reducing proportional valve  33 FR operates in response to a control current input from the controller  30 . Specifically, when no control current is input from the controller  30 , the pressure reducing proportional valve  33 FR outputs a pilot pressure commensurate with the forward travel operation of the right travel lever  26 DR directly to the secondary side. In contrast, when a control current is input from the controller  30 , the pressure reducing proportional valve  33 ER reduces the pilot pressure of a secondary-side pilot line corresponding to the forward travel operation of the right travel lever  26 DR to an extent corresponding to the control current, and outputs the reduced pilot pressure to the one inlet port of the shuttle valve  32 FR. This enables the pressure reducing proportional valve  33 FR to forcibly control or stop the operation of the travel hydraulic motor  2 MR corresponding to the forward travel operation on an as-needed basis even during the forward travel operation of the right travel lever  26 DR. Furthermore, the pressure reducing proportional valve  33 FR can cause the pilot pressure acting on the one inlet port of the shuttle valve  32 FR to be lower than the pilot pressure acting on the other inlet port of the shuttle valve  32 FR from the proportional valve  31 FR even during the forward travel operation of the right travel lever  26 DR. Therefore, the controller  30  can ensure that a desire pilot pressure acts on the forward-travel-side pilot port of the control valve  172  by controlling the proportional valve  31 FR and the pressure reducing proportional valve  33 FR. 
     Thus, the pressure reducing proportional valves  33 FL and  33 FR can forcibly control or stop the operations of the travel hydraulic motor  2 MR corresponding to the forward and the backward operating state of the right travel lever  26 DR. Furthermore, the pressure reducing proportional valves  33 FL and  33 FR can assist in ensuring that the pilot pressures of the proportional valves  31 FL and  31 FR act on the pilot ports of the control valve  172  through the shuttle valves  32 FL and  32 FR by reducing pilot pressures acting on the one inlet ports of the shuttle valves  32 FL and  32 FR. 
     The controller  30  may forcibly control or stop the operation of the travel hydraulic motor  2 MR corresponding to the backward travel operation of the right travel lever  26 DR by controlling the proportional valve  31 FR instead of controlling the pressure reducing proportional valve  33 FL. For example, in the case of performing the backward travel operation with the right travel lever  26 DR, the controller  30  may control the proportional valve  31 FR to act on the forward-travel-side pilot port of the control valve  172  from the proportional valve  31 FR via the shuttle valve  32 FR. This causes a pilot pressure to act on the forward-travel-side pilot port of the control valve  172  against a pilot pressure acting on the backward-travel-side pilot port of the control valve  172  from the right travel lever  26 DR via the shuttle valve  32 FL. Therefore, the controller  30  can forcibly move the control valve  172  toward a neutral position to forcibly control or stop the operation of the travel hydraulic motor  2 MR corresponding to the backward travel operation of the right travel lever  26 DR. Likewise, the controller  30  may forcibly control or stop the operation of the travel hydraulic motor  2 MR corresponding to the forward travel operation of the right travel lever  26 DR by controlling the proportional valve  31 FL instead of controlling the pressure reducing proportional valve  33 FR. 
     The operating pressure sensor  29 DR detects the details of the operator&#39;s forward or the backward operation of the right travel lever  26 DR in the form of pressure, and a detection signal corresponding to the detected pressure is fed into the controller  30 . This enables the controller  30  to determine the details of the forward or the backward operation of the right travel lever  26 DR. 
     The controller  30  can cause hydraulic oil discharged from the pilot pump  15  to be supplied to the right pilot port of the control valve  172  via the proportional valve  31 FR and the shuttle valve  32 FR, independent of the operator&#39;s forward travel operation on the right travel lever  26 DR. Furthermore, the controller  30  can cause hydraulic oil discharged from the pilot pump  15  to be supplied to the left pilot port of the control valve  172  via the proportional valve  31 FL and the shuttle valve  32 FL, independent of the operator&#39;s backward travel operation on the right travel lever  26 DR. That is, the controller  30  can automatically control the forward and backward operation of the right crawler  1 CR. 
     Next, the control system of the shovel  100  according to this embodiment includes the controller  30 , a space recognition device  70 , an orientation detector  71 , an input device  72 , a positioning device  73 , an external display device  74 , an external audio output device  75 , a display device D 1 , an audio output device D 2 , a boom angle sensor S 1 , an arm angle sensor S 2 , a bucket angle sensor S 3 , a machine body tilt sensor S 4 , a swing state sensor S 5 , and a communications device T 1 . 
     The space recognition device  70  is configured to detect or recognize an object present in a three-dimensional space surrounding the shovel  100  and measure (calculate) a positional relationship such as a distance from the space recognition device  70  or the shovel  100  to the recognized object. Examples of the space recognition device  70  may include an ultrasonic sensor, a millimeter wave radar, a monocular camera, a stereo camera, a LIDAR (Light Detecting and Ranging), a distance image sensor, and an infrared sensor. According to this embodiment, the space recognition device  70  includes a forward recognition sensor  70 F attached to the front end of the upper surface of the cabin  10 , a backward recognition sensor  70 B attached to the back end of the upper surface of the upper swing structure  3 , a leftward recognition sensor  70 L attached to the left end of the upper surface of the upper swing structure  3 , and a rightward recognition sensor  70 R attached to the right end of the upper surface of the upper swing structure  3 . Furthermore, an upward recognition sensor that recognizes an object present in a space above the upper swing structure  3  may be attached to the shovel  100 . 
     The location of installation of the forward recognition sensor  70 F is not limited to the upper surface of the cabin  10 , and may be determined as desired to the extent that the location allows an object in front of the upper swing structure  3  to be recognized. Specifically, the forward recognition sensor  70 F may be placed in such a manner as to be directly attached to a desired part of the front end of the upper swing structure  3  or may be placed on a component installed at the front end of the upper swing structure  3  other than the cabin  10 , such as the boom  4  or the arm  5  of the attachment. 
     The orientation detector  71  detects information on the relative relationship between the orientation of the upper swing structure  3  and the orientation of the lower traveling structure  1  (for example, the swing angle of the upper swing structure  3  relative to the lower traveling structure  1 ). 
     The orientation detector  71  may include, for example, a combination of a geomagnetic sensor attached to the lower traveling structure  1  and a geomagnetic sensor attached to the upper swing structure  3 . Furthermore, the orientation detector  71  may also include a combination of a GNSS (Global Navigation Satellite System) receiver attached to the lower traveling structure  1  and a GNSS receiver attached to the upper swing structure  3 . The orientation detector  71  may also include a rotary encoder, a rotary position sensor, etc., that can detect the swing angle of the upper swing structure  3  relative to the lower traveling structure  1 , namely, the below-described swing state sensor S 5 , and may be, for example, attached to a center joint provided in relation to the swing mechanism  2  that achieves relative rotation between the lower traveling structure  1  and the upper swing structure  3 . The orientation detector  71  may also include a camera attached to the upper swing structure  3 . In this case, the orientation detector  71  performs known image processing on an image captured by a camera attached to the upper swing structure  3  (an input image) to detect an image of the lower traveling structure  1  included in the input image. The orientation detector  71  may identify the longitudinal direction of the lower traveling structure  1  by detecting an image of the lower traveling structure  1  using a known image recognition technique and derive the angle formed between the direction of the longitudinal axis of the upper swing structure  3  and the longitudinal direction of the lower traveling structure  1 . At this point, the direction of the longitudinal axis of the upper swing structure  3  may be derived from the attachment position of the camera. In particular, the crawlers  1 C protrude from the upper swing structure  3 . Therefore, the orientation detector  71  can identify the longitudinal direction of the lower traveling structure  1  by detecting an image of the crawlers  1 C. 
     In the case where the upper swing structure  3  is configured to be driven by an electric motor instead of the swing hydraulic motor  2 A to swing, the orientation detector  71  may be a resolver. 
     The input device  72  is provided within the reach of the operator seated in the cabin  10 , and receives the operator&#39;s various operation inputs to output signals corresponding to the operation inputs. The input device  72  includes a touchscreen provided on the display of the display device D 1  that displays various information images, a knob switch provided at the end of the left operating lever  26 L or the right operating lever  26 R, and a button switch, a lever, a toggle, a dial, etc., provided around the display device D 1 . A signal corresponding to the details of operation on the input device  72  is fed into the controller  30 . 
     The positioning device  73  measures the position and the orientation of the upper swing structure  3 . The positioning device  73  is, for example, a GNSS compass, and detects the position and the orientation of the upper swing structure  3 . A detection signal corresponding to the position and the orientation of the upper swing structure  3  is fed into the controller  30 . Furthermore, among the functions of the positioning device  73 , the function of detecting the orientation of the upper swing structure  3  may be replaced with a direction sensor attached to the upper swing structure  3 . 
     The external display device  74  is attached outside the cabin  10 , for example, a side surface of the upper swing structure  3  (specifically, the front side surface, the back side surface or the like of the upper swing structure  3  (the cabin  10 )), and displays various kinds of image information to the outside of the cabin  10 , namely, workers, etc., around the shovel  100 , under the control of the controller  30 . Examples of the external display device  74  include a liquid crystal display and an electronic message board. 
     The external audio output device  75  is, for example, attached to the upper swing structure  3 , and outputs audio to the outside of the cabin  10 , namely, workers, etc., around the shovel  100 . Examples of the external audio output device  75  include a loudspeaker and a buzzer. The same is true for the below-described audio output device D 2 . 
     The display device D 1  is provided at such a position as to be easily visible by the operator seated in the cabin  10 , and displays various information images under the control of the controller  30 . Examples of the display device D 1  include a liquid crystal display and an organic EL (Electroluminescence) display. The display device D 1  may be connected to the controller  30  via an in-vehicle communications network such as a CAN (Controller Area Network) or may be connected to the controller  30  via a one-to-one dedicated line. 
     The audio output device D 2  is, for example, provided in the cabin  10 , and outputs various kinds of audio information in response to audio output commands from the controller  30 . 
     The boom angle sensor S 1  is attached to the boom  4  to detect the elevation angle of the boom  4  relative to the upper swing structure  3  (hereinafter, “boom angle”), for example, the angle of a straight line connecting the pivot points of the boom  4  at its both ends to the swing plane of the upper swing structure  3  in a side view. Examples of the boom angle sensor S 1  may include a rotary encoder, an acceleration sensor, a six-axis sensor, and an IMU (Inertial Measurement Unit), which is hereinafter also the case with the arm angle sensor S 2 , the bucket angle sensor S 3 , and the machine body tilt sensor S 4 . A detection signal corresponding to the boom angle detected by the boom angle sensor S 1  is fed into the controller  30 . 
     The arm angle sensor S 2  is attached to the arm  5  to detect the pivot angle of the arm  5  relative to the boom  4  (hereinafter “arm angle”), for example, the angle of a straight line connecting the pivot points of the arm  5  at its both ends to the straight line connecting the pivot points of the boom  4  at its both ends in a side view. A detection signal corresponding to the arm angle detected by the arm angle sensor S 2  is fed into the controller  30 . 
     The bucket angle sensor S 3  is attached to the bucket  6  to detect the pivot angle of the bucket  6  relative to the arm  5  (hereinafter “bucket angle”), for example, the angle of a straight line connecting the pivot point and the distal end (blade edge) of the bucket  6  to the straight line connecting the pivot points of the arm  5  at its both ends in a side view. A detection signal corresponding to the bucket angle detected by the bucket angle sensor S 3  is fed into the controller  30 . 
     The machine body tilt sensor S 4  detects the tilt state of the machine body (for example, the upper swing structure  3 ) relative to a predetermined reference plane (for example, a horizontal plane). The machine body tilt sensor S 4  is, for example, attached to the upper swing structure  3  to detect the tilt angles of the shovel  100  (namely, the upper swing structure  3 ) about two axes in its longitudinal direction and lateral direction (hereinafter “longitudinal tilt angle” and “lateral tilt angle”). Detection signals corresponding to the tilt angles (longitudinal tilt angle and lateral tilt angle) detected by the machine body tilt sensor S 4  are fed into the controller  30 . 
     The swing state sensor S 5  is attached to the upper swing structure  3  to output detection information regarding the swing state of the upper swing structure  3 . The swing state sensor S 5  detects, for example, the swing angular velocity and the swing angle of the upper swing structure  3 . Examples of the swing state sensor S 5  include a gyroscope, a resolver, and a rotary encoder. The detection information regarding the swing state detected by the swing state sensor S 5  is fed into the controller  30 . 
     When the machine body tilt sensor S 4  includes a gyroscope, a six-axis sensor, an IMU or the like that can detect angular velocities about three axes, the swing state (for example, the swing angular velocity) of the upper swing structure  3  may be detected based on a detection signal of the machine body tilt sensor S 4 . In this case, the swing state sensor S 5  may be omitted. 
     The communications device T 1  performs communications with external apparatuses through a predetermined network including a mobile communication network including a base station as a terminal end, a satellite communication network using a communications satellite, or the Internet. The communications device T 1  is, for example, a mobile communication module compliant with a mobile communication standard such as LTE (Long Term Evolution), 4G (4th Generation), or 5G (5 th  generation), a satellite communication module for connecting to a satellite communication network, or the like. 
     [Gesture Operation Function of Shovel] 
     Next, the function of enabling the operating elements of the shovel  100  to be operated with a gesture from a worker or the like around the shovel  100  (hereinafter “gesture operation function”) is described with reference to  FIGS. 7 through 13 . 
     &lt;First Example of Gesture Operation Function of Shovel&gt; 
     First, a configuration associated with the gesture operation function of the shovel  100  is described with reference to  FIG. 7 . 
       FIG. 7  is a functional block diagram illustrating a first example of the configuration associated with the gesture operation function of the shovel  100  (the controller  30 ). 
     For example, as functional parts associated with the gesture operation function implemented by executing one or more programs stored in the secondary storage on the CPU, the controller  30  includes a gesture recognition part  301 , an operation control part  302 , and an alert notification part  303 . Furthermore, the controller  30  includes, for example, a storage part  300  serving as a storage area specified in an internal memory such as a non-volatile secondary storage. 
     The gesture recognition part  301  recognizes a person around the shovel  100 , for example, a worker, a work site foreman, or the like (hereinafter “worker”), and recognizes a predetermined gesture (hereinafter “recognition target gesture”) made by the recognized worker. The recognition target gesture is one or more gestures predefined for a worker to operate the shovel  100  from an area outside (around) the shovel  100 . Specifically, the gesture recognition part  301  recognizes a worker around the shovel  100  and a recognition target gesture made by the worker based on information input from the space recognition device  70 , for example, a captured image of an area surrounding the shovel  100 , through application of a known image recognition process. 
     The function of the gesture recognition part  301  may be built into the space recognition device  70  (an example of a recognition part). 
     For example, the gesture recognition part  301  recognizes and pre-records an instructor who makes a recognition target gesture to give instructions for the operation control part  302  to perform operation control as described below (hereinafter “gesture instructor”). In other words, the shovel  100  may switch to a mode in which operations are performed through gestures (hereinafter “gesture operation mode”) serving as one of operating modes in response to the recording of a gesture instructor by the gesture recognition part  301 . Specifically, the gesture recognition part  301  may recognize and record a worker as a gesture instructor when the worker has continued the action of staring at the lens of an image capturing device serving as the space recognition device  70  for a certain period of time or more (the start of the gesture operation mode). The gesture recognition part  301  recognizes a recognition target gesture made by the recorded gesture instructor. 
     When the operating mode of the shovel  100  switches from other than the gesture operation mode to the gesture operation mode, the rotational speed of the engine  11  is changed to a rotational speed predetermined for the gesture operation mode (hereinafter “gesture operation mode rotational speed”). The gesture operation mode rotational speed is set to a value lower than the rotational speed of the engine  11  in the normal operation mode of the shovel  100 . Thus, in the case of the gesture operation mode, the operating speed of hydraulic actuators is limited to be lower than in the case of the normal operating mode. Therefore, in the gesture operation mode, the limit values (upper limit values) of the travel operating speed of the lower traveling structure  1 , the swing operating speed of the upper swing structure  3 , and the operating speed of the attachment are set (restricted) to be lower than in the normal operating mode. Hereinafter, the same may be true for the below-described cases of second through fourth examples. 
     The gesture recognition part  301  may cancel the recording of a worker as a gesture instructor when an action necessary for the worker being recorded as a gesture instructor (for example, the action of staring at the lens of an image capturing device) has not been performed for a certain period of time after the recording of the worker as a gesture instructor. In this case, the gesture operation mode is canceled. 
     Furthermore, the gesture recognition part  301  may recognize a worker not recorded as a gesture instructor (hereinafter “non-gesture-instructor”) and exceptionally recognize particular kinds of recognition target gestures made by the non-gesture-instructor. The recognition target gestures that are exceptionally processed may be recognition target gestures whose priorities predetermined in view of the safety of the shovel  100  are relatively high among the recognition target gestures. Examples of the recognition target gestures having relatively high priorities to be exceptionally processed may include “stop gesture,” “sudden stop gesture,” and “cancel gesture” as described below. This makes it possible for even a worker who is not recorded as a gesture instructor to stop or suddenly stop the shovel  100  or cancel control of the operation of the shovel  100  to ensure the safety of the shovel and an area surrounding the shovel  100 . 
     The operation control part  302  controls the operation of an operating element of the shovel  100  (specifically, at least one of the lower traveling structure  1 , the upper swing structure  3 , the boom  4 , the arm  5 , the bucket  6 , etc.) in response to a worker&#39;s recognition target gesture recognized by the gesture recognition part  301 . For example, the operation control part  302  controls the operation of an operating element of the shovel  100  based on gesture-operation correspondence table information  300 A (an example of correspondence information) stored in the storage part  300 . The operation control part  302  can cause various operating elements of the shovel  100  to automatically operate by causing a pilot pressure to act on a control valve corresponding to a hydraulic actuator via the proportional valve  31  and the shuttle valve  32  independent of the operating state of the operating device  26  as described above. 
     For example,  FIG. 8  is a diagram explaining the gesture-operation correspondence table information  300 A. Specifically,  FIG. 8  is a diagram illustrating an example of the correspondence between recognition target gestures and the operation details of operating elements defined by the gesture-operation correspondence table information  300 A. 
     As illustrated in  FIG. 8 , according to this example, seven recognition target gestures are defined and the operation details of an operating element with respect to each of the seven recognition target gestures are defined in the gesture-operation correspondence table information  300 A. 
     Specifically, according to this example, a recognition target gesture for raising the attachment AT (for example, raising the boom  4 ) (hereinafter “attachment raising gesture”) is defined in the gesture-operation correspondence table information  300 A. More specifically, the attachment raising gesture is the gesture of moving up a closed first from a level with only the thumb pointed upward. The attachment raising gesture may also be the gesture of moving up a closed first from a level with only the thumb pointed upward after placing the first on the head. 
     Furthermore, according to this example, a recognition target gesture for lowering the attachment AT (for example, lowering the boom  4 ) (hereinafter “attachment lowering gesture”) is defined in the gesture-operation correspondence table information  300 A. More specifically, the attachment lowering gesture is the gesture of moving down a closed first from a level with only the thumb pointed downward. The attachment raising gesture may also be the gesture of moving down a closed first from a level with only the thumb pointed downward after placing the first on the head. 
     Furthermore, according to this example, a recognition target gesture for horizontally moving the shovel  100  (for example, swinging the upper swing structure  3  or causing the lower traveling structure  1  to travel) (hereinafter “horizontal movement gesture”) is defined in the gesture-operation correspondence table information  300 A. More specifically, the horizontal movement gesture is the gesture of extending an arm substantially horizontally and moving the palm a few times in the direction of movement. 
     With respect to whether the horizontal movement caused by the horizontal movement gesture corresponds to the swing operation of the upper swing structure  3  or the travel operation of the lower traveling structure  1 , a setting may be recorded in the controller  30  (for example, the storage part  300 ) through the input device  72  or the like, for example. Furthermore, different recognition target gestures may be provided one for each of the swing operation and the travel operation of the shovel  100 . 
     Furthermore, according to this example, a recognition target gesture for causing the lower traveling structure  1  (the crawlers  1 C) to do a spin turn (hereinafter “crawler spin turn”) (hereinafter “spin turn gesture”) is defined in the gesture-operation correspondence table information  300 A. More specifically, the spin turn gesture is the gesture of horizontally extending both arms substantially parallel to each other and substantially horizontally turning the alms in such a manner as to wrap the arms in a direction in which the crawlers  1 C are caused to do a spin turn. 
     Furthermore, according to this example, a recognition target gesture for stopping (specifically, stopping and keeping stopped) an operating element of the shovel  100  (hereinafter “stop gesture”) is defined in the gesture-operation correspondence table information  300 A. More specifically, the stop gesture is the gesture of raising a palm high. The stop gesture may also be the action of raising a palm high and thereafter clenching the fingers. 
     Furthermore, according to this example, a recognition target gesture for suddenly stopping (specifically, suddenly stopping and keeping stopped) an operating element of the shovel  100  (hereinafter “sudden stop gesture”) is defined in the gesture-operation correspondence table information  300 A. More specifically, the sudden stop gesture is the gesture of spreading both arms, raising them high, and waving them wildly from side to side. 
     Furthermore, according to this example, a gesture for canceling the operation of an operating element of the shovel  100  using the gesture operation function, namely, a gesture for canceling the operation control part  302 &#39;s control of the operation of an operating element of the shovel  100  based on a recognition target gesture (hereinafter “cancel gesture”), is defined in the gesture-operation correspondence table information  300 A. More specifically, the cancel gesture is a hand salute gesture. The cancel gesture may also be the gesture of crossing both hands (both arms) above the head. 
     The recognition target gestures of  FIG. 8  are examples, and recognition target gestures corresponding to other operation details of operating elements of the shovel  100  may be further defined in the gesture-operation correspondence table information  300 A. For example, a recognition target gesture for causing the shovel  100  to move (travel) following the movement of a worker while keeping the interval between the worker and the shovel  100  constant, etc., may be defined in the gesture-operation correspondence table information  300 A. This enables a worker to easily move the shovel  100  to a desired location. 
     The correspondence between recognition target gestures and their respective operation details of operating elements may be defined in a format other than a table format such as the gesture-operation correspondence table information  300 A. 
     The operation control part  302  selects the operation details of an operating element corresponding to the details of a recognition target gesture recognized by the gesture recognition part  301  from the gesture-operation correspondence table information  300 A, and causes the operating element to execute the selected operation details. This enables a worker around the shovel  100  to combine recognition target gestures (for example, the seven recognition target gestures of  FIG. 8 ) to cause the shovel  100  to operate as desired, independent of the operation of the operator in the cabin  10 . That is, even in the absence of the operator of the shovel  100 , a worker around the shovel  100  can manipulate the operation of the shovel  100  from the surrounding area. For example, a worker can cause the shovel  100  to travel and guide the shovel  100  to a predetermined position with gestures from outside the shovel  100  without riding in the cabin  10  of the shovel  100 . Furthermore, for example, even in the absence of the operator of the shovel  100 , a worker outside the shovel  100  can alone replace the bucket  6  or perform crane work. 
     Even when a recognition target gesture is recognized by the gesture recognition part  301 , the operation control part  302  does not perform (prevents) operation control of an operating element corresponding to the recognition target gesture if a predetermined condition for permitting execution of the operation details of the operating element corresponding to the recognition target gesture (hereinafter “operation permission condition”) is not satisfied. The operation permission condition may include, for example, the condition that “the weight of a load suspended from a hook during crane work is not in a state corresponding to overloading (specifically, a state in which a load exceeds a predetermined reference).” In this case, the weight of the suspended load may be calculated based on the detection value of the pressure sensor of the bottom-side oil chamber of the boom cylinder  7  attached to the boom cylinder  7  and the pose of the attachment AT derived from the detection values of the boom angle sensor S 1 , the arm angle sensor S 2 , and the bucket angle sensor S 3 . Furthermore, the operation permission condition may include, for example, the condition that “the pose of the shovel  100  is stable (specifically, not in a state where the degree of stability with respect to the pose of the shovel  100  is lower than a predetermined reference).” In this case, the degree of stability with respect to the shovel  100  may be calculated from, for example, the pose of the attachment AT derived from the detection values of the boom angle sensor S 1 , the arm angle sensor S 2 , and the bucket angle sensor S 3 , the pose of the machine body derived from the detection value of the machine body tilt sensor S 4  (the tilt state of the upper swing structure  3 ), or the like. 
     Referring back to  FIG. 7 , when an operation permission condition corresponding to a recognition target gesture recognized by the gesture recognition part  301  is not satisfied, the alert notification part  303  notifies (imparts) alert information (an alert) to that effect to a worker around the shovel  100 . Specifically, the alert notification part  303  notifies a worker around the shovel  100  of alert information (an alert) through the external display device  74  or the external audio output device  75 . 
     Next, a control process associated with the gesture operation function (hereinafter “gesture operation control process”) executed by the controller  30  of the shovel  100  is described with reference to  FIG. 9 . 
       FIG. 9  is a flowchart schematically illustrating an example of the gesture operation control process executed by the controller  30 . This flowchart is repeatedly executed at predetermined processing intervals, for example, during a period after the completion of the initial processing of the controller  30  at the time of starting the shovel  100  before the start of the termination processing of the controller  30  at the time of stopping the shovel  100 . 
     As illustrated in  FIG. 9 , at step S 102 , the gesture recognition part  301  determines whether a recognition target gesture made by a gesture instructor is recognized. The gesture recognition part  301  proceeds to step S 104  if a recognition target gesture made by a gesture instructor is recognized, and ends the process according to this flowchart of this time if no recognition target gesture made by a gesture instructor is recognized. 
     At step S 104 , the operation control part  302  compares the recognition target gesture recognized by the gesture recognition part  301  with pre-recorded gesture details, and determines whether a condition for permitting execution of the operation details of an operating element corresponding to the recognized recognition target gesture is satisfied. The operation control part  302  proceeds to step S 106  if the condition for permitting execution is satisfied, and proceeds to step S 115  if the condition for permitting execution is not satisfied. 
     At step S 106 , the operation control part  302  performs (starts) operation control with respect to the operation details of an operating element corresponding to the recognition target gesture recognized by the gesture recognition part  301  at step S 102 . 
     At step S 108 , the gesture recognition part  301  determines whether a recognition target gesture other than a cancel gesture made by a worker corresponding to the recognition target gesture recognized at step S 102 , namely, the gesture instructor, is again recognized. The gesture recognition part  301  returns to step S 104  if a recognition target gesture other than a cancel gesture made by the gesture instructor is recognized, and otherwise, proceeds to step S 110 . 
     At step S 110 , the operation control part  302  determines whether a predetermined time has passed since the start of the operation control at step S 106 . The predetermined time is wait time for canceling the operation control because of the continuance of the absence of operation performed by the worker around the shovel  100  (gesture instructor) (a time lag for determining the cancellation). The operation control part  302  proceeds to step S 112  if a predetermined time has not passed since the start of the operation control, and proceeds to step S 116  if a predetermined time has passed since the start of the operation control. 
     At step S 112 , the gesture recognition part  301  determines whether a cancel gesture made by the gesture instructor is recognized. The gesture recognition part  301  proceeds to step S 114  if no cancel gesture made by the gesture instructor is recognized, and proceeds to step S 116  if a cancel gesture made by the gesture instructor is recognized. 
     As described above, the gesture recognition part  301  may recognize a cancel gesture made by a non-gesture-instructor, and in this case, the gesture recognition part  301  proceeds to step S 116  if a cancel gesture made by the non-gesture-instructor is recognized. 
     At step S 114 , the gesture recognition part  301  determines whether the gesture instructor can be recognized. The gesture recognition part  301  returns to step S 108  if the gesture instructor can be recognized, and proceeds to step S 116  if the gesture instructor cannot be recognized. 
     At step S 115 , the alert notification part  303  outputs an alert to the effect that the condition for permitting execution is not satisfied (hereinafter “unsatisfied execution permission condition alert”) to a worker around the shovel  100  (including the gesture instructor) through the external display device  74  or the external audio output device  75 , and proceeds to step S 116 . 
     At step S 116 , the operation control part  302  stops all operating elements and thereafter cancels (ends) the operation control started at step S 106  to end the process according to this flowchart of this time. 
     Thus, according to this example, the operation control part  302  controls the operation of an operating element (at least one of the lower traveling structure  1 , the upper swing structure  3 , the boom  4 , the arm  5 , the bucket  6 , etc.) in response to a worker&#39;s predetermined gesture (recognition target gesture) recognized by the gesture recognition part  301 . 
     This enables a worker around the shovel  100  to operate the shovel  100  with a predetermined gesture even in the absence of the operator of the shovel  100  in the cabin  10  as described above. 
     Furthermore, according to this example, the operation control part  302  may start to control the operation of an operating element in response to a predetermined gesture (recognition target gesture) recognized by the gesture recognition part  301  and thereafter cancel the operation control in response to the passage of a predetermined time. 
     This enables the controller  30  to cancel unnecessary operation control in such a case as when the absence of operation continues after the start of the operation performed by a worker around the shovel  100  based on the gesture operation function. Therefore, for example, it is possible to prevent unnecessary continuation of a predetermined operation of an operating element to improve the safety of the shovel  100 . 
     Furthermore, according to this example, in the case of having started operation control in response to a predetermined gesture (recognition target gesture) made by a worker recognized by the gesture recognition part  301  (gesture instructor), the operation control part  302  cancels the operation control when a cancel gesture made by the worker is thereafter recognized by the gesture recognition part  301 . In other words, the operation control part  302  does not have to cancel the operation control when a cancel gesture made by another worker different from the worker is recognized by the gesture recognition part  301 . 
     This enables the controller  30  to avoid such a situation where another worker different from a worker who has started operation of the shovel  100  based on the gesture operation function cancels control of the operation of the shovel  100 . 
     Furthermore, according to this example, in the case of having started controlling the operation of an operating element in response to a predetermined gesture (recognition target gesture) made by a worker recognized by the gesture recognition part  301 , the operation control part  302  stops the operating element (that is, cancels the gesture operation mode) when the worker (gesture instructor) is no longer recognized by the gesture recognition part  301  thereafter. 
     This makes it possible to stop the shovel  100  even when a worker who has started operation of the shovel  100  based on the gesture operation function leaves an area surrounding the shovel  100  without canceling the operation control of the shovel  100 . Therefore, it is possible to achieve both the gesture operation function and the safety of the shovel  100 . 
     &lt;Second Example of Gesture Operation Function of Shovel&gt; 
     First, an overview of a remote control system SYS that serves as a basis for the gesture function of the shovel  100  is given with reference to  FIGS. 10 and 11 . 
       FIG. 10  is a schematic diagram illustrating an example of a configuration of the remote control system SYS including the shovel  100 .  FIG. 11  is a functional block diagram illustrating a second example of the configuration associated with the gesture operation function of the shovel  100 , and is specifically a functional block diagram of the remote control system SYS configured to include the second example of the configuration associated with the gesture operation function of the shovel  100  and an example configuration of the management apparatus  200  related to this example. 
     As illustrated in  FIG. 10 , the remote control system SYS includes the shovel  100  and the management apparatus  200  connected to the shovel  100  through a communications network CN in such a manner as to be able to bidirectionally communicate with the shovel  100 , and is configured in such a manner as to enable a remote operator to remotely control the shovel  100  from the management apparatus  200 . 
     As illustrated in  FIG. 11 , the management apparatus  200  includes a controller  210 , a communications device  220 , an operation input device  230 , and a display device  240 . 
     The controller  210  executes various control processes associated with the management apparatus  200 . The controller  210  may be constituted mainly of one or more server computers each including a CPU, a memory unit such as a RAM, a secondary storage such as a ROM, and various input/output interfaces. For example, the controller  210  includes a display control part  2101  and a command transmission part  2102  as functional parts implemented by executing one or more programs stored in the secondary storage on the CPU. 
     The communications device  220  is any device that performs bilateral communications with the shovel  100  through the communications network CN under the control of the controller  210 . 
     The operation input device  230  receives various operation inputs to the controller  210  and outputs operation signals corresponding to the details of the operation inputs to the controller  210 . The operation input device  230  includes a remote controller  230   a.    
     The remote controller  230   a  receives operation inputs for remotely controlling operating elements of the shovel  100  (the lower traveling structure  1 , the upper swing structure  3 , the boom  4 , the arm  5 , the bucket  6 , etc.) and outputs remote control signals corresponding to the details of the operation inputs to the controller  210 . The remote controller  230   a  may be constituted mainly of a lever operating device (for example, a joystick or the like) the same as the operating device  26  of the shovel  100 , for example. Hereinafter, an operator who remotely controls the shovel  100  through the remote controller  230   a  may be referred to as “remote operator” for convenience. 
     The display device  240  is, for example, a liquid crystal display or an organic EL display, and displays various information images under the control of the controller  210 . 
     The display control part  2101  causes the display device  240  to display various information images. 
     For example, the display control part  2101  causes the display device  240  to display captured images (specifically, captured images captured by the space recognition device  70 ) of an area surrounding the upper swing structure  3  (the cabin  10 ) successively transmitted from the shovel  100 . This enables the remote operator to remotely control the shovel  100  while being aware of the surroundings of the upper swing structure  3  and the status of the attachment. Furthermore, as described below, when remote control of the shovel  100  from the management apparatus  200  is restricted, the remote operator can be aware of a work site situation when the remote control is restricted. 
     Furthermore, when a notification to the effect that remote control from the management apparatus  200  is restricted (prevented) (hereinafter “remote control restriction notification”) is received from the shovel  100  through the communications device  220 , the display control part  2101  causes the display device  240  to display an information image indicating that remote control is restricted. This enables the remote operator to be aware that a worker&#39;s operation of the shovel  100  based on the gesture operation function on a work site is prioritized and that remote control is prevented as described below. 
     The command transmission part  2102  transmits, in response to a remote control signal input from the remote controller  230   a , command information for causing an operating element of the shovel  100  to execute operation details identified by the remote control signal to the shovel  100  through the communications device  220 . 
     Next, the configuration associated with the gesture control function of the shovel  100  is described with reference to  FIG. 11 . 
     The controller  30  of the shovel  100  includes the gesture recognition part  301 , the operation control part  302 , the alert notification part  303 , and a remote control restriction notification part  304 . Furthermore, the same as in the case of the above-described example, the controller  30 , for example, includes the storage part  300  serving as a storage area specified in an internal memory such as a secondary storage, and the gesture-operation correspondence table information  300 A is stored in the storage part  300 . The following description focuses on differences from the above-described first example ( FIGS. 7 through 9 ). 
     The operation control part  302  controls, in response to a command signal received from the management apparatus  200  through the communications device T 1 , the operation of an operating element of the shovel  100  according to operation details specified by the command signal. Specifically, the operation control part  302  can cause various operating elements of the shovel  100  to automatically operate by causing a pilot pressure to act on a control valve corresponding to a hydraulic actuator via the proportional valve  31  and the shuttle valve  32  independent of the operating state of the operating device  26  as described above. This enables the remote operator of the management apparatus  200  to remotely control the shovel  100 . 
     When a recognition target gesture is recognized by the gesture recognition part  301  during execution of the operation control of the shovel  100  based on remote control from the management apparatus  200 , the operation control part  302  prioritizes operation control based on the gesture operation function. That is, in this case, the operation control part  302  restricts (prevents) the remote control of the shovel  100  by stopping the operation control based on the remote control, and starts to control the operation of the shovel  100  based on the gesture operation function. This enables the controller  30  to stop the operation of the shovel  100  independent of the details of remote control when the recognition target gesture is, for example, a stop gesture. During remote control of the shovel  100  from the management apparatus  200 , an abnormality or the like that cannot be recognized by the remote operator may occur at a work site or in the shovel  100 . In response to this, the controller  30  can improve the safety of the shovel  100  by giving priority to the gesture operation function over the remote control function, that is, giving priority to the determination of a worker around the shovel  100  who is likely to be more familiar with the work site situation over the determination of the remote operator. A description of operation control of the shovel  100  performed based on the gesture operation function by the operation control part  302 , which is the same as in the above-described example as illustrated in  FIGS. 7 through 9 , is omitted. 
     When operation control based on remote control, namely, remote control of the shovel  100  from the management apparatus  200 , is restricted (prevented) by the operation control part  302 , the remote control restriction notification part  304  transmits a notification to that effect (hereinafter “remote control restriction notification”) from the shovel  100  to the management apparatus  200 . This enables the remote operator of the management apparatus  200  to look at information corresponding to the remote control restriction notification displayed on the display device  240  to be aware that remote control of the shovel  100  is restricted as described above. 
     &lt;Third Example of Gesture Operation Function of Shovel&gt; 
     A configuration associated with the gesture operation function is described with reference to  FIGS. 12A and 12B . The following description focuses on differences from the above-described first and second examples, and a description of the same or corresponding portion may be omitted. 
       FIGS. 12A and 12B  are functional block diagrams illustrating a third example of the configuration associated with the gesture operation function of the shovel  100 . 
     According to this example, the shovel  100  is remotely controlled from the management apparatus  200  the same as in the above-described second example to implement the semi-automatic operation function of causing at least one of operating elements (driven elements) to automatically operate in response to a remote control signal received from the management apparatus  200 . 
     As illustrated in  FIG. 12A , the controller  30  includes a current surroundings information obtaining part F 101 , an intended trajectory generating part F 102 , a current bucket position calculating part F 103 , an intended bucket position calculating part F 104 , an operation command generating part F 105 , a worker recognition part F 106 , a gesture recognition part F 107 , an operation command generating part F 108 , a switch part F 109 , an operation restricting part F 110 , and a command value calculating part F 111 . Furthermore, as illustrated in  FIG. 12B , the controller  30  includes a boom current command generating part F 11 , a boom spool displacement amount calculating part F 12 , a boom angle calculating part F 13 , an arm current command generating part F 21 , an arm spool displacement amount calculating part F 22 , an arm angle calculating part F 23 , a bucket current command generating part F 31 , a bucket spool displacement amount calculating part F 32 , a bucket angle calculating part F 33 , a swing current command generating part F 41 , a swing spool displacement amount calculating part F 42 , and a swing angle calculating part F 43 . These functions may be implemented by desired hardware or a combination of desired hardware and software. The controller  30  implements these functions by executing, on the CPU, various programs installed in the secondary storage, for example. 
     The current surroundings information obtaining part F 101  obtains information on the current surroundings of the shovel  100  (hereinafter “current surroundings information”) based on the output of the space recognition device  70 . The current surroundings information includes, for example, infatuation (for example, the three-dimensional data of a three-dimensional point cloud, surface, or the like) on the shape of the surrounding terrain of the shovel  100 . The current surroundings information may include, for example, information on the presence or absence of an object that is a monitoring target in an area surrounding the shovel  100  and its position, orientation, state, etc. Examples of monitoring targets may include persons, animals, work vehicles (for example, dump trucks), construction machines (for example, other shovels, bulldozers, etc.), walls, fences, holes, helmets, and safety vests. For example, when the monitoring target is a dump truck, the current surroundings information may include the position of the dump truck, the amount of earth in the bed, and the shape of earth in the bed. 
     The intended trajectory generating part F 102  generates a trajectory intended for the working part (for example, teeth tips, a back surface, or the like) of the bucket  6  which serves as a reference based on the current surroundings information and information on a work target (for example, information on an intended work surface) received from the management apparatus  200  through the communications device T 1 . 
     The current bucket position calculating part F 103  calculates the current position of the working part of the bucket  6  (hereinafter “current bucket position”). The current bucket position may be either a position relative to a local reference such as the terrain of or a dump truck in an area surrounding the shovel  100  or an absolute position (absolute coordinates) in the world geodetic system using a GNSS. Specifically, the current bucket position calculating part F 103  calculates the current bucket position based on a boom angle α, an arm angle β, a bucket angle γ, a right drive wheel rotation angle ε 1 , and a left drive wheel rotation angle ε 2  fed back from the boom angle calculating part F 13 , the arm angle calculating part F 23 , the bucket angle calculating part F 33 , the swing angle calculating part F 43 , etc., the output of the orientation detector  71 , etc. 
     The intended bucket position calculating part F 104  calculates the next intended position of the working part of the bucket  6  (hereinafter “intended bucket position”) based on the details of a remote control signal received through the communications device T 1 , the intended trajectory for the working part of the bucket  6 , and the current bucket position. 
     The operation command generating part F 105  generates an operation command for the shovel  100  (for example, an operation command for the bucket  6 ) for attaining the intended bucket position based on the intended bucket position. The operation command generating part F 105  may generate, for example, a speed command for the bucket  6 . 
     The worker recognition part F 106  recognizes a worker around the shovel  100  based on the output of the space recognition device  70 . 
     The gesture recognition part F 107  (an example of a recognition part) recognizes a recognition target gesture made by a worker around the shovel  100  when the worker is recognized by the worker recognition part F 106 . 
     The functions of the worker recognition part F 106  and the gesture recognition part F 107  may be included in the space recognition device  70  (an example of a recognition part). Hereinafter, the same applies to the functions of a worker recognition part F 209  and a gesture recognition part F 210  as described below. 
     The operation command generating part F 108  generates an operation command for causing the shovel  100  to perform an operation corresponding to the details of a recognition target gesture when the recognition target gesture is recognized by the gesture recognition part F 107 . 
     The switch part F 109  (an example of a control part) switches an operation command for the shovel  100  to be input to the operation restricting part F 110  between the output of the operation command generating part F 105  based on remote control of the shovel  100  and the output of the operation command generating part F 108  based on the gesture operation function of the shovel  100 . Specifically, normally, that is, when the gesture recognition part F 107  recognizes no recognition target gesture of a worker and the operation command generating part F 108  outputs no operation command, the switch part F 109  outputs an operation command generated by the operation command generating part F 105  to the operation restricting part F 110 . When the gesture recognition part F 107  recognizes a recognition target gesture of a worker and the operation command generating part F 108  outputs an operation command, the switch part F 109  inputs the operation command of the operation command generating part F 108  to the operation restricting part F 110 . 
     The operation restricting part F 110  restricts the operation of the shovel  100  corresponding to an operation command input through the switch part F 109  according to a predetermined operation restricting condition. Restrictions on the operation of the shovel  100  include not only controlling (decelerating) the operation of the shovel  100  but also stopping the operation of the shovel  100 . Examples of operation restricting conditions may include the condition that “the operation of the shovel  100  corresponding to an operation command may cause a part of the shovel  100  other than the working part to contact a surrounding object.” Furthermore, examples of operation restricting conditions may include the condition that “the operation of the shovel  100  corresponding to an operation command may cause the angular velocity of the operating axis of the attachment to be out of its allowable range.” Hereinafter, the same applies to an operation restricting part F 213  as described below. Specifically, if the operation restricting condition is satisfied, the operation restricting part F 110  outputs, to the command value calculating part F 111 , a corrected operation command into which an operation command input through the switch part F 109  is corrected in such a manner as to correct the operation of the shovel  100 . If the operation restricting condition is not satisfied, the operation restricting part F 110  outputs an operation command input through the switch part F 109  directly to the command value calculating part F 111 . 
     The command value calculating part F 111  outputs command values to driven elements (the boom  4 , the arm  5 , the bucket  6 , the upper swing structure  3 , and the right and left crawlers  1 CL and  1 CR of the lower traveling structure  1 ) based on an operation command or a corrected operation command input from the operation restricting part F 110 . Specifically, the command value calculating part F 111  outputs a boom command value α* for the boom  4 , an arm command value β* for the arm  5 , a bucket command value γ* for the bucket  6 , a swing command value δ* for the upper swing structure  3 , a right travel command value ε 1 * for the right crawler  1 CR, and a left travel command value ε 2 * for the left crawler  1 CL. 
     Thus, the controller  30  can give priority to the gesture operation function over the semi-automatic operation function through remote control of the shovel  100  by the action of the switch part F 109  when a recognition target gesture made by a worker is recognized in an area surrounding the shovel  100 . In other words, the controller  30  can give priority to the determination (the details of a recognition target gesture) of a worker around the shovel  100  who is likely to be more familiar with a work site situation over the determination (the details of remote control) of a remote operator. Thus, even when an abnormality or the like at a work site or in the shovel  100  which cannot be recognized by the remote operator occurs, it is possible to stop the operation of the shovel  100  at the discretion of the worker at the work site. Therefore, it is possible to improve the safety of the shovel  100  when the shovel  100  is remotely controlled. 
     The boom current command generating part F 11  outputs a boom current command to the boom proportional valve  31 B. 
     The boom spool displacement amount calculating part F 12  calculates the amount of displacement of the boom spool of the control valve  175  corresponding to the boom cylinder  7  based on the output of a boom spool displacement sensor S 16 . 
     The boom angle calculating part F 13  calculates the boom angle α based on the output of the boom angle sensor S 1 . 
     The boom current command generating part F 11  basically generates a boom current command for the boom proportional valve  31 B such that the difference between the boom command value α* generated by the command value calculating part F 111  and the boom angle α calculated by the boom angle calculating part F 13  is zero. In this case, the boom current command generating part F 11  adjusts the boom current command to eliminate the difference between the intended amount of the displacement of the boom spool derived from the boom current command and the amount of the displacement of the boom spool calculated by the boom spool displacement amount calculating part F 12 . The boom current command generating part F 11  outputs the adjusted boom current command to the boom proportional valve  31 B. 
     The boom proportional valve  31 B changes its opening area according to the boom current command and causes a pilot pressure commensurate with the magnitude of the boom current command to act on a pilot port of the control valve  175 . The control valve  175  moves the boom spool according to the pilot pressure to cause hydraulic oil to flow into the boom cylinder  7 . The boom spool displacement sensor S 16  detects the displacement of the boom spool and feeds the detection result back to the boom spool displacement amount calculating part F 12  of the controller  30 . The boom cylinder  7  extends or retracts as hydraulic oil flows in to raise or lower the boom  4 . The boom angle sensor S 1  detects the rotation angle of the rising or lowering boom  4  and feeds the detection result back to the boom angle calculating part F 13  of the controller  30 . The boom angle calculating part F 13  feeds the calculated boom angle α back to the current bucket position calculating part F 103 . 
     The arm current command generating part F 21  outputs an arm current command to the arm proportional valve  31 A. 
     The arm spool displacement amount calculating part F 22  calculates the amount of displacement of the arm spool of the control valve  176  corresponding to the arm cylinder  8  based on the output of an arm spool displacement sensor S 17 . 
     The arm angle calculating part F 23  calculates the arm angle β based on the output of the arm angle sensor S 2 . The arm current command generating part F 21  basically generates an arm current command for the arm proportional valve  31 A such that the difference between the arm command value β* generated by the command value calculating part F 111  and the arm angle β calculated by the arm angle calculating part F 23  is zero. In this case, the arm current command generating part F 21  adjusts the arm current command to eliminate the difference between the intended amount of the displacement of the arm spool derived from the arm current command and the amount of the displacement of the arm spool calculated by the arm spool displacement amount calculating part F 22 . The arm current command generating part F 21  outputs the adjusted arm current command to the arm proportional valve  31 A. 
     The arm proportional valve  31 A changes its opening area according to the arm current command and causes a pilot pressure commensurate with the magnitude of the arm current command to act on a pilot port of the control valve  176 . The control valve  176  moves the arm spool according to the pilot pressure to cause hydraulic oil to flow into the arm cylinder  8 . The arm spool displacement sensor S 17  detects the displacement of the arm spool and feeds the detection result back to the arm spool displacement amount calculating part F 22  of the controller  30 . The arm cylinder  8  extends or retracts as hydraulic oil flows in to close or open the arm  5 . The arm angle sensor S 2  detects the rotation angle of the closing or opening arm  5  and feeds the detection result back to the arm angle calculating part F 23  of the controller  30 . The arm angle calculating part F 23  feeds the calculated arm angle β back to the current bucket position calculating part F 103 . 
     The bucket current command generating part F 31  outputs a bucket current command to the bucket proportional valve  31 C. 
     The bucket spool displacement amount calculating part F 32  calculates the amount of displacement of the bucket spool of the control valve  174  corresponding to the bucket cylinder  9  based on the output of a bucket spool displacement sensor S 18 . 
     The bucket angle calculating part F 33  calculates the bucket angle γ based on the output of the bucket angle sensor S 3 . 
     The bucket current command generating part F 31  basically generates a bucket current command for the bucket proportional valve  31 C such that the difference between the bucket command value γ* generated by the command value calculating part F 111  and the bucket angle γ calculated by the bucket angle calculating part F 33  is zero. In this case, the bucket current command generating part F 31  adjusts the bucket current command to eliminate the difference between the intended amount of the displacement of the bucket spool derived from the bucket current command and the amount of the displacement of the bucket spool calculated by the bucket spool displacement amount calculating part F 32 . The bucket current command generating part F 31  outputs the adjusted bucket current command to the bucket proportional valve  31 C. 
     The bucket proportional valve  31 C changes its opening area according to the bucket current command and causes a pilot pressure commensurate with the magnitude of the bucket current command to act on a pilot port of the control valve  174 . The control valve  174  moves the bucket spool according to the pilot pressure to cause hydraulic oil to flow into the bucket cylinder  9 . The bucket spool displacement sensor S 18  detects the displacement of the bucket spool and feeds the detection result back to the bucket spool displacement amount calculating part F 32  of the controller  30 . The bucket cylinder  9  extends or retracts as hydraulic oil flows in to close or open the bucket  6 . The bucket angle sensor S 3  detects the rotation angle of the closing or opening bucket  6  and feeds the detection result back to the bucket angle calculating part F 33  of the controller  30 . The bucket angle calculating part F 33  feeds the calculated bucket angle γ back to the current bucket position calculating part F 103 . 
     The swing current command generating part F 41  outputs a swing current command to the swing proportional valve  31 D. 
     The swing spool displacement amount calculating part F 42  calculates the amount of displacement of the swing spool of the control valve  173  corresponding to the swing hydraulic motor  2 A based on the output of a swing spool displacement sensor S 19 . 
     The swing angle calculating part F 43  calculates the swing angle δ based on the output of the swing state sensor S 5 . 
     The swing current command generating part F 41  basically generates a swing current command for the swing proportional valve  31 D such that the difference between the swing command value δ* generated by the command value calculating part F 111  and the swing angle δ calculated by the swing angle calculating part F 43  is zero. In this case, the swing current command generating part F 41  adjusts the swing current command to eliminate the difference between the intended amount of the displacement of the swing spool derived from the swing current command and the amount of the displacement of the swing spool calculated by the swing spool displacement amount calculating part F 42 . The swing current command generating part F 41  outputs the adjusted swing current command to the swing proportional valve  31 D. 
     The swing proportional valve  31 D changes its opening area according to the swing current command and causes a pilot pressure commensurate with the magnitude of the swing current command to act on a pilot port of the control valve  173 . The control valve  173  moves the swing spool according to the pilot pressure to cause hydraulic oil to flow into the swing hydraulic motor  2 A. The swing spool displacement sensor S 19  detects the displacement of the swing spool and feeds the detection result back to the swing spool displacement amount calculating part F 42  of the controller  30 . The swing hydraulic motor  2 A rotates as hydraulic oil flows in to swing the upper swing structure  3 . The swing state sensor S 5  detects the swing angle of the swinging upper swing structure  3  and feeds the detection result back to the swing angle calculating part F 43  of the controller  30 . The swing angle calculating part F 43  feeds the calculated swing angle δ back to the current bucket position calculating part F 103 . 
     Furthermore, for the left crawler  1 CL and the right crawler  1 CR of the lower traveling structure  1  as well, the same feedback loop as for other driven elements (operating elements) such as the boom  4 , the arm  5 , the bucket  6 , and the upper swing structure  3  is provided. That is, a feedback loop based on the input of the right travel command value ε 1 * and the left travel command value ε 2 * generated by the command value calculating part F 111  is configured. From this feedback loop, the right drive wheel rotation angle ε 1  and the left drive wheel rotation angle ε 2  representing the rotational positions (rotation angles) of the drive wheels of the right crawler  1 CR and the left crawler  1 CL are fed back to the current bucket position calculating part F 103 . 
     Thus, the controller  30  configures a three-stage feedback loop for each driven element (operating element). That is, the controller  30  configures a feedback loop associated with the amount of displacement of the spool of a control valve in the control valve  17 , a feedback loop associated with the rotation angle of a driven element (operating element), and a feedback loop associated with the position of a working part (for example, the position of the teeth tips) of the bucket  6 . Thus, the controller  30  can control the movement of a working part of the bucket  6  with high accuracy in the automatic operation function based on remote control performed by a remote operator. Furthermore, the controller  30  can control the movement of the shovel  100  with high accuracy in the gesture operation function based on a recognition target gesture made by a worker around the shovel  100 . 
     &lt;Fourth Example of Gesture Operation Function of Shovel&gt; 
     A configuration associated with the gesture operation function is described with reference to  FIG. 13 . The following description focuses on differences from the above-described first through third examples, and a description of the same or corresponding portion may be omitted. 
       FIG. 13  is a functional block diagram illustrating a fourth example of the configuration associated with the gesture operation function of the shovel  100 . 
     The functional configuration of causing hydraulic actuators of the shovel  100  to operate based on the output of a command value calculating part F 214  in  FIG. 13  is equal to a configuration of  FIGS. 12A and 12B  in which the reference numerals “F 103 ” and “F 111 ” are read as “F 201 ” and “F 214 ”, respectively. Therefore, a graphical representation and a description thereof is omitted. 
     According to this example, the shovel  100  has a machine learning function and an autonomous operation function for autonomously determining its operation details for achieving the intended state of a work site. 
     As illustrated in  FIG. 13 , the controller  30  includes a current bucket position calculating part F 201 , a current surroundings information obtaining part F 202 , an intended state information obtaining part F 203 , a comparison part F 204 , a work start determining part F 205 , a procedure and work setup part F 206 , an operation details determining part F 207 , an operation command generating part F 208 , the worker recognition part F 209 , the gesture recognition part F 210 , an operation command generating part F 211 , a switch part F 212 , the operation restricting part F 213 , and the command value calculating part F 214 . These functions may be implemented by desired hardware or a combination of desired hardware and software. The controller  30  implements these functions by executing, on the CPU, various programs installed in the secondary storage, for example. 
     A description of the current bucket position calculating part F 201  and the current surroundings information obtaining part F 202 , which are equal in function to the current bucket position calculating part F 103  and the current surroundings information obtaining part F 101 , respectively, of the above-described third example, is omitted. 
     The intended state information obtaining part F 203  obtains information on the intended state of a work site (hereinafter “intended state information”) received from the management apparatus  200  through the communications device T 1 . 
     The comparison part F 204  compares the current surroundings of the shovel  100  corresponding to the current surroundings information and the intended state of the work site corresponding to the intended state information, and outputs information on their difference (hereinafter “difference information”) to a learning part F 300 . 
     The work start determining part F 205  determines the start of work in response to a command received from the management apparatus  200  through the communications device T 1 . 
     The procedure and work setup part F 206  (an example of a setup part) sets up a procedure at a work site and the details of work included in the procedure in response to a command received from the management apparatus  200  through the communications device T 1 . The set-up procedure and work details are input to the learning part F 300  and the operation details determining part F 207 . 
     The operation details determining part F 207  (an example of a determination part) autonomously determines operation details that are in line with the procedure and work details set up by the procedure and work setup part F 206  in response to a command from the learning part F 300 . Furthermore, the determined operation details are input to the learning part F 300  and the operation command generating part F 208 . 
     The operation command generating part F 208  generates an operation command for the shovel  100  (for example, an operation command for the bucket  6 ) in accordance with a command from the learning part F 300 , the operation details determined by the operation details determining part F 207 , and the current position of a working part (for example, the teeth tips, the back surface, or the like) of the bucket  6  (current bucket position). The operation command generating part F 208  may generate, for example, a speed command for the bucket  6 . The generated operation command is input to the learning part F 300  and a switch part F 212 . 
     A description of the worker recognition part F 209 , the gesture recognition part F 210  (an example of a recognition part), and the operation command generating part F 211 , which are equal in function to the worker recognition part F 106 , the gesture recognition part F 107 , and the operation command generating part F 108 , respectively, of the above-described third example, is omitted. 
     The switch part F 212  (an example of a control part) switches an operation command for the shovel  100  to be input to the operation restricting part F 213  between the output of the operation command generating part F 208  based on the autonomous operation function of the shovel  100  and the output of the operation command generating part F 211  based on the gesture operation function of the shovel  100 . Specifically, normally, that is, when the gesture recognition part F 210  recognizes no recognition target gesture of a worker and the operation command generating part F 211  outputs no operation command, the switch part F 212  outputs an operation command generated by the operation command generating part F 208  to the operation restricting part F 213 . When the gesture recognition part F 210  recognizes a recognition target gesture of a worker and the operation command generating part F 211  outputs an operation command, the switch part F 212  inputs the operation command of the operation command generating part F 211  to the operation restricting part F 213 . 
     A description of the operation restricting part F 213  and the command value calculating part F 214 , which are equal in function to the operation restricting part F 110  and the command value calculating part F 111  of the above-described third example, is omitted. 
     The learning part F 300  implements the machine learning function and the operation assist function of the shovel  100 . Specifically, the learning part F 300  implements the autonomous operation function of the shovel  100  by outputting a command to the procedure and work setup part F 206 , the operation details determining part F 207 , and the operation command generating part F 208  based on the output of a state detector S 20 , using a trained model received from the management apparatus  200  through the communications device T 1 . 
     The state detector S 20  outputs information detected with respect to various states of the shovel  100 . The detected information output from the state detector S 20  is fed into the controller  30 . 
     For example, the state detector S 20  detects the pose state or operating state of the attachment. Specifically, the state detector S 20  may detect the boom angle, the arm angle, and the bucket angle. That is, the state detector S 20  may include the boom angle sensor S 1 , the arm angle sensor S 2 , and the bucket angle sensor S 3  that detects the boom angle, the arm angle, and the bucket angle, respectively. Furthermore, the state detector S 20  may detect the accelerations, the angular accelerations, etc., of the boom  4 , the arm  5 , and the bucket  6 . In this case, the state detector S 20  may include, for example, a rotary encoder, an acceleration sensor, an angular acceleration sensor, a six-axis sensor, an IMU or the like attached to each of the boom  4 , the arm  5 , and the bucket  6 . Furthermore, the state detector S 20  may include cylinder sensors that detect the cylinder positions, speeds, accelerations, etc., of the boom cylinder  7 , the arm cylinder  8 , and the bucket cylinder  9  that drive the boom  4 , the arm  5 , and the bucket  6 , respectively. 
     Furthermore, for example, the state detector S 20  detects the pose state of the machine body, namely, the lower traveling structure  1  and the upper swing structure  3 . Specifically, the state detector S 20  may detect the tilt state of the machine body relative to a horizontal plane. That is, the state detector S 20  may include the machine body tilt sensor S 4 . 
     Furthermore, for example, the state detector S 20  detects the swing state of the upper swing structure  3 . Specifically, the state detector S 20  detects the swing angular velocity and the swing angle of the upper swing structure  3 . In this case, the state detector S 20  may include, for example, a gyroscope, a resolver, a rotary encoder or the like that is attached to the upper swing structure  3 . That is, the state detector S 20  may include the swing state sensor S 5 . 
     Furthermore, for example, the state detector S 20  detects the state of action of a force acting on the shovel  100  through the attachment. Specifically, the state detector S 20  may detect the working pressures (cylinder pressures) of hydraulic actuators. In this case, the state detector S 20  may include pressure sensors that detect the pressures of the rod-side oil chamber and the bottom-side oil chamber of each of the boom cylinder  7 , the arm cylinder  8 , and the bucket cylinder  9 . 
     Furthermore, for example, the state detector S 20  may include a sensor that detects the displacement of the spool of a control valve in the control valve  17 . Specifically, the state detector S 20  may include the boom spool displacement sensor S 16  that detects the displacement of the boom spool of the control valve  175 . Furthermore, the state detector S 20  may include the arm spool displacement sensor S 17  that detects the displacement of the arm spool of the control valve  176 . Furthermore, the state detector S 20  may include the bucket spool displacement sensor S 18  that detects the displacement of the bucket spool of the control valve  174 . Furthermore, the state detector S 20  may include the swing spool displacement sensor S 19  that detects the displacement of the swing spool of the control valve  173 . Furthermore, the state detector S 20  may include a right travel spool displacement sensor and a left travel spool displacement sensor that detect the displacements of the right travel spool and the left travel spool of a right travel control valve and a left travel control valve, respectively. 
     Furthermore, for example, the state detector S 20  detects the position of the shovel  100 , the orientation of the upper swing structure  3 , etc. In this case, the state detector S 20  may include, for example, a GNSS (Global Navigation Satellite System) compass, a GNSS sensor, a direction sensor or the like attached to the upper swing structure  3 . 
     The learning part F 300  may perform reinforcement learning based on actual performance information obtained during the actual work and procedure, while causing its machine (the shovel  100 ) to execute the actual work and procedure. This causes the trained model to be additionally trained, thus making it possible to improve performance with respect to the autonomous operation function of the shovel  100 . The actual performance information includes actual performance information regarding the procedure, work, and operation of the shovel  100  fed back from the procedure and work setup part F 206 , the operation details determining part F 207 , and the operation command generating part F 208 . Furthermore, the actual performance information includes actual performance information regarding an environmental condition such as the current surroundings of the shovel  100  input from the current surroundings information obtaining part F 202  through the comparison part F 204 . Furthermore, the actual performance information includes actual performance information regarding the results of the procedure, work, and operation of the shovel  100 , such as the difference information input from the comparison part F 204 . This enables the learning part F 300  to generate, from the actual performance information, such a work pattern and a procedure pattern as to relatively increase a predetermined target index (an optimum work pattern and an optimum procedure pattern) with respect to each work type or (type of) combination of work details and each environmental condition. The learning part F 300  outputs a command corresponding to the optimum work pattern and the optimum procedure pattern under a current environmental condition (for example, a current terrain shape) to the procedure and work setup part F 206 , the operation details determining part F 207 , and the operation command generating part F 208  based on the difference information input from the comparison part F 204 . This enables the controller  30  (the operation command generating part F 208 ) to autonomously control its machine (the shovel  100 ) based on the optimum work pattern and the optimum procedure pattern. 
     Instead of or in addition to the shovel  100 , the management apparatus  200  may additionally train the trained model. In this case, the trained model subjected to additional training (hereinafter “additionally trained model”) is transmitted to the shovel  100  with its timing being predetermined, so that the trained model of the shovel  100  is updated to the additionally trained model. Furthermore, the trained model additionally trained in the shovel  100  may be transmitted to the management apparatus  200  with its timing being predetermined. This enables the management apparatus  200  to apply the results of the machine learning of the shovel  100  to other shovels  100  or further perform additional learning from the results of the machine learning of the shovel  100 . 
     Thus, when a recognition target gesture made by a worker is recognized in an area surrounding the shovel  100 , the controller  30  can give priority to the gesture operation function over the autonomous operation function of the shovel  100  by the action of the switch part F 212 . In other words, the controller  30  can give priority to the determination (the details of a recognition target gesture) of a worker around the shovel  100  who is likely to be more familiar with a work site situation over the determination of its machine. Thus, even when a situation where the learning part F 300  is prevented from making an appropriate determination occurs at a work site or in the shovel  100  or an abnormality occurs in the autonomous operation function, it is possible to stop the operation of the shovel  100  at the discretion of the worker at the work site. Therefore, it is possible to improve the safety of the shovel  100  in the case of the autonomous operation of the shovel  100 . 
     VARIATIONS AND MODIFICATIONS 
     An embodiment of the present invention is described in detail above. The present invention, however, is not limited to such a particular embodiment, and variations and modifications may be made without departing from the scope of the subject matter of the present invention described in the claims. 
     For example, according to the above-described embodiment, the shovel  100  is configured such that various operating elements such as the lower traveling structure  1 , the upper swing structure  3 , the boom  4 , the arm  5 , and the bucket  6  are all hydraulically driven. The shovel  100 , however, may also be configured such that one or more of them are electrically driven. That is, the configuration, etc., disclosed in the above-described embodiment may also be applied to hybrid shovels, electric shovels, etc.