System and method for controlling work machine

Abstract

This system includes a controller. The controller acquires a target line extending on a terrain subject to construction by a work machine. The controller acquires a current position of the work machine. The controller acquires the azimuth of the work machine. In first steering control, the controller determines the turning radius of a traveling body on the basis of an azimuth deviation, which is the difference between the azimuth of the target line and the azimuth of the work machine, and a position deviation, which is the distance between the target line and the current position of the work machine, and automatically steers the traveling body on the basis of the turning radius.

Description

System and method for controlling a work machine

[0001] TECHNICAL FIELD The present disclosure relates to systems and methods for controlling a work machine.

[0002] Some work machines include a vehicle body and a working implement, and perform tasks such as excavation using the working implement. For example, a work machine may be used to dig a long, linear trench. The operator of the work machine operates the work machine to move the work machine along a target line extending on the terrain to be worked on. The operator excavates the terrain on the target line using the work implement. The operator then reverses the work machine along the target line. By repeating this excavation and reverse movement, a long, linear trench is constructed on the terrain (see, for example, Patent Document 1).

[0003] International Publication No. WO2017 / 010563

[0004] In the above-described work, if the work machine is away from the target line, it is first necessary to move the work machine closer to the target line. In this case, it is preferable to make the work machine's heading parallel to the target line to facilitate subsequent work. However, to do this, the operator must not only drive the work machine toward the target line, but also precisely steer the work machine so that the heading of the work machine is parallel to the target line when the work machine reaches the target line, which places a heavy burden on the operator. An object of the present disclosure is to reduce the burden on the operator of adjusting the heading of the work machine to be parallel to the target line when the work machine reaches the target line.

[0005] A system according to one aspect of the present disclosure is a system for controlling a work machine including a work implement and a traveling body. The system includes a controller. The controller acquires a target line extending on terrain to be worked on by the work implement. The controller acquires the current position of the work machine. The controller acquires the orientation of the work machine. In a first steering control, the controller determines a turning radius of the traveling body based on an orientation error, which is the difference between the orientation of the target line and the orientation of the work machine, and a position error, which is the distance between the target line and the current position of the work machine, and automatically steers the traveling body based on the turning radius.

[0006] A method according to another aspect of the present disclosure is a method for controlling a work machine including a work implement, the method comprising: acquiring a target line extending on terrain to be worked on by the work implement; acquiring a current position of the work machine; acquiring an orientation of the work machine; determining a turning radius of a traveling body based on an orientation error that is the difference between the orientation of the target line and the orientation of the work machine and a position error that is the distance between the target line and the current position of the work machine; and controlling the work machine by a first steering control that automatically steers the traveling body based on the turning radius.

[0007] According to the present disclosure, in the first steering control, the turning radius of the vehicle is determined based on the heading deviation and the position deviation. The vehicle is then automatically steered in accordance with the turning radius, so that the heading of the work machine becomes parallel to the target line when the work machine reaches the target line. This reduces the burden on the operator.

[0008] FIG. 1 is a perspective view of a work machine. FIG. 2 is a block diagram showing the configuration of the work machine and its control system. FIG. 3 is a flowchart showing the automatic steering control process. FIG. 4 is a top view showing the work machine, a design line, and a target line. FIG. 5 is a top view showing the work machine and a target line. FIG. 6 is a top view showing the work machine and a target line. FIG. 7 is a diagram showing an example of angle threshold data. FIG. 8 is a diagram showing a method for determining a reduction ratio. FIG. 9 is a diagram showing an example of reduction ratio data. FIG. 10 is a top view showing the travel trajectory of the work machine under first steering control and second steering control.

[0009] A work machine according to an embodiment will now be described with reference to the drawings. Figure 1 is a side view of a work machine 1. In this embodiment, the work machine 1 is an excavator such as a hydraulic excavator or an electric excavator.

[0010] As shown in Figure 1, the work machine 1 includes a vehicle body 2 and a working implement 3. The vehicle body 2 includes a revolving unit 4 and a running unit 5. The working implement 3 is attached to the revolving unit 4. The revolving unit 4 is connected to the running unit 5 so as to be able to rotate. The revolving unit 4 is able to rotate around a rotation axis that extends in the vertical direction. A cab 6 is disposed on the revolving unit 4.

[0011] The traveling body 5 includes a left traveling unit 5A and a right traveling unit 5B. The left traveling unit 5A includes a left crawler 7A. The right traveling unit 5B includes a right crawler 7B. The work machine 1 travels by driving the left crawler 7A and the right crawler 7B. The work machine 1 also turns by creating a speed difference between the left crawler 7A and the right crawler 7B. For example, the work machine 1 turns left by slowing down the drive speed of the left crawler 7A compared to the right crawler 7B. The work machine 1 turns right by slowing down the drive speed of the right crawler 7B compared to the left crawler 7A.

[0012] The work implement 3 is attached to the rotating unit 4 so as to be movable up and down. The work implement 3 includes a boom 11, an arm 12, and a bucket 13. The boom 11 is rotatably attached to the rotating unit 4. The arm 12 is rotatably attached to the boom 11. The bucket 13 is rotatably attached to the arm 12.

[0013] Figure 2 is a block diagram showing the configuration of the work machine 1 and its control system. As shown in Figure 2, the work machine 1 includes a drive source 21, a hydraulic pump 22, a power transmission device 23, and a controller 24. The drive source 21 is controlled by a command signal from the controller 24. The drive source 21 is, for example, an internal combustion engine. Alternatively, the drive source 21 may include a drive source such as an electric motor or a hydrogen engine. The hydraulic pump 22 is driven by the drive source 21 and discharges hydraulic oil. The hydraulic pump 22 supplies hydraulic oil to the work implement 3 via a control valve 27.

[0014] The power transmission device 23 transmits the driving force of the drive source 21 to the traveling body 5. The tracks 7A, 7B are driven by the driving force from the power transmission device 23 to travel the work machine 1. The power transmission device 23 may be, for example, a torque converter or a transmission having a plurality of speed change gears. Alternatively, the power transmission device 23 may be another type of transmission such as an HST (Hydro Static Transmission) or an HMT (Hydraulic Mechanical Transmission).

[0015] The controller 24 includes a processor 31 such as a CPU, and a storage device 32. The processor 31 performs processing for controlling the work machine 1. The storage device 32 includes memory such as RAM or ROM, and an auxiliary storage device such as an HDD (Hard Disk Drive) or SSD (Solid State Drive). The storage device 32 stores data and programs for controlling the work machine 1.

[0016] The control system includes an operation device 33 and an input device 34. The operation device 33 and the input device 34 are disposed in the cab 6. The operation device 33 can be operated by an operator. The operation device 33 includes a travel operation device 33A and a steering operation device 33B.

[0017] The travel operation device 33A can be operated by an operator to manually control the forward and reverse travel of the work machine 1. The travel operation device 33A includes, for example, a lever. However, the travel operation device 33A may also include other members such as a switch. The travel operation device 33A outputs an operation signal to the controller 24 in response to operation by the operator.

[0018] The steering operation device 33B can be operated by the operator to manually operate the steering of the work machine 1. The steering operation device 33B includes, for example, a lever. However, the steering operation device 33B may include other components such as a switch. The travel operation device 33A and the steering operation device 33B may be a common component. The steering operation device 33B outputs an operation signal to the controller 24 in response to operation by the operator.

[0019] The controller 24 controls the drive source 21 and the power transmission device 23 in response to operation of the travel operation device 33A by the operator so as to travel the work machine 1. As a result, the work machine 1 travels forward or backward in response to operation of the travel operation device 33A.

[0020] The controller 24 controls the left traveling device 5A and the right traveling device 5B so as to steer the work machine 1 to the left or right in response to operation of the steering operation device 33B by the operator. The controller 24 controls the left traveling device 5A and the right traveling device 5B in response to operation of the steering operation device 33B so as to create a speed difference between the left crawler track 7A and the right crawler track 7B. As a result, the work machine 1 is steered to the left or right in response to operation of the steering operation device 33B.

[0021] The input device 34 can be operated by an operator. The input device 34 is, for example, a touch screen. However, the input device 34 may also include hardware keys. The operator operates the input device 34 to input various settings related to the work machine 1. The input device 34 outputs an input signal in response to the operator's operation.

[0022] The control system includes a position sensor 36. The position sensor 36 detects the position and orientation of the work machine 1. The position sensor 36 includes, for example, a sensor based on a Global Navigation Satellite System (GNSS). The position sensor 36 outputs position data indicating the position and orientation of the rotating bed 4. The position sensor 36 may include an Inertial Measurement Unit (IMU).

[0023] The controller 24 receives operation signals from an operation device 33. The controller 24 receives input signals from an input device 34. The controller 24 receives position data from a position sensor 36. The position of the work machine 1 is indicated by planar coordinates and altitude at the work site. The direction of the work machine 1 is indicated by east-west, north-south azimuth coordinates.

[0024] Next, we will explain the automatic steering control of the work machine 1. The controller 24 executes automatic steering control of the work machine 1 based on the position and orientation of the work machine 1. In this embodiment, the work machine 1 moves along a target line L1 (see FIG. 5 ) that extends on the terrain to be worked on by the work implement 3, and performs work to form a long trench at the work site by excavating the terrain.

[0025] During the above work, if the work machine 1 is away from the target line L1, the operator causes the work machine 1 to travel toward the target line L1 and approach the target line L1. At that time, the controller 24 uses automatic steering control to automatically steer the work machine 1 so that the heading of the work machine 1 is parallel to the target line L1 when the work machine 1 reaches the target line L1. The operator can set the automatic steering control to be enabled or disabled by operating the input device 34. The travel of the work machine 1 may also be controlled by the operator manually operating the travel control device 33A. Alternatively, the travel of the work machine 1 may be controlled by automatic control by the controller 24.

[0026] FIG. 3 is a flowchart showing the automatic steering control process. As shown in FIG. 3, in step S101, the controller 24 acquires a target line L1. The position of the target line L1 is stored in the storage device 32. The target line L1 is determined, for example, based on a construction plan or a design line set by surveying the topography of the work site. The design line indicates, for example, the center of a trench. As shown in FIG. 4, when the center C1 of the bucket 13 and the center C2 of the vehicle body are offset by an offset amount D1 in the left-right direction of the vehicle, the controller 24 may determine, as the target line L1, a line obtained by offsetting the design line L2 by the offset amount D1. Alternatively, the controller 24 may determine the design line L2 as the target line L1. For example, the controller 24 may acquire data indicating the position of the design line L2 from an external computer. Alternatively, the controller 24 may acquire the position of the design line L2 via the input device 34.

[0027] In step S102, the controller 24 acquires the current position P0 of the work machine 1. The controller 24 acquires the current position of the vehicle body center C2 as the current position P0 of the work machine 1. The vehicle body center C2 coincides with the position of the rotation axis of the rotating unit 4. The controller 24 acquires the current position of the vehicle body center C2 based on the position data described above. Note that the controller 24 may acquire a position other than the vehicle body center C2 of the vehicle body 2 as the current position P0 of the work machine 1. Alternatively, the controller 24 may acquire a part included in the work implement 3, such as the center C1 of the bucket 13, as the current position P0 of the work machine 1.

[0028] In step S103, the controller 24 acquires the orientation of the work machine 1. The orientation of the work machine 1 means the heading of the direction of travel of the work machine 1. The controller 24 acquires the orientation of the work machine 1 based on the position data described above.

[0029] In step S104, the controller 24 acquires the orientation deviation θ1 between the target line L1 and the work machine 1. As shown in FIG. 5, the orientation deviation θ1 is the difference between the orientation of the target line L1 and the orientation of the work machine 1. When the orientation of the work machine 1 matches the orientation of the target line L1, the orientation deviation θ1 is 0 degrees. As shown in FIG. 5, when the orientation of the work machine 1 is oriented toward the target line L1 rather than in a direction parallel to the target line L1, the orientation deviation θ1 takes a positive value. As shown in FIG. 6, when the orientation of the work machine 1 is oriented toward the opposite side of the target line L1 rather than in a direction parallel to the target line L1, the orientation deviation θ1 takes a negative value. The controller 24 acquires the orientation deviation θ1 based on the orientation of the target line L1 and the orientation of the work machine 1.

[0030] In step S105, the controller 24 acquires the position deviation X1. As shown in Fig. 5, the position deviation X1 is the shortest distance between the current position P0 of the work machine 1 and the target line L1. The controller 24 acquires the position deviation X1 based on the position of the target line L1 and the current position P0 of the work machine 1.

[0031] In step S106, the controller 24 determines the angle threshold Th1. The controller 24 determines the angle threshold Th1 in accordance with the position deviation X1. In particular, the controller 24 stores angle threshold data that defines the relationship between the position deviation X1 and the angle threshold Th1. FIG. 7 is a diagram showing an example of the angle threshold data. The controller 24 determines the angle threshold Th1 from the position deviation X1 by referencing the angle threshold data. As shown in FIG. 7, the angle threshold data defines the angle threshold Th1 that increases as the position deviation X1 increases. Therefore, the larger the position deviation X1, the larger the angle threshold Th1 the controller 24 sets. In other words, the further the current position P0 of the work machine 1 is from the target line L1, the larger the angle threshold Th1 the controller 24 sets.

[0032] In step S107, the controller 24 determines whether the heading deviation θ1 is greater than the angle threshold value Th1. If the heading deviation θ1 is greater than the angle threshold value Th1, in step S108 the controller 24 controls the work machine 1 using first steering control. In the first steering control, the controller 24 determines the turning radius of the traveling object 5 based on the heading deviation θ1 and the position deviation X1, and automatically steers the work machine 1 based on the turning radius.

[0033] In detail, as shown in Fig. 8 , the controller 24 determines the radius R1 of the arc-shaped trajectory L3 as the turning radius. The trajectory L3 extends from the current position P0 of the work machine 1 toward the target line L1 and is indicated by an arc that is tangent to the target line L1. The controller 24 calculates the radius R1 of the trajectory L3 based on the position and direction of the target line L1 and the current position P0 and direction of the work machine 1. In other words, the controller 24 calculates the radius R1 of the trajectory L3 based on the direction deviation θ1 and position deviation X1 of the work machine 1.

[0034] In the first steering control, the controller 24 determines the reduction ratio of the crawler tracks 7A, 7B based on the turning radius R1, and controls the drive speeds of the left crawler track 7A and the right crawler track 7B based on the reduction ratio. The reduction ratio indicates the ratio of the drive speed of the inner crawler track to the drive speed of the outer crawler track during turning. That is, the reduction ratio is expressed by the following equation (1): Rr1=C1 / C2 (1)

[0035] Rr1 is the reduction ratio. C1 is the drive speed of the inner crawler when turning. C2 is the drive speed of the outer crawler when turning. The controller 24 turns the work machine 1 by slowing the drive speed of the inner crawler down below the drive speed of the outer crawler based on the reduction ratio.

[0036] The smaller the reduction ratio, the greater the difference in drive speed between the left crawler 7A and the right crawler 7B. In other words, the smaller the reduction ratio, the greater the turning angle of the traveling body 5, and the sharper the turn of the work machine 1. The larger the reduction ratio, the smaller the difference in drive speed between the left crawler 7A and the right crawler 7B. In other words, the larger the reduction ratio, the smaller the turning angle of the work machine 1, and the more gently the work machine 1 turns.

[0037] As shown in Fig. 8, the controller 24 determines the reduction ratio based on the central angle θ2 and radius R1 of the arc of the trajectory L3, and the distance W1 between the left crawler track 7A and the right crawler track 7B of the work machine 1. In Fig. 8, the length of the arc indicated by C1 corresponds to the drive speed of the inner crawler track, and the length of the arc indicated by C2 corresponds to the drive speed of the outer crawler track. The controller 24 determines the ratio of the arc lengths C1 and C2 as the reduction ratio.

[0038] Thereafter, the controller 24 repeatedly executes the processing of steps S102 to S108, thereby changing the reduction ratio each time the position and orientation of the work machine 1 changes.

[0039] If the heading deviation θ1 is equal to or less than the angle threshold value Th1 in step S107, then in step S109 the controller 24 controls the work machine 1 using the second steering control. In the second steering control, the controller 24 automatically steers the work machine 1 so that the heading deviation θ1 increases. That is, in the second steering control, the controller 24 steers the work machine 1 so that the work machine 1 faces the target line L1 until the heading deviation θ1 becomes greater than the angle threshold value Th1. Note that even if the position deviation X1 is 0, if the heading deviation is equal to or less than the angle threshold value Th1, the controller 24 controls the work machine 1 using the second steering control.

[0040] In detail, in the second steering control, the controller 24 determines the reduction ratio of the tracks 7A, 7B based on the position deviation X1 and the orientation deviation θ1, and controls the drive speeds of the left track 7A and the right track 7B based on the reduction ratio. The controller 24 stores reduction ratio data that defines the relationship between the position deviation X1, the orientation deviation θ1, and the reduction ratio. The controller 24 determines the reduction ratio of the tracks 7A, 7B based on the position deviation X1 and the orientation deviation θ1 by referencing the reduction ratio data. Note that, as in the first steering control, in the second steering control, the controller 24 repeatedly executes the processing of steps S102 to S109. As a result, the reduction ratio is changed each time the position and orientation of the work machine 1 change.

[0041] FIG. 9 is a diagram showing an example of reduction ratio data. In the reduction ratio data, when the position deviation X1 is 0 and the absolute value |θ1| of the heading deviation θ1 (hereinafter referred to as heading deviation |θ1|) is 0, the reduction ratio is 1. The reduction ratio data defines a reduction ratio that increases as the position deviation X1 decreases when the position deviation X1 is between 0 and the position deviation threshold Th2. The reduction ratio data defines a constant reduction ratio when the position deviation X1 is equal to or greater than the position deviation threshold Th2. Therefore, in the second steering control, when the position deviation X1 is between 0 and the position deviation threshold Th2, the controller 24 increases the reduction ratio as the position deviation X1 becomes smaller. Therefore, in the second steering control, when the position deviation X1 is between 0 and the position deviation threshold Th2, the closer the work machine 1 is to the target line L1, the more gently the work machine 1 turns. This prevents the work machine 1 from making sharp turns at positions close to the target line L1. Conversely, the farther the work machine 1 is from the target line L1, the sharper the turn of the work machine 1. As a result, the work machine 1 turns sharply so that the work machine 1 quickly faces the target line L1.

[0042] The reduction ratio data defines a reduction ratio that increases as the heading deviation |θ1| decreases when the heading deviation |θ1| is from 0 to the heading deviation threshold Th3. The reduction ratio data defines a constant reduction ratio when the heading deviation |θ1| is equal to or greater than the heading deviation threshold Th3. Therefore, in the second steering control, when the heading deviation |θ1| is from 0 to the heading deviation threshold Th3, the controller 24 increases the reduction ratio the smaller the heading deviation |θ1|. Conversely, in the second steering control, when the heading deviation |θ1| is from 0 to the heading deviation threshold Th3, the controller 24 decreases the reduction ratio the larger the heading deviation |θ1|. Therefore, in the second steering control, when the heading deviation |θ1| is from 0 to the heading deviation threshold Th3, the more the work machine 1 faces in the direction opposite to the target line L1, the sharper the turn of the work machine 1. As a result, the more the work machine 1 faces in the direction away from the target line L1, the more quickly the work machine 1 will make a sharp turn toward the target line L1. Conversely, the more the work machine 1 faces toward the target line L1, the more gently the work machine 1 will turn. As a result, the more the work machine 1 faces toward the target line L1, the more the work machine 1 will be prevented from making a sharp turn.

[0043] When the work machine 1 is steered by the second steering control so that the work machine 1 faces toward the target line L1, the heading deviation |θ1| gradually decreases until the work machine 1 faces a direction parallel to the target line L1. Then, after the work machine 1 faces a direction parallel to the target line L1, the heading deviation |θ1| gradually increases. Then, when the heading deviation θ1 becomes larger than the angle threshold Th1, the controller 24 switches the automatic steering control from the second steering control to the first steering control. For example, as shown in FIG. 10 , at point P1, the work machine 1 faces in a direction opposite to the target line L1, relative to a direction parallel to the target line L1. Therefore, the controller 24 automatically steers the work machine 1 using the second steering control. As a result, the work machine 1 is steered so that the work machine 1 quickly faces toward the target line L1, while traveling along the trajectory L4 indicated by the dashed dotted line.

[0044] When the work machine 1 faces the target line L1 with respect to a direction parallel to the target line L1, and the heading deviation θ1 becomes greater than the angle threshold value Th1 at point P2, the controller 24 switches the automatic steering control from the second steering control to the first steering control. While traveling along the trajectory L5 shown by the dashed line from point P2 to point P3, the controller 24 automatically steers the work machine 1 using the first steering control so that the work machine 1 faces a direction parallel to the target line L1. As a result, when the work machine 1 reaches the target line L1 at point P3, the heading of the work machine 1 is parallel to the target line L1. Depending on the road surface conditions, there may be cases where the control switches from the second steering control to the first steering control and then transitions back to the second steering control.

[0045] As described above, in the control system for the work machine 1 according to this embodiment, the work machine 1 is automatically steered based on the turning radius R1, so that when the work machine 1 reaches the target line L1, the heading of the work machine 1 becomes parallel to the target line L1, thereby reducing the burden on the operator.

[0046] Although one embodiment of the present invention has been described above, the present invention is not limited to the above embodiment, and various modifications are possible without departing from the gist of the invention.

[0047] The work machine 1 may be equipped with wheels and tires instead of tracks. The work machine 1 may be remotely operable. The operation device 33 and the input device 34 may be located outside the work machine 1. Part of the automatic control processing described above may be executed by a controller 24 external to the work machine 1. The automatic control processing may be distributed and executed among multiple controllers 24.

[0048] The work performed by the work machine 1 under automatic control is not limited to the work of forming a ditch, and may be other work. For example, automatic control may be applied to the work of filling a ditch with earth and sand. The automatic control process is not limited to that of the above embodiment and may be modified. For example, the condition for switching between the first steering control and the second steering control is not limited to an angle threshold value alone and may include other conditions. The automatic steering control may be enabled when the position deviation X1 is equal to or less than a predetermined value. The automatic steering control may be enabled when the heading deviation |θ| is within a predetermined range or outside the predetermined range. For example, the automatic steering control may be disabled when the heading deviation |θ| is between 80° and 100°.

[0049] In the above embodiment, the first steering control is executed when the heading deviation θ1 is greater than the angle threshold Th1, and the second steering control is executed when the heading deviation θ1 is equal to or less than the angle threshold Th1. However, the first steering control may be executed when the heading deviation θ1 is equal to or greater than the angle threshold Th1, and the second steering control may be executed when the heading deviation θ1 is less than the angle threshold Th1.

[0050] The angle threshold data is not limited to that of the above embodiment and may be changed. For example, in the angle threshold data, the relationship between the position deviation X1 and the angle threshold Th1 is not limited to a linear function and may be expressed by another relationship. The angle threshold data is not limited to an equation or a graph and may be expressed in other forms such as a correlation table. The reduction ratio data is not limited to that of the above embodiment and may be changed. The reduction ratio data is not limited to an equation or a graph and may be expressed in other forms such as a correlation table.

[0051] In the above embodiment, the controller 24 reduces the drive speed of the inner track compared to the drive speed of the outer track, thereby turning the work machine 1. However, the controller 24 may also increase the drive speed of the outer track compared to the drive speed of the inner track, thereby turning the work machine 1. The turning radius R1 and / or the reduction ratio may be determined or corrected based on vehicle dimensions, vehicle performance, terrain information such as slope, soil information of the terrain, or weather information.

[0052] The target line L1 is not limited to a straight line, and may have other shapes such as a curve or a broken line. In this case, the controller 24 may set any point on the target line L1 as the target point, and control the work machine 1 based on the position of the target point and the orientation of the tangent to the target line at the target point. For example, the target point may be a point on the target line that is a predetermined distance ahead of the work machine 1 in the direction of travel. In the above embodiment, the direction of travel is ahead of the work machine 1, but it may also be behind the work machine 1.

[0053] According to the present disclosure, the burden on the operator to adjust the orientation of the work machine to be parallel to the target line when the work machine reaches the target line is reduced.

[0054] 1: Work machine, 3: Work equipment, 5A: Left traveling device, 5B: Right traveling device, 24: Controller, L1: Target line

Claims

1. A system for controlling a work machine including a work implement and a traveling body, comprising a controller, wherein the controller: acquires a target line extending on a terrain to be worked by the work implement; acquires the current position of the work machine; acquires the orientation of the work machine; determines a turning radius of the traveling body based on an orientation deviation, which is the difference between the orientation of the target line and the orientation of the work machine, and a position deviation, which is the distance between the target line and the current position of the work machine; and controls the work machine using a first steering control that automatically steers the traveling body based on the turning radius.

2. The system according to claim 1, wherein the controller determines the radius of an arc that extends from the current position of the work machine toward the target line and is tangent to the target line as the turning radius.

3. The system according to claim 1, wherein the controller determines whether the heading deviation is greater than an angle threshold, and controls the work machine using the first steering control if the heading deviation is greater than the angle threshold.

4. The system according to claim 3, wherein the controller controls the work machine by a second steering control that automatically steers the vehicle so as to increase the heading deviation when the heading deviation is smaller than the angle threshold value.

5. The system according to claim 4, wherein the controller, in the second steering control, causes the traveling vehicle to turn more gently as the absolute value of the heading deviation becomes smaller.

6. The system described in claim 5, wherein the running body includes a left running device and a right running device, and the controller, when the running body turns, turns the running body by slowing down the inner running device of the left and right running devices more than the outer running device, and in the second steering control, the smaller the absolute value of the heading deviation, the greater the reduction ratio of the inner running device relative to the outer running device.

7. The system according to claim 4, wherein the controller, in the second steering control, causes the traveling vehicle to turn more gently as the position deviation becomes smaller.

8. The system described in claim 7, wherein the running body includes a left running device and a right running device, and the controller, when the running body turns, turns the running body by slowing down the inner running device of the left running device and the right running device more than the outer running device, and in the second steering control, the reduction ratio is increased as the position deviation becomes smaller.

9. The system of claim 3, wherein the controller determines the angle threshold in response to the position deviation.

10. The system according to claim 9, wherein the controller increases the angle threshold as the position deviation increases.

11. A method for controlling a work machine including a work implement and a traveling body, comprising: acquiring a target line extending on a terrain to be worked by the work implement; acquiring the current position of the work machine; acquiring the orientation of the work machine; determining a turning radius of the traveling body based on an orientation deviation, which is the difference between the orientation of the target line and the orientation of the work machine, and a position deviation, which is the distance between the target line and the current position of the work machine; and controlling the work machine by a first steering control that automatically steers the traveling body based on the turning radius.

12. The method according to claim 11, wherein the turning radius is determined to be the radius of an arc that extends from the current position of the work machine toward the target line and is tangent to the target line.

13. The method of claim 11, comprising: determining whether the heading deviation is greater than an angle threshold; and controlling the work machine with the first steering control if the heading deviation is greater than the angle threshold.

14. The method according to claim 13, further comprising controlling the work machine by a second steering control that automatically steers the vehicle so as to increase the heading deviation when the heading deviation is smaller than the angle threshold value.

15. The method according to claim 14, further comprising: in the second steering control, turning the traveling vehicle more gently as the absolute value of the heading deviation becomes smaller.

16. The method according to claim 15, further comprising: the traveling body includes a left traveling device and a right traveling device; when the traveling body turns, the inner traveling device of the left traveling device and the right traveling device is slowed down more than the outer traveling device, thereby turning the work machine; and in the second steering control, the smaller the absolute value of the heading deviation, the larger the reduction ratio of the inner traveling device relative to the outer traveling device.

17. The method according to claim 14, further comprising: in the second steering control, turning the traveling object more gently as the position deviation becomes smaller.

18. The method according to claim 17, further comprising: the running body includes a left running device and a right running device; when the running body turns, the running body is turned by slowing down the inner running device of the left running device and the right running device more than the outer running device; and in the second steering control, the reduction ratio is increased as the position deviation becomes smaller.

19. The method of claim 13, further comprising: determining the angle threshold in response to the position deviation.

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