System and method for controlling work machine

Abstract

A system for controlling a work machine includes a position sensor that outputs position data indicating a position of the work machine, and a controller that acquires the position data from the position sensor. The controller acquires current topography data indicating current topography of a work site, acquires a target design surface at least a part of which is located below the current topography, sequentially determines a target excavation surface upward from the target design surface, determines a plurality of excavation paths that each extends in a predetermined work direction on the target excavation surface and is arranged in a direction intersecting the predetermined work direction, and controls the work machine according to the plurality of excavation paths.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a U.S. National stage application of International Application No. PCT / JP2023 / 042672, filed on Nov. 29, 2023. This U.S. National stage application claims priority under 35 U.S.C. § 119(a) to Japanese Patent Application No. 2023-023305, filed in Japan on Feb. 17, 2023. The entire contents of Japanese Patent Application No. 2023-023305 is hereby incorporated herein by reference.BACKGROUNDTechnical Field

[0002] The present disclosure relates to a system and method for controlling a work machine.Background Art

[0003] Some work machines perform a ground leveling work. For example, in a mine, bulk pushing is performed after earth and sand in a prescribed section are crushed by blasting. The bulk pushing is a work of excavating the ground surface and carrying excavated earth and sand to a predetermined soil discharging position. As the bulk pushing is repeated, the ground surface is gradually lowered. Immediately after earth and sand are crushed by blasting, the ground surface is uneven. Therefore, a ground leveling work for leveling the ground surface is performed. Alternatively, in a work site other than a mine, a ground leveling work may be performed by a work machine.

[0004] For example, JP 2021-101078 A discloses a technique for performing a ground leveling work by automatic control of a work machine. In the technique, a controller of the work machine sequentially determines a temporary excavation surface from above current topography toward a target design surface. The controller determines a portion located above the temporary excavation surface in the current topography as the target excavation portion. The controller calculates a soil amount of the target excavation portion. The controller determines whether the soil amount of the target excavation portion is equal to or more than a threshold. The controller determines the temporary excavation surface as the target excavation surface if the soil amount of the target excavation portion is equal to or more than the threshold. The controller controls the work machine according to the target excavation surface. As a result, the target excavation portion is excavated so that a ground leveling work is performed.SUMMARY

[0005] According to the automatic control of the work machine described above, a ground leveling work can be easily performed by the work machine even if the operator is not skilled. However, more efficiently performing a ground leveling work by the work machine is required. An object of the present disclosure is to efficiently perform a ground leveling work by automatic control of a work machine.

[0006] A system according to one aspect of the present disclosure is a system for controlling a work machine, and includes a position sensor and a controller. The position sensor outputs position data indicating the position of the work machine. The controller acquires the position data from the position sensor. The controller acquires current topography data indicating current topography of a work site. The controller acquires a target design surface at least a part of which is located below the current topography. The controller sequentially determines a target excavation surface upward from the target design surface. The controller determines a plurality of excavation paths that each extends in a predetermined work direction on the target excavation surface and is arranged in a direction intersecting the predetermined work direction. The controller controls the work machine according to the plurality of excavation paths.

[0007] A method according to another aspect of the present disclosure is a method for controlling a work machine, and includes: acquiring current topography data indicating current topography of a work site; acquiring a target design surface at least a part of which is located below the current topography; sequentially determining a target excavation surface upward from the target design surface; determining a plurality of excavation paths that each extends in a predetermined work direction on the target excavation surface and is arranged in a direction intersecting the predetermined work direction; and controlling the work machine according to the plurality of excavation paths.

[0008] According to the present disclosure, a ground leveling work can be efficiently performed by automatic control of a work machine.BRIEF DESCRIPTION OF DRAWINGS

[0009] Referring now to the attached drawings which form a part of this original disclosure, an illustrative embodiment is shown.

[0010] FIG. 1 is a perspective view illustrating a work machine according to an embodiment.

[0011] FIG. 2 is a block diagram illustrating a configuration of a drive system and a control system of the work machine.

[0012] FIG. 3 is a side view illustrating an example of current topography of a work site.

[0013] FIG. 4 is a flowchart illustrating processing of automatic control of the work machine.

[0014] FIG. 5 is a side view illustrating an example of current topography and a target design surface.

[0015] FIG. 6 is a diagram illustrating a method of determining a temporary excavation surface.

[0016] FIG. 7 is a diagram illustrating a method of determining the temporary excavation surface.

[0017] FIG. 8 is a diagram illustrating a method of determining a target excavation surface.

[0018] FIG. 9 is a diagram illustrating a method of determining the target excavation surface.

[0019] FIG. 10 is a diagram illustrating an example of excavation paths.

[0020] FIG. 11 is a diagram illustrating a method of determining a target excavation surface according to a modification.DETAILED DESCRIPTION OF EMBODIMENT(S)

[0021] Hereinafter, a control system and a control method for a work machine according to an embodiment will be described with reference to the drawings. FIG. 1 is a perspective view illustrating a work machine 1 according to the embodiment. The work machine 1 according to the present embodiment is a bulldozer. The work machine 1 includes a vehicle body 11 and a work implement 13.

[0022] The vehicle body 11 includes a traveling device 12, a cab 14, and a drive source chamber 15. A driver's seat (not illustrated) is disposed in the cab 14. The drive source chamber 15 is disposed in front of the cab 14. The traveling device 12 is attached to a lower portion of the vehicle body 11. The traveling device 12 includes a pair of left and right crawler belts 16. In FIG. 1, only the left crawler belt 16 is illustrated. The work machine 1 travels by rotation of the crawler belts 16.

[0023] The work implement 13 is attached to the vehicle body 11. The work implement 13 includes a lift frame 17, a blade 18, and lift cylinders 19A and 19B. The lift frame 17 is attached to the vehicle body 11 so as to be movable up and down. The lift frame 17 supports the blade 18.

[0024] The blade 18 is disposed in front of the vehicle body 11. The blade 18 moves up and down as the lift frame 17 moves up and down. The lift cylinders 19A and 19B are connected to the vehicle body 11 and the blade 18. The lift cylinders 19A and 19B may be connected to the lift frame 17. When the lift cylinders 19A and 19B extend and contract, the blade 18 moves up and down.

[0025] FIG. 2 is a block diagram illustrating a configuration of a drive system 2 and a control system 3 of the work machine 1. As illustrated in FIG. 2, the drive system 2 includes a drive source 22, a hydraulic pump 23, and a power transmission device 24. The drive source 22 is, for example, an internal combustion engine. However, the drive source 22 may include an electric motor.

[0026] The hydraulic pump 23 is driven by the drive source 22 and discharges hydraulic oil. The hydraulic oil discharged from the hydraulic pump 23 is supplied to a hydraulic actuator 25. The hydraulic actuator 25 includes the lift cylinder 19 described above. Although one hydraulic pump 23 is illustrated in FIG. 2, a plurality of hydraulic pumps may be included.

[0027] A control valve 26 is disposed between the hydraulic actuator 25 and the hydraulic pump 23. The control valve 26 is a proportional control valve, and controls the flow rate of hydraulic oil supplied from the hydraulic pump 23 to the lift cylinder 19. The control valve 26 may be a pressure proportional control valve. Alternatively, the control valve 26 may be an electromagnetic proportional control valve.

[0028] The power transmission device 24 transmits the driving force of the drive source 22 to the traveling device 12. The power transmission device 24 may be, for example, a torque converter or a transmission including a plurality of transmission gears. Alternatively, the power transmission device 24 may be a power transmission device of another system such as a hydro static transmission (HST).

[0029] The control system 3 includes a controller 31, a machine position sensor 32, a communication device 33, a storage 34, and an input device 35. The controller 31 is programmed so as to control the work machine 1 on the basis of acquired data. The controller 31 includes a memory 38 and a processor 39. The memory 38 includes, for example, a random access memory (RAM) and a read only memory (ROM). The storage 34 includes, for example, a semiconductor memory, a hard disk, or the like. The memory 38 and the storage 34 record computer commands and data for controlling the work machine 1.

[0030] The processor 39 is, for example, a CPU, but may be another type of processor. The processor 39 executes processing for controlling the work machine 1 on the basis of computer commands and data stored in the memory 38 or the storage 34. The communication device 33 is, for example, a module for wireless communication, and communicates with a device outside the work machine 1. The communication device 33 may use a mobile communication network. Alternatively, the communication device 33 may use another network such as a local area network (LAN) or the Internet.

[0031] The machine position sensor 32 detects the position of the work machine 1. The machine position sensor 32 includes, for example, a global navigation satellite system (GNSS) receiver such as a global positioning system (GPS). The machine position sensor 32 is included in the vehicle body 11. Alternatively, the machine position sensor 32 may be included at another position such as the work implement 13. The controller 31 acquires current position data indicating the current position of the work machine 1 from the machine position sensor 32.

[0032] The input device 35 can be operated by an operator. The input device 35 includes, for example, a touch screen. Alternatively, the input device 35 may include another operator such as a hard key. The input device 35 receives an operation by the operator and outputs a signal indicating the operation by the operator to the controller 31.

[0033] The controller 31 controls the drive source 22, the hydraulic pump 23, the power transmission device 24, and the control valve 26 by outputting command signals to these devices. For example, the controller 31 operates the hydraulic actuator 25 by controlling the capacity of the hydraulic pump 23 and the opening degree of the control valve 26. As a result, the controller 31 operates the work implement 13.

[0034] The controller 31 causes the work machine 1 to travel by controlling the rotational speed of the drive source 22 and the power transmission device 24. For example, in a case where the power transmission device 24 is the HST, the controller 31 controls the capacity of the hydraulic pump and the capacity of the hydraulic motor of the HST. In a case where the power transmission device 24 is a transmission including a plurality of transmission gears, the controller 31 controls an actuator for gear shift. Furthermore, the controller 31 controls the power transmission device 24 such that a speed difference occurs between the left and right crawler belts 16, thereby turning the work machine 1.

[0035] Next, automatic control of the work machine 1 executed by the controller 31 will be described. The controller 31 causes the work machine 1 to automatically travel by controlling the drive source 22 and the power transmission device 24. Furthermore, the controller 31 automatically controls the work implement 13 by controlling the drive source 22, the hydraulic pump 23, and the control valve 26.

[0036] Hereinafter, automatic control of a ground leveling work performed by the work machine 1 at the work site will be described. FIG. 3 is a side view of current topography 40 of the work site. FIG. 4 is a flowchart illustrating processing of automatic control of the work machine 1. As illustrated in FIG. 4, in step S101, the controller 31 acquires current position data. The controller 31 acquires the current position data of the work machine 1 from the machine position sensor 32.

[0037] In step S102, the controller 31 acquires current topography data. The current topography data is data indicating the current topography 40 of the work site. For example, the current topography data includes plane coordinates and a height of a surface of the current topography 40. The current topography data may be stored in the storage 34 in advance. The controller 31 may acquire the current topography data by recording the locus of the bottom portion of the work implement 13 or the traveling device 12. Alternatively, the current topography data may be measured by lidar (laser imaging detection and ranging [LIDAR]) or a measuring device such as a camera. The controller 31 may acquire the current topography data from the measuring device. The measuring device may be included in the work machine 1. The measuring device may be disposed outside the work machine 1.

[0038] In step S103, the controller 31 acquires a target design surface 50. As illustrated in FIG. 3, at least a part of the target design surface 50 is located below the current topography 40. The target design surface 50 indicates the shape of the target topography by a work of the work machine 1. The target design surface 50 may be predetermined and stored in the storage 34. The target design surface 50 may be input by an operator via the input device 35. Alternatively, the controller 31 may acquire the target design surface 50 from an external computer via the communication device 33.

[0039] Specifically, the target design surface 50 includes a final design surface 51, a low wall design surface 52, a high wall design surface 53, and a pivot point 54. The final design surface 51 is located at the bottom of the target design surface 50. The final design surface 51 extends in a predetermined work direction A1. The predetermined work direction A1 will be described below. The final design surface 51 is, for example, horizontal. However, the final design surface 51 may be inclined with respect to the horizontal direction.

[0040] The low wall design surface 52 extends upward from the final design surface 51 in the predetermined work direction A1. The low wall design surface 52 is inclined with respect to the final design surface 51. The high wall design surface 53 extends upward from the final design surface 51 in a direction opposite to the predetermined work direction A1. The high wall design surface 53 is inclined with respect to the final design surface 51. The pivot point 54 is determined on the basis of an intersection of the low wall design surface 52 and the current topography 40. For example, the pivot point 54 is an intersection of the low wall design surface 52 and the initial current topography 40.

[0041] In automatic control of a ground leveling work, the controller 31 excavates the current topography 40 such that the current topography 40 has the shapes of the high wall design surface 53 and the final design surface 51. The controller 31 stacks the excavated earth and sand on the current topography 40 such that the current topography 40 has the shape of the low wall design surface 52.

[0042] As illustrated in FIG. 3, the controller 31 determines a target excavation surface 60 on the basis of the target design surface 50. The target excavation surface 60 includes a plurality of target excavation surfaces 61 to 64 arranged in order upward from the final design surface 51. The controller 31 performs excavation by the work machine 1 according to the target excavation surfaces 61 to 64 in the order from the target excavation surface 64 located at the uppermost position to the target excavation surface 61 located at the lowermost position. Thereby, processing for determining the target excavation surface 60 to be excavated such that the current topography 40 has the shapes of the high wall design surface 53 and the final design surface 51 will be described below.

[0043] As illustrated in FIG. 4, in step S104, the controller 31 determines a temporary excavation surface. The controller 31 sequentially determines a temporary excavation surface upward from the target design surface 50.

[0044] Specifically, as illustrated in FIG. 5, the controller 31 determines a half straight line Lv1 that extends upward from an uppermost point 531 of the high wall design surface 53. Note that “upward” means upward in the direction of gravity. As illustrated in FIG. 6, the controller 31 determines straight lines Lh1 to Lh7 parallel to the final design surface 51 located at every predetermined height H1 upward from the final design surface 51. The predetermined height H1 is determined in a range of 0.5 m to 3.0 m, for example. The predetermined height H1 may be, for example, 1.2 m. The controller 31 determines intersections of the straight lines Lh1 to Lh7 with the high wall design surface 53 and the half straight line Lv1 as reference points R1 to R7. As illustrated in FIG. 7, the controller 31 determines a plane that connects the lowermost first reference point R1 and the pivot point 54 as a first temporary excavation surface 71.

[0045] In step S105, the controller 31 determines the target excavation surface 60. The controller 31 determines the target excavation surface 60 on the basis of the temporary excavation surface. Specifically, in a case where the inclination angle of the temporary excavation surface with respect to the horizontal direction is equal to or less than a predetermined angle threshold, the controller 31 determines the temporary excavation surface as the target excavation surface 60. For example, as illustrated in FIG. 7, in a case where an inclination angle θ1 of the first temporary excavation surface 71 with respect to the horizontal direction is equal to or less than the angle threshold, the controller 31 determines the first temporary excavation surface 71 as the first target excavation surface 61 illustrated in FIG. 8. The angle threshold is determined on the basis of, for example, an inclination angle at which the work machine 1 can travel. The angle threshold is determined, for example, in a range of 15 degrees to 30 degrees. The angle threshold may be, for example, 15 degrees.

[0046] In step S106, the controller 31 determines whether the target excavation surface 60 includes an intersection with the current topography 40. If the target excavation surface 60 includes an intersection with the current topography 40, the processing returns to step S104. By the processing of steps S104 to S106 being repeated, as illustrated in FIGS. 7 and 8, the controller 31 determines a second temporary excavation surface 72 that connects a second reference point R2 and the pivot point 54 as a second target excavation surface 62. The controller 31 determines a third temporary excavation surface 73 that connects a third reference point R3 and the pivot point 54 as a third target excavation surface 63.

[0047] On the other hand, in step S105, in a case where the inclination angle of the temporary excavation surface that passes through a certain reference point is larger than the angle threshold, the controller 31 determines a plane that passes through the reference point and is parallel to the temporary excavation surface located one level lower as the target excavation surface. For example, as illustrated in FIG. 7, in a case where an inclination angle θ4 of a fourth temporary excavation surface 74 that passes through a fourth reference point R4 is larger than the angle threshold, the controller 31 determines a plane that passes through the fourth reference point R4 and parallel to a third target excavation surface 63 as a fourth target excavation surface 64 as illustrated in FIG. 8.

[0048] As illustrated in FIG. 7, similarly for fifth to seventh temporary excavation surfaces 75 to 77, in a case where the inclination angle of each of the fifth to seventh temporary excavation surfaces 75 to 77 is larger than the angle threshold, the controller 31 determines planes that pass through fifth to seventh reference points R5 to R7 and are parallel to the third target excavation surface 63 as fifth to seventh target excavation surfaces 65 to 67 as illustrated in FIG. 8.

[0049] By the above processing being repeated, the controller 31 sequentially determines the next target excavation surfaces 62 to 67 upward from the target excavation surface 61 located at the lowermost position, and determines the target excavation surface 60 until there is no intersection of the target excavation surface 60 with the current topography 40. For example, as illustrated in FIG. 8, the seventh target excavation surface 67 does not include an intersection with the current topography 40. In this case, the controller 31 excludes the seventh target excavation surface 67 from the target excavation surface 60.

[0050] Furthermore, even in a case where a certain target excavation surface includes an intersection with the current topography 40, the controller 31 excludes the target excavation surface in a case where the height of the current topography 40 on the target excavation surface is equal to or less than a predetermined height threshold. For example, as illustrated in FIG. 8, if the height of a portion 41 of the current topography 40 on the sixth target excavation surface 66 is equal to or less than the height threshold, the controller 31 excludes the sixth target excavation surface 66 from the target excavation surface 60. Accordingly, as illustrated in FIG. 9, the controller 31 determines the first to fifth target excavation surfaces 61 to 65 as the target excavation surface 60. The predetermined height threshold is determined, for example, in a range of 0.5 m to 1.5 m. The predetermined height threshold may be, for example, 1.0 m. Alternatively, the predetermined height threshold may be determined on the basis of the predetermined height H1. The predetermined height threshold may be, for example, a half of the predetermined height H1.

[0051] Note that the height of the portion 41 of the current topography 40 may be a dimension in a direction perpendicular to the target excavation surface 60. Alternatively, the height of the portion 41 of the current topography 40 may be a dimension in the gravity direction. In step S106, if the target excavation surface 60 does not include an intersection with the current topography 40, the processing proceeds to step S108.

[0052] In step S108, the controller 31 determines a plurality of excavation paths P1 to P6. FIG. 10 is a top view of the current topography 40 of the work site. As illustrated in FIG. 10, the controller 31 determines the plurality of excavation paths P1 to P6 in a predetermined work area 100. Each of the excavation paths P1 to P6 extends in the predetermined work direction A1. The predetermined work area 100 and the predetermined work direction A1 are determined in advance and stored in the storage 34. Alternatively, the predetermined work area 100 and the predetermined work direction A1 may be determined by the operator via the input device 35.

[0053] The plurality of excavation paths P1 to P6 is arranged in the lateral direction. The lateral direction is a direction intersecting the predetermined work direction A1. For example, the controller 31 may determine the plurality of excavation paths P1 to P6 such that the plurality of excavation paths P1 to P6 is arranged at regular intervals in the lateral direction. Alternatively, the controller 31 may determine the plurality of excavation paths P1 to P6 in consideration of the amount of soil to be excavated. The controller 31 determines the plurality of excavation paths P1 to P6 such that the plurality of excavation paths P1 to P6 extends in the predetermined work direction A1 on each of the target excavation surface 61 to 65 and is arranged in the lateral direction.

[0054] In step S109, the controller 31 controls the work machine 1 according to the plurality of excavation paths P1 to P6. For example, the controller 31 advances the work machine 1 according to the first excavation path P1 and operates the work implement 13 according to the fifth target excavation surface 65 located at the uppermost position. In a case where excavation according to the first excavation path P1 is completed, the controller 31 retracts the work machine 1. Next, the controller 31 advances the work machine 1 according to the second excavation path P2 and operates the work implement 13 according to the fifth target excavation surface 65. Thereafter, similarly, the work machine 1 is advanced according to each of the remaining excavation paths P3 to P6, and the work implement 13 is operated according to the fifth target excavation surface 65 in each of the excavation paths P3 to P6. As a result, the current topography 40 in the work area 100 is excavated so as to have the shape of the fifth target excavation surface 65.

[0055] Next, the controller 31 advances the work machine 1 according to each of the excavation paths P1 to P6, and operates the work implement 13 according to the fourth target excavation surface 64 located below the fifth target excavation surface 65 in each of the excavation paths P1 to P6. As a result, the current topography 40 in the work area 100 is excavated so as to have the shape of the fourth target excavation surface 64. Hereinafter, a work similar to the work described above is sequentially repeated according to the third to first target excavation surfaces 63 to 61, and then excavation is performed to the final design surface 51. Although detailed description is omitted, the controller 31 transports earth and sand excavated by the excavation work and stacks the earth and sand such that the earth and sand have the shape of the low wall design surface 52. Through the above work, the shape of the current topography 40 becomes the shape of the target design surface 50.

[0056] In the control system and the control method of the work machine 1 according to the present embodiment described above, the target excavation surfaces 61 to 65 and the excavation paths P1 to P6 are determined as described above, and the work machine 1 is automatically controlled according to the target excavation surfaces 61 to 65 and the excavation paths P1 to P6. Therefore, aground leveling work can be easily performed by automatic control of the work machine 1.

[0057] Furthermore, the target excavation surfaces 61 to 65 are sequentially determined upward from the target excavation surface located below. The target excavation surface located below often has a larger area to be excavated. Therefore, since the target excavation surfaces 61 to 65 are determined from the one located below, excavation can be efficiently performed.

[0058] Although one embodiment of the present invention has been described above, the present invention is not limited to the above embodiment, and various modifications can be made without departing from the gist of the invention. The work machine 1 is not limited to a bulldozer, and may be another machine such as a wheel loader. The traveling device 12 is not limited to a crawler belt, and may include a tire. The work machine 1 may be a remotely steerable vehicle. In this case, the cab may be omitted from the work machine 1.

[0059] The controller 31 may include a plurality of controllers separated from each other. The above-described processing by the controller 31 may be executed in a distributed manner by a plurality of controllers.

[0060] A ground leveling work may be simultaneously performed by a plurality of work machines. In this case, controllers included in the plurality of work machines may autonomously execute processing for the ground leveling work. Alternatively, a controller common to the plurality of work machines may execute the processing for the ground leveling work on the plurality of work machines. The controller may execute the processing for a ground leveling work on the work machine remotely from the outside of the work machine.

[0061] The processing for performing a ground leveling work is not limited to the above-described processing, and may be changed. For example, a part of the above processing may be changed or omitted. Processing different from the above processing may be added to the processing for performing a ground leveling work.

[0062] For example, in the above embodiment, in a case where the inclination angle of the temporary excavation surface with respect to a certain reference point is larger than the angle threshold, the controller 31 determines a plane that passes through the reference point and is parallel to the temporary excavation surface one level below the temporary excavation surface as the target excavation surface. However, in a case where the inclination angle of the temporary excavation surface with respect to a certain reference point is larger than the angle threshold, the controller 31 may determine a plane that passes through the reference point and is inclined at the angle threshold with respect to the horizontal direction as the target excavation surface.

[0063] The number of reference points, the number of temporary excavation surfaces, the number of target excavation surfaces, or the number of excavation paths is not limited to those in the above embodiment, and may be changed. The method of determining the temporary excavation surface or the target excavation surface is not limited to that of the above embodiment, and may be changed. For example, as illustrated in FIG. 11, the controller 31 may determine planes that connect the reference points R1 to R5 on the high wall design surface 53 and the pivot point 54 as target excavation surfaces 61 to 65. Furthermore, the controller 31 may determine planes that passes through the reference points R6 and R7 on the half straight line Lv1 and are parallel to the closest target excavation surface 65 that passes through the reference point R5 on the high wall design surface 53 as the target excavation surfaces 66 and 67.

[0064] The controller 31 may determine a portion located above the temporary excavation surface in the current topography 40 as the target excavation portion. The controller 31 may calculate the height of the target excavation portion. In a case where the height of the target excavation portion is equal to or less than a predetermined height threshold, the controller 31 may determine the corresponding temporary excavation surface as the target excavation surface 60. The height threshold may be determined, for example, on the basis of the excavatable height of the blade.

[0065] According to the present disclosure, a ground leveling work can be efficiently performed by automatic control of a work machine.

Claims

1. A system for controlling a work machine, the system comprising:a position sensor that outputs position data indicating a position of the work machine; anda controller that acquires the position data from the position sensor, the controller being configured toacquire current topography data indicating current topography of a work site,acquire a target design surface at least a part of which is located below the current topography,sequentially determine a target excavation surface upward from the target design surface,determine a plurality of excavation paths that each extends in a predetermined work direction on the target excavation surface and is arranged in a direction intersecting the predetermined work direction, andcontrol the work machine according to the plurality of excavation paths.

2. The system according to claim 1, whereinthe target design surface includesa final design surface located at a bottom of the target design surface, anda high wall design surface that extends upward from the final design surface in a direction opposite to the predetermined work direction, andthe controllerdetermines a reference point on the high wall design surface located at every predetermined height upward from the final design surface,determines a temporary excavation surface that passes through the reference point, anddetermines the target excavation surface on a basis of the temporary excavation surface.

3. The system according to claim 1, whereinthe target design surface includesa final design surface located at a bottom of the target design surface, anda high wall design surface that extends upward from the final design surface in a direction opposite to the predetermined work direction, andthe controllerdetermines a half straight line that extends upward from an uppermost point of the high wall design surface,determines a temporary excavation surface that passes through a reference point on the high wall design surface located at every predetermined height upward from the final design surface and the half straight line, anddetermines the target excavation surface on a basis of the temporary excavation surface.

4. The system according to claim 2, whereinthe target design surface further includesa low wall design surface that extends upward from the final design surface in the predetermined work direction, anda pivot point at which the low wall design surface and the current topography intersect with each other, andthe controller determines a plane that connects the reference point and the pivot point as the temporary excavation surface.

5. The system according to claim 4, whereinthe controllerdetermines a plane that connects a first reference point on the high wall design surface and the pivot point as a first temporary excavation surface,determines a plane that connects a second reference point on the high wall design surface located at the predetermined height upward from the first reference point and the pivot point as a second temporary excavation surface,determines the first temporary excavation surface as a first target excavation surface in a case in which a first inclination angle of the first temporary excavation surface with respect to a horizontal direction is equal to or less than a predetermined angle threshold, andin a case in which a second inclination angle of the second temporary excavation surface with respect to a horizontal direction is larger than the angle threshold, determines a plane that passes through the second reference point and is parallel to the first temporary excavation surface as a second target excavation surface.

6. The system according to claim 4, whereinthe controllerdetermines a plane that connects a first reference point on the high wall design surface and the pivot point as a first temporary excavation surface,determines a plane that connects a second reference point on the high wall design surface located at the predetermined height upward from the first reference point and the pivot point as a second temporary excavation surface,determines the first temporary excavation surface as a first target excavation surface in a case in which a first inclination angle of the first temporary excavation surface with respect to a horizontal direction is equal to or less than a predetermined angle threshold, andin a case in which a second inclination angle of the second temporary excavation surface with respect to a horizontal direction is larger than the angle threshold, determines a plane that passes through the second reference point and is inclined at the angle threshold with respect to the horizontal direction as a second target excavation surface.

7. A method for controlling a work machine, the method comprising:acquiring current topography data indicating current topography of a work site;acquiring a target design surface at least a part of which is located below the current topography;sequentially determining a target excavation surface upward from the target design surface;determining a plurality of excavation paths that each extends in a predetermined work direction on the target excavation surface and is arranged in a direction intersecting the predetermined work direction; andcontrolling the work machine according to the plurality of excavation paths.

8. The method according to claim 7, whereinthe target design surface includesa final design surface located at a bottom of the target design surface; anda high wall design surface that extends upward from the final design surface in a direction opposite to the predetermined work direction, andthe method includes:determining a temporary excavation surface that passes through a reference point on the high wall design surface located at every predetermined height upward from the final design surface; anddetermining the target excavation surface on a basis of the temporary excavation surface.

9. The method according to claim 7, whereinthe target design surface includesa final design surface located at a bottom of the target design surface, anda high wall design surface that extends upward from the final design surface in a direction opposite to the predetermined work direction, andthe method includes:determining a half straight line that extends upward from an uppermost point of the high wall design surface;determining a temporary excavation surface that passes through a reference point on the high wall design surface located at every predetermined height upward from the final design surface and the half straight line; anddetermining the target excavation surface on a basis of the temporary excavation surface.

10. The method according to claim 8, whereinthe target design surface further includesa low wall design surface that extends upward from the final design surface in the predetermined work direction, anda pivot point at which the low wall design surface and the current topography intersect with each other, andthe method further includes determining a plane that connects the reference point and the pivot point as the temporary excavation surface.

11. The method according to claim 10, further comprising:determining a plane that connects a first reference point on the high wall design surface and the pivot point as a first temporary excavation surface;determining a plane that connects a second reference point on the high wall design surface located at the predetermined height upward from the first reference point and the pivot point as a second temporary excavation surface;determining the first temporary excavation surface as a first target excavation surface in a case in which a first inclination angle of the first temporary excavation surface with respect to a horizontal direction is equal to or less than a predetermined angle threshold; andin a case in which a second inclination angle of the second temporary excavation surface with respect to a horizontal direction is larger than the angle threshold, determining a plane that passes through the second reference point and is parallel to the first temporary excavation surface as a second target excavation surface.

12. The method according to claim 10, further comprising:determining a plane that connects a first reference point on the high wall design surface and the pivot point as a first temporary excavation surface;determining a plane that connects a second reference point on the high wall design surface located at the predetermined height upward from the first reference point and the pivot point as a second temporary excavation surface;determining the first temporary excavation surface as a first target excavation surface in a case in which a first inclination angle of the first temporary excavation surface with respect to a horizontal direction is equal to or less than a predetermined angle threshold; andin a case in which a second inclination angle of the second temporary excavation surface with respect to a horizontal direction is larger than the angle threshold, determining a plane that passes through the second reference point and is inclined at the angle threshold with respect to the horizontal direction as a second target excavation surface.

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