SYSTEM AND METHOD FOR CONTROLLING WORK MACHINE, AND WORK MACHINE

A system controls a work machine including a work implement. The system includes a sensor and a controller. The controller acquires current position data of the work machine, acquires actual topography data, acquire default target displacement data that defines a target displacement according to a movement amount of the work machine, acquires a work interval indicative of a distance between a previous start position of work by the work machine and a current start position behind the previous start position, generates modified data with the default target displacement data modified according to the work interval, refers to the modified data to determine the target displacement according to the movement amount of the work machine from the current start position, determines topography data with the actual topography data vertically displaced downward by the target displacement as a target profile, and moves the work implement according to the target profile.

BACKGROUND

Technical Field

The present invention relates to a system and a method for controlling a work machine, and a work machine.

Background Information

A control for automatically adjusting a position of a work implement such as a blade has been conventionally proposed for work machines such as bulldozers, graders, or the like. For example, in International Publication No. WO2018/179383, a controller acquires actual topography data indicative of an actual topography. The controller determines a topography in which the actual topography is vertically displaced by a target displacement as a target profile. The controller operates a work implement according to the target profile. Thus, the actual topography is formed into a shape according to the target profile.

SUMMARY

The work machine travels forward, starts work with the work implement from a predetermined start position, and operates the work implement according to the target profile. Then, upon reaching a predetermined end position, the work machine travels in reverse to a next start position. In this way, the work machine performs work in one work path. The work path means a series of work steps from the predetermined start position to the predetermined end position.

As described above, in a case where the topography in which the actual topography is vertically displaced by the target displacement is determined as the target profile, the target profile is affected by the actual topography. In a case where the target profile for the next work path is determined repeatedly along the previous work path, the target profile for the next work path is affected by the actual topography resulting from the previous work path. Therefore, the actual topography resulting from the previous work path may result in steep inclinations or unevenness in the target profile for the next work path. In that case, work quality or work efficiency will suffer. For example, if a cutting angle suddenly increases, a load applied to the work implement will suddenly increase, causing a reduction in work efficiency. Moreover, if the work implement is controlled along the target profile including a lot of unevenness, the finish topography will also include a lot of unevenness, resulting in a reduction in quality. An object of the present disclosure is to reduce an influence of the topography resulting from the previous work path and improve work quality or work efficiency in the next work path under the automatic control of the work machine.

A system according to a first aspect of the present disclosure is a system for controlling a work machine including a work implement. The system according to the present aspect includes a sensor and a controller. The sensor detects a current position of the work machine. The controller communicates with the sensor. The controller is programmed to execute the following processes. The controller acquires current position data indicative of the current position of the work machine. The controller acquires actual topography data indicative of an actual topography. The controller acquires default target displacement data. The default target displacement data defines a target displacement according to a movement amount of the work machine. The controller acquires a work interval. The work interval indicates a distance between a previous start position of work by the work machine and a current start position positioned behind the previous start position. The controller generates modified data in which the default target displacement data is modified according to the work interval. The controller refers to the modified data to determine the target displacement according to the movement amount of the work machine from the current start position. The controller determines topography data in which the actual topography is vertically displaced downward by the target displacement as a target profile. The controller moves the work implement according to the target profile.

A method according to a second aspect of the present disclosure is a method for controlling a work machine including a work implement. The method according to the present aspect includes the following processes. A first process is to acquire current position data indicative of a current position of the work machine. A second process is to acquire actual topography data indicative of an actual topography. A third process is to acquire default target displacement data. The default target displacement data defines a target displacement according to a movement amount of the work machine. A fourth process is to acquire a work interval. The work interval indicates a distance between a previous start position of work by the work machine and a current start position positioned behind the previous start position. A fifth process is to generate modified data in which the default target displacement data is modified according to the work interval. A sixth process is to refer to the modified data to determine the target displacement according to the movement amount of the work machine from the current start position. A seventh process is to determine topography data in which the actual topography data is vertically displaced downward by the target displacement as a target profile. An eighth process is to move the work implement according to the target profile. The order in which each process is executed is not limited to the aforementioned order and may be changed. A work machine according to a third aspect of the present disclosure includes a work implement, a sensor, and a controller. The sensor detects a current position of the work machine. The controller communicates with the sensor. The controller is programmed to execute the following processes. The controller acquires current position data indicative of the current position of the work machine. The controller acquires actual topography data indicative of an actual topography. The controller acquires default target displacement data. The default target displacement data defines a target displacement according to a movement amount of the work machine. The controller acquires a work interval. The work interval indicates a distance between a previous start position of work by the work machine and a current start position positioned behind the previous start position. The controller generates modified data in which the default target displacement data is modified according to the work interval. The controller refers to the modified data to determine the target displacement according to the movement amount of the work machine from the current start position. The controller determines topography data in which the actual topography data is vertically displaced downward by the target displacement as a target profile. The controller moves the work implement according to the target profile.

According to the present disclosure, the modified data is generated in which the default target displacement data is modified according to the distance between the previous start position and the current start position. Then, the target displacement is determined with reference to the modified data, and the topography data in which the actual topography data is vertically displaced downward by the target displacement is determined as the target profile. Therefore, the target profile for the current work path is determined in consideration of the topography resulting from the previous work path. As a result, it is possible to reduce the influence of the topography resulting from the previous work path and improve work quality or work efficiency.

DETAILED DESCRIPTION OF EMBODIMENT(S)

A work machine according to an embodiment will be described below with reference to the drawings.FIG.1is a side view of a work machine1according to the embodiment. The work machine1according to the present embodiment is a bulldozer. The work machine1includes a vehicle body11, a travel device12, and a work implement13.

The vehicle body11includes an operating cabin14and an engine compartment15. A driver's seat that is not illustrated is disposed in the operating cabin14. The engine compartment15is disposed in front of the operating cabin14. The travel device12is attached to a lower portion of the vehicle body11. The travel device12includes a pair of left and right crawler belts16. Only the left crawler belt16is illustrated inFIG.1. The work machine1travels due to the rotation of the crawler belt16. The travel of the work machine1may be either autonomous travel, semi-autonomous travel, or travel under operation by an operator.

The work implement13is attached to the vehicle body11and the travel device12. The work implement13includes a lift frame17, a blade18, and a lift cylinder19. A trunnion (cylindrical protrusion) is disposed on each of the left and right sides of the travel device12around an axis X extending in the vehicle width direction. The lift frame17is attached to the travel device12via the trunnions so as to be movable up and down. The lift frame17supports the blade18. The blade18is disposed in front of the vehicle body11. The blade18moves up and down accompanying the up and down movements of the lift frame17. The lift cylinder19is coupled to the vehicle body11and the lift frame17. Due to the extension and contraction of the lift cylinder19, the lift frame17rotates up and down around the axis X. The lift cylinder19extends, causing the blade18to be raised. The lift cylinder19contracts, causing the blade18to be lowered.

FIG.2is a block diagram illustrating a configuration of a drive system2and a control system3of the work machine1. As illustrated inFIG.2, the drive system2includes an engine22, a hydraulic pump23, and a power transmission device24. The hydraulic pump23is driven by the engine22to discharge hydraulic fluid. The hydraulic fluid discharged from the hydraulic pump23is supplied to the lift cylinder19. Although one hydraulic pump23is illustrated inFIG.2, a plurality of hydraulic pumps may be provided.

The power transmission device24transmits the driving force of the engine22to the travel device12. The power transmission device24may be, for example, a hydro static transmission (HST). Alternatively, the power transmission device24may be, for example, a transmission including a torque converter or a plurality of transmission gears.

The control system3includes an operating device25a, an input device25b, a controller26, a storage device28, and a control valve27. The operating device25ais a device for operating the work implement13and the travel device12. The operating device25ais disposed in the operating cabin14. The operating device25areceives an operation by an operator for driving the work implement13and the travel device12, and outputs an operation signal corresponding to the operation. The operating device25aincludes, for example, an operating lever, a pedal, a switch, and the like.

For example, the operating device25afor traveling is configured to be operated in a forward position, a reverse position, and a neutral position. The operating device25afor the work implement13is configured to be operated in a raising position and a lowering position. The operation signal indicative of a position of the operating device25ais output to the controller26. When the operating position of the operating device25ais in the forward position, the controller26controls the travel device12or the power transmission device24so that the work machine1travels forward. When the operating position of the operating device25ais in the reverse position, the controller26controls the travel device12or the power transmission device24so that the work machine1travels in reverse.

The input device25bis, for example, a touch screen type input device. However, the input device25bmay be another input device such as a switch, or the like. The operator can input a setting for automatic control described later using the input device25b.

The controller26is programmed to control the work machine1based on acquired data. The controller26includes the storage device28and a processor30. The processor30includes, for example, a CPU. The storage device28includes, for example, a memory and an auxiliary storage device. The storage device28may be, for example, a RAM or a ROM. The storage device28may be a semiconductor memory, a hard disk, or the like. The storage device28is an example of a non-transitory computer-readable recording medium. The storage device28stores computer instructions that are executable by the processor30and for controlling the work machine1.

The controller26acquires an operation signal from the operating device25a. The controller26controls the control valve27based on the operation signal. The control valve27is a proportional control valve and is controlled by a command signal from the controller26. The control valve27is disposed between a hydraulic actuator such as the lift cylinder19and the hydraulic pump23. The control valve27controls the flow rate of the hydraulic fluid supplied from the hydraulic pump23to the lift cylinder19. The controller26generates the command signal to the control valve27so that the blade18operates according to the operation of the operating device25aas described above. Thus, the lift cylinder19is controlled according to the operation amount of the operating device25a.

For example, when the operating position of the operating device25ais in the raising position, the controller26controls the control valve27so that the work implement13is raised. When the operating position of the operating device25ais in the lowering position, the controller26controls the control valve27so that the work implement13is lowered. The control valve27may be a pressure proportional control valve. Alternatively, the control valve27may be an electromagnetic proportional control valve.

The control system3includes a stroke sensor29. The stroke sensor29detects a stroke length of the lift cylinder19(hereinafter referred to as “lift cylinder length”). The controller26calculates a lift angle θ lift of the blade18based on the lift cylinder length.FIG.3is a schematic view illustrating a configuration of the work machine1.

InFIG.3, the origin position of the work implement13is indicated by a chain double-dashed line. The origin position of the work implement13is the position of the blade18in a state where a tip of the blade18is in contact with the ground surface on a horizontal ground surface. The lift angle θ lift is the angle, when the work machine1is viewed from the side, between a lower end of the blade18(blade tip position P0) at the origin position, the axis X, and a lower end of the blade18(blade tip position P0) when the blade is operated up and down.

As illustrated inFIG.2, the control system3includes a position sensor31. The position sensor31measures a position of the work machine1. The position sensor31includes a global navigation satellite system (GNSS) receiver32, an IMU33, and an antenna35. The GNSS receiver32is, for example, a receiver for global positioning system (GPS). The GNSS receiver32receives a positioning signal from a satellite, computes the position of the antenna35based on the positioning signal, and generates vehicle body position data. The controller26acquires the vehicle body position data from the GNSS receiver32.

The IMU33is an inertial measurement unit. The IMU33acquires vehicle body tilt angle data and vehicle body acceleration data. The vehicle body tilt angle data includes an angle with respect to the horizontal in the vehicle longitudinal direction (pitch angle) and an angle with respect to the horizontal in the vehicle lateral direction (roll angle). The body acceleration data includes the acceleration of the work machine1. The controller acquires the traveling direction and the vehicle speed of the work machine1from the vehicle body acceleration data. The controller26acquires the vehicle body tilt angle data and the vehicle body acceleration data from the IMU33.

The controller26calculates a blade tip position P0from the lift cylinder length, the vehicle body position data, and the vehicle body tilt angle data. The controller26calculates global coordinates of the antenna35based on the vehicle body position data. The controller26calculates the lift angle θ lift based on the lift cylinder length and vehicle body dimension data. The vehicle body dimension data is stored in the storage device28and includes data indicative of a position of the work implement13with respect to the axis X. The controller26calculates local coordinates of the blade tip position P0with respect to the antenna35based on the lift angle θ lift and the vehicle body dimension data. The controller26calculates the traveling direction and the vehicle speed of the work machine1from the vehicle body acceleration data. The vehicle body dimension data includes data indicative of a position of the work implement13with respect to the antenna35. The controller26calculates global coordinates of the blade tip position P0based on the global coordinates of the antenna35, the local coordinates of the blade tip position P0, and the vehicle body tilt angle data. The controller26acquires the global coordinates of the blade tip position P0as blade tip position data.

The storage device28stores work site data and design topography data. The work site data indicates an actual topography of the work site. The work site data is, for example, an actual topography survey map in a three-dimensional data format. The work site data can be acquired, for example, by aerial laser survey. Alternatively, the work site data may be acquired based on a work result of the work machine that operates at the work site.

The actual topography data is acquired by computing with the controller26from the work site data, the position of the work machine1acquired from the aforementioned position sensor31, and the traveling direction of the work machine1. The actual topography data may be data acquired from the work site data, the position of the work machine1acquired from the position sensor31, and the traveling direction of the work machine1, with smoothing process applied.

Specifically, the actual topography data includes heights Z0to Zn of the actual topography50at a plurality of reference points from a current position to a predetermined topography recognition distance do in the traveling direction of the work machine1. In the present embodiment, the current position is a position determined based on the current blade tip position P0of the work machine1. The current position may be determined based on a current position of another portion of the work machine1. The current position may be updated as appropriate according to the travel of the work machine. The plurality of reference points are aligned at a predetermined interval, for example, every one meter.

The design topography data indicates a final design topography60. The final design topography60is a final target shape of a surface of the work site. The design topography data is acquired from a construction drawing in a three-dimensional data format, for example. As illustrated inFIG.4, the design topography data includes a height Zdesign of the final design topography60at a plurality reference points in the travel direction of the work machine1. The plurality of reference points indicate a plurality of points at a predetermined interval along the traveling direction of the work machine1. InFIG.4, the actual topography50and the final design topography60have a flat shape parallel to the horizontal direction, but may have a different shape.

The controller26automatically controls the work implement13based on the actual topography data, the design topography data, and the blade tip position data. The automatic control of the work implement13in digging executed by the controller26will be described below.FIG.5is a flowchart illustrating processes of the automatic control of the work implement13in digging work.FIG.5illustrates the processes in one work path in digging work. The one work path means steps from when the work machine1starts traveling forward from a start position and then performs a series of digging work until the work machine1starts traveling in reverse in order to move to a next start position.

As illustrated inFIG.5, in step S101, the controller26acquires current position data. At this time, the controller26acquires the current blade tip position data of the blade18as the current position data as described above. In step S102, the controller26acquires the aforementioned design topography data. In step S103, the controller26acquires the aforementioned actual topography data.

In step S104, the controller26acquires a start position of work. For example, the controller26acquires, as the start position, the position when the blade tip position P0first drops below the height Z0of the actual topography50. As a result, the position where the tip of the blade18is lowered and digging of the actual topography50is started is acquired as the start position. For example, the start position of work may be acquired when the work implement13is lowered by the operator operating the operating device25a. Alternatively, the start position of work may be acquired when the work implement13is lowered by the controller26automatically controlling the work implement13. However, the controller26may acquire the start position by another method. For example, the controller26may acquire the start position based on an operation of a button, a screen operation with a touch screen, or the like.

In step S105, the controller26acquires a movement amount of the work machine1. The controller26acquires, as the movement amount, the distance that the work machine1travels from the start position to the current position. The movement amount of the work machine1may be the movement amount of the vehicle body11. Alternatively, the movement amount of the work machine1may be the movement amount of the blade tip position P0of the blade18.

In step S106, the controller26determines a target profile70. As illustrated inFIG.4, the target profile70indicates a desired trajectory of the tip of the blade18in work. The target profile70is a target shape of the topography to be worked and indicates a desired shape as a result of digging work.

The controller26determines the target profile70so that the target profile70does not go below the final design topography60. Therefore, the controller26determines the target profile70positioned at or above the final design topography60and below the actual topography50during digging work.

As illustrated inFIG.4, the controller26determines the target profile70that is displaced downward from the actual topography50by a target displacement dz. The target displacement dz is a target depth at each reference point in a vertical direction. Alternatively, the target displacement dz may be a target depth in a perpendicular direction of the actual topography50. The controller26refers to target displacement data C to determine the target displacement dz according to the movement amount of the work machine1. The target displacement data C is stored in the storage device28.FIG.6is a graph illustrating an example of the target displacement data C. The target displacement data C defines the target displacement dz with respect to a movement amount n of the work machine1in the horizontal direction. The controller26refers to the target displacement data C illustrated inFIG.6to determine the target displacement dz from the movement amount n of the work machine1.

The target displacement data C includes data at start C1, data during digging C2, data during transition C3, and data during soil transportation C4. The data at start C1defines the relation between the movement amount n and the target displacement dz in a digging start region. The digging start region is a region where the movement amount n is from 0 to a value b1. As indicated by the data at start C1, the target displacement dz that gradually increases as the movement amount n increases is defined in the digging start region. The data at start C1defines the target displacement dz that linearly increases to a first target value a1 with respect to the movement amount n. The data at start C1includes an inclination A1. The inclination A1is a ratio of a change amount of the target displacement dz with respect to a change amount of the movement amount n in the data at start C1. In the digging start region, the target displacement dz at a position where the movement amount n is 0, that is, at a start position of work, is a start value a0.

The data during digging C2defines the relation between the movement amount n and the target displacement dz in a digging region. The digging region is a region where the movement amount n is from a value b1 to a value b2. As indicated by the data during digging C2, the data during digging C2defines the target displacement dz that is constant with respect to the movement amount n. The target displacement dz in the digging region is constant at the first target value a1.

The data during transition C3defines the relation between the movement amount n and the target displacement dz in a transitional soil transportation region. The transitional soil transportation region is a region where the movement amount n is from the value b2 to a value b3. As indicated by the data during transition C3, the target displacement dz that gradually decreases as the movement amount n increases is defined in the transitional soil transportation region. The data during transition C3defines the target displacement dz that linearly decreases to a second target value a2 with respect to the movement amount n. The data during transition C3includes an inclination A2. The inclination A2is a ratio of a change amount of the target displacement dz with respect to a change amount of the movement amount n in the data during transition C3.

The data during soil transportation C4defines the relation between the movement amount n and the target displacement dz in a soil transportation region. The soil transportation region is a region where the movement amount n is greater than or equal to the value b3. As indicated by the data during soil transportation C4, the target displacement dz is defined as a constant value in the soil transportation region. The target displacement dz in the soil transportation region is constant at the second target value a2. The second target value a2 is smaller than the first target value a1. Therefore, the target displacement dz defined in the digging region is larger than the target displacement dz in the soil transportation region.

The start value a0, the first target value a1, and the second target value a2 are constants and stored in the storage device28. The start value a0 is preferably a small value at which the load applied to the blade at the digging start will not be excessively large. The first target value a1 is preferably a value at which the efficient digging according to the performance of the work machine1can be performed and the traveling resistance will not be excessively large. The second target value a2 is preferably set to a value suitable for the soil transportation work.

The inclinations A1and A2are constants and stored in the storage device28. The inclination A1in the data at start C1is preferably a value at which a quick transition from the digging start to the digging work can be performed and the load applied to the blade18will not be excessively large. The inclination A2in the data during transition C3is preferably a value at which a quick transition from the digging work to the soil transportation work and the load applied to the blade18will not be excessively large.

The value b1 of the movement amount n when the digging region starts is calculated from the inclination A1, the start value a0, and the first target value a1. The value b2 of the movement amount n when the digging region ends is the movement amount when a current amount of soil held by the blade18exceeds a predetermined threshold. Therefore, the controller26decreases the target displacement dz from the first target value a1 when the current amount of soil held by the blade18has exceeded the predetermined threshold. The predetermined threshold is determined based, for example, on the maximum capacity of the blade18. For example, the current amount of soil held by the blade18may be determined by measuring the load applied to the blade18and calculating from the load. Alternatively, the current amount of soil held by the blade18may be calculated by capturing an image of the blade18with a camera and analyzing the image. A predetermined initial value is set as the value b2. In a case where the amount of soil held by the blade18exceeds the predetermined threshold before reaching the value b2, the value b2 is updated to a value based on the movement amount when the amount of soil held by the blade18has exceeded the predetermined threshold, instead of the above initial value. The movement amount when the held soil amount has exceeded the predetermined threshold may be set as the updated value b2. A value smaller than the movement amount when the held soil amount has exceeded the predetermined threshold may be set as the updated value b2.

The value b3 of the movement amount n when the soil transportation region starts is calculated from the inclination A2in the data during transition C3, the first target value a1, and the second target value a2. The values b1, b2, and b3 may be stored in storage device28as constants. The value b3 may be defined as b2+constant. When the value b2 is updated, the value b3 may be updated in conjunction with the value b2.

The controller26determines the target displacement dz according to the movement amount n from the target displacement data C. Then, the controller26determines a height Z of the target profile70(thick dashed line) illustrated inFIG.4from the height Z of the actual topography50and the target displacement dz.

FIG.7is a graph illustrating an example of the target profile70. The target profile70inFIG.7is an example of the target profile determined based on the target displacement data inFIG.6and the actual topography50. In the example illustrated inFIG.7, the work machine1starts work from a start position Ps1and finishes the work at an end position Pe1. As illustrated inFIG.7, the target profile70includes a first target surface71, a second target surface72, a third target surface73, and a fourth target surface74.

The first target surface71is the target profile in the digging start region. The controller26refers to the data at start C1to determine the target displacement dz on the first target surface71from the movement amount. The first target surface71is inclined downward toward front of the work machine1. The second target surface72is the target profile in the digging region. The controller26refers to the data during digging C2to determine the target displacement dz on the second target surface72from the movement amount. The second target surface72is parallel to the actual topography50. In the present embodiment, the second target surface72extends horizontally. The third target surface73is the target profile in the transitional soil transportation region. The controller26refers to the data during transition C3to determine the target displacement dz on the third target surface73from the movement amount. The third target surface73is inclined upward toward front of the work machine1. The fourth target surface74is the target profile in the soil transportation region. The controller refers to the data during soil transportation C4to determine the target displacement dz on the fourth target surface74from the movement amount. The fourth target surface74is parallel to the actual topography50. In the present embodiment, the fourth target surface74extends horizontally.

In step S107illustrated inFIG.5, the controller26controls the blade18according to the target profile70. At this time, the controller26generates a command signal to the work implement13so that the blade tip position P0of the blade18moves according to the target profile70determined in step S106. The generated command signal is input to the control valve27. As a result, the blade tip position P0of the work implement13moves along the target profile70.

As illustrated inFIG.7, in the digging region, the target displacement dz between the actual topography50and the target profile70is large in comparison with the other regions. Accordingly, the digging work of the actual topography50is performed in the digging region. In the soil transportation region, the target displacement dz between the actual topography50and the target profile70is small in comparison with the other regions. Accordingly, the digging of the ground surface is suppressed and the soil held by the blade18is transported in the transportation region.

In step S108, the controller26updates the work site data. The controller26acquires the position data indicative of the latest trajectory of the blade tip position P0as the actual topography data and updates the work site data according to the acquired actual topography data. Alternatively, the controller26may calculate a position of the bottom surface of the crawler belts16from the vehicle body position data and the vehicle body dimension data and acquire the position data indicative of the actual trajectory of the bottom surface of the crawler belts16as the actual topography data. In this case, the update of the work site data can be performed instantly.

Alternatively, the actual topography data may be generated from survey data measured by a survey device outside of the work machine1. For example, aerial laser survey may be used as an external survey device. Alternatively, the actual topography may be captured by a camera and the actual topography data may be generated from image data acquired by the camera. For example, aerial photographic survey using unmanned aerial vehicle (UAV) may be used. In the case of using the external survey device or camera, the work site data may be updated at a predetermined interval, or as appropriate.

In step S109, the controller26determines whether the current work path has been completed. The controller26determines that the current work path has been completed upon the work machine1reaching a predetermined work end position. For example, the controller26determines that the current work path has been completed upon determining that the blade tip position P0reaches the end position Pe1based on the actual position data. Alternatively, the controller26may determine that the current work path has been completed upon the work implement13being raised by the operator operating the operating device25a. Alternatively, the controller26may determine that the current work path has been completed upon the work machine1being switched from the forward travel to the travel in reverse. When the current work path is not completed, the process returns to step S105.

Upon the current work path being completed, the work machine1travels in reverse on a straight route in order to move to a next start position. Then, the work machine1travels forward again to start a next work path. The switching between the forward travel and the reverse travel of the work machine1may be performed by the operator operating the operating device25a. Alternatively, the switching between the forward travel and the reverse travel of the work machine1may be performed under the automatic control of the controller26. The controller26also executes the above processes for the next work path. By repeating such processes, the digging is performed so that the actual topography50approaches the final design topography60.

The second and subsequent work paths may be affected by the topography resulting from the previous work path. Therefore, the controller26modifies the target displacement dz according to the distance between the start position of the previous work path and the start position of the current work path (hereinafter referred to as “work interval”). Specifically, the controller26modifies the target displacement data C according to the work interval, thereby modifying the target displacement dz according to the movement amount of the work machine1.FIG.8is a flowchart illustrating processes for modifying the target displacement data C.

As illustrated inFIG.8, in step S201, the controller26determines whether a first condition is satisfied. The first condition indicates that the current work path is not affected by the topography resulting from the previous work path or is less affected. The first condition includes that the current work path is a first work path. Also, the first condition includes that the work interval is larger than the value b2 that is the movement amount of a terminating end of the digging region.

When the first condition is satisfied, the process proceeds to step S202. In step S202, the controller26uses default target displacement data C. That is, the controller26refers to the aforementioned target displacement data C to determine the target displacement dz from the movement amount n of the work machine1.

When the first condition is not satisfied in step S201, the process proceeds to step S203. In step S203, the controller26determines whether a second condition is satisfied. The second condition indicates that the current work path is affected by the topography resulting from the previous work path because the current start position is close to the previous start position. The second condition includes that the work interval is smaller than a first threshold. The first threshold is, for example, the same as the value b1 that is the movement amount of the terminating end of the digging start region. However, the first threshold may be different from the value b1.

When the second condition is satisfied, the process proceeds to step S204. In step S204, the controller26modifies the target displacement data C by a first modification process.FIG.9is a graph illustrating an example of data generated from the target displacement data C by the first modification process (hereinafter referred to as “first modified data C′”).FIG.10is a graph illustrating the target profile70generated from the first modified data C′.

As illustrated inFIG.10, the actual topography50is the topography formed by the previous work path (hereinafter referred to as “first work path”). The first work path is not limited to the work path that is first performed on the actual topography50. The first work path may be a second or subsequent work path performed on the actual topography50.

In the first work path, the work is started from a first start position Ps1and finished at a first end position Pe1. In the first work path, the controller26determines the target profile70by vertically displacing the actual topography50by the target displacement dz determined from the target displacement data C in the same way as illustrated inFIG.7. Subsequently, the work machine1travels backward by the operation of the operator or the automatic control and starts a second work path from a second start position Ps2. The controller26acquires the second start position Ps2and calculates a work interval b0 between the first start position Ps1and the second start position Ps2. When the work interval b0 is smaller than the first threshold, the controller26modifies the target displacement data C to generate the first modified data C′ illustrated inFIG.9.

As illustrated inFIG.9, the controller26modifies the target displacement data C so that a position where the movement amount n from the second start position Ps2is the work interval b0 is a position of the terminating end of the digging start region in the second work path. The controller26changes the first target value from the value a1 to a value a1′ without changing the inclination A1. The modified first target value a1′ is smaller than the first target value a1 before modification.

As illustrated inFIG.9, the digging start region is a region where the movement amount n is from 0 to the work interval b0 in the first modified data C′. Data at start C1′ of the first modified data C′ defines the target displacement dz that is the same as the target displacement dz in the target displacement data C, with respect to the movement amount n from 0 to the work interval b0. That is, in the data at start C1′, the target displacement dz linearly increases to the modified first target value a1′ at the inclination A1with respect to the movement amount n from 0 to the work interval b0. The controller26calculates the modified first target value a1′ from the start value a0, the inclination A1, and the work interval b0. As illustrated inFIG.10, the controller26generates the first target surface71inclined downward in the region from the second start position Ps2to the first start position Ps1by the data at start C1′.

In the first modified data C′, the digging region is a region where the movement amount n is from the work interval b0 to a value b2+x. Data during digging C2′ of the first modified data C′ defines the target displacement dz that is constant with respect to the movement amount n in the digging region. In the data during digging C2′, the target displacement dz in the digging region is constant at the modified first target value a1′. The controller26generates the second target surface72in the digging region as indicated by the thick dashed line inFIG.10by the data during digging C2′. The second target surface72includes a first part72a, a second part72b, and a third part72c. The first part72ais positioned in front of the first target surface71. The first part72ais inclined downward. The inclination angle of the first part72ais the same as that of the first target surface71. The second part72bextends horizontally. The third part72cis positioned in front of the second part72b. The third part72cis inclined upward.

InFIG.10,80indicates the target profile in the second work path determined by the unmodified target displacement data C. In a case where the second start position Ps2is too close to the first start position Ps1, the inclination of the target profile80will suddenly increase at the point where the movement amount n is the work interval b0. On the other hand, with the control system3of the work machine1according to the present embodiment, in a case where the second start position Ps2is too close to the first start position Ps1, the controller26determines the target profile70by the first modified data C′. Accordingly, the controller26can generate the first target surface71inclined at a constant angle and the first part72aof the second target surface72. This reduces the occurrence of increase in cutting angle in the digging region, thereby preventing the load applied to the blade from suddenly increasing.

In the first modified data C′, the transitional soil transportation region is a region where the movement amount n is from the value b2+x to a value b3+y. Data during transition C3′ of the first modified data C′ defines the target displacement dz that linearly decreases at the inclination A2with respect to the movement amount n from the value b2+x to the value b3+y.

As illustrated inFIG.10, the controller26generates the third target surface73inclined upward in the transitional soil transportation region by the data during transition C3′. The controller26determines a value x and a value y so that the dug soil amount by the first modified data C′ is equal to the dug soil amount by the target displacement data C. The dug soil amount by the first modified data C′ is indicated by an area of the first modified data C′ inFIG.9. The dug soil amount by the target displacement data C is indicated by an area of the target displacement data C inFIG.9. Therefore, the controller26determines the value x and the value y when the area of the first modified data C′ and the area of the target displacement data C illustrated inFIG.9are to be the same in size. That is, the controller26determines the value x and the value y so that an area B1and an area B2that are hatched inFIG.9are the same in size. The controller26limits the maximum value of the value y to the work interval b0. This prevents the work machine1from digging ahead of the transitional soil transportation region of the first work path.

In the first modified data C′, the soil transportation region is a region where the movement amount n is greater than or equal to the value b3+y. Data during soil transportation C4′ of the first modified data C′ defines the target displacement dz that is constant with respect to the movement amount n in the soil transportation region. In the data during soil transportation C4′, the target displacement dz in the soil transportation region is constant at the second target value a2. As illustrated inFIG.10, the controller26generates the fourth target surface74parallel to the actual topography50in the soil transportation region10by the data during soil transportation C4′.

When it is determined in step S203that the second condition is not satisfied, the process proceeds to step S205. The fact that the second condition is not satisfied indicates that the current work path is affected by the topography resulting from the previous work path because the current start position is far from the previous start position. The controller26may execute the process in step S205when a third condition is satisfied. The third condition may include that the work interval is greater than or equal to a second threshold. The second threshold may be equal to the first threshold. The second threshold may be greater than the first threshold. The second threshold may be greater than or equal to the value b1 that is the movement amount of the terminating end of the digging start region and smaller than the value b2 that is the movement amount of the terminating end of the digging region.

In step S205, the controller26modifies the target displacement data C (chain line) by a second modification process.FIG.11is a graph illustrating an example of data generated from the target displacement data C by the second modification process (hereinafter referred to as “second modified data C″”).FIG.12is a graph illustrating the target profile70(thick dashed line) generated from the second modified data C″.

As illustrated inFIG.12, the controller26modifies the target displacement data C in the second work path so that the target displacement dz gradually increases from the second start position Ps2to the first start position Ps1.

As illustrated inFIG.11, in the second modified data C″, the digging start region is a region where the movement amount n is from 0 to the work interval b0. Data at start C1″ of the second modified data C″ defines the target displacement dz that gradually increases with respect to the movement amount n from 0 to the work interval b0. That is, in the data at start C1″, the target displacement dz linearly increases to the first target value a1 at a modified inclination A1″ with respect to the movement amount n from 0 to the work interval b0. The modified inclination A1″ is smaller than the inclination A1. The controller26calculates the modified inclination A1″ from the start value a0, the first target value a1, and the work interval b0. As illustrated inFIG.12, the controller26generates the first target surface71inclined downward in the region from the second start position Ps2to the first start position Ps1by the data at start C1″.80indicated by the chain line is the target profile generated from the default target displacement data C. As indicated by the target profile80, in a case where the second start position Ps2is too far from the first start position Ps1, the digging start region ends and the digging region starts before the movement amount n has reached the work interval b0. As a result, the target profile80will have unevenness. On the other hand, with the control system3of the work machine1according to the present embodiment, in the case where the second start position Ps2is too far from the first start position Ps1, the controller26determines the target profile70by the second modified data C″. Accordingly, the controller26can reduce the variation in the inclination angle between the first target surface71and the first part72aof the second target surface72. This reduces the occurrence of unevenness, thereby preventing the load applied to the blade18from suddenly increasing.

In the second modified data C″, the digging region is a region where the movement amount n is from the work interval b0 to the value b2+x. Data during digging C2″ of the second modified data C″ defines the target displacement dz that is constant with respect to the movement amount n in the digging region. In the data during digging C2″, the target displacement dz in the digging region is constant at the first target value a1. As illustrated inFIG.12, the controller26generates the second target surface72in the digging region by the data during digging C2″. The second target surface72includes the first part72aand the second part72b. The first part72ais positioned in front of the first target surface71. The first part72ais inclined downward. The inclination angle of the first part72ais an angle corresponding to the inclination of the actual topography50formed by the first work path, and the inclination angle of the first target surface71is an angle corresponding to the inclination A1″. However, the first target surface71and the first part72aof the second target surface72are continuously connected without forming a horizontal part therebetween.

In the second modified data C″, the transitional soil transportation region is a region where the movement amount n is from the value b2+x to the value b3+y. Data during transition C3″ of the second modified data C″ defines the target displacement dz that gradually decreases with respect to the movement amount n from the value b2+x to the value b3+y. In the data during transition C3″, the target displacement dz linearly decreases to the second target value a2 at the inclination A2with respect to the movement amount n from the value b2+x to the value b3+y.

As illustrated inFIG.12, the controller26generates the third target surface73inclined upward in the transitional soil transportation region by the data during transition C3″. The controller26determines the value x and the value y when the dug soil amount by the second modified data C″ and the dug soil amount by the target displacement data C are to be equal to each other. That is, the controller26determines the value x and the value y so that an area B3and an area B4that are hatched inFIG.11are the same in size.

In the second modified data C″, the soil transportation region is a region where the movement amount n is greater than or equal to the value b3+y. Data during soil transportation C4″ of the second modified data C″ defines the target displacement dz that is constant with respect to the movement amount n in the soil transportation region. In the data during soil transportation C4″, the target displacement dz in the soil transportation region is constant at the second target value a2. As illustrated inFIG.12, the controller26generates the fourth target surface74parallel to the actual topography50in the soil transportation region by the data during soil transportation C4″. Unevenness is formed from a terminating end of the transitional soil transportation region inFIG.12. Since the unevenness in the transitional soil transportation region and thereafter does not lead to a sudden increase in the load applied to the blade, the unevenness may be inevitably formed in the present embodiment. However, the value y may be determined so that unevenness is not formed.

The aforementioned processes illustrated inFIG.8are repeated in a third work path. In the third work path, the distance between a third start position of the third work path and the aforementioned second start position is used as the work interval. The controller26modifies the target displacement data C according to the work interval to generate the first modified data C′ or the second modified data C″. The controller26refers to the first modified data C′ or the second modified data C″ to determine the target displacement dz according to the movement amount from the third start position. The controller26determines a topography in which the actual topography50is vertically displaced downward by the target displacement dz as the target profile70in the third work path. The controller26repeats the same processes for a fourth and subsequent work paths.

With the control system3of the work machine1according to the present embodiment as described above, in the first work path, the target displacement dz (first target displacement) according to the movement amount is determined with reference to the default target displacement data C. Then, the topography in which the actual topography50is vertically displaced downward by the target displacement dz is determined as the target profile70in the first work path. In a case where the work interval between the first work path and the second work path is less than or equal to the value b2, the first modified data C′ or the second modified data C″ in which the default target displacement data C is modified is generated according to the work interval. The target displacement dz (second target displacement) is determined with reference to the modified data C′, C″. Then, the topography in which the actual topography50is vertically displaced downward by the target displacement dz is determined as the target profile70in the second work path. Therefore, the target profile70in the second work path is determined in consideration of the topography resulting from the first work path. As a result, it is possible to reduce the influence of the topography resulting from the previous work path and improve work quality or work efficiency.

Although one embodiment of the present invention has been described above, the present invention is not limited to the above embodiment and various modifications may be made without departing from the gist of the invention.

The work machine1is not limited to a bulldozer and may be another vehicle such as a wheel loader, a motor grader, or the like.

The work machine1may be a vehicle that can be remotely controlled. In this case, a portion of the control system3may be disposed outside of the work machine1. For example, the controller26may be disposed outside of the work machine1. The controller26may be disposed in a control center that is away from the work site.

The controller26may have a plurality of controllers that are separate from each other. For example, as illustrated inFIG.13, the controller26may include a remote controller261disposed outside of the work machine1and an onboard controller262mounted on the work machine1. The remote controller261and the onboard controller262may be able to wirelessly communicate with each other via communication devices38and39. A portion of the aforementioned functions of the controller26may be executed by the remote controller261and the remaining functions may be executed by the onboard controller262. For example, the processes for determining the target profile70may be executed by the remote controller261and the processes for outputting the command signal to the work implement13may be executed by the onboard controller262.

The operating device25aand the input device25bmay be disposed outside of the work machine1. In this case, the operating cabin may be omitted from the work machine1. Alternatively, the operating device25aand the input device25bmay be omitted from the work machine1. The work machine1may be operated with only the automatic control by the controller26without operations by the operating device25a.

The actual topography50may be acquired by another device, instead of the aforementioned position sensor31. For example, as illustrated inFIG.14, the actual topography50may be acquired by an interface device37that receives data from an external device. The interface device37may wirelessly receive the actual topography data measured by a measuring device41disposed outside. Alternatively, the interface device37may be a recording medium reading device and may receive the actual topography data measured by the external measuring device41via the recording medium.

The processes by the controller26are not limited to those of the above embodiment and may be changed. A portion of the aforementioned processes may be omitted. Alternatively, a portion of the aforementioned processes may be changed. For example, the processes for determining the target profile70may be changed.

FIG.15is a graph illustrating first modified data Cm′ according to a modified example. As illustrated inFIG.15, in the first modified data Cm′ according to the modified example, the digging start region is a region where the movement amount n is from 0 to the work interval b0. Data at start Cm1′ of the first modified data Cm′ defines the target displacement dz that is the same as the target displacement dz in the target displacement data C, with respect to the movement amount n from 0 to the work interval b0. That is, in the data at start Cm1′, the target displacement dz linearly increases to the modified first target value a1′ at the inclination A1with respect to the movement amount n from 0 to the work interval b0.

In the first modified data Cm′, the digging region is a region where the movement amount n is from the work interval b0 to the value b2+x. Data during digging Cm2′ of the first modified data Cm′ defines the target displacement dz that is constant at the modified first target value a1′ with respect to the movement amount n from the work interval b0 to a value b1+b0. Further, the data during digging Cm2′ defines the target displacement dz that linearly increases to the first target value a1 at the inclination A1with respect to the movement amount n from the value b1+b0 to a value 2b1. The data during digging Cm2′ defines the target displacement dz that is constant at the first target value a1 with respect to the movement amount n from the value 2b1 to the value b2+x. As illustrated inFIG.16, the controller26generates the first target surface71inclined downward in the region from the second start position Ps2to the first start position Ps1by the data at start Cm1′. As illustrated inFIG.16, the controller26generates the second target surface72in the digging region by the data during digging Cm2′. The second target surface72includes the first part72aand the second part72b. The first part72ais positioned in front of the first target surface71. The first part72ais inclined downward. The inclination angle of the first part72ais the same as that of the first target surface71. The second part72bextends horizontally.

In the first modified data Cm′, the transitional soil transportation region is a region where the movement amount n is from the value b2+x to the value b3+y. Data during transition Cm3′ of the first modified data Cm′ defines the target displacement dz that linearly decreases at the inclination A2with respect to the movement amount n from the value b2+x to the value b3+y.

As illustrated inFIG.16, the controller26generates the third target surface73inclined upward in the transitional soil transportation region by the data during transition Cm3′. The controller26determines the value x and the value y so that the dug soil amount by the first modified data Cm′ is equal to the dug soil amount by the target displacement data C. That is, the controller26determines the value x and the value y so that an area B5and an area B6that are hatched inFIG.15are the same in size.

In the first modified data Cm′, the soil transportation region is a region where the movement amount n is greater than or equal to the value b3+y. Data during soil transportation Cm4′ of the first modified data Cm′ defines the target displacement dz that is constant with respect to the movement amount n in the soil transportation region. In the data during soil transportation Cm4′, the target displacement dz in the soil transportation region is constant at the second target value a2. As illustrated inFIG.16, the controller26generates the fourth target surface74parallel to the actual topography50in the soil transportation region by the data during soil transportation Cm4′.

FIG.17is a graph illustrating second modified data Cm″ according to a modified example. As illustrated inFIG.17, in the second modified data Cm″, the digging start region is a region where the movement amount n is from 0 to the work interval b0. Data at start Cm1″ of the second modified data Cm″ defines the target displacement dz that gradually increases with respect to the movement amount n from 0 to the work interval b0. That is, in the data at start Cm1″, the target displacement dz linearly increases to a modified first target value a1″ at the inclination A1with respect to the movement amount n from 0 to the work interval b0.

The modified first target value a1″ is larger than the first target value a1. The controller26calculates the modified first target value a1″ from the start value a0, the inclination A1, and the work interval b0. As illustrated inFIG.18, the controller26generates the first target surface71inclined downward in the region from the second start position Ps2to the first start position Ps1by the data at start Cm1″.

In the second modified data Cm″, the digging region is a region where the movement amount n is from the value b0 to a value b2−x. Data during digging Cm2″ of the second modified data Cm″ defines the target displacement dz that is constant with respect to the movement amount n in the digging region. In the data during digging Cm2″, the target displacement dz in the digging region is constant at the modified first target value a1″. As illustrated inFIG.18, the controller26generates the second target surface72in the digging region by the data during digging Cm2″. The second target surface72includes the first part72aand the second part72b. The first part72ais positioned in front of the first target surface71. The first part72ais inclined downward. The inclination angle of the first part72ais the same as that of the first target surface71. The first target surface71and the first part72aof the second target surface72are continuously connected without forming a horizontal part therebetween.

In the second modified data Cm″, the transitional soil transportation region is a region where the movement amount n is from the value b2−x to a value b3−y. Data during transition Cm3″ of the second modified data Cm″ defines the target displacement dz that gradually decreases with respect to the movement amount n from the value b2−x to the value b3−y. In the data during transition Cm3″, the target displacement dz linearly decreases at the inclination A2with respect to the movement amount n from the value b2−x to the value b3−y.

As illustrated inFIG.18, the controller26generates the third target surface73inclined upward in the transitional soil transportation region by the data during transition Cm3″. The controller26determines the value x and the value y so that the dug soil amount by the second modified data Cm″ is equal to the dug soil amount by the target displacement data C. That is, the controller26determines the value x and the value y so that an area B7and an area B8that are hatched inFIG.17are the same in size.

In the second modified data Cm″, the soil transportation region is a region where the movement amount n is greater than or equal to the value b3−y. Data during soil transportation Cm4″ of the second modified data Cm″ defines the target displacement dz that is constant with respect to the movement amount n in the soil transportation region. In the data during soil transportation Cm4″, the target displacement dz in the soil transportation region is constant at the second target value a2. As illustrated inFIG.18, the controller26generates the fourth target surface74parallel to the actual topography50in the soil transportation region by the data during soil transportation Cm4″.

The method for determining the value x and the value y may be different from that as described above. The dug soil amount by the first modified data C′ may be different from the dug soil amount by the target displacement data C. The dug soil amount by the second modified data C″ may be different from the dug soil amount by the target displacement data C. The shape of the target displacement data C may be different from that as described above.

According to the present disclosure, it is possible to reduce an influence of the topography resulting from the previous work path and improve work quality or work efficiency.