Work machine

Abstract

To easily and accurately compensate for the gravity of a work machine.SOLUTION: A work implement includes a boom 11 supported by 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 a boom drive torque that moves the boom 11 relative to the vehicle body frame 3. A second actuator generates an arm drive torque that moves 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 form a link mechanism. A first elastic member compensates for the gravity of the boom. A second elastic member 221 compensates for the gravity of the arm 12.SELECTED DRAWING: Figure 13

Description

Technical Field

[0001] The present disclosure relates to a working machine.

Background Art

[0002] As a prior art, a working machine described in Japanese Patent Application Laid-Open No. 2015-105560 (Patent Document 1) is exemplified. This working machine has a configuration in which a boom of a working attachment is rotatably attached to an upper slewing 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 slewing body. By the spring force of the weight compensation spring, the torque due to the total weight of the working attachment acting on the rotation axis on the proximal end side of the boom is compensated.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In a working machine provided with a gravity compensation mechanism that mechanically compensates for the gravity of a working machine, it is required that the gravity compensation can be performed simply and accurately.

[0005] In the present disclosure, a working machine that can simply and accurately compensate for the gravity of a working machine is proposed.

Means for Solving the Problems

[0006] The work machine according to the present disclosure includes a vehicle 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 vehicle body frame, an arm connected to the boom, and an attachment connected to the arm. The first actuator generates a boom drive torque that relatively moves the boom with respect to the vehicle body frame. The second actuator generates an arm drive torque that relatively moves the arm with respect to the boom. The power transmission device mechanically transmits the arm drive torque to the arm. The power transmission device and the boom constitute 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.

Advantages of the Invention

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

Brief Description of the Drawings

[0008]

Figure 1

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Mode for Carrying Out the Invention

[0009] Hereinafter, 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, for convenience of explanation, the configuration may be omitted or simplified in some cases. It is also initially planned that any configuration is extracted from the embodiments and they are arbitrarily combined.

[0010] In the following description, "up", "down", "front", "rear", "left", and "right" are directions based on the operator seated on the driver's seat 4S in the cab 4.

[0011] <Overall Configuration> FIG. 1 is a side view schematically showing the configuration of an electric excavator 30 as an example of a working machine. In FIG. 1, a schematic configuration of the electric excavator 30 viewed from the side from the right is shown. As shown in FIG. 1, the electric excavator 30 of the embodiment mainly includes a revolving body 2, a traveling body 5, and a working device 10. The revolving body 2 and the traveling body 5 constitute the vehicle body 1 of the electric excavator 30.

[0012] The traveling body 5 has a pair of left and right crawler devices 5Cr. Each of the pair of left and right crawler devices 5Cr has a crawler. By rotationally driving the pair of left and right crawlers, the electric excavator 30 self-propels. The traveling body 5 may have wheels (tires) instead of the crawler devices 5Cr.

[0013] The revolving body 2 is rotatably installed with respect to the traveling body 5. The revolving body 2 mainly has a vehicle body frame 3, a cab 4, and a counterweight 6. The cab 4 and the counterweight 6 are mounted on the vehicle body frame 3.

[0014] The operator boards the cab 4 and operates the electric excavator 30. The cab 4 is arranged, for example, on the front left side (front side of the vehicle) of the revolving body 2. Inside the cab 4, a driver's seat 4S for the operator to sit is arranged. In the present disclosure, the electric excavator 30 is operated from inside the cab 4, but the electric excavator 30 may be remotely operated wirelessly from a location away from the electric excavator 30. The counterweight 6 is arranged on the rear side (rear side of the vehicle) of the revolving body 2 with respect to the cab 4. The counterweight 6 is arranged at the rear of the revolving body 2.

[0015] The working device 10 is supported by the revolving body 2 at the front part of the revolving body 2, for example, on the right side of the cab 4. The working device 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 slewing body 2 by a boom foot pin 15. The boom foot pin 15 extends in the left-right direction and penetrates 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 end of the boom 11 by an arm connection pin 16. The arm connection pin 16 extends in the left-right direction and penetrates the tip end of the boom 11 and the base end of the arm 12. The bucket 13 is rotatably connected to the tip end of the arm 12 by an attachment connection pin 17. The attachment connection pin 17 extends in the left-right direction and penetrates the tip end of the arm 12 and the base end of the bucket 13.

[0017] The bucket 13 constitutes the tip portion of the working machine 10. The bucket 13 of the embodiment is connected to the boom 11 via the arm 12. By the bucket 13 rotating about the attachment connection pin 17 and / or the arm 12 rotating about the arm connection pin 16, the bucket 13 moves relative to the boom 11. The bucket 13 is configured to be movable relative to the boom 11.

[0018] The bucket 13 has a plurality of blades. The tip end of the bucket 13 is referred to as a cutting edge 13A. Note that the bucket 13 may not have blades. The tip end 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 working machine 10 and rotatable relative to the arm 12. Depending on the type of work, the attachment can be replaced with a breaker, grapple, or lifting magnet, etc.

[0020] The work machine 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 so as to be relatively rotatable. The first member 22 and the second member 23 are pin-connected 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 portion of the bucket 13 by a link pin 26.

[0021] The first member 22 has a rod-like shape. The first member 22 is connected to the second member 23 at one end and is connected to the arm 12 at the other end. The second member 23 has a rod-like shape. The second member 23 is connected to the first member 22 at one end and is connected to the bucket 13 at the other end.

[0022] A vehicle body IMU (Inertial Measurement Unit) 40 is attached to the revolving body 2, typically the vehicle body frame 3. The vehicle body IMU 40 measures the acceleration of the revolving body 2 in the front-rear direction, left-right direction, and up-down direction, and the angular velocity of the revolving body 2 around the front-rear direction, left-right direction, and up-down direction. The vehicle body IMU 40 corresponds to an example of an "angle sensor" that detects the angle of the vehicle body frame 3 with respect 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 front-rear direction, left-right direction, and up-down direction, and the angular velocity of the boom 11 around the front-rear direction, left-right direction, and up-down direction. The arm IMU 42 measures the acceleration of the arm 12 in the front-rear direction, left-right direction, and up-down direction, and the angular velocity of the arm 12 around the front-rear direction, left-right direction, and up-down direction. The bucket IMU 43 measures the acceleration of the bucket 13 in the front-rear direction, left-right direction, and up-down direction, and the angular velocity of the bucket 13 around the front-rear direction, left-right direction, and up-down direction. The boom IMU 41, the arm IMU 42, and the 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 with respect to the vehicle body 1.

[0025] Figure 2 is a perspective view of the vehicle body frame 3 and the work implement 10. Figure 3 is a plan view of the vehicle body frame 3 and the work implement 10. The vehicle body frame 3 has a pair of left and right vertical plates 7, 8. The vertical plates 7, 8 extend in the front-rear direction (the left-right direction in the figure in FIG. 3). The vertical plates 7, 8 are arranged at intervals in the width direction (left-right direction) of the revolving body 2. The vertical plates 7, 8 are composed of plates standing in the up-down direction and are arranged at a distance from each other in the left-right direction. The driver's cab 4 is arranged to the left of the left vertical plate 7. The work implement 10 is arranged between the vertical plates 7, 8 in the left-right direction. The work implement 10 is arranged 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 excavator 30 of the embodiment includes at least one electric motor. In the electric excavator 30, the driving force for driving the working machine 10 to relatively move the attachment with respect to the vehicle body frame 3 is generated by the electric motor 100. The electric motor 100 can drive the working machine 10. When the boom 11 and the arm 12 are driven by the electric motor 100, the operation of the working machine 10 becomes possible. The electric motor 100 is disposed on the vehicle body frame 3. The electric motor 100 has a boom electric motor 110 and an arm electric motor 140. Both the boom electric motor 110 and the arm electric motor 140 are supported by the vehicle body frame 3. The boom electric motor 110 and the arm electric motor 140 are disposed on the right side of the working machine 10.

[0027] The boom electric motor 110 rotationally drives the boom 11 and generates a rotational force for relatively moving the boom 11 with respect to the vehicle body frame 3. The boom electric motor 110 corresponds to an example of a "first actuator" that generates boom driving torque. The boom 11 can rotate relative to the vehicle body frame 3 about the boom foot pin 15 by being driven by the boom electric motor 110. The boom foot pin 15 is disposed across both the left and right vertical plates 7 and 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. Thereby, the boom 11 is supported by the vehicle body frame 3 so as to be rotatable about the boom foot pin 15.

[0028] The boom electric motor 110 has a pair of first boom electric motors 111 and a second boom electric motor 121. The first boom electric motor 111 and the second boom electric motor 121 have the same specifications. The first boom electric motor 111 and the second boom electric motor 121 have the same rated output. Here, the rated output of an electric motor refers to the maximum output that the electric motor can safely achieve under specified conditions.

[0029] The arm motor 140 generates a rotational force that rotationally drives the arm 12 and causes the arm 12 to move relative to the vehicle body frame 3. The arm motor 140 corresponds to an example of a "second actuator" that generates an arm driving torque. The arm 12 is rotatable relative to the vehicle body frame 3 about the arm connecting pin 16 and rotatable relative to the boom 11 about the arm connecting pin 16 by the drive of the arm motor 140. When the boom 11 is moved relative to the vehicle body frame 3 while maintaining the relative position of the arm 12 with respect to the boom 11, the arm 12 moves relative to the vehicle body frame 3. In this case, the arm 12 is driven by the arm motor 140.

[0030] The arm motor 140 has a pair of first arm motors 141 and second arm motors 151. The first arm motor 141 and the second arm motor 151 have the same specifications. The first arm motor 141 and the second arm motor 151 have the same rated output.

[0031] <Power transmission device> The electric excavator 30 of the present embodiment includes a power transmission device that mechanically transmits the driving force generated by the motor 100 to the working machine 10. Hereinafter, the power transmission device will be described.

[0032] FIG. 4 is a diagram showing a schematic configuration of a power transmission device that transmits a 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 substantially fan-shaped shape and has a tooth shape on a substantially fan-shaped arc portion. As shown in FIGS. 2 and 3, the boom gear member 131 is fixed to the side surface of the boom 11, more specifically, the right surface of the boom 11. The boom gear member 131 is disposed at the base end portion of the boom 11. The boom gear member 131 is integrally formed with the boom 11 and is rotatable about the boom foot pin 15.

[0034] The output gear 119 for the first boom is an external gear and meshes with the boom gear member 131. The output gear 119 for the first boom is arranged concentrically with the first boom motor 111. The first boom motor 111 transmits a driving force to the output gear 119 for the first boom. The output gear 129 for the second boom is an external gear and meshes with the boom gear member 131. The output gear 129 for the second boom is arranged concentrically with the second boom motor 121. The second boom motor 121 transmits a driving force to the output gear 129 for the second boom.

[0035] FIG. 5 is a skeleton diagram of the power transmission path from the first boom motor 111 and the second boom 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 motor 111 to the boom gear member 131. In the present embodiment, the first boom motor 111 and the planetary gear reducer 113 have an integral structure. The power transmission device that transmits the driving force of the first boom motor 111 to the boom gear member 131 includes a geared motor 117 in which the first boom motor 111 and the planetary gear reducer 113 are integrated.

[0037] The planetary gear reducer 113 has a plurality of rotating elements. The plurality of rotating elements of the planetary gear reducer 113 include a sun gear 114, a planetary gear 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 motor 111. The output shaft 112 is connected to the sun gear 114. The rotational driving force of the first boom motor 111 is input to the sun gear 114.

[0038] The planetary gear reducer 113 and the boom 1 output gear 119 are connected by a connecting shaft 118. More specifically, the connecting shaft 118 has one end connected to the planetary carrier that supports the planetary gear 115 and the other end connected to the boom 1 output gear 119. The planetary carrier and the boom 1 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 boom 2 motor 121 to the boom gear member 131. In this embodiment, the boom 2 motor 121 and the planetary gear reducer 123 have an integral structure. The power transmission device that transmits the driving force of the boom 2 motor 121 to the boom gear member 131 includes a geared motor 127 in which the boom 2 motor 121 and the planetary gear reducer 123 are integrated.

[0040] The planetary gear reducer 123 has a plurality of rotating elements. The plurality of rotating elements of the planetary gear reducer 123 include 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 boom 2 motor 121. The output shaft 122 is connected to the sun gear 124. The rotational driving force of the boom 2 motor 121 is input to the sun gear 124.

[0041] The planetary gear reducer 123 and the boom 2 output gear 129 are connected by a connecting shaft 128. More specifically, the connecting shaft 128 has one end connected to the planetary carrier that supports the planetary gear 125 and the other end connected to the boom 2 output gear 129. The planetary carrier and the boom 2 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 boom output gear 119 for the first boom meshes with the boom gear member 131. The driving force generated by the first boom motor 111 is transmitted to the boom gear member 131 via the boom output gear 119 for the first boom. The boom output gear 129 for the second boom meshes with the boom gear member 131. The driving force generated by the second boom motor 121 is transmitted to the boom gear member 131 via the boom output gear 129 for the second boom. The boom gear member 131 receives the transmission of the driving force from the first boom motor 111 and the second boom 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 rotationally driven about the boom foot pin 15.

[0043] The planetary gear reducer 113, the connecting shaft 118, and the boom output gear 119 for the first boom mechanically transmit the driving force generated by the first boom motor 111 to the boom 11. The planetary gear reducer 123, the connecting shaft 128, and the boom output gear 129 for the second boom mechanically transmit the driving force generated by the second boom motor 121 to the boom 11. The planetary gear reducers 113, 123, the connecting shafts 118, 128, and the boom output gear 119 for the first boom and the boom output gear 129 for the second boom constitute a boom power transmission device that mechanically transmits the driving force generated by the boom motor 110 to the boom 11.

[0044] The boom power transmission device is disposed on the side opposite to the cab 4 with respect to the work implement 10. In the case of the configuration of the embodiment in which the cab 4 is disposed on the front left side of the vehicle body frame 3 and the cab 4 is disposed 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] FIG. 6 is a diagram showing a schematic configuration of a power transmission device 160 that transmits a driving force to the arm 12. The power transmission device 160 that mechanically transmits the driving force generated by the arm motor 140 to the arm 12 includes 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 substantially fan-shaped shape and has a tooth profile on the arc portion of the substantially fan shape. As shown in FIGS. 2 and 3, the arm gear member 161 is separate from the boom gear member 131 and is arranged to the right of the boom gear member 131 away from the boom gear member 131. A gap is interposed between the boom gear member 131 and the arm gear member 161 in the left-right direction. The arm gear member 161 is arranged at the base end portion of the boom 11. The arm gear member 161 is concentric with the boom foot pin 15 and relatively rotates with respect to the vehicle 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 motor 141. The first arm motor 141 transmits a 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 motor 151. The second arm motor 151 transmits a driving force to the second arm output gear 159.

[0048] The power transmission path from the first arm motor 141 and the second arm 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 motor 141 to the arm gear member 161. The first arm motor 141 and the planetary gear reducer have an integral structure. A planetary gear reducer is provided in the power transmission path from the second arm motor 151 to the arm gear member 161. The second arm motor 151 and the planetary gear reducer have an integral structure. The arm gear member 161 rotates by receiving the transmission of the driving force from the first arm motor 141 and the second arm motor 151.

[0049] The rotating member 162 is fixed to the arm gear member 161 and relatively rotates with respect to the vehicle body frame 3 concentrically with the boom foot pin 15 integrally with the arm gear member 161.

[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. The first link member 171 is connected to the rotating member 162 via a connecting pin 177 at its first end. The first link member 171 is connected to the intermediate member 173 via a connecting pin 174 at its second end. 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. The second link member 172 is connected to the intermediate member 173 via a connecting pin 175 at its first end. The second link member 172 is connected to the arm 12 via a connecting pin 176 at its second end. The second link member 172 connects the intermediate member 173 and the arm 12. The second link member 172 transmits 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 sequence to the arm 12.

[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 proximal end may be connected to the boom 11.

[0054] The arm link 170 (the first link member 171, the second link member 172, and the 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 vehicle body frame 3. The power transmission device 160 and the boom 11 constitute a link mechanism.

[0055] Although the example in which the power transmission device 160 has a rod-shaped link member has been described, the power transmission device 160 may have a mechanism other than the link member as long as it can mechanically transmit the driving force of the arm 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, etc.

[0056] <Double motor drive> Generally, in a gear mechanism, there is backlash, which is a gap provided between the tooth surfaces of meshing gears, so the accuracy in positioning a movable member connected to the driven gear decreases. In the case of a working machine, the backlash of the gear mechanism provided at the base portion of the boom 11 causes misalignment of the attachment at the tip portion of the working machine 10. In order to reduce the backlash, the power transmission device of the embodiment is a double motor drive that drives one gear member using two electric motors.

[0057] Specifically, the boom gear member 131 that transmits the driving force to the boom 11 is driven by the first boom motor 111 and the second boom motor 121. The arm gear member 161 that transmits the driving force to the arm 12 is driven by the first arm motor 141 and the second arm motor 151. Hereinafter, the double motor drive will be described by taking as an example the structure in which the arm gear member 161 is driven by the first arm motor 141 and the second arm motor 151.

[0058] FIG. 7 is a schematic diagram of double-motor drive. In FIG. 7, since the double-motor drive is schematically illustrated, the shape of the arm gear member 161, the shape of the rotating member 162, the arrangement of the first arm output gear 149 and the second arm output gear 159 with respect to the arm gear member 161, etc. are different from those of the embodiment shown in FIG. 6.

[0059] Engaged with the arm gear member 161 fixed to the rotating member 162 are a first arm output gear 149 and a second arm output gear 159. The first arm output gear 149 is connected to a first arm electric motor 141, and when the first arm electric motor 141 rotates, the first arm output gear 149 rotates. The second arm output gear 159 is connected to a second arm electric motor 151, and when the second arm electric motor 151 rotates, the second arm output gear 159 rotates.

[0060] In the arrangement shown in FIG. 7, for each gear, the clockwise direction is defined as the positive direction of rotation, and the counterclockwise direction is defined as the negative direction of rotation.

[0061] By the coordinated control of the first arm electric motor 141 and the second arm electric motor 151, backlash removal control for bringing the tooth surfaces of the gears into contact without gaps can be executed to improve the positioning accuracy of the attachment at the tip of the working machine 10. Also, in order to improve the efficiency of the power transmission device, the backlash removal control can be made non-executable. By switching between the execution and non-execution of the backlash removal control, either a high-precision attachment position or high-efficiency power transmission can be selected, and with the adoption of a high-efficiency planetary gear mechanism, regeneration by the kinetic energy of the working machine 10 becomes possible.

[0062] When executing the backlash removal control, the first arm electric motor 141 constantly applies an offset torque in the positive direction to the arm gear member 161, and the second arm electric motor 151 constantly applies an offset torque in the negative direction to the arm gear member 161.

[0063] When stopping the arm gear member 161, the first arm motor 141 and the second arm motor 151 apply offset torques of the same magnitude but in opposite directions to the arm gear member 161. The magnitude of the total torque of the torque that the first arm motor 141 loads on the arm gear member 161 and the torque that the second arm motor 151 loads on the arm gear member 161 is zero.

[0064] At this time, both the first arm output gear 149 and the second arm output gear 159 try to rotate in opposite directions and sandwich 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 rotating the arm gear member 161 counterclockwise at a low speed, the torque generated by the first arm motor 141 is increased. By increasing the torque of the first arm motor 141, the arm gear member 161 is driven in the negative direction (counterclockwise direction). At this time, the second arm motor 151 continues to apply an offset torque in the direction opposite to the rotation direction of the arm gear member 161. The first arm motor 141 drives the arm gear member 161, and the second arm motor 151 is in a state of applying a slight brake to the arm gear member 161.

[0066] When rotating the arm gear member 161 in the clockwise direction at a low speed, the torque generated by the second arm motor 151 is increased. By increasing the torque of the second arm motor 151, the arm gear member 161 is driven in the positive direction (clockwise direction). At this time, the first arm motor 141 continues to apply an offset torque in the direction opposite to the rotation direction of the arm gear member 161. The second arm motor 151 drives the arm gear member 161, and the first arm motor 141 applies a slight brake to the arm gear member 161.

[0067] At this time, both the first arm output gear 149 and the second arm output gear 159 try to rotate in the reverse direction and sandwich 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 removal control, the positioning accuracy of the attachment at the tip of the work machine 10 can be increased, and high-precision work using the attachment becomes possible.

[0069] When backlash removal control is not executed, no offset torque is applied to the arm gear member 161 from the first arm motor 141 and the second arm motor 151. To rotate the arm gear member 161 at a high speed, driving torque in the same direction is applied to the arm gear member 161 from the first arm motor 141 and the second arm motor 151.

[0070] Both the first arm motor 141 and the second arm motor 151 apply driving torque to the arm gear member 161. Neither the first arm motor 141 nor the second arm motor 151 applies a brake to 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 implement 10 decreases, this is not a problem because high positioning accuracy is not required for the attachment during high-speed movement.

[0071] The power transmission path from the first arm motor 141 to the first arm output gear 149 has a highly efficient planetary gear reducer. The power transmission path from the second arm motor 151 to the second arm output gear 159 has a highly efficient planetary gear reducer. When backlash elimination control is not executed, when a large external force acts on the attachment due to the attachment at the tip of the work implement 10 colliding with an object or the like, the external force is transmitted to the first arm motor 141 and the second arm motor 151 through the planetary gear reducer.

[0072] The rotor parts of the first arm motor 141 and the second arm motor 151 have no contact parts other than the bearings that rotatably support the rotor parts. Therefore, when a large external force acts, an angular displacement occurs in the rotor part. As a result, damage to the planetary gear reducer can be prevented by the first arm motor 141 and the second arm motor 151 becoming out of tune.

[0073] During the execution of backlash elimination control, the attachment at the tip of the work implement 10 is stopped or, if it is moving, it is moving at a low speed. Since the moving speed of the attachment at the tip of the work implement 10 is small and the impact when the attachment collides with an object is small, damage to the planetary gear reducer is prevented.

[0074] In addition, when the positioning accuracy of the attachment at the tip of the working machine 10 is not required, either one or both of the boom gear member 131 and the arm gear member 161 can be driven by a single motor driven by one electric motor.

[0075] <Gravity compensation mechanism 200> When the working machine 10 performs an operation of raising the boom 11, for example, it moves vertically against gravity. If an attempt is made to support the weight of the boom 11 with the boom electric motor 110, it is necessary to select a boom electric motor 110 with a large rated output. In this case, the weight, installation area, and energy consumption of the boom electric motor 110 increase, and it becomes disadvantageous for high-acceleration motion. Therefore, the electric excavator 30 of the embodiment is provided with a gravity compensation mechanism 200 that compensates mechanically so as to balance the weight of the loaded working machine 10.

[0076] FIG. 8 is a diagram showing a schematic configuration of a first mechanism 210 that compensates mechanically so as to balance the weight of the boom 11. The gravity compensation mechanism 200 of the 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 stretchable and contractible in the extending direction of the first rod member 212. The first elastic member 211 is disposed between a first tip support portion 213 and a 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 (in FIG. 9, the left end in the figure) is attached to the first tip support portion 213 and is supported by the first tip support portion 213. The first elastic member 211 shown in FIG. 8 is shorter in length than its natural length. The first elastic member 211 is compressed. The first elastic member 211 acts with an elastic force to extend. The first elastic member 211 is, for example, a spring.

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

[0079] A first bottom surface part 216 is attached to the other end of the first cylinder part 215 facing the base end of the first rod member 212. The first cylinder part 215 and the first bottom surface part 216 constitute a hollow bottomed cylinder. The first bottom surface part 216 has a plate shape. A through hole penetrating the first bottom surface part 216 in the thickness direction is formed in the first bottom surface part 216. The first rod member 212 passes through the through hole.

[0080] The first bottom surface part 216 is not fixed to the first rod member 212. The first cylinder part 215 and the first bottom surface part 216 are integrally relatively movable with respect to the first rod member 212. The first cylinder part 215 and the first bottom surface part 216 are reciprocally movable in the extending direction of the first rod member 212. On the other hand, the first cylinder part 215 and the first bottom surface part 216 are relatively rotatable with respect to the vehicle body frame 3 integrally with the first rod member 212.

[0081] The first bottom surface part 216 constitutes the first base end support part 214. The base end (the right end in the figure in FIG. 9) of the first elastic member 211 is attached to and supported by the first base end support part 214 (the first bottom surface part 216). As the first bottom surface part 216 relatively moves with respect 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 composed of a first cylinder part 215 and a first bottom face part 216. The pin holder 218H supports a first rotation center pin 218. The pin holder 218H is rotatable relative to the first rotation center pin 218 around the first rotation center pin 218. The first rotation center pin 218 is fixed to the vehicle body frame 3. The first rotation center pin 218 may be fixed to one or both of, for example, the vertical plates 7 and 8. A bracket (not shown) may be fixed to the vehicle body frame 3, and the first rotation center pin 218 may be fixed to the bracket and fixed to the vehicle 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 relative to the first movable pin 217 around 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 a first elastic member 211, a first rod member 212, a first tip support part 213, a first cylinder part 215, a first bottom face part 216 (first base end support part 214), and pin holders 217H and 218H is hereinafter referred to as the first assembly. The first assembly is supported by the first movable pin 217 and is rotatable relative to the boom 11 around the first movable pin 217. And the first assembly is supported by the first rotation center pin 218. The first assembly is supported by the vehicle body frame 3 via the first rotation center pin 218 and is rotatable relative to the vehicle body frame 3 around the first rotation center pin 218.

[0085] The boom 11 rotates relative to the vehicle body frame 3 about the boom foot pin 15 by the boom drive torque generated by the boom motor 110. The first movable pin 217 rotates relative to the vehicle body frame 3 about 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 vehicle body frame 3, the relative position of the first rotation center pin 218 with respect to the vehicle body frame 3 does not change. The above-described first assembly rotates relative to the vehicle body frame 3 about the first rotation center pin 218 as the center of rotation.

[0086] FIG. 10 is a schematic view showing the first mechanism 210 in a posture where the boom 11 is raised. Compared with FIG. 8, the boom 11 rotates counterclockwise in the figure about 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 relative position of the first rotation center pin 218 with respect to the vehicle body frame 3 remains unchanged. The above-described first assembly rotates counterclockwise in the figure about the first rotation center pin 218 as the center.

[0087] The first movable pin 217 is approaching 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 moving away from the first rotation center pin 218. The first tip support portion 213 is disposed farther from the first rotation center pin 218. The first base end support portion 214 keeps the position of the first rotation center pin 218 in the radial direction with respect to the first rotation center pin 218 unchanged. The distance between the first tip support portion 213 and the first base end support portion 214 is increasing. Therefore, in the arrangement shown in FIG. 10, the first elastic member 211 is extended compared with FIG. 8.

[0088] The first elastic member 211 shown in FIG. 10 is still in a compressed state with a length shorter than its natural length, but has a length closer to its natural length. The amount of deformation of the first elastic member 211 from its natural length has decreased. Therefore, the elastic force exerted by the first elastic member 211 is smaller compared to FIG. 8.

[0089] FIG. 11 is a schematic view showing the first mechanism 210 in a posture where the boom 11 is lowered. Compared with FIG. 8, the boom 11 rotates in the clockwise direction 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 with respect to the boom foot pin 15. The first rotation center pin 218 keeps the relative position with respect to the vehicle body frame 3 unchanged. The above-mentioned first assembly rotates in the clockwise direction in the figure around the first rotation center pin 218.

[0090] The first movable pin 217 is moving away from the first rotation center pin 218. The other end of the first rod member 212 is arranged farther from the first rotation center pin 218. Since the extending length of the first rod member 212 is constant, one end of the first rod member 212 is approaching the first rotation center pin 218. The first tip support portion 213 is arranged closer to the first rotation center pin 218. The first base end support portion 214 keeps the position with respect to the first rotation center pin 218 in the radial direction of the first rotation center pin 218 unchanged. The distance between the first tip support portion 213 and the first base end support portion 214 is decreasing. Therefore, in the arrangement shown in FIG. 11, the first elastic member 211 is compressed compared to FIG. 8.

[0091] Since the amount of deformation of the first elastic member 211 from its natural length has increased, the elastic force exerted by the first elastic member 211 is larger compared to FIG. 8.

[0092] Figure 12 is a table showing the moment generated by the first elastic member 211. "During boom" shown in Figure 12 indicates the posture of the boom 11 shown in Figure 8. The magnitude of the elastic force (spring force) exerted by the first elastic member 211 in the state of "during boom" is taken as "medium", and the moment arm is taken as "medium". The moment exerted by the first elastic member 211 around the boom foot pin 15 is obtained by the product of the spring force and the moment arm. The first elastic member 211 exerts a moment of magnitude "medium" around the boom foot pin 15.

[0093] "Above boom" shown in Figure 12 indicates the posture in which the boom 11 is raised as compared with Figure 8, as shown in Figure 10. In the state of "above boom", the moment arm increases and becomes "large" compared with the state of "during boom", but since the amount of deformation from the natural length of the first elastic member 211 decreases, the magnitude of the spring force becomes "small small". The magnitude of the moment exerted by the first elastic member 211 around the boom foot pin 15 decreases to "small".

[0094] "Below boom" shown in Figure 12 indicates the posture in which the boom 11 is lowered as compared with Figure 8, as shown in Figure 11. In the state of "below boom", since the amount of deformation of the first elastic member 211 increases, the magnitude of the spring force becomes "large", but due to the change in the posture of the boom 11, the moment arm decreases and becomes "small small". The magnitude of the moment exerted by the first elastic member 211 around the boom foot pin 15 decreases to "small".

[0095] The moment exerted by the first elastic member 211 is in the opposite direction to the moment due to the weight of the work machine 10. The first elastic member 211 exerts a moment in the direction of raising the boom 11. Thereby, the moment generated by the weight of the work machine 10 is canceled out. 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 to balance the weight of the arm 12. In FIG. 13 and 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 manner. The gravity compensation mechanism 200 of the embodiment includes the second mechanism 220. The second mechanism 220 has 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 stretchable and contractible in the extending direction of the second rod member 222. The second elastic member 221 is disposed between a second tip support portion 223 and a second base end support portion 224. The tip (the left end in the figure in FIG. 14) of the second elastic member 221 is attached to and supported by the second tip support portion 223. The second elastic member 221 shown in FIG. 13 has a length shorter than its natural length. The second elastic member 221 is compressed. The second elastic member 221 exerts an elastic force to try to extend. 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 relatively movable with respect to the second rod member 222. The second tip support portion 223 is reciprocally movable in the extending direction of the second rod member 222. As the second tip support portion 223 relatively moves with respect to the second rod member 222, the second elastic member 221 expands and contracts, and the elastic force of the second elastic member 221 changes. On the other hand, the second tip support portion 223 and the second rod member 222 are integrally rotatable relative to the vehicle body frame 3.

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

[0100] A 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 a power transmission device 160 that transmits the driving force generated by the arm 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 relative to the second movable pin 227 around 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) is hereinafter referred to as the second assembly. The second assembly is supported by the second movable pin 227 and is rotatable relative to the rotating member 162 and the first link member 171 around the second movable pin 227. Also, the second assembly is supported by the second rotation center pin 228. The second assembly is supported by the vehicle body frame 3 via the second rotation center pin 228 and is rotatable relative to the vehicle body frame 3 around the second rotation center pin 228.

[0102] Due to the arm driving torque generated by the arm motor 140, the arm gear member 161 and the rotating member 162 rotate relative to the vehicle body frame 3 about the boom foot pin 15. The connecting pin 177 (second movable pin 227) rotates relative to the vehicle body frame 3 about 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 vehicle body frame 3, the relative position of the second rotation center pin 228 with respect to the vehicle body frame 3 does not change. The second assembly described above rotates relative to the vehicle body frame 3 with the second rotation center pin 228 as the center of rotation.

[0103] FIG. 15 is a schematic view showing the second mechanism 220 in a posture where the arm 12 is moved in the dump direction (the direction in which the arm 12 is separated from the boom 11). In FIGS. 13, 15, and 16, the posture of the boom 11 with respect to the vehicle body frame 3 is unchanged. In the posture shown in FIG. 13, the arm 12 extends substantially in the vertical direction.

[0104] Compared with FIG. 13, in FIG. 15, the arm gear member 161 and the rotating member 162 rotate counterclockwise in the figure about 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 rotates counterclockwise in the figure about the pin 178.

[0105] The connecting pin 175 rotates counterclockwise in the figure about the 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 about the arm connecting pin 16. The arm 12 extends obliquely 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 keeps the relative position with respect to the vehicle body frame 3 unchanged. The above-described second assembly rotates in the clockwise direction in the figure about the second rotation center pin 228.

[0107] The second movable pin 227 moves away from the second rotation center pin 228. The other end of the second rod member 222 is disposed farther from the second rotation center pin 228. The second base end support portion 224 is disposed farther 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 increasing. Therefore, in the arrangement shown in FIG. 15, the second elastic member 221 is extended as compared with FIG. 13.

[0108] The second elastic member 221 shown in FIG. 15 is still in a compressed state with a length shorter than its natural length, but has a length closer to its natural length. The amount of deformation of the second elastic member 221 from its natural length is decreasing. Therefore, the elastic force exerted by the second elastic member 221 is smaller as compared with FIG. 13.

[0109] FIG. 16 is a schematic view showing the second mechanism 220 in a posture where the arm 12 is moved in the excavation direction (the direction in which the arm 12 approaches the boom 11). In FIG. 16 as compared with FIG. 13, the arm gear member 161 and the rotating member 162 rotate in the clockwise direction in the figure about the boom foot pin 15. The connecting pin 177 rotates together with the rotating member 162 and approaches 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 pushed rightward in the figure by the rotating member 162. The intermediate member 173 rotates in the clockwise direction in the figure about the pin 178.

[0110] The connecting pin 175, together with the intermediate member 173, rotates in the clockwise direction in the figure about the pin 178. 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 rightward in the figure. As a result, the arm 12 rotates in the clockwise direction in the figure about the arm connecting pin 16. The arm 12 extends obliquely 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 keeps the relative position with respect to the vehicle body frame 3 unchanged. The above-mentioned second assembly rotates in the counterclockwise direction in the figure about the second rotation center pin 228.

[0112] The second movable pin 227 is moving away from the second rotation center pin 228. The other end of the second rod member 222 is arranged further away from the second rotation center pin 228. The second proximal end support portion 224 is arranged further away from the second rotation center pin 228. The distance between the second distal end support portion 223 and the second proximal end support portion 224 is increasing. Therefore, in the arrangement shown in FIG. 16, the second elastic member 221 is extended as compared with FIG. 13.

[0113] The second elastic member 221 shown in FIG. 16 is still in a state of being compressed with a length shorter than its natural length, but has a length closer to its natural length. The amount of deformation from the natural length of the second elastic member 221 is decreasing. Therefore, the elastic force exerted by the second elastic member 221 is smaller as compared with FIG. 13.

[0114] Figure 17 is a table showing the moment generated by the second elastic member 221. The "arm upright" shown in Figure 17 indicates the posture of the arm 12 shown in Figure 13. The magnitude of the elastic force (spring force) acting on the second elastic member 221 in the state of "arm upright" is defined as "large". The moment exerted by the second elastic member 221 around the arm connection pin 16 is obtained by the product of the spring force and the moment arm. In the state of "arm upright", since the moment arm is "0", the magnitude of the moment exerted by the second elastic member 221 around the arm connection pin 16 is "0".

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

[0116] The "arm damping" shown in Figure 17 indicates the posture in which the arm 12 is away from the boom 11 compared to Figure 13, as shown in Figure 15. In the state of "arm damping", since the deformation amount of the second elastic member 221 decreases, the magnitude of the spring force decreases to "medium", and the moment arm increases to "medium". The second elastic member 221 exerts a moment of magnitude "medium" around the arm connection pin 16.

[0117] The moment exerted by 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 exerts a moment in the direction of tilting the arm 12 with respect to the vertical direction. The second elastic member 221 exerts a moment in the direction opposite to the direction of making the arm 12 upright. Thereby, the moment generated by the weight of the arm 12 is canceled out. The second elastic member 221 compensates for the gravity of the arm 12.

[0118] As described above, the electric excavator 30 of the embodiment separately includes a first mechanism 210 for compensating the gravity of the boom 11 and a second mechanism 220 for compensating the gravity of the arm 12. At least a part of the gravity of the boom 11 is compensated by the moment exerted by the first elastic member 211. At least a part of the gravity of the arm 12 is compensated by the moment exerted by the second elastic member 221.

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

[0120] The gravity can be compensated by balancing the moments due to the self-weight of the arm 12 and the self-weight of the boom 11 with the first elastic member 211. Since the weight of the arm 12 is always constant, the gravity compensation of the boom 11 depends only on the angle of the boom 11, simplifying the gravity compensation. Since the gravity compensation of the boom 11 and the gravity compensation of the arm 12 can be set independently, the gravity of the working machine 10 can be compensated simply and accurately. Thereby, the operability of the working machine 10 can be improved, the responsiveness of the operation of the working machine 10 can be improved, and the positioning accuracy of the bucket 13 at the tip of the working machine 10 can be improved.

[0121] As shown in FIGS. 8, 10 to 11, the first elastic member 211 may be supported by a first rod member 212 that is supported by the vehicle body frame 3 so as to be rotatable relative to the vehicle body frame 3. As the electric shovel 30 operates to rotate the boom 11 about the boom foot pin 15, the first rod member 212 rotates about the first rotation center pin 218, and at this time, the first elastic member 211 expands and contracts to change the magnitude of the spring force. Thereby, appropriate gravity compensation can be performed according to the posture of the boom 11.

[0122] As shown in FIGS. 8, 10 to 11, the first movable pin 217 that supports the end of the first rod member 212 may be attached to the boom 11. In this way, as the boom 11 rotates, the first rod member 212 can be rotated to surely change the magnitude of the spring force of the first elastic member 211.

[0123] As shown in FIGS. 13, 15 to 16, the second elastic member 221 may be supported by a second rod member 222 that is supported by the vehicle body frame 3 so as to be rotatable relative to the vehicle body frame 3. As the electric shovel 30 operates to rotate the arm 12 about the arm connection pin 16, the second rod member 222 rotates about the second rotation center pin 228, and at this time, the second elastic member 221 expands and contracts to change the magnitude of the spring force. Thereby, appropriate gravity compensation can be performed according to the posture of the arm 12.

[0124] As shown in FIGS. 13, 15 to 16, the second movable pin 227 that supports the end of the second rod member 222 may be attached to the power transmission device 160 that transmits the arm driving torque to the arm 12. In this way, as the arm 12 rotates, the second rod member 222 can be rotated to surely change the magnitude of the spring force of the second elastic member 221.

[0125] In the previous description, an example was given in which the first elastic member 211 and the second elastic member 221 are springs designed to change the magnitude of the elastic force by stretching and contracting. Either one or both of the first elastic member 211 and the second elastic member 221 may be a constant load spring that generates a substantially constant elastic force regardless of the length by which the spring is stretched.

[0126] <Driving Torque on Inclined Ground> FIG. 18 is a schematic diagram showing the moment of the working machine 10 on horizontal ground. Let the length of the boom 11 be l1, the distance from the boom foot pin 15 to the center of gravity of the boom 11 be lg1, the distance from the arm connection pin 16 to the center of gravity of the arm 12 be lg2, the self-weight of the boom 11 be m1, the self-weight of the arm 12 be m2, and the gravitational acceleration be g. Let the angle of the boom 11 with respect to the vehicle body frame 3 be θ1, and the angle of the arm 12 with respect to the boom 11 be θ2. When the ground on which the electric excavator 30 is located is horizontal, the moment τ1 around the boom foot pin 15 due to the self-weight of the arm 12 and the self-weight of the boom 11 is expressed by the following formula (1).

[0127]

Equation

[0128] Also, the moment τ2 around the arm connection pin 16 due to the self-weight of the arm 12 is expressed by the following formula (2).

[0129]

Equation

[0130] FIG. 19 is a schematic diagram showing the moment of the working machine 10 on inclined ground. When the ground on which the electric excavator 30 is located is inclined at an angle θ p to the horizontal, the moment τ1' around the boom foot pin 15 due to the self-weight of the arm 12 and the self-weight of the boom 11 is expressed by the following formula (3).

[0131]

Equation

[0132] Further, the moment τ2' around the arm connection pin 16 due to the self-weight of the arm 12 is expressed by the following formula (4).

[0133]

Equation

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

[0135] The boom IMU 41, the arm IMU 42, and the bucket IMU 43 shown also in FIG. 1 constitute the working machine attitude detector 44. The boom IMU 41 detects the angle of the boom 11 with respect to the vehicle body frame 3. The arm IMU 42 detects the angle of the arm 12 with respect to the boom 11 in the region where the arm 12 rotates in a side view. The bucket IMU 43 detects the angle of the bucket 13 with respect to the arm 12 in the region where the bucket 13 rotates in a side view. The boom IMU 41, the arm IMU 42, and the bucket IMU 43 output the detection signals of the angles to the controller 50.

[0136] The controller 50 is configured to include a CPU (Central Processing Unit) or the like. The controller 50 has a storage unit 58.

[0137] The storage unit 58 is a non-volatile memory and is provided as an area for storing necessary data. The storage unit 58 stores a control program for controlling various operations of the electric excavator 30 and various data necessary for the execution of the control program. The storage unit 58 also temporarily stores working data generated along with the operation of the electric excavator 30. The controller 50 executes various processes for controlling the operation of the electric excavator 30 by executing the control program stored in the storage unit 58.

[0138] The controller 50 outputs a control signal for operating the working machine 10 to the electric motor 100. The controller 50 outputs a control signal for relatively moving the boom 11 with respect to the vehicle body frame 3 to the boom electric motor 110. The controller 50 outputs a control signal for relatively moving the arm 12 with respect to the vehicle body frame 3 to the arm electric motor 140.

[0139] The controller 50 includes a vehicle body attitude acquisition unit 51, a working 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 a process for determining the drive torque of the working machine 10 considering the gravity compensation torque on a sloping ground in the electric excavator 30.

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

[0143] In step S3, the gravity compensation torque calculation unit 54 calculates the boom gravity compensation torque BT1 on an inclined ground. The boom gravity compensation torque BT1 is the moment τ1’ obtained by the above formula (3).

[0144] In step S4, the gravity compensation torque calculation unit 54 calculates the arm gravity compensation torque AT1 on an inclined ground. The arm gravity compensation torque AT1 is the moment τ2’ obtained by the above formula (4).

[0145] In step S5, the gravity compensation torque calculation unit 54 calculates the boom gravity compensation torque BT2 on a horizontal ground. The boom gravity compensation torque BT2 is the moment τ1 obtained by the above formula (1).

[0146] In step S6, the gravity compensation torque calculation unit 54 calculates the arm gravity compensation torque AT2 on a horizontal ground. The arm gravity compensation torque AT2 is the moment τ2 obtained by the above formula (2).

[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 the difference between the moment τ1’ of the working machine 10 on an inclined ground and the moment τ1 of the working machine 10 on a horizontal ground, and is represented by the following formula (5).

[0148]

Equation

[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 the difference between the moment τ2' of the arm 12 on an inclined ground and the moment τ2 of the arm 12 on a horizontal ground, and is expressed by the following formula (6).

[0150]

Equation

[0151] In step S9, the drive torque calculation unit 53 calculates the torque to be generated in the boom 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 uses the added value as the boom drive torque. The drive torque calculation unit 53 outputs a control signal to the boom motor 110 so as to generate the calculated boom drive torque in the boom motor 110.

[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 uses this as the arm drive torque. The drive torque calculation unit 53 outputs a control signal to the arm motor 140 so as to generate the calculated arm drive torque in the arm motor 140. Then, the process ends (at "END" in FIG. 21).

[0153] The electric excavator 30 operates even in a non-horizontal location. With only the gravity compensation by the first elastic member 211 and the second elastic member 221 described above, accurate gravity compensation may not be achieved on an inclined ground, and the responsiveness of the operation of the working machine 10 may decrease.

[0154] Therefore, the pitch angle of the vehicle body frame 3 is detected by the vehicle body IMU 40 attached to the vehicle body frame 3. The boom gravity compensation torque difference ΔBT, which is the difference between the gravity compensation torque of the boom 11 on an inclined ground and the gravity compensation torque on a horizontal ground, is calculated. The boom gravity compensation torque difference ΔBT is added to the boom drive torque. By generating a torque considering the boom gravity compensation torque difference ΔBT in the boom motor 110, the responsiveness of the operation of the boom 11 can be improved.

[0155] The 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 horizontal ground, is calculated. The arm gravity compensation torque difference ΔAT is added to the arm drive torque. By generating a torque considering the arm gravity compensation torque difference ΔAT in the arm motor 140, the responsiveness of the operation of the arm 12 can be improved.

[0156] In the embodiment, an example in which the motor 100 has the boom motor 110 and the arm motor 140 individually has been described. The motor 100 that generates the driving forces of the boom 11 and the arm 12 does not necessarily have to be provided separately. It may be configured such that power is distributed from the output shaft of one motor 100 and transmitted to the boom 11 and the arm 12 as driving forces respectively. In this case, the switching of the transmission of the driving force to the boom 11 and the arm 12 may be performed by the operation of an operator boarding the cab 4.

[0157] In the embodiment, an example in which the cab 4 is arranged on the front left side of the vehicle body frame 3, the work implement 10 is arranged on the right side of the cab 4, and the boom motor 110 and the arm motor 140 are arranged on the right side of the work implement 10 has been described. The arrangement is not limited to this. For example, by arranging the cab 4 behind the work implement 10, it becomes possible to arrange the motors 100 on both the left and right sides of the work implement 10, so that the degree of freedom in the arrangement of the motors 100 can be improved.

[0158] In the embodiment, an electric excavator 30 including an electric motor that generates a driving force for driving a working machine 10 has been described. The electric excavator 30 may be an electric vehicle in which the electric motor also generates a driving force for the traveling of the traveling body 5 and the turning of the revolving body 2 with respect to the traveling body 5. The electric excavator 30 may not include an internal combustion engine. The electric excavator 30 may not include a hydraulic circuit.

[0159] In the embodiment, an example in which both the first actuator that generates a boom driving torque and the second actuator that generates an arm driving torque are electric motors has been described. Instead of the electric motor, a hydraulic motor may generate the boom driving torque and the arm driving torque. The idea of the embodiment may be applied to a working machine that hydraulically drives the working machine 10.

[0160] In the embodiment, an example in which the power transmission device has a planetary gear reducer has been described. Instead of the planetary gear reducer, the power transmission device may have a spur reducer in which a plurality of gears are combined by meshing one gear with one gear.

[0161] The embodiments disclosed this time should be considered as illustrative in all respects and not restrictive. The scope of the present invention is shown not by the above description but by the claims, and it is intended that all modifications within the meaning and scope equivalent to the claims are included.

Explanation of Reference Numerals

[0162] 1 Body, 2 Swivel body, 3 Body frame, 5 Running body, 7, 8 Vertical plates, 10 Working machine, 11 Boom, 12 Arm, 13 Bucket, 15 Boom foot pin, 16 Arm connection pin, 17 Attachment connection pin, 21 Bucket link, 22 First member, 23 Second member, 30 Electric excavator, 40 Body IMU, 41 Boom IMU, 42 Arm IMU, 43 Bucket IMU, 44 Working machine attitude detector, 50 Controller, 51 Body attitude acquisition unit, 52 Working machine attitude acquisition unit, 53 Driving 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 member, 174 - 177 Connection pins, 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 surface portion, 217 First movable pin, 217H, 218H Pin holders, 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. 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 working machine including the same, 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, a second elastic member that compensates for the gravity of the arm, a working machine provided with the same.

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

3. The working 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 working machine according to claim 1, further comprising a second rod member that is supported by the vehicle body frame so as to be relatively rotatable with respect to the vehicle body frame and supports the second elastic member.

5. The working 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. An angle sensor that detects an angle of the vehicle body frame with respect to the horizontal direction, a controller that calculates a moment of the working machine around a rotation center of the boom with respect to the vehicle body frame, and generates the boom drive torque for the first actuator in consideration of a difference between a moment on an inclined ground and a moment on a horizontal ground, the working machine according to any one of claims 1 to 5.

7. An angle sensor that detects an angle of the vehicle body frame with respect to the horizontal direction, a controller that calculates a moment of the working machine around a rotation center of the arm with respect to the boom, and generates the arm drive torque for the second actuator in consideration of a difference between a moment on an inclined ground and a moment on a horizontal ground, the working machine according to any one of claims 1 to 5.

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