A drive system for a work machine, a control method for a work machine, and a control program for a work machine.

Abstract

Reduce the power consumption of electric actuators. [Solution] The excavator includes a first electric actuator that drives a first movable member, a second electric actuator that drives a second movable member connected to the first movable member, a brake device capable of applying braking force to the first output shaft of the first electric actuator, and a control device. If the reaction torque acting on the first output shaft as a result of the second electric actuator outputting torque is greater than a threshold (step S140: NO), the control device controls the first electric actuator so that the first output shaft outputs torque in the opposite direction to the reaction torque (step S170). If the reaction torque is less than or equal to the threshold (step S140: YES), the brake device applies braking force to the first output shaft and stops the power supply to the first electric actuator (step S150).

Description

Technical Field

[0001] The present invention relates to a drive system for a work machine, a control method for a work machine, and a control program for a work machine.

Background Art

[0002] The excavator disclosed in Patent Document 1 includes a vehicle body, a boom, an arm, and a bucket. The boom is connected to the front end of the vehicle body. The boom is rotatable up and down relative to the vehicle body. The arm is connected to the tip of the boom. The arm is rotatable up and down relative to the boom. The bucket is connected to the tip of the arm. The bucket is rotatable up and down relative to the arm.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problem to be Solved by the Invention

[0004] In techniques such as that disclosed in Patent Document 1, an electric actuator may be adopted as the actuator for rotating each movable member such as the boom, arm, and bucket. When this type of actuator is employed, it is desirable to minimize the power consumption of each actuator as much as possible. Here, for example, when performing excavation work, there are cases where a specific one of a plurality of movable members is rotated while the position of another is held substantially constant. At this time, a reaction force associated with the operation of the rotating movable member acts on the actuator of the movable member whose position is being held. If the actuator is energized to hold the position of the movable member against this reaction force, the power consumption of the actuator may increase depending on the magnitude of the reaction force.

Means for Solving the Problem

[0005] A drive system for a work machine to solve the above problems is applied to a work machine having a first movable member and a second movable member rotatably connected to the first movable member, and comprises a first electric actuator having a first output shaft that outputs torque to the first movable member, a second electric actuator attached to the first movable member and having a second output shaft that outputs torque to the second movable member, a brake device that switches between a braking state that applies braking torque to the first output shaft and a release state that releases the application of braking torque to the first output shaft, and a control device that controls the first electric actuator, the second electric actuator, and the brake device, wherein the torque output by the second output shaft acts on the first output shaft. When the reaction torque is defined as the reaction torque, the control device, while performing drive control to control the second electric actuator so that the second output shaft outputs torque, executes a first process to reduce the rotational speed of the first output shaft to a predetermined set value or less by controlling the first electric actuator so that the first output shaft outputs torque in the opposite direction to the reaction torque, if the reaction torque is less than or equal to the threshold value, controls the brake device to a braking state and stops the power supply to the first electric actuator.

[0006] According to the above configuration, power supply to the first electric actuator can be stopped until the reaction torque acting on the first output shaft exceeds a threshold. As a result, the driving time of the first electric actuator can be shortened, and thus the power consumption of the first electric actuator can be reduced.

[0007] In a drive system for a work machine, the control device may, in the first process, control the brake device and the first electric actuator such that the sum of the braking torque applied by the brake device and the torque output by the first output shaft is equal to the magnitude of the reaction torque.

[0008] In a drive system for a work machine, the work machine includes a third movable member rotatably connected to the second movable member, and the control device may perform a third process of estimating the positional relationship between the first output shaft and the third movable member based on the relative position of the second movable member with respect to the first movable member and the relative position of the third movable member with respect to the second movable member, and a fourth process of calculating the reaction torque based on the positional relationship estimated in the third process.

[0009] A drive system for a work machine to solve the above problems is applied to a work machine having a first movable member and a second movable member rotatably connected to the first movable member, and comprises a first electric actuator having a first output shaft that outputs torque to the first movable member, a second electric actuator attached to the first movable member and having a second output shaft that outputs torque to the second movable member, a brake device that switches between a braking state that applies braking torque to the second output shaft and a release state that releases the application of braking torque to the second output shaft, and a control device that controls the first electric actuator, the second electric actuator and the brake device, wherein the second output shaft is acted upon in conjunction with the torque output by the first output shaft. When the reaction torque is defined as the reaction torque, the control device, while performing drive control to control the first electric actuator so that the first output shaft outputs torque, executes a first process to reduce the rotational speed of the second output shaft to a predetermined set value or less by controlling the second electric actuator so that the second output shaft outputs torque in the opposite direction to the reaction torque, if the reaction torque is less than or equal to the threshold value, while the drive control is being performed, executes a second process to control the brake device to a braking state and stop the power supply to the second electric actuator.

[0010] With the above configuration, power supply to the second electric actuator can be stopped until the reaction torque acting on the second output shaft exceeds a threshold. As a result, the driving time of the second electric actuator can be shortened, and thus the power consumption of the second electric actuator can be reduced.

[0011] In a drive system for a work machine, the control device may, in the first process, control the brake device and the second electric actuator such that the sum of the braking torque applied by the brake device and the torque output by the second output shaft is equal to the magnitude of the reaction torque.

[0012] In a drive system for a work machine, the work machine includes a third movable member rotatably connected to the second movable member, and the control device may perform a third process of estimating the positional relationship between the second output shaft and the third movable member based on the relative position of the third movable member with respect to the second movable member, and a fourth process of calculating the reaction torque based on the positional relationship estimated in the third process.

[0013] A control method for a work machine to solve the above problems is applied to a work machine comprising: a first electric actuator having a first output shaft that outputs torque; a first movable member that rotates based on the torque from the first output shaft; a second electric actuator attached to the first movable member and having a second output shaft that outputs torque; a second movable member that rotates based on the torque from the second output shaft; a brake device that switches between a braking state that applies braking torque to the first output shaft and a release state that releases the application of braking torque to the first output shaft; and a control device that controls the first electric actuator, the second electric actuator, and the brake device, wherein the torque output by the second output shaft has a corresponding reaction on the first output shaft. When the torque of a force is defined as the reaction torque, if the control device is performing drive control to control the second electric actuator so that the second output shaft outputs torque, and the reaction torque is greater than a predetermined threshold value which is less than or equal to the maximum braking torque that the brake device can apply to the first output shaft, then the control device performs a first process to control the first electric actuator so that the first output shaft outputs torque in the opposite direction to the reaction torque, thereby reducing the rotational speed of the first output shaft to a predetermined set value or less. If the reaction torque is less than or equal to the threshold value while the drive control is being performed, the control device performs a second process to control the brake device to a braking state and to stop the power supply to the first electric actuator.

[0014] According to the above method, power supply to the first electric actuator can be stopped until the reaction torque acting on the first output shaft exceeds a threshold. As a result, the driving time of the first electric actuator can be shortened, and thus the power consumption of the first electric actuator can be reduced.

[0015] A control method for a work machine to solve the above problem is applied to a work machine comprising: a first electric actuator having a first output shaft that outputs torque; a first movable member that rotates based on the torque from the first output shaft; a second electric actuator attached to the first movable member and having a second output shaft that outputs torque; a second movable member that rotates based on the torque from the second output shaft; a brake device that switches between a braking state that applies braking torque to the second output shaft and a release state that releases the application of braking torque to the second output shaft; and a control device that controls the first electric actuator, the second electric actuator, and the brake device, wherein the torque output by the first output shaft affects the second output shaft. When the torque of a force is defined as the reaction torque, if the control device is performing drive control to control the first electric actuator so that the first output shaft outputs torque, and the reaction torque is greater than a predetermined threshold value which is less than or equal to the maximum braking torque that the brake device can apply to the second output shaft, then the first process is performed to control the second electric actuator so that the second output shaft outputs torque in the opposite direction to the reaction torque, thereby reducing the rotational speed of the second output shaft to a predetermined set value or less. If the reaction torque is less than or equal to the threshold value while the drive control is being performed, then the second process is performed to control the brake device to a braking state and to stop the power supply to the second electric actuator.

[0016] According to the above method, power supply to the second electric actuator can be stopped until the reaction torque acting on the second output shaft exceeds a threshold. As a result, the driving time of the second electric actuator can be shortened, and thus the power consumption of the second electric actuator can be reduced.

[0017] A control program for a work machine to solve the above problems is applied to a work machine comprising: a first electric actuator having a first output shaft that outputs torque; a first movable member that rotates based on the torque from the first output shaft; a second electric actuator attached to the first movable member and having a second output shaft that outputs torque; a second movable member that rotates based on the torque from the second output shaft; a brake device that switches between a braking state that applies braking torque to the first output shaft and a release state that releases the application of braking torque to the first output shaft; and a control device that controls the first electric actuator, the second electric actuator, and the brake device, wherein the program controls the reaction that acts on the first output shaft as the second output shaft outputs torque. When the torque of a force is defined as the reaction torque, the control device is instructed to perform a first process to reduce the rotational speed of the first output shaft to a predetermined set value or less by controlling the first electric actuator so that the first output shaft outputs a torque in the opposite direction to the reaction torque, if the reaction torque is greater than a predetermined threshold value which is less than or equal to the maximum braking torque that the brake device can apply to the first output shaft, while the drive control is in operation and the reaction torque is less than or equal to the threshold value, and to perform a second process to control the brake device to a braking state and stop the power supply to the first electric actuator.

[0018] According to the above program, power supply to the first electric actuator can be stopped until the reaction torque acting on the first output shaft exceeds a threshold. As a result, the driving time of the first electric actuator can be shortened, and thus the power consumption of the first electric actuator can be reduced.

[0019] A control program for a work machine to solve the above problems is applied to a work machine comprising: a first electric actuator having a first output shaft that outputs torque; a first movable member that rotates based on the torque from the first output shaft; a second electric actuator attached to the first movable member and having a second output shaft that outputs torque; a second movable member that rotates based on the torque from the second output shaft; a brake device that switches between a braking state that applies braking torque to the second output shaft and a release state that releases the application of braking torque to the second output shaft; and a control device that controls the first electric actuator, the second electric actuator, and the brake device, wherein the program controls the reaction that acts on the second output shaft as the first output shaft outputs torque. When the torque of a force is defined as the reaction torque, the control device is instructed to perform a first process to reduce the rotational speed of the second output shaft to a predetermined set value or less by controlling the second electric actuator so that the second output shaft outputs a torque in the opposite direction to the reaction torque, if the reaction torque is greater than a predetermined threshold value which is less than or equal to the maximum braking torque that the brake device can apply to the second output shaft, while the drive control is in operation and the reaction torque is less than or equal to the threshold value, and to perform a second process to control the brake device to a braking state and stop the power supply to the second electric actuator.

[0020] According to the program described above, power supply to the second electric actuator can be stopped until the reaction torque acting on the second output shaft exceeds a threshold. As a result, the driving time of the second electric actuator can be shortened, thereby reducing the power consumption of the second electric actuator. [Effects of the Invention]

[0021] The above technical concept makes it possible to reduce the power consumption of electric actuators. [Brief explanation of the drawing]

[0022] [Figure 1] Figure 1 is a side view schematically illustrating a shovel. [Figure 2] Figure 2 is a plan view schematically illustrating a shovel. [Figure 3] Figure 3 is a diagram illustrating the electrical configuration and power transmission paths of the shovel. [Figure 4] Figure 4 is a cross-sectional view schematically illustrating a boom actuator and a first brake device. [Figure 5] Figure 5 is a flowchart illustrating the processing procedure of holding control. [Figure 6] Figure 6 is a side view for explaining a calculation method of reaction torque acting on a first drive shaft. [Figure 7] Figure 7 is a side view for explaining a calculation method of reaction torque acting on a second drive shaft. [Figure 8] Figure 8 is a side view for explaining a calculation method of reaction torque acting on a third drive shaft. [Mode for Carrying Out the Invention]

[0023] <First Embodiment> Hereinafter, a first embodiment of a work machine drive system, a work machine control method, and a work machine control program will be described taking a construction machine as an example. Note that in the drawings, components may be illustrated in an enlarged scale for ease of understanding. In addition, the dimensional ratios of components may differ from the actual ones or from those in other drawings.

[0024] <Overall Configuration> As shown in Figures 1 and 2, the excavator 10, a construction machine, comprises a lower body 13 and an upper body 14. The upper body 14 is located on the opposite side of the lower body 13 from the ground G. In this embodiment, the direction in which the upper body 14 is located, as viewed from the lower body 13, is the upward direction, and the opposite direction is the downward direction. Furthermore, one of the directions perpendicular to the upward direction is the forward direction, and the opposite direction is the backward direction. In addition, one of the directions perpendicular to both the upward and forward directions is the left direction, and the other is the right direction. The forward and backward directions are sometimes collectively referred to as the X direction. The left and right directions are sometimes collectively referred to as the Y direction. The upward and downward directions are sometimes collectively referred to as the Z direction.

[0025] The lower body 13 and the upper body 14 constitute the vehicle body 15. The lower body 13 is, for example, rectangular parallelepiped. The upper body 14 comprises a main housing section 14A and a front housing section 14B. The main housing section 14A is, for example, rectangular parallelepiped. The interior of the main housing section 14A is a hollow storage space. The storage space houses various equipment for operating the excavator 10. The front housing section 14B is located on the front side of the main housing section 14A. The front housing section 14B is located approximately in the center of the main housing section 14A in the Y direction. The front housing section 14B is fixed to the front of the main housing section 14A. The front housing section 14B is, for example, a smaller rectangular parallelepiped than the main housing section 14A. The interior of the front housing section 14B is hollow. Although not shown in the illustration, the upper body 14 includes a cabin in which an operator sits. The cabin is integrally fixed to the main housing section 14A. The upper body 14 is sometimes referred to as the upper rotating body.

[0026] As shown in Figures 1 and 2, the excavator 10 is equipped with a slewing bearing 18. The slewing bearing 18 is located between the lower body 13 and the upper body 14. In Figure 1, the vertical width of the slewing bearing 18 is exaggerated and shown as large with respect to the Z direction. As shown in Figure 2, the slewing bearing 18 comprises an annular inner ring 18A, an annular outer ring 18B, and a plurality of rolling elements. In Figure 2, the rolling elements are not shown. The outer diameter of the inner ring 18A is smaller than the inner diameter of the outer ring 18B. The slewing axis 10J, which is the central axis of the inner ring 18A, approximately coincides with the central axis of the outer ring 18B. The slewing axis 10J extends vertically across the vehicle body 15, i.e., in the Z direction. As shown in Figure 1, the slewing axis 10J passes vertically through both the upper body 14 and the lower body 13. The plurality of rolling elements are located between the inner ring 18A and the outer ring 18B. Multiple rolling elements support the inner ring 18A and the outer ring 18B so that they can rotate relative to each other. As a result, the outer ring 18B is rotatable relative to the inner ring 18A about the pivot axis 10J. The inner ring 18A is fixed to the lower body 13. The outer ring 18B is fixed to the main housing portion 14A of the upper body 14. That is, the upper body 14 is rotatable relative to the lower body 13 about the pivot axis 10J. It can also be said that the upper body 14 rotates relative to the lower body 13.

[0027] As shown in Figures 1 and 2, the excavator 10 is equipped with a pair of running gears 12. The pair of running gears 12 are located on the left and right sides of the lower body 13. Both running gears 12 are connected to the lower body 13. Each pair of running gears 12 includes a crawler for travel and an operating mechanism for rotating the crawler. The crawler is an endless belt shape. The crawler has openings on both the left and right sides. The underside of the crawler is in contact with the ground G. The excavator 10 moves as the crawler rotates. The running gears 12 and the lower body 13 are sometimes collectively referred to as the lower running gear.

[0028] As shown in Figures 1 and 2, the excavator 10 is equipped with a swing bracket 17. The swing bracket 17 is located on the front side of the main housing portion 14A of the upper body 14. The swing bracket 17 comprises a first swing wall 17A and a second swing wall 17B. The first swing wall 17A is located on the upper surface of the front housing portion 14B of the upper body 14. The first swing wall 17A is, for example, disc-shaped. The first swing wall 17A is connected to the front housing portion 14B. The first swing wall 17A is rotatable around the front housing portion 14B about a fourth rotation axis 61J that extends vertically from the vehicle body 15. The fourth rotation axis 61J is substantially parallel to the pivot axis 10J. The second swing wall 17B protrudes upward from the upper surface of the first swing wall 17A. The second swing wall 17B is, for example, rectangular plate-shaped.

[0029] <Work Attachment> As shown in Figures 1 and 2, the drive system of the excavator 10 is equipped with a work attachment 20. The work attachment 20 has a boom 21, an arm 23, and a bucket 25.

[0030] As shown in Figures 1 and 2, the boom 21 is located on the front side relative to the upper body 14. The boom 21 is a long, plate-like or columnar shape. For example, the boom 21 is bent in the middle of its longitudinal direction. As shown in Figure 2, the first longitudinal end 21A of the boom 21 is aligned with the second swing wall 17B of the swing bracket 17 in the direction along the first rotation axis 31J. The first rotation axis 31J is a virtual axis that intersects the fourth rotation axis 61J. More specifically, the first rotation axis 31J is approximately perpendicular to the fourth rotation axis 61J. The first end 21A of the boom 21 is rotatably connected to the second swing wall 17B. The boom 21 corresponds to the first movable member. The first rotation axis 31J corresponds to the first axis.

[0031] As shown in Figures 1 and 2, the arm 23 extends from the second end 21B of the boom 21, opposite to the first end 21A. The arm 23 is a long, plate-like or columnar shape. As shown in Figure 2, the longitudinal first end 23A of the arm 23 is aligned with the second end 21B of the boom 21 in the direction along the second rotation axis 41J. The second rotation axis 41J is a virtual axis approximately parallel to the first rotation axis 31J. The first end 23A of the arm 23 is rotatably connected to the second end 21B of the boom 21. The arm 23 corresponds to the second movable member. The second rotation axis 41J corresponds to the second axis.

[0032] As shown in Figures 1 and 2, the bucket 25 is located near the second end 23B of the arm 23, opposite to the first end 23A. The bucket 25 comprises a bucket body 26, a plurality of claws 27, and a bucket connecting wall 28. The bucket body 26 is box-shaped. That is, as shown in Figure 2, the bucket body 26 has an opening 26A. The claws 27 protrude from one side of the rectangular opening edge of the bucket body 26. The bucket connecting wall 28 protrudes from the outer wall of the bucket body 26, on the opposite side of the opening 26A from the claws 27. As shown in Figure 2, the bucket connecting wall 28 is aligned with the second end 23B of the arm 23 in the direction along the third rotation axis 51J. The third rotation axis 51J is a virtual axis that is substantially parallel to both the first rotation axis 31J and the second rotation axis 41J. The bucket connecting wall 28 is rotatably connected to the second end 23B of the arm 23. Bucket 25 corresponds to the third movable member. The third rotation axis 51J corresponds to the third axis. The tip of the claw 27 of bucket 25 corresponds to a specific part of bucket 25.

[0033] <Electric actuator> As shown in Figure 3, the drive system of the excavator 10 includes a boom actuator 31, an arm actuator 41, and a bucket actuator 51. The boom actuator 31 drives the boom 21. The arm actuator 41 drives the arm 23. The bucket actuator 51 drives the bucket 25. The excavator 10 also includes a first inverter 35, a second inverter 45, a third inverter 55, and a battery 19. Although not shown in the figure, the first inverter 35, the second inverter 45, the third inverter 55, and the battery 19 are housed in the main housing 14A of the upper body 14. The boom actuator 31 corresponds to the first electric actuator. The arm actuator 41 corresponds to the second electric actuator.

[0034] As shown in Figure 2, the boom actuator 31 is located between the second swing wall 17B of the swing bracket 17 and the first end 21A of the boom 21. As shown in Figures 3 and 4, the boom actuator 31 includes a first electric motor 32 and a first reduction gear 33. The first electric motor 32 is a three-phase AC motor. The first electric motor 32 is electrically connected to the battery 19 via a first inverter 35. The first electric motor 32 includes a housing 32A, a first drive shaft 32B, a stator 32C, and a rotor 32D. The stator 32C is located inside the housing 32A. The stator 32C is fixed to the housing 32A. The stator 32C is cylindrical. Although not shown, a coil is wound around the stator 32C. The coil is electrically connected to the battery 19 via the first inverter 35. The rotor 32D is located inside the stator 32C. The rotor 32D is rotatable relative to the stator 32C. The first drive shaft 32B is fixed to the rotor 32D. The first drive shaft 32B rotates integrally with the rotor 32D. The first drive shaft 32B protrudes from the inside to the outside of the housing 32A. The first drive shaft 32B is cylindrical. The first drive shaft 32B is rotatable relative to the housing 32A about its own axis of rotation, the first rotation axis 31J. That is, the first drive shaft 32B outputs torque about the first rotation axis 31J. The first drive shaft 32B is rotatable in both directions about the first rotation axis 31J. As shown in Figure 2, the first rotation axis 31J passes through both the second swing wall 17B of the swing bracket 17 and the first end 21A of the boom 21. The first drive shaft 32B corresponds to the first output shaft.

[0035] As shown in Figures 3 and 4, the first reduction gear 33 comprises a housing 33A, a reduction mechanism 33B, and an output member 33C. The housing 33A is attached to the housing 32A of the first electric motor 32. The reduction mechanism 33B is located inside the housing 33A. Torque is input to the reduction mechanism 33B from the first drive shaft 32B of the first electric motor 32. The reduction mechanism 33B amplifies the torque from the first electric motor 32 at a predetermined ratio and outputs it to the output member 33C. The reduction mechanism 33B is, for example, an eccentric oscillating gear type or a planetary gear type. The output member 33C is cylindrical. The central axis of the output member 33C substantially coincides with the first rotation axis 31J. The output member 33C is rotatable relative to the housing 33A. The output member 33C rotates about the first rotation axis 31J in response to the rotation of the first drive shaft 32B of the first electric motor 32. The output member 33C is attached to the first end 21A of the boom 21. In other words, the output member 33C inputs torque to the boom 21 about the first rotation axis 31J. The boom 21 is able to rotate about the first rotation axis 31J based on the torque from the first drive shaft 32B and, consequently, the torque from the output member 33C.

[0036] As shown in Figures 3 and 4, the drive system of the excavator 10 includes a first brake device 81 for the boom actuator 31. As shown in Figure 2, the first brake device 81 is located on the opposite side of the first reduction gear 33 from the first electric motor 32. That is, in the direction along the first rotation axis 31J, the first brake device 81 is located between the first electric motor 32 and the second swing wall 17B of the swing bracket 17. As shown in Figures 3 and 4, the first brake device 81 is fixed to the housing 32A of the first electric motor 32. The first brake device 81 is connected to the first drive shaft 32B of the first electric motor 32. The first brake device 81 is electrically connected to the battery 19.

[0037] Furthermore, the first brake device 81 switches between a braking state in which braking torque is applied to the first drive shaft 32B and a release state in which the application of braking torque to the first drive shaft 32B is released. More specifically, when the power supply from the battery 19 is cut off, the first brake device 81 enters a braking state in which braking torque is applied to the first drive shaft 32B. At the same time, the first brake device 81 makes the first drive shaft 32B unable to rotate. On the other hand, when the first brake device 81 is receiving power from the battery 19, it enters a release state in which the application of braking torque to the first drive shaft 32B is released. Therefore, in this case, the first drive shaft 32B can rotate freely. In this embodiment, the braking torque that the first brake device 81 can apply to the first drive shaft 32B is a constant fixed value. This fixed value is the maximum value of the braking torque that the first brake device 81 can apply to the first drive shaft 32B, i.e., the maximum braking torque.

[0038] The first brake device 81 comprises a housing 81A, an excitation coil 81B, a contact plate 81C, a movable plate 81D, and a relay 81E. The housing 81A is cylindrical. The central axis of the housing 81A substantially coincides with the first rotation axis 31J of the housing 32A of the first electric motor 32. One end of the housing 81A in the direction along its central axis is closed. The other end of the housing 81A is fixed to the housing 32A. A portion of the first drive shaft 32B of the first electric motor 32 is located inside the housing 81A.

[0039] The excitation coil 81B, contact plate 81C, and movable plate 81D are located inside the housing 81A. The contact plate 81C is located closer to the housing 32A in the direction along the central axis of the housing 81A. The contact plate 81C is disc-shaped. The first drive shaft 32B of the first electric motor 32 passes through the vicinity of the center of the contact plate 81C. The contact plate 81C rotates integrally with the first drive shaft 32B.

[0040] The excitation coil 81B is located on the opposite side of the housing 32A, with the contact plate 81C in between. Although detailed illustrations are omitted, the excitation coil 81B comprises a coil body and a spring. The excitation coil 81B is fixed to the housing 81A. The coil body receives power from the battery 19 and is interrupted by the power supply.

[0041] The movable plate 81D is located between the excitation coil 81B and the contact plate 81C. The movable plate 81D is disc-shaped. There is a hole in the center of the movable plate 81D. The diameter of the hole is larger than the diameter of the first drive shaft 32B of the first electric motor 32. The first drive shaft 32B is inserted through this hole. The movable plate 81D is movable in a direction along the first rotation axis 31J of the first drive shaft 32B. The movable plate 81D receives a biasing force toward the contact plate 81C from the spring of the excitation coil 81B.

[0042] Relay 81E is located in the middle of the power line 81F connected to the coil body of the excitation coil 81B. Depending on whether relay 81E is turned on or off, the energization of the coil body of the excitation coil 81B is switched on or off. The excitation coil 81B changes the position of the movable plate 81D depending on whether or not the coil body is energized. When the excitation coil 81B is de-energized, the spring presses the movable plate 81D against the contact plate 81C. Consequently, a braking torque is applied to the contact plate 81C and, consequently, to the first drive shaft 32B of the first electric motor 32, which brakes the rotation of the first drive shaft 32B. In other words, the movable plate 81D applies a braking torque to the first drive shaft 32B. On the other hand, when the excitation coil 81B is energized, the movable plate 81D is separated from the contact plate 81C against the biasing force of the spring. In this case, the braking force on the contact plate 81C and the first drive shaft 32B is released. The power line 81F on which the relay 81E is located is connected, for example, to the power line 89 that connects the first inverter 35 and the first electric motor 32. Although not shown in the diagram, on the power line 81F, a converter for DC to AC conversion is provided on the first inverter 35 side relative to the relay 81E.

[0043] As shown in Figure 2, the arm actuator 41 is attached to the boom 21. The arm actuator 41 is located between the second end 21B of the boom 21 and the first end 23A of the arm 23. The configuration of the arm actuator 41 is basically the same as that of the boom actuator 31, except for details such as dimensions, reduction ratio, and output. Therefore, the configuration of the arm actuator 41 will be briefly described below.

[0044] As shown in Figure 3, the arm actuator 41 comprises a second electric motor 42 and a second reduction gear 43. The second electric motor 42 is electrically connected to the battery 19 via a second inverter 45. The second drive shaft 42B of the second electric motor 42 outputs torque around its own central axis, the second rotation axis 41J. The second drive shaft 42B is rotatable in both directions around the second rotation axis 41J. As shown in Figure 2, the second rotation axis 41J passes through both the second end 21B of the boom 21 and the first end 23A of the arm 23. The output member 43C of the second reduction gear 43 is attached to the first end 23A of the arm 23. As shown in Figure 3, the output member 43C outputs torque around the second rotation axis 41J. The arm 23 is rotatable around a second rotation axis 41J, which is parallel to the first rotation axis 31J, based on the torque from the second drive shaft 42B and, consequently, the torque from the output member 43C. The functions of the housing 43A and reduction mechanism 43B of the second reduction gear 43 are the same as those of the housing 33A and reduction mechanism 33B of the first reduction gear 33. The second drive shaft 42B corresponds to the second output shaft.

[0045] As shown in Figure 3, the drive system of the excavator 10 is equipped with a second brake device 82 for the arm actuator 41. The configuration of the second brake device 82 is basically the same as that of the first brake device 81, except for details such as dimensions. Therefore, the configuration of the second brake device 82 will be briefly described below. As shown in Figure 2, the second brake device 82 is located on the opposite side of the second reduction gear 43, with the second electric motor 42 in between. That is, in the direction along the second rotation axis 41J, the second brake device 82 is located between the second electric motor 42 and the second end 21B of the boom 21. As shown in Figure 3, the second brake device 82 is fixed to the housing 42A of the second electric motor 42. The second brake device 82 is connected to the second drive shaft 42B of the second electric motor 42. The second brake device 82 is electrically connected to the battery 19.

[0046] Furthermore, the second brake device 82 switches between a braking state in which braking torque is applied to the second drive shaft 42B and a release state in which the application of braking torque to the second drive shaft 42B is released. More specifically, when the power supply from the battery 19 is cut off, the second brake device 82 enters a braking state in which braking torque is applied to the second drive shaft 42B. At the same time, the second brake device 82 makes the second drive shaft 42B unable to rotate. On the other hand, when the second brake device 82 is receiving power from the battery 19, it enters a release state in which the application of braking torque to the second drive shaft 42B is released. Therefore, in this case, the second drive shaft 42B can rotate freely. The braking torque that the second brake device 82 can apply to the second drive shaft 42B is a constant fixed value. This fixed value is the maximum value of the braking torque that the second brake device 82 can apply to the second drive shaft 42B, i.e., the maximum braking torque.

[0047] The second brake device 82 comprises a housing 82A and an excitation coil 82B. The housing 82A is cylindrical. The central axis of the housing 82A substantially coincides with the second rotation axis 41J of the housing 42A of the second electric motor 42. One end of the housing 82A in the direction along its central axis is closed. The other end of the housing 82A is fixed to the housing 42A. A portion of the second drive shaft 42B of the second electric motor 42 is located inside the housing 82A.

[0048] The excitation coil 82B is located inside the housing 82A. When the excitation coil 82B is de-excited, a braking torque is applied to the second drive shaft 42B of the second electric motor 42 to brake its rotation. Conversely, when the excitation coil 82B is excited, the braking of the second drive shaft 42B of the second electric motor 42 is released. Although not shown in the figures, the second brake device 82 includes a relay that switches between energizing and de-exciting the excitation coil 82B. The power line on which the relay is located is connected to the power line connecting the second inverter 45 and the second electric motor 42.

[0049] As shown in Figure 2, the bucket actuator 51 is located between the second end 23B of the arm 23 and the bucket connecting wall 28 of the bucket 25. The configuration of the bucket actuator 51 is basically the same as that of the boom actuator 31, except for details such as dimensions, reduction ratio, and output. Therefore, the configuration of the bucket actuator 51 will be briefly described below.

[0050] As shown in Figure 3, the bucket actuator 51 comprises a third electric motor 52 and a third reduction gear 53. The third electric motor 52 is electrically connected to the battery 19 via a third inverter 55. The third drive shaft 52B of the third electric motor 52 outputs torque around its own central axis, the third rotation axis 51J. The third drive shaft 52B is rotatable in both directions around the third rotation axis 51J. As shown in Figure 2, the third rotation axis 51J passes through both the second end 23B of the arm 23 and the bucket connecting wall 28. The output member 53C of the third reduction gear 53 is attached to the bucket connecting wall 28. As shown in Figure 3, the output member 53C outputs torque around the third rotation axis 51J. The bucket 25 is rotatable around a third rotation axis 51J, which is parallel to the first rotation axis 31J and the second rotation axis 41J, based on the torque from the third drive shaft 52B and, consequently, the torque from the output member 53C. The functions of the housing 53A and reduction mechanism 53B of the third reduction gear 53 are the same as those of the housing 33A and reduction mechanism 33B of the first reduction gear 33.

[0051] As shown in Figure 3, the drive system of the excavator 10 is equipped with a third brake device 83 for the bucket actuator 51. The configuration of the third brake device 83 is basically the same as that of the first brake device 81, except for details such as dimensions. Therefore, the configuration of the third brake device 83 will be briefly described below. As shown in Figure 2, the third brake device 83 is located on the opposite side of the third reduction gear 53, with the third electric motor 52 in between. That is, in the direction along the third rotation axis 51J, the third brake device 83 is located between the third electric motor 52 and the second end 23B of the arm 23. As shown in Figure 3, the third brake device 83 is fixed to the housing 52A of the third electric motor 52. The third brake device 83 is connected to the third drive shaft 52B of the third electric motor 52. The third brake device 83 is electrically connected to the battery 19.

[0052] Furthermore, the third brake device 83 switches between a braking state in which braking torque is applied to the third drive shaft 52B and a release state in which the application of braking torque to the third drive shaft 52B is released. More specifically, when the power supply from the battery 19 is cut off, the third brake device 83 enters a braking state in which braking torque is applied to the third drive shaft 52B. At the same time, the third brake device 83 makes the third drive shaft 52B unable to rotate. On the other hand, when the third brake device 83 is receiving power from the battery 19, it enters a release state in which the application of braking torque to the third drive shaft 52B is released. Therefore, in this case, the third drive shaft 52B can rotate freely. The braking torque that the third brake device 83 can apply to the third drive shaft 52B is a constant fixed value. This fixed value is the maximum value of the braking torque that the third brake device 83 can apply to the third drive shaft 52B, i.e., the maximum braking torque.

[0053] The third brake device 83 comprises a housing 83A and an excitation coil 83B. The housing 83A is cylindrical. The central axis of the housing 83A substantially coincides with the third rotation axis 51J of the housing 52A of the third electric motor 52. One end of the housing 83A in the direction along its central axis is closed. The other end of the housing 83A is fixed to the housing 52A. A portion of the third drive shaft 52B of the third electric motor 52 is located inside the housing 83A.

[0054] The excitation coil 83B is located inside the housing 83A. When the excitation coil 83B is de-excited, a braking torque is applied to the third drive shaft 52B of the third electric motor 52 to brake its rotation. Conversely, when the excitation coil 83B is excited, the braking of the third drive shaft 52B of the third electric motor 52 is released. Although not shown in the diagram, the third brake device 83 includes a relay that switches between energizing and de-exciting the excitation coil 83B. The power line on which the relay is located is connected to the power line connecting the third inverter 55 and the third electric motor 52.

[0055] As shown in Figure 3, the excavator 10 is equipped with a swing actuator 61 and a fourth inverter 65. As shown in Figure 1, the swing actuator 61 is housed in the front part 14B of the housing of the upper body 14. Although not shown in the figure, the fourth inverter 65 is housed in the main part 14A of the housing of the upper body 14. The configuration of the swing actuator 61 is basically the same as that of the boom actuator 31, except for details such as dimensions, reduction ratio, and output. Therefore, the configuration of the swing actuator 61 will be briefly described below.

[0056] As shown in Figure 3, the swing actuator 61 comprises a fourth electric motor 62 and a fourth reduction gear 63. The fourth electric motor 62 is electrically connected to the battery 19 via a fourth inverter 65. The fourth electric motor 62 comprises a housing 62A and a fourth drive shaft 62B. The fourth drive shaft 62B outputs torque around its own central axis, the fourth rotation axis 61J. The fourth drive shaft 62B is rotatable in both directions around the fourth rotation axis 61J. The output member 63C of the fourth reduction gear 63 is attached to the first swing wall 17A of the swing bracket 17. The output member 63C outputs torque around the fourth rotation axis 61J. The swing bracket 17 rotates around the fourth rotation axis 61J in response to the torque from the output member 63C. Furthermore, the functions of the housing 63A and reduction mechanism 63B of the fourth reduction gear 63 are the same as those of the housing 33A and reduction mechanism 33B of the first reduction gear 33.

[0057] As shown in Figure 3, the excavator 10 is equipped with a slewing actuator 71 and a fifth inverter 75. The slewing actuator 71 and the fifth inverter 75 are housed in the main housing 14A of the upper body 14. The configuration of the slewing actuator 71 is basically the same as that of the boom actuator 31, except for details such as dimensions, reduction ratio, and output. Therefore, the configuration of the slewing actuator 71 will be briefly described below.

[0058] As shown in Figure 3, the slewing actuator 71 comprises a fifth electric motor 72 and a fifth reduction gear 73. The fifth electric motor 72 is electrically connected to the battery 19 via a fifth inverter 75. The housing 72A of the fifth electric motor 72 is attached to the main housing portion 14A of the upper body 14. The fifth drive shaft 72B of the fifth electric motor 72 outputs torque around its own central axis, the fifth rotation axis 71J. The fifth drive shaft 72B is rotatable in both directions around the fifth rotation axis 71J. Multiple teeth are formed on the output member 73C of the fifth reduction gear 73. These teeth mesh with the teeth formed on the inner ring 18A of the slewing bearing 18. The output member 73C outputs torque around the fifth rotation axis 71J. In response to this torque, the upper body 14 rotates together with the housing 72A of the fifth electric motor 72 relative to the inner ring 18A and, consequently, the lower body 13. In other words, the slewing actuator 71 rotates the upper body 14 relative to the lower body 13. The functions of the housing 73A and reduction mechanism 73B of the fifth reduction gear 73 are the same as those of the housing 33A and reduction mechanism 33B of the first reduction gear 33.

[0059] <Sensor> As shown in Figure 3, the drive system of the excavator 10 includes a first angle sensor 38, a second angle sensor 48, and a third angle sensor 58. The first angle sensor 38 detects the angular position 38S of the first drive shaft 32B of the first electric motor 32. The second angle sensor 48 detects the angular position 48S of the second drive shaft 42B of the second electric motor 42. The third angle sensor 58 detects the angular position 58S of the third drive shaft 52B of the third electric motor 52. The angular position detected by each angle sensor indicates a value in the range of "0 degrees to 360 degrees," with a predetermined reference position of "0 degrees." In other words, each angular position indicates the absolute angle of the drive shaft of each electric motor. Each angle sensor repeatedly transmits the information it has detected to the control device 100, which will be described later.

[0060] In addition to the sensors mentioned above, the drive system of the excavator 10 is equipped with various other sensors necessary for operating the excavator 10. For example, the drive system of the excavator 10 is equipped with a first current sensor 91, a second current sensor 92, and a third current sensor 93. The first current sensor 91 detects a first current value 91S, which is the magnitude of the current supplied to the first electric motor 32 of the boom actuator 31. The second current sensor 92 detects a second current value 92S, which is the magnitude of the current supplied to the second electric motor 42 of the arm actuator 41. The third current sensor 93 detects a third current value 93S, which is the magnitude of the current supplied to the third electric motor 52 of the bucket actuator 51. Each current sensor repeatedly transmits the information it has detected to the control device 100.

[0061] The drive system of the excavator 10 is equipped with various operating devices 90 that are operated by the operator. Figure 3 shows the various operating devices together. The various operating devices 90 are located in the cabin. The various operating devices 90 transmit various signals 90S to the control device 100 in response to the operator's actions, for example.

[0062] <Control device> As shown in Figure 3, the drive system of the excavator 10 includes a control device 100. The control device 100 controls the boom actuator 31, the arm actuator 41, the bucket actuator 51, the swing actuator 61, and the slewing actuator 71. The control device 100 also controls the first brake device 81, the second brake device 82, and the third brake device 83. The control device 100 is a computer equipped with a processing circuit. The processing circuit includes a CPU 101 and a memory 102. The memory 102 includes three types: RAM, ROM, and electrically rewritable non-volatile memory. In this embodiment, these three types are collectively referred to as memory 102. The memory 102 pre-stores various control programs 102A that describe the processing to be executed by the CPU 101. The memory 102 pre-stores various data 102B necessary for the CPU 101 to execute the control programs 102A. The processing circuit includes a communication circuit for wireless communication with the outside.

[0063] Furthermore, the CPU 101 can receive the angular position 38S transmitted from the first angular sensor 38. The CPU 101 can receive the angular position 48S transmitted from the second angular sensor 48. The CPU 101 can receive the angular position 58S transmitted from the third angular sensor 58. The CPU 101 can receive the first current value 91S transmitted from the first current sensor 91. The CPU 101 can receive the second current value 92S transmitted from the second current sensor 92. The CPU 101 can receive the third current value 93S transmitted from the third current sensor 93. The CPU 101 can receive the signal 90S transmitted from the operating device 90.

[0064] The CPU 101 converts the angular position 38S received from the first angle sensor 38 into a first angular position related to the boom 21 from the actual angle of the first electric motor 32. The first angular position is the angular position of the boom 21 from a predetermined first position. The first position and the first angular position are defined in a specific plan view when viewing the excavator 10 facing in the direction along the first rotation axis 31J. An example of the first position is an angular position in which both the first end 21A and the second end 21B of the boom 21 are positioned on a virtual straight line perpendicular to both the first rotation axis 31J and the fourth rotation axis 61J. In this example of the first position, the second end 21B of the boom 21 is positioned on the opposite side from the vehicle body 15 with the first rotation axis 31J in between. The first angular position indicates the relative position of the boom 21 with respect to the swing bracket 17 or the vehicle body 15. The first angle sensor 38, which detects the actual angle of the first electric motor 32, substantially detects the first angular position.

[0065] The CPU 101 converts the angular position 48S received from the second angle sensor 48 into a second angular position related to the arm 23, similar to the case of the first electric motor 32 described above, from the actual angle of the second electric motor 42. The second angular position is the angular position of the arm 23 from a predetermined second position. The second position and the second angular position are defined in a specific plan view when viewing the excavator 10 facing along the second rotation axis 41J, which is parallel to the first rotation axis 31J. An example of the second position is an angular position where both the first end 23A and the second end 23B of the arm 23 are positioned on a virtual straight line passing through the first rotation axis 31J and the second rotation axis 41J. In this example of the second position, the second end 23B of the arm 23 is positioned on the opposite side of the second rotation axis 41J from the first rotation axis 31J. The second angular position indicates the relative position of the arm 23 with respect to the boom 21. The second angle sensor 48, which detects the actual angle of the second electric motor 42, effectively detects the second angular position.

[0066] The CPU 101 converts the angular position 58S received from the third angle sensor 58 into a third angular position related to the bucket 25, based on the actual angle of the third electric motor 52, similar to the case of the electric motors 32 and 42 described above. The third angular position is the angular position of the bucket 25 from a predetermined third position. The third position and the third angular position are defined in a specific plan view when viewing the excavator 10 facing along the third rotation axis 51J, which is parallel to the first rotation axis 31J. An example of the third position is the angular position where the claws 27 of the bucket 25 are positioned on a virtual straight line passing through the second rotation axis 41J and the third rotation axis 51J. In this example of the third position, the claws 27 of the bucket 25 are positioned on the opposite side of the third rotation axis 51J from the second rotation axis 41J. The third angular position indicates the relative position of the bucket 25 with respect to the arm 23. The third angle sensor 58, which detects the actual angle of the third electric motor 52, effectively detects the third angular position.

[0067] The CPU 101 calculates the first angular position each time it receives the angular position 38S from the first angular sensor 38. In other words, the CPU 101 repeatedly calculates the first angular position. The CPU 101 calculating the first angular position is equivalent to the CPU 101 acquiring the first angular position. Similar to the first angular position, the CPU 101 repeatedly calculates the second and third angular positions. Similar to the first angular position, the CPU 101 calculating these angular positions is equivalent to the CPU 101 acquiring each of these angular positions.

[0068] <Holding control> The CPU 101 is capable of controlling the drive of each movable component of the work attachment 20, such as the boom 21, arm 23, and bucket 25. In each drive control, the CPU 101 controls the electric motors of each actuator so that the target movable component rotates. For example, in the case of drive control for the arm 23, the CPU 101 controls the second electric motor 42 so that the second drive shaft 42B of the second electric motor 42 outputs torque in order to rotate the arm 23. The CPU 101 executes each drive control in accordance with the drive signals for each movable component transmitted from the operating device 90 in response to the operator's operation. In essence, the CPU 101 controls the inverters connected to each electric motor when controlling each electric motor.

[0069] The CPU 101 is capable of performing holding control for the boom 21. Holding control for the boom 21 is a control for maintaining the angular position of the boom 21 at a substantially constant level. When the CPU 101 receives a holding signal for the boom 21 transmitted from the operating device 90, it starts holding control for the boom 21. In this embodiment, the holding control for the boom 21 is performed in parallel with the drive control for the arm 23. That is, the CPU 101 performs holding control for the boom 21 while the drive control for the arm 23 is being performed. Note that all torques discussed in this specification are positive values.

[0070] As shown in Figure 5, when the CPU 101 starts holding control for the boom 21, it first performs the process in step S100. In step S100, the CPU 101 performs preparatory processing to control the first brake device 81 to a braking state and to stop the power supply to the first electric motor 32. Specifically, the CPU 101 turns off the relay 81E of the first brake device 81 and cuts off the power supply to the excitation coil 81B. As a result, the excitation coil 81B of the first brake device 81 is not energized from the battery 19, and braking torque is applied to the first drive shaft 32B. This braking torque is the maximum braking torque of the first brake device 81. The CPU 101 also stops the power supply from the battery 19 to the first electric motor 32 through the control of the first inverter 35. After performing the preparatory processing, the CPU 101 proceeds to step S110 while maintaining the execution state of this preparatory processing.

[0071] In step S110, the CPU 101 calculates the pressing reaction force FA1 shown in Figure 6. The pressing reaction force FA1 is the reaction force that acts on the bucket 25 from the object when the bucket 25 is pressed against the object by rotating the arm 23. The pressing reaction force FA1 acts in a direction perpendicular to the virtual line A2 in a specific plane. The virtual line A2 is a virtual line that passes through the second rotation axis 41J and the tip of the claw 27 of the bucket 25 in a specific plane view. An example of the object is the ground G. In Figure 6, the force acting from the bucket 25 on the object is represented by F.

[0072] When the CPU 101 calculates the pressing reaction force FA1, it first calculates the output torque of the arm actuator 41. The output torque of the arm actuator 41 is the torque output from the second drive shaft 42B of the second electric motor 42, amplified by the second reduction gear 43, and output from the output member 43C. Memory 102 has pre-stored torque conversion information as information for the CPU 101 to calculate the output torque of the arm actuator 41. The torque conversion information represents the relationship between the output torque of the arm actuator 41 and the second current value 92S supplied to the second electric motor 42. The CPU 101 calculates the output torque of the arm actuator 41 by applying the latest second current value 92S received from the second current sensor 92 to the torque conversion information.

[0073] Next, the CPU 101 calculates the second distance L2, which is the distance from the second rotation axis 41J to the claws 27 of the bucket 25 in a specific planar view. The second distance L2 is an index that shows the positional relationship between the second rotation axis 41J and the tip of the claws 27 of the bucket 25. Memory 102 has pre-stored second distance information as information for the CPU 101 to calculate the second distance L2. The second distance information represents the relationship between the third angular position and the second distance L2. In detail, the second distance information represents the second distance L2 for each third angular position when the third angular position changes in various ways. The second distance information is composed of, for example, a table, a graph, or a mathematical formula. When calculating the second distance L2, the CPU 101 obtains the latest third angular position. Then, the CPU 101 calculates the second distance L2 by applying the obtained third angular position to the second distance information. In this way, the CPU 101 calculates the second distance L2 based on the third angular position.

[0074] The CPU 101 calculates the output torque of the arm actuator 41 and the second distance L2, and then calculates the pressing reaction force FA1 by dividing the output torque of the arm actuator 41 by the second distance L2. As shown in Figure 5, once the CPU 101 has calculated the pressing reaction force FA1, it proceeds to step S120.

[0075] In step S120, the CPU 101 calculates the orthogonal component A of the pressing reaction force FA1. As shown in Figure 6, the orthogonal component A is the component of the pressing reaction force FA1 in a direction perpendicular to the virtual line A1 that passes through the first rotation axis 31J and the tip of the claw 27 in a specific plan view. That is, the orthogonal component A is calculated by the product of the pressing reaction force FA1 and cosθ. The angle θ is the inferior angle of the angle formed by the direction perpendicular to the virtual line A1 and the direction in which the pressing reaction force FA1 acts. The memory 102 has pre-stored angle information regarding the angle θ. The angle information represents the relationship between the first angular position, the second angular position, and the third angular position and the angle θ. In detail, the angle information represents the angle θ for various combinations of the first angular position, the second angular position, and the third angular position. The angle information is composed of, for example, tables, graphs, or mathematical formulas. When calculating the angle θ, the CPU 101 obtains the latest first angular position, the latest second angular position, and the latest third angular position. Then, the CPU 101 calculates the angle θ by applying the obtained first, second, and third angular positions to the angular information. In this way, the CPU 101 calculates the angle θ based on the latest first, second, and latest third angular positions. Once the angle θ is calculated, the CPU 101 calculates the orthogonal component A as the product of the pressing reaction force FA1 obtained in step S110 and cosθ. As shown in Figure 5, once the CPU 101 calculates the orthogonal component A, it proceeds to step S130.

[0076] In step S130, the CPU 101 calculates the reaction torque FR1. The reaction torque FR1 is the torque of the reaction force that acts on the first drive shaft 32B of the boom actuator 31 through the bucket 25, arm 23, and boom 21 as the pressing reaction force FA1 exerts. The reaction torque FR1 can also be said to be the torque of the reaction force that acts on the first drive shaft 32B through the bucket 25, arm 23, and boom 21 as the second drive shaft 42B outputs torque. In calculating the reaction torque FR1, the CPU 101 first calculates the first distance L1. As shown in Figure 6, the first distance L1 is the distance from the first rotation axis 31J to the tip of the claw 27 in a specific plan view. The first distance L1 is an index that shows the positional relationship between the first rotation axis 31J and the tip of the claw 27 of the bucket 25. Note that the calculation of the first distance L1 by the CPU 101 is equivalent to the CPU 101 estimating the above positional relationship. Memory 102 pre-stores first distance information as information for CPU 101 to calculate the first distance L1. The first distance information represents the relationship between the second and third angular positions and the first distance L1. In detail, the first distance information represents the first distance L1 for various combinations of the second and third angular positions. The first distance information is composed of, for example, a table, a graph, or a mathematical formula. When calculating the first distance L1, CPU 101 obtains the latest second and third angular positions. Then, CPU 101 calculates the first distance L1 by applying the obtained second and third angular positions to the first distance information. In this way, CPU 101 calculates the first distance L1 based on the second and third angular positions. Once CPU 101 has calculated the first distance L1, it calculates the product of this first distance L1 and the orthogonal component A calculated in step S120 as a provisional value. This provisional value is the reaction torque acting on the output member 33C of the first reduction gear 33. The CPU 101 converts this provisional value into the reaction torque FR1 acting on the first drive shaft 32B, taking into account the reduction ratio of the first reduction gear 33. In this way, the CPU 101 calculates the reaction torque FR1 based on the first distance L1.Furthermore, the orthogonal component A used by the CPU 101 when calculating the reaction force torque FR1 reflects the pressing reaction force FA and, consequently, the second current value 92S detected by the second current sensor 92. In other words, the CPU 101 calculates the reaction force torque FR1 based on the second current value 92S. Once the CPU 101 has calculated the reaction force torque FR1, it proceeds to step S140. Note that the processing in step S130 also serves as the third and fourth processing.

[0077] In step S140, the CPU 101 determines whether the reaction force torque FR1 is less than or equal to the determination threshold Q1. The determination threshold Q1 is the maximum braking torque of the first brake device 81. The memory 102 has the determination threshold Q1 stored in advance. If the reaction force torque FR1 calculated in step S130 is less than or equal to the determination threshold Q1 (step S140: YES), the CPU 101 proceeds to step S150.

[0078] As a prerequisite for explaining step S150, in conjunction with step S170 described later, it is possible that power is being supplied to the first electric motor 32 when the process proceeds to step S150. On the other hand, in conjunction with steps S100 and S170, the first brake device 81 is in a braking state when the process proceeds to step S150. In step S150, the CPU 101 maintains the braking state of the first brake device 81, which was started in the preparation process, while stopping the power supply to the first electric motor 32. That is, in step S150, the CPU 101 performs a second process that controls the first brake device 81 to a braking state and stops the power supply to the first electric motor 32. The CPU 101 proceeds to step S180 while maintaining the execution state of this second process. The CPU 101 maintains the execution state of the second process until it performs the next process, either step S150 or step S170 described later.

[0079] On the other hand, in step S140, if the reaction force torque FR1 is greater than the judgment threshold Q1 (step S140: NO), the CPU 101 proceeds to step S160. In step S160, the CPU 101 calculates the required torque FN1. The required torque FN1 is the amount of torque required to compensate for the insufficient braking force of the first brake device 81 in order to maintain the angular position of the boom 21. The CPU 101 calculates the required torque FN1 by subtracting the judgment threshold Q1 from the reaction force torque FR1 calculated in step S130. Once the CPU 101 has calculated the required torque FN1, the process proceeds to step S170.

[0080] In step S170, the CPU 101 maintains the braking state of the first brake device 81, which was started in the preparation process, and controls the first electric motor 32 so that the first drive shaft 32B outputs a torque equal to the required torque FN1 in the opposite direction to the reaction torque FR1. That is, in step S170, the CPU 101 performs a first process that controls the first brake device 81 to a braking state and controls the first electric motor 32 so that the first drive shaft 32B outputs a torque in the opposite direction to the reaction torque FR1. The CPU 101 can determine the rotational direction of the reaction torque FR1 acting on the first drive shaft 32B based on the rotational direction of the arm 23 due to the drive control for the arm 23. The memory 102 stores information regarding the direction of the reaction torque FR1 acting on the first drive shaft 32B during the execution of the drive control for the arm 23.

[0081] Here, the required torque FN1 is the absolute value of the difference between the judgment threshold Q1 and the reaction torque FR1. The judgment threshold Q1 is the maximum braking torque. Therefore, when the first drive shaft 32B outputs the required torque FN1, the following first relationship holds in relation to the reaction torque FR1. The first relationship is that the sum of the braking torque applied by the first brake device 81 to the first drive shaft 32B and the torque output by the first drive shaft 32B is equal to the magnitude of the reaction torque FR1. In the first process, the CPU 101 controls the first brake device 81 and the boom actuator 31 to satisfy this first relationship. As a result, in the first process, the CPU 101 sets the rotational speed of the first drive shaft 32B to a set value or less. The set value is predetermined as a value at which the first drive shaft 32B can be considered to be not rotating. The CPU 101 proceeds to step S180 while maintaining this execution state of the first process. Similar to the case of step S150, the CPU 101 maintains the execution state of the first process until it performs the next process of step S150 or step S170 described later.

[0082] In step S180, the CPU 101 determines whether the termination condition is met. The termination condition is, for example, when the CPU 101 receives a termination signal for the holding control of the boom 21 from the operating device 90. If the termination condition is not met (step S180: NO), the CPU 101 returns to the process in step S110. On the other hand, if the termination condition is met (step S180: YES), the CPU 101 releases the execution state of the first or second process. Then, the CPU 101 terminates the holding control for the boom 21. After this, the CPU 101 controls the power supply to the first electric motor 32 and the first brake device 81 in response to the operator's operation of the operating device 90, etc. Regarding the holding control described above, the CPU 101 performs the processing of each step quickly, for example, on a time scale of less than 1 second.

[0083] <Operation of the First Embodiment> Now, the bucket 25 excavates the ground G by rotating the arm 23 while maintaining the angular position of the boom 21 at a substantially constant level. At this time, a pressing reaction force FA1 acts on the bucket 25 as a result of excavating the ground G. This pressing reaction force FA1 acts on the first drive shaft 32B as a reaction torque FR1 that attempts to rotate the first drive shaft 32B through the bucket 25, arm 23, and boom 21. In the holding control for the boom 21, if this reaction torque FR1 is less than or equal to the maximum braking torque of the first brake device 81 (step S140: YES), the CPU 101 maintains the angular position of the boom 21 at a substantially constant level using only the braking torque of the first brake device 81 (step S150). On the other hand, if the reaction torque FR1 is greater than the maximum braking torque (step S140: NO), the CPU 101 uses the first electric motor 32 in addition to the first brake device 81 to maintain the angle position of the boom 21 at approximately a constant level (step S170). When the arm 23 is rotated to excavate the ground G, the pressing reaction force FA1 changes sequentially in accordance with changes in the angle position of the arm 23. In the holding control for the boom 21, the CPU 101 adjusts the amount of assistance for maintaining the angle position of the boom 21 using the first electric motor 32 in accordance with the change in the pressing reaction force FA1. That is, in the holding control, the CPU 101 repeats the process of step S150 or step S170 as long as the judgment in step S180 remains NO. In this way, the CPU 101 sequentially changes the torque output by the first electric motor 32 and, consequently, the amount of assistance mentioned above. As a result, the CPU 101 maintains the angle position of the boom 21 at a nearly constant level regardless of changes in the angle position of the arm 23 and, consequently, changes in the pressing reaction force FA1.

[0084] <Effects of the First Embodiment> (1-1) In this embodiment, the CPU 101 energizes the first electric motor 32 only when the reaction torque FR1 is greater than the maximum braking torque of the first brake device 81, in order to maintain the angular position of the boom 21 at a substantially constant level. That is, the CPU 101 stops supplying power to the first electric motor 32 until the reaction torque FR1 exceeds the maximum braking torque. Therefore, in this embodiment, the driving time of the first electric motor 32 can be shortened, and thus the power consumption of the first electric motor 32 can be reduced.

[0085] (1-2) In this embodiment, when the reaction torque FR1 exceeds the maximum braking torque, the CPU 101 maintains the angular position of the boom 21 at a substantially constant level by using the first brake device 81 and the first electric motor 32 in combination. At that time, the CPU 101 outputs only the amount that is insufficient from the maximum braking torque of the first brake device 81 to maintain the angular position of the boom 21 to the first electric motor 32. In this way, by outputting only the amount that is insufficient from the maximum braking torque to the first electric motor 32, the torque output by the first electric motor 32 and, consequently, the power consumption of the first electric motor 32 can be minimized. When the first brake device 81 and the first electric motor 32 are used in combination to maintain the angular position of the boom 21, the first electric motor 32 can assist the insufficient braking force of the first brake device 81. With this assistance, even if a first brake device 81 with a relatively small maximum braking torque is used, it becomes possible to maintain the angular position of the boom 21. Therefore, in the configuration of this embodiment, it is permissible to use a first electric motor 32 that has a relatively small maximum braking torque and, consequently, a small size. This contributes to miniaturizing the first electric motor 32.

[0086] (1-3) The CPU 101 of this embodiment calculates a first distance L1, which is the distance from the first rotation axis 31J to the tip of the claw 27, based on the relative position of the arm 23 with respect to the boom 21 and the relative position of the bucket 25 with respect to the arm 23. The CPU 101 then calculates the reaction force torque FR1 based on the calculated first distance L1. As a result, the CPU 101 can accurately calculate the reaction force torque FR1 in real time according to the posture of the boom 21, arm 23, and bucket 25.

[0087] <Second Embodiment> The following describes a second embodiment of the drive system for the work machine, the control method for the work machine, and the control program for the work machine. In this embodiment, the target of the holding control differs from that of the first embodiment. Aside from this, the content of the second embodiment is the same as that of the first embodiment. In the following, the differences between the second embodiment and the first embodiment will be mainly described, and parts that overlap with the content of the first embodiment will be omitted or simplified as appropriate.

[0088] The CPU 101 in this embodiment is capable of performing holding control for the arm 23. Holding control for the arm 23 is a control for maintaining the angular position of the arm 23 at a substantially constant level. When the CPU 101 receives a holding signal for the arm 23 from the operating device 90, it starts holding control for the arm 23. Holding control for the arm in this embodiment is performed in parallel with drive control for the boom 21. That is, the CPU 101 performs holding control for the arm 23 while drive control for the boom 21 is being performed. In the drive control for the boom 21, the CPU 101 controls the first electric motor 32 so that the first drive shaft 32B of the first electric motor 32 outputs torque in order to rotate the boom 21.

[0089] The holding control for arm 23 is the same as the holding control for boom 21, but with each process replaced for holding the position of arm 23. Therefore, the basic concept is the same as the holding control for boom 21. In the following, the content of each process of the holding control for arm 23 will be explained, mainly focusing on the differences from the holding control for boom 21.

[0090] As shown in Figure 5, in the holding control for the arm 23, the CPU 101 first performs the process in step S100. In step S100, the CPU 101 performs preparatory processing to control the second brake device 82 to a braking state and to stop the power supply to the second electric motor 42. The CPU 101 proceeds to step S110 while maintaining the execution state of this preparatory processing. When the CPU 101 puts the second brake device 82 to a braking state, it cuts off the power supply to the excitation coil 82B by turning off the relay. The CPU 101 also stops the power supply to the second electric motor 42 through the control of the second inverter 45.

[0091] In step S110, the CPU 101 calculates the pressing reaction force FA2 shown in Figure 7. The pressing reaction force FA2 is the reaction force that acts on the bucket 25 from the object when the bucket 25 is pressed against the object by rotating the boom 21. The pressing reaction force FA2 acts in a direction perpendicular to the virtual line A1 in a specific plan view. The CPU 101 calculates the pressing reaction force FA2 by dividing the output torque of the boom actuator 31 by the first distance L1. The CPU 101 calculates the first distance L1 by applying the latest second angular position and the latest third angular position to the first distance information stored in the memory 102. The CPU 101 also converts the output torque of the boom actuator 31 based on the first current value 91S detected by the first current sensor 91. The memory 102 has pre-stored the information necessary for this conversion.

[0092] As shown in Figure 5, after step S110, the CPU 101 calculates the orthogonal component B in step S120. As shown in Figure 7, the orthogonal component B is the component of the pressing reaction force FA2 that is perpendicular to the virtual line A2 in a specific plan view. The CPU 101 converts the pressing reaction force FA2 into the orthogonal component B based on the latest first angular position, the latest second angular position, and the latest third angular position.

[0093] Next, in step S130, the CPU 101 calculates the reaction torque FR2. The reaction torque FR2 is the torque of the reaction force that the pressing reaction force FA2 acts on the second drive shaft 42B of the arm actuator 41 through the bucket 25 and arm 23. The reaction torque FR2 can also be said to be the torque of the reaction force that acts on the second drive shaft 42B through the bucket 25 and arm 23 as a result of the first drive shaft 32B outputting torque. The CPU 101 converts the product of the orthogonal component B calculated in step S120 and the second distance L2 into the reaction torque FR2, taking into account the reduction ratio of the second reduction gear 43. In this way, the CPU 101 calculates the reaction torque FR2 based on the orthogonal component B and its source, the first current value 91S, and the second distance L2. This process is the fourth process. The CPU 101 calculates the second distance L2 by applying the latest third angular position to the second distance information stored in the memory 102. In other words, the CPU 101 calculates the second distance L2 based on the third angular position. This process is the third process. The calculation of the second distance L2 by the CPU 101 is equivalent to the CPU 101 estimating the positional relationship between the second rotation axis 41J and the tip of the claw 27 of the bucket 25.

[0094] After step S130, in step S140, the CPU 101 determines whether the reaction torque FR2 calculated in step S130 is less than or equal to the determination threshold Q2. The determination threshold Q2 is the maximum braking torque of the second brake device 82. If the reaction torque FR2 is less than or equal to the determination threshold Q2 (step S140: YES), the CPU 101 proceeds to step S150. Then, in step S150, the CPU 101 stops the power supply to the second electric motor 42. In conjunction with the preparation process, in step S150, the CPU 101 performs a second process that controls the second brake device 82 to a braking state and stops the power supply to the second electric motor 42. The CPU 101 proceeds to step S180 while maintaining the execution state of the second process.

[0095] On the other hand, in step S140, if the reaction torque FR2 is greater than the judgment threshold Q2 (step S140: NO), the CPU 101 proceeds to step S160. Then, in step S160, the CPU 101 calculates the required torque FN2 by subtracting the judgment threshold Q2 from the reaction torque FR2. Then, in step S170, the CPU 101 controls the second electric motor 42 so that the second drive shaft 42B outputs a torque equal to the required torque FN2 in the opposite direction to the reaction torque FR2. In other words, the CPU 101 performs a first process in which it controls the second brake device 82 to a braking state and controls the second electric motor 42 so that the second drive shaft 42B outputs a torque in the opposite direction to the reaction torque FR2. The CPU 101 proceeds to step S180 while maintaining the execution state of the first process. Then, in step S180, the CPU 101 determines whether the termination condition is met. One example of a termination condition is when the CPU 101 receives a termination signal for hold control for arm 23 from the operating device 90.

[0096] In the first process of step S170, the CPU 101 controls the second brake device 82 and the arm actuator 41 so that the sum of the braking torque applied by the second brake device 82 to the second drive shaft 42B and the torque output by the second drive shaft 42B is equal to the magnitude of the reaction torque FR2. As a result, in the first process, the CPU 101 reduces the rotational speed of the second drive shaft 42B to below a set value.

[0097] <Operation and Effects of the Second Embodiment> The configuration of this embodiment provides the same operation as the first embodiment, and furthermore, the same effects as (1-1) to (1-3), with respect to the arm 23, the second electric motor 42, and the second brake device 82.

[0098] <Example of changes> Each of the above embodiments can be implemented with the following modifications. Each of the above embodiments and the following modifications can be combined with each other to the extent that they do not contradict each other technically.

[0099] With respect to the first embodiment, instead of, or in addition to, performing holding control for the boom 21, holding control for the bucket 25 may be performed. That is, holding control for the bucket 25 may be performed while drive control for the arm 23 is being performed. Similarly, with respect to the second embodiment, instead of, or in addition to, performing holding control for the arm 23, holding control for the bucket 25 may be performed. That is, holding control for the bucket 25 may be performed while drive control for the boom 21 is being performed.

[0100] The following explanation uses an example of the process when holding control for the bucket 25 is performed while drive control for the arm 23 is being executed. In holding control for the bucket 25, the CPU 101 performs the following processing at each step shown in Figure 5. In step S100, the CPU 101 controls the third brake device 83 to a braking state and stops the power supply to the third electric motor 52. In step S110, the CPU 101 calculates the pressing reaction force FA1 in the same manner as the holding control for the boom 21. In step S120, the CPU 101 calculates the orthogonal component C shown in Figure 8. The orthogonal component C is the component of the pressing reaction force FA1 in a direction orthogonal to the virtual straight line A3 that passes through the third rotation axis 51J and the tip of the claw 27 in a specific plan view. In step S130, the CPU 101 converts the product of the orthogonal component C and the third distance L3 into a reaction torque FR3 acting on the third drive shaft 52B, taking into account the reduction ratio of the third reduction gear 53. The third distance L3 is the distance from the third rotation axis 51J to the tip of the claw 27 of the bucket 25 in a specific planar view. In step S140, the CPU 101 compares the reaction torque FR3 with the judgment threshold Q3. The judgment threshold Q3 is the maximum braking torque of the third brake device 83. If the reaction torque FR3 is less than or equal to the judgment threshold Q3, in step S150, the CPU 101 stops the power supply to the third electric motor 52 while maintaining the third brake device 83 in a braking state. On the other hand, if the reaction torque FR3 is greater than the judgment threshold Q3, in step S170, the CPU 101 causes the third electric motor 52 to output the required torque, which is the difference between the reaction torque FR3 and the judgment threshold Q3, while maintaining the third brake device 83 in a braking state. At this time, the CPU 101 controls the third electric motor 52 so that the third drive shaft 52B outputs a torque in the opposite direction to the reaction torque FR3. Then, in step S180, when the CPU 101 receives a signal to terminate the holding control, it terminates the holding control for the bucket 25. In this example of holding control for the bucket 25, each component corresponds to the following elements: The arm 23 corresponds to the first movable member. The arm actuator 41 corresponds to the first electric actuator. The second drive shaft 42B of the arm actuator 41 corresponds to the first output shaft. The bucket 25 corresponds to the second movable member.The bucket actuator 51 corresponds to the second electric actuator. The third drive shaft 52B of the bucket actuator 51 corresponds to the second output shaft.

[0101] As described in relation to the holding control for bucket 25, the member treated as the first movable member and the member treated as the second movable member of the work attachment 20 can be changed as appropriate. Depending on which member is treated as the first movable member, the actuator constituting the first electric actuator may change. If the first movable member is changed from the example of the above embodiment, the first electric actuator may be an actuator that rotates the first movable member. Similarly, depending on which member is treated as the second movable member, the actuator constituting the second electric actuator may change. The second electric actuator may be an actuator that rotates the second movable member. Furthermore, if another movable member different from the first movable member is connected to the second movable member, this movable member constitutes the third movable member. The actuator that rotates this third movable member constitutes the third electric actuator.

[0102] While drive control for the bucket 25 is being performed, at least one of holding control for the arm 23 and holding control for the boom 21 may be performed. In this case, the pressing reaction force is the value obtained by dividing the output torque of the bucket actuator 51 by the third distance L3. The output torque of the bucket actuator 51 can be calculated based on the third current value 93S detected by the third current sensor 93. Once the pressing reaction force can be calculated, the reaction torque acting on the first drive shaft 32B or the second drive shaft 42B can be calculated based on the pressing reaction force. For example, in the case of the first drive shaft 32B, the product of the component of the pressing reaction force perpendicular to the virtual straight line A1 and the first distance L1 can be converted into the reaction torque acting on the first drive shaft 32B, taking into account the reduction ratio of the first reduction gear 33.

[0103] The configuration of each brake device is not limited to the examples of the embodiments described above. The brake device only needs to be able to apply and release braking force to the output shaft of the object to be braked. For example, the first brake device 81 may be one that can adjust the braking force applied to the first drive shaft 32B. In this case, the braking force that the first brake device 81 applies to the first drive shaft 32B in the preparation process may be set to a predetermined value less than or equal to the maximum braking torque, which is the braking torque that the first brake device 81 can apply to the first drive shaft 32B. The determination threshold Q1 may also be set to this predetermined value. In a similar manner, the determination thresholds Q2 and Q3 may be changed in accordance with the configuration of the second brake device 82 and the third brake device 83 and the braking force set in the preparation process.

[0104] As described in the above modification example, the judgment threshold is not limited to the maximum braking torque of each brake device. The judgment threshold only needs to be a value less than or equal to the maximum braking torque of each brake device. As shown in the above example of modifications, when using the first brake device 81 which can adjust the braking force, the braking force that the first brake device 81 applies to the first drive shaft 32B may be of a different magnitude in each of the preparation process, the first process, and the second process. The same applies to the second brake device 82 and the third brake device 83.

[0105] The first brake device 81 may be configured to apply braking torque to the output member 33C of the first reduction gear 33. In this case, the first brake device 81 can indirectly apply braking torque to the first drive shaft 32B, which is the first output shaft. The output member 33C may also be treated as the first output shaft. Similar to the first brake device 81, the second brake device 82 and the third brake device 83 may also be configured to apply braking torque to the output members of the reduction gears. Furthermore, the output member 43C of the second reduction gear 43 may be treated as the second output shaft, or the output member 53C of the third reduction gear 53 may be treated as the third output shaft.

[0106] The configuration of the electrical system that supplies power to the first brake device 81 is not limited to the examples of each embodiment described above. For example, the relay 81E may be omitted. In this case, whether or not the first electric motor 32 is energized is directly reflected in whether or not the excitation coil 81B is energized. When this configuration is adopted, the CPU 101 can cut off the power supply to both the first electric motor 32 and the first brake device 81 by stopping the power supply to the first electric motor 32 during the preparation process and the second process for holding control for the boom 21. Alternatively, the relay 81E may not be omitted, and the power line 81F may be directly connected to the battery 19 without going through the power line 89 that connects the first inverter 35 and the first electric motor 32. In a similar view, the electrical systems of the second brake device 82 and the third brake device 83 are not limited to the examples of the embodiments described above.

[0107] In relation to the above-mentioned example of electrical system modification, in the first process of holding control for the boom 21, power may be supplied to the first electric motor 32, thereby supplying power to the first brake device 81 along with the first electric motor 32. In this case, the position of the boom 21 may be held approximately constant by the torque of the first electric motor 32 alone, with the braking of the first drive shaft 32B by the first brake device 81 released. In this case, the CPU 101 may omit step S160, and in step S170, while supplying power to the first brake device 81, control the first electric motor 32 so that the first drive shaft 32B outputs a torque equal to the reaction torque FR1 in the opposite direction to the reaction torque FR1. In this case, the CPU 101 may simply set the rotational speed of the first drive shaft 32B to below a set value. Here, holding control for the boom 21 has been used as an example, but the same applies to holding control of other movable members. In other words, when maintaining the angular position of the movable member at approximately a constant level in the first process of each holding control, it is not essential to use both a brake device and an electric motor in combination.

[0108] Regarding the first process, the method for determining the set value is not limited to the examples of the embodiments described above. The set value may be determined to be an appropriate value from the viewpoint of holding the target movable member in approximately the same position. The method for calculating the reaction torque is not limited to the examples of the embodiments described above. For example, a sensor that can be used to calculate the reaction torque, such as a strain sensor, may be installed on the excavator 10. The reaction torque may then be calculated based on the detected value of such a sensor. Any calculation method is acceptable as long as it can appropriately calculate the reaction torque.

[0109] • While holding control is being performed on one of the three movable members of the work attachment 20, drive control may be performed on two or more movable members. In this case as well, it is sufficient to calculate the reaction torque acting on the output shaft corresponding to the movable member that holds its position. At the same time, either the first or second process may be performed depending on the magnitude of this reaction torque.

[0110] The specific location on the bucket 25 is not limited to the tip of the claw 27 of the bucket 25. It is preferable to set the specific location on the bucket 25 to a point where force from the object acts when the bucket 25 strikes the object, such as soil, during the operation of the excavator 10.

[0111] The overall configuration of the work attachment 20 is not limited to the examples of the above embodiments. The work attachment 20 may be configured by adopting appropriate movable members depending on the work. For example, something other than the bucket 25 may be adopted as the third movable member. Depending on the third movable member adopted, the specific location of the third movable member may change. The third movable member may be eliminated. The work attachment 20 only needs to have two or more movable members.

[0112] The shape of the first drive shaft 32B of the first electric motor 32 and the shape of the output member 33C of the first reduction gear 33 are not limited to a cylindrical shape. The first drive shaft 32B and the output member 33C only need to be shaped to transmit torque to the mating member. Similarly, the shape of the second drive shaft 42B of the second electric motor 42 and the output member 43C of the second reduction gear 43 are not limited to a cylindrical shape. The same applies to the shape of the third drive shaft 52B of the third electric motor 52 and the output member 53C of the third reduction gear 53.

[0113] The configuration of the boom actuator 31 is not limited to the examples of the embodiments described above. The boom actuator 31 only needs to include an electric motor and be able to drive the rotation of the boom 21. For example, the first reduction gear 33 may be omitted from the boom actuator 31. Furthermore, the boom actuator 31 is not limited to outputting torque coaxial with the drive shaft of the electric motor to the outside.

[0114] The mounting configuration of the boom actuator 31 to the boom 21 and swing bracket 17 is not limited to the examples of the above embodiment. Any mounting configuration is acceptable as long as the boom actuator 31 can rotate the boom 21. For example, the orientation of the boom actuator 31 between the second swing wall 17B of the swing bracket 17 and the boom 21 may be reversed. That is, the boom actuator 31 may be mounted to the boom 21 and swing bracket 17 such that the first reduction gear 33 is positioned closer to the second swing wall 17B and the first electric motor 32 is positioned closer to the boom 21.

[0115] Similar to the above examples of modifications to the boom actuator 31, the configuration and mounting of the arm actuator 41 are not limited to the examples of each embodiment described above. The arm actuator 41 only needs to include an electric motor and be able to drive the rotation of the arm 23.

[0116] Similar to the above examples of modifications to the boom actuator 31, the configuration and mounting of the bucket actuator 51 are not limited to the examples of each embodiment described above. The bucket actuator 51 only needs to include an electric motor and be able to drive the rotation of the bucket 25.

[0117] The configuration of the upper body 14 is not limited to the example of the upper embodiment. For example, the cabin may be eliminated from the upper body 14. The shape of the main housing portion 14A and the front housing portion 14B may be other than a rectangular parallelepiped. The upper body 14 only needs to be configured to realize the necessary functions, such as housing various equipment.

[0118] As shown in the above example of modification, the operating equipment 90 may be removed from the upper body 14 in conjunction with the removal of the cabin from the upper body 14. At the same time, various signals that instruct the operation of the excavator 10 to the control device 100 may be transmitted wirelessly from equipment outside the vehicle body 15.

[0119] The components included in the drive system of the excavator 10 are not limited to the examples of the above embodiment. For example, the work attachment 20 may be treated as a component not included in the drive system. For example, various sensors and various operating devices may be treated as components not included in the drive system.

[0120] The overall configuration of the vehicle body 15, and by extension the excavator 10, is not limited to the examples of the above embodiments. For example, the overall shape of the vehicle body 15 may be changed from the examples of the above embodiments in conjunction with changing the shape of the upper body 14, as in the modified example above. It is sufficient that the excavator 10 as a whole is configured to perform the required work, such as excavation.

[0121] • The work machine is not limited to the excavator 10. The work machine may be any construction machine other than the excavator 10. Furthermore, the work machine is not limited to construction machines. Examples of work machines other than construction machines include machines used in forestry, quarrying, industrial waste treatment, and agriculture.

[0122] The processing circuit of the control device 100 may have any of the following configurations (a) to (c). (a) The processing circuit comprises one or more processors that perform various processes according to a computer program. The processor includes a CPU 101 and memory 102 such as RAM and ROM. Memory 102 stores program code or instructions configured to cause the CPU 101 to perform the processes. Memory 102, i.e., computer-readable media, includes any available media that can be accessed by a general-purpose or dedicated computer.

[0123] (b) The processing circuit comprises one or more dedicated hardware circuits that perform various processing tasks. Examples of dedicated hardware circuits include application-specific integrated circuits, i.e., ASICs or FPGAs.

[0124] (c) The processing circuit comprises a processor that executes a portion of the various processes according to a computer program, and a dedicated hardware circuit that executes the remaining parts of the various processes.

[0125] In the above embodiment, a structure composed of multiple objects may be integrated, or conversely, a structure composed of a single object may be divided into multiple objects. Whether or not the objects are integrated, the structure should be configured in a way that achieves the objective of the invention.

[0126] In the above embodiment, if multiple functions are provided in a distributed manner, some or all of those multiple functions may be consolidated and provided together. Conversely, if multiple functions are consolidated and provided together, some or all of those multiple functions may be distributed and provided together. Regardless of whether the functions are consolidated or distributed, it is sufficient that the device is configured to achieve the objective of the invention.

[0127] Next, we will describe the technical concepts that can be understood from each of the above embodiments and their modifications. (A) In claim 1 or 2, the second movable member is rotatable about a second axis parallel to a first axis which is the rotation axis of the first output shaft, and the working machine comprises a third movable member rotatably connected to the second movable member about a third axis parallel to the first axis, a current sensor for detecting a current value supplied to the second electric actuator, a second angle sensor for detecting a second angular position which is the angular position of the second movable member, and a third angle sensor for detecting a third angular position which is the angular position of the third movable member, and the control device faces in a direction parallel to the first axis and controls the working machine A drive system for a work machine that, when viewing is a specific planar view, stores distance information in advance that represents the correspondence between the second angular position and the third angular position and the first distance, which is the distance from the first axis to a specific point on the third movable member in the specific planar view; and during the execution of the drive control, performs a third process of acquiring the current value, the second angular position and the third angular position, and calculating the first distance by applying the acquired second angular position and the third angular position to the distance information; and a fourth process of calculating the reaction torque based on the calculated first distance and the current value.

[0128] (B) The work machine according to claim 4 or 5, comprising: a third movable member rotatably connected to the second movable member about a third axis parallel to a first axis which is the rotation axis of the first output shaft; a current sensor for detecting a current value supplied to the first electric actuator; and an angle sensor for detecting the angular position of the third movable member, wherein the control device pre-stores distance information representing the correspondence between the angular position and a second distance which is the distance from the second axis to a specific point on the third movable member in the specific planar view, when the work machine is viewed in a direction parallel to the first axis, and during the execution of the drive control, a third process for obtaining the current value and the angular position, and calculating the second distance by applying the obtained angular position to the distance information; and a fourth process for calculating the reaction torque based on the calculated second distance and the current value.

[0129] According to the configuration of (A) or (B) above, the real-time reaction torque corresponding to the posture can be accurately calculated. [Explanation of symbols]

[0130] 10... Excavator 21... Boom 23... Arm 25… Bucket 31…Boom actuator 32B...First drive shaft 41…Actuator for arm 42B...Second drive shaft 81...First braking device 82...Second braking device 100...Control device 102A... Control program FR1, FR2… Reaction torque

Claims

1. This invention is applied to a work machine comprising a first movable member and a second movable member rotatably connected to the first movable member. A first electric actuator having a first output shaft that outputs torque to the first movable member, A second electric actuator is attached to the first movable member and has a second output shaft that outputs torque to the second movable member, A brake device that switches between a braking state in which braking torque is applied to the first output shaft, and a release state in which the application of braking torque to the first output shaft is released, The system comprises the first electric actuator, the second electric actuator, and a control device for controlling the brake device, When the reaction torque acting on the first output shaft as a result of the second output shaft outputting torque is defined as the reaction torque, The control device is During the execution of drive control that controls the second electric actuator so that the second output shaft outputs torque, if the reaction torque is greater than a predetermined threshold value which is less than or equal to the maximum braking torque that the brake device can apply to the first output shaft, a first process is executed to reduce the rotational speed of the first output shaft to a predetermined set value or less by controlling the first electric actuator so that the first output shaft outputs torque in the opposite direction to the reaction torque. During the execution of the drive control, if the reaction torque is below the threshold, a second process is performed to control the brake device to a braking state and to stop the power supply to the first electric actuator. A drive system for industrial machinery.

2. In the first process, the control device controls the brake device and the first electric actuator so that the sum of the braking torque applied by the brake device and the torque output by the first output shaft is equal to the magnitude of the reaction torque. A drive system for a work machine according to claim 1.

3. The aforementioned work machine includes a third movable member that is rotatably connected to the second movable member, The control device is A third process for estimating the positional relationship between the first output shaft and the third movable member based on the relative position of the second movable member with respect to the first movable member and the relative position of the third movable member with respect to the second movable member, A fourth process for calculating the reaction torque based on the positional relationship estimated in the third process, Execute A drive system for a work machine according to claim 1.

4. This invention is applied to a work machine comprising a first movable member and a second movable member rotatably connected to the first movable member. A first electric actuator having a first output shaft that outputs torque to the first movable member, A second electric actuator is attached to the first movable member and has a second output shaft that outputs torque to the second movable member, A brake device that switches between a braking state in which braking torque is applied to the second output shaft, and a release state in which the application of braking torque to the second output shaft is released, The system comprises the first electric actuator, the second electric actuator, and a control device for controlling the brake device, When the reaction torque acting on the second output shaft as a result of the first output shaft outputting torque is defined as the reaction torque, The control device is During the execution of drive control that controls the first electric actuator so that the first output shaft outputs torque, if the reaction torque is greater than a predetermined threshold value which is less than or equal to the maximum braking torque that the brake device can apply to the second output shaft, a first process is executed to reduce the rotational speed of the second output shaft to a predetermined set value or less by controlling the second electric actuator so that the second output shaft outputs torque in the opposite direction to the reaction torque. During the execution of the drive control, if the reaction torque is below the threshold, a second process is performed to control the brake device to a braking state and to stop the power supply to the second electric actuator. A drive system for industrial machinery.

5. In the first process, the control device controls the brake device and the second electric actuator so that the sum of the braking torque applied by the brake device and the torque output by the second output shaft is equal to the magnitude of the reaction torque. The drive system for the work machine according to claim 4.

6. The aforementioned work machine includes a third movable member that is rotatably connected to the second movable member, The control device is A third process for estimating the positional relationship between the second output shaft and the third movable member based on the relative position of the third movable member with respect to the second movable member, A fourth process for calculating the reaction torque based on the positional relationship estimated in the third process, Execute The drive system for the work machine according to claim 4.

7. A first electric actuator having a first output shaft that outputs torque, A first movable member that rotates based on the torque from the first output shaft, A second electric actuator is attached to the first movable member and has a second output shaft that outputs torque, A second movable member that rotates based on the torque from the second output shaft, A brake device that switches between a braking state in which braking torque is applied to the first output shaft, and a release state in which the application of braking torque to the first output shaft is released, This is applied to a work machine comprising the first electric actuator, the second electric actuator, and a control device for controlling the brake device, When the reaction torque acting on the first output shaft as a result of the second output shaft outputting torque is defined as the reaction torque, The control device, During the execution of drive control that controls the second electric actuator so that the second output shaft outputs torque, if the reaction torque is greater than a predetermined threshold value which is less than or equal to the maximum braking torque that the brake device can apply to the first output shaft, a first process is executed to reduce the rotational speed of the first output shaft to a predetermined set value or less by controlling the first electric actuator so that the first output shaft outputs torque in the opposite direction to the reaction torque. During the execution of the drive control, if the reaction torque is below the threshold, a second process is performed to control the brake device to a braking state and to stop the power supply to the first electric actuator. A method for controlling industrial machinery.

8. A first electric actuator having a first output shaft that outputs torque, A first movable member that rotates based on the torque from the first output shaft, A second electric actuator is attached to the first movable member and has a second output shaft that outputs torque, A second movable member that rotates based on the torque from the second output shaft, A brake device that switches between a braking state in which braking torque is applied to the second output shaft, and a release state in which the application of braking torque to the second output shaft is released, This is applied to a work machine comprising the first electric actuator, the second electric actuator, and a control device for controlling the brake device, When the reaction torque acting on the second output shaft as a result of the first output shaft outputting torque is defined as the reaction torque, The control device, During the execution of drive control that controls the first electric actuator so that the first output shaft outputs torque, if the reaction torque is greater than a predetermined threshold value which is less than or equal to the maximum braking torque that the brake device can apply to the second output shaft, a first process is executed to reduce the rotational speed of the second output shaft to a predetermined set value or less by controlling the second electric actuator so that the second output shaft outputs torque in the opposite direction to the reaction torque. During the execution of the drive control, if the reaction torque is below the threshold, a second process is performed to control the brake device to a braking state and to stop the power supply to the second electric actuator. A method for controlling industrial machinery.

9. A first electric actuator having a first output shaft that outputs torque, A first movable member that rotates based on the torque from the first output shaft, A second electric actuator is attached to the first movable member and has a second output shaft that outputs torque, A second movable member that rotates based on the torque from the second output shaft, A brake device that switches between a braking state in which braking torque is applied to the first output shaft, and a release state in which the application of braking torque to the first output shaft is released, This is applied to a work machine comprising the first electric actuator, the second electric actuator, and a control device for controlling the brake device, When the reaction torque acting on the first output shaft as a result of the second output shaft outputting torque is defined as the reaction torque, The control device, During the execution of drive control that controls the second electric actuator so that the second output shaft outputs torque, if the reaction torque is greater than a predetermined threshold value which is less than or equal to the maximum braking torque that the brake device can apply to the first output shaft, the first electric actuator is controlled so that the first output shaft outputs torque in the opposite direction to the reaction torque, thereby executing a first process to reduce the rotational speed of the first output shaft to a predetermined set value or less. If the reaction torque is below the threshold while the drive control is being executed, a second process is performed to control the brake device to a braking state and to stop the power supply to the first electric actuator. Control program for industrial machinery.

10. A first electric actuator having a first output shaft that outputs torque, A first movable member that rotates based on the torque from the first output shaft, A second electric actuator is attached to the first movable member and has a second output shaft that outputs torque, A second movable member that rotates based on the torque from the second output shaft, A brake device that switches between a braking state in which braking torque is applied to the second output shaft, and a release state in which the application of braking torque to the second output shaft is released, This is applied to a work machine comprising the first electric actuator, the second electric actuator, and a control device for controlling the brake device, When the reaction torque acting on the second output shaft as a result of the first output shaft outputting torque is defined as the reaction torque, The control device, During the execution of drive control that controls the first electric actuator so that the first output shaft outputs torque, if the reaction torque is greater than a predetermined threshold value which is less than or equal to the maximum braking torque that the brake device can apply to the second output shaft, the second electric actuator is controlled so that the second output shaft outputs torque in the opposite direction to the reaction torque, thereby executing a first process to reduce the rotational speed of the second output shaft to a predetermined set value or less. If the reaction torque is below the threshold while the drive control is being executed, a second process is performed to control the brake device to a braking state and to stop the power supply to the second electric actuator. Control program for industrial machinery.

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