Work machine and method for controlling work machine

Abstract

The present invention suppresses vibration of a vehicle body. A work machine according to the present invention comprises a vehicle body frame, a work machine, at least one electric motor, and a controller. The work machine includes: a boom that is supported by the vehicle body frame; an arm that is connected to the boom; and an attachment that is connected to the arm. The electric motor generates drive force for moving the attachment relative to the vehicle body frame. The controller restricts the angular acceleration of the work machine on the basis of a result of determination of whether or not the rotational moment which acts on the work machine at an end portion of the movable range of the work machine is not more than a threshold value.

Description

Work machine and work machine control method

[0001] The present disclosure relates to a work machine and a method for controlling a work machine.

[0002] An example of prior art is a work machine described in Japanese Patent Laid-Open Publication No. 2003-184133 (Patent Document 1). This work machine is equipped with a vibration suppression device. The vibration suppression device suppresses vibrations that occur when a movable part that is rotationally driven by a hydraulic actuator relative to the upper rotating body accelerates or decelerates. The vibration suppression device includes a rotation angle sensor and a controller.

[0003] The rotation angle sensors detect the rotation angles of the boom, arm, and bucket, and input angle signals to the controller. The controller calculates the rotational moments generated when the boom, arm, and bucket accelerate or decelerate, and calculates the moment of inertia of the entire work machine relative to the center of rotation about which the work machine attempts to rotate due to that rotational moment. The controller determines, from that rotational moment and the moment of inertia of the entire hydraulic excavator, whether the angular acceleration of the entire hydraulic excavator about its center of rotation exceeds a preset allowable angular acceleration. If the allowable angular acceleration is exceeded, the controller corrects the command signals related to the boom, arm, and bucket, and limits the acceleration and deceleration of the boom, arm, and bucket.

[0004] Japanese Patent Application Laid-Open No. 2003-184133

[0005] When vibrations occur in the vehicle body of a work machine, the vibrations are transmitted to the operator's cab mounted on the vehicle body, resulting in a decrease in the riding comfort of the operator sitting in the cab.

[0006] The present disclosure proposes a work machine and a control method for the work machine that are capable of suppressing vibrations of the vehicle body.

[0007] A work machine according to one aspect of the present disclosure includes a body frame, a work implement, at least one electric motor, and a controller. The work implement includes a boom supported by the body frame, an arm connected to the boom, and an attachment connected to the arm. The electric motor generates a driving force that moves the attachment relative to the body frame. The controller limits the angular acceleration of the work implement based on a determination result of whether a rotational moment acting on the work implement at an end of the work implement's movable range is equal to or less than a threshold.

[0008] A method for controlling a work machine according to one aspect of the present disclosure includes the following steps: a first step of determining whether a rotational moment acting on the work machine is equal to or less than a threshold value at an end of a movable range of the work machine, which is supported by a body frame and moves relative to the body frame by the driving force of an electric motor; and a second step of limiting the angular acceleration of the work machine based on the result of the above determination.

[0009] According to the work machine and the control method for the work machine of the present disclosure, vibrations of the vehicle body can be suppressed.

[0010] 8 is a side view showing a schematic configuration of an electric shovel. FIG. 9 is a perspective view of a body frame and a working implement. FIG. 10 is a plan view of the body frame and the working implement. FIG. 11 is a diagram showing a schematic configuration of a power transmission device that transmits driving force to a boom. FIG. 12 is a skeleton diagram of a power transmission path from an electric motor to a gear member. FIG. 13 is a diagram showing a schematic configuration of a power transmission device that transmits driving force to an arm. FIG. 14 is a schematic diagram of double motor drive. FIG. 15 is a diagram showing a schematic configuration of a power transmission device that transmits driving force to a bucket. FIG. 16 is a schematic diagram of a power transmission device as seen from the direction of arrow IX in FIG. 8. FIG. 17 is a block diagram showing a schematic configuration of a control system that controls an electric shovel. FIG. 18 is a flowchart showing a process flow for suppressing vibration of a body in an electric shovel. FIG. 19 is a schematic diagram of a working implement for explaining moment balance. FIG. 19 is a graph showing the relationship between boom attitude and speed. FIG. 19 is a graph showing the relationship between boom attitude and speed after angular acceleration limiting.

[0011] Hereinafter, the embodiments will be described with reference to the drawings. In the following description, the same parts and components are denoted by the same reference numerals. Their names and functions are also the same. Therefore, detailed descriptions thereof will not be repeated. In the drawings, configurations may be omitted or simplified for the sake of convenience. It is also intended from the beginning that any configurations may be extracted from the embodiments and arbitrarily combined.

[0012] In the following description, the terms "up," "down," "front," "rear," "left," and "right" refer to directions relative to the operator seated in the driver's seat 4S in the driver's cab 4.

[0013] <Overall Configuration> Fig. 1 is a side view that schematically shows the configuration of an electric shovel 30 as an example of a work machine. Fig. 1 shows the schematic configuration of the electric shovel 30 as viewed from the right side. As shown in Fig. 1, the electric shovel 30 of this embodiment mainly has a revolving unit 2, a running unit 5, and a work implement 10. The revolving unit 2 and the running unit 5 form a vehicle body 1 of the electric shovel 30.

[0014] The running body 5 has a pair of left and right track devices 5Cr. Each of the pair of left and right track devices 5Cr has a track. The pair of left and right tracks are rotationally driven to self-propel the electric excavator 30. The running body 5 may have wheels (tires) instead of the track devices 5Cr.

[0015] The rotating unit 2 is installed so as to be freely rotatable relative to the running unit 5. The rotating unit 2 mainly includes a body frame 3, an operator's cab 4, and a counterweight 6. The operator's cab 4 and the counterweight 6 are mounted on the body frame 3.

[0016] An operator sits in the cab 4 and operates the electric shovel 30. The cab 4 is located, for example, on the front left side (front side of the vehicle) of the rotating unit 2. A driver's seat 4S for the operator to sit in is located in the interior space of the cab 4. In the present disclosure, the electric shovel 30 is operated from inside the cab 4, but the electric shovel 30 may also be remotely operated wirelessly from a location distant from the electric shovel 30. The counterweight 6 is located on the rear side of the rotating unit 2 (rear side of the vehicle) relative to the cab 4. The counterweight 6 is located at the rear of the rotating unit 2.

[0017] The work implement 10 is supported by the revolving unit 2 at the front of the revolving unit 2, for example, on the right side of the operator's cab 4. The work implement 10 has a boom 11, an arm 12, and a bucket 13.

[0018] The base end of the boom 11 is rotatably connected to the rotating bed 2 by a boom foot pin 15. The boom foot pin 15 extends in the left-right direction and passes through the base end of the boom 11. The boom 11 is supported by the vehicle body frame 3. The base end of the arm 12 is rotatably connected to the tip of the boom 11 by an arm connecting pin 16. The arm connecting pin 16 extends in the left-right direction and passes through the tip of the boom 11 and the base end of the arm 12. The bucket 13 is rotatably connected to the tip of the arm 12 by an attachment connecting pin 17. The attachment connecting pin 17 extends in the left-right direction and passes through the tip of the arm 12 and the base end of the bucket 13.

[0019] The bucket 13 forms the tip portion of the work machine 10. In this embodiment, the bucket 13 is connected to the boom 11 via the arm 12. The bucket 13 moves relative to the boom 11 as the bucket 13 rotates about the attachment connecting pin 17 and / or the arm 12 rotates about the arm connecting pin 16. The bucket 13 is configured to be movable relative to the boom 11.

[0020] The bucket 13 has a plurality of blades. The tip of the bucket 13 is referred to as a cutting edge 13A. The bucket 13 does not necessarily have to have blades. The tip of the bucket 13 may be formed of a straight steel plate.

[0021] The bucket 13 is an example of an attachment that is detachably attached to the tip of the work machine 10 and is rotatable relative to the arm 12. Depending on the type of work, the attachment can be changed to a breaker, a grapple, a lifting magnet, or the like.

[0022] The work implement 10 has a bucket link 21. The bucket link 21 has a first member 22 and a second member 23. The first member 22 and the second member 23 are connected to each other so as to be rotatable relative to each other. The first member 22 and the second member 23 are connected to each other by a link pin 24. The first member 22 is rotatably connected to the arm 12 by a link pin 25. The second member 23 is rotatably connected to a bracket at the base of the bucket 13 by a link pin 26.

[0023] The first member 22 has a rod-like shape. One end of the first member 22 is connected to the second member 23, and the other end is connected to the arm 12. The second member 23 has a rod-like shape. One end of the second member 23 is connected to the first member 22, and the other end is connected to the bucket 13.

[0024] FIG. 2 is a perspective view of the body frame 3 and the work implement 10. FIG. 3 is a plan view of the body frame 3 and the work implement 10. The body frame 3 has a pair of left and right vertical plates 7, 8. The vertical plates 7, 8 extend in the front-to-rear direction (the left-to-right direction in FIG. 3 ). The vertical plates 7, 8 are spaced apart in the width direction (left-to-right direction) of the rotating unit 2. The vertical plates 7, 8 are made up of plates that stand upright in the vertical direction and are spaced apart from each other in the left-to-right direction. The operator's cab 4 is located to the left of the left vertical plate 7. The work implement 10 is located between the vertical plates 7, 8 in the left-to-right direction. The work implement 10 is located to the right of the left vertical plate 7 and to the left of the right vertical plate 8.

[0025] <Electric Motor 100> The electric shovel 30 of this embodiment includes at least one electric motor. In the electric shovel 30, the electric motor 100 generates a driving force that drives the work implement 10 and moves the attachment relative to the vehicle body frame 3. The electric motor 100 is capable of driving the work implement 10. The boom 11 and the arm 12 are driven by the electric motor 100, thereby enabling the work implement 10 to operate. The electric motor 100 is disposed on the vehicle body frame 3. The electric motor 100 includes a boom motor 110 and an arm motor 140. The boom motor 110 and the arm motor 140 are both supported by the vehicle body frame 3. The boom motor 110 and the arm motor 140 are disposed to the right of the work implement 10.

[0026] The boom electric motor 110 drives the boom 11 and generates a driving force that moves the boom 11 relative to the body frame 3, with the base end of the boom 11 as a fulcrum. Driven by the boom electric motor 110, the boom 11 can rotate relatively to the body frame 3 about a boom foot pin 15. The boom foot pin 15 is disposed across both the left and right vertical plates 7, 8. The left end of the boom foot pin 15 is supported by the left vertical plate 7, and the right end of the boom foot pin 15 is supported by the right vertical plate 8. As a result, the boom 11 is supported by the body frame 3 so as to be rotatable about the boom foot pin 15.

[0027] The boom motor 110 has a pair of a first boom motor 111 and a second boom motor 121. The first boom motor 111 and the second boom motor 121 have the same specifications. The first boom motor 111 and the second boom motor 121 have the same rated output. Here, the rated output of a motor refers to the maximum output that the motor can safely achieve under specified conditions.

[0028] The arm electric motor 140 drives the arm 12 to generate a driving force that moves the arm 12 relative to the body frame 3, with the tip of the boom 11 as a fulcrum. Driven by the arm electric motor 140, the arm 12 is rotatable relative to the body frame 3 about the arm connecting pin 16, and is also rotatable relative to the boom 11 about the arm connecting pin 16. When the boom 11 is moved relative to the body frame 3 while maintaining the relative position of the arm 12 to the boom 11, the arm 12 moves relative to the body frame 3. In this case, the arm 12 is driven by the arm electric motor 140.

[0029] The arm electric motor 140 has a pair of a first arm electric motor 141 and a second arm electric motor 151. The first arm electric motor 141 and the second arm electric motor 151 have the same specifications. The first arm electric motor 141 and the second arm electric motor 151 have the same rated output.

[0030] <Power Transmission Device> The electric shovel 30 of this embodiment is equipped with a power transmission device that mechanically transmits the driving force generated by the electric motor 100 to the work machine 10. The power transmission device will be described below.

[0031] 4 is a diagram showing a schematic configuration of a power transmission device that transmits driving force to the boom 11. The power transmission device has a first boom output gear 119, a second boom output gear 129, and a boom gear member 131.

[0032] The boom gear member 131 has a generally fan-shaped configuration, with teeth formed on the arc portion of the generally fan-shaped configuration. As shown in Figures 2 and 3, the boom gear member 131 is fixed to the side of the boom 11, more specifically, to the right surface of the boom 11. The boom gear member 131 is disposed at the base end of the boom 11. The boom gear member 131 is rotatable integrally with the boom 11 around the boom foot pin 15.

[0033] The first boom output gear 119 is an external gear and meshes with a boom gear member 131. The first boom output gear 119 is arranged concentrically with the first boom electric motor 111. The first boom electric motor 111 transmits driving force to the first boom output gear 119. The second boom output gear 129 is an external gear and meshes with the boom gear member 131. The second boom output gear 129 is arranged concentrically with the second boom electric motor 121. The second boom electric motor 121 transmits driving force to the second boom output gear 129.

[0034] FIG. 5 is a skeleton diagram of the power transmission path from the first boom electric motor 111 and the second boom electric motor 121 to the boom gear member 131.

[0035] A planetary gear reducer 113 is provided in the power transmission path from the first boom electric motor 111 to the boom gear member 131. In this embodiment, the first boom electric motor 111 and the planetary gear reducer 113 have an integrated structure. The power transmission device that transmits the driving force of the first boom electric motor 111 to the boom gear member 131 includes a geared motor 117 in which the first boom electric motor 111 and the planetary gear reducer 113 are integrated together.

[0036] The planetary gear reducer 113 has a plurality of rotating elements. The plurality of rotating elements of the planetary gear reducer 113 includes a sun gear 114, planetary gears 115, and a ring gear 116. The output shaft 112 of the first boom electric motor 111 is connected to the sun gear 114. The driving force of the first boom electric motor 111 is input to the sun gear 114.

[0037] The planetary gear reducer 113 and the first boom output gear 119 are connected by a connecting shaft 118. More specifically, the connecting shaft 118 has one end connected to a planet carrier that supports the planetary gear 115, and the other end connected to the first boom output gear 119. The planet carrier and the first boom output gear 119 are connected via the connecting shaft 118. The connecting shaft 118 may be arranged concentrically with the output shaft 112.

[0038] A planetary gear reducer 123 is provided in the power transmission path from the second boom electric motor 121 to the boom gear member 131. In this embodiment, the second boom electric motor 121 and the planetary gear reducer 123 have an integrated structure. The power transmission device that transmits the driving force of the second boom electric motor 121 to the boom gear member 131 includes a geared motor 127 in which the second boom electric motor 121 and the planetary gear reducer 123 are integrated together.

[0039] The planetary gear reducer 123 has a plurality of rotating elements. The plurality of rotating elements of the planetary gear reducer 123 includes a sun gear 124, a planetary gear 125, and a ring gear 126. The output shaft 122 of the second boom electric motor 121 is connected to the sun gear 124. The driving force of the second boom electric motor 121 is input to the sun gear 124.

[0040] The planetary gear reducer 123 and the second boom output gear 129 are connected by a connecting shaft 128. More specifically, the connecting shaft 128 has one end connected to a planet carrier that supports the planetary gear 125, and the other end connected to the second boom output gear 129. The planet carrier and the second boom output gear 129 are connected via the connecting shaft 128. The connecting shaft 128 may be arranged concentrically with the output shaft 122.

[0041] The first boom output gear 119 meshes with the boom gear member 131. The driving force generated by the first boom electric motor 111 is transmitted to the boom gear member 131 via the first boom output gear 119. The second boom output gear 129 meshes with the boom gear member 131. The driving force generated by the second boom electric motor 121 is transmitted to the boom gear member 131 via the second boom output gear 129. The boom gear member 131 receives the driving forces transmitted from the first boom electric motor 111 and the second boom electric motor 121 and rotates integrally with the boom 11 to which the boom gear member 131 is fixed. As a result, the boom 11 is driven to rotate about the boom foot pin 15.

[0042] The planetary gear reducer 113, the connecting shaft 118, and the first boom output gear 119 mechanically transmit the driving force generated by the first boom electric motor 111 to the boom 11. The planetary gear reducer 123, the connecting shaft 128, and the second boom output gear 129 mechanically transmit the driving force generated by the second boom electric motor 121 to the boom 11. The planetary gear reducers 113, 123, the connecting shafts 118, 128, the first boom output gear 119, and the second boom output gear 129 constitute a boom power transmission device that mechanically transmits the driving force generated by the boom electric motor 110 to the boom 11.

[0043] The boom power transmission device is disposed on the opposite side of the operator's cab 4 with respect to the work implement 10. In the configuration of the embodiment in which the operator's cab 4 is disposed on the front left side of the body frame 3 and on the left side with respect to the work implement 10, the boom power transmission device is disposed on the right side with respect to the work implement 10.

[0044] 6 is a diagram showing a schematic configuration of a power transmission device 160 that transmits driving force to the arm 12. The power transmission device 160, which mechanically transmits driving force generated by the arm electric motor 140 to the arm 12, has a first arm output gear 149, a second arm output gear 159, an arm gear member 161, a rotating member 162, and an arm link 170.

[0045] The arm gear member 161 has a generally fan-shaped configuration, with teeth on the arc portion of the generally fan-shaped configuration. As shown in Figures 2 and 3, the arm gear member 161 is separate from the boom gear member 131 and is disposed to the right of the boom gear member 131, away from the boom gear member 131. A gap is provided between the boom gear member 131 and the arm gear member 161 in the left-right direction. The arm gear member 161 is disposed at the base end of the boom 11. The arm gear member 161 is concentric with the boom foot pin 15 and rotates relative to the body frame 3.

[0046] The first arm output gear 149 is an external gear and meshes with the arm gear member 161. The first arm output gear 149 is arranged concentrically with the first arm electric motor 141. The first arm electric motor 141 transmits driving force to the first arm output gear 149. The second arm output gear 159 is an external gear and meshes with the arm gear member 161. The second arm output gear 159 is arranged concentrically with the second arm electric motor 151. The second arm electric motor 151 transmits driving force to the second arm output gear 159.

[0047] The power transmission path from the first arm electric motor 141 and the second arm electric motor 151 to the arm gear member 161 is the same as the power transmission path to the boom gear member 131 shown in Fig. 5. A planetary gear reducer is provided in the power transmission path from the first arm electric motor 141 to the arm gear member 161. The first arm electric motor 141 and the planetary gear reducer have an integrated structure. A planetary gear reducer is provided in the power transmission path from the second arm electric motor 151 to the arm gear member 161. The second arm electric motor 151 and the planetary gear reducer have an integrated structure. The arm gear member 161 rotates by receiving driving force transmitted from the first arm electric motor 141 and the second arm electric motor 151.

[0048] The rotating member 162 is fixed to the arm gear member 161 and rotates integrally with the arm gear member 161 concentrically with the boom foot pin 15 relative to the body frame 3 .

[0049] The arm link 170 has a first link member 171, a second link member 172, and an intermediate member 173. The intermediate member 173 is connected to the boom 11 via a pin 178. The boom 11 has a bent shape when viewed from the side, and the intermediate member 173 is connected to the bent portion of the boom 11.

[0050] The first link member 171 has a rod-like shape. The first link member 171 extends along the boom 11. A first end of the first link member 171 is connected to the rotating member 162 via a connecting pin 177. A second end of the first link member 171 is connected to the intermediate member 173 via a connecting pin 174. The first link member 171 connects the rotating member 162 and the intermediate member 173. The first link member 171 transmits the driving force generated by the arm motor 140 and transmitted to the rotating member 162 via the arm gear member 161 to the intermediate member 173.

[0051] The second link member 172 has a rod-like shape. The second link member 172 extends along the boom 11. A first end of the second link member 172 is connected to the intermediate member 173 via a connecting pin 175. A second end of the second link member 172 is connected to the arm 12 via a connecting pin 176. The second link member 172 connects the intermediate member 173 to the arm 12. The second link member 172 transmits to the arm 12 the driving force generated by the arm motor 140 and transmitted to the intermediate member 173 via the arm gear member 161, the rotating member 162, and the first link member 171 in this order.

[0052] The intermediate member 173 may have a substantially polygonal shape. The first link member 171 and the second link member 172 may be connected to the intermediate member 173 near different vertices of the substantially polygonal shape of the intermediate member 173. The intermediate member 173 is not limited to a substantially polygonal shape and may have any shape. For example, the intermediate member 173 may have a rod-like shape, and its base end may be connected to the boom 11.

[0053] The arm link 170 (first link member 171 , second link member 172 and intermediate member 173 ) transmits power to the arm 12 by the relative rotational movement of the arm gear member 161 and the rotating member 162 with respect to the body frame 3 .

[0054] Although an example has been described in which the power transmission device 160 has a rod-shaped link member, the power transmission device 160 may have a mechanism other than a link member as long as it can mechanically transmit the driving force of the arm electric motor 140 to the arm 12. For example, the power transmission device 160 may have any one or a combination of a steel cable, a chain, a pulley, a rack and pinion, and the like.

[0055] <Double Motor Drive> Gear mechanisms generally have backlash, which is a gap between the tooth surfaces of meshing gears, which reduces the accuracy of positioning a movable member connected to a driven gear. In the case of a work machine, backlash in the gear mechanism provided at the base of the boom 11 causes misalignment of the attachment at the tip of the work implement 10. To reduce backlash, the power transmission device of the embodiment is double motor driven, using two electric motors to drive one gear member.

[0056] Specifically, the boom gear member 131 that transmits driving force to the boom 11 is driven by the first boom electric motor 111 and the second boom electric motor 121. The arm gear member 161 that transmits driving force to the arm 12 is driven by the first arm electric motor 141 and the second arm electric motor 151. Double motor drive will be described below using as an example a structure in which the arm gear member 161 is driven by the first arm electric motor 141 and the second arm electric motor 151.

[0057] Fig. 7 is a schematic diagram of double motor drive. Since Fig. 7 shows double motor drive in a schematic manner, the shape of the arm gear member 161 and the arrangement of the first arm output gear 149 and the second arm output gear 159 relative to the arm gear member 161 are different from those of the embodiment shown in Fig. 6.

[0058] A first arm output gear 149 and a second arm output gear 159 mesh with the arm gear member 161 fixed to the rotating member 162. The first arm output gear 149 is connected to the first arm electric motor 141, and the first arm output gear 149 rotates when the first arm electric motor 141 is driven to rotate. The second arm output gear 159 is connected to the second arm electric motor 151, and the second arm output gear 159 rotates when the second arm electric motor 151 is driven to rotate.

[0059] In the arrangement shown in FIG. 7, for each gear, the clockwise direction is the positive direction of rotation and the counterclockwise direction is the negative direction of rotation.

[0060] By controlling the first arm electric motor 141 and the second arm electric motor 151 in coordination, backlash elimination control can be performed to bring the gear tooth surfaces into contact with each other without any gaps, thereby increasing the positioning accuracy of the attachment at the tip of the work machine 10. Furthermore, backlash elimination control can also be disabled to improve the efficiency of the power transmission device. By switching between enabling and disabling backlash elimination control, it is possible to select either highly accurate attachment positioning or highly efficient power transmission, and the use of a highly efficient planetary gear mechanism enables regeneration using the kinetic energy of the work machine 10.

[0061] When performing backlash elimination control, the first arm electric motor 141 constantly applies a positive offset torque to the arm gear member 161, and the second arm electric motor 151 constantly applies a negative offset torque to the arm gear member 161.

[0062] When the arm gear member 161 is stopped, the first arm electric motor 141 and the second arm electric motor 151 apply offset torques of the same magnitude but in opposite directions to the arm gear member 161. The total torque magnitude of the torque applied to the arm gear member 161 by the first arm electric motor 141 and the torque applied to the arm gear member 161 by the second arm electric motor 151 is zero.

[0063] At this time, both the first arm output gear 149 and the second arm output gear 159 attempt to rotate in opposite directions, sandwiching the arm gear member 161. The arm gear member 161 is held in a state where the tooth surface of the first arm output gear 149 contacts the tooth surface of the arm gear member 161 and the tooth surface of the second arm output gear 159 contacts the tooth surface of the arm gear member 161. By pressing both the first arm output gear 149 and the second arm output gear 159 against the arm gear member 161, backlash can be suppressed.

[0064] When the arm gear member 161 is rotated counterclockwise at a low speed, the torque generated by the first arm electric motor 141 is increased. Increasing the torque of the first arm electric motor 141 drives the arm gear member 161 in the negative direction (counterclockwise direction). At this time, the second arm electric motor 151 continues to apply an offset torque in the opposite direction to the rotation direction of the arm gear member 161. The first arm electric motor 141 drives the arm gear member 161, and the second arm electric motor 151 enters a state in which it slightly brakes the arm gear member 161.

[0065] When the arm gear member 161 is rotated clockwise at a low speed, the torque generated by the second arm electric motor 151 is increased. Increasing the torque of the second arm electric motor 151 drives the arm gear member 161 in the positive direction (clockwise direction). At this time, the first arm electric motor 141 continues to apply an offset torque in the opposite direction to the rotation direction of the arm gear member 161. The second arm electric motor 151 drives the arm gear member 161, and the first arm electric motor 141 enters a state in which it slightly brakes the arm gear member 161.

[0066] At this time, both the first arm output gear 149 and the second arm output gear 159 attempt to rotate in opposite directions, sandwiching the arm gear member 161. The tooth surface of the first arm output gear 149 comes into contact with the tooth surface of the arm gear member 161, and the tooth surface of the second arm output gear 159 comes into contact with the tooth surface of the arm gear member 161. By pressing both the first arm output gear 149 and the second arm output gear 159 against the arm gear member 161, backlash can be suppressed.

[0067] By executing backlash elimination control, it is possible to increase the positioning accuracy of the attachment at the tip of the work machine 10, making it possible to perform work using the attachment with high precision.

[0068] When backlash elimination control is not executed, no offset torque is applied from the first arm electric motor 141 and the second arm electric motor 151 to the arm gear member 161. To rotate the arm gear member 161 at high speed, drive torques in the same direction are applied from the first arm electric motor 141 and the second arm electric motor 151 to the arm gear member 161.

[0069] Both the first arm electric motor 141 and the second arm electric motor 151 apply drive torque to the arm gear member 161. Neither the first arm electric motor 141 nor the second arm electric motor 151 brakes the arm gear member 161. By not executing backlash elimination control, power can be transmitted to the arm gear member 161 with high efficiency. Although the positioning accuracy of the attachment at the tip of the work machine 10 will be lower, this is not a problem because high positioning accuracy is not required for an attachment that is moving at high speed.

[0070] A highly efficient planetary gear reducer is provided in the power transmission path from the first arm electric motor 141 to the first arm output gear 149. A highly efficient planetary gear reducer is provided in the power transmission path from the second arm electric motor 151 to the second arm output gear 159. When backlash elimination control is not being executed and a large external force acts on the attachment, for example, when the attachment at the tip of the work implement 10 collides with an object, the external force is transmitted to the first arm electric motor 141 and the second arm electric motor 151 through the planetary gear reducer.

[0071] The rotors of the first arm motor 141 and the second arm motor 151 have no contact parts other than the bearings that rotatably support the rotors. Therefore, when a large external force is applied, angular displacement occurs in the rotors. Loss of synchronization between the first arm motor 141 and the second arm motor 151 can prevent damage to the planetary gear reducer.

[0072] During execution of backlash elimination control, the attachment at the tip of the work machine 10 is stopped or moves at a low speed, if it moves at all. Since the movement speed of the attachment at the tip of the work machine 10 is low and the impact when the attachment collides with an object is small, damage to the planetary gear reducer is prevented.

[0073] <Attachment electric motor 220> Figure 8 is a diagram showing a schematic configuration of a power transmission device 210 that transmits driving force to the bucket 13. Figure 9 is a schematic diagram of the power transmission device 210 as viewed from the direction of arrow IX in Figure 8. In the electric shovel 30, the attachment electric motor 220 generates the driving force that drives the bucket 13. The electric motor 100 has the attachment electric motor 220.

[0074] The attachment motor 220 is capable of driving the bucket 13. The bucket 13 can be operated by being driven by the attachment motor 220. The bucket 13 can rotate relatively to the arm 12 around the attachment connecting pin 17 by being driven by the attachment motor 220. The power transmission device 210 mechanically transmits the driving force generated by the attachment motor 220 to the bucket 13.

[0075] The attachment motor 220 is mounted on the arm 12. A buffer mechanism 229 is attached to the arm 12. The buffer mechanism 229 has the function of buffering the load input to the arm 12. The attachment motor 220 is mounted on the arm 12 via the buffer mechanism 229. The attachment motor 220 has a pair of a first electric motor 221 and a second electric motor 231. The first electric motor 221 and the second electric motor 231 have the same specifications. The first electric motor 221 and the second electric motor 231 have the same rated output.

[0076] The output shaft of the first electric motor 221 is connected to a flexible shaft 222. The flexible shaft 222 has a base end connected to the first electric motor 221. The tip of the flexible shaft 222 is connected to a bevel gear 223. The bevel gear 223 is in mesh with a bevel gear 224. The bevel gear 224 is connected to a planetary gear reducer 225.

[0077] The planetary gear reducer 225 has a plurality of rotating elements. The plurality of rotating elements of the planetary gear reducer 225 includes a sun gear, planetary gears, and a ring gear. The bevel gear 224 is connected to the sun gear of the planetary gear reducer 225. The driving force of the first electric motor 221 is input to the sun gear of the planetary gear reducer 225 via the flexible shaft 222 and the bevel gears 223 and 224.

[0078] The planetary gear reducer 225 reduces the rotation speed of the first electric motor 221 and increases the driving force to be output. A planet carrier of the planetary gear reducer 225 is connected to an output shaft 227. The output shaft 227 has one end connected to the planet carrier and the other end connected to a pinion 228. The pinion 228 meshes with a rack 240.

[0079] The output shaft of the second electric motor 231 is connected to a flexible shaft 232. The flexible shaft 232 has a base end connected to the second electric motor 231. The tip end of the flexible shaft 232 is connected to a bevel gear 233. The bevel gear 233 meshes with a bevel gear 234. The bevel gear 234 is connected to a planetary gear reducer 235.

[0080] The planetary gear reducer 235 has a plurality of rotating elements. The plurality of rotating elements of the planetary gear reducer 235 includes a sun gear, planetary gears, and a ring gear. The bevel gear 234 is connected to the sun gear of the planetary gear reducer 235. The driving force of the second electric motor 231 is input to the sun gear of the planetary gear reducer 235 via the flexible shaft 232 and the bevel gears 233 and 234.

[0081] The planetary gear reducer 235 reduces the rotation speed of the second electric motor 231 and increases the driving force to be output. A planet carrier of the planetary gear reducer 235 is connected to an output shaft 237. The output shaft 237 has one end connected to the planet carrier and the other end connected to a pinion 238. The pinion 238 meshes with a rack 240.

[0082] The pinions 228, 238 and the rack 240 are supported by a support member 250 via a pin 251. The support member 250 is fixed to the arm 12. The rack 240 and the pinions 228, 238 are supported by the arm 12 via the support member 250.

[0083] The rack 240 is coupled to a link pin 24 that connects the first member 22 and the second member 23 of the bucket link 21. The rack 240 is connected to the bucket 13 via the bucket link 21.

[0084] The driving force generated by the first electric motor 221 is transmitted to the pinion 228, causing the pinion 228 to rotate. The driving force generated by the second electric motor 231 is transmitted to the pinion 238, causing the pinion 238 to rotate. The rack 240 moves in the longitudinal direction in accordance with the rotation of the pinions 228, 238.

[0085] As rack 240 moves away from arm connecting pin 16, which connects boom 11 and arm 12, and in a direction toward attachment connecting pin 17, which connects arm 12 and bucket 13, bucket 13 is driven to rotate about attachment connecting pin 17. Bucket 13 moves in the excavation direction (a direction in which cutting edge 13A of bucket 13 approaches arm 12; in FIG. 8 , this is a counterclockwise direction about attachment connecting pin 17).

[0086] As the rack 240 moves in a direction away from the attachment connecting pin 17 and toward the arm connecting pin 16, the bucket 13 is driven to rotate around the attachment connecting pin 17. The bucket 13 moves in the dump direction (a direction in which the cutting edge 13A of the bucket 13 moves away from the arm 12; in FIG. 8 , this is a clockwise direction around the attachment connecting pin 17).

[0087] Pinions 228 and 238 mesh with rack 240. Pinion 228 is connected to first electric motor 221, and pinion 228 rotates when first electric motor 221 is driven to rotate. Pinion 238 is connected to second electric motor 231, and pinion 238 rotates when second electric motor 231 is driven to rotate. Power transmission device 210 is a double motor drive system that uses two electric motors, namely first electric motor 221 and second electric motor 231, to drive rack 240, which is a single gear member.

[0088] Backlash elimination control can be performed by cooperative control of the first electric motor 221 and the second electric motor 231, thereby improving the positioning accuracy of the bucket 13. Furthermore, in order to improve the efficiency of the power transmission device 210, backlash elimination control can also be disabled.

[0089] The rotation direction of the first electric motor 221 and the second electric motor 231 and the generated driving force are adjusted in response to the operation of the operator to operate the bucket 13. The operator seated in the driver's seat 4S can move the bucket 13 in the excavation direction by moving the operation lever located to the right of the driver's seat 4S to the left with his right hand, or move the operation lever to the right to move the bucket 13 in the dumping direction. According to the operator's intentions, the bucket 13 at the tip of the work implement 10 can be moved at high speed with high efficiency, moved at a slow speed with high positional accuracy, or stopped with high positional accuracy.

[0090] In addition, if precision in positioning the attachment at the tip of the work machine 10 is not required, it is also possible to use a single motor drive for one or more of the boom gear member 131, the arm gear member 161, and the rack 240, which are driven by a single electric motor.

[0091] The attachment electric motor 220 that generates the driving force for driving the bucket 13 does not necessarily have to be mounted on the arm 12. The attachment electric motor 220 may be disposed on the vehicle body frame 3. The driving force generated by the attachment electric motor 220 fixed to the vehicle body frame 3 may be configured to be mechanically transmitted to the bucket 13 via an attachment power transmission device.

[0092] <System Configuration> Fig. 10 is a block diagram showing a schematic configuration of a control system that controls the electric shovel 30. Fig. 10 shows only a part of the system that configures the electric shovel 30 of this embodiment. The electric shovel 30 includes a work implement attitude detector 40 that detects the attitude of the work implement 10, and a controller 50 that controls the operation of the electric shovel 30.

[0093] The work machine attitude detector 40 includes a boom angle sensor 41, an arm angle sensor 42, and an attachment angle sensor 43. The boom angle sensor 41 detects the angle of the boom 11 relative to the vehicle body frame 3. The arm angle sensor 42 detects the angle of the arm 12 relative to the boom 11 in a region where the arm 12 rotates in a side view. The attachment angle sensor 43 detects the angle of the bucket 13 relative to the arm 12 in a region where the bucket 13 rotates in a side view. The boom angle sensor 41, arm angle sensor 42, and attachment angle sensor 43 output angle detection signals to the controller 50.

[0094] The boom angle sensor 41, the arm angle sensor 42, and the attachment angle sensor 43 may be potentiometers or rotary encoders. The boom angle sensor 41 may be attached around the boom foot pin 15. The arm angle sensor 42 may be attached around the arm connecting pin 16. The attachment angle sensor 43 may be attached around the attachment connecting pin 17.

[0095] The boom angle sensor 41 may be an IMU (Inertial Measurement Unit) attached to the boom 11. The arm angle sensor 42 may be an IMU attached to the arm 12. The attachment angle sensor 43 may be an IMU attached to the bucket link 21 (first member 22).

[0096] The controller 50 includes a CPU (Central Processing Unit) etc. The controller 50 has a storage unit 58 and a timer 59.

[0097] The storage unit 58 is a non-volatile memory and is provided as an area for storing necessary data. The storage unit 58 stores control programs for controlling various operations of the electric shovel 30 and various data required for executing the control programs. The storage unit 58 also temporarily stores working data generated in conjunction with the operation of the electric shovel 30. The controller 50 executes various processes for controlling the operation of the electric shovel 30 by executing the control programs stored in the storage unit 58. The timer 59 measures the time.

[0098] The controller 50 outputs a control signal to the electric motor 100 to operate the work machine 10. The controller 50 outputs a control signal to the boom electric motor 110 to move the boom 11 relative to the body frame 3. The controller 50 outputs a control signal to the arm electric motor 140 to move the arm 12 relative to the body frame 3. The controller 50 outputs a control signal to the attachment electric motor 220 to move the bucket 13 relative to the arm 12.

[0099] The controller 50 has an angle acquisition unit 51 , an angular acceleration calculation unit 52 , an attachment total weight calculation unit 53 , an inertia moment calculation unit 54 , a rotational moment calculation unit 55 , and an angular acceleration restriction unit 56 .

[0100] <Vibration Suppression Control> Fig. 11 is a flowchart showing the flow of processing for suppressing vibration of the vehicle body 1 in the electric shovel 30. With reference to Figs. 10 and 11 and subsequent figures as appropriate, processing for suppressing vibration of the vehicle body 1 when the electric shovel 30 is operating will be described.

[0101] In step S1, the angle acquisition unit 51 receives a detection signal of the angle of the boom 11 relative to the vehicle body frame 3 from the boom angle sensor 41. The angle acquisition unit 51 receives a detection signal of the angle of the arm 12 relative to the boom 11 from the arm angle sensor 42. The angle acquisition unit 51 receives a detection signal of the angle of the bucket 13 relative to the arm 12 from the attachment angle sensor 43. The angle acquisition unit 51 acquires the current posture of the work implement 10. The angle acquisition unit 51 stores the angles of the boom 11, the arm 12, and the bucket 13 and the times when the angles were acquired in the memory unit 58.

[0102] In step S2, angular acceleration calculation unit 52 reads from memory unit 58 the time before the time when the angle of work machine 10 was acquired in step S1, and the angles of boom 11, arm 12, and bucket 13 at that time. Angular acceleration calculation unit 52 calculates the angular velocity of rotating work machine 10 using the elapsed time, the angle of work machine 10 at the start of that elapsed time, and the angle of work machine 10 at the end of that elapsed time. Angular acceleration calculation unit 52 calculates the angular acceleration of work machine 10 from the change in the angular velocity of work machine 10 over time.

[0103] In step S3, the attachment total weight calculation unit 53 calculates the weight of the load carried in the bucket 13 (bucket load value).

[0104] Figure 12 is a schematic diagram of a work machine for explaining moment balance. As shown in Figure 12, in this embodiment, the current load value W in the bucket 13 is detected from the moment balance. Specifically, the current load value W in the bucket 13 is detected from the balance of each moment about the boom foot pin 15. Here, the balance of each moment about the boom foot pin 15 is expressed by the following equation (1).

[0105]

[0106] In equation (1), Tboom is the torque generated by the boom motor 110. Tarm is the torque generated by the arm motor 140. Tbucket is the torque generated by the attachment motor 220. Mboom is the moment of the boom 11 around the boom foot pin 15. Marm is the moment of the arm 12 around the boom foot pin 15. Mbucket is the moment of the bucket 13 around the boom foot pin 15. W is the current load value in the bucket 13. L is the horizontal distance from the boom foot pin 15 to the attachment connecting pin 17.

[0107] Tboom is calculated from the rated output of the boom motor 110 and the rotation speed of the boom motor 110. Tarm is calculated from the rated output of the arm motor 140 and the rotation speed of the arm motor 140. Tbucket is calculated from the rated output of the attachment motor 220 and the rotation speed of the attachment motor 220.

[0108] Mboom is calculated by multiplying the distance r1 between the center of gravity C1 of the boom 11 and the boom foot pin 15 by the weight M1 of the boom 11 (r1 × M1). The position of the center of gravity C1 of the boom 11 is calculated from the angle A1 of the boom 11 with respect to the body frame 3, etc. The weight M1 of the boom 11, etc. are stored in the memory unit 58.

[0109] Marm is calculated as the product (r2 × M2) of the distance r2 between the center of gravity C2 of the arm 12 and the boom foot pin 15 and the weight M2 of the arm 12. The position of the center of gravity C2 of the arm 12 is calculated from the angle A2 of the arm 12 with respect to the boom 11, etc. The weight M2 of the arm 12, etc. are stored in the memory unit 58.

[0110] Mbucket is calculated by multiplying the distance r3 between the center of gravity C3 of the bucket 13 and the boom foot pin 15 by the weight M3 of the bucket 13 (r3 × M3). The position of the center of gravity C3 of the bucket 13 is calculated from the angle A3 of the bucket 13 with respect to the arm 12, etc. The weight M3 of the bucket 13, etc. are stored in the memory unit 58.

[0111] In calculating the current load value W in the bucket 13, the attachment total weight calculation unit 53 calculates the positions of the centers of gravity C1, C2, and C3 based on the attitude of the work machine 10 acquired by the angle acquisition unit 51. The attachment total weight calculation unit 53 calculates the distances r1, r2, and r3 between the centers of gravity C1, C2, and C3 and the boom foot pin 15.

[0112] The total attachment weight calculation unit 53 reads out the weight M1 of the boom 11 from the memory unit 58, and calculates the product of the distance r1 and the weight M1 as the moment Mboom of the boom 11 about the boom foot pin 15. The total attachment weight calculation unit 53 reads out the weight M2 of the arm 12 from the memory unit 58, and calculates the product of the distance r2 and the weight M2 as the moment Marm of the arm 12 about the boom foot pin 15. The total attachment weight calculation unit 53 reads out the weight M3 of the bucket 13 from the memory unit 58, and calculates the product of the distance r3 and the weight M3 as the moment Mbucket of the bucket 13 about the boom foot pin 15.

[0113] The total attachment weight calculation unit 53 reads out the length L1 of the boom 11 and the length L2 of the arm 12 from the memory unit 58. The total attachment weight calculation unit 53 calculates the horizontal distance L from the boom foot pin 15 to the attachment connecting pin 17 based on the angles A1, A2 calculated above and the lengths L1, L2 of the boom 11 and arm 12.

[0114] The total attachment weight calculation unit 53 substitutes the torques Tboom, Tarm, and Tbucket, the moments Mboom, Marm, and Mbucket, and the distance L calculated as above into the above equation (1). In this way, the total attachment weight calculation unit 53 calculates the current load value W in the bucket 13. The total attachment weight calculation unit 53 calculates the total weight of the bucket 13 (attachment) as the sum of the bucket 13's own weight M3 and the load value W, which is the weight of the load carried on the bucket 13. Calculating the total weight of the bucket 13 in this way makes it possible to more accurately calculate the moment of inertia Ib and rotational moment Hb, which will be described later.

[0115] 11 , in step S4, the moment of inertia calculation unit 54 calculates the moment of inertia Ib about the boom foot pin 15. The moment of inertia Ib varies in accordance with changes in the posture of the work implement 10. The moment of inertia Ib varies in accordance with the weight of the load carried on the bucket 13.

[0116] The moment of inertia calculation unit 54 calculates the moment of inertia of the boom 11 around the boom foot pin 15 based on the weight M1, length L1, and angle A1 of the boom 11. The moment of inertia calculation unit 54 calculates the moment of inertia of the arm 12 around the boom foot pin 15 based on the weight M2 of the arm 12, and the lengths L1 and L2 and angles A1 and A2 of the boom 11 and arm 12. The moment of inertia calculation unit 54 calculates the moment of inertia of the bucket 13 and the loaded load around the boom foot pin 15 based on the total weight of the attachment calculated as above, and the lengths L1 and L2 and angles A1 and A2 of the boom 11 and arm 12. The moment of inertia calculation unit 54 calculates the sum of these moments of inertia as the moment of inertia Ib.

[0117] In step S5, the rotational moment calculation unit 55 calculates the product of the moment of inertia Ib and the angular acceleration of the work implement 10 calculated in step S2 as the rotational moment Hb of the boom 11. That is, the rotational moment Hb of the boom 11 is expressed by the following equation (2).

[0118]

[0119] In equation (2), v is the speed of the boom 11 rotating around the boom foot pin 15, and t is time. The angular acceleration of the boom 11 is the time derivative of the speed of the boom 11.

[0120] Figure 13 is a graph showing the relationship between the attitude of the boom 11 and the speed of the boom 11. The horizontal axis of Figure 13 is the angle A1 (unit: degrees) of the boom 11 with respect to the body frame 3, and the vertical axis is the speed of the boom 11. When the arm connecting pin 16 is higher than the boom foot pin 15, the angle A1 has a positive value. As shown in Figure 13, the movable range of the boom 11 is a range where the angle A1 is approximately minus 45 degrees to approximately plus 100 degrees. Angle A1 of approximately minus 45 degrees is one end of the movable range of the boom 11. Angle A1 of approximately plus 100 degrees is the other end of the movable range of the boom 11.

[0121] The speed of the boom 11 becomes zero at the end of the movable range of the boom 11, and as the rotating boom 11 approaches the end of the movable range, the speed of the boom 11 decreases. The slope of the graph shown in Figure 13 is the angular acceleration of the boom 11. The rotational moment calculation unit 55 calculates the product of the angular acceleration of the boom 11 when it decelerates and the moment of inertia Ib as the rotational moment acting on the work implement 10 at the end of the movable range of the boom 11.

[0122] In step S6, the angular acceleration limiting unit 56 reads out the rotational moment threshold value from the memory unit 58. The rotational moment threshold value is stored in advance in the memory unit 58. The rotational moment threshold value is set, for example, as a value that prevents the crawler device 5Cr from lifting off the ground. The angular acceleration limiting unit 56 compares the rotational moment acting on the work implement 10 at the end of the movable range of the boom 11, calculated in step S5, with the threshold value, and determines whether the rotational moment is equal to or less than the threshold value.

[0123] If it is determined that the rotational moment is greater than the threshold value (NO in step S6), there is a possibility that the rotational moment when the boom 11 reaches the end of the movable range will cause the track unit 5Cr to lift off the ground. If the track unit 5Cr lifts off the ground, the impact when the track unit 5Cr touches the ground again will be large, causing vibrations in the vehicle body 1. In this case, therefore, in step S7, the angular acceleration limiting unit 56 limits the angular acceleration of the work implement 10. The angular acceleration limiting unit 56 limits the angular acceleration of the work implement 10 based on the result of the determination in step S6.

[0124] Figure 14 is a graph showing the relationship between the attitude of the boom 11 and the speed of the boom 11 after angular acceleration has been limited. As with Figure 13, the horizontal axis of the graph in Figure 14 represents the angle A1 of the boom 11, and the vertical axis represents the speed of the boom 11. The movable range of the boom 11 is the same as in Figure 13. As shown in Figure 14, the speed of the boom 11 gradually decreases as the boom 11 approaches the end of its movable range. The slope of the graph is smaller than in Figure 13. The angular acceleration of the boom 11 as it approaches the end of its movable range is limited.

[0125] The rotational moment Hb of the boom 11 is calculated as the product of the moment of inertia Ib and the angular acceleration, as expressed by the above equation (2). By reducing the angular acceleration of the boom 11, the value of the rotational moment Hb acting on the boom 11 at the end of the movable range of the boom 11 becomes smaller. This suppresses the crawler unit 5Cr from lifting off the ground when the boom 11 reaches the end of the movable range. Since it is possible to suppress the occurrence of an event in which the crawler unit 5Cr lifts off and then touches the ground again, it is possible to suppress vibration of the vehicle body 1. Since the transmission of vibration to the cab 4 mounted on the vehicle body 1 is suppressed, it is possible to improve the riding comfort of the operator sitting in the cab 4.

[0126] In step S8, the angular acceleration limiting unit 56 determines the attitude at which the angular velocity is reduced. The maximum value of the velocity of the boom 11 is the same in Fig. 13 and Fig. 14 . In order to gradually reduce the velocity of the boom 11 to zero at the end of the movable range, the start point for reducing the velocity must be a position farther away from the end of the movable range. In the example shown in Fig. 13 , the velocity reduction of the boom 11 starts at a position approximately 20° away from the end of the movable range. On the other hand, in Fig. 14 , the velocity reduction of the boom 11 starts at a position approximately 40° away from the end of the movable range.

[0127] As described above, the moment of inertia of the work implement 10 changes depending on the attitude of the work implement 10 and changes depending on the load value W. The angular acceleration limiting unit 56 determines the attitude of the work implement 10 when the moving work implement 10 begins to reduce its speed, according to the moment of inertia of the work implement 10 about the boom foot pin 15. In this way, it is possible to improve the ride comfort for the operator without sacrificing the workability of the electric excavator 30 as much as possible.

[0128] The process returns to step S6, where it is determined again whether the rotation moment is equal to or less than the threshold value. If it is determined in step S6 that the rotation moment is equal to or less than the threshold value (YES in step S6), the process ends ("END" in FIG. 11).

[0129] In the embodiment, an example has been described in which the electric motor 100 includes the boom motor 110 and the arm motor 140 separately. The electric motors 100 that generate the driving force for the boom 11 and the arm 12 do not necessarily have to be provided separately. A configuration may be adopted in which power is distributed from the output shaft of a single electric motor 100 and the driving force is transmitted to the boom 11 and the arm 12, respectively. In this case, the transmission of the driving force to the boom 11 and the arm 12 may be switched by an operation by an operator in the cab 4.

[0130] In the embodiment, an example has been described in which the cab 4 is disposed on the front left side of the body frame 3, the work implement 10 is disposed to the right of the cab 4, and the boom motor 110 and the arm motor 140 are disposed to the right of the work implement 10. The arrangement is not limited to this, and for example, by disposing the cab 4 behind the work implement 10, it becomes possible to dispose the electric motors 100 on both the left and right sides of the work implement 10, thereby improving the degree of freedom in disposing the electric motors 100.

[0131] In the embodiment, the electric shovel 30 is described as including an electric motor that generates driving force for driving the work machine 10. The electric shovel 30 may be an electric vehicle in which the electric motor also generates driving force for traveling the traveling body 5 and for rotating the rotating body 2 relative to the traveling body 5. The electric shovel 30 does not have to include an internal combustion engine. The electric shovel 30 does not have to include a hydraulic circuit.

[0132] In the embodiment, an example has been described in which the power transmission device includes a planetary gear reducer. Instead of the planetary gear reducer, the power transmission device may include a spur reducer in which a plurality of gears are combined by meshing one gear with another gear.

[0133] The embodiments disclosed herein are to be considered in all respects as illustrative and not restrictive. The scope of the present invention is defined by the claims, not by the above description, and is intended to include all modifications within the meaning and scope of the claims.

[0134] 1 Body, 2 Swing unit, 3 Body frame, 4 Cab, 4S Cab, 5 Running unit, 5Cr Track device, 10 Work machine, 11 Boom, 12 Arm, 13 Bucket, 15 Boom foot pin, 16 Arm connecting pin, 17 Attachment connecting pin, 30 Electric excavator, 40 Work machine attitude detector, 41 Boom angle sensor, 42 Arm angle sensor, 43 Attachment angle sensor, 50 Controller, 51 Angle acquisition unit, 52 Angular acceleration calculation unit, 53 Attachment total weight calculation unit, 54 Inertia moment calculation unit, 55 Rotational moment calculation unit, 56 Angular acceleration limiting unit, 58 Memory unit, 59 Timer, 100 Electric motor, 110 Boom electric motor, 140 Arm electric motor, 160, 210 Power transmission device, 220 Attachment electric motor.

Claims

1. A working machine comprising a vehicle body frame, a boom supported by the vehicle body frame, an arm connected to the boom, and an attachment connected to the arm; at least one electric motor that generates a driving force for relatively moving the attachment with respect to the vehicle body frame; and a controller that limits an angular acceleration of the working machine based on a determination result as to whether a rotational moment acting on the working machine at an end of a movable range of the working machine is equal to or less than a threshold value.

2. The working machine according to claim 1, further comprising a working machine attitude detector that detects an attitude of the working machine, wherein the controller calculates a total weight of the attachment using the attitude of the working machine and the driving force generated by the electric motor, calculates a moment of inertia about a rotation axis of the working machine using the attitude of the working machine and the total weight of the attachment, and calculates the rotational moment using the moment of inertia.

3. The working machine according to claim 1, wherein the controller determines an attitude of the working machine when the moving working machine starts to reduce its speed.

4. The working machine according to any one of claims 1 to 3, wherein the electric motor includes a boom electric motor that generates a driving force for relatively moving the boom with respect to the vehicle body frame with a base end portion of the boom as a fulcrum.

5. The working machine according to any one of claims 1 to 3, wherein the electric motor includes an arm electric motor that generates a driving force for relatively moving the arm with respect to the vehicle body frame with a tip end portion of the boom as a fulcrum.

6. The working machine according to any one of claims 1 to 3, wherein the electric motor includes an attachment electric motor that generates a driving force for relatively moving the attachment with respect to the arm.

7. The working machine according to claim 2, wherein the attachment is a bucket, and the total weight of the attachment includes the self-weight of the bucket and the weight of a load mounted on the bucket.

8. A control method for a working machine, comprising: determining whether a rotational moment acting on the working machine at an end of a movable range of the working machine, which is supported by a vehicle body frame and relatively moves with respect to the vehicle body frame by a driving force of an electric motor, is equal to or less than a threshold value; and limiting an angular acceleration of the working machine based on a result of the determination.

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