Work machine

Abstract

This invention compensates for working machine gravity with ease and accuracy. This work machine includes: a boom (11) supported on a vehicle body frame (3); an arm (12) connected to the boom (11); and an attachment connected to the arm (12). A first actuator generates boom drive torque for moving the boom (11) relative to the vehicle body frame (3). A second actuator generates arm drive torque for moving the arm (12) relative to the boom (11). A power transmission device mechanically transmits the arm drive torque to the arm. The power transmission device and the boom (11) make up a link mechanism. A first elastic member compensates for boom gravity. A second elastic member (221) compensates for arm (12) gravity.

Description

Work machinery

[0001] The present disclosure relates to work machines.

[0002] An example of prior art is the work machine described in Japanese Patent Laid-Open Publication No. 2015-105560 (Patent Document 1). This work machine has a configuration in which a boom of a work attachment is rotatably attached to an upper rotating body. One end of a weight compensation spring is attached to the boom, and the other end of the weight compensation spring is attached to the upper rotating body. The spring force of the weight compensation spring compensates for torque acting on the rotating shaft at the base end of the boom due to the total weight of the work attachment.

[0003] JP 2015-105560 A

[0004] In a work machine equipped with a gravity compensation mechanism that mechanically compensates for the gravity of the work machine, there is a demand for gravity compensation to be performed simply and accurately.

[0005] The present disclosure proposes a work machine that can easily and accurately compensate for the gravity of the work machine.

[0006] A work machine according to the present disclosure includes a body frame, a work implement, a first actuator, a second actuator, a power transmission device, a first elastic member, and a second elastic member. 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 first actuator generates a boom drive torque that moves the boom relative to the body frame. The second actuator generates an arm drive torque that moves the arm relative to the boom. The power transmission device mechanically transmits the arm drive torque to the arm. The power transmission device and the boom form a link mechanism. The first elastic member compensates for the gravity of the boom. The second elastic member compensates for the gravity of the arm.

[0007] According to the work machine of the present disclosure, the weight of the work implement can be easily and accurately compensated for.

[0008] FIG. 1 is a side view schematically showing the configuration of an electric excavator. FIG. 2 is a perspective view of a body frame and a work implement. FIG. 3 is a plan view of the body frame and the work implement. FIG. 4 is a diagram showing the schematic configuration of a power transmission device that transmits driving force to a boom. FIG. 5 is a skeleton diagram of a power transmission path from an electric motor to a gear member. FIG. 6 is a diagram showing the schematic configuration of a power transmission device that transmits driving force to an arm. FIG. 7 is a schematic diagram of a double motor drive. FIG. 8 is a diagram showing the schematic configuration of a first mechanism that mechanically compensates to balance the weight of the boom. FIG. 9 is an enlarged view of the first mechanism. FIG. 10 is a schematic view showing the first mechanism in a position where the boom is raised. FIG. 11 is a schematic view showing the first mechanism in a position where the boom is lowered. FIG. 12 is a table showing the moment generated by a first elastic member. FIG. 13 is a diagram showing the schematic configuration of a second mechanism that mechanically compensates to balance the weight of the arm. FIG. 14 is an enlarged view of the second mechanism. FIG. 15 is a schematic view showing the second mechanism in a position where the arm is moved in the dumping direction. FIG. 16 is a schematic view showing the second mechanism in a position where the arm is moved in the excavation direction. FIG. 17 is a table showing the moment generated by the second elastic member. It is a schematic diagram showing the moment of the work machine on a slope.It is a block diagram showing the outline configuration of a control system.It is a flowchart showing the flow of a process for determining the drive torque on a slope.

[0009] 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.

[0010] 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.

[0011] <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.

[0012] 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.

[0013] 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.

[0014] 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.

[0015] 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.

[0016] 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.

[0017] 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.

[0018] 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.

[0019] 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.

[0020] 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.

[0021] 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.

[0022] A vehicle body IMU (Inertial Measurement Unit) 40 is attached to the rotating unit 2, typically the vehicle body frame 3. The vehicle body IMU 40 measures the acceleration of the rotating unit 2 in the longitudinal, lateral, and vertical directions, and the angular velocity of the rotating unit 2 about the longitudinal, lateral, and vertical directions. The vehicle body IMU 40 corresponds to an example of an "angle sensor" that detects the angle of the vehicle body frame 3 relative to the horizontal direction.

[0023] A boom IMU 41 is attached to the boom 11. An arm IMU 42 is attached to the arm 12. A bucket IMU 43 is attached to the first member 22.

[0024] The boom IMU 41 measures the acceleration of the boom 11 in the fore-and-aft, left-and-right, and up-and-down directions, and the angular velocities of the boom 11 in the fore-and-aft, left-and-right, and up-and-down directions. The arm IMU 42 measures the acceleration of the arm 12 in the fore-and-aft, left-and-right, and up-and-down directions, and the angular velocities of the arm 12 in the fore-and-aft, left-and-right, and up-and-down directions. The bucket IMU 43 measures the acceleration of the bucket 13 in the fore-and-aft, left-and-right, and up-and-down directions, and the angular velocities of the bucket 13 in the fore-and-aft, left-and-right, and up-and-down directions. The boom IMU 41, arm IMU 42, and bucket IMU 43 constitute a work implement attitude sensor that is attached to the work implement 10 and detects the attitude of the work implement 10 relative to the vehicle body 1.

[0025] 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.

[0026] <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.

[0027] The boom electric motor 110 rotates the boom 11, generating a rotational force that moves the boom 11 relative to the body frame 3. The boom electric motor 110 corresponds to an example of a "first actuator" that generates a boom drive torque. Driven by the boom electric motor 110, the boom 11 can rotate relative 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.

[0028] 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.

[0029] The arm electric motor 140 generates a rotational force that rotationally drives the arm 12 and moves the arm 12 relative to the body frame 3. The arm electric motor 140 corresponds to an example of a "second actuator" that generates an arm drive torque. 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, and in this case, the arm 12 is driven by the arm electric motor 140.

[0030] 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.

[0031] <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.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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 rotates in the circumferential direction of the output shaft 112 by the rotational torque generated by the first boom electric motor 111. The output shaft 112 is connected to the sun gear 114. The rotational drive force of the first boom electric motor 111 is input to the sun gear 114.

[0038] 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.

[0039] 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.

[0040] 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 rotates in the circumferential direction of the output shaft 122 by the rotational torque generated by the second boom electric motor 121. The output shaft 122 is connected to the sun gear 124. The rotational drive force of the second boom electric motor 121 is input to the sun gear 124.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] 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 .

[0050] 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.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] 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. The power transmission device 160 and the boom 11 form a link mechanism.

[0055] 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.

[0056] <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.

[0057] 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.

[0058] 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, the shape of the rotating member 162, 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.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] 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.

[0064] 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.

[0065] 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.

[0066] 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.

[0067] 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.

[0068] 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.

[0069] 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.

[0070] 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.

[0071] 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.

[0072] 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.

[0073] While backlash elimination control is being executed, the attachment at the tip of the work machine 10 is stopped or moves only at a slow speed. Since the movement speed of the attachment at the tip of the work machine 10 is slow and the impact when the attachment collides with an object is small, damage to the planetary gear reducer is prevented.

[0074] 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 either or both of the boom gear member 131 and the arm gear member 161, which are driven by a single electric motor.

[0075] <Gravity Compensation Mechanism 200> When the work implement 10, for example, raises the boom 11, it moves vertically against gravity. If the boom motor 110 is to support the weight of the boom 11, it is necessary to select a boom motor 110 with a high rated output. In this case, the weight, installation area, and energy consumption of the boom motor 110 increase, and it is also disadvantageous for high-acceleration movement. Therefore, the electric excavator 30 of this embodiment is provided with a gravity compensation mechanism 200 that mechanically compensates for the weight of the work implement 10 when it is loaded.

[0076] Fig. 8 is a diagram showing a schematic configuration of a first mechanism 210 that mechanically compensates for the gravity of the boom 11 so as to balance the weight of the boom 11. The gravity compensation mechanism 200 of this embodiment includes the first mechanism 210. The first mechanism 210 has a first elastic member 211 and a first rod member 212. The first rod member 212 has a rod-like shape. Fig. 9 is an enlarged view of the first mechanism 210.

[0077] The first elastic member 211 is supported by the first rod member 212 and is configured to be expandable and contractible in the extending direction of the first rod member 212. The first elastic member 211 is disposed between the first tip support portion 213 and the first base end support portion 214. The first tip support portion 213 is fixed to the tip of the first rod member 212. The tip of the first elastic member 211 (the left end in FIG. 9 ) is attached to and supported by the first tip support portion 213. The first elastic member 211 shown in FIG. 8 is shorter than its natural length. The first elastic member 211 is compressed. The first elastic member 211 exerts an elastic force that tends to extend it. The first elastic member 211 is, for example, a spring.

[0078] The first cylinder portion 215 has a hollow cylindrical shape. The axial direction of the first cylinder portion 215 coincides with the extension direction of the first rod member 212. The first elastic member 211 is disposed inside the first cylinder portion 215 and is guided by the first cylinder portion 215 in the extension direction of the first rod member 212. The first cylinder portion 215 has an open end facing the tip of the first rod member 212.

[0079] A first bottom surface portion 216 is attached to the other end of the first cylinder portion 215, which faces the base end of the first rod member 212. The first cylinder portion 215 and the first bottom surface portion 216 form a hollow, bottomed cylinder. The first bottom surface portion 216 has a plate-like shape. A through-hole is formed in the first bottom surface portion 216, penetrating the first bottom surface portion 216 in the thickness direction. The first rod member 212 passes through the through-hole.

[0080] The first bottom surface portion 216 is not fixed to the first rod member 212. The first cylinder portion 215 and the first bottom surface portion 216 are movable integrally relative to the first rod member 212. The first cylinder portion 215 and the first bottom surface portion 216 are movable back and forth in the extension direction of the first rod member 212. Meanwhile, the first cylinder portion 215 and the first bottom surface portion 216 are rotatable integrally with the first rod member 212 relative to the body frame 3.

[0081] The first bottom surface portion 216 constitutes the first base end support portion 214. The base end of the first elastic member 211 (the right end in FIG. 9 ) is attached to the first base end support portion 214 (first bottom surface portion 216) and is supported by the first base end support portion 214 (first bottom surface portion 216). As the first bottom surface portion 216 moves relative to the first rod member 212, the first elastic member 211 expands and contracts, and the elastic force of the first elastic member 211 changes.

[0082] A pin holder 218H is fixed to a cylindrical member made up of a first cylinder portion 215 and a first bottom surface portion 216. The pin holder 218H supports a first rotation center pin 218. The pin holder 218H is rotatable around the first rotation center pin 218 relative to the first rotation center pin 218. The first rotation center pin 218 is fixed to the body frame 3. The first rotation center pin 218 may be fixed to, for example, one or both of the vertical plates 7, 8. A bracket (not shown) may be fixed to the body frame 3, and the first rotation center pin 218 may be fixed to the bracket and then fixed to the body frame 3 via the bracket.

[0083] A pin holder 217H is fixed to the other end of the first rod member 212. The pin holder 217H supports a first movable pin 217. The pin holder 217H is rotatable around the first movable pin 217 relative to the first movable pin 217. The first movable pin 217 is attached to the boom 11. The first movable pin 217 may be fixed to the boom 11. The first movable pin 217 supports the other end of the first rod member 212.

[0084] An assembly including the first elastic member 211, the first rod member 212, the first tip support portion 213, the first cylinder portion 215, the first bottom surface portion 216 (the first base end support portion 214), and the pin holders 217H, 218H will be referred to as the first assembly hereinafter. The first assembly is supported by a first movable pin 217 and is rotatable relative to the boom 11 around the first movable pin 217. The first assembly is also supported by a first rotation center pin 218. The first assembly is supported by the body frame 3 via the first rotation center pin 218 and is rotatable relative to the body frame 3 around the first rotation center pin 218.

[0085] The boom driving torque generated by the boom electric motor 110 causes the boom 11 to rotate relative to the body frame 3 around the boom foot pin 15. The first movable pin 217 rotates relative to the body frame 3 around the boom foot pin 15 in accordance with the rotational movement of the boom 11. While the first movable pin 217 rotates relative to the body frame 3, the first rotation center pin 218 does not change its position relative to the body frame 3. The first assembly described above rotates relative to the body frame 3 around the first rotation center pin 218 as the center of rotation.

[0086] Figure 10 is a schematic diagram showing the first mechanism 210 in a position in which the boom 11 is raised. Compared to Figure 8, the boom 11 rotates counterclockwise in the figure around the boom foot pin 15. The first movable pin 217 rotates together with the boom 11 and moves to a position almost directly above the boom foot pin 15. The first rotation center pin 218 remains in an unchanged position relative to the body frame 3. The first assembly described above rotates counterclockwise in the figure around the first rotation center pin 218.

[0087] The first movable pin 217 is closer to the first rotation center pin 218. The other end of the first rod member 212 is disposed closer to the first rotation center pin 218. Since the extension length of the first rod member 212 is constant, one end of the first rod member 212 is farther from the first rotation center pin 218. The first tip support portion 213 is disposed farther from the first rotation center pin 218. The position of the first base end support portion 214 relative to the first rotation center pin 218 in the radial direction of the first rotation center pin 218 remains unchanged. The distance between the first tip support portion 213 and the first base end support portion 214 has increased. Therefore, in the arrangement shown in FIG. 10 , the first elastic member 211 is elongated compared to FIG. 8 .

[0088] 10 is still compressed and shorter than its natural length, but is closer to its natural length. The amount of deformation of the first elastic member 211 from its natural length is reduced. Therefore, the elastic force acting on the first elastic member 211 is smaller than that in FIG. 8.

[0089] Figure 11 is a schematic diagram showing the first mechanism 210 with the boom 11 lowered. Compared to Figure 8, the boom 11 rotates clockwise in the figure around the boom foot pin 15. The first movable pin 217 rotates together with the boom 11 and moves to a position diagonally downward to the right in the figure relative to the boom foot pin 15. The first rotation center pin 218 remains in an unchanged position relative to the body frame 3. The first assembly described above rotates clockwise in the figure around the first rotation center pin 218.

[0090] The first movable pin 217 is moved away from the first rotation center pin 218. The other end of the first rod member 212 is disposed farther away from the first rotation center pin 218. Since the extension length of the first rod member 212 is constant, one end of the first rod member 212 is closer to the first rotation center pin 218. The first tip support portion 213 is disposed closer to the first rotation center pin 218. The position of the first base end support portion 214 relative to the first rotation center pin 218 in the radial direction of the first rotation center pin 218 remains unchanged. The distance between the first tip support portion 213 and the first base end support portion 214 is reduced. Therefore, in the arrangement shown in FIG. 11 , the first elastic member 211 is compressed compared to FIG. 8 .

[0091] Since the deformation amount of the first elastic member 211 from its natural length is increased, the elastic force acting on the first elastic member 211 is greater than that in FIG.

[0092] Figure 12 is a table showing the moment generated by the first elastic member 211. "Boom in" in Figure 12 refers to the posture of the boom 11 shown in Figure 8. The magnitude of the elastic force (spring force) acting on the first elastic member 211 in the "boom in" state is set to "medium," and the moment arm is set to "medium." The moment acting on the boom foot pin 15 by the first elastic member 211 is calculated by multiplying the spring force by the moment arm. The first elastic member 211 acts on the boom foot pin 15 with a moment of "medium" magnitude.

[0093] "Boom up" in Figure 12 indicates a posture shown in Figure 10 in which the boom 11 is raised compared to Figure 8. In the "boom up" state, the moment arm is increased to "large" compared to the "boom down" state, but the amount of deformation of the first elastic member 211 from its natural length is reduced, so the magnitude of the spring force is "small." The magnitude of the moment acting around the boom foot pin 15 by the first elastic member 211 is reduced to "small."

[0094] "Boom down" in Figure 12 indicates a posture shown in Figure 11 in which the boom 11 is lowered compared to Figure 8. In the "boom down" state, the deformation amount of the first elastic member 211 increases, so the magnitude of the spring force is "large," but the change in posture of the boom 11 reduces the moment arm to "small." The magnitude of the moment acting around the boom foot pin 15 by the first elastic member 211 is reduced to "small."

[0095] The moment acting on the first elastic member 211 is in the opposite direction to the moment due to the weight of the work implement 10. The first elastic member 211 acts on the boom 11 in a direction to raise the boom 11. This cancels out the moment caused by the weight of the work implement 10. The first elastic member 211 compensates for the gravity of the boom 11.

[0096] FIG. 13 is a diagram showing a schematic configuration of a second mechanism 220 that mechanically compensates for the weight of the arm 12 to balance it. In FIG. 13 and the subsequent FIGS. 15 and 16, the arm gear member 161, the rotating member 162, the first link member 171, and the second link member 172 are shown in a simplified form. The gravity compensation mechanism 200 of this embodiment includes a second mechanism 220. The second mechanism 220 includes a second elastic member 221 and a second rod member 222. The second rod member 222 has a rod-like shape. FIG. 14 is an enlarged view of the second mechanism 220.

[0097] The second elastic member 221 is supported by the second rod member 222 and is configured to be expandable and contractible in the extending direction of the second rod member 222. The second elastic member 221 is disposed between the second tip support portion 223 and the second base end support portion 224. The tip of the second elastic member 221 (the left end in FIG. 14 ) is attached to the second tip support portion 223 and supported by the second tip support portion 223. The second elastic member 221 shown in FIG. 13 is shorter than its natural length. The second elastic member 221 is compressed. The second elastic member 221 exerts an elastic force that tends to extend it. The second elastic member 221 is, for example, a spring.

[0098] The second base end support portion 224 is fixed to the base end of the second rod member 222. The second tip support portion 223 is not fixed to the second rod member 222. The second tip support portion 223 is movable relative to the second rod member 222. The second tip support portion 223 is movable back and forth in the extension direction of the second rod member 222. As the second tip support portion 223 moves relative to the second rod member 222, the second elastic member 221 expands and contracts, changing the elastic force of the second elastic member 221. Meanwhile, the second tip support portion 223 and the second rod member 222 are rotatable together relative to the body frame 3.

[0099] The second rotation center pin 228 is fixed to the body frame 3. The second rotation center pin 228 may be fixed to either or both of the vertical plates 7, 8, for example. A bracket (not shown) may be fixed to the body frame 3, and the second rotation center pin 228 may be fixed to the bracket and then fixed to the body frame 3 via the bracket. The pin holder 228H supports the second rotation center pin 228. The pin holder 228H is rotatable around the second rotation center pin 228 relative to the second rotation center pin 228. The pin holder 228H constitutes the second tip support portion 223.

[0100] The connecting pin 177 that connects the rotating member 162 and the first link member 171 constitutes the second movable pin 227. The second movable pin 227 is attached to the power transmission device 160 that transmits the driving force generated by the arm electric motor 140 to the arm 12. A pin holder 227H is fixed to the other end of the second rod member 222. The pin holder 227H supports the second movable pin 227. The pin holder 227H is rotatable around the second movable pin 227 relative to the second movable pin 227. The second movable pin 227 supports the other end of the second rod member 222. The pin holder 227H constitutes the second base end support portion 224.

[0101] An assembly including the second elastic member 221, the second rod member 222, the pin holder 228H (second tip support portion 223), and the pin holder 227H (second base end support portion 224) will be referred to as the second assembly hereinafter. The second assembly is supported by a second movable pin 227 and is rotatable about the second movable pin 227 relative to the rotating member 162 and the first link member 171. The second assembly is also supported by a second rotation center pin 228. The second assembly is supported by the body frame 3 via the second rotation center pin 228 and is rotatable about the second rotation center pin 228 relative to the body frame 3.

[0102] The arm drive torque generated by the arm electric motor 140 causes the arm gear member 161 and the rotating member 162 to rotate relative to the body frame 3 around the boom foot pin 15. The connecting pin 177 (second movable pin 227) rotates relative to the body frame 3 around the boom foot pin 15 in accordance with the rotational movement of the rotating member 162. While the second movable pin 227 rotates relative to the body frame 3, the second rotation center pin 228 does not change its position relative to the body frame 3. The second assembly described above rotates relative to the body frame 3 around the second rotation center pin 228 as the center of rotation.

[0103] Figure 15 is a schematic diagram showing the second mechanism 220 in a position where the arm 12 has been moved in the dumping direction (a direction in which the arm 12 is moved away from the boom 11). Note that the position of the boom 11 relative to the body frame 3 remains unchanged in Figures 13, 15, and 16. In the position shown in Figure 13, the arm 12 extends substantially in the vertical direction.

[0104] 15, compared to FIG. 13, the arm gear member 161 and the rotating member 162 are rotating counterclockwise in the figure around the boom foot pin 15. The connecting pin 177 rotates together with the rotating member 162 and moves away from the pin 178. The first link member 171 connected to the connecting pin 177 and the connecting pin 174 connected to the first link member 171 are pulled to the left in the figure by the rotating member 162. The intermediate member 173 is rotating counterclockwise in the figure around the pin 178.

[0105] The connecting pin 175 rotates counterclockwise in the figure around pin 178 together with the intermediate member 173. The second link member 172 connected to the connecting pin 175 and the connecting pin 176 connected to the second link member 172 are pulled to the left in the figure. As a result, the arm 12 rotates counterclockwise in the figure around the arm connecting pin 16. The arm 12 extends diagonally downward to the right from the arm connecting pin 16.

[0106] The second movable pin 227 rotates together with the rotating member 162. The second rotation center pin 228 maintains an unchanging position relative to the body frame 3. The second assembly rotates clockwise in the drawing around the second rotation center pin 228.

[0107] 15, the second movable pin 227 is moved away from the second rotation center pin 228. The other end of the second rod member 222 is disposed farther away from the second rotation center pin 228. The second base end support portion 224 is disposed farther away from the second rotation center pin 228. The distance between the second tip support portion 223 and the second base end support portion 224 is increased. Therefore, in the arrangement shown in FIG. 15, the second elastic member 221 is elongated compared to FIG. 13.

[0108] 15 shows the second elastic member 221 in a compressed state, shorter than its natural length, but closer to its natural length. The amount of deformation of the second elastic member 221 from its natural length is reduced. Therefore, the elastic force acting on the second elastic member 221 is smaller than that shown in FIG. 13.

[0109] Figure 16 is a schematic diagram showing the second mechanism 220 in an attitude in which the arm 12 has been moved in the excavation direction (a direction in which the arm 12 approaches the boom 11). Compared to Figure 13 , in Figure 16 , the arm gear member 161 and the rotating member 162 are rotating clockwise in the figure around the boom foot pin 15. The connecting pin 177 rotates together with the rotating member 162 and approaches pin 178. The first link member 171 connected to the connecting pin 177 and the connecting pin 174 connected to the first link member 171 are pushed to the right in the figure by the rotating member 162. The intermediate member 173 is rotating clockwise in the figure around the pin 178.

[0110] The connecting pin 175 rotates clockwise in the figure around pin 178 together with the intermediate member 173. The second link member 172 connected to the connecting pin 175 and the connecting pin 176 connected to the second link member 172 are pushed to the right in the figure. As a result, the arm 12 rotates clockwise in the figure around the arm connecting pin 16. The arm 12 extends diagonally downward to the left from the arm connecting pin 16.

[0111] The second movable pin 227 rotates together with the rotating member 162. The second rotation center pin 228 maintains an unchanging position relative to the body frame 3. The second assembly rotates counterclockwise in the drawing around the second rotation center pin 228.

[0112] 16, the second movable pin 227 is moved away from the second rotation center pin 228. The other end of the second rod member 222 is disposed farther away from the second rotation center pin 228. The second base end support portion 224 is disposed farther away from the second rotation center pin 228. The distance between the second tip support portion 223 and the second base end support portion 224 is increased. Therefore, in the arrangement shown in FIG. 16, the second elastic member 221 is elongated compared to FIG. 13.

[0113] 16 is still compressed and shorter than its natural length, but is closer to its natural length. The amount of deformation of the second elastic member 221 from its natural length is reduced. Therefore, the elastic force acting on the second elastic member 221 is smaller than that in FIG. 13.

[0114] FIG. 17 is a table showing the moment generated by the second elastic member 221. "Arm upright" shown in FIG. 17 refers to the posture of the arm 12 shown in FIG. 13. The magnitude of the elastic force (spring force) acting on the second elastic member 221 in the "arm upright" state is set to "large." The moment acting on the second elastic member 221 around the arm connecting pin 16 is calculated by multiplying the spring force by the moment arm. In the "arm upright" state, the moment arm is "0," so the magnitude of the moment acting on the second elastic member 221 around the arm connecting pin 16 is "0."

[0115] "Arm excavation" shown in Figure 17 indicates a posture in which the arm 12 is closer to the boom 11 compared to Figure 13, as shown in Figure 16. In the "arm excavation" state, the deformation amount of the second elastic member 221 decreases, so the magnitude of the spring force decreases to "medium", and the moment arm increases to "medium". The second elastic member 221 acts on the arm connecting pin 16 with a moment of "medium" magnitude.

[0116] The "arm dump" state shown in Figure 17 indicates the posture shown in Figure 15 in which the arm 12 is further away from the boom 11 than in Figure 13. In the "arm dump" state, the deformation amount of the second elastic member 221 decreases, so the magnitude of the spring force decreases to "medium," and the moment arm increases to "medium." The second elastic member 221 acts on the arm connecting pin 16 with a moment of "medium" magnitude.

[0117] The moment acting on the second elastic member 221 is in the opposite direction to the moment due to the weight of the arm 12. The second elastic member 221 acts on the arm 12 in a direction that tilts the arm 12 relative to the vertical direction. The second elastic member 221 acts on the arm 12 in a direction opposite to the direction that makes the arm 12 stand upright. This cancels out the moment caused by the weight of the arm 12. The second elastic member 221 compensates for the gravity of the arm 12.

[0118] As described above, the electric shovel 30 of this embodiment is separately provided with the first mechanism 210 for compensating for the gravity of the boom 11 and the second mechanism 220 for compensating for the gravity of the arm 12. At least a portion of the gravity of the boom 11 is compensated for by the moment acting on the first elastic member 211. At least a portion of the gravity of the arm 12 is compensated for by the moment acting on the second elastic member 221.

[0119] A link mechanism is made up of the boom 11 and a power transmission device 160 that mechanically transmits the arm drive torque generated by the arm motor 140 to the arm 12. The boom 11 and arm 12 are pin-jointed by an arm connecting pin 16. The arm connecting pin 16 is a pin joint between the boom 11 and the arm 12, and the arm 12 rotates like a hinge relative to the boom 11. Therefore, the moment due to the weight of the arm 12 is not transmitted to the arm connecting pin 16, but the weight of the arm 12 is transmitted to the arm connecting pin 16. This does not change regardless of the posture of the arm 12.

[0120] Gravity can be compensated for by balancing the moment due to the weight of the arm 12 and the weight of the boom 11 with the first elastic member 211. Because the weight of the arm 12 is always constant, gravity compensation for the boom 11 is determined only by the angle of the boom 11, making gravity compensation simple. Gravity compensation for the boom 11 and gravity compensation for the arm 12 can be set independently, so gravity of the work implement 10 can be compensated for simply and accurately. This improves the operability of the work implement 10, improves the operational responsiveness of the work implement 10, and improves the positioning accuracy of the bucket 13 at the tip of the work implement 10.

[0121] 8 and 10 to 11 , the first elastic member 211 may be supported by a first rod member 212 that is supported on the body frame 3 so as to be rotatable relative to the body frame 3. As the electric shovel 30 operates to rotate the boom 11 around the boom foot pin 15, the first rod member 212 rotates around the first rotation center pin 218, and at this time the first elastic member 211 expands and contracts, changing the magnitude of the spring force. This makes it possible to perform appropriate gravity compensation in accordance with the attitude of the boom 11.

[0122] 8 and 10 to 11, the first movable pin 217 supporting the end of the first rod member 212 may be attached to the boom 11. In this way, the first rod member 212 can be rotated in accordance with the rotation of the boom 11, thereby reliably changing the magnitude of the spring force of the first elastic member 211.

[0123] 13 and 15 to 16 , the second elastic member 221 may be supported by a second rod member 222 that is supported on the body frame 3 so as to be rotatable relative to the body frame 3. In response to the operation of the electric shovel 30 to rotate the arm 12 around the arm connecting pin 16, the second rod member 222 rotates around the second rotation center pin 228, and at this time the second elastic member 221 expands and contracts, changing the magnitude of the spring force. This makes it possible to perform appropriate gravity compensation in accordance with the posture of the arm 12.

[0124] 13, 15 and 16, the second movable pin 227 supporting the end of the second rod member 222 may be attached to a power transmission device 160 that transmits the arm drive torque to the arm 12. In this way, the second rod member 222 is rotated in accordance with the rotation of the arm 12, and the magnitude of the spring force of the second elastic member 221 can be reliably changed.

[0125] In the above description, the first elastic member 211 and the second elastic member 221 are springs that change the magnitude of their elastic force by expanding and contracting. Either or both of the first elastic member 211 and the second elastic member 221 may be a constant force spring that generates a substantially constant elastic force regardless of the length to which the spring is stretched.

[0126] <Driving torque on slope> Fig. 18 is a schematic diagram showing the moment of the work machine 10 on level ground. １ , the distance from the boom foot pin 15 to the center of gravity of the boom 11 is lg １ , the distance from the arm connecting pin 16 to the center of gravity of the arm 12 is lg ２ , the weight of the boom 11 is m １ , the weight of the arm 12 is m ２ , and the acceleration of gravity is g. The angle of the boom 11 with respect to the body frame 3 is θ １ , the angle of the arm 12 relative to the boom 11 is θ ２ When the ground on which the electric shovel 30 is positioned is horizontal, a moment τ around the boom foot pin 15 due to the weight of the arm 12 and the weight of the boom 11 is １ is expressed by the following equation (1).

[0127]

[0128] In addition, the moment τ around the arm connecting pin 16 due to the weight of the arm 12 ２ is expressed by the following equation (2).

[0129]

[0130] 19 is a schematic diagram showing the moment of the work machine 10 on a slope. The ground on which the electric shovel 30 is located is at an angle θ ｐ When the arm 12 is tilted, a moment τ around the boom foot pin 15 due to the weight of the arm 12 and the weight of the boom 11 is １ ' is expressed by the following formula (3).

[0131]

[0132] In addition, the moment τ around the arm connecting pin 16 due to the weight of the arm 12 ２ ' is expressed by the following formula (4).

[0133]

[0134] Fig. 20 is a block diagram showing a schematic configuration of a control system for controlling the electric shovel 30. Fig. 20 shows only a part of the system that constitutes the electric shovel 30 of this embodiment. The electric shovel 30 includes the vehicle body IMU 40 also shown in Fig. 1, a work machine attitude detector 44 that detects the attitude of the work machine 10, and a controller 50 that controls the operation of the electric shovel 30. The acceleration and angular velocity of the revolving unit 2 detected by the vehicle body IMU 40 are input to the controller 50.

[0135] 1 constitute a work implement attitude detector 44. The boom IMU 41, arm IMU 42, and bucket IMU 43 are also shown in FIG. 1 and constitute a work implement attitude detector 44. The boom IMU 41 detects the angle of the boom 11 relative to the vehicle body frame 3. The arm IMU 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 bucket IMU 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 IMU 41, arm IMU 42, and bucket IMU 43 output angle detection signals to the controller 50.

[0136] The controller 50 includes a CPU (Central Processing Unit) etc. The controller 50 has a storage unit 58 .

[0137] The storage unit 58 is a non-volatile memory 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 the control programs stored in the storage unit 58 to perform various processes for controlling the operation of the electric shovel 30.

[0138] 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.

[0139] The controller 50 has a vehicle body attitude acquisition unit 51 , a work machine attitude acquisition unit 52 , a drive torque calculation unit 53 , and a gravity compensation torque calculation unit 54 .

[0140] FIG. 21 is a flowchart showing the flow of processing in the electric shovel 30 for determining the drive torque of the work machine 10 taking into account the gravity compensation torque on sloped ground.

[0141] In step S1, the work implement attitude acquisition unit 52 receives a detection signal of the angle of the work implement 10 from the work implement attitude detector 44. The work implement attitude acquisition unit 52 receives a detection signal of the angle of the boom 11 relative to the vehicle body frame 3 from the boom IMU 41. The work implement attitude acquisition unit 52 receives a detection signal of the angle of the arm 12 relative to the boom 11 from the arm IMU 42. The work implement attitude acquisition unit 52 acquires the current attitude of the work implement 10. The work implement attitude acquisition unit 52 stores the angles of the boom 11 and the arm 12 in the memory unit 58.

[0142] In step S2, the vehicle body attitude acquisition unit 51 receives a detection signal of the angle of the vehicle body frame 3 with respect to the horizontal direction from the vehicle body IMU 40. In particular, the vehicle body attitude acquisition unit 51 acquires the angle of the vehicle body frame 3 in the pitch direction. The vehicle body attitude acquisition unit 51 stores the angle of the vehicle body frame 3 in the memory unit 58.

[0143] In step S3, the gravity compensation torque calculation unit 54 calculates the boom gravity compensation torque BT1 on a slope. The boom gravity compensation torque BT1 is calculated based on the moment τ １ ' is.

[0144] In step S4, the gravity compensation torque calculation unit 54 calculates the arm gravity compensation torque AT1 on a slope. The arm gravity compensation torque AT1 is calculated based on the moment τ ２ ' is.

[0145] In step S5, the gravity compensation torque calculation unit 54 calculates the boom gravity compensation torque BT2 on level ground. The boom gravity compensation torque BT2 is calculated based on the moment τ １ is.

[0146] In step S6, the gravity compensation torque calculation unit 54 calculates the arm gravity compensation torque AT2 on level ground. The arm gravity compensation torque AT2 is calculated based on the moment τ ２ is.

[0147] In step S7, the gravity compensation torque calculation unit 54 calculates the boom gravity compensation torque difference ΔBT. The boom gravity compensation torque difference ΔBT is calculated based on the moment τ １ ' and the moment τ of the work machine 10 on the horizontal ground １ and is expressed by the following formula (5):

[0148]

[0149] In step S8, the gravity compensation torque calculation unit 54 calculates the arm gravity compensation torque difference ΔAT. The arm gravity compensation torque difference ΔAT is calculated based on the moment τ ２ ' and the moment τ of the arm 12 on the horizontal ground ２ and is expressed by the following equation (6).

[0150]

[0151] In step S9, the drive torque calculation unit 53 calculates the torque to be generated in the boom electric motor 110 to cause the boom 11 to perform the intended operation. The drive torque calculation unit 53 further adds the boom gravity compensation torque difference ΔBT to the calculated torque, and sets the resulting value as the boom drive torque. The drive torque calculation unit 53 outputs a control signal to the boom electric motor 110 so that the boom electric motor 110 generates the calculated boom drive torque.

[0152] In step S10, the drive torque calculation unit 53 calculates the torque to be generated in the arm motor 140 to cause the arm 12 to perform the intended operation. The drive torque calculation unit 53 further adds the arm gravity compensation torque difference ΔAT to the calculated torque, and sets this as the arm drive torque. The drive torque calculation unit 53 outputs a control signal to the arm motor 140 so that the arm motor 140 generates the calculated arm drive torque. Then, the process ends ("End" in FIG. 21).

[0153] The electric shovel 30 can also operate on uneven ground. Gravity compensation using only the first elastic member 211 and the second elastic member 221 described above may not be accurate on sloping ground, resulting in a decrease in the operational responsiveness of the work machine 10.

[0154] Therefore, the pitch angle of the body frame 3 is detected by the body IMU 40 attached to the body frame 3. A boom gravity compensation torque difference ΔBT, which is the difference between the gravity compensation torque of the boom 11 on inclined ground and the gravity compensation torque on level ground, is calculated. The boom gravity compensation torque difference ΔBT is added to the boom drive torque. By having the boom electric motor 110 generate a torque that takes into account the boom gravity compensation torque difference ΔBT, the responsiveness of the operation of the boom 11 can be improved.

[0155] An arm gravity compensation torque difference ΔAT, which is the difference between the gravity compensation torque of the arm 12 on an inclined ground and the gravity compensation torque on a level ground, is calculated. The arm gravity compensation torque difference ΔAT is added to the arm drive torque. By causing the arm motor 140 to generate a torque that takes into account the arm gravity compensation torque difference ΔAT, the responsiveness of the operation of the arm 12 can be improved.

[0156] 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.

[0157] 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.

[0158] 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.

[0159] In the embodiment, an example has been described in which the first actuator that generates the boom drive torque and the second actuator that generates the arm drive torque are both electric motors. However, instead of electric motors, hydraulic motors may be used to generate the boom drive torque and the arm drive torque. The concept of the embodiment may also be applied to a work machine in which the work implement 10 is hydraulically driven.

[0160] 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.

[0161] 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.

[0162] 1 Vehicle body, 2 Swing body, 3 Vehicle body frame, 5 Traveling body, 7, 8 Vertical plate, 10 Work implement, 11 Boom, 12 Arm, 13 Bucket, 15 Boom foot pin, 16 Arm connecting pin, 17 Attachment connecting pin, 21 Bucket link, 22 First member, 23 Second member, 30 Electric excavator, 40 Vehicle body IMU, 41 Boom IMU, 42 Arm IMU, 43 Bucket IMU, 44 Work implement attitude detector, 50 Controller, 51 Vehicle body attitude acquisition unit, 52 Work implement attitude acquisition unit, 53 Drive torque calculation unit, 54 Gravity compensation torque calculation unit, 58 Memory unit, 100 Electric motor, 110 Boom electric motor, 140 Arm electric motor, 160 Power transmission device, 161 Arm gear member, 162 Rotating member, 170 Arm link, 171 First link member, 172 Second link member, 173 Intermediate members, 174 to 177 Connecting pin, 178 Pin, 200 Gravity compensation mechanism, 210 First mechanism, 211 First elastic member, 212 First rod member, 213 First tip support portion, 214 First base end support portion, 215 First cylinder portion, 216 First bottom portion, 217 First movable pin, 217H, 218H Pin holder, 218 First rotation center pin, 220 Second mechanism, 221 Second elastic member, 222 Second rod member, 223 Second tip support portion, 224 Second base end support portion, 227 Second movable pin, 228 Second rotation center pin.

Claims

1. An operating 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; a first actuator that generates a boom drive torque for relatively moving the boom with respect to the vehicle body frame; a second actuator that generates an arm drive torque for relatively moving the arm with respect to the boom; a power transmission device that mechanically transmits the arm drive torque to the arm and constitutes a link mechanism together with the boom; a first elastic member that compensates for the gravity of the boom; and a second elastic member that compensates for the gravity of the arm.

2. The operating machine according to claim 1, further comprising a first rod member that is supported by the vehicle body frame so as to be rotatable relative to the vehicle body frame and supports the first elastic member.

3. The operating machine according to claim 2, further comprising a first movable pin that is attached to the boom and supports an end of the first rod member.

4. The operating machine according to claim 1, further comprising a second rod member that is supported by the vehicle body frame so as to be rotatable relative to the vehicle body frame and supports the second elastic member.

5. The operating machine according to claim 4, further comprising a second movable pin that is attached to the power transmission device and supports an end of the second rod member.

6. The operating machine according to any one of claims 1 to 5, further comprising: an angle sensor that detects an angle of the vehicle body frame with respect to the horizontal direction; and a controller that calculates a moment of the operating machine about a rotation center of the boom with respect to the vehicle body frame and causes the first actuator to generate the boom drive torque in consideration of a difference between a moment on an inclined ground and a moment on a horizontal ground.

7. The operating machine according to any one of claims 1 to 5, further comprising: an angle sensor that detects an angle of the vehicle body frame with respect to the horizontal direction; and a controller that calculates a moment of the operating machine about a rotation center of the arm with respect to the boom and causes the second actuator to generate the arm drive torque in consideration of a difference between a moment on an inclined ground and a moment on a horizontal ground.

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