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

Abstract

Reduce the peripheral speed of the attachment tip. [Solution] The excavator includes an attachment having a first movable member and a second movable member, a drive unit having a first electric actuator having a first output shaft for rotating the first movable member and a second electric actuator having a second output shaft for rotating the second movable member, and a control device for controlling the drive unit. The control device performs a first process (step S40) to calculate the upper limit rotation speed W1U of the first output shaft based on the relative position of the second movable member with respect to the first movable member, and a second process (step S80) to control the first electric actuator so that the rotation speed of the first output shaft is less than or equal to the upper limit rotation speed W1U. In the first process, the longer the distance between the first output shaft and the tip of the attachment opposite to the connection point with the first output shaft, the smaller the upper limit rotation speed W1U becomes.

Description

TECHNICAL FIELD

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

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

[0003] PATENT DOCUMENT 1 Japanese Unexamined Patent Application Publication No. 2001-254395 SUMMARY OF THE INVENTION PROBLEMS TO BE SOLVED BY THE INVENTION

[0004] In techniques such as that disclosed in Patent Document 1, an electric actuator that outputs torque may be disposed at a joint portion such as the connection point between the vehicle body and the boom. Such electric actuators may rotate each movable member such as the boom, the arm, and the bucket. When this type of structure is adopted, the movable range of each movable member becomes wide. Accompanying this, the distance from the output shaft of the electric actuator that rotates the boom to the tip of the bucket can become considerably long. If the boom is rotated in this state, the circumferential speed of the bucket tip can become considerably high due to the long distance described above. In this case, there is a problem that the impact applied to the attachment increases when the tip of the bucket collides with an excavation target or an obstacle. MEANS FOR SOLVING THE PROBLEMS

[0005] A drive system for a work machine to solve the above problems is applied to a work machine equipped with an attachment having a first movable member and a second movable member rotatably connected to the first movable member, and comprises a drive unit having a first electric actuator having a first output shaft for rotating the first movable member and a second electric actuator having a second output shaft for rotating the second movable member, and a control device for controlling the drive unit, wherein the control device performs a first process of calculating a limit value for the rotational speed of the first output shaft based on the relative position of the second movable member with respect to the first movable member, and a second process of controlling the first electric actuator so that the rotational speed of the first output shaft is less than or equal to the limit value, and in the first process, when the distance from the first output shaft to the tip of the attachment opposite to the connection point with the first output shaft is a first value, the limit value is made smaller than when the distance is a second value which is smaller than the first value.

[0006] According to the above configuration, when the distance between the first output shaft and the tip of the attachment is long, the rotational speed limit of the first output shaft is reduced. This makes it possible to suppress the peripheral speed of the tip of the attachment even when the distance is long.

[0007] In a drive system for a work machine, when the upper limit of the peripheral speed with respect to the tip of the attachment is set as the upper limit peripheral speed, the control device may, in the first process, calculate a value corresponding to the division value obtained by dividing the predetermined upper limit peripheral speed by the distance as the limit value.

[0008] In a drive system for a work machine, the attachment has a third movable member rotatably connected to the second movable member, the drive unit has a third electric actuator having a third output shaft for rotating the third movable member, the tip of the attachment is the tip of the third movable member opposite to the connection point with the third output shaft, and the control device may calculate the limit value in the first process based on the relative position of the second movable member with respect to the first movable member and the relative position of the third movable member with respect to the second movable member.

[0009] In a drive system for a work machine, when the limit value is set to a first limit value, the control device calculates the first limit value, a second limit value which is the limit value for the rotational speed of the second output shaft, and a third limit value which is the limit value for the rotational speed of the third output shaft, based on the relative position of the second movable member with respect to the first movable member and the relative position of the third movable member with respect to the second movable member in the first process; in the second process, the control device controls the first electric actuator so that the rotational speed of the first output shaft is less than or equal to the first limit value, the second electric actuator so that the rotational speed of the second output shaft is less than or equal to the second limit value, and the third electric actuator so that the rotational speed of the third output shaft is less than or equal to the third limit value; and in the first process, when the distance between the first output shaft and the tip of the attachment is a first value, the first limit value, the second limit value, and the third limit value may be smaller than when the distance is a second value.

[0010] In a drive system for a work machine, the work machine may be a construction machine, the first movable member may be a boom, the second movable member may be an arm, and the third movable member may be a bucket.

[0011] A control device for a work machine to solve the above problems is applied to a work machine comprising: an attachment having a first movable member and a second movable member rotatably connected to the first movable member; a drive unit having a first electric actuator having a first output shaft for rotating the first movable member and a second electric actuator having a second output shaft for rotating the second movable member; and a first process that calculates a limit value for the rotational speed of the first output shaft based on the relative position of the second movable member with respect to the first movable member; and a second process that controls the first electric actuator so that the rotational speed of the first output shaft is less than or equal to the limit value. In the first process, when the distance from the first output shaft to the tip of the attachment opposite to the connection point with the first output shaft is a first value, the limit value is made smaller than when the distance is a second value which is smaller than the first value.

[0012] According to the above configuration, when the distance between the first output shaft and the tip of the attachment is long, the rotational speed limit of the first output shaft is reduced. This makes it possible to suppress the peripheral speed of the tip of the attachment even when the distance is long.

[0013] A control method for a work machine to solve the above problems is provided, which is applied to a work machine comprising: an attachment having a first movable member and a second movable member rotatably connected to the first movable member; a drive unit having a first electric actuator having a first output shaft for rotating the first movable member and a second electric actuator having a second output shaft for rotating the second movable member; a control device that performs a first process of calculating a limit value for the rotational speed of the first output shaft based on the relative position of the second movable member with respect to the first movable member; and a second process of controlling the first electric actuator so that the rotational speed of the first output shaft is less than or equal to the limit value, wherein in the first process, when the distance from the first output shaft to the tip of the attachment opposite to the connection point with the first output shaft is a first value, the limit value is made smaller than when the distance is a second value which is smaller than the first value.

[0014] According to the above method, when the distance between the first output shaft and the tip of the attachment is long, the rotational speed limit of the first output shaft is reduced. This makes it possible to suppress the peripheral speed of the tip of the attachment even when the distance is long.

[0015] 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 attachment having a first movable member and a second movable member rotatably connected to the first movable member; a drive unit having a first electric actuator having a first output shaft for rotating the first movable member and a second electric actuator having a second output shaft for rotating the second movable member; a first process for calculating a limit value for the rotational speed of the first output shaft based on the relative position of the second movable member with respect to the first movable member; and a second process for controlling the first electric actuator so that the rotational speed of the first output shaft is less than or equal to the limit value. In the first process, when the distance from the first output shaft to the tip of the attachment opposite to the connection point with the first output shaft is a first value, the limit value is made smaller than when the distance is a second value which is smaller than the first value.

[0016] According to the program described above, if the distance between the first output shaft and the tip of the attachment is long, the control device reduces the limit on the rotational speed of the first output shaft. This makes it possible to suppress the peripheral speed of the tip of the attachment even when the distance is long. [Effects of the Invention]

[0017] The above technical concept allows for suppressing the peripheral speed at the tip of the attachment. [Brief explanation of the drawing]

[0018] [Figure 1] Figure 1 is a schematic side view of the excavator according to the first embodiment. [Figure 2] Figure 2 is a schematic plan view of an excavator. [Figure 3]Figure 3 is a diagram showing the electrical configuration and power transmission paths of a shovel. [Figure 4] Figure 4 is a flowchart showing the processing procedure of drive control according to the first embodiment. [Figure 5] Figure 5 is a flowchart showing the processing procedure of drive control according to the second embodiment. [Figure 6] Figure 6 is a side view for explaining the peripheral speed of the tip of the bucket. [Mode for Carrying Out the Invention]

[0019] <First Embodiment> Hereinafter, the first embodiment of the work machine drive system, work machine control device, work machine control method, and work machine control program will be described taking a construction machine as an example. For the sake of simplicity and clarity of description, the components shown in the drawings are not necessarily drawn to a fixed scale.

[0020] <Overall Configuration> As shown in Figure 1 and Figure 2, a shovel 10 which is a work machine and 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 located 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.

[0021] As shown in Figure 1, 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, the upper body 14 includes a cabin in which an operator sits. The upper body 14 is sometimes referred to as the upper rotating body.

[0022] As shown in Figures 1 and 2, the excavator 10 is equipped with a slewing bearing 18. The slewing bearing 18 is located between the lower body 13 and the upper body 14. In Figure 1, the vertical width of the slewing bearing 18 is exaggerated and shown as large with respect to the Z direction. As shown in Figure 2, the slewing bearing 18 comprises an annular inner ring 18A, an annular outer ring 18B, and a plurality of rolling elements. In Figure 2, the rolling elements are not shown. The outer diameter of the inner ring 18A is smaller than the inner diameter of the outer ring 18B. The slewing axis 10J, which is the central axis of the inner ring 18A, approximately coincides with the central axis of the outer ring 18B. The slewing axis 10J extends vertically across the vehicle body 15, i.e., in the Z direction. As shown in Figure 1, the slewing axis 10J passes vertically through both the upper body 14 and the lower body 13. The plurality of rolling elements are located between the inner ring 18A and the outer ring 18B. Multiple rolling elements support the inner ring 18A and the outer ring 18B so that they can rotate relative to each other. As a result, the outer ring 18B is rotatable relative to the inner ring 18A about the pivot axis 10J. The inner ring 18A is fixed to the lower body 13. The outer ring 18B is fixed to the main housing portion 14A of the upper body 14. That is, the upper body 14 is rotatable relative to the lower body 13 about the pivot axis 10J.

[0023] As shown in Figure 2, the excavator 10 is equipped with a slewing actuator 71. The slewing actuator 71 comprises an electric motor and a reduction gear that amplifies and outputs the torque of the electric motor. The slewing actuator 71 is housed in the main housing portion 14A of the upper body 14. The slewing actuator 71 rotates the upper body 14 relative to the lower body 13 by outputting torque.

[0024] As shown in Figures 1 and 2, the excavator 10 is equipped with a pair of running gears 12. The pair of running gears 12 are located on the left and right sides of the lower body 13. Both running gears 12 are connected to the lower body 13. Each pair of running gears 12 includes a crawler for travel and an operating mechanism for rotating the crawler. The crawler is an endless belt shape. The crawler has openings on both the left and right sides. The underside of the crawler is in contact with the ground G. The excavator 10 moves as the crawler rotates. The running gears 12 and the lower body 13 are sometimes collectively referred to as the lower running gear.

[0025] 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 second swing wall 17B protrudes upward from the upper surface of the first swing wall 17A. The second swing wall 17B is, for example, rectangular plate-shaped.

[0026] As shown in Figure 1, the excavator 10 is equipped with a swing actuator 61. The swing actuator 61 is housed in the front part 14B of the housing of the upper body 14. The swing actuator 61 comprises an electric motor and a reduction gear that amplifies and outputs the torque of the electric motor. The swing actuator 61 outputs torque around a fourth axis 61J that extends vertically from the vehicle body 15. The fourth axis 61J is approximately parallel to the pivot axis 10J. The output shaft of the swing actuator 61 is connected to the first swing wall 17A. The swing actuator 61 rotates the swing bracket 17 relative to the front part 14B of the housing.

[0027] <Attachment> As shown in Figures 1 and 2, the drive system of the excavator 10 includes an attachment 20. The attachment 20 has a boom 21, an arm 23, and a bucket 25.

[0028] As shown in Figures 1 and 2, 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. For example, the boom 21 is bent in the middle of its longitudinal direction. As shown in Figure 2, the first longitudinal end 21A of the boom 21 is aligned with the second swing wall 17B of the swing bracket 17 in the direction along the first axis 31J. The first axis 31J is a virtual axis that is substantially perpendicular to the fourth axis 61J. The first end 21A of the boom 21 is rotatably connected to the second swing wall 17B. The boom 21 corresponds to the first movable member.

[0029] As shown in Figures 1 and 2, the arm 23 extends from the second end 21B of the boom 21, opposite to the first end 21A. The arm 23 is a long, plate-like or columnar shape. As shown in Figure 2, the longitudinal first end 23A of the arm 23 is aligned with the second end 21B of the boom 21 in the direction along the second axis 41J. The second axis 41J is a virtual axis approximately parallel to the first axis 31J. The first end 23A of the arm 23 is rotatably connected to the second end 21B of the boom 21. The arm 23 corresponds to the second movable member.

[0030] As shown in Figures 1 and 2, the bucket 25 is located near the second end 23B of the arm 23, opposite to the first end 23A. The bucket 25 comprises a bucket body 26, a plurality of claws 27, and a bucket connecting wall 28. The bucket body 26 is box-shaped. That is, as shown in Figure 2, the bucket body 26 has an opening 26A. The claws 27 protrude from one side of the rectangular opening edge of the bucket body 26. The bucket connecting wall 28 protrudes from the outer wall of the bucket body 26, on the opposite side of the opening 26A from the claws 27. As shown in Figure 2, the bucket connecting wall 28 is aligned with the second end 23B of the arm 23 in the direction along the third 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. The bucket connecting wall 28 is rotatably connected to the second end 23B of the arm 23. Bucket 25 corresponds to the third movable member.

[0031] <Drive Unit> As shown in Figure 3, the drive system of the excavator 10 includes a drive unit 30. The drive unit 30 includes a boom actuator 31, an arm actuator 41, and a bucket actuator 51. The excavator 10 also includes a first inverter 35, a second inverter 45, a third inverter 55, and a battery 19. Although not shown in the figure, the first inverter 35, the second inverter 45, the third inverter 55, and the battery 19 are housed in the main housing 14A of the upper body 14. The boom actuator 31 corresponds to the first electric actuator. The arm actuator 41 corresponds to the second electric actuator. The bucket actuator 51 corresponds to the third electric actuator.

[0032] As shown in Figure 2, the boom actuator 31 is located between the second swing wall 17B of the swing bracket 17 and the first end 21A of the boom 21. As shown in Figure 3, the boom 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 a first drive shaft 32B. The housing 32A is attached to the second swing wall 17B of the swing bracket 17. The first drive shaft 32B protrudes from the inside to the outside of the housing 32A. The first drive shaft 32B is cylindrical. The first drive shaft 32B is rotatable relative to the housing 32A about its own central axis, the first axis 31J. That is, the first drive shaft 32B outputs torque about the first axis 31J. The first drive 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.

[0033] 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 first drive shaft 32B of the first electric motor 32. The reduction mechanism 33B amplifies the torque from the first drive shaft 32B 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 is approximately coincident 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 first drive shaft 32B. 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 around the first axis 31J. The boom 21 receives this torque and rotates around the first axis 31J. Through this series of torque transmissions, the first drive shaft 32B rotates the boom 21 via the reduction mechanism 33B and the output member 33C. The first drive shaft 32B corresponds to the first output shaft.

[0034] As shown in Figure 2, the arm actuator 41 is located between the second end 21B of the boom 21 and the first end 23A of the arm 23. The configuration of the arm actuator 41 is basically the same as that of the boom actuator 31, except for details such as dimensions, reduction ratio, and output. Therefore, the configuration of the arm actuator 41 will be briefly described below.

[0035] As shown in Figure 3, the arm actuator 41 comprises a second electric motor 42 and a second reduction gear 43. The second electric motor 42 is electrically connected to the battery 19 via a second inverter 45. The housing 42A of the second electric motor 42 is attached to the second end 21B of the boom 21. The second drive 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 torque output by the second drive shaft 42B is input to the arm 23 via the reduction mechanism 43B and output member 43C of the second reduction gear 43. The arm 23 rotates together with the output member 43C around the second axis 41J. In this manner, the second drive shaft 42B rotates the arm 23 via the reduction mechanism 43B and the output member 43C. The second drive shaft 42B corresponds to the second output shaft. The housing 43A of the second reduction gear 43 is attached to the housing 42A of the second electric motor 42.

[0036] As shown in Figure 2, the bucket actuator 51 is located between the second end 23B of the arm 23 and the bucket connecting wall 28 of the bucket 25. The configuration of the bucket actuator 51 is basically the same as that of the boom actuator 31, except for details such as dimensions, reduction ratio, and output. Therefore, the configuration of the bucket actuator 51 will be briefly described below.

[0037] As shown in Figure 3, the bucket actuator 51 comprises a third electric motor 52 and a third reduction gear 53. The third electric motor 52 is electrically connected to the battery 19 via a third inverter 55. The housing 52A of the third electric motor 52 is attached to the second end 23B of the arm 23. The third drive 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 torque output by the third drive shaft 52B is input to the bucket connecting wall 28 via the reduction mechanism 53B and output member 53C of the third reduction gear 53. The bucket connecting wall 28 rotates together with the output member 53C around the third axis 51J. In this manner, the third drive shaft 52B rotates the bucket 25 via the reduction mechanism 53B and the output member 53C. The third drive shaft 52B corresponds to the third output shaft. The housing 53A of the third reduction gear 53 is attached to the housing 52A of the third electric motor 52.

[0038] <Sensor> As shown in Figure 3, the drive system of the excavator 10 includes a first angle sensor 38, a second angle sensor 48, and a third angle sensor 58. The first angle sensor 38 detects the angular position 38S of the first drive shaft 32B of the first electric motor 32. The second angle sensor 48 detects the angular position 48S of the second drive shaft 42B of the second electric motor 42. The third angle sensor 58 detects the angular position 58S of the third drive shaft 52B of the third electric motor 52. The angular positions detected by each angle sensor 38, 48, and 58 are shown in the range of "0 degrees to 360 degrees," with a predetermined reference position set at "0 degrees." In other words, each angular position indicates the absolute angle of the drive shaft of each electric motor 32, 42, and 52. Each angle sensor 38, 48, and 58 transmits a signal corresponding to the information it has detected to the control device 100, which will be described later.

[0039] Although not shown in the diagram, the drive system of the excavator 10 is equipped with various sensors necessary for operating the excavator 10, in addition to the sensors mentioned above. For example, the drive system of the excavator 10 is equipped with sensors that detect the current value flowing to each electric motor 32, 42, and 52, and sensors that detect the temperature of the battery 19. In addition, the drive system of the excavator 10 is equipped with various operating devices 90 that are operated by the operator. In the drawing, the various operating devices 90 are shown as a group. The various operating devices 90 are located in the cabin. The various operating devices 90 transmit signals 90S corresponding to the operator's operation to the control device 100, which will be described later.

[0040] <Control device> As shown in Figure 3, the drive system of the excavator 10 includes a control device 100. The control device 100 is a computer equipped with a processing circuit. The processing circuit includes a CPU 101 and a memory 102. The memory 102 includes three types: RAM, ROM, and electrically rewritable nonvolatile memory. In this embodiment, these three types are collectively referred to as memory 102. The memory 102 pre-stores various control programs 102A that describe the processing to be executed by the CPU 101. The memory 102 pre-stores various data 102B necessary for the CPU 101 to execute the control programs 102A. The processing circuit includes a communication circuit for wireless communication with the outside.

[0041] The CPU 101 can receive the angular position 38S transmitted from the first angular sensor 38. The CPU 101 can receive the angular position 48S transmitted from the second angular sensor 48. The CPU 101 can receive the angular position 58S transmitted from the third angular sensor 58. The CPU 101 can receive the signal 90S transmitted from the operating device 90.

[0042] The CPU 101 converts the angular position 38S received from the first angle sensor 38 into a first angular position 21S relating to the boom 21, based on the actual angle of the first electric motor 32. The first angular position 21S is the angular position of the boom 21 from a predetermined first position. The first position and the first angular position 21S are defined in a specific plan view when viewing the excavator 10 facing in the direction along the first axis 31J. An example of the first position is an angular 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 fourth axis 61J. In this example of the first position, the second end 21B of the boom 21 is positioned on the opposite side from the vehicle body 15, with the first axis 31J in between. The first angular position 21S indicates the relative position of the boom 21 with respect to the swing bracket 17 or the vehicle body 15. Furthermore, the first angle sensor 38, which detects the actual angle of the first electric motor 32, effectively detects the first angular position 21S.

[0043] The CPU 101 converts the angular position 48S received from the second angle sensor 48 into a second angular position 23S related to the arm 23, based on the actual angle of the second electric motor 42. The second angular position 23S is the angular position of the arm 23 from a predetermined second position. The second position and the second angular position 23S are defined in the specific plan view described above. An example of the second position is the angular position where both the first end 23A and the second end 23B of the arm 23 are positioned on a virtual straight line passing through the first axis 31J and the second axis 41J. In this example of the second position, the second end 23B of the arm 23 is positioned on the opposite side of the second axis 41J from the first axis 31J. The second angular position 23S indicates the relative position of the arm 23 with respect to the boom 21. The second angle sensor 48, which detects the actual angle of the second electric motor 42, effectively detects the second angular position 23S.

[0044] The CPU 101 converts the angular position 58S received from the third angle sensor 58 into a third angular position 25S related to the bucket 25, based on the actual angle of the third electric motor 52. The third angular position 25S is the angular position of the bucket 25 from a predetermined third position. The third position and the third angular position 25S are defined in the specific plan view described above. An example of the third position is the angular 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 position, 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 angular position 25S indicates the relative position of the bucket 25 with respect to the arm 23. The third angle sensor 58, which detects the actual angle of the third electric motor 52, effectively detects the third angular position 25S.

[0045] The CPU 101 calculates the first angular position 21S each time it receives an angular position 38S from the first angular sensor 38. In other words, the CPU 101 repeatedly calculates the first angular position 21S. The CPU 101 calculating the first angular position 21S is equivalent to the CPU 101 acquiring the first angular position 21S. Similar to the first angular position 21S, the CPU 101 repeatedly calculates the second angular position 23S and the third angular position 25S. Similar to the first angular position 21S, the CPU 101 calculating these angular positions 23S and 25S is equivalent to the CPU 101 acquiring each of these angular positions 23S and 25S.

[0046] <Restrictions> The CPU 101 controls the drive unit 30. Specifically, the CPU 101 controls the first electric motor 32 of the boom actuator 31, the second electric motor 42 of the arm actuator 41, and the third electric motor 52 of the bucket actuator 51. In controlling each of the electric motors 32, 42, and 52, the CPU 101 essentially controls the inverters 35, 45, and 55 connected to each of the electric motors 32, 42, and 52.

[0047] When the CPU 101 controls each of the electric motors 32, 42, and 52, it sets a target value for the rotational speed of each drive shaft 32B, 42B, and 52B. Then, it controls each of the electric motors 32, 42, and 52 so that the actual rotational speed matches this target value. In this embodiment, the rotational speed is used when describing the rotational speed of the drive shafts 32B, 42B, and 52B of each of the electric motors 32, 42, and 52. For example, for the rotational speed of the first drive shaft 32B of the first electric motor 32, the rotational speed of the first drive shaft 32B is used. The rotational speed is the number of times the drive shaft rotates per unit time.

[0048] The CPU 101 is capable of performing drive control. In this embodiment, the drive control is directed at the first electric motor 32. In the drive control, the CPU 101 rotates the boom 21 by driving the first electric motor 32. In this embodiment, this drive control is performed under the condition that the angular position of the arm 23 and the angular position of the bucket 25 are kept constant. The following describes the contents of the series of processes performed by the CPU 101 in the drive control.

[0049] For example, when the CPU 101 receives a signal 90S from the control device 90 instructing the rotation of the boom 21, it starts drive control. As shown in Figure 4, when the CPU 101 starts drive control, it first performs the process in step S10.

[0050] In step S10, the CPU 101 obtains the latest first base rotation speed W1. The first base rotation speed W1 is a command value that indicates the rotation speed of the first electric motor 32. The first base rotation speed W1 is calculated in a base value calculation process, which is a separate process from this drive control. For example, when an operator operates the lever, which is the operating device 90, the CPU 101 calculates the first base rotation speed W1 in the base value calculation process according to the amount the lever is operated. At that time, the CPU 101 calculates the first base rotation speed W1 as a value less than the limit rotation speed. The limit rotation speed is the physical limit value of the rotation speed of the first drive shaft 32B, which is determined from the specifications of the first electric motor 32. After the processing in step S10, the CPU 101 proceeds to step S20.

[0051] In step S20, the CPU 101 obtains the latest second angular position 23S and the latest third angular position 25S. After this, the CPU 101 proceeds to step S30. In step S30, the CPU 101 calculates the target distance L. As shown in Figure 6, the target distance L is the distance from the first axis 31J to the tip of the claw 27 of the bucket 25 in a specific plan view. Here, the tip of the claw 27 of the bucket 25 is the tip of the bucket 25 opposite to the point where it is connected to the third drive shaft 52B. The tip of the claw 27 of the bucket 25 can also be said to be a specific point on the bucket 25. Furthermore, the tip of the claw 27 of the bucket 25 is the tip of the attachment 20 opposite to the first end 21A of the boom 21. The first end 21A of the boom 21 is the point where it is connected to the first drive shaft 32B in the attachment 20. In other words, the target distance L corresponds to the distance from the first drive shaft 32B to the tip of the attachment 20 opposite to the point where it is connected to the first drive shaft 32B in a specific plan view. The target distance L is an indicator showing the positional relationship between the first drive shaft 32B and thus the first axis 31J, and the tip of the claw 27 of the bucket 25. In step S30, the CPU 101 calculates the target distance L and also estimates the above positional relationship. The method for calculating the target distance L is described below.

[0052] Memory 102 pre-stores distance information as information for CPU 101 to calculate the target distance L. The distance information represents the relationship between the second angular position 23S and the third angular position 25S and the target distance L. In detail, the distance information represents the target distance L for various combinations of the second angular position 23S and the third angular position 25S. The distance information is composed of, for example, a table, a graph, or a mathematical formula. When CPU 101 calculates the target distance L, it applies the latest second angular position 23S and the latest third angular position 25S obtained in step S20 to the distance information to calculate the target distance L. Thus, in step S30, CPU 101 calculates the target distance L based on the second angular position 23S and the third angular position 25S. As shown in Figure 4, once CPU 101 has calculated the target distance L, it proceeds to step S40.

[0053] In step S40, the CPU 101 calculates the upper limit rotational speed W1U. The upper limit rotational speed W1U is the limit value for the rotational speed of the first drive shaft 32B. More specifically, the upper limit rotational speed W1U is a limit value that defines the upper limit of the rotational speed that is allowed for the first drive shaft 32B. The upper limit rotational speed W1U is the first limit value. In this step S40, the CPU 101 converts the upper limit peripheral speed Vmax stored in memory 102 into rotational speed, taking into account the target distance L calculated in step S30. Specifically, the CPU 101 first calculates a division value obtained by dividing the upper limit peripheral speed Vmax by the target distance L. Then, the CPU 101 calculates the upper limit rotational speed W1U by dividing this division value by a predetermined coefficient. The predetermined coefficient is a constant that takes into account unit conversions and pi, etc. For example, let's assume that the units of time are set to "1 minute" and the unit of length to "m", such as peripheral speed [m / min], target distance L [m], and rotational speed [ / min]. In this case, the predetermined coefficient is twice the value of pi. Not limited to this example, the predetermined coefficient may also be a value incorporated for correction to adjust the magnitude of the upper limit rotational speed W1U. Thus, the upper limit rotational speed W1U is a value corresponding to the division value obtained by dividing the upper limit peripheral speed Vmax by the target distance L.

[0054] The upper limit peripheral speed Vmax is the upper limit of the peripheral speed V predetermined for the tip of the tines 27 of the bucket 25. Here, as shown in Figure 6, a virtual circle centered on the first axis 31J in a specific plan view, with a radius of the target distance L, is called the specific virtual circle Q. The peripheral speed V at the tip of the tines 27 of the bucket 25 is the speed in the direction along the tangent to the specific virtual circle Q. The upper limit peripheral speed Vmax is the maximum peripheral speed V at which the attachment 20 can be considered protected when the tip of the tines 27 of the bucket 25 collides with the excavation target or obstacle. The upper limit peripheral speed Vmax is a value predetermined by experiment or simulation.

[0055] As described above, in step S40, the CPU 101 calculates the upper limit rotational speed W1U based on the upper limit peripheral speed Vmax and the target distance L calculated in step S30. Here, the upper limit rotational speed W1U is the reciprocal of the target distance L. Therefore, when the same upper limit peripheral speed Vmax is used, the CPU 101 calculates the upper limit rotational speed W1U as a smaller value as the target distance L increases. The target distance L is a value calculated based on the second angular position 23S and the third angular position 25S. In other words, the CPU 101 calculates the upper limit rotational speed W1U based on the second angular position 23S and the third angular position 25S through steps S30 and S40. These processes in steps S30 and S40 constitute the first process. As shown in Figure 4, after executing the process in step S40, the CPU 101 proceeds to step S50.

[0056] In step S50, the CPU 101 determines whether the first base rotational speed W1 obtained in step S10 is less than or equal to the upper limit rotational speed W1U calculated in step S40. If the first base rotational speed W1 is less than or equal to the upper limit rotational speed W1U (step S50: YES), the CPU 101 proceeds to step S60. In this case, in step S60, the CPU 101 sets the first base rotational speed W1 as the target rotational speed W1F for the first drive shaft 32B.

[0057] On the other hand, if in step S50 the first base rotational speed W1 is greater than the upper limit rotational speed W1U (step S50: NO), the CPU 101 proceeds to step S70. In this case, in step S70, the CPU 101 sets the upper limit rotational speed W1U as the target rotational speed W1F for the first drive shaft 32B. After calculating the target rotational speed W1F, the CPU 101 proceeds to step S80. In this way, through steps S50, S60, and S70, the CPU 101 sets the smaller of the first base rotational speed W1 and the upper limit rotational speed W1U as the target rotational speed W1F for the first drive shaft 32B.

[0058] In step S80, the CPU 101 controls the first electric motor 32 based on the target rotation speed W1F calculated in step S60 or step S70. Specifically, the CPU 101 controls the first electric motor 32 so that the target rotation speed W1F matches the actual rotation speed of the first drive shaft 32B. Here, in conjunction with the processing in steps S50, S60, and S70, the target rotation speed W1F is less than or equal to the upper limit rotation speed W1U. Therefore, in step S80, the CPU 101 controls the first electric motor 32 so that the rotation speed of the first drive shaft 32B is less than or equal to the upper limit rotation speed W1U. The CPU 101 continues the processing in step S80 until the termination condition is met. An example of a termination condition is that a predetermined first control period has elapsed since the start of step S80. The first control period is, for example, a few seconds. The first control period should be a period suitable for continuing the rotation of the boom 21 in various operations such as excavation. Another example of a termination condition is receiving a signal 90S from the control device 90 instructing the boom 21 to stop rotating. When the termination condition is met, the CPU 101 terminates the drive control. The processing in step S80 is the second process.

[0059] <Operation of the First Embodiment> As shown in Figure 6, the target distance L is the radius of rotation when the arm 23 and bucket 25 are rotated together with the boom 21 around the first drive shaft 32B as the center of rotation. When the target distance L increases, the peripheral speed V at the tip of the tine 27 increases for the same rotational speed of the first drive shaft 32B. Along with this, the kinetic energy near the tip of the tine 27 increases. In this case, when the tip of the tine 27 collides with the object to be excavated or an obstacle, a large amount of energy is applied, which leads to the problem of a larger impact being applied to the attachment 20.

[0060] Therefore, in drive control, the CPU 101 reduces the upper limit rotational speed W1U as the target distance L, which is the turning radius, increases (step S40). Then, the CPU 101 controls the first electric motor 32 so that the rotational speed of the first drive shaft 32B is less than or equal to the upper limit rotational speed W1U (steps S50 to S80). In this way, by suppressing the rotational speed of the first drive shaft 32B according to the target distance L, the CPU 101 can keep the peripheral speed V at the tip of the claw 27 of the bucket 25 below the upper limit peripheral speed Vmax, regardless of the size of the target distance L.

[0061] <Effects of the First Embodiment> (1-1) As described in the section on the operation of the embodiment, the CPU 101 of this embodiment can suppress the peripheral speed V of the tip of the claw 27 of the bucket 25, regardless of the size of the target distance L. As a result, the CPU 101 can mitigate the impact applied to the attachment 20 when the bucket 25 collides with the object to be excavated or an obstacle.

[0062] (1-2) In the first process of step S40, the CPU 101 converts the upper limit peripheral speed Vmax into rotational speed by dividing the upper limit peripheral speed Vmax by the target distance L. By limiting the rotational speed of the first drive shaft 32B so that it is less than or equal to this converted value, the upper limit rotational speed W1U, the CPU 101 can reliably keep the peripheral speed V at the tip of the claw 27 below the upper limit peripheral speed Vmax.

[0063] (1-3) The target distance L, which is the turning radius of the bucket 25, changes depending on the orientation of the attachment 20. In the first process of step S30, the CPU 101 of this embodiment calculates the target distance L based on the angular position of each movable member that reflects the orientation of the attachment 20. In this way, the CPU 101 can accurately calculate the target distance L, and therefore the upper limit rotation speed W1U, according to the orientation of the attachment 20.

[0064] (1-4) Excavators 10 often perform operations that involve colliding the attachment 20 with objects such as soil and sand. Therefore, applying the drive control of this embodiment to the excavator 10 is particularly effective because it increases the opportunities to utilize the technology of this embodiment to mitigate the impact applied to the attachment 20.

[0065] <Second Embodiment> The following describes a second embodiment of the drive system, control device, control method, and control program for the work machine. In this embodiment, the drive control differs from that of the first embodiment. Aside from this, the content of the second embodiment is basically the same as that of the first embodiment. The following description of the second embodiment will mainly focus on the differences from the first embodiment, and parts that overlap with the content of the first embodiment will be omitted or simplified as appropriate.

[0066] The drive control in this embodiment is for the first electric motor 32, the second electric motor 42, and the third electric motor 52. In the drive control, the CPU 101 performs the rotational drive of the boom 21 by the first electric motor 32, the rotational drive of the arm 23 by the second electric motor 42, and the rotational drive of the bucket 25 by the third electric motor 52 in parallel. Note that the drive control in this embodiment is an extension of the drive control of the first embodiment for three electric motors, and the basic concept is the same as the drive control of the first embodiment. For this reason, the drive control will be described in a simplified manner below.

[0067] For example, when the CPU 101 receives a signal 90S from the control device 90 instructing the rotation of the boom 21, arm 23, and bucket 25, it starts drive control. As shown in Figure 5, when the CPU 101 starts drive control, it first performs the process in step S110.

[0068] In step S110, the CPU 101 obtains the latest first base rotation speed W1, the latest second base rotation speed W2, and the latest third base rotation speed W3. Each base rotation speed W1, W2, and W3 is calculated by a base value calculation process according to the operation of the control device 90 by the operator. Similar to the first base rotation speed W1, the second base rotation speed W2 and the third base rotation speed W3 are below the physical limit values ​​of the rotation speed of their respective drive shafts 42B and 52B. Once the CPU 101 obtains each base rotation speed W1, W2, and W3, it proceeds to step S120.

[0069] In step S120, the CPU 101 obtains the latest first angular position 21S, the latest second angular position 23S, and the latest third angular position 25S. After this, the CPU 101 proceeds to step S130.

[0070] In step S130, CPU 101 calculates the target distance L in the same manner as in step S30 of the first embodiment. After processing in step S130, CPU 101 proceeds to step S140.

[0071] In step S140, the CPU 101 calculates the first upper limit rotational speed W1U, the second upper limit rotational speed W2U, and the third upper limit rotational speed W3U. The first upper limit rotational speed W1U is a limit value that defines the upper limit of the rotational speed allowed for the first drive shaft 32B. The second upper limit rotational speed W2U is a limit value that defines the upper limit of the rotational speed allowed for the second drive shaft 42B. The third upper limit rotational speed W3U is a limit value that defines the upper limit of the rotational speed allowed for the third drive shaft 52B. The first upper limit rotational speed W1U is the first limit value. The second upper limit rotational speed W2U is the second limit value. The third upper limit rotational speed W3U is the third limit value. In step S140, the CPU 101 reduces the first upper limit rotational speed W1U, the second upper limit rotational speed W2U, and the third upper limit rotational speed W3U as the target distance L increases. The CPU 101 appropriately sets the first upper limit rotation speed W1U, the second upper limit rotation speed W2U, and the third upper limit rotation speed W3U using relational formulas determined based on experiments or simulations. At this time, the CPU 101 controls each of the electric motors 32, 42, and 52 in the subsequent step S160 so that the peripheral speed V at the tip of the claw 27 of the bucket 25 is less than or equal to the upper limit peripheral speed Vmax. For example, the CPU 101 may calculate the first upper limit rotation speed W1U using the same method as in step S40 of the first embodiment. When calculating each upper limit rotation speed W1U, W2U, and W3U, the CPU 101 may adjust each upper limit rotation speed W1U, W2U, and W3U based on the angular positions 21S, 23S, and 25S obtained in step S110. Once the CPU 101 has calculated each upper limit rotation speed W1U, W2U, and W3U, it proceeds to step S150. In steps S130 and S140, the CPU 101 calculates the upper limits of rotational speeds W1U, W2U, and W3U based on the target distance L calculated from the second angular position 23S and the third angular position 25S. These processes in steps S130 and S140 constitute the first process.

[0072] In step S150, the CPU 101 calculates the first target rotational speed W1F, the second target rotational speed W2F, and the third target rotational speed W3F. The first target rotational speed W1F is the target rotational speed of the first drive shaft 32B. The second target rotational speed W2F is the target rotational speed of the second drive shaft 42B. The third target rotational speed W3F is the target rotational speed of the third drive shaft 52B. The CPU 101 calculates each target rotational speed W1F, W2F, and W3F in the same manner as in steps S50 to S70 of the first embodiment. That is, the CPU 101 sets the first target rotational speed W1F to the smaller of the first base rotational speed W1 and the first upper limit rotational speed W1U. The CPU 101 sets the second target rotational speed W2F to the smaller of the second base rotational speed W2 and the second upper limit rotational speed W2U. The CPU 101 sets the third target rotation speed W3F to the smaller of the third base rotation speed W3 and the third upper limit rotation speed W3U. Note that if the base rotation speed and the upper limit rotation speed are the same, the CPU 101 should use the base rotation speed as the target rotation speed. As a result of setting each target rotation speed W1F, W2F, and W3F in this way, each target rotation speed W1F, W2F, and W3F will be less than or equal to their respective upper limits W1U, W2U, and W3U. After calculating each target rotation speed W1F, W2F, and W3F, the CPU 101 proceeds to step S160.

[0073] In step S160, the CPU 101 controls the respective electric motors 32, 42, and 52 based on the target rotational speeds W1F, W2F, and W3F. For example, for the second electric motor 42, the CPU 101 controls the second electric motor 42 so that the rotational speed of the second drive shaft 42B matches the second target rotational speed W2F. The same applies to the other two electric motors 32 and 52. In conjunction with the target rotational speeds W1F, W2F, and W3F calculated in step S150, the CPU 101 controls the electric motors 32, 42, and 52 as follows: The CPU 101 controls the first electric motor 32 so that the rotational speed of the first drive shaft 32B is less than or equal to the first upper limit rotational speed W1U. The CPU 101 controls the second electric motor 42 so that the rotational speed of the second drive shaft 42B is less than or equal to the second upper limit rotational speed W2U. The CPU 101 controls the third electric motor 52 so that the rotational speed of the third drive shaft 52B is less than or equal to the third upper limit rotational speed W3U. The CPU 101 continues the process of step S160 for a predetermined second control period. An example of the second control period is a few seconds. The CPU 101 terminates the process of step S160 after the second control period has elapsed since the start of the process of step S160. The process of step S160 is the second process.

[0074] When CPU 101 finishes processing in step S160, it returns to processing in step S110. Then, CPU 101 repeats the processing from step S110 onward. In this way, CPU 101 repeats the processing from step S110 to step S160. If a termination condition is met during this repetition, CPU 101 terminates the drive control. An example of a termination condition is receiving a signal 90S from the control device 90 instructing the boom 21, arm 23, and bucket 25 to stop rotating.

[0075] <Operation and Effects of the Second Embodiment> The configuration of this embodiment provides the same effects as (1-1) to (1-4). Furthermore, the configuration of this embodiment also provides the following effects.

[0076] (2-1) In this embodiment, the CPU 101 drives three drive shafts 32B, 42B, and 52B to operate the boom 21, arm 23, and bucket 25 in parallel. In this case, the target distance L changes sequentially according to the changes in the positions of the boom 21, arm 23, and bucket 25. Under these circumstances, the CPU 101 decreases the first upper limit rotation speed W1U of the first drive shaft 32B, the second upper limit rotation speed W2U of the second drive shaft 42B, and the third upper limit rotation speed W3U of the third drive shaft 52B as the target distance L increases. By setting each upper limit rotation speed W1U, W2U, and W3U in accordance with the change in target distance L in this way, the peripheral speed V of the tip of the claw 27 can be suppressed even when the trajectory of the tip of the claw 27 changes freely.

[0077] <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.

[0078] The upper limit peripheral speed Vmax is not limited to the examples of the above embodiment. Depending on the work performed by the excavator 10, it may be desirable to limit the peripheral speed V at the tip of the tines 27 for purposes other than protecting the attachment 20. In such cases, an appropriate value may be set to the upper limit peripheral speed Vmax as needed. Furthermore, the upper limit peripheral speed Vmax is not limited to one value, but may have multiple predetermined values. That is, the memory 102 may store multiple upper limit peripheral speed Vmax values ​​to match various work performed by the excavator 10, for example. In this case, in step S40 of the first embodiment, the CPU 101 can select one of these multiple upper limit peripheral speed Vmax values ​​to calculate the upper limit rotational speed W1U.

[0079] The method for calculating the first limit value is not limited to the examples of each embodiment described above. The first limit value should be smaller when the target distance L is a first value than when the target distance L is a second value. The second value is smaller than the first value. It is not essential that the first limit value decreases as the target distance L increases. For example, the first limit value may change in steps with respect to the target distance L. It is not essential to use the upper limit peripheral speed Vmax of the tip of the tines 27 of the bucket 25 when calculating the first limit value. An appropriate calculation method may be adopted so that the peripheral speed V of the tip of the tines 27 can be suppressed regardless of the length of the target distance L. In that case, it is sufficient that the first limit value is calculated based on at least the information of the second angular position 23S.

[0080] Regarding the second embodiment, the method for calculating the second and third limit values ​​is not limited to the example above. Similar to the first limit value, it is not essential to calculate the second and third limit values ​​such that the value decreases as the target distance L increases. Furthermore, at least one of the second and third limit values ​​may be abolished. For example, by setting the first limit value strictly, it may be possible to suppress the peripheral speed V at the tip of the claw 27 even if the second and third limit values ​​are abolished.

[0081] The electric motors to be driven in the drive control are not limited to the examples of the embodiments described above. For example, in the drive control, two of the three electric motors 32, 42, and 52, the first electric motor 32 and the second electric motor 42, may be driven. The boom 21 and the arm 23 may then be rotated. In this case, setting both the first limit value and the second limit value is suitable for suppressing the peripheral speed V at the tip of the claw 27. In this case, as in the second embodiment, it is conceivable to calculate both the first limit value and the second limit value such that the value decreases as the target distance L increases.

[0082] In the drive control, two of the three electric motors 32, 42, and 52, specifically the second electric motor 42 and the third electric motor 52, may be driven. This may then rotate the arm 23 and the bucket 25. In this case, the arm 23 constitutes the first movable member, and the arm actuator 41 constitutes the first electric actuator. The bucket 25 constitutes the second movable member, and the bucket actuator 51 constitutes the second electric actuator. In such a configuration, for example, the target distance may be the distance from the second axis 41J to the tip of the claw 27 of the bucket 25 in a specific planar view. At the same time, this target distance may be calculated based on the third angular position 25S, and the limit value of the second drive shaft 42B may be calculated according to the target distance L.

[0083] As described in the above modification examples, the member treated as the first movable member and the member treated as the second movable member of the attachment 20 can be changed as appropriate. Depending on which member is treated as the first movable member, the actuator constituting the first electric actuator may change. If the first movable member is changed from the example of the above embodiment, the first electric actuator may be an actuator that rotates the first movable member. Similarly, depending on which member is treated as the second movable member, the actuator constituting the second electric actuator may change. The second electric actuator may be an actuator that rotates the second movable member. Furthermore, if another movable member different from the first movable member is connected to the second movable member, this movable member may be treated as the third movable member. Then, the actuator that rotates this third movable member may be treated as the third electric actuator.

[0084] • Instead of rotational speed, angular velocity, which is the change in the angular position of the drive shaft per unit time, may be used as the rotational speed of each drive shaft 32B, 42B, and 52B. In this case, each limit value should be expressed using angular velocity.

[0085] The overall configuration of the attachment 20 is not limited to the examples of each embodiment described above. The attachment 20 may be configured by adopting appropriate movable members depending on the work. For example, something other than the bucket 25 may be adopted as the third movable member. Depending on the third movable member adopted, the end of the third movable member opposite to the connection point with the third output shaft may change. Accordingly, the end of the attachment 20 opposite to the connection point with the first output shaft may also change. The third movable member may be eliminated. The attachment 20 only needs to have two or more movable members. If the third movable member is eliminated, the end of the attachment 20 opposite to the connection point with the first output shaft will be composed of the second movable member.

[0086] - Instead of the first drive shaft 32B of the first electric motor 32, the first output member 33C of the first reduction gear 33 may be treated as the first output shaft. In this case, the values ​​of each parameter, such as base rotational speed, upper limit rotational speed, and target rotational speed, which were determined for the first drive shaft 32B, should be converted to values ​​corresponding to the first output member 33C, taking into account the reduction ratio of the first reduction gear 33. Similarly, instead of the second drive shaft 42B of the second electric motor 42, the output member 43C of the second reduction gear 43 may be treated as the second output shaft. Instead of the third drive shaft 52B of the third electric motor 52, the output member 53C of the third reduction gear 53 may be treated as the third output shaft.

[0087] The shape of the first drive shaft 32B of the first electric motor 32 and the shape of the output member 33C of the first reduction gear 33 are not limited to a cylindrical shape. The first drive shaft 32B and the output member 33C only need to be shaped to transmit torque to the mating member. Similarly, the shape of the second drive shaft 42B of the second electric motor 42 and the output member 43C of the second reduction gear 43 are not limited to a cylindrical shape. The same applies to the shape of the third drive shaft 52B of the third electric motor 52 and the output member 53C of the third reduction gear 53.

[0088] The configuration of the boom actuator 31 is not limited to the examples of the embodiments described above. The boom actuator 31 only needs to include an electric motor and be able to drive the rotation of the boom 21. For example, the first reduction gear 33 may be omitted from the boom actuator 31. Furthermore, the boom actuator 31 is not limited to outputting torque coaxial with the drive shaft of the electric motor to the outside.

[0089] The mounting configuration of the boom actuator 31 to the boom 21 and swing bracket 17 is not limited to the examples of the above embodiments. Any mounting configuration is acceptable as long as the boom actuator 31 can rotate the boom 21. For example, the orientation of the boom actuator 31 between the second swing wall 17B of the swing bracket 17 and the boom 21 may be reversed. That is, the boom actuator 31 may be mounted to the boom 21 and swing bracket 17 such that the first reduction gear 33 is located closer to the second swing wall 17B and the first electric motor 32 is located closer to the boom 21.

[0090] Similar to the above examples of modifications to the boom actuator 31, the configuration and mounting of the arm actuator 41 are not limited to the examples of each embodiment described above. The arm actuator 41 only needs to include an electric motor and be able to drive the rotation of the arm 23.

[0091] Similar to the above examples of modifications to the boom actuator 31, the configuration and mounting of the bucket actuator 51 are not limited to the examples of each embodiment described above. The bucket actuator 51 only needs to include an electric motor and be able to drive the rotation of the bucket 25.

[0092] The configuration of the upper body 14 is not limited to the example of the upper embodiment. For example, the cabin may be eliminated from the upper body 14. The shape of the main housing portion 14A and the front housing portion 14B may be other than a rectangular parallelepiped. The upper body 14 only needs to be configured to realize the necessary functions, such as housing various equipment.

[0093] As shown in the above example of modification, the operating equipment 90 may be removed from the upper body 14 in conjunction with the removal of the cabin from the upper body 14. At the same time, various signals that instruct the operation of the excavator 10 to the control device 100 may be transmitted wirelessly from equipment outside the vehicle body 15.

[0094] The components included in the drive system of the excavator 10 are not limited to the examples of the above embodiment. For example, the attachment 20 may be treated as a component not included in the drive system. The drive system may include the drive unit 30 and the control device 100.

[0095] The overall configuration of the vehicle body 15 and, by extension, the excavator 10 is not limited to the examples of each embodiment described above. For example, the overall shape of the vehicle body 15 may be changed from the examples of the embodiments as a result of changing the shape of the upper body 14, as in the modified example described above. It is sufficient that the excavator 10 as a whole is configured to perform the required work, such as excavation.

[0096] • 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.

[0097] 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.

[0098] (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.

[0099] (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.

[0100] 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.

[0101] 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]

[0102] 10... Excavator 20... Attachments 21... Boom 23... Arm 25… Bucket 30…Drive unit 31…Boom actuator 32B...First drive shaft 41…Actuator for arm 42B...Second drive shaft 51…Actuator for bucket 52B...Third drive shaft 100...Control device 102A... Control program L...Target distance Vmax… Maximum speed per week

Claims

1. This is applied to a work machine equipped with an attachment having a first movable member and a second movable member rotatably connected to the first movable member. A drive unit comprising a first electric actuator having a first output shaft for rotating the first movable member, and a second electric actuator having a second output shaft for rotating the second movable member, The system includes a control device for controlling the drive unit, The control device is A first process for calculating a limit value for the rotational speed of the first output shaft based on the relative position of the second movable member with respect to the first movable member, A second process is performed to control the first electric actuator so that the rotational speed of the first output shaft is less than or equal to the limit value. In the first process, when the distance from the first output shaft to the tip of the attachment opposite to the connection point with the first output shaft is a first value, the limit value is reduced compared to when the distance is a second value which is smaller than the first value. A drive system for industrial machinery.

2. When the upper limit of the peripheral speed with respect to the tip of the attachment is defined as the upper limit peripheral speed, In the first process, the control device calculates a limit value corresponding to the division value obtained by dividing the predetermined upper limit peripheral speed by the distance. A drive system for a work machine according to claim 1.

3. The attachment has a third movable member that is rotatably connected to the second movable member, The drive unit has a third electric actuator having a third output shaft for rotating the third movable member, The tip of the attachment is the tip of the third movable member opposite to the connection point with the third output shaft. The control device is In the first process, the limit value is calculated based on the relative position of the second movable member with respect to the first movable member, and the relative position of the third movable member with respect to the second movable member. A drive system for a work machine according to claim 1.

4. When the aforementioned limit value is defined as the first limit value, The control device is In the first process described above, Based on the relative position of the second movable member with respect to the first movable member, and the relative position of the third movable member with respect to the second movable member, the first limit value, the second limit value which is the limit value for the rotational speed of the second output shaft, and the third limit value which is the limit value for the rotational speed of the third output shaft are calculated. In the second process, the first electric actuator is controlled so that the rotational speed of the first output shaft is less than or equal to the first limit value, the second electric actuator is controlled so that the rotational speed of the second output shaft is less than or equal to the second limit value, and the third electric actuator is controlled so that the rotational speed of the third output shaft is less than or equal to the third limit value. In the first process, when the distance between the first output shaft and the tip of the attachment is a first value, the first limit value, the second limit value, and the third limit value are reduced compared to when the distance is a second value. A drive system for a work machine according to claim 3.

5. The work machine is a construction machine, The first movable member is a boom, The second movable member is an arm, The third movable member is a bucket. A drive system for a work machine according to claim 3.

6. An attachment having a first movable member and a second movable member rotatably connected to the first movable member, This is applied to a work machine comprising a drive unit having a first electric actuator having a first output shaft for rotating the first movable member, and a second electric actuator having a second output shaft for rotating the second movable member. A first process for calculating a limit value for the rotational speed of the first output shaft based on the relative position of the second movable member with respect to the first movable member, A second process is performed to control the first electric actuator so that the rotational speed of the first output shaft is less than or equal to the limit value. In the first process, when the distance from the first output shaft to the tip of the attachment opposite to the connection point with the first output shaft is a first value, the limit value is reduced compared to when the distance is a second value which is smaller than the first value. Control device for industrial machinery.

7. An attachment having a first movable member and a second movable member rotatably connected to the first movable member, A control device applied to a work machine comprising a drive unit having a first electric actuator having a first output shaft for rotating the first movable member, and a second electric actuator having a second output shaft for rotating the second movable member, A first process for calculating a limit value for the rotational speed of the first output shaft based on the relative position of the second movable member with respect to the first movable member, A second process is performed to control the first electric actuator so that the rotational speed of the first output shaft is less than or equal to the limit value. In the first process, when the distance from the first output shaft to the tip of the attachment opposite to the connection point with the first output shaft is a first value, the limit value is reduced compared to when the distance is a second value which is smaller than the first value. A method for controlling industrial machinery.

8. An attachment having a first movable member and a second movable member rotatably connected to the first movable member, A control device applied to a work machine comprising a drive unit having a first electric actuator having a first output shaft for rotating the first movable member, and a second electric actuator having a second output shaft for rotating the second movable member, A first process for calculating a limit value for the rotational speed of the first output shaft based on the relative position of the second movable member with respect to the first movable member, A second process is performed to control the first electric actuator so that the rotational speed of the first output shaft is less than or equal to the limit value. In the first process, when the distance from the first output shaft to the tip of the attachment opposite to the connection point with the first output shaft is a first value, the limit value is made smaller compared to when the distance is a second value which is smaller than the first value. Control program for industrial machinery.

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