Patent Publication Number: US-11377815-B2

Title: Construction machine

Description:
TECHNICAL FIELD 
     The present invention relates to a construction machine such as a hydraulic excavator. 
     BACKGROUND ART 
     As shown in, for example, Patent Documents 1 and 2, there is known a technique as to a construction machine including a boom, an arm and a bucket, in which a hydraulic cylinder selected from a boom cylinder, an arm cylinder and a bucket cylinder is operated so as to oscillate the bucket during excavation work to thereby reduce an excavation resistance (a resistance that the bucket entering the ground receives from the ground). 
     However, each of the boom cylinder, the arm cylinder, and the bucket cylinder as described above is generally a hydraulic cylinder having a relatively large capacity, which makes it difficult to oscillate the bucket quickly (that is, in a short cycle). 
     Besides, since the boom cylinder, the arm cylinder, and the bucket cylinder normally move the boom, the arm, and the bucket rotationally in the pitch direction, respectively, the oscillation of the bucket made by the operation control of the hydraulic cylinders is a rotational oscillation in the pitch direction, which is likely to cause undulations and irregularities in the construction surface formed by excavation work. 
     In addition, for example, during ground leveling work for smoothing the ground, oscillating the bucket by operation control of any of a boom cylinder, an arm cylinder and a bucket cylinder to reduce movement resistance of the bucket makes it difficult to smooth the ground well. 
     CITATION LIST 
     Patent Literature 
     Patent Literature 1: JP H08-165678 A 
     Patent Literature 2: JP H02-024424 A 
     SUMMARY OF INVENTION 
     An object of the present invention is to provide a construction machine capable of reducing a resistance that a bucket receives from the ground and improving smoothness of a construction surface. 
     Provided is a construction machine comprising a machine body, a working device mounted on the machine body, and a control device for controlling a motion of the working device, wherein: the working device includes a working device body having a proximal end portion connected to the machine body and a distal end opposite thereto, a bucket attached to the distal end of the working device body so as to be capable of performing a first rotational motion and a second rotational motion relative to the distal end of the working device body, and a plurality of bucket actuators that actuate the bucket relatively to the working device body; the first rotational motion is a pitch motion that is a rotational motion about a bucket lateral axis parallel to a width direction of the bucket; the second rotational motion is a rotational motion about an axis in a direction orthogonal to the bucket lateral axis; the plurality of bucket actuators include a first bucket actuator that makes the bucket perform the first rotational motion and a second bucket actuator that makes the bucket perform the second rotational motion; and the control device is configured to control the second bucket actuator so as to make the second bucket actuator periodically oscillate the bucket based on the second rotational motion in a state where the bucket is in pressure contact with the ground. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a side view showing the entire hydraulic excavator which is a construction machine according to a first embodiment of the present invention. 
         FIG. 2  is a side view showing a main part including a bucket according to the first embodiment. 
         FIG. 3  is a block diagram showing a functional configuration of a control device of the construction machine according to the first embodiment. 
         FIG. 4  is a graph showing temporal change in the yaw angle of the bucket according to the first embodiment. 
         FIG. 5  is a bottom view showing a yaw oscillation of the bucket according to the first embodiment. 
         FIG. 6  is a side view showing the main part including the bucket according to the first embodiment. 
         FIG. 7  is a side view showing a main part including a bucket of a construction machine according to the second embodiment of this invention. 
         FIG. 8  is a block diagram showing a functional configuration of a control device of the construction machine according to the second embodiment. 
         FIG. 9  is a graph showing temporal change in the tilt angle of the bucket according to the second embodiment. 
         FIG. 10  is a rear view showing the tilt oscillation of the bucket according to the second embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     A first embodiment of the present invention will be described below with reference to  FIGS. 1 to 6 .  FIG. 1  shows a construction machine  1  according to the embodiment. The construction machine  1  is, for example, a hydraulic excavator. The construction machine  1  includes a crawler-type travelling body  2 , a slewing body  3  as a machine body mounted on the travelling body  2  so as to be capable of slewing, and a working device  4  attached to the slewing body  3 . The travelling motion of the travelling body  2  and the slewing motion of the slewing body  3  are generated by a not-graphically-shown hydraulic motor. 
     The slewing body  3  includes a cab  3   a  located in the front portion of the slewing body  3  and a machine room  3   b  located in the rear portion. The machine room  3   b  houses a not-graphically-shown engine and various hydraulic devices (a hydraulic pump, a direction selector valve, etc.). 
     The working device  4  includes a boom  10 , an arm  20 , a bucket  30 , and a plurality of hydraulic cylinders. In this embodiment, the boom  10  and the arm  20  constitute a working device body. The boom  10  has a proximal end portion and a distal end portion opposite thereto. The proximal end portion corresponds to the proximal end portion of the working device body, being connected to the slewing body  3  in a posture where the boom  10  extends from an appropriate position of the slewing body  3 , for example, a position sideward of the cab  3   a . The arm  20  has a proximal end portion connected to the distal end portion of the boom  10  in such a posture that the arm  20  extends beyond the distal end portion of the boom  10  and a distal end portion opposite thereto. The bucket  30  is attached to the distal end of the arm  20  as the distal end of the working device body. The plurality of hydraulic cylinders include a boom cylinder  12 , an arm cylinder  22 , and a bucket cylinder  32 . 
     The boom  10  is pivotally supported by the slewing body  3  through a support shaft  11  so as to be capable of performing a pitch motion relative to the slewing body  3 . In this embodiment, the pitch motion is a rotational motion around the axis lateral of the slewing body  3 . The boom  10  is connected to the slewing body  3  through the boom cylinder  12  which is a hydraulic cylinder for the boom. The boom cylinder  12  expands and contracts so as to make the boom  10  perform a rotational motion around the axis of the support shaft  11 , namely, the pitch motion. 
     The arm  20  is attached to the distal end of the boom  10  through a support shaft  21  so as to be capable of performing the pitch motion, that is, a rotational motion around the axis lateral of the stewing body  3 , relative to the boom  10 . The arm  20  is connected to the boom  10  via the arm cylinder  22  which is a hydraulic cylinder for the arm. The arm cylinder  22  expands and contracts so as to make the arm  20  perform the pitch motion around the axis of the support shaft  21 . 
     The bucket  30  is attached to the distal end portion of the arm  20 , which portion corresponds to the distal end portion of the working device body, so as to be capable of performing both of a first rotational motion relative to the arm  20  and a second rotational motion. The first rotational motion is a pitch motion, that is, the rotational motion about a bucket lateral axis parallel to the width direction of the bucket  30 . The second rotational motion is a rotational motion about an axis orthogonal to the bucket lateral axis, namely, a yaw motion in the first embodiment as described later in detail. 
     As shown in  FIG. 2 , the bucket  30  includes a plurality of claw portions  30   a  that constitute a tip portion of the bucket  30 , a bottom portion  30   b , and a bucket-side attachment member  30   c . The plurality of claw portions  30   a  project in the same direction from the distal edge portion of the open end of the bucket  30 , that is, the distal end portion of a bucket body of the bucket  30 , the bucket body serving as a portion to accommodate soil. The bucket-side attachment member  30   c  forms a proximal end portion of the bucket  30 , that is, an end portion opposite to the plurality of claw portions  30   a , being attached to the arm  20  through an arm-side attachment member  33 . 
     The arm-side attachment member  33  is pivotally supported by the distal end of the arm  20  through a support shaft  31  so as to be capable of performing the first rotational motion, namely, the pitch motion, relative to the arm  20 , and connected to the arm  20  through the first link arm  34 A and the second link arm  34 B. The first and second link arms  34 A,  34 B have respective one ends that are connected to each other through a pin  34 C so as to be capable of relative and rotational movement and the other ends opposite to the one ends. The other end of the first link arm  34 A is pivotally supported by the arm-side attachment member  33 , and the other end of the second link arm  34 B is pivotally supported by the arm  20 . 
     The bucket cylinder  32  is a hydraulic cylinder for bucket, corresponding to the first bucket actuator according to the present invention, that is, an actuator that makes the bucket  30  perform the pitch motion relative to the arm  20 . Specifically, the bucket cylinder  32  has a head-side end (an upper end in  FIG. 1 ) and a rod-side end (a lower end in  FIG. 1 ) opposite thereto. The head-side end portion is connected to the arm  20  through a pin  23  so as to be capable of rotational movement, and the rod-side end portion is connected to the one end portions of the first and second link arms  34 A,  34 B through the pin  34 C so as to be capable of rotational movement. The bucket cylinder  32  expands and contracts so as to make the arm-side attachment member  33  and the bucket  30  connected to the arm-side attachment member  33  perform the pitch motion around the axis of the support shaft  31 . 
     The bucket-side attachment member  30   c  is supported by the arm-side attachment member  33  so as to be capable of performing the second rotational motion relative to the arm-side attachment member  33  and the arm  20 , namely, a yaw motion in this embodiment, specifically, the rotational motion about the yaw axis C 1  shown in  FIG. 2 . The yaw axis C 1  extends in a direction orthogonal to a ground contact wall surface  30   f  which is a wall surface from the bottom portion  30   b  of the bucket  30  to the plurality of claw portions  30   a  at the distal end (including a direction substantially orthogonal to the ground contact wall surface  30   f ), that is, an axis extending in a direction parallel to the normal direction of the ground contact wall surface  30   f  (including a direction substantially parallel to the normal direction), being an axis extending in a direction orthogonal to the axis of the support shaft  31 , which is the axis of the first rotational motion of the arm-side attachment member  33 , namely, the bucket lateral axis (including a direction substantially orthogonal to the bucket lateral axis). 
     The working device  4  further includes a bucket rotating motor  35  formed of a hydraulic motor. The bucket rotating motor  35  corresponds to a second bucket actuator that makes the bucket  30  perform the second rotational motion, namely, the yaw motion. The bucket rotating motor  35  includes a motor main body fixed to the arm-side attachment member  33  and an output shaft connected to the bucket-side attachment member  30   c . The motor main body operates to rotate the output shaft to thereby make the bucket  30  including the bucket-side attachment member  30   c  perform the yaw motion relative to the arm-side attachment member  33  and the arm  20  connected thereto, the yaw motion being the second rotational motion, that is, a rotational motion around the yaw axis C 1 . 
     The yaw actuator (the second bucket actuator referred to in the present invention) that makes the bucket  30  perform the second rotational motion, namely, the yaw motion, relative to the arm  20  is not limited to the bucket rotating motor  35 . The yaw actuator may be, for example, a hydraulic cylinder that moves the bucket-side attachment member  30   c  rotationally around the yaw axis C 1  through a linear/rotational motion conversion mechanism such as a crank arm. Alternatively, the yaw actuator may be, for example, an electric motor. 
     The construction machine  1  includes a controller  60 , a proportional valve group  65 , and a control valve unit  70  as shown in  FIG. 3 . These function as a control device that controls the operation of the working device  4 , specifically making it possible to carry out an automatic operation of the bucket  30  for excavation work of excavating the ground or ground leveling work of leveling the ground. 
     The control valve unit  70  includes direction selector valves  71 ,  72 ,  73 ,  74 , which are provided in hydraulic oil supply passages for respective actuators of the boom cylinder  12 , the arm cylinder  22 , the bucket cylinder  32 , and the bucket rotating motor  35 , respectively, and opened and closed so as to control the supply of hydraulic oil from a not-graphically-shown hydraulic pump to the actuator. Each of the direction selector valves  71  to  74  is a pilot operated hydraulic selector valve having a pair of pilot ports, being configured to be opened, by a pilot pressure that is input to one of the pair of pilot ports, in the direction corresponding to the pilot port to which the pilot pressure is input and at the opening degree corresponding to the magnitude of the pilot pressure. 
     The proportional valve group  65  includes a plurality of proportional valves  66  that correspond to the direction selector valves  71 ,  72 ,  73 ,  74 , respectively. Each of the plurality of proportional valves  66  is formed of an electromagnetic valve, being interposed between the corresponding direction selector valve of the direction selector valves  71  to  74  and a not-graphically-shown pilot hydraulic pressure source, and configured to be opened at the opening degree corresponding to a command signal input from the controller  60  to thereby change the magnitude of the pilot pressure to be input to the direction selector valve. 
     The controller  60  inputs an appropriate command signal to each of the plurality of proportional valves  66  to operate the direction selector valves  71  to  74  through the plurality of proportional valves  66 , respectively, thereby controlling respective operations of the boom cylinder  12 , the arm cylinder  22 , the bucket cylinder  32 , and the bucket rotating motor  35 . 
     Since each of the direction selector valves  71 ,  72 ,  73 ,  74  has the pair of pilot ports, the plurality of proportional valves  66  are provided for respective pairs of pilot ports of the direction selector valves  71 ,  72 ,  73 ,  74 . In addition to the direction selector valves  71  to  74 , the control valve unit  70  may include a direction selector valve connected to a hydraulic motor that makes the travelling body  2  perform a travelling motion or a direction selector valve connected to a hydraulic motor that makes the slewing body  3  perform a slewing motion. Similarly, in addition to the plurality of proportional valves  66 , the proportional valve group  65  may include a proportional valve for controlling the pilot pressure of the direction selector valve connected to each of the above hydraulic motors. 
     The construction machine  1  further includes: a GNSS receiver  50  (GNNS: Global Navigation Satellite System) for detecting the existence position of the construction machine  1 ; a plurality of posture sensors  51  for detecting the posture state of the working device  4 ; an inclination sensor  52  for detecting the inclination angle of the stewing body  3  (machine body); a plurality of actuator operation sensors  53  for detecting respective states of the operations for a plurality of hydraulic actuators including the boom cylinder  12 , the arm cylinder  22 , the bucket cylinder  32 , and the bucket rotating motor  35 ; a bucket motion setting operation unit  54  to which a setting operation related to the second rotational motion (yaw motion) of the bucket  30  is applied; and an automatic operation switch  55  for setting the necessity of automatic operation of the bucket  30  for excavation work or ground leveling work (for switching ON/OFF of the automatic operation). 
     The plurality of posture sensors  51  includes a plurality of angle sensors: for example, an angle sensor that detects a pitch angle that is a rotation angle of the boom  10  relative to the slewing body  3  in the direction of the pitching motion (the direction of the rotation around the axis of the support shaft  11 ), an angle sensor that detects a pitch angle that is a rotation angle of the arm  20  relative to the boom  10  in the direction of the pitch motion (the direction of the rotation around the axis of the support shaft  21 ), an angle sensor that detects the pitch angle θp of the bucket  30  to the arm  20 , that is, the rotation angle of the bucket  30  in the pitch direction, which is the direction of pitch motion of the bucket  30  (the direction of rotation around the axis of the support shaft  31 ), and an angle sensor that detects the yaw angle θy of the bucket  30  to the arm  20 , that is, the rotation angle of the bucket  30  in a yaw direction, which is the direction of the yaw motion of the bucket  30  (the direction of the first rotation motion around the yaw axis C 1 ). Each of the plurality of angle sensors can be formed of, for example, a rotary encoder, a resolver, or the like. 
     The plurality of posture sensors  51  are not limited to the plurality of angle sensors that detect respective pitch angles of the boom  10 , the arm  20 , and the bucket  30 . The plurality of posture sensors  51  may include, for example, a plurality of stroke sensors that detect respective stroke displacements of the boom cylinder  12 , the arm cylinder  22 , and the bucket cylinder  32 , respectively. 
     The inclination sensor  52  includes, for example, an inertial sensor having respective functions of an acceleration sensor and an angular velocity sensor. Based on the detection signal of the inertial sensor can be specified the inclination angle of the slewing body  3  through a strapdown method or the like. 
     The plurality of actuator operation sensors  53  include, for example, a plurality of pilot pressure sensors. The plurality of pilot pressure sensors are formed of respective pressure sensors that detect respective pilot pressures applied to the pair of pilot ports of the direction selector valves  71 ,  72 ,  73 ,  74 . 
     The bucket motion setting operation unit  54  and the automatic operation switch  55  are disposed in the cab  3   a . In the present embodiment, the bucket motion setting operation unit  54  is configured to allow a plurality of setting operations to be applied to the operation unit  54  during excavation work or ground leveling work. The plurality of setting operations are with respect to, for example, the necessity of a yaw oscillation that is the oscillation of the bucket  30  in the yaw direction (the periodically rotational motion of cyclically by a predetermined angle alternately in the forward rotational direction and the reverse rotational direction around the yaw axis C 1 , namely, the oscillation based on the second rotational motion), the cycle Ty (or frequency) of the yaw oscillation, and the amplitude Ay of the yaw oscillation (maximum rotation angle in the forward rotation direction and the reverse rotation direction). The cycle Ty (or frequency) of the yaw oscillation and the amplitude Ay of the yaw oscillation can be set within respective predetermined ranges. 
     The bucket motion setting operation unit  54  may receive not only an operation for setting the operation of the bucket  30  but also various other setting operations for the construction machine  1 . Besides, the bucket motion setting operation unit  54  and the automatic operation switch  55  may be configured to be integral with each other. 
     The controller  60  is formed of an electronic circuit unit including a microcomputer, a memory, an interface circuit and the like. To the controller  60  are input a GNSS signal (a detection signal as to the existence position of the construction machine  1 ) received by the GNSS receiver  50 , respective detection signals generated by the posture sensor  51 , the inclination sensor  52 , and the actuator operation sensors  53 , and respective operation signals generated by the bucket motion setting operation unit  54  and the automatic operation switch  55 . 
     In the controller  60 , three-dimensional map data is stored in advance or downloaded from an external server or the like. The map data includes information about the actual topography of the work site where the work by the construction machine  1  is performed, and information about the target topography to be achieved by the work. 
     The controller  60  has a function of generating an appropriate command signal for each of the plurality of proportional valves  66  and inputting it to the proportional valve  66  during excavation work or ground leveling work to operate the direction selector valves  71  to  74  and thereby controlling respective operations of the boom cylinder  12 , the arm cylinder  22 , the bucket cylinder  32 , and the bucket rotating motor  35 . This function is achieved by at least one of a hardware configuration and a program (software configuration) installed in the controller  60 . 
     Next will be described actions performed by the construction machine  1  according to the first embodiment during excavation work and ground leveling work. The construction machine  1  of the present embodiment is able to perform excavation work or ground leveling work by the bucket  30  while oscillating the bucket  30  based on the second rotational motion, namely, the yaw oscillation. 
     The excavation work is performed, for example, as follows. The operator of the construction machine  1  applies an operation for setting the cycle (or frequency) and the amplitude of the yaw oscillation of the bucket  30  to the bucket motion setting operation unit  54 , and further an operation for setting the execution of the yaw oscillation (the operation for turning on the yaw oscillation). 
     Furthermore, the operator applies an appropriate travelling operation to a not-graphically-shown travelling operation lever to thereby move the construction machine  1  to a predetermined work place. Then, at the work place, the operator applies an appropriate work operation to a not-graphically-shown work operation lever for actuating the working device  4  to thereby actuate the boom  10  and the arm  20  to move the bucket  30  to the start position of the excavation work. 
     Next, the operator applies an ON operation to the automatic operation switch  55 , and further applies a predetermined operation to a predetermined operation lever for starting the actual movement of the bucket  30  (for example, an arm operation lever for moving the arm  20 ). With this operation, the controller  60  determines a target movement path of the bucket  30  based on the current position of the construction machine  1  that is grasped from the GNSS signal input from the GNSS receiver  50 , the inclination angle of the slewing body  3  that is grasped from the detection signal input from the inclination sensor  52 , and work information stored in advance, that is, information on the actual topography of the work site and information on the target topography by excavation work (information on the position and orientation of the target construction surface St indicated by the two-dot chain line in  FIG. 2 ), and further determine the trajectory of the target posture of the boom  10 , the arm  20 , and the bucket  30  (time-series pattern) respect to the pitch direction for realizing the target movement. 
     The target posture of the bucket  30  is determined, for example, so as to make a ground contact wall surface  30   f  (or the distal end portion of the claw portion  30   a ) follow the target construction surface St, as shown in  FIG. 2 , after the claw portion  30   a  of the bucket  30  bites into the ground, the ground contact wall surface  30   f  being a wall surface from the bottom portion  30   b  of the bucket  30  to the claw portion  30   a.    
     Besides, the controller  60  determines a target waveform pattern of the yaw angle (the rotation angle around the yaw axis C 1 ) θy (the pattern of temporal change in the target value of the yaw angle θy) so as to make the bucket  30  perform the yaw oscillation with the cycle and the amplitude set by the operation applied to the bucket motion setting operation unit  54 . The target waveform pattern is set to, for example, a triangular wave pattern illustrated in  FIG. 4 . The target waveform pattern is not limited to the triangular wave pattern, but may be a smooth curved pattern such as a sine wave pattern. 
     The yaw angle θy of the bucket  30  shown in  FIG. 4  is set so as to be zero in the state where the width direction of the bucket  30  (the direction in which the plurality of claw portions  30   a  are aligned in this embodiment) is coincident or substantially coincident with the direction of the bucket lateral axis (the axis of the support shaft  31  in this embodiment) that is the center axis of the first rotational motion, namely, the pitch motion, of the bucket  30  (that is, in the standard posture state of the bucket  30  with respect to the yaw direction). 
     The controller  60  inputs an appropriate command signal to the plurality of proportional valves  66  corresponding to the direction selector valves  71  to  73 , respectively, to operate the pilot pressure to be applied to each of the direction selector valves  71  to  73  so as to make respective actual postures of the boom  10 , the arm  20  and the bucket  30  with respect to the pitch direction follow the target posture, the actual postures being grasped from respective detection signals of the plurality of posture sensors  51 . Thus, the control of respective operations of the boom cylinder  12 , the arm cylinder  22 , and the bucket cylinder  32  is performed to make the actual postures of the boom  10 , the arm  20 , and the bucket  30  in the pitch direction follow the target posture. 
     Besides, the controller  60  inputs an appropriate command signal to the proportional valve  66  corresponding to the direction selector valve  74  to control the pilot pressure to be applied to the direction selector valve  74  so that the yaw angle θy of the bucket  30  grasped from the detection signals of the plurality of posture sensors  51  changes according to a preset target waveform pattern. This causes the actual yaw angle θy of the bucket  30  to change so as to follow the target waveform pattern. Thus, as shown in  FIG. 5 , the yaw oscillation of the bucket  30  is achieved such that the actual yaw angle of the bucket  30  changes alternately in the forward rotational direction and the reverse rotational direction at a constant amplitude and cycle. 
     Such control of the operation of the working device  4  allows a ground excavation work to be performed in which the bucket  30  is moved along the target movement path with the yaw oscillation of the bucket  30 . 
     The bucket rotating motor  35  for causing the yaw oscillation of the bucket  30  in the yaw oscillation is allowed to be relatively small. This makes it possible to make the bucket  30  perform the yaw oscillation at a relatively short cycle. This allows the number of repetitions of the yaw motion per unit movement amount of the bucket  30  during excavation work to be increased, thereby effectively reducing the resistance which the bucket  30  receives during its movement with pressure contact with the ground, specifically, with the plurality of claw portions  30   a  biting into the ground. 
     Furthermore, it is possible to form a smooth construction surface by moving the bucket  30  along the target construction surface St with the yaw oscillation thereof while constantly keeping at least one of the ground contact wall surface  30   f  and the distal ends of the plurality of claw portions  30   a  of the bucket  30  following the target construction surface St. 
     The ground leveling work is performed, for example, as follows. Similarly to the case of the excavation work, the operator of the construction machine  1  applies to the bucket motion setting operation unit  54  an operation of setting the cycle Ty (or frequency) and the amplitude Ay of the yaw oscillation of the bucket  30  and further an operation of turning on the yaw oscillation. Moreover, the operator applies an appropriate travelling operation to the travelling operation lever to move the construction machine  1  to a predetermined work place, and, at the work place, applies an appropriate operation lever to an operation lever for operating the working device  4  to thereby actuate the boom  10  and the arm  20  as the working device body to move the bucket  30  to the start position for the ground leveling work. 
     Next, the operator applies an ON operation to the automatic operation switch  55  and further applies a predetermined operation to a predetermined operation lever (for example, the arm operation lever) for starting the actual movement of the bucket  30 . In accordance with this operation, the controller  60  determines the target movement path of the bucket  30  and further determines a trajectory (time-series pattern) of the target posture of each of the boom  10 , the arm  20 , and the bucket  30  with respect to the pitch direction for realizing the target movement path, as in the case of the excavation work. 
     As shown in  FIG. 6 , the target movement path and the target posture of the bucket  30  are determined so as to make the ground contact wall surface  30   f , which is the wall surface of the bucket  30  from the bottom portion  30   b  to the plurality of claw portions  30   a , follow the target construction surface (target ground surface) St. 
     Besides, as in the case of excavation work, the controller  60  determines the target waveform pattern of the angle θy of the bucket  30  so as to make the bucket  30  perform the yaw oscillation at the cycle and the amplitude set by the operation applied to the bucket motion setting operation unit  54 . 
     As in the case of excavation work, the controller  60  inputs appropriate command signals to the proportional valves  66  corresponding to the direction selector valves  71  to  73 , respectively, to control respective operations of the boom cylinder  12 , the arm cylinder  22  and the bucket cylinder  32  so as to make respective actual postures of the boom  10 , the arm  20 , and the bucket  30  with respect to the pitch direction follow the target posture. 
     Besides, as in the case of excavation work, the controller  60  inputs appropriate command signals to the proportional valve  66  corresponding to the direction selector valve  74  to control the operation of the bucket rotating motor  35  so as to change the actual yaw angle θy of the bucket  30  according to the target waveform pattern, thereby making the bucket  30  perform the yaw oscillation corresponding to the target waveform pattern. 
     Conducting such control of the operation of the working device  4  enables the ground leveling work of moving the bucket  30  along the target movement path with the yaw oscillation of the bucket  30  to be achieved. 
     Also in the ground leveling work, as in the excavation work, the bucket  30  can be yaw-oscillated at a relatively short cycle, which effectively reduces the resistance which the bucket  30  receives when the bucket  30  is moved along the target movement path with pressure contact with the ground, specifically, while the ground contact wall surface  30   f  is pressed against the ground. 
     In addition, a smooth construction surface can be formed by moving the bucket  30  along the target movement path with the yaw oscillation of the bucket  30  while constantly keeping at least one of the ground contact wall surface  30   f  and the distal end portions of the plurality of claw portions  30   a  of the bucket  30  following the target construction surface St. 
     Next will be below described a second embodiment of the present invention with reference to  FIGS. 7 to 10 . Among the components included in the second embodiment, the same components as those included in the first embodiment will not be described. 
     As shown in  FIG. 7 , the bucket  30  according to the second embodiment includes a plurality of claw portions  30   a  and a bucket-side attachment member  30   c , as well as the bucket  30  according to the first embodiment, and is attached to the distal end of an arm  20  so as to be able to perform a pitch motion and a tilt motion relatively to the arm  20 . The tilt motion is a rotational motion around a tilt axis C 2  extending in a direction parallel to (including almost coincident with) the extending direction of the plurality of claw portions  30   a  in the bucket  30 , that is, the projecting direction of the plurality of claw portions  30   a . The tilt axis C 2  is preferably located immediately above the bucket  30  when viewed along the direction of the tilt axis C 2  as shown in  FIG. 10 . 
     In other words, the tilt axis C 2  according to the second embodiment is an axis parallel (including substantially parallel) to the ground contact wall surface  30   f  and orthogonal (including a substantially orthogonal) to the bucket lateral axis. The “tilt motion” according to the second embodiment, therefore, corresponds to a rotational motion around an axis in a direction orthogonal to the bucket lateral axis, namely, a second rotating operation according to the present invention. 
     Specifically, the bucket-side attachment member  30   c  includes a flat plate-shaped main body, to which a rotary shaft  30   d  is fixed. The rotary shaft  30   d  is fixed to the bucket-side attachment member  30   c  in a posture of extending in a direction parallel to the main body of the bucket-side attachment member  30   c , and the axis of the rotary shaft  30   d  is aligned with the tilt axis C 2 . On the other hand, similarly to the first embodiment, the arm-side attachment member  33  is attached to the arm  20  so as to be capable of performing the pitch motion, that is, a rotational motion around the axis in the left-right direction of the slewing body  3 , supporting the opposite ends of the rotary shaft  30   d  rotationally movably around the tilt axis C 2  through bearings  33   a  and  33   b , respectively. 
     The construction machine  1  according to the second embodiment includes, as a tilt actuator for making the bucket  30  perform the tilt motion, that is, a second bucket actuator for making the bucket  30  perform a second rotating operation, a pair of right and left bucket tilt cylinders  36  each being a hydraulic cylinder. The pair of right and left bucket tilt cylinders  36  are provided between the right and left side surfaces of the bucket  30  and the arm-side attachment member  33 . In the example shown in  FIG. 7 , each of the pair of bucket tilt cylinders  36  includes a rod-side end portion (lower end portion in the posture shown in  FIG. 7 ) connected to the right and left side surfaces of the bucket  30  and a head-side end portion (upper end portion in the posture shown in  FIG. 7 ) connected to the arm-side attachment member  33 .  FIG. 7  shows only the left bucket tilt cylinder  36 . The head-side end portion is an end portion opposite to the rod of the cylinder body of the bucket tilt cylinder  36 , and connected to the bracket  33   e  fixed to the arm-side attachment member  33  so as to be swingable about an axis in a direction parallel to the tilt axis C 2 . The rod-side end portion is a distal end portion of the rod, being connected to brackets  30   e  fixed to the right and left side surfaces of the bucket  30  so as to be swingable about an axis in a direction parallel to the tilt axis C 2 . 
     The bucket  30  according to the second embodiment, therefore, performs the first rotational motion around the axis of the support shaft  31 , namely, the pitch motion, in response to the expansion and contraction motions of the bucket cylinder  32 , similarly to the first embodiment, and the second tilting motion about the tilt axis C 2  in response to the expansion/contraction motion of the bucket tilt cylinder  36 , specifically, the expansion motion of one of the bucket tilt cylinders  36  and the contraction motion of the other of the bucket tilt cylinders  36 . 
     The tilt actuator that rotationally moves the bucket  30  in the tilt direction (the second bucket actuator according to the invention) is not limited to the pair of bucket tilt cylinders  36 . The tilt actuator may be, for example, a hydraulic motor or an electric motor that is connected to the rotary shaft  30   d  and rotates the rotary shaft  30   d  to thereby move the bucket  30  rotationally about the tilt axis C 2 . 
     Similarly to the first embodiment, the construction machine  1  according to the second embodiment includes a controller  60 , a proportional valve group  65 , and a control valve unit  70  as shown in  FIG. 8 , but the control valve unit  70  includes a pilot operated direction selector valves  75  connected to the pair of bucket tilt cylinders  36 , respectively, in place of the direction selector valve  74  connected to the bucket rotating motor  35  in the first embodiment, and the proportional valve group  65  includes a proportional valve  66  connected to a pair of pilot ports of the direction selector valve  75  in place of the proportional valve  66  connected to the pair of pilot ports of the direction selector valve  74  in the first embodiment. 
     Besides, while the construction machine  1  according to the second embodiment includes a plurality of posture sensors  51  similarly to the first embodiment, the plurality of posture sensors  51  includes an angle sensor that detects the tilt angle θt that is the rotation angle of the bucket  30  in the tilt direction, that is, the rotation angle around the tilt axis C 2 , in place of the angle sensor that detects the yaw angle θy of the bucket  30  in the first embodiment. 
     While the construction machine  1  according to the second embodiment includes the bucket motion setting operation unit  54  similarly to the first embodiment, the bucket motion setting operation unit  54  is configured to allow an operation to be applied to the bucket motion setting operation unit  54  during the excavation work by the construction machine  1 , the operation being an operation for setting necessity of tilt oscillation, which is the oscillation in the tilt direction of the bucket  30  (a cyclically rotational motion by a predetermined angle alternately in the forward rotation direction and the reverse rotation direction around the tilt axis C 2 , that is, an oscillation based on the second rotational motion), the cycle Tt (or frequency) of a tilt oscillation, and the tilt oscillation amplitude At (maximum rotation angle in the forward rotation direction and the reverse rotation direction). The cycle Tt (or frequency) and the amplitude At of the tilt oscillation can be set within respective predetermined ranges. 
     Next will be described an action performed by the construction machine  1  according to the second embodiment during excavation work. The construction machine  1  is capable of performing excavation work by the bucket  30  while oscillating the bucket  30  based on the second rotational motion thereof, namely, the tilt oscillation. 
     The excavation work is performed, for example, as follows. The operator of the construction machine  1  applies an operation for setting the cycle (or frequency) and amplitude of the tilt oscillation of the bucket  30  to the bucket motion setting operation unit  54 , and further applies an operation for setting the execution of the tilt oscillation (tilt oscillation ON operation). 
     Furthermore, the operator applies an appropriate travelling operation to a not-graphically-shown travelling operation lever to thereby move the construction machine  1  to a predetermined work place. Then, at the work place, the operator applies an appropriate work operation to a not-graphically-shown work operation lever for moving the working device  4  to thereby actuate the boom  10  and the arm  20  to move the bucket  30  to the start position of the excavation work. 
     Next, the operator applies an ON operation to the automatic operation switch  55 , and further applies a predetermined operation to a predetermined operation lever (for example, the arm operation lever) for starting the actual movement of the bucket  30 . In accordance with this operation, the controller  60  determines a target movement path of the bucket  30 , similarly to the controller  60  according to the first embodiment, and further determines the trajectory of respective target postures (time-series patterns) of the boom  10 , the arm  20 , and the bucket  30  with respect to the pitch direction to achieve the arm  20  for realizing the target movement path. 
     The target movement path and the target posture of the bucket  30  are determined, for example, so that the lowermost one of the plurality of claw portions  30   a  of the bucket  30  follows the target construction surface St indicated by the chain double-dashed line shown in  FIG. 7  when the bucket  30  performs the tilt motion by the maximum angle in each of the forward rotation direction and the reverse rotation direction as shown in  FIG. 10  with the amplitude set by the bucket motion setting operation unit  54  (that is, when performing a rotational motion around the tilt axis C 2 ) after the claw portion  30   a  of the bucket  30  bites into the ground. 
     Besides, the controller  60  determines a target waveform pattern of the tilt angle (rotation angle around the tilt axis C 2 ) θt of the bucket  30  (a pattern of temporal change in the target value of the tilt angle θt) so as to make the bucket  30  perform the tilt oscillation at the cycle and the amplitude set by an operation applied to the bucket motion setting operation unit  54 . The target waveform pattern is set to, for example, a triangular wave pattern illustrated in  FIG. 9 . The target waveform pattern is not limited to the triangular wave pattern, but may be a smooth curved pattern such as a sine wave pattern. 
     The tilt angle θt of the bucket  30  shown in  FIG. 9  is set so as to be zero in a state where the width direction of the bucket  30  (the direction in which the plurality of claw portions  30   a  are aligned) coincides or substantially coincides with the direction of the bucket lateral axis (the axis of the support shaft  31  in this embodiment) that is the axis of the first rotational motion of the bucket  30 , namely, the pitch motion (that is, the standard posture state of the bucket  30  with respect to the tilt direction). 
     Similarly to the controller  60  according to the first embodiment, the controller  60  inputs appropriate command signals to the plurality of proportional valves  66  corresponding to the direction selector valves  71  to  73 , respectively, to thereby control respective operations of the boom cylinder  12 , the arm cylinder  22  and the bucket cylinder  32  so as to make the actual postures of the boom  10 , the arm  20 , and the bucket  30  with respect to the pitch direction follow the target posture. 
     Besides, the controller  60  inputs an appropriate command signal to the proportional valve  66  corresponding to the direction selector valve  75  to operate the pilot pressure applied to the direction selector valve  75  so as to cause the actual tilt angle θt of the bucket  30  grasped from respective detection signals of the plurality of posture sensors  51  to change according to a preset target waveform pattern. The actual tilt angle θt of the bucket  30  thereby changes so as to follow the target waveform pattern. Specifically, as shown in  FIG. 10 , the bucket  30  performs such a second rotational motion (tilt motion) that the actual tilt angle θt of the bucket  30 , that is, the rotation angle around the tilt axis C 2 , changes alternately in the forward rotation direction and the reverse rotation direction with a constant amplitude At and cycle Tt. 
     Conducting such operation control of the working device  4  during excavation work enables excavation work to the ground to be performed so as to move the bucket  30  along the target movement path with the tilt oscillation thereof. 
     The pair of bucket tilt cylinders  36  for tilt-oscillating the bucket  30  are allowed to be relatively small. This makes it possible to make the bucket  30  perform the tilt oscillation at a relatively short cycle, thus allowing the number of times the tilt motion is repeated per unit movement amount of the bucket  30  during excavation work to be increased. This effectively reduces the resistance that the bucket  30  receives during its movement with the claw portion  30   a  biting into the ground. 
     Besides, the tilt oscillation of the bucket  30 , that is, the oscillation based on the rotational motion around the tilt axis C 2  in the direction parallel to the extending direction of the plurality of claw portions  30   a , involving no fluctuation of respective orientations of the plurality of claw portions  30   a  of the bucket  30 , allows the orientations of the plurality of claw portions  30   a  to be constantly kept in the direction parallel to the moving direction of the bucket  30  regardless of the tilt oscillation. This enables the smoothness of the construction surface achieved by the excavation work to be ensured. 
     Furthermore, as described above, setting the bucket  30  so as to make the lowest claw portion  30   a  of the plurality of claw portions  30   a  follow the target construction surface when the bucket  30  is rotationally moved by the maximum angle in each of the forward rotation direction and the reverse rotation direction in the tilt oscillation enables the construction surface achieved by the excavation work to be prevented from being deeper than the target construction surface St. 
     The present invention is not limited to the embodiments described above. The present invention, for example, includes the following aspects. 
     While the yaw oscillation and the tilt oscillation of the bucket  30  in the first and second embodiments are performed during the excavation work and the ground preparation work by automatic control, the aspects of the excavation work and the ground preparation work according to the present invention are not limited. For example, the yaw oscillation or the tilt oscillation of the bucket  30  may be performed when an operator applies a manual operation to a predetermined operation button or the like for an excavation work or a leveling work. 
     While the bucket  30  in the first embodiment and the second embodiment is rotationally movable only in one of the yaw direction and the tilt direction, the present invention is not limited to this. The bucket according to the present invention may be attached to the distal end of the working device body (for example, the distal end of the arm  20 ) so as to be rotationally movable in both the yaw direction and the tilt direction. 
     While both of the amplitude and the cycle of the yaw oscillation and the tilt oscillation of the bucket  30  in the first embodiment and the second embodiment are variable and can be set by the operator or the like, the present invention is not limited to this. For example, only one of the amplitude and the cycle may be variable, or both the amplitude and the cycle may be fixed to constant values. 
     The construction machine according to the present invention is not limited to the crawler type hydraulic excavator as shown in  FIG. 1 . The construction machine according to the present invention may be, for example, a wheel type excavator. Besides, the construction machine according to the present invention may include no slewing body slewable relatively to the travelling body. Besides, the working device body (for example, the boom  10 ) may be capable of performing, in addition to the pitch motion, a yaw motion that is a rotational motion about a vertical axis and/or a sliding motion parallel to the width direction of the slewing body  3 . 
     As described above, performed is a construction machine capable of reducing the resistance that a bucket receives from the ground and improving the smoothness of the construction surface. Provided is a construction machine comprising a machine body, a working device mounted on the machine body, and a control device for controlling a motion of the working device. The working device includes a working device body having a proximal end portion connected to the machine body and a distal end opposite thereto, a bucket attached to the distal end of the working device body so as to be capable of performing a first rotational motion and a second rotational motion relative to the distal end of the working device body, and a plurality of bucket actuators that actuate the bucket relatively to the working device body. The first rotational motion is a pitch motion that is a rotational motion about a bucket lateral axis parallel to a width direction of the bucket. The second rotational motion is a rotational motion about an axis in a direction orthogonal to the bucket lateral axis. The plurality of bucket actuators include a first bucket actuator that makes the bucket perform the first rotational motion and a second bucket actuator that makes the bucket perform the second rotational motion. The control device is configured to control the second bucket actuator so as to make the second bucket actuator periodically oscillate the bucket based on the second rotational motion in a state where the bucket is in pressure contact with the ground. 
     In the construction machine, the second bucket actuator for making the bucket perform the second rotational motion (for example, a yaw motion or a tilt motion) is allowed to be smaller than the first actuator that makes the bucket perform the first rotational motion that is the pitch motion. This makes it possible to make the bucket perform the second rotational motion (for example, the yaw motion or the tilt motion) quickly at a relatively short cycle. Hence, periodically oscillating the bucket based on the second rotational motion during work with pressure contact of the bucket with the ground (for example, during excavation work or ground leveling work) effectively reduces the resistance that the bucket receives from the ground. 
     In the case where the bucket includes a bottom portion, a plurality of claw portions projecting in the direction at the distal end of the bucket, and a ground contact wall surface that is a wall surface from the bottom portion to the plurality of claw portions and contactable with a construction surface, it is preferable that the second rotational motion is, for example, a yaw motion that is a rotational motion around an axis in a direction orthogonal to the ground contact wall surface. Hence, it is preferable that the control device is configured to control the second bucket actuator so as to make the second bucket actuator oscillate the bucket in a yaw direction that is the direction of the yaw motion. With the yaw motion, the bucket can be oscillated while keeping the ground contact wall surface, that is, the wall surface from the bottom portion of the bucket to the plurality of claw portions, in a substantially constant posture. This makes it possible to move the bucket with restraint of undulations from occurring in the construction surface to thereby form a smooth construction surface with reduced resistance that the bucket receives from the ground during its movement. 
     In such mode that the bucket is able to perform the yaw motion, it is preferable that the control device is configured to control an operation of the working device to move the bucket so as to make at least one of the ground contact wall surface and the distal end portions of the plurality of claw portions follow a target construction surface during excavation work for excavating the ground with the bucket. This allows the construction surface achieved by the excavation work to be accurately coincided with the target construction surface. 
     Besides, the control device is preferably configured to control an operation of the second bucket actuator so as to make the second bucket actuator periodically oscillate the bucket in a yaw direction that is a direction of the yaw motion during ground leveling work for leveling the ground by moving the bucket while pressing the ground contact wall surface against the ground. The yaw motion of the bucket, allowing the ground contact wall surface of the bucket to be kept in a substantially constant posture, enables the ground to be smooth leveled. 
     It is preferable that the control device is configured to control the operation of the working device to move the bucket so as to make the ground contact wall surface of the bucket follow a target construction surface during the ground leveling work. This control allows the construction surface achieved by the leveling work to be accurately coincided with the target construction surface. 
     In the case where the bucket includes a bottom portion, a plurality of claw portions projecting in the same direction at the distal end of the bucket, and a ground contact wall surface that is a wall surface from the bottom portion to the plurality of claw portions and contactable with a construction surface, the second rotational motion may be a tilt motion that is a rotational motion around an axis in a direction in which the plurality of claw portions project. In short, the control device may be configured to control the second bucket actuator so as to make the second bucket actuator oscillate the bucket in the direction of the tilt motion. The tilt motion allows the projecting direction of the plurality of claw portions to be kept in the same direction as the moving direction of the bucket (excavation direction) during excavation work. This allows the bucket to be moved with restraint of undulations from occurring in the construction surface, thereby making it possible to form a smooth construction surface with reduced resistance that the bucket receives from the ground during its movement. 
     In the mode where the bucket is able to perform the tilt motion as described above, the control device is preferably configured to control the operation of the working device to move the bucket so as to make the lowermost claw portion of the plurality of claw portions of the bucket follow a target construction surface when the bucket is rotationally moved in a direction of the tilt motion by the maximum rotational motion amount in the oscillation of the bucket in the direction of the tilt motion during excavation work for excavating the ground with the bucket. This control prevents the tilt motion from rendering the construction surface achieved by the excavation work deeper than the target construction surface. 
     It is preferable that the control device is configured to make at least one of a cycle and an amplitude of oscillation of the bucket be changeable. This allows at least one of the cycle and the amplitude of the bucket oscillation to be set to a value suitable, for example, for the state of the ground as a work target.