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

Abstract

This reduces the moment load acting on the electric actuator that drives the attachment. [Solution] The excavator comprises a swing bracket rotatable about a swing axis relative to the upper body, a swing actuator for rotating the swing bracket, an electric actuator attached to the swing bracket that outputs torque about an axis intersecting the swing axis, an attachment driven by the electric actuator, and a control device that performs specific control to control the swing actuator to maintain the rotational position of the swing bracket. If the load torque FU acting from the attachment to the swing bracket about the swing axis during specific control exceeds the limit torque FK (S101:YES), the control device controls the swing actuator to reduce the load torque FU (S102).

Description

Technical Field

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

Background Art

[0002] The shovel disclosed in Patent Document 1 includes a vehicle body, a boom, an arm, and a bucket. The boom is connected to the front end portion of the vehicle body. The boom is rotatable up and down relative to the vehicle body. The arm is connected to the tip end portion of the boom. The arm is rotatable up and down relative to the boom. The bucket is connected to the tip end portion 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, various work attachments such as a boom, an arm, and a bucket may be driven by electric actuators that output torque. At the same time, such electric actuators may be arranged at respective joint portions, for example, the connection portion between the vehicle body and the boom, or the connection portion between the boom and the arm. When this type of structure is adopted, moment loads may act on the electric actuators located at the respective joint portions during work using the respective attachments. It is desired to reduce the burden on the electric actuators caused by such moment loads. Note that similar problems may arise not only in shovels but also in any structure where moment loads directly act on electric actuators.

Means for Solving the Problem

[0005] A drive system for a work machine to solve the above problems comprises: a slewing actuator that rotates the upper body about a rotation axis relative to the lower body; a swing actuator that rotates the swing bracket relative to the upper body about a swing axis parallel to the rotation axis; an electric actuator attached to the swing bracket that drives an attachment by outputting torque about an axis intersecting the swing axis; and a control device that performs specific control to control the swing actuator so as to maintain a constant rotational position of the swing bracket relative to the upper body. If the load torque, which is the torque acting on the swing bracket about the swing axis, exceeds a limit torque during the specific control, the control device performs load reduction control to control at least one of the slewing actuator and the swing actuator so as to reduce the load torque.

[0006] The load torque acting on the swing bracket reflects the moment load acting on the electric actuator that drives the attachment. In the above configuration, the moment load acting on the electric actuator can be reduced through load reduction control.

[0007] The drive system of the work machine includes a swing position sensor that detects the swing rotation position, which is the rotational position of the swing bracket, and the swing actuator has an electric motor that serves as a drive source. The control device repeatedly performs the following in the specific control: a first process to acquire the swing rotation position; a second process to perform feedback control of the electric motor so as to eliminate the discrepancy between the acquired swing rotation position and the swing rotation position at the start of the specific control, and to acquire the current value supplied to the electric motor during the feedback control; and a third process to calculate the load torque based on the current value acquired in the second process. If the load torque calculated in the third process exceeds the limit torque, the second process is terminated, and in the load reduction control, the power supply to the electric motor may be controlled so that the current value supplied to the electric motor becomes closer to zero than the value supplied to the electric motor at the point when the load torque reaches the limit torque.

[0008] In a drive system for a work machine, the swing actuator includes a hydraulic cylinder to which hydraulic fluid is supplied and discharged, and a piston rod that protrudes from the inside to the outside of the hydraulic cylinder and is attached to the swing bracket, and whose protrusion amount from the hydraulic cylinder changes in accordance with the supply and discharge of hydraulic fluid to the hydraulic cylinder. The control device further includes a hydraulic circuit for adjusting the supply and discharge of hydraulic fluid to the hydraulic cylinder and a hydraulic sensor for detecting the internal hydraulic pressure of the hydraulic cylinder. In the specific control, the control device performs a first process of controlling the supply and discharge of hydraulic fluid to the hydraulic cylinder so as to maintain the position of the piston rod at the start of the specific control, and a second process of repeatedly acquiring the internal hydraulic pressure and calculating the load torque based on the acquired internal hydraulic pressure during the first process. If the calculated load torque becomes equal to or greater than the limit torque, the first process is terminated. In the load reduction control, the supply and discharge of hydraulic fluid may be controlled so as to move the piston rod from the position of the piston rod at the time the load torque reaches the limit torque.

[0009] In a drive system for a work machine, when the electric actuator is referred to as the first electric actuator and the attachment as the first attachment, the system includes a second electric actuator attached to the first attachment that drives the second attachment by outputting torque around a second axis parallel to the first axis which is the axis of the first electric actuator, and a third electric actuator attached to the second attachment that drives the third attachment by outputting torque around a third axis parallel to the first axis, wherein the control device controls the moment allowed for the first electric actuator. A first allowable moment load, which is the maximum value of the load, a second allowable moment load, which is the maximum value of the moment load allowed on the second electric actuator, and a third allowable moment load, which is the maximum value of the moment load allowed on the third electric actuator, may be stored in advance, and during the specific control, a calculation process may be executed to calculate the limit torque such that the moment load acting on the first electric actuator is less than or equal to the first allowable moment load, the moment load acting on the second electric actuator is less than or equal to the second allowable moment load, and the moment load acting on the third electric actuator is less than or equal to the third allowable moment load.

[0010] The drive system of the work machine includes a first position sensor for detecting a first rotational position, which is the rotational position of the first attachment; a second position sensor for detecting a second rotational position, which is the rotational position of the second attachment; and a third position sensor for detecting a third rotational position, which is the rotational position of the third attachment. The control device includes first relationship information representing the relationship between the second and third rotational positions and a first distance, which is the distance from a specific point on the third attachment to the first axis in a specific planar view that is a planar view oriented in the direction along the first axis. Second relationship information representing the relationship between the third rotation position and the second distance, which is the distance from the specific point on the third attachment to the second axis in the specific plan view; fourth relationship information representing the relationship between the third distance, which is the distance from the specific point on the third attachment to the third axis in the specific plan view; the first rotation position, the second rotation position, and the third rotation position and the fourth distance, which is the distance from the specific point on the third attachment to the swing axis in the direction along the axis perpendicular to both the swing axis and the first axis; Information and are stored in advance, and in the calculation process, a first calculation process that acquires the first rotation position, the second rotation position, and the third rotation position; a second calculation process that calculates the first distance by applying the acquired second and third rotation positions to the first relational information, and calculates the first allowable lateral force by dividing the first allowable moment load by the calculated first distance; and calculates the second distance by applying the acquired third rotation position to the second relational information, and calculates the second The following calculations may be performed: a third calculation process that calculates a second allowable lateral force by dividing the allowable moment load; a fourth calculation process that calculates a third allowable lateral force by dividing the third allowable moment load by the third distance; a fifth calculation process that calculates the fourth distance by applying the acquired first rotation position, second rotation position, and third rotation position to the fourth relational information; and a sixth calculation process that calculates the limit torque as a value less than or equal to the product of the minimum value among the calculated first allowable lateral force, second allowable lateral force, and third allowable lateral force and the fourth distance.

[0011] In a drive system for a work machine, the control device may, in the specific control, control the slewing actuator so that the upper body rotates relative to the lower body. In a drive system for a work machine, the control device may, in the load reduction control, control the slewing actuator such that the rotational speed of the upper body becomes lower than the point at which the load torque reaches the limit torque.

[0012] In a drive system for a work machine, when the electric actuator is referred to as the first electric actuator and the attachment as the first attachment, the system includes: a second electric actuator attached to the first attachment that drives the second attachment by outputting torque around a second axis parallel to the first axis which is the axis of the first electric actuator; a third electric actuator attached to the second attachment that drives the third attachment by outputting torque around a third axis parallel to the first axis; a first position sensor that detects the first rotational position which is the rotational position of the first attachment; and a second rotational position sensor that detects the second rotational position which is the rotational position of the second attachment. The control device includes a second position sensor for detecting the position and a third position sensor for detecting the third rotation position, which is the rotation position of the third attachment. The control device pre-stores opposing distance information that represents the relationship between the first rotation position, the second rotation position, and the third rotation position and the estimated opposing distance, which is an estimated value of the shortest distance from a specific point on the third attachment to the ground. The control device may perform a pre-processing to obtain the first rotation position, the second rotation position, and the third rotation position, and to calculate the estimated opposing distance by applying the obtained first rotation position, the second rotation position, and the third rotation position to the opposing distance information. The specific control may be executed on the condition that the estimated opposing distance is less than or equal to a predetermined approach distance.

[0013] In a drive system for a work machine, if the load torque becomes greater than or equal to a countermeasure torque defined as a value smaller than the limit torque during the specific control, the control device may perform countermeasure control by controlling one or more of the first electric actuator, the second electric actuator, and the third electric actuator to move the specific location upward from the point in time when the load torque became the countermeasure torque.

[0014] A control device for a work machine to solve the above problems is applied to a work machine comprising: an upper body rotatable about a rotation axis relative to a lower body; a slewing actuator for rotating the upper body relative to the lower body; a swing bracket connected to the upper body and rotatable about a swing axis parallel to the rotation axis relative to the upper body; a swing actuator for rotating the swing bracket relative to the upper body; an electric actuator attached to the swing bracket and outputting torque about an axis intersecting the swing axis; and an attachment attached to the electric actuator and driven by the electric actuator. The control device performs specific control to control the swing actuator so as to maintain a constant rotational position of the swing bracket relative to the upper body; and load reduction control to control at least one of the slewing actuator and the swing actuator so as to reduce the load torque if the load torque, which is the torque acting on the swing bracket about the swing axis, exceeds a limit torque during the specific control.

[0015] A control device applied to a work machine that solves the above problems includes: an upper body rotatable about a rotation axis relative to a lower body; a slewing actuator for rotating the upper body relative to the lower body; a swing bracket connected to the upper body and rotatable about a swing axis parallel to the rotation axis relative to the upper body; a swing actuator for rotating the swing bracket relative to the upper body; an electric actuator attached to the swing bracket and outputting torque about an axis intersecting the swing axis; and an attachment attached to the electric actuator and driven by the electric actuator. The control device performs specific control to control the swing actuator so as to maintain a constant rotational position of the swing bracket relative to the upper body; and load reduction control to control at least one of the slewing actuator and the swing actuator so as to reduce the load torque if the load torque, which is the torque acting on the swing bracket about the swing axis, exceeds a limit torque during the specific control.

[0016] A control program for a work machine to solve the above problems is provided for a control device applied to a work machine comprising: an upper body rotatable about a rotation axis relative to a lower body; a slewing actuator for rotating the upper body relative to the lower body; a swing bracket connected to the upper body and rotatable about a swing axis parallel to the rotation axis relative to the upper body; a swing actuator for rotating the swing bracket relative to the upper body; an electric actuator attached to the swing bracket and outputting torque about an axis intersecting the swing axis; and an attachment attached to the electric actuator and driven by the electric actuator. The control device is provided to perform specific control to control the swing actuator so as to maintain a constant rotational position of the swing bracket relative to the upper body; and load reduction control to control at least one of the slewing actuator and the swing actuator so as to reduce the load torque if the load torque, which is the torque acting on the swing bracket about the swing axis, exceeds a limit torque during the specific control.

[0017] The load torque acting on the swing bracket reflects the moment load acting on the electric actuator that drives the attachment. In the control device, control method, and control program of the above-described work machine, the moment load acting on the electric actuator can be reduced through load reduction control.

[0018] A work machine for solving the above problems comprises: an upper body rotatable about a rotation axis relative to a lower body; a slewing actuator for rotating the upper body relative to the lower body; a swing bracket connected to the upper body and rotatable about a swing axis parallel to the rotation axis relative to the upper body; a swing actuator for rotating the swing bracket relative to the upper body; an electric actuator attached to the swing bracket and outputting torque about an axis intersecting the swing axis; an attachment attached to the electric actuator and driven by the electric actuator; and a control device that performs specific control to control the swing actuator so as to maintain a constant rotational position of the swing bracket relative to the upper body. The control device performs load reduction control to control at least one of the slewing actuator and the swing actuator so as to reduce the load torque if the load torque, which is the torque acting on the swing bracket about the swing axis, exceeds a limit torque during the specific control.

[0019] The load torque acting on the swing bracket reflects the moment load acting on the electric actuator that drives the attachment. In the above-described work machine, the moment load acting on the electric actuator can be reduced through load reduction control. [Effects of the Invention]

[0020] The above technical concept can reduce the moment load acting on the electric actuator that drives the attachment. [Brief explanation of the drawing]

[0021] [Figure 1] Figure 1 is a schematic side view of an excavator. [Figure 2] Figure 2 is a schematic plan view of an excavator. [Figure 3] Figure 3 shows the electrical configuration and power transmission path of the excavator. [Figure 4] Figure 4 is a diagram showing the processing content of the specific control. [Figure 5] Figure 5 is a flowchart showing the processing procedure of the swing process. [Figure 6] Figure 6 is a flowchart showing the processing procedure of the calculation process. [Figure 7] Figure 7 is a flowchart showing the processing procedure of the load reduction routine. [Figure 8] Figure 8 is a diagram schematically showing the bucket and the third actuator. [Figure 9] Figure 9 is a diagram showing a modified example of the swing actuator. [Mode for Carrying Out the Invention]

[0022] Hereinafter, an embodiment of the drive system for a work machine, the control device for a work machine, the control method for a work machine, the control program for a work machine, and the work machine will be described taking a construction machine as an example. For the sake of simplicity and clarity, the components shown in the drawings are not necessarily drawn to a constant scale.

[0023] <Overall Configuration> As shown in Figure 1, an excavator 10 which is a construction machine includes a lower traveling body 13 and an upper revolving body 14. The upper revolving body 14 is located on the side opposite to the ground G with respect to the lower traveling body 13. In the present embodiment, the direction in which the upper revolving body 14 is positioned when viewed from the lower traveling body 13 is the upward direction, and the opposite direction is the downward direction. Further, a specific direction among the directions orthogonal to the upward direction is the forward direction, and the opposite direction is the rearward direction. Furthermore, one of the directions orthogonal to both the upward direction and the forward direction is the left direction, and the other is the right direction. The forward direction and the rearward direction may be collectively referred to as the X direction. The left direction and the right direction may be collectively referred to as the Y direction. The upward direction and the downward direction may be collectively referred to as the Z direction.

[0024] 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.

[0025] As shown in Figure 1, 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. The pivot axis 10J is the axis of rotation when the upper body 14 rotates relative to the lower body 13.

[0026] 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. Each pair of running gears 12 is 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.

[0027] 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 about the swing axis 61J relative to the front housing portion 14B. The swing axis 61J is approximately parallel to the pivot axis 10J. Details of the swing axis 61J will be described later. The second swing wall 17B protrudes upward from the upper surface of the first swing wall 17A. The second swing wall 17B is rectangular plate-shaped. The excavator 10 is equipped with a drive system. The drive system includes a swing bracket 17 and an upper body 14.

[0028] <Attachment> As shown in Figure 1, the excavator 10 is equipped with a work unit 20. The work unit 20 comprises a boom 21, an arm 23, and a bucket 25. The boom 21 is the first attachment. The arm 23 is the second attachment. The bucket 25 is the third attachment. The work unit 20 is included as a component of the drive system.

[0029] As shown in Figure 1, the boom 21 is located on the front side relative to the main housing portion 14A of the upper body 14. The boom 21 is a long, plate-like or columnar shape. As shown in Figure 2, the first longitudinal end 21A of the boom 21 is aligned with the second swing wall 17B in the direction along the first axis 31J. The first axis 31J is a virtual axis that is approximately perpendicular to the swing axis 61J. Details of the first axis 31J will be described later. The first end 21A of the boom 21 is rotatably connected to the second swing wall 17B of the swing bracket 17.

[0030] As shown in Figure 1, 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 axis 41J. The second axis 41J is a virtual axis that is approximately parallel to the first axis 31J. Details of the second axis 41J will be described later. The first end 23A of the arm 23 is rotatably connected to the second end 21B of the boom 21.

[0031] As shown in Figure 1, 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, the bucket body 26 comprises a rectangular bottom wall and four peripheral walls rising from each of the four sides of the bottom wall. The four peripheral walls are connected. The boundary between one of the four peripheral walls, a specific wall 25F, and the bottom wall constitutes a specific location 25E in this embodiment. As shown in Figure 2, the ends of the four peripheral walls opposite to the bottom wall define the opening 26A. The claws 27 protrude from the end of the specific wall 25F opposite to the bottom wall. The bucket connecting wall 28 protrudes from the wall portion of the bucket body 26 that faces the specific wall 25F. The bucket connecting wall 28 is aligned with the second end 23B of the arm 23 in the direction along the third axis 51J. The third axis 51J is a virtual axis that is substantially parallel to both the first axis 31J and the second axis 41J. Details of the third axis 51J will be described later. The bucket connecting wall 28 is rotatably connected to the second end 23B of the arm 23.

[0032] <Actuator> As shown in Figure 3, the work unit 20 includes a first actuator 31, a second actuator 41, and a third actuator 51. The excavator 10 also includes a first inverter 35, a second inverter 45, a third inverter 55, and a battery 19 as components related to the work unit 20. 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.

[0033] As shown in Figure 2, the first 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 Figure 3, the first actuator 31 comprises 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 comprises a housing 32A and an output shaft 32B rotatable relative to the housing 32A. The housing 32A is attached to the second swing wall 17B of the swing bracket 17. The output shaft 32B protrudes from the inside to the outside of the housing 32A. The output shaft 32B is cylindrical. The output shaft 32B is rotatable relative to the housing 32A about its own central axis, the first axis 31J. That is, the output shaft 32B outputs torque about the first axis 31J. The output shaft 32B is rotatable in both forward and reverse directions around the first axis 31J. As shown in Figure 2, the first axis 31J passes through both the second swing wall 17B of the swing bracket 17 and the first end 21A of the boom 21.

[0034] As shown in Figure 3, 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 output 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 axis 31J. The output member 33C is rotatable relative to the housing 33A. The output member 33C rotates about the first axis 31J in accordance with the rotation of the output shaft 32B of the first electric motor 32. The output member 33C is attached to the first end 21A of the boom 21. That is, the output member 33C inputs torque to the boom 21. The boom 21 receives this torque and rotates about the first axis 31J. That is, the boom 21 is driven by the first actuator 31. As described above, the first actuator 31 is electrically driven, with the first electric motor 32 as the drive source. The first actuator 31 constitutes the first electric actuator.

[0035] As shown in Figure 2, the second 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 second actuator 41 is basically the same as that of the first actuator 31, except for details such as dimensions, reduction ratio, and output. Therefore, the configuration of the second actuator 41 will be briefly described below.

[0036] As shown in Figure 3, the second 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 housing 42A of the second electric motor 42 is attached to the second end 21B of the boom 21. The output shaft 42B of the second electric motor 42 outputs torque around its own central axis, the second axis 41J. As shown in Figure 2, the second 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 axis 41J. The arm 23 rotates around the second axis 41J in response to the torque from the output member 43C. That is, the arm 23 is driven by the second actuator 41. As described above, the second actuator 41 is electrically driven by the second electric motor 42. The second actuator 41 constitutes the second electric actuator. 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.

[0037] As shown in Figure 2, the third 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 third actuator 51 is basically the same as that of the first actuator 31, except for details such as dimensions, reduction ratio, and output. Therefore, the configuration of the third actuator 51 will be briefly described below.

[0038] As shown in Figure 3, the third 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 housing 52A of the third electric motor 52 is attached to the second end 23B of the arm 23. The output shaft 52B of the third electric motor 52 outputs torque around its own central axis, the third axis 51J. As shown in Figure 2, the third 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 axis 51J. The bucket 25 rotates around the third axis 51J in response to the torque from the output member 53C. That is, the bucket 25 is driven by the third actuator 51. As described above, the third actuator 51 is electrically driven by the third electric motor 52. The third actuator 51 constitutes the third electric actuator. 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.

[0039] As shown in Figure 3, the excavator 10 is equipped with a swing actuator 61 and a fourth inverter 65. The swing actuator 61 is a component of the drive system. 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, 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 first 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.

[0040] As shown in Figure 3, the swing actuator 61 comprises a fourth electric motor 62, which serves as the drive source, and a fourth reduction gear 63. The fourth electric motor 62 is electrically connected to the battery 19 via a fourth inverter 65. The housing 62A of the fourth electric motor 62 is attached to the front part 14B of the housing of the upper body 14. The output shaft 62B of the fourth electric motor 62 outputs torque around its own central axis, the swing 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 swing axis 61J. The swing bracket 17 rotates around the swing axis 61J in response to the torque from the output member 63C. In other words, the swing actuator 61 rotates the swing bracket 17 relative to the upper body 14. 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.

[0041] The swing actuator 61 is equipped with a braking device 64. The braking device 64 applies braking torque to the output shaft 62B of the fourth electric motor 62 or the output member 63C of the fourth reduction gear 63. The magnitude of the braking torque is adjustable. Although not shown in the figures, other actuators are also equipped with braking devices similar to those of the swing actuator 61.

[0042] As shown in Figure 3, the excavator 10 is equipped with a slewing actuator 71 and a fifth inverter 75. The slewing actuator 71 is included as a component of the drive system. 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 first 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.

[0043] 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. 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 coaxial with the central axis 71J of the output shaft 72B of the fifth electric motor 72. In response to this torque, the upper body 14 rotates with respect to the inner ring 18A and, consequently, the lower body 13, together with the housing 72A of the fifth electric motor 72. In other words, the slewing actuator 71 rotates the upper body 14 relative to the lower body 13. Furthermore, 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.

[0044] <Sensor> As shown in Figure 3, the excavator 10 is equipped with a first position sensor 38, a second position sensor 48, a third position sensor 58, and a swing position sensor 68. The first position sensor 38, the second position sensor 48, the third position sensor 58, and the swing position sensor 68 are components of the drive system.

[0045] The first position sensor 38 detects the rotational position 38S of the first electric motor 32. Strictly speaking, the rotational position 38S of the first electric motor 32 is the rotational position of the output shaft 32B of the first electric motor 32. For the other electric motors, the output shaft is omitted from the description of the rotational position. The second position sensor 48 detects the rotational position 48S of the second electric motor 42. The third position sensor 58 detects the rotational position 58S of the third electric motor 52. The swing position sensor 68 detects the rotational position 68S of the fourth electric motor 62. The rotational position detected by each position sensor indicates a value in the range of "0 degrees to 360 degrees," with a predetermined reference position being "0 degrees." In other words, each rotational position indicates the absolute angle of each electric motor. Each position sensor repeatedly transmits a signal corresponding to the information it detected to the control device 100, which will be described later.

[0046] The excavator 10 is equipped with a tilt sensor 81 and a current sensor 82. The tilt sensor 81 and the current sensor 82 are components of the drive system. The tilt sensor 81 is mounted on the vehicle body 15. For example, the tilt sensor 81 is mounted on the main housing portion 14A of the upper body 14. The tilt sensor 81 detects the inclination 81S of the upper body 14 and thus the vehicle body 15 with respect to the horizontal plane. The current sensor 82 detects the swing current value SC, which is the current value supplied to the fourth electric motor 62. The swing current value SC takes on positive or negative values ​​depending on the rotation direction of the output shaft 62B of the fourth electric motor 62. The tilt sensor 81 and the current sensor 82 repeatedly transmit signals corresponding to the information they have detected to the control device 100, which will be described later.

[0047] The excavator 10 is equipped with various operating devices 90. These operating devices 90 are located, for example, in the cabin. The operating devices 90 include levers, switches, etc., that can be operated by the operator. Figure 3 shows these operating devices 90 together. The operating devices 90 transmit signals 90S corresponding to the operator's operation to the control device 100, which will be described later. The operating devices 90 are included as components of the drive system.

[0048] <Control device> As shown in Figure 3, the excavator 10 is equipped with a control device 100. The control device 100 is a component of the drive system. The control device 100 is a computer equipped with a processing circuit. The processing circuit includes a CPU 101, which is an execution unit, and a memory 102, which is a storage unit. 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 control 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.

[0049] The CPU 101 receives detection signals from various sensors mounted on the excavator 10. For example, the CPU 101 receives detection signals from the tilt sensor 81 and the current sensor 82. The CPU 101 also receives detection signals from the swing position sensor 68. When the CPU 101 receives a detection signal from the swing position sensor 68, it converts the received rotational position 68S of the fourth electric motor 62 into a swing rotational position SW. The swing rotational position SW is the rotational position of the swing bracket 17 from a predetermined swing reference position. An example of a swing reference position is the rotational position where both main surfaces of the plate-shaped second swing wall 17B of the swing bracket 17 are facing in the Y direction. The CPU 101 converts the rotational position 68S of the fourth electric motor 62 into a swing rotational position SW, taking into account the reduction ratio of the fourth reduction gear 63 and the rotational history of the fourth electric motor 62. Calculating the swing rotational position SW through this conversion is equivalent to obtaining the swing rotational position SW. While a detailed explanation is omitted, calculating the rotational position for the other rotational positions described later is equivalent to obtaining the respective rotational positions. The swing rotational position SW can also be described as the rotational position of the swing bracket 17 relative to the upper body 14. As can be seen from converting the rotational position 68S of the fourth electric motor 62 to the swing rotational position SW, the swing position sensor 68, which detects the rotational position 68S of the fourth electric motor 62, can also be said to effectively detect the swing rotational position SW.

[0050] The CPU 101 receives a detection signal from the first position sensor 38. Upon receiving the detection signal from the first position sensor 38, the CPU 101 converts the received rotational position 38S of the first electric motor 32 into a first rotational position 21W. The first rotational position 21W is the rotational position of the boom 21 from a predetermined first reference position. The first reference position is defined by viewing the excavator 10 facing in the direction along the first axis 31J. An example of the first reference position is a rotational position where 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 axis 31J and the swing axis 61J. In this example of the first reference position, the second end 21B of the boom 21 is positioned on the opposite side from the upper body 14, with the first axis 31J in between. The first rotational position 21W can also be described as the rotational position of the boom 21 relative to the swing bracket 17. Similar to the swing position sensor 68, the first position sensor 38, which detects the rotational position 38S of the first electric motor 32, effectively detects the first rotational position 21W.

[0051] The CPU 101 receives a detection signal from the second position sensor 48. As with other position sensors, when the CPU 101 receives a detection signal from the second position sensor 48, it converts the received rotation position 48S of the second electric motor 42 into a second rotation position 23W. The second rotation position 23W is the rotation position of the arm 23 from a predetermined second reference position. The second reference position is defined by viewing the excavator 10 facing in the direction along the second axis 41J. An example of the second reference position is a rotation 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 axis 31J and the second axis 41J. In this example of the second reference position, the second end 23B of the arm 23 is positioned on the opposite side of the second axis 41J from the first axis 31J. The second rotation position 23W can also be said to be the rotation position of the arm 23 relative to the boom 21. Similar to other position sensors, the second position sensor 48, which detects the rotational position 48S of the second electric motor 42, effectively detects the second rotational position 23W.

[0052] The CPU 101 receives a detection signal from the third position sensor 58. As with other angle sensors, when the CPU 101 receives a detection signal from the third position sensor 58, it converts the received rotational position 58S of the third electric motor 52 into a third rotational position 25W. The third rotational position 25W is the rotational position of the bucket 25 from a predetermined third reference position. The third reference position is defined by viewing the excavator 10 facing in the direction along the third axis 51J. An example of the third reference position is the rotational position where the tips of the claws 27 of the bucket 25 are positioned on a virtual straight line passing through the second axis 41J and the third axis 51J. In this example of the third reference position, the tips of the claws 27 of the bucket 25 are positioned on the opposite side of the third axis 51J from the second axis 41J. The third rotational position 25W can also be said to be the rotational position of the bucket 25 relative to the arm 23. Like other position sensors, the third position sensor 58, which detects the rotational position 58S of the third electric motor 52, effectively detects the third rotational position 25W.

[0053] The CPU 101 calculates the first rotational position 21W, the second rotational position 23W, and the third rotational position 25W, and then calculates two pieces of information indicating the positional relationship between the bucket 25 and the ground G. These two pieces of information are the estimated opposing distance 25M and the attitude index value 25N.

[0054] The estimated opposing distance of 25M is an estimate of the shortest distance from a specific point 25E on the bucket 25 to the ground G. Memory 102 pre-stores opposing distance information that represents the relationship between the first rotation position 21W, the second rotation position 23W, and the third rotation position 25W, the inclination 81S of the vehicle body 15, and the estimated opposing distance of 25M. The opposing distance information is composed of, for example, a table, a graph, or a mathematical formula. The opposing distance information is created, for example, by a simulation using a model that simulates the excavator 10. The opposing distance information is a type of control data 102B stored in memory 102. The CPU 101 calculates the latest estimated opposing distance of 25M based on this opposing distance information. That is, when the CPU 101 obtains the latest first rotation position 21W, the latest second rotation position 23W, the latest third rotation position 25W, and the latest inclination 81S of the vehicle body 15, it applies each of these obtained pieces of information to the opposing distance information. Based on this, the CPU 101 calculates an estimated opposing distance of 25M corresponding to the current posture of the work unit 20 and the inclination 81S of the vehicle body 15. The CPU 101 repeats the calculation of the estimated opposing distance of 25M. The process by which the CPU 101 repeatedly calculates the estimated opposing distance of 25M is the first preprocessing step.

[0055] The attitude index value 25N is an index value indicating the attitude of the bucket 25. The attitude index value 25N takes either a first or second value. The first value indicates that a specific wall 25F of the bucket 25 is estimated to be approximately parallel to the ground G. The second value indicates that a specific wall 25F of the bucket 25 is estimated to be not parallel to the ground G. Memory 102 pre-stores bucket attitude information that represents the relationship between the first rotation position 21W, the second rotation position 23W, and the third rotation position 25W, the inclination 81S of the vehicle body 15, and the attitude index value 25N. The bucket attitude information is composed of, for example, a table, a graph, or a mathematical formula. The bucket attitude information is created, for example, by a model simulation that simulates the excavator 10. The bucket attitude information is a type of control data 102B stored in memory 102. The CPU 101 calculates the latest attitude index value 25N based on this bucket attitude information. In other words, when the CPU 101 acquires the latest first rotation position 21W, the latest second rotation position 23W, the latest third rotation position 25W, and the latest tilt 81S of the vehicle body 15, it applies each of these acquired pieces of information to the bucket attitude information. By doing so, the CPU 101 calculates an attitude index value 25N corresponding to the current attitude of the work unit 20 and the tilt 81S of the vehicle body 15. The CPU 101 repeats the calculation of the attitude index value 25N. The process by which the CPU 101 repeatedly calculates the estimated opposing distance 25M is the second preprocessing step.

[0056] As described above, the CPU 101 takes into account the inclination 81S of the vehicle body 15 when calculating the estimated opposing distance of 25M and the attitude index value of 25N. This is for the following reason: At the work site of the excavator 10, for example, the ground G on which the vehicle body 15 is located may be inclined with respect to the horizontal plane, while the ground G in front of the vehicle body, which is the target of the work unit 20, may be horizontal, or vice versa. When considering such work sites, taking into account the inclination 81S of the vehicle body 15 when calculating the estimated opposing distance of 25M and the attitude index value of 25N allows for obtaining appropriate estimated opposing distance of 25M and attitude index value of 25N.

[0057] <Control details> The CPU 101 receives an operation signal 90S from the control device 90. In response to the operation signal 90S from the control device 90, the CPU 101 controls the slewing actuator 71, the swing actuator 61, and the actuators of the work unit 20. In controlling these actuators, the CPU 101 essentially controls the respective electric motors, and more precisely, the inverters connected to each electric motor. It can also be said that the CPU 101 controls the power supply to the electric motors through the control of the inverters.

[0058] The CPU 101 can perform specific control as part of the control of the slewing actuator 71, the swing actuator 61, and the actuators of the work unit 20. In the specific control, the CPU 101 controls the swing actuator 61 to maintain the swing rotation position SW constant. At the same time, in the specific control, the CPU 101 controls the slewing actuator 71 so that the upper body 14 rotates relative to the lower body 13. As a prerequisite for performing the specific control, the CPU 101 determines whether the execution conditions for the specific control are met. The execution conditions are that all three of the following requirements (A1), (A2), and (A3) are met. (A1) An estimated opposing distance of 25M is less than or equal to the approach distance GM. (A2) The attitude index value 25N is the first value. That is, the specific wall 25F of the bucket 25 is approximately parallel to the ground G. (A3) The device is receiving an operation signal 90S to rotate the upper body 14.

[0059] Regarding requirement (A1), the approach distance GM is predetermined as the distance at which it is considered highly likely that a specific point 25E of the bucket 25 will come into contact with the ground G. For example, the approach distance GM is 30 cm. As can be seen from this setting of the approach distance GM, when requirements (A1) and (A2) are met, the entire specific wall 25F, including the specific point 25E of the bucket 25, is in a position close to the ground G. In specific control, the CPU 101 performs a ground leveling operation by rotating the bucket 25 along the ground G in this close-proximity state.

[0060] The CPU 101 repeatedly determines whether the execution conditions are met based on the latest values ​​of the parameters related to requirements (A1), (A2), and (A3). Then, the CPU 101 performs specific control if the execution conditions are met, that is, if all three requirements are satisfied. The CPU 101 continues specific control for as long as the execution conditions are met. It can also be said that the CPU 101 automatically determines that there is a request to perform the ground leveling work if the execution conditions are met.

[0061] <Details of specific control measures> As shown in Figure 4, the specific control includes a turning process Q1, an attachment process Q2, a swing process Q3, and a calculation process Q4. Note that the calculation process Q4 may be treated as a separate process from the specific control, rather than being part of the specific control.

[0062] The rotation process Q1 is a process for rotating the upper body 14 relative to the lower body 13. In the rotation process Q1, the CPU 101 controls the rotation actuator 71 so that the upper body 14 rotates at a set rotational speed. The set rotational speed may be a single value suitable for ground leveling work, or it may be a set of multiple values. If there are multiple set rotational speeds, the CPU 101 should select a value corresponding to the operation signal 90S from the operating device 90.

[0063] Attachment processing Q2 is a process for adjusting the first rotation position 21W, the second rotation position 23W, and the third rotation position 25W. Ground leveling work is basically often performed while maintaining the first rotation position 21W, the second rotation position 23W, and the third rotation position 25W at a constant level. However, in some cases, the worker may want to fine-tune the first rotation position 21W, the second rotation position 23W, and the third rotation position 25W. In attachment processing Q2, the CPU 101 controls one or more of the first actuator 31, the second actuator 41, and the third actuator 51 in response to the operation signal 90S from the operating device 90.

[0064] <Processing for swing> The swing process Q3 is a process for controlling the swing actuator 61 to maintain a constant swing rotation position SW. The swing process Q3 is also a process for calculating the load torque FU. The load torque FU is the torque acting from the work unit 20 to the swing bracket 17, centered on the swing axis 61J. More specifically, the load torque FU is the torque acting on the swing bracket 17 in accordance with the force acting on a specific point 25E of the bucket 25 in the direction along the third axis 51J.

[0065] As shown in Figure 5, in the swing processing Q3, the CPU 101 first performs the process in step S11. In step S11, the CPU 101 acquires the latest swing rotation position SW. The process in step S11 is the first process. Note that if the CPU 101 performs the process in step S11 for the first time after the start of specific control and thus the swing processing Q3, it stores the acquired swing rotation position SW as the initial position SWA in memory 102. After executing the process in step S11, the CPU 101 proceeds to the process in step S12.

[0066] In step S12, the CPU 101 performs feedback control of the fourth electric motor 62 in the swing actuator 61. Specifically, the CPU 101 performs feedback control of the fourth electric motor 62 so that the discrepancy between the swing rotation position SW acquired in step S11 and the initial position SWA is eliminated. Specifically, the CPU 101 calculates a target current value necessary to eliminate the difference between the swing rotation position SW and the initial position SWA. The target current value takes a positive or negative value corresponding to the rotation direction of the output shaft 62B of the fourth electric motor 62. Therefore, the target current value reflects both the amount and direction of current supplied to the fourth electric motor 62. Once the CPU 101 has calculated the target current value, it supplies power to the fourth electric motor 62 so that this target current value flows. The CPU 101 performs feedback control of the fourth electric motor 62 for a predetermined control time. The control time is, for example, less than 1 second. After executing the process in step S12, the CPU 101 proceeds to step S13. The process in step S12 is the second process. Note that the CPU 101 calculating the target current value corresponds to the CPU 101 acquiring the swing current value SC during the feedback control described above. The CPU 101 may also acquire the actual swing current value SC from the current sensor 82 while executing step S12.

[0067] In step S13, the CPU 101 calculates the load torque FU. Specifically, the CPU 101 converts the swing current value SC obtained in step S12 into the torque output by the fourth electric motor 62. Furthermore, the CPU 101 converts the converted torque into the torque acting from the output member 63C of the fourth reduction gear 63 to the swing bracket 17, taking into account the reduction ratio of the fourth reduction gear 63. The CPU 101 treats the absolute value of this torque as the load torque FU. In this way, the CPU 101 calculates the load torque FU based on the swing current value SC obtained in step S12. The memory 102 has in advance stored various information necessary for the process of converting the load torque FU from the swing current value SC as control data 102B. After executing the process in step S13, the CPU 101 returns to the process in step S11. Then, the CPU 101 quickly executes the process in step S11. In this way, the CPU 101 repeats the processes of steps S11, S12, and S13 in the swing process Q3. Note that the process in step S13 is the third process.

[0068] Here, in relation to the processing in step S13, we will explain the relationship between the swing current value SC and the load torque FU. Now, assume that in the execution state of step S12, a load torque FU of a certain magnitude is acting on the swing bracket 17. As described above, in step S12, the CPU 101 performs feedback control of the fourth electric motor 62 to maintain the rotational position of the swing bracket 17 at the initial position SWA. At this time, the torque of the swing actuator 61 required to maintain the rotational position of the swing bracket 17 at a constant level is the same magnitude as the load torque FU, but in the opposite direction. Therefore, if the torque of the swing actuator 61 is known, the load torque FU can be determined. And, as is well known, the torque of the swing actuator 61 and, consequently, the torque of the fourth electric motor 62, reflects the swing current value SC. Because of this relationship, the CPU 101 can calculate the load torque FU from the swing current value SC in step S13.

[0069] <Calculation Process> Calculation process Q4 is a process for calculating the limit torque FK. The limit torque FK is a value that serves as a standard for determining the magnitude of the load torque FU.

[0070] As shown in Figure 6, in the calculation process Q4, the CPU 101 first executes the process in step S51. In step S51, the CPU 101 obtains the latest first rotation position 21W, the latest second rotation position 23W, and the latest third rotation position 25W. After this, the CPU 101 proceeds to step S52. The process in step S51 is the first calculation process.

[0071] In step S52, the CPU 101 calculates the first allowable lateral force FH1. The nature of the first allowable lateral force FH1 will be explained later, along with the second allowable lateral force FH2 and the third allowable lateral force FH3, which will be described later. In calculating the first allowable lateral force FH1, the CPU 101 first calculates the first distance L1. As shown in Figure 1, viewing the excavator 10 in a plan view facing the direction along the first axis 31J is called a specific plan view. The first distance L1 is the distance from a specific point 25E on the bucket 25 to the first axis 31J in the specific plan view. Memory 102 has pre-stored first relationship information related to the first distance L1. The first relationship information represents the relationship between the second rotation position 23W and the third rotation position 25W and the first distance L1. In detail, the first relational information represents the first distance L1 for each combination of the second rotational position 23W and the third rotational position 25W when the second rotational position 23W and the third rotational position 25W change in various ways. The first relational information is composed of, for example, a table, a graph, or a mathematical formula. The first relational information is created, for example, by a model simulation that simulates an excavator 10. The first relational information is a type of control data 102B stored in memory 102. The CPU 101 calculates the first distance L1 corresponding to the current posture of the work unit 20 by applying the second rotational position 23W and the third rotational position 25W acquired in step S51 to this first relational information. After calculating the first distance L1, the CPU 101 calculates the first allowable lateral force FH1 by dividing the first allowable moment load M1 by the calculated first distance L1. Memory 102 has the first allowable moment load M1 stored in advance as control data 102B. The first allowable moment load M1 is the maximum value of the moment load allowed on the first actuator 31. Moment loads will be explained later. As shown in Figure 6, once the CPU 101 calculates the first allowable lateral force FH1, it proceeds to step S53. The process in step S52 is the second calculation process.

[0072] In step S53, the CPU 101 calculates the second allowable lateral force FH2. In calculating the second allowable lateral force FH2, the CPU 101 first calculates the second distance L2. As shown in Figure 1, the second distance L2 is the distance from a specific point 25E on the bucket 25 to the second axis 41J in a specific plan view. Memory 102 has pre-stored second relationship information related to the second distance L2. The second relationship information represents the relationship between the third rotation position 25W and the second distance L2. In other words, the second relationship information represents the second distance L2 for each third rotation position 25W when the third rotation position 25W changes in various ways. The second relationship information is composed of, for example, a table, a graph, or a mathematical formula. The second relationship information is created, for example, by a model simulation that simulates an excavator 10. The second relationship information is a type of control data 102B stored in memory 102. The CPU 101 applies the third rotational position 25W acquired in step S51 to this second relationship information to calculate the second distance L2 corresponding to the current orientation of the work unit 20. After calculating the second distance L2, the CPU 101 calculates the second allowable lateral force FH2 by dividing the second allowable moment load M2 by the calculated second distance L2. The memory 102 has previously stored the second allowable moment load M2 as control data 102B. The second allowable moment load M2 is the maximum value of the moment load allowed on the second actuator 41. As shown in Figure 6, after calculating the second allowable lateral force FH2, the CPU 101 proceeds to step S54. The processing in step S53 is the third calculation process.

[0073] In step S54, the CPU 101 calculates the third allowable lateral force FH3. In calculating the third allowable lateral force FH3, the CPU 101 refers to two pieces of information stored in memory 102 as control data 102B. One of the two pieces of information is the third distance L3. As shown in Figure 1, the third distance L3 is the distance from a specific point 25E on the bucket 25 to the third axis 51J in a specific plan view. The other piece of information is the third allowable moment load M3. The third allowable moment load M3 is the maximum value of the moment load allowed on the third actuator 51. In step S54, the CPU 101 calculates the third allowable lateral force FH3 by dividing the third allowable moment load M3 by the third distance L3. As shown in Figure 6, once the CPU 101 has calculated the third allowable lateral force FH3, it proceeds to step S55. The process in step S54 is the fourth calculation process.

[0074] In step S55, the CPU 101 calculates the fourth distance L4. As shown in Figure 1, the fourth distance L4 is the distance from a specific point 25E on the bucket 25 to the swing axis 61J in a direction perpendicular to both the swing axis 61J and the first axis 31J. The memory 102 has pre-stored fourth relational information regarding the fourth distance L4. The fourth relational information represents the relationship between the first rotation position 21W, the second rotation position 23W, and the third rotation position 25W, and the fourth distance L4. In detail, the fourth relational information represents the fourth distance L4 for each combination of rotation positions when the first rotation position 21W, the second rotation position 23W, and the third rotation position 25W change in various ways. The fourth relational information is composed of, for example, a table, a graph, or a mathematical formula. The fourth relational information is created, for example, by a model simulation that simulates the excavator 10. The fourth relational information is a type of control data 102B stored in memory 102. The CPU 101 applies the first rotational position 21W, the second rotational position 23W, and the third rotational position 25W acquired in step S51 to this fourth relational information to calculate the fourth distance L4 corresponding to the current orientation of the work unit 20. As shown in Figure 6, once the CPU 101 has calculated the fourth distance L4, it proceeds to step S56. The processing in step S55 is the fifth calculation process.

[0075] In step S56, the CPU 101 calculates the limit torque FK. Specifically, the CPU 101 selects the minimum value among the first allowable lateral force FH1 calculated in step S52, the second allowable lateral force FH2 calculated in step S53, and the third allowable lateral force FH3 calculated in step S54 as the minimum lateral force. Then, the CPU 101 calculates the product of this minimum lateral force and the fourth distance L4 calculated in step S55 as the provisional value FKA. The CPU 101 calculates the limit torque FK as a set percentage of this provisional value FKA. An example of a set percentage is 90%. The set percentage is predetermined as a value that provides some margin in the limit torque FK in order to satisfy the requirements (B1), (B2), and (B3) described later. The CPU 101 may also calculate the provisional value FKA as the limit torque FK. The limit torque FK only needs to be less than or equal to the provisional value FKA. Once CPU 101 calculates the limit torque FK, it completes the process in step S56. Then, CPU 101 returns to the process in step S51. CPU 101 then promptly executes the process in step S51. In this way, CPU 101 repeats the processes in steps S51 to S56 in the calculation process Q4. Note that the process in step S56 is the sixth calculation process.

[0076] As explained above, in this embodiment, various information and calculation methods for calculating the limit torque FK are predetermined. This embodiment is also included in the case where the limit torque FK is predetermined. In other words, the case where the limit torque FK is predetermined is not limited to the case where the limit torque FK is predetermined as a fixed value.

[0077] <Load reduction routine> While the specific control is being executed, the CPU 101 executes the load reduction routine shown in Figure 7. When the specific control is started, the CPU 101 starts the load reduction routine in parallel. When the specific control is terminated, the load reduction routine also terminates at that time.

[0078] In the load reduction routine, CPU 101 first performs the process in step S101. In step S101, CPU 101 compares the latest load torque FU calculated in step S13 of the swing process Q3 with the latest limit torque FK calculated in step S56 of the calculation process Q4. If the load torque FU is less than the limit torque FK (step S101: NO), CPU 101 performs the process in step S101 again. CPU 101 repeats the process in step S101 as long as the load torque FU remains below the limit torque FK. When the load torque FU becomes equal to or greater than the limit torque FK (step S101: YES), CPU 101 proceeds to step S102.

[0079] In step S102, the CPU 101 performs load reduction control. In load reduction control, the CPU 101 controls the swing actuator 61 so that the load torque FU decreases below the point in time when it is determined that the load torque FU has exceeded the limit torque FK. The timing at which it is determined that the load torque FU has exceeded the limit torque FK is called the determination timing. The timing at which the load torque FU reaches the limit torque FK is called the arrival timing. The determination timing is approximately the same as the arrival timing. In other words, the determination timing can be considered as the arrival timing. The swing current value SC at the arrival timing is called the limit current value. In load reduction control, the CPU 101 controls the power supply to the fourth electric motor 62 so that the current value supplied to the fourth electric motor 62 is closer to zero than the limit current value. By doing so, the CPU 101 controls the swing actuator 61 so that the load torque FU decreases. In this embodiment, the CPU 101 sets the current value supplied to the fourth electric motor 62 to zero. The CPU 101 continues the processing in step S102 until a predetermined termination condition is met. An example of a termination condition is an operation signal 90S from the operation device 90. For example, in step S102, the CPU 101 performs a process to notify the worker that the load acting on the work unit 20 has increased, in parallel with the load reduction control. That is, the CPU 101 provides voice guidance through a speaker installed in the cabin or displays a message indicating that the load is high on a display installed in the cabin. When the worker operates the operation device 90 in response to this notification, the termination condition is met. The termination condition may also be that a predetermined period of time has elapsed since the start of the load reduction control. Note that when the CPU 101 performs load reduction control, it cancels the specific control swing processing Q3. When the termination condition is met, the CPU 101 terminates the processing in step S102. At the same time, the CPU 101 terminates the load reduction routine.

[0080] <Regarding the meaning of each parameter calculated in the calculation process> First, let's explain the moment loads acting on each actuator of the work unit 20. Here, we will use the third actuator 51 as an example among the three actuators.

[0081] As shown in Figure 8, the force acting on the bucket body 26 in a direction along the third axis 51J is called the lateral force FH. When the lateral force FH acts on the bucket body 26, this lateral force FH acts on the third actuator 51 as a moment load M via the bucket connecting wall 28. The moment load M acting on the third actuator 51 is the force that attempts to bend the output member 53C of the third reduction gear 53 and the output shaft 52B of the third electric motor 52 in the third actuator 51 with respect to the third axis 51J. For example, when the lateral force FH acts on a specific point 25E of the bucket 25, the moment load M is given as the product of this lateral force FH and the third distance L3. The third allowable moment load M3 used in step S54 of the calculation process is the maximum value of the moment load M that the third actuator 51 can withstand. As explained in Figure 1, the third distance L3 is the distance from a specific point 25E on the bucket 25 to the third axis 51J in a specific plan view. Figure 8 shows a simplified example of this third distance L3.

[0082] Here, when a moment load M acts on the third actuator 51, the third actuator 51 receives this load primarily with the bearing 53D that supports the output member 53C in the third reduction gear 53. Although only one bearing 53D is shown in Figure 8, in reality, there are two bearings 53D in the direction along the third axis 51J. The third allowable moment load M3 is determined in consideration of the limit of the magnitude of the force that these bearings 53D can withstand. It can also be said that the third allowable moment load M3 is determined by the specifications of the third actuator 51. Similar to the third allowable moment load M3, the first allowable moment load M1 is the maximum value of the moment load M that the first actuator 31 can withstand. The second allowable moment load M2 is the maximum value of the moment load M that the second actuator 41 can withstand.

[0083] Next, the meanings of the first allowable lateral force FH1, the second allowable lateral force FH2, and the third allowable lateral force FH3 will be explained. As described above, the lateral force FH is a force acting on the bucket body 26 in a direction along the third axis 51J. Each allowable lateral force is the maximum value of the lateral force FH that each actuator can withstand with respect to this lateral force FH. For example, as shown in Figure 8, the third allowable lateral force FH3 is the maximum value of the lateral force FH that the third actuator 51 can withstand in relation to the third allowable moment load M3. Here, the lateral force FH acting on the bucket body 26 also generates a moment load M on the second actuator 41 via the bucket 25, the third actuator 51, and the arm 23. The second allowable lateral force FH2 is the maximum value of the lateral force FH that the second actuator 41 can withstand in relation to the second allowable moment load M2 under such a force transmission path. Similarly, the first allowable lateral force FH1 is the maximum value of the lateral force FH that the first actuator 31 can withstand in relation to the first allowable moment load M1.

[0084] Next, we will explain the meaning of the limit torque FK. As mentioned above, in step S56 of calculation process Q4, the limit torque FK is calculated in relation to the minimum value among the first allowable lateral force FH1, the second allowable lateral force FH2, and the third allowable lateral force FH3. Here, we consider a first situation in which the minimum lateral force, which is the smallest of these three allowable lateral forces, is the third allowable lateral force FH3. In this first situation, suppose that the lateral force FH actually acting on the bucket 25 gradually increases from a state that is smaller than the minimum lateral force until it reaches the minimum lateral force. At this time, if the lateral force FH acting on the bucket 25 is quickly reduced, no force exceeding the third allowable moment load M3 will act on the third actuator 51, which is the target of the third allowable lateral force FH3. Also, in the first situation, the first allowable lateral force FH1 and the second allowable lateral force FH2 are greater than the third allowable lateral force FH3, which is the minimum lateral force. Therefore, if the lateral force FH acting on the bucket 25 is quickly reduced when the lateral force FH reaches its minimum, no force exceeding the allowable moment load will act on the other two electric actuators. In this way, the minimum lateral force is defined as a value such that the moment load acting on each of the three actuators does not exceed their respective allowable moment loads. The limit torque FK is the value obtained by converting this minimum lateral force into the torque acting on the swing actuator 61. In other words, the limit torque FK is calculated to satisfy the following requirements (B1), (B2), and (B3). (B1) The moment load acting on the first actuator 31 is less than or equal to the first allowable moment load M1. (B2) The moment load acting on the second actuator 41 is less than or equal to the second allowable moment load M2. (B3) The moment load acting on the third actuator 51 is less than or equal to the third allowable moment load M3.

[0085] <Operation of the Embodiment> During ground leveling work, the work unit 20 and, consequently, the bucket 25 are rotated together with the upper body 14 while maintaining a constant swing rotation position SW. During such ground leveling work, obstacles such as soil clumps or stones may be present in the path of the bucket body 26. When the bucket body 26 hits this obstacle, a lateral force FH acts on the bucket body 26. At the same time, the load torque FU acting on the work unit 20 and, consequently, the swing bracket 17 may increase. As a result, the moment load acting on each actuator in the work unit 20 may exceed their respective allowable moment loads.

[0086] Therefore, in this embodiment, the CPU 101 performs load reduction control when the load torque FU exceeds the limit torque FK during ground leveling work. Specifically, the CPU 101 terminates the feedback control of the fourth electric motor 62 that it had been performing up to that point, and also reduces the amount of current supplied to the fourth electric motor 62 to zero. As a result, rotation of the swing bracket 17 is permitted. By allowing the rotation of the swing bracket 17, the force acting on the entire work unit 20, including the bucket 25, is relieved. Therefore, it is possible to prevent forces exceeding the allowable moment load from acting on each actuator of the work unit 20.

[0087] <Effects of the Embodiment> (1) As described in the operation of the embodiment, when the load torque FU exceeds the limit torque FK, the CPU 101 controls the swing actuator 61 so that the load torque FU decreases. This prevents excessive load from being placed on each actuator of the work unit 20.

[0088] (2) In specific control mode, the CPU 101 performs feedback control of the fourth electric motor 62 to maintain a constant rotational position of the swing bracket 17. The current value supplied to the fourth electric motor 62 at this time reflects the load torque FU. Therefore, the CPU 101 can accurately calculate the load torque FU by calculating it based on the swing current value SC during feedback control. In addition, in load reduction control mode, the CPU 101 reduces the current value supplied to the fourth electric motor 62. This allows the swing bracket 17 to rotate, as described in the operation of the above embodiment. This reduces the moment load acting on each actuator of the work unit 20.

[0089] (3) In calculation process Q4, the CPU 101 calculates the limit torque FK so as not to exceed the allowable moment load of each of the three actuators in the work unit 20. By using this limit torque FK as the execution decision criterion for load reduction control, it is possible to prevent a moment load exceeding the allowable value from acting on each of the three actuators.

[0090] (4) The allowable lateral force of each actuator in the work unit 20 changes each time depending on the posture of the work unit 20. In this embodiment, the CPU 101 calculates the limit torque FK in calculation process Q4 based on the latest first rotation position 21W, the latest second rotation position 23W, and the latest third rotation position 25W. In other words, the CPU 101 calculates the limit torque FK according to the real-time posture of the work unit 20. By using this limit torque FK as the execution decision criterion for load reduction control, it is possible to prevent moment loads exceeding the allowable value from acting on the three actuators at all times.

[0091] (5) During the rotation of the upper body 14, the direction of movement of the work unit 20 can be approximated as being along the third axis 51J of the third actuator 51. In conjunction with this direction of movement, if the bucket 25 hits an obstacle during the rotation of the upper body 14, the impact is likely to act as a lateral force FH on the bucket 25. In other words, during the rotation of the upper body 14, there are many opportunities for a lateral force FH to act on the bucket 25. At the same time, during the rotation of the upper body 14, there are many opportunities for moment loads to act on each actuator of the work unit 20. Implementing load reduction control under these conditions is particularly effective in suppressing the load acting on each actuator of the work unit 20.

[0092] In addition to (6) and (5), during ground leveling work, the bucket 25 passes through a position close to the ground G, which means that there are many opportunities for moment loads to act on each actuator of the work unit 20. Implementing load reduction control under these conditions is very effective in suppressing the load acting on each actuator of the work unit 20.

[0093] <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.

[0094] The contents of the load reduction control are not limited to the examples of the above embodiment. In the load reduction control, when the load torque FU exceeds the limit torque FK, it is sufficient to control at least one of the swing actuator 61 and the slewing actuator 71 so that the load torque FU is lower than the load torque FU at the point when it reaches the limit torque FK. For example, in the load reduction control, instead of or in addition to the embodiments described above, the slewing actuator 71 may be controlled to lower the rotational speed of the upper body 14 to a level lower than the load torque FU at the point when it reaches the limit torque FK. For example, the upper body 14 may be stopped. The method for reducing the load torque FU in the load reduction control may be an appropriate one, in conjunction with the processing content for maintaining the swing rotation position SW constant in the specific control.

[0095] The processing content for maintaining a constant swing rotation position SW in specific control is not limited to the example of the above embodiment. For example, instead of the swing processing Q3, processing to control the brake device 64 of the swing actuator 61 may be performed. The swing rotation position SW may then be maintained at a constant level by the processing to control this brake device 64. When maintaining a constant swing rotation position SW using the brake device 64, for example, the following approach can be considered. That is, the CPU 101 obtains the latest limit torque FK calculated in the calculation processing Q4. Then, the CPU 101 controls the brake device 64 so that a braking torque of the same magnitude as this limit torque FK and in the opposite direction to the limit torque FK acts on the swing bracket 17. By repeating these processes, the swing rotation position SW can also be maintained at a constant level. When maintaining a constant swing rotation position SW in this way, the load torque FU may be calculated separately using the method of the modified example below, and the following approach can be considered for load reduction control. That is, when the load torque FU becomes greater than or equal to the limit torque FK, the CPU 101 lowers the braking torque from that point onward. The CPU 101 may set the braking torque to zero. This allows the swing bracket 17 to rotate, thus reducing the load torque FU.

[0096] The method for calculating the load torque FU is not limited to the examples of the above embodiments. Any method is acceptable as long as it can appropriately calculate the load torque FU. For example, a strain sensor may be installed on the work unit 20, and the load torque FU may be calculated based on the value detected by the strain sensor. It is preferable to install the strain sensor at a location where strain is likely to occur in response to the lateral force FH on the bucket 25. Examples of such locations include the mounting location of the first actuator 31 on the boom 21, the mounting location of the second actuator 41 on the arm 23, and the mounting location of the third actuator 51 on the bucket 25.

[0097] The configuration of the swing actuator is not limited to the examples of the embodiments described above. For example, the swing actuator may be equipped with a hydraulic motor instead of an electric motor as the drive source. Also, a linear-acting type may be used as the swing actuator instead of a rotary type.

[0098] The following example of a case where a linear-acting swing actuator is used will be explained using Figure 9. As a premise, the swing bracket 17 shown in Figure 9 includes a first swing wall 17A and a second swing wall 17B, as well as a first support shaft 17C and a second support shaft 17D. Note that the second swing wall 17B is not shown in Figure 9. The first support shaft 17C protrudes downward from the lower surface of the first swing wall 17A. The first support shaft 17C is cylindrical. The central axis of the first support shaft 17C extends in the Z direction. The central axis of the first support shaft 17C is approximately the same as the central axis of the first swing wall 17A. The central axis of the first support shaft 17C constitutes the swing axis. Although not shown, the first support shaft 17C is rotatably supported at the front part 14B of the housing of the upper body 14. The first swing wall 17A is rotatable about the swing axis together with the first support shaft 17C. The second support shaft 17D protrudes upward from the upper surface of the first swing wall 17A. The second support shaft 17D is located closer to the outer circumference of the first swing wall 17A. The second support shaft 17D is cylindrical. The central axis of the second support shaft 17D extends in the Z direction.

[0099] As shown in Figure 9, the swing actuator 130 comprises a hydraulic cylinder 131 and a piston rod 132. The hydraulic cylinder 131 is housed in the main housing portion 14A of the upper body 14. The hydraulic cylinder 131 is hollow and columnar. For example, the overall shape of the hydraulic cylinder 131 is cylindrical. The inside of the hydraulic cylinder 131 is a hydraulic chamber through which hydraulic fluid is supplied and discharged. The central axis of the hydraulic cylinder 131 extends in a direction approximately perpendicular to the Z direction.

[0100] The piston rod 132 comprises a rod body 132A and a piston 132B. The rod body 132A is rod-shaped. The rod body 132A protrudes from the inside to the outside of the hydraulic cylinder 131. The central axis of the rod body 132A substantially coincides with the central axis of the hydraulic cylinder 131. The rod body 132A is reciprocally movable in a direction along the central axis of the hydraulic cylinder 131. The protruding end of the rod body 132A, which is the tip that protrudes from the hydraulic cylinder 131, is rotatably connected to the first swing wall 17A of the swing bracket 17. A housing portion, which is a hole or recess for housing the second support shaft 17D, is formed at the protruding end of the rod body 132A. The rod body 132A is attached to the first swing wall 17A by housing the second support shaft 17D in this housing portion. The rod body 132A is rotatable relative to the second support shaft 17D and, consequently, the first swing wall 17A.

[0101] The piston 132B is located inside the hydraulic cylinder 131. The piston 132B is connected to the end of the rod body 132A opposite to the protruding end. The piston 132B is disc-shaped. The piston 132B divides the inside of the hydraulic cylinder 131 into two. As a result of the piston 132B dividing the inside of the hydraulic cylinder 131, the inside of the hydraulic cylinder 131 is divided into a first oil chamber 131A and a second oil chamber 131B. In the example in Figure 9, the first oil chamber 131A is located on the side of the piston rod 132 that protrudes from the second oil chamber 131B.

[0102] As a configuration for driving the swing actuator 130, the excavator 10 is equipped with a hydraulic circuit 140. The hydraulic circuit 140 includes a tank 142, a pump 144, and a control valve 145. The tank 142 stores hydraulic fluid. The pump 144 pumps the hydraulic fluid from the tank 142 to the control valve 145. The pump 144 is driven, for example, by an electric motor. The control valve 145 includes, for example, an electromagnetic proportional valve and a spool that operates with the pilot pressure generated by the electromagnetic proportional valve. Under the control of the CPU 101, the control valve 145 adjusts the supply and discharge of hydraulic fluid to the first oil chamber 131A and the second oil chamber 131B. That is, the CPU 101 adjusts the flow rate of hydraulic fluid flowing to the first oil chamber 131A and the second oil chamber 131B, respectively, and switches the direction of the hydraulic fluid flow. In response to the supply and discharge of hydraulic fluid to the first oil chamber 131A and the second oil chamber 131B, the piston 132B and, consequently, the rod body 132A reciprocate in a direction along its central axis. Simultaneously, the amount of protrusion of the piston rod 132 from the hydraulic cylinder 131 changes. Along with this change in the protrusion of the piston rod 132, the swing bracket 17 rotates about the swing axis. Figure 9 schematically represents the hydraulic circuit 140.

[0103] As part of the configuration related to the swing actuator 130, the excavator 10 is equipped with a first hydraulic sensor 181 and a second hydraulic sensor 182. The first hydraulic sensor 181 detects the hydraulic pressure in the first oil chamber 131A of the internal hydraulic pressure of the hydraulic cylinder 131 as the first pressure. The second hydraulic sensor 182 detects the hydraulic pressure in the second oil chamber 131B of the internal hydraulic pressure of the hydraulic cylinder 131 as the second pressure. The first hydraulic sensor 181 and the second hydraulic sensor 182 repeatedly transmit signals to the control device 100 according to the information they have detected. The first hydraulic sensor 181, the second hydraulic sensor 182, and the hydraulic circuit 140 are included as components of the drive system of the excavator 10 together with the swing actuator 130.

[0104] When the above-described swing actuator 130 is used, the CPU 101 performs the following first and second processes as a swing process Q3 to maintain a constant swing rotation position SW. In the first process, the CPU 101 controls the supply and discharge of hydraulic fluid to the hydraulic cylinder 131 to maintain the position of the piston rod 132 at the start of the specific control. For example, when the specific control is started, the CPU 101 controls the control valve 145 to shut off the flow of hydraulic fluid to both the first oil chamber 131A and the second oil chamber 131B. That is, the CPU 101 shuts off the supply of hydraulic fluid from the pump 144 to both the first oil chamber 131A and the second oil chamber 131B, and also shuts off the discharge of hydraulic fluid to the tank 142. The CPU 101 then maintains a state in which the flow of hydraulic fluid to both the first oil chamber 131A and the second oil chamber 131B is shut off. Regarding the first process, the CPU 101 may repeatedly acquire the latest swing rotation position SW and adjust the flow rate or switch the flow path so that this latest swing rotation position SW matches the swing rotation position SW at the start of the specific control. Instead of using the swing rotation position SW, the excavator 10 may be equipped with a sensor that detects the amount of protrusion of the piston rod 132 relative to the hydraulic cylinder 131, or the position of the piston rod 132 in the direction along the central axis. Based on the information detected by this sensor, the hydraulic circuit 140 may be controlled so that the latest position of the piston rod 132 matches the position of the piston rod 132 at the start of the specific control.

[0105] The CPU 101 continues the first process described above, and performs the second process in parallel with the first process. In the second process, the CPU 101 acquires the latest internal hydraulic pressure, i.e., the latest first pressure and the latest second pressure. Then, the CPU 101 calculates the latest load torque FU based on the acquired first and second pressures. During the first process, the CPU 101 repeatedly acquires the latest internal hydraulic pressure and calculates the latest load torque FU based on the acquired internal hydraulic pressure. Memory 102 stores relationship information representing the relationship between internal hydraulic pressure and load torque FU. In this relationship information, the larger the internal hydraulic pressure, the larger the load torque FU. The CPU 101 calculates the load torque FU by applying the internal hydraulic pressure acquired in the second process to this relationship information. For example, the CPU 101 selects the larger of the acquired first and second pressures as the target hydraulic pressure. Then, the CPU 101 calculates the load torque FU by applying this target hydraulic pressure to the relationship information. Here, when a load torque FU acts on the swing bracket 17, the load torque FU becomes a force that tries to move the piston rod 132. Consequently, a difference arises between the first pressure and the second pressure. For example, if the load torque FU acts to push the piston rod 132 towards the back of the hydraulic cylinder 131, the second pressure may be higher than the first pressure. The back of the hydraulic cylinder 131 is the side of the hydraulic cylinder 131 opposite to the side from which the piston rod 132 protrudes. On the other hand, if the load torque FU acts to pull the piston rod 132 back from the hydraulic cylinder 131, the first pressure may be higher than the second pressure. Taking these relationships into consideration, the CPU 101 can calculate the load torque FU from the target hydraulic pressure. In the swing processing Q3, the CPU 101 continues the above first and second processing.

[0106] When the above-described swing actuator 130 and swing processing Q3 are used, the CPU 101 controls the supply and discharge of hydraulic fluid to the first oil chamber 131A and the second oil chamber 131B in load reduction control so that the target hydraulic pressure drops below the point at which the load torque FU reaches the limit torque FK. For example, the CPU 101 controls the control valve 145 so that the hydraulic fluid in the target oil chamber, which is the oil chamber for which the target hydraulic pressure is detected, flows into the tank 142. It can also be said that the CPU 101 controls the control valve 145 so that the movement of the piston rod 132 in accordance with the load torque FU is permitted. In this way, in the second processing, the CPU 101 controls the supply and discharge of hydraulic fluid to the first oil chamber 131A and the second oil chamber 131B so that the piston rod 132 moves from the position of the piston rod 132 when the load torque FU reaches the limit torque FK. Note that when the CPU 101 executes the above-described load reduction control, it cancels the swing processing Q3.

[0107] The contents of the load reduction routine are not limited to the examples of the above embodiment. For example, the CPU 101 may perform corrective control in the load reduction routine before executing load reduction control. Corrective control is control to reduce the load torque FU in the stage before executing load reduction control. When such corrective control is incorporated into the load reduction routine, the CPU 101 first determines whether the load torque FU has become equal to or greater than the corrective torque. The corrective torque is, for example, 70% of the latest limit torque FK. That is, the corrective torque is set to a value smaller than the limit torque FK. The corrective torque should be a value that is deemed to require temporary measures to reduce the load torque FU. If the load torque FU becomes equal to or greater than the corrective torque, the CPU 101 performs corrective control. Specifically, in the corrective control, the CPU 101 controls one or more of the three actuators in the work unit 20 so that a specific point 25E of the bucket 25 moves upward by the corrective distance. The CPU 101 increases the response distance the shorter the current estimated opposing distance of 25M is. The response distance is predetermined in correspondence with the estimated opposing distance of 25M so as to satisfy the requirements (A1) of the execution conditions for specific control. Memory 102 stores information representing the relationship between the estimated opposing distance of 25M and the response distance as control data 102B. The CPU 101 calculates the response distance based on this information. For example, the ground G to be leveled may be locally raised. The response control moves the bucket 25 to the top of the raised ground G in such a location. If the load torque FU is still large even after performing this response control, the CPU 101 performs load reduction control. That is, after performing the response control, the CPU 101 proceeds to step S101 described in the above embodiment.

[0108] • A camera may be used to determine whether the requirements (A1) and (A2) for the execution conditions of the specific control are met. That is, a camera may be mounted on the excavator 10 and the area around the bucket 25 may be imaged by the camera. Then, the requirements (A1) and (A2) may be met by analyzing the captured images.

[0109] The execution conditions for the specific control and the content of the processing performed by the specific control are not limited to the examples of the above embodiment. For example, requirements (A1) and (A2) may be removed from the execution conditions for the specific control. That is, the specific control may be performed for purposes other than ground leveling work. Furthermore, the specific control may be performed for purposes other than rotating the upper body 14. For example, the specific control may be performed for excavation work while maintaining the rotational position of the upper body 14. The specific control only needs to include processing to maintain the swing rotation position SW. The execution conditions for the specific control may be appropriately determined depending on the purpose for which the specific control is performed.

[0110] The method for determining the limit torque FK is not limited to the example of the above embodiment. Not limited to the example of calculation process Q4 of the above embodiment, if the limit torque FK can be determined to satisfy requirements (B1), (B2), and (B3), it is possible to prevent a moment load exceeding the allowable value from acting on each actuator of the work unit 20.

[0111] The limit torque FK may be a predetermined fixed value. Depending on the work performed by the excavator 10, the moment load that will act on each actuator of the work unit 20 can be determined in advance through experiments or other means. In such cases, it is possible to set the limit torque FK as a fixed value. It is sufficient to set an appropriate limit torque FK so that each actuator of the work unit 20 is not subjected to excessive load.

[0112] The configuration of the first actuator 31 is not limited to the examples of the above embodiment. The first actuator 31 may include an electric motor and only need to be able to output torque around an axis intersecting the swing axis. For example, the first reduction gear 33 may be omitted from the first actuator 31. Similar to the first actuator 31, the second actuator 41 may include an electric motor and only need to be able to output torque around an axis intersecting the swing axis. The same applies to the third actuator 51.

[0113] The mounting configuration of the first actuator 31 is not limited to the examples of the above embodiment. The first actuator 31 only needs to be able to rotate the first attachment relative to the swing bracket 17. For example, the orientation of the first actuator 31 between the second swing wall 17B of the swing bracket 17 and the first attachment may be reversed. That is, the housing 32A of the first electric motor 32 may be attached to the first attachment, and the output member 33C of the first reduction gear 33 may be attached to the second swing wall 17B. Similar to the first actuator 31, the mounting configuration of the second actuator 41 is not limited to the examples of the above embodiment. The second actuator 41 only needs to be able to rotate the second attachment relative to the first attachment. Similarly, the mounting configuration of the third actuator 51 is not limited to the examples of the above embodiment. The third actuator 51 only needs to be able to rotate the third attachment relative to the second attachment.

[0114] The specific location 25E of the bucket 25 is not limited to the example of the above embodiment. For example, in operations involving the rotation of the work unit 20, such as ground leveling work, a location where a lateral force FH is likely to act on the bucket 25 may be appropriately designated as the specific location 25E. Similarly, the specific wall 25F of the bucket 25 is not limited to the example of the above embodiment. A wall portion used in ground leveling work, etc., may be appropriately designated as the specific wall 25F.

[0115] The shape of the bucket 25 is not limited to the examples of the above embodiment. The bucket 25 has an opening 26A and can hold soil or other materials inside, as long as it has a shape. For example, the bottom wall of the bucket 25 may be a polygon other than a rectangle. It is also possible that the bucket 25 does not have a wall portion categorized as a bottom wall.

[0116] The third attachment is not limited to the bucket 25. Depending on the work, an appropriate device, mechanism, or tool may be adopted as the third attachment. If a third attachment that does not require rotation is adopted, the third actuator 51 may be eliminated and the third attachment may be directly connected to the arm 23.

[0117] The third attachment may be eliminated. The third actuator 51 may also be eliminated at the same time. The second attachment is not limited to the arm 23. If the second attachment is a long member, it is effective in widening the working range of the work unit 20.

[0118] The second attachment may be eliminated. The second actuator 41 may also be eliminated along with it. The first attachment is not limited to the boom 21. If the first attachment is a long member, it is effective in widening the working range of the work unit 20.

[0119] • Various position sensors, such as the first position sensor 38, second position sensor 48, third position sensor 58, and swing position sensor 68, are not essential. If specific control and load reduction control can be achieved without these sensors, they may be eliminated as appropriate. For example, as described in the above modification example, if the limit torque FK is set as a fixed value, it is not necessary to provide each position sensor for the purpose of calculating the limit torque FK. Similar to position sensors, the current sensor 82 and tilt sensor 81 are not essential. For example, if the tilt of the vehicle body 15 is not considered when calculating the estimated opposing distance of 25M and the attitude index value of 25N, the tilt sensor 81 may be eliminated.

[0120] The configuration of the swing bracket 17 is not limited to the examples of the above embodiment. For example, the shape of the second swing wall 17B may be a polygon other than a rectangle. The swing bracket 17 only needs to be connected to the vehicle body 15 so that it can rotate about a swing axis that extends vertically over the vehicle body 15. At the same time, the swing bracket 17 only needs to be connected to the first attachment so that it can rotate about an axis that intersects the swing axis. Depending on the configuration of the swing bracket 17 and the configuration of the swing actuator 61, the configuration for connecting the swing bracket 17 and the swing actuator 61 may change. In other words, the configuration for connecting the swing bracket 17 and the swing actuator 61 is not limited to the examples of the above embodiment.

[0121] The manner in which the swing bracket 17 is connected to the vehicle body 15 is not limited to the examples of the above embodiment. For example, the shape of the front part 14B of the housing may be other than a rectangular parallelepiped. If the swing bracket 17 can be connected to the vehicle body 15 without using the wall portion called the front part 14B of the housing, then the front part 14B of the housing may be abolished.

[0122] The configuration of the upper body 14 is not limited to the examples of the above embodiments. For example, the cabin may be eliminated from the upper body 14. The shape of the upper body 14 may be other than a rectangular parallelepiped. The upper body 14 only needs to be configured to fulfill the necessary functions, such as housing various pieces of equipment.

[0123] 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, the operating signal 90S may be transmitted wirelessly from equipment outside the vehicle body 15. In other words, the equipment that transmits the operating signal 90S is not limited to equipment mounted on the vehicle body 15.

[0124] The components of the drive system are not limited to the examples of the embodiments described above. The components of the drive system may change depending on the various modifications described in each of the above examples of modifications. The drive system may include a slewing actuator 71, a swing actuator 61, an electric actuator for driving the attachment, and a control device 100.

[0125] It is not essential that the upper body 14 is rotatable relative to the lower body 13. In other words, the slewing bearing 18 and the slewing actuator 71 may be eliminated. For an excavator 10 in which the upper body 14 is not rotatable relative to the lower body 13, a specific control may be performed to maintain a constant swing rotation position SW. If the load torque FU increases during this specific control, a load reduction control may be performed to decrease the load torque FU.

[0126] The overall configuration of the vehicle body 15 and, by extension, the excavator 10 is not limited to the example of the above embodiment. For example, the overall shape of the vehicle body 15 may be changed from the example of the above embodiment in conjunction with changing the shape of the upper body 14 as in the modified example above. For example, the entire excavator 10 should be configured to perform the required work, such as leveling or excavation.

[0127] • 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.

[0128] 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.

[0129] (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.

[0130] (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.

[0131] 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.

[0132] 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. [Explanation of symbols]

[0133] 10... Excavator 13…Lower body 14…Upper body 17…Swing bracket 21... Boom (First Attachment) 23... Arm (Second Attachment) 25... Bucket (3rd attachment) 31…First Actuator 38…First position sensor 41...Second Actuator 48...Second position sensor 51…Third actuator 58...Third position sensor 61,130... Swing Actuator 62…Fourth electric motor 68...Swing position sensor 71... Swivel actuator 100...Control device 131... Hydraulic cylinder 132... Piston rod 140... Hydraulic circuit 181...1st hydraulic sensor 182...Second hydraulic sensor

Claims

1. A pivot actuator that rotates the upper body around a rotation axis relative to the lower body, A swing actuator that rotates the swing bracket relative to the upper body about a swing axis parallel to the rotation axis, An electric actuator is attached to the swing bracket and drives the attachment by outputting torque centered on an axis intersecting the swing axis, The system includes a control device that performs specific control to control the swing actuator so as to maintain a constant rotational position of the swing bracket relative to the upper body, If the load torque, which is the torque acting on the swing bracket around the swing axis during the specific control, exceeds the limit torque, the control device executes load reduction control, which controls at least one of the pivot actuator and the swing actuator to reduce the load torque. A drive system for industrial machinery.

2. The system includes a swing position sensor that detects the swing rotation position, which is the rotational position of the swing bracket, The swing actuator has an electric motor that serves as a driving source, The control device is In the aforementioned specific control, A first process for obtaining the aforementioned swing rotation position, A second process involves performing feedback control of the electric motor so as to eliminate the discrepancy between the acquired swing rotation position and the swing rotation position at the start of the specific control, and acquiring the current value supplied to the electric motor during the feedback control. The process of calculating the load torque based on the current value obtained in the second process is repeated, If the load torque calculated in the third process exceeds the limit torque, the second process is terminated, and in the load reduction control, the current supplied to the electric motor is controlled so that the current supplied to the electric motor becomes closer to zero than the current supplied to the electric motor at the point when the load torque reached the limit torque. A drive system for a work machine according to claim 1.

3. The aforementioned swing actuator is A hydraulic cylinder through which hydraulic fluid is supplied and discharged, The hydraulic cylinder has a piston rod that protrudes from the inside to the outside and is attached to the swing bracket, and the amount of protrusion from the hydraulic cylinder changes in accordance with the supply and discharge of hydraulic fluid to the hydraulic cylinder, A hydraulic circuit that adjusts the supply and discharge of hydraulic fluid to the hydraulic cylinder, The hydraulic sensor further comprises a hydraulic sensor for detecting the internal hydraulic pressure of the hydraulic cylinder, The control device is In the aforementioned specific control, A first process that controls the supply and discharge of hydraulic fluid to the hydraulic cylinder so as to maintain the position of the piston rod at the start of the specific control, During the first process, a second process is performed which involves repeatedly acquiring the internal hydraulic pressure and calculating the load torque based on the acquired internal hydraulic pressure. If the calculated load torque exceeds the limit torque, the first process is terminated, and in the load reduction control, the supply and discharge of hydraulic fluid is controlled so that the piston rod moves from the position of the piston rod at the time the load torque reached the limit torque. A drive system for a work machine according to claim 1.

4. When the electric actuator is referred to as the first electric actuator and the attachment as the first attachment, A second electric actuator is attached to the first attachment and drives the second attachment by outputting torque around a second axis parallel to the first axis, which is the axis of the first electric actuator. The system includes a third electric actuator, which is attached to the second attachment and drives the third attachment by outputting torque centered on a third axis parallel to the first axis, The control device is The first allowable moment load, which is the maximum allowable moment load for the first electric actuator, the second allowable moment load, which is the maximum allowable moment load for the second electric actuator, and the third allowable moment load, which is the maximum allowable moment load for the third electric actuator, are stored in advance. During the aforementioned specific control, A calculation process is performed to calculate the limit torque such that the moment load acting on the first electric actuator is less than or equal to the first allowable moment load, the moment load acting on the second electric actuator is less than or equal to the second allowable moment load, and the moment load acting on the third electric actuator is less than or equal to the third allowable moment load. A drive system for a work machine according to claim 1.

5. A first position sensor for detecting a first rotational position, which is the rotational position of the first attachment, A second position sensor detects a second rotational position, which is the rotational position of the second attachment, The system includes a third position sensor that detects a third rotational position, which is the rotational position of the third attachment, The control device is First relational information representing the relationship between the second rotation position and the third rotation position, and the first distance, which is the distance from a specific point on the third attachment to the first axis in a specific plan view that is a plan view oriented in a direction along the first axis, Second relational information representing the relationship between the third rotational position and the second distance, which is the distance from the specific location of the third attachment in the specific plan view to the second axis, The third distance is the distance from the specific location of the third attachment in the specific plan view to the third axis, The system pre-stores fourth relational information that represents the relationship between the first rotational position, the second rotational position, and the third rotational position, and a fourth distance, which is the distance from the specific location of the third attachment to the swing axis in a direction along an axis perpendicular to both the swing axis and the first axis. In the calculation process described above, A first calculation process for obtaining the first rotation position, the second rotation position, and the third rotation position, A second calculation process calculates the first distance by applying the acquired second rotation position and third rotation position to the first relational information, and calculates the first allowable lateral force by dividing the first allowable moment load by the calculated first distance. A third calculation process calculates the second distance by applying the acquired third rotational position to the second relational information, and calculates the second allowable lateral force by dividing the second allowable moment load by the calculated second distance, A fourth calculation process is performed to calculate the third allowable lateral force as the value obtained by dividing the third allowable moment load by the third distance, A fifth calculation process that calculates the fourth distance by applying the acquired first rotation position, second rotation position, and third rotation position to the fourth relational information, A sixth calculation process is performed to calculate the limit torque as a value less than or equal to the product of the minimum value among the calculated first allowable lateral force, second allowable lateral force, and third allowable lateral force, and the fourth distance. The drive system for the work machine according to claim 4.

6. The control device controls the pivot actuator in the specific control so that the upper body rotates relative to the lower body. A drive system for a work machine according to claim 1.

7. In the load reduction control, the control device, The slewing actuator is controlled so that the rotational speed of the upper body is lower than the point at which the load torque reaches the limit torque. The drive system for the work machine according to claim 6.

8. When the electric actuator is referred to as the first electric actuator and the attachment as the first attachment, A second electric actuator is attached to the first attachment and drives the second attachment by outputting torque around a second axis parallel to the first axis, which is the axis of the first electric actuator. A third electric actuator is attached to the second attachment and drives the third attachment by outputting torque centered on a third axis parallel to the first axis, A first position sensor for detecting a first rotational position, which is the rotational position of the first attachment, A second position sensor detects a second rotational position, which is the rotational position of the second attachment, The system includes a third position sensor that detects a third rotational position, which is the rotational position of the third attachment, The control device is The system pre-stores information representing the relationship between the first rotation position, the second rotation position, and the third rotation position, and the estimated opposing distance, which is the estimated shortest distance from a specific point on the third attachment to the ground. The first rotation position, the second rotation position, and the third rotation position are acquired, and a preprocessing step is performed to calculate the estimated opposing distance by applying the acquired first rotation position, the second rotation position, and the third rotation position to the opposing distance information. The specific control is executed on the condition that the estimated opposing distance is less than or equal to a predetermined approach distance. The drive system for the work machine according to claim 6.

9. The control device is If, during the specified control, the load torque exceeds a predetermined countermeasure torque that is smaller than the limit torque, then a countermeasure control is executed that controls one or more of the first, second, and third electric actuators to move the specified location upward from the point in time when the load torque reached the countermeasure torque. The drive system for a work machine according to claim 8.

10. An upper body that can rotate around a rotation axis relative to the lower body, A pivot actuator that rotates the upper body relative to the lower body, A swing bracket connected to the upper body and rotatable relative to the upper body about a swing axis parallel to the rotation axis, A swing actuator that rotates the swing bracket relative to the upper body, An electric actuator is attached to the swing bracket and outputs torque around an axis intersecting the swing axis, This is applied to a work machine comprising an attachment mounted on the aforementioned electric actuator and driven by the aforementioned electric actuator, A specific control that controls the swing actuator to maintain a constant rotational position of the swing bracket relative to the upper body, If, during the aforementioned specific control, the load torque, which is the torque acting on the swing bracket around the swing axis, exceeds the limit torque, load reduction control is performed to control at least one of the pivot actuator and the swing actuator so that the load torque decreases. Control device for industrial machinery.

11. An upper body that can rotate around a rotation axis relative to the lower body, A pivot actuator that rotates the upper body relative to the lower body, A swing bracket connected to the upper body and rotatable relative to the upper body about a swing axis parallel to the rotation axis, A swing actuator that rotates the swing bracket relative to the upper body, An electric actuator is attached to the swing bracket and outputs torque around an axis intersecting the swing axis, A control device applied to a work machine comprising an attachment mounted on the electric actuator and driven by the electric actuator, A specific control that controls the swing actuator to maintain a constant rotational position of the swing bracket relative to the upper body, If, during the aforementioned specific control, the load torque, which is the torque acting on the swing bracket around the swing axis, exceeds the limit torque, load reduction control is performed to control at least one of the pivot actuator and the swing actuator so that the load torque decreases. A method for controlling industrial machinery.

12. An upper body that can rotate around a rotation axis relative to the lower body, A pivot actuator that rotates the upper body relative to the lower body, A swing bracket connected to the upper body and rotatable relative to the upper body about a swing axis parallel to the rotation axis, A swing actuator that rotates the swing bracket relative to the upper body, An electric actuator is attached to the swing bracket and outputs torque around an axis intersecting the swing axis, A control device applied to a work machine comprising an attachment mounted on the electric actuator and driven by the electric actuator, A specific control that controls the swing actuator to maintain a constant rotational position of the swing bracket relative to the upper body, If, during the specified control, the load torque, which is the torque acting on the swing bracket around the swing axis, exceeds the limit torque, load reduction control is performed to control at least one of the pivot actuator and the swing actuator so that the load torque decreases. Control program for industrial machinery.

13. An upper body that can rotate around a rotation axis relative to the lower body, A pivot actuator that rotates the upper body relative to the lower body, A swing bracket connected to the upper body and rotatable relative to the upper body about a swing axis parallel to the rotation axis, A swing actuator that rotates the swing bracket relative to the upper body, An electric actuator is attached to the swing bracket and outputs torque around an axis intersecting the swing axis, An attachment mounted on the aforementioned electric actuator and driven by the aforementioned electric actuator, The system includes a control device that performs specific control to control the swing actuator so as to maintain a constant rotational position of the swing bracket relative to the upper body, If the load torque, which is the torque acting on the swing bracket around the swing axis during the specific control, exceeds the limit torque, the control device executes load reduction control, which controls at least one of the pivot actuator and the swing actuator to reduce the load torque. A type of machinery used for industrial work.

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