Work vehicle, work vehicle control system and control method

Abstract

To reduce an estimation error of an azimuth angle during dead reckoning.SOLUTION: A work vehicle includes: a positioning system that outputs first time-series data; an inertia measurement system that outputs second time-series data based on measurement values of each of an acceleration sensor and an angular velocity sensor; and a control device. In a first state where positioning by the positioning system is possible, the control device sequentially estimates a first azimuth angle on the basis of the first time-series data and the second time-series data, sequentially estimates a second azimuth angle on the basis of the second time-series data, calculates an azimuth error change rate of the second azimuth angle on the basis of a difference between the first azimuth angle and the second azimuth angle sequentially estimated in the first state, and, in a second state where reliability of positioning by the positioning system is reduced, performs a steering control of the work vehicle on the basis of an azimuth angle obtained by correcting the second azimuth angle estimated on the basis of the second time-series data, on the basis of the azimuth error change rate.SELECTED DRAWING: Figure 12

Description

[Technical Field]

[0001] The present disclosure relates to a work vehicle, a control system and a control method for a work vehicle. [Background technology]

[0002] Research and development is underway to automate work vehicles such as tractors used in farm fields. For example, work vehicles that run with automatic steering using positioning systems such as the Global Navigation Satellite System (GNSS), which enables precise positioning, have been put into practical use. Work vehicles that not only automatically steer but also automatically control speed have also been put into practical use.

[0003] Patent Document 1 discloses a GNSS / INS navigation system that performs vehicle positioning by combining GNSS and an IMU (Inertial Measurement Unit). This system can operate in a dead reckoning mode, performing positioning based on signals from the IMU when GNSS signals cannot be obtained. The document discloses that during dead reckoning operation, drift errors in measurements of rotation around the vehicle's z-axis (yaw axis) are corrected.

[0004] Patent Document 2 discloses that in a positioning system equipped with a GNSS and an INS (Inertial Navigation System), in a situation where a sufficient amount of GNSS signals is not available, a pre-trained neural network prediction model is used to predict the output error of the GNSS and correct the output of the INS. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] US Patent Application Publication No. 2018 / 0292212 [Patent Document 2] U.S. Patent Application Publication No. 2021 / 0095965 Summary of the Invention [Problem to be solved by the invention]

[0006] A work vehicle traveling with automatic steering controls steering along a target route while performing self-localization, which estimates the vehicle's position and orientation. Self-localization is performed based on the output of various sensors, such as GNSS and IMU. The environment in which a work vehicle travels may contain obstacles that block the reception of GNSS signals. For example, windbreaks and other trees may be present in the driving environment, reducing the reliability of positioning based on GNSS signals. In such cases, dead reckoning may be performed, using signals from the IMU to supplement the positioning results. However, the azimuth angle estimated based on signals from the IMU suffers from the problem of accumulating drift errors over time. It is therefore necessary to reduce the error due to drift in the azimuth angle estimated during dead reckoning.

[0007] The present disclosure provides systems and methods for reducing azimuth angle estimation errors during dead reckoning operations. [Means for solving the problem]

[0008] A work vehicle according to an exemplary embodiment of the present disclosure is capable of automatic steering operation. The work vehicle includes a positioning system that outputs first time-series data including position information of the work vehicle, an inertial measurement system that includes an acceleration sensor and an angular velocity sensor and outputs second time-series data based on measurement values ​​of the acceleration sensor and measurement values ​​of the angular velocity sensor, and a control device that estimates a position and azimuth angle of the work vehicle based on the first time-series data and the second time-series data, and performs steering control of the work vehicle based on the estimated position and azimuth angle and a preset target route. In a first state in which positioning by the positioning system is possible, the control device sequentially estimates a first azimuth angle of the work vehicle based on the first time series data and the second time series data, sequentially estimates a second azimuth angle of the work vehicle based on the second time series data, performs steering control of the work vehicle based on the first azimuth angle, calculates an azimuth error change rate of the second azimuth angle based on the difference between the first azimuth angle and the second azimuth angle sequentially estimated in the first state, and when the state changes from the first state to a second state in which the reliability of positioning by the positioning system has decreased, performs steering control of the work vehicle based on the second azimuth angle estimated based on the second time series data, corrected based on the azimuth error change rate, until returning to the first state.

[0009] A general or specific aspect of the present disclosure may be realized by an apparatus, a system, a method, an integrated circuit, a computer program, or a computer-readable non-transitory storage medium, or any combination thereof. The computer-readable storage medium may include a volatile storage medium or a non-volatile storage medium. An apparatus may be composed of multiple devices. When an apparatus is composed of two or more devices, the two or more devices may be located in a single device or may be located separately in two or more separate devices. [Effects of the Invention]

[0010] According to an embodiment of the present disclosure, it is possible to reduce the estimation error of the azimuth angle during the dead reckoning operation. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a perspective view showing an example of the appearance of a work vehicle in a first embodiment. [Figure 2] 1 is a side view that schematically illustrates an example of a work vehicle and a work implement coupled to the work vehicle. [Figure 3] FIG. 1 is a block diagram showing an example of a schematic configuration of a work vehicle and a work machine. [Figure 4] FIG. 1 is a conceptual diagram showing an example of a work vehicle that performs positioning using RTK-GNSS. [Figure 5] FIG. 2 is a schematic diagram showing an example of an operation terminal and an operation switch group provided inside the cabin. [Figure 6] FIG. 10 is a diagram illustrating an example of the traveling of a work vehicle in automatic steering mode. [Figure 7] FIG. 1 is a diagram schematically illustrating an example of a target route for a work vehicle traveling in a farm field using automatic steering. [Figure 8] 4 is a flowchart showing an example of an operation during automatic steering executed by the control device. [Figure 9A] FIG. 1 is a diagram illustrating an example of a work vehicle traveling along a target route. [Figure 9B] FIG. 10 is a diagram illustrating an example of a work vehicle at a position shifted to the right from the target route. [Figure 9C] FIG. 10 is a diagram illustrating an example of a work vehicle that is shifted to the left from the target route. [Figure 9D] FIG. 10 is a diagram illustrating an example of a work vehicle facing in an inclined direction relative to a target route. [Figure 10] FIG. 1 is a diagram illustrating an example of a situation in which the reception strength of a GNSS signal decreases. [Figure 11] 10 is a graph showing an example of a change in azimuth angle over time. [Figure 12] 10 is a flowchart illustrating an example of a position and orientation estimation operation. [Figure 13A]10 shows an example of the reception strength of each GNSS signal when there is no reception obstruction. [Figure 13B] 10 shows an example of the reception strength of each GNSS signal when reception interference occurs. [Figure 14A] 10A and 10B are diagrams showing an example of the change in azimuth deviation over time when correction processing is performed and when correction processing is not performed. [Figure 14B] 10A and 10B are diagrams illustrating an example of a change in position deviation over time when a correction process is performed and when a correction process is not performed. [Figure 15] FIG. 10 is a diagram illustrating an example of a display on an operation terminal. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, embodiments of the present disclosure will be described. However, more detailed descriptions than necessary may be omitted. For example, detailed descriptions of already well-known matters and redundant descriptions of substantially identical configurations may be omitted. This is to avoid unnecessary redundancy in the following description and to facilitate understanding by those skilled in the art. Note that the inventors provide the accompanying drawings and the following description to enable those skilled in the art to fully understand the present disclosure, and do not intend for them to limit the subject matter described in the claims. In the following description, components having the same or similar functions are designated by the same reference numerals.

[0013] The following embodiments are examples, and the technology of the present disclosure is not limited to the following embodiments. For example, the numerical values, shapes, steps, the order of the steps, the layout of the display screen, and the like shown in the following embodiments are merely examples, and various modifications are possible as long as no technical contradiction occurs. Furthermore, one aspect can be combined with another aspect as long as no technical contradiction occurs.

[0014] An embodiment in which the technology of the present disclosure is applied to an agricultural tractor, which is an example of a work vehicle, will be described below. The technology of the present disclosure is not limited to tractors, but can be applied to any work vehicle that travels with automatic steering. The work vehicle may be, for example, a rice transplanter, a combine harvester, a mower, a harvester, a snowplow, or a construction vehicle.

[0015] (Embodiment) A work vehicle and a control system for the work vehicle in an exemplary embodiment of the present disclosure will be described.

[0016] The work vehicle in this embodiment is equipped with a control system that performs control to achieve automatic steering operation. The control system is a computer system including a storage device and a control device. The storage device includes one or more storage media and stores various data such as a target route for the work vehicle. The control device includes one or more computers, processors, or control circuits and controls the operation of the work vehicle. The control device can operate in both automatic steering mode and manual steering mode. The control device switches between the automatic steering mode and the manual steering mode in response to, for example, a driver's operation. In the automatic steering mode, the control device controls the steering of the work vehicle so that the work vehicle travels along the target route based on the position of the work vehicle determined by the positioning system and the target route stored in the storage device. The positioning system is located inside or outside the work vehicle. The positioning system includes, for example, a GNSS receiver and determines the position of the work vehicle based on signals from multiple GNSS satellites and outputs time-series position data. The positioning system may also include devices other than the GNSS receiver, such as a LiDAR sensor or a camera. The position of the work vehicle can be estimated by matching data acquired by the LiDAR sensor or camera with a pre-prepared environmental map. The target route is a route that is set within the area in which the work vehicle will travel and serves as a target for travel. The target route is set and recorded in a storage device before automatic steering operation begins. The target route may be set within a farm field, for example.

[0017] The work vehicle in this embodiment is equipped with a positioning system, an inertial measurement system, and a control device. The positioning system outputs first time series data including position information of the work vehicle. The inertial measurement system includes an acceleration sensor and an angular velocity sensor, and outputs second time series data based on measurement values ​​of the acceleration sensor and measurement values ​​of the angular velocity sensor. The control device estimates the position and azimuth angle of the work vehicle based on the first time series data and the second time series data, and performs steering control of the work vehicle based on the estimated position and azimuth angle and a predetermined target route. The control device performs the following operations (1) to (3). (1) In a first state in which positioning by the positioning system is possible, the azimuth angle of the work vehicle (hereinafter also referred to as the "first azimuth angle") is sequentially estimated based on the first time series data and the second time series data, the azimuth angle of the work vehicle (hereinafter also referred to as the "second azimuth angle") is sequentially estimated based on the second time series data, and steering control of the work vehicle is performed based on the first azimuth angle. (2) Calculating the azimuth error change rate of the second azimuth angle based on the difference between the first azimuth angle and the second azimuth angle successively estimated in the first state. (3) When the state changes from the first state to a second state in which the reliability of positioning by the positioning system has decreased, steering control of the work vehicle is performed based on an azimuth angle that is estimated based on the second time series data and corrected based on the azimuth error change rate until the state returns to the first state.

[0018] The positioning system may include, for example, a GNSS receiver, and the inertial measurement system may be, for example, an IMU or a combination of an acceleration sensor and an angular velocity sensor, each of which is provided separately.

[0019] In the first state, the control device can estimate the position and first azimuth angle of the work vehicle from the first time series data and the second time series data, for example, by processing using an extended Kalman filter. The control device can also estimate the second azimuth angle by processing such as integrating the angular velocity measurement values ​​included in the second time series data. Here, the azimuth angle refers to the yaw angle, which is the angle of rotation around the vertical axis of the work vehicle.

[0020] The first state is a state in which there are no obstacles around the work vehicle that prevent GNSS signal reception, making it possible to perform highly reliable positioning based on GNSS signals. The second state is a state in which the reliability of GNSS signal-based positioning is low or even impossible due to the presence of obstacles around the work vehicle that prevent GNSS signal reception. The environment in which agricultural work vehicles travel may contain obstacles that prevent GNSS signal reception. For example, windbreaks may be present on the periphery of a field, and when the work vehicle turns near the windbreaks, reception of GNSS signals may be prevented, reducing the reliability of self-location estimation. In such cases, the control device performs dead reckoning, which uses signals from an inertial measurement system to estimate the vehicle's position.

[0021] During dead reckoning, the heading of the work vehicle can be calculated by integrating the angular velocity measured by the angular velocity sensor. The heading is determined by the yaw angle. Because the yaw angle cannot be corrected based on the tilt with respect to the direction of gravity obtained from the acceleration sensor measurements, an error in the angular velocity in the yaw direction accumulates. This error is called a "drift error." The drift error occurs depending on the characteristics of elements in the inertial measurement system or on environmental factors such as temperature.

[0022] In this embodiment, to compensate for the drift error, the control device calculates the azimuth error change rate of the second azimuth angle based on the difference between the first azimuth angle and the second azimuth angle that are sequentially estimated in a first state in which positioning by the positioning system is possible. The control device calculates the azimuth error change rate based on the time change rate of the difference between the first azimuth angle and the second azimuth angle in the first state. In a second state in which the reliability of positioning by the positioning system has decreased, the control device performs steering control of the work vehicle based on the azimuth angle that is obtained by correcting the second azimuth angle estimated based on the second time-series data based on the azimuth error change rate. This operation suppresses a decrease in the reliability of self-position estimation due to azimuth angle (yaw angle) drift and stabilizes automatic steering during dead reckoning.

[0023] The configuration and operation of the work vehicle of this embodiment will be described in more detail below.

[0024] <Configuration> FIG. 1 is a perspective view showing an example of the appearance of a work vehicle 100 in this embodiment. FIG. 2 is a side view that schematically shows an example of the work vehicle 100 and an implement 300 coupled to the work vehicle 100. The work vehicle in this embodiment is a tractor used in farm fields. The technology in this embodiment can also be applied to work vehicles other than tractors.

[0025] The work vehicle 100 in this embodiment is equipped with a positioning system 120 and one or more obstacle sensors 130. Although one obstacle sensor 130 is illustrated in FIG. 1, the obstacle sensors 130 may be provided at multiple locations on the work vehicle 100. Note that the obstacle sensors 130 are provided as needed. If not needed, the work vehicle 100 does not have to be equipped with the obstacle sensors 130.

[0026] As shown in Fig. 2, work vehicle 100 includes a vehicle body 101, a prime mover (engine) 102, and a transmission 103. Vehicle body 101 is provided with wheels 104 with tires and a cabin 105. Wheels 104 include a pair of front wheels 104F and a pair of rear wheels 104R. Inside cabin 105, a driver's seat 107, a steering device 106, a plurality of pedals 109, an operation terminal 200, and a group of switches for operation are provided. One or both of front wheels 104F and rear wheels 104R may be replaced with a plurality of wheels (crawlers) equipped with tracks rather than with tires.

[0027] The positioning system 120 in this embodiment includes a GNSS receiver. The GNSS receiver may include an antenna that receives signals from GNSS satellites and a processor that determines the position of the work vehicle 100 based on the signals received by the antenna. The positioning system 120 receives GNSS signals transmitted from multiple GNSS satellites and performs positioning based on the GNSS signals. GNSS is a general term for satellite positioning systems such as GPS (Global Positioning System), QZSS (Quasi-Zenith Satellite System, e.g., Michibiki), GLONASS, Galileo, and BeiDou. The positioning system 120 in this embodiment is provided on top of the cabin 105, but may be provided in another location.

[0028] The positioning system 120 may include other types of devices, such as a LiDAR sensor or a camera (including an image sensor), instead of or in addition to a GNSS receiver. If there are features that function as characteristic points in the environment in which the work vehicle 100 travels, the position of the work vehicle 100 can be estimated with high accuracy based on data acquired by the LiDAR sensor or camera and an environmental map that is pre-recorded in the storage device 170. The LiDAR sensor Summer A LiDAR sensor or camera may be used in conjunction with a GNSS receiver. Summer Alternatively, by using data acquired by a camera to correct or complement position data based on GNSS signals, the position of the work vehicle 100 can be identified with higher accuracy.

[0029] In the example shown in FIGS. 1 and 2 , the obstacle sensor 130 is provided at the rear of the vehicle body 101. The obstacle sensor 130 may also be provided at a location other than the rear of the vehicle body 101. For example, one or more obstacle sensors 130 may be provided at any of the sides, front, and cabin 105 of the vehicle body 101. The obstacle sensor 130 detects objects present around the work vehicle 100. The obstacle sensor 130 may include, for example, a laser scanner or an ultrasonic sonar. The obstacle sensor 130 outputs a signal indicating the presence of an obstacle when an object is present closer than a predetermined distance from the obstacle sensor 130. Multiple obstacle sensors 130 may be provided at different positions on the body of the work vehicle 100. For example, multiple laser scanners and multiple ultrasonic sonars may be provided at different positions on the body. Providing such a large number of obstacle sensors 130 reduces blind spots in monitoring obstacles around the work vehicle 100. As described above, the work vehicle 100 does not necessarily have to include the obstacle sensor 130.

[0030] The prime mover 102 may be, for example, a diesel engine. An electric motor may be used instead of a diesel engine. The transmission 103 can change the propulsive force and travel speed of the work vehicle 100 by changing gears. The transmission 103 can also switch the work vehicle 100 between forward and reverse travel.

[0031] The steering device 106 includes a steering wheel, a steering shaft connected to the steering wheel, and a power steering device that assists steering by the steering wheel. The front wheels 104F are steerable wheels, and the traveling direction of the work vehicle 100 can be changed by changing the turning angle (also referred to as the "steering angle"). The steering angle of the front wheels 104F can be changed by operating the steering wheel. The power steering device includes a hydraulic device or an electric motor that supplies an assisting force to change the steering angle of the front wheels 104F. When automatic steering is performed, the steering angle is automatically adjusted by the force of the hydraulic device or electric motor under control of a control device arranged inside the work vehicle 100.

[0032] The pedals 109 include an accelerator pedal, a clutch pedal, and a brake pedal. Each pedal is provided with a sensor that detects when the pedal is depressed.

[0033] A coupling device 108 is provided at the rear of the vehicle body 101. The coupling device 108 includes, for example, a three-point support device (also referred to as a "three-point link" or "three-point hitch"), a PTO (Power Take Off) shaft, a universal joint, and a communication cable. The coupling device 108 allows the work implement 300 to be attached to and detached from the work vehicle 100. The coupling device 108 can raise and lower the three-point link using, for example, a hydraulic device, to control the position or attitude of the work implement 300. Power can also be sent from the work vehicle 100 to the work implement 300 via the universal joint. The work vehicle 100 can cause the work implement 300 to perform a predetermined task while towing the work implement 300. The coupling device may be provided at the front of the vehicle body 101. In this case, the work implement can be connected to the front of the work vehicle 100.

[0034] 2 is a rotary tiller, but the work machine 300 is not limited to a rotary tiller. Any work machine, such as a mower, seeder, spreader, rake, baler, harvester, sprayer, or harrow, can be connected to the work vehicle 100 and used.

[0035] 3 is a block diagram showing an example of a schematic configuration of the work vehicle 100 and the work implement 300. The work vehicle 100 and the work implement 300 can communicate with each other via a communication cable included in the coupling device 108.

[0036] 3 includes a positioning system 120, an obstacle sensor 130, an operation terminal 200, an inertial measurement system 125, a drive unit 140, a group of sensors 150, a control system 160, a communication interface (I / F) 190, a group of operation switches 210, and a buzzer 220. These components are connected to each other via a bus so that they can communicate with each other.

[0037] The positioning system 120 includes a GNSS receiver 121, an RTK receiver 122, and a processor 123. The inertial measurement system 125 includes an acceleration sensor 126, an angular velocity sensor 127, and a processor 128. The sensor group 150 includes, for example, a steering wheel sensor 152, a turning angle sensor 154, and a transmission (T / M) rotation sensor 156. The control system 160 includes a storage device 170 and a control device 180. The control device 180 includes multiple electronic control units (ECUs) 182, 183, 184, and 185. The work implement 300 includes a drive device 340, a control device 380, and a communication interface (I / F) 390. Note that FIG. 3 shows components that are relatively closely related to the automatic steering or automatic driving operation of the work vehicle 100, and does not show other components.

[0038] The GNSS receiver 121 in the positioning system 120 receives satellite signals (also referred to as "GNSS signals") transmitted from multiple GNSS satellites and generates GNSS data based on the satellite signals. The GNSS data is generated in a predetermined format, such as the NMEA-0183 format. The GNSS data may include, for example, the identification number of each satellite from which the satellite signal is received, an elevation angle, an azimuth angle, and a value indicating reception strength. The reception strength may be expressed, for example, as a value such as the carrier-to-noise power density ratio (C / N0). The GNSS data may also include position information of the work vehicle 100 calculated based on the multiple received satellite signals, and information indicating the reliability of the position information. The position information may be represented, for example, by latitude, longitude, and height above mean sea level. The reliability of the position information may be represented, for example, by a DOP value indicating the satellite configuration.

[0039] The positioning system 120 shown in FIG. 3 performs positioning of the work vehicle 100 using RTK (Real Time Kinematic)-GNSS. FIG. 4 is a conceptual diagram showing an example of a work vehicle 100 performing positioning using RTK-GNSS. Positioning using RTK-GNSS uses satellite signals transmitted from multiple GNSS satellites 50 as well as correction signals transmitted from a reference station 60. The reference station 60 may be installed near the field where the work vehicle 100 will be traveling (for example, within 10 km of the work vehicle 100). The reference station 60 generates correction signals, for example in RTCM format, based on the satellite signals received from the multiple GNSS satellites 50 and transmits them to the positioning system 120. The RTK receiver 122 includes an antenna and a modem and receives the correction signals transmitted from the reference station 60. A processor 123 of the positioning system 120 corrects the positioning results obtained by the GNSS receiver 121 based on the correction signals. By using RTK-GNSS, it is possible to perform positioning with an accuracy of, for example, a few centimeters. Position information including latitude, longitude, and altitude information is acquired through highly accurate positioning using RTK-GNSS. The processor 123 of the positioning system 120 calculates the position of the work vehicle 100, for example, at a frequency of approximately 1 to 10 times per second. The positioning system 120 outputs first time-series data including information on the calculated position (coordinates).

[0040] The positioning method is not limited to RTK-GNSS, and any positioning method (such as interferometric positioning or differential positioning) that can obtain position information with the required accuracy can be used. For example, positioning may be performed using a Virtual Reference Station (VRS) or a Differential Global Positioning System (DGPS). If position information with the required accuracy can be obtained without using a correction signal transmitted from the reference station 60, the position information may be generated without using a correction signal. In this case, the positioning system 120 does not need to be equipped with an RTK receiver 122.

[0041] The inertial measurement system 125 is, for example, an IMU. Alternatively, the inertial measurement system 125 may be a combination of an acceleration sensor 126 and an angular velocity sensor 127 that are provided separately. The acceleration sensor 126 is, for example, a triaxial acceleration sensor. The angular velocity sensor 127 is, for example, a triaxial gyroscope. The processor 128 can output second time-series data including information on the position and orientation of the work vehicle 100 by performing processing such as time integration of the measurement values ​​of the acceleration sensor 126 and the angular velocity sensor 127. Instead of performing the processing described above, the processor 128 may perform necessary correction processing on the measurement values ​​of the acceleration sensor 126 and the angular velocity sensor 127, and output data including information on the corrected acceleration and angular velocity and measurement time as the second time-series data. The inertial measurement system 125 may also be equipped with an orientation sensor such as a triaxial geomagnetic sensor. The inertial measurement system 125 functions as a motion sensor and can output signals indicating various quantities such as the acceleration, speed, displacement, and attitude of the work vehicle 100. The inertial measurement system 125 can output these signals at a frequency of, for example, about several tens to several thousands of times per second.

[0042] The positioning system 120 and the inertial measurement system 125 may be integrated into a single device. The processing of the processors 123 and 128 may be performed by a single processor. At least a portion of the processing of the processors 123 and 128 may be performed by a processor included in the control device 180. Such a processor can estimate the position and orientation of the work vehicle 100 with higher accuracy based on the signals output from the inertial measurement system 125 in addition to the GNSS signals and correction signals. The signals output from the inertial measurement system 125 can be used to correct or supplement the position calculated based on the GNSS signals and correction signals. The inertial measurement system 125 can output signals at a higher frequency than the positioning system 120. The high-frequency signals can be used to measure the position and orientation of the work vehicle 100 at a higher frequency (e.g., 10 Hz or higher).

[0043] The positioning system 120 may include other types of sensors, such as a LiDAR sensor or an image sensor, in addition to or instead of the GNSS receiver 121 and the RTK receiver 122. If there are features that can serve as landmarks in the environment in which the work vehicle 100 travels, the position and orientation of the work vehicle 100 can be estimated by matching the sensor data output from these sensors with an environmental map. In such a configuration, an external sensor, such as a LiDAR sensor or an image sensor, may be included in the positioning system.

[0044] The drive device 140 includes various devices necessary for the travel of the work vehicle 100 and the driving of the work implement 300, such as the aforementioned prime mover 102, transmission 103, steering device 106, and coupling device 108. The prime mover 102 may be equipped with an internal combustion engine such as a diesel engine. The drive device 140 may be equipped with an electric motor for traction instead of or in addition to the internal combustion engine.

[0045] The steering wheel sensor 152 measures the rotation angle of the steering wheel of the work vehicle 100. The turning angle sensor 154 measures the turning angle of the front wheels 104F, which are the steered wheels.

[0046] The T / M rotation sensor 156 is a sensor for measuring the rotational speed of the axle connected to the wheel 104, i.e., the number of rotations per unit time. The T / M rotation sensor 156 may be a sensor that uses, for example, a magnetoresistive element (MR), a Hall element, or an electromagnetic pickup. The T / M rotation sensor 156 outputs, for example, a pulse signal that is proportional to the rotational speed of a gear included in the transmission. The T / M rotation sensor 156 may be used to determine the vehicle speed and direction of travel of the work vehicle 100.

[0047] The measurement values ​​from the steering wheel sensor 152, the turning angle sensor 154, and the T / M rotation sensor 156 are used for steering control by the control device 180.

[0048] Storage device 170 includes one or more storage media, such as flash memory or a magnetic disk. Storage device 170 stores various data generated by each sensor and control device 180. The data stored in storage device 170 may include map data of the environment in which work vehicle 100 travels, and target route data for automatic steering. Storage device 170 also stores computer programs that cause each ECU in control device 180 to perform various operations, which will be described later. Such computer programs may be provided to work vehicle 100 via a storage medium (e.g., a semiconductor memory or an optical disk) or an electric communication line (e.g., the Internet). Such computer programs may be sold as commercial software.

[0049] The control device 180 includes multiple ECUs. The multiple ECUs include an ECU 182 for driving control, an ECU 183 for automatic steering control, an ECU 184 for work equipment control, and an ECU 185 for display control. The ECU 182 controls the speed of the work vehicle 100 by controlling the prime mover 102, transmission 103, accelerator, and brake included in the drive unit 140. The ECU 182 also controls the steering of the work vehicle 100 by controlling the hydraulic device or electric motor included in the steering device 106 based on measurement values ​​from the steering wheel sensor 152. The ECU 183 performs calculations and controls to achieve automatic steering operation based on signals output from the positioning system 120, the inertial measurement system 125, the steering wheel sensor 152, the turning angle sensor 154, the T / M rotation sensor 156, etc. During automatic steering operation, the ECU 183 sends a command to the ECU 182 to change the steering angle. The ECU 182 changes the steering angle by controlling the steering device 106 in response to the command. The ECU 184 controls the operation of the coupling device 108 to cause the work implement 300 to perform the desired operation. The ECU 184 also generates a signal to control the operation of the work implement 300 and transmits this signal to the work implement 300 from the communication I / F 190. The ECU 185 controls the display of the operation terminal 200. For example, the ECU 185 causes the display device of the operation terminal 200 to display various items such as a map of the field, the position and target route of the work vehicle 100 on the map, pop-up notifications, and setting screens.

[0050] Through the operation of these ECUs, the control device 180 realizes operation by manual steering or automatic steering. During automatic steering operation, the control device 180 controls the drive device 140 based on the position and orientation of the work vehicle 100 measured or estimated by the positioning system 120 and the inertial measurement system 125, and the target route stored in the storage device 170. In this way, the control device 180 can cause the work vehicle 100 to travel along the target route. Note that the control device 180 may automatically control not only the steering of the work vehicle 100 but also the vehicle speed. In other words, the control device 180 may be configured to operate in an automatic driving mode in which the work vehicle 100 is automatically driven along a preset target route.

[0051] The multiple ECUs included in the control device 180 can communicate with each other in accordance with a vehicle bus standard such as CAN (Controller Area Network). In FIG. 3, ECUs 182, 183, 184, and 185 are shown as individual blocks, but the functions of each of these may be realized by multiple ECUs. Also, an on-board computer that integrates at least some of the functions of ECUs 182, 183, 184, and 185 may be provided. The control device 180 may include ECUs other than ECUs 182, 183, 184, and 185. Any number of ECUs may be provided depending on the functions. Each ECU includes a control circuit including one or more processors.

[0052] The communication I / F 190 is a circuit that communicates with the communication I / F 390 of the work implement 300. The communication I / F 190 transmits and receives signals compliant with ISOBUS standards such as ISOBUS-TIM to and from the communication I / F 390 of the work implement 300. This makes it possible to cause the work implement 300 to perform desired operations and to obtain information from the work implement 300. The communication I / F 190 may communicate with an external computer via a wired or wireless network. The external computer may be, for example, a server computer in a farming support system that centrally manages information about farm fields on the cloud and supports agriculture by utilizing data on the cloud.

[0053] The operation terminal 200 is a terminal through which the user performs operations related to the travel of the work vehicle 100 and the operation of the work implement 300, and is also referred to as a virtual terminal (VT). The operation terminal 200 may include a display device such as a touch screen, and / or one or more buttons. By operating the operation terminal 200, the user can perform various operations, such as switching the automatic steering mode on / off, setting the initial position of the work vehicle 100, setting a target route, recording or editing a map, and switching the work implement 300 on / off. At least some of these operations can also be performed by operating the operation switch group 210. The display on the operation terminal 200 is controlled by the ECU 185.

[0054] Buzzer 220 is an audio output device that emits a warning sound to alert the user to an abnormality. For example, buzzer 220 emits a warning sound when work vehicle 100 deviates from the target route by a predetermined distance or more during automatic steering operation. Instead of buzzer 220, a similar function may be realized by a speaker of operation terminal 200.

[0055] The drive unit 340 in the work implement 300 performs the operations required for the work implement 300 to perform a predetermined task. The drive unit 340 includes devices appropriate for the intended use of the work implement 300, such as a hydraulic system, an electric motor, or a pump. The control device 380 controls the operation of the drive unit 340. The control device 380 causes the drive unit 340 to perform various operations in response to signals transmitted from the work vehicle 100 via the communication I / F 390. The control device 380 can also transmit signals appropriate to the state of the work implement 300 from the communication I / F 390 to the work vehicle 100.

[0056] 5 is a diagram showing an example of the operation terminal 200 and operation switch group 210 provided inside the cabin 105. The switch group 210, which includes a plurality of switches that can be operated by the user, is arranged inside the cabin 105. The switch group 210 may include, for example, a switch for switching between an automatic steering (auto-steer) mode and a manual steering (manual-steer) mode, a switch for switching between forward and reverse travel (e.g., a shuttle lever or shuttle switch), a switch for selecting a gear stage of the main transmission or the auxiliary transmission, and a switch for raising and lowering the work implement 300.

[0057] <Operation> Next, the operation of the work vehicle 100 will be described. The control device 180 in this embodiment can switch between manual steering mode and automatic steering mode in response to operation by the user (e.g., the driver) of the work vehicle 100. In manual steering mode, the control device 180 controls steering by driving the power steering device in response to operation of the steering wheel by the user. In automatic steering mode, the control device 180 controls steering by driving the power steering device based on the position and direction (azimuth) of the work vehicle 100 estimated based on data output from the positioning system 120 and the inertial measurement system 125, and a pre-recorded target route. Even in automatic steering mode, the speed is adjusted by accelerator and brake operation by the user.

[0058] FIG. 6 is a diagram showing an example of the travel of the work vehicle 100 in the automatic steering mode. (a) of FIG. 6 schematically shows the work vehicle 100 traveling along a straight target route P. (b) of FIG. 6 schematically shows the work vehicle 100 traveling along a curved target route P. (c) of FIG. 6 schematically shows the work vehicle 100 traveling along a target route P that includes two adjacent straight routes and a curved route connecting them. The target route P is set in advance and recorded in the storage device 170. When the work vehicle 100 is traveling in the automatic steering mode, the control device 180 calculates the deviation between the target route P and the position and orientation of the work vehicle 100 estimated based on data output from the positioning system 120 and the inertial measurement system 125, and repeats the operation of controlling the steering device to reduce the deviation. This causes the work vehicle 100 to travel along the target route P.

[0059] FIG. 7 is a diagram schematically illustrating an example of a target route for the work vehicle 100 traveling through a field using automatic steering. In this example, the field includes a work area 70 where the work vehicle 100 and the work implement 300 will work, and a headland 80 located near the outer periphery of the field. The user can set in advance which areas on the field map correspond to the work area 70 and the headland 80 by operating the operation terminal 200. The target route includes multiple parallel main paths P1 and multiple turning paths P2 connecting the multiple main paths P1. The main paths P1 are located within the work area 70, and the turning paths P2 are located in the headland 80. The dashed line in FIG. 7 represents the working width of the work implement 300. The working width is set in advance and recorded in the storage device 170. The working width can be set by the user operating the operation terminal 200 and recorded in the storage device 170. Alternatively, the working width may be automatically recognized when the work implement 300 is connected to the work vehicle 100 and recorded in the storage device 170. The spacing between the multiple main paths P1 is adjusted to the working width. The target path may be determined based on a user operation before automatic steering operation is started.

[0060] Next, an example of control performed by the control device 180 during automatic steering will be described.

[0061] FIG. 8 is a flowchart showing an example of the operation during automatic steering executed by the control device 180. The control device 180 performs automatic steering operation by executing the operations of steps S101 to S105 shown in FIG. 8 while the work vehicle 100 is traveling. The control device 180 first estimates the position and orientation of the work vehicle 100 based on data output from the positioning system 120 and the inertial measurement system 125 (step S101). The method of estimating the position and orientation will be described in detail later. Next, the control device 180 calculates the deviations between the position and orientation of the work vehicle 100 and the target route (step S102). The position deviation represents the distance between the position of the work vehicle 100 at that time and the target route. The orientation deviation represents the magnitude of the angle between the orientation of the work vehicle 100 at that time and the direction of the target route. The control device 180 determines whether the calculated position deviation exceeds a preset threshold value and whether the calculated orientation deviation exceeds another preset threshold value (step S103). If at least one of the position deviation and the orientation deviation exceeds the respective threshold, the control device 180 changes the steering angle by changing the control parameters of the steering device included in the drive device 140 so that the deviation decreases. If neither the position nor the orientation deviation exceeds the respective threshold in step S103, the operation of step S104 is skipped. In the following step S105, the control device 180 determines whether or not a command to end the operation has been received. The command to end the operation may be issued, for example, when the user issues an instruction to stop the automatic steering mode using the operation terminal 200 or when the work vehicle 100 has reached its destination. If the command to end the operation has not been issued, the process returns to step S101 and executes the same operation based on the newly measured position of the work vehicle 100. The control device 180 repeats the operations of steps S101 to S105 until a command to end the operation is issued. The above operations are executed by the ECU 183 in the control device 180.

[0062] An example of steering control by the control device 180 will be described in more detail below with reference to FIGS. 9A to 9D.

[0063] FIG. 9A is a diagram showing an example of a work vehicle 100 traveling along a target route P. FIG. 9B is a diagram showing an example of a work vehicle 100 shifted to the right from the target route P. FIG. 9C is a diagram showing an example of a work vehicle 100 shifted to the left from the target route P. FIG. 9D is a diagram showing an example of a work vehicle 100 facing in an oblique direction with respect to the target route P. In these figures, the pose indicating the position and orientation of the work vehicle 100 estimated based on signals output from the positioning system 120 and the inertial measurement system 125 is expressed as r(x, y, θ). (x, y) are coordinates representing the position of the reference point of the work vehicle 100 in the XY coordinate system, which is a two-dimensional coordinate system fixed to the Earth. In the examples shown in FIGS. 9A to 9D, the reference point of the work vehicle 100 is located at the position where the GNSS antenna on the cabin is installed, but the position of the reference point is arbitrary. θ is an angle representing the measured orientation of the work vehicle 100. In the illustrated example, the target path P is parallel to the Y axis, but in general, the target path P is not necessarily parallel to the Y axis.

[0064] As shown in FIG. 9A, if the position and orientation of the work vehicle 100 do not deviate from the target route P, the control device 180 maintains the steering angle and speed of the work vehicle 100 unchanged.

[0065] As shown in Fig. 9B, when the position of work vehicle 100 has shifted to the right from target route P, control device 180 changes the steering angle by changing the rotation angle of the steering wheel included in drive device 140 so that the traveling direction of work vehicle 100 tilts to the left and approaches route P. At this time, the speed may also be changed in addition to the steering angle. The magnitude of the steering angle can be adjusted, for example, according to the magnitude of position deviation Δx.

[0066] As shown in Fig. 9C, when the position of the work vehicle 100 has shifted to the left from the target route P, the control device 180 changes the steering angle by changing the rotation angle of the steering wheel so that the traveling direction of the work vehicle 100 tilts to the right and approaches the route P. In this case, too, the speed may be changed in addition to the steering angle. The amount of change in the steering angle may be adjusted, for example, according to the magnitude of the position deviation Δx.

[0067] As shown in FIG. 9D , when the position of the work vehicle 100 is not significantly deviated from the target route P but the heading is different from the direction of the target route P, the control device 180 changes the steering angle to reduce the azimuth deviation Δθ. In this case, the speed may also be changed in addition to the steering angle. The magnitude of the steering angle may be adjusted, for example, according to the magnitudes of the position deviation Δx and the azimuth deviation Δθ. For example, the smaller the absolute value of the position deviation Δx, the greater the amount of change in the steering angle according to the azimuth deviation Δθ. When the absolute value of the position deviation Δx is large, the steering angle will be changed significantly to return to the route P, which inevitably increases the absolute value of the azimuth deviation Δθ. Conversely, when the absolute value of the position deviation Δx is small, it is necessary to bring the azimuth deviation Δθ closer to zero. For this reason, it is appropriate to relatively increase the weight of the azimuth deviation Δθ (i.e., the control gain) used to determine the steering angle.

[0068] Control techniques such as PID control or MPC control (model predictive control) can be applied to the steering control and speed control of work vehicle 100. By applying these control techniques, it is possible to smooth the control that brings work vehicle 100 closer to target path P.

[0069] If an obstacle is detected by one or more obstacle sensors 130 while the work vehicle 100 is traveling, the control device 180 stops the work vehicle 100 or switches from automatic steering mode to manual steering mode. The control device 180 may also control the drive device 140 to avoid the obstacle when an obstacle is detected.

[0070] <Estimating heading drift during dead reckoning> Next, the dead reckoning operation that is performed when the reception strength of the GNSS signal decreases in the automatic steering mode will be described.

[0071] In the environment in which the work vehicle 100 travels, there may be obstacles that prevent the reception of GNSS signals. For example, as shown in FIG. 10 , trees 90, such as windbreaks, may be planted in the headland 80 of a farm field. When the work vehicle 100 approaches such trees 90, the received strength of the GNSS signals decreases, reducing the reliability of positioning. Furthermore, when the work vehicle 100 travels in an environment with many trees, such as an orchard or forest, the reliability of positioning based on GNSS signals frequently decreases, reducing the stability of automatic steering operation.

[0072] Therefore, in this embodiment, when the reception strength of the GNSS signal is reduced, the control device 180 performs a dead reckoning operation to estimate the position and orientation of the work vehicle 100 based solely on the signal output from the inertial measurement system 125.

[0073] During dead reckoning, as mentioned above, estimation errors in the azimuth angle (yaw angle) accumulate over time, reducing the reliability of self-localization. Figure 11 is a graph showing an example of temporal changes in azimuth angle. Figure 11 shows an example of temporal changes in the first azimuth angle estimated by processing using an extended Kalman filter (EFK) based on GNSS signals and signals from the IMU, and the second azimuth angle estimated based on signals from the IMU, when GNSS signals are received normally. As shown in Figure 11, compared to the first azimuth angle, the deviation (drift) from the true value of the second azimuth angle increases over time. Therefore, during dead reckoning, it is necessary to correct the second azimuth angle to suppress this azimuth drift.

[0074] To solve this problem, in a state (first state) in which GNSS signals can be received normally, the control device 180 in this embodiment not only sequentially estimates the position and first azimuth angle of the work vehicle 100 based on the first time series data output from the positioning system 120 and the second time series data output from the inertial measurement system 125, but also sequentially estimates the second azimuth angle based on the second time series data. The control device 180 calculates an azimuth error change rate based on the sequentially estimated first azimuth angle and second azimuth angle. The azimuth error change rate is a value representing the time rate of change of the second azimuth angle and corresponds to the gradient of the azimuth drift shown in FIG. 11 . In a second state in which the reception strength of the GNSS signals has decreased, the control device 180 corrects the second azimuth angle estimated based on the second time series data based on the above-mentioned azimuth error change rate. Then, the control device 180 performs steering control of the work vehicle 100 based on the corrected second azimuth angle. This makes it possible to suppress azimuth drift in the second state and improve the performance of automatic steering.

[0075] Fig. 12 is a flowchart showing an example of a position and orientation estimation operation executed by the control device 180. The operation shown in Fig. 12 can be executed in step S101 shown in Fig. 8. The operation shown in Fig. 12 is executed by the ECU 183 in the control device 180. The operation of each step will be described below.

[0076] In step S120, the control device 180 determines whether or not a GNSS signal reception problem has occurred. "GNSS signal reception problem" refers to a state in which the reliability of satellite positioning has decreased compared to normal due to a deterioration in the reception conditions of GNSS signals (satellite signals). Reception problem can occur, for example, when the number of detected satellites is small (e.g., three or less), when the reception strength of each satellite signal is low, or when multipath occurs. The control device 180 can determine whether or not a reception problem has occurred based on information about satellites included in the GNSS data output from the GNSS receiver 121 in the positioning system 120. For example, the presence or absence of reception problem can be determined based on the reception strength value for each satellite included in the GNSS data, or a DOP (Dilution of Precision) value indicating the satellite positioning status.

[0077] 13A and 13B are diagrams illustrating an example of a method for determining whether or not there is a reception disturbance based on the value of the reception strength of a GNSS signal. FIG. 13A shows an example of the reception strength of each GNSS signal when there is no reception disturbance. FIG. 13B shows an example of the reception strength of each GNSS signal when there is a reception disturbance. In this example, GNSS signals from 12 satellites are received, and the reception strength is expressed as a C / N0 value. Note that this is just one example, and the number of satellites from which GNSS signals can be received and the expression of the reception strength depend on the system. The control device 180 can determine whether or not there is a reception disturbance, for example, by determining whether or not the number of satellites whose reception strength exceeds a preset reference value is equal to or greater than a threshold value (e.g., 4). In FIGS. 13A and 13B, an example of the reference value for reception strength is indicated by a dashed line. When the threshold value is 4, in the example of FIG. 13A, the number of satellites whose reception strength exceeds the reference value is 5, which is equal to or greater than the threshold value. Therefore, in such a case, the control device 180 can determine that there is no reception disturbance. On the other hand, in the example of FIG. 13B, the number of satellites whose reception strength exceeds the reference value is one, which is less than the threshold value. Therefore, in such a case, the control device 180 can determine that reception interference is occurring. Note that this determination method is merely an example. The control device 180 may determine whether reception interference is occurring using other methods. For example, if the positioning system 120 outputs a value indicating the reliability of positioning, the control device 180 may determine whether reception interference is occurring based on the reliability value.

[0078] In this way, the first time series data output from positioning system 120 may include information indicating the reliability of the positioning. Control device 180 may be configured to determine the reliability of the first time series data based on the information, and to distinguish between the first state and the second state based on the reliability.

[0079] The control device 180 may change the level of reliability degradation at which it is determined that reception interference has occurred, according to a user setting. For example, the criterion for determining reliability may be changed according to the required operation accuracy set by the user. The operation accuracy may be specified according to the positioning method used, such as RTK (high), DGPS (medium), or independent positioning (low).

[0080] If the control device 180 determines in step S120 that a GNSS signal reception failure is not occurring (No), the process proceeds to step S121. This state corresponds to the above-mentioned "first state." If the control device 180 determines that a GNSS signal reception failure is occurring (Yes), the process proceeds to step S126. This state corresponds to the above-mentioned "second state."

[0081] In step S121, the control device 180 estimates the position and azimuth angle (first azimuth angle) of the work vehicle 100 based on the first time series data output from the positioning system 120 and the second time series data output from the inertial measurement system 125. For this estimation, an estimation algorithm using an extended Kalman filter, for example, may be used. The estimation of the position and azimuth angle is not limited to an extended Kalman filter and can be performed using any estimation algorithm.

[0082] In step S122, the control device 180 estimates the azimuth angle (second azimuth angle) of the work vehicle 100 based on the second time-series data. The second azimuth angle can be estimated, for example, by processing such as time integration of the angular velocity measurement values ​​included in the second time-series data. Note that the processing of step S122 may be performed before step S121 or may be performed simultaneously with step S121.

[0083] In step S123, the control device 180 calculates the orientation error change rate based on the time change rate of the difference between the first orientation angle and the second orientation angle. The method for calculating the orientation error change rate will be described in detail later. The control device 180 stores the calculated orientation error change rate in the storage device 170.

[0084] In step S124, control device 180 determines the position and first azimuth angle estimated in step S121 as the position and azimuth angle of work vehicle 100. Control device 180 executes steering control from step S102 onwards in Fig. 8 based on the determined position and azimuth angle of work vehicle 100.

[0085] The processes of steps S121 to S124 are repeatedly executed in the first state in which no GNSS signal reception failure occurs. When a GNSS signal reception failure occurs, the processes of steps S126 to S128 are executed.

[0086] In step S126, the control device 180 estimates the position and azimuth angle (second azimuth angle) of the work vehicle 100 based on the second time-series data output from the inertial measurement system 125. The control device 180 determines the estimated values ​​of the position and azimuth angle of the work vehicle 100 by processing such as integrating the measurement values ​​obtained from the acceleration sensor 126 and the angular velocity sensor 127 after the occurrence of the GNSS signal reception failure, using as a reference the estimated values ​​of the position and azimuth angle.

[0087] In step S127, the control device 180 corrects the second azimuth angle based on the azimuth error change rate calculated in step S123. Specifically, the control device 180 can obtain a correction value for the second azimuth angle by multiplying the azimuth error change rate by the time elapsed since the previous azimuth estimation process was performed (i.e., the processing cycle in FIG. 12), and subtracting the result from the second azimuth angle. The control device 180 may use, for example, the azimuth error change rate calculated immediately before, or may use the azimuth error change rate based on data acquired during the period when GNSS signals were acquired most stably.

[0088] In step S128, the control device 180 calculates the position estimated in step S126 and the 127The controller 180 determines the second azimuth angle corrected in step S102 as the position and azimuth of the work vehicle 100. The controller 180 executes the steering control from step S102 onwards in Figure 8 based on the determined position and azimuth angle of the work vehicle 100.

[0089] Here, an example of a method for calculating the azimuth error change rate in step S123 will be described. Here, it is assumed that an extended Kalman filter (EKF) process is performed based on data output from the positioning system 120 and the inertial measurement system 125 (e.g., IMU). A highly accurate first azimuth angle calculated by the EKF process is defined as θ1, and a second azimuth angle calculated based only on data from the inertial measurement system 125 is defined as θ2. In a first state in which the reception strength of the GNSS signal is sufficiently high, the control device 180 divides the difference between the first azimuth angle θ1 and the second azimuth angle θ2 by unit time Δt to calculate an azimuth error change rate Δθ, which represents the gradient of the azimuth angle drift. drift That is, the control device 180 calculates the heading error change rate Δθ by performing the calculation of the following equation 1. drift can be calculated. Δθ drift =(θ1-θ2) / Δt (Equation 1) Here, the unit time Δt can be set to a value of, for example, about 0.1 seconds to several seconds.

[0090] In reality, the difference between the first azimuth angle θ1 and the second azimuth angle θ2 fluctuates minutely over time, as shown in Fig. 11. For this reason, the control device 180 adjusts Δθ calculated based on Equation 1. drift Alternatively, the azimuth error change rate may be determined as a statistical value (e.g., average value) of the difference between the first azimuth angle θ1 and the second azimuth angle θ2 over a predetermined time period. That is, the control device 180 may repeatedly calculate the time change rate of the difference between the first azimuth angle θ1 and the second azimuth angle θ2 at predetermined time intervals, and calculate the azimuth error change rate as a statistical value (e.g., average value) of the time change rates calculated multiple times (e.g., 3 to 10 times). The predetermined time interval may be set to any value, for example, 1 to 20 seconds.

[0091] 14A and 14B are diagrams illustrating the effects of this embodiment. FIG. 14A shows an example of the change over time in azimuth deviation when the above correction is performed and when it is not performed. FIG. 14B shows an example of the change over time in position deviation when the above correction is performed and when it is not performed. The azimuth deviation represents the difference from the true value of the azimuth angle, and the position deviation represents the difference from the true value of the position coordinate. As shown in these figures, it was confirmed that the application of the correction process of this embodiment can significantly reduce the deviations in both azimuth and position.

[0092] As described above, while the work vehicle 100 is traveling, the control device 180 repeatedly calculates the azimuth error change rate and records it in the storage device 170 during a period (first state) when the reliability of the first time series data output from the positioning system 120 is high. When the work vehicle 100 enters a second state where the reliability of the first time series data is low due to, for example, a GNSS signal interruption, the control device 180 performs a dead reckoning operation to estimate the position and second azimuth based on the second time series data output from the inertial measurement system 125. In the dead reckoning operation, the control device 180 corrects the second azimuth angle based on the azimuth error change rate calculated in the first state and performs steering control based on the corrected second azimuth angle. This operation reduces the effects of azimuth drift and improves the reliability of self-position estimation during dead reckoning.

[0093] 12, the control device 180 calculates the heading error change rate in a first state in which there is no GNSS signal reception interference. However, the calculation of the heading error change rate may also be performed in a second state in which there is GNSS signal reception interference. In this case, in step S123, instead of calculating the heading error change rate, the control device 180 may calculate the time change rate of the difference between the first azimuth angle and the second azimuth angle and record the time change rate in the storage device 170 in association with the time. Alternatively, the control device 180 may record the first azimuth angle and the second azimuth angle in association with the time in the storage device 170. By performing such recording, the control device 180 can calculate the heading error change rate in the second state based on the stored information.

[0094] The control device 180 may also correct the second azimuth angle based on the azimuth error change rate in the second state only if the duration of the first state is longer than the first time. The first time may be set to a value of, for example, 20 seconds or more. By using the azimuth error change rate acquired over such a relatively long period, the second azimuth angle in the second state can be corrected to a good value. Furthermore, when sufficient travel time is not available in a situation where the GNSS positioning accuracy is good, it is possible to avoid correcting the azimuth angle to an incorrect value using an unreliable azimuth error change rate.

[0095] 12 can be executed not only when the work vehicle 100 is traveling straight using automatic steering, but also when traveling along a curved route or turning on a headland. Because the tendency of azimuth drift remains the same whether traveling straight or turning, the azimuth error change rate based on data acquired while traveling straight and the azimuth error change rate based on data acquired while turning can be used without distinguishing between them. For example, the azimuth error change rate based on data acquired while turning can be used to correct the azimuth angle when the GNSS signal is interrupted while traveling straight or while turning.

[0096] The control device 180 may output a warning when the first state changes to the second state. For example, when the control device 180 detects a change from the first state to the second state, the control device 180 may display a warning on the display device of the operation terminal 200 or may cause the buzzer 220 to emit a warning sound. Furthermore, if the second state continues for a second time period or longer, the control device 180 may stop automatic steering and output a warning to the operation terminal 200 or the buzzer 220. The second time period may be set to any value, for example, between 10 seconds and 30 seconds.

[0097] FIG. 15 is a diagram showing an example of a display on the operation terminal 200. In this example, the control device 180 displays a map of the field including the work vehicle 100 and the target route P on the display of the operation terminal 200. In the example of FIG. 15, an icon 86 indicating whether the automatic steering mode is on or off and a warning message 92 are displayed. For example, when the reception strength of the GNSS signal (e.g., a GPS signal) falls below a reference level for a predetermined period of time or longer, the control device 180 may cancel the automatic steering and change the color of the icon 86, for example, from green to gray. Also, as shown in FIG. 15, the control device 180 may display a warning message 92 on the operation terminal 200, such as "GPS signal has been lost. Automatic steering has been canceled." In addition to displaying such a warning, the control device 180 may also cause the buzzer 220 to emit a warning sound. By outputting such a warning, the user can be effectively notified that automatic steering has been canceled.

[0098] In the above embodiment, the positioning system 120 includes the GNSS receiver 121. However, instead, the positioning system 120 may include an external sensor such as a LiDAR sensor or an image sensor. When the reliability of the self-location estimation based on such an external sensor decreases, dead reckoning including the above-described correction process may be performed. Even in this case, the reliability of the self-location estimation in dead reckoning can be improved.

[0099] The correction process in this embodiment can be applied not only to automatic steering driving, but also to automatic driving in which both steering and driving speed are automatically controlled.

[0100] In the above embodiments, work vehicle 100 may be an unmanned work vehicle that performs autonomous driving. In that case, components that are only necessary for manned driving, such as a cabin, driver's seat, steering wheel, and operation terminal, may not be provided in work vehicle 100. An unmanned work vehicle may perform operations similar to those in the above embodiments by autonomous driving or by remote control by a user.

[0101] A control system that provides the various functions described in the above embodiments can also be retrofitted to a work vehicle that does not have those functions. Such a control system can be manufactured and sold independently of the work vehicle. A computer program used in such a control system can also be manufactured and sold independently of the work vehicle. The computer program can be provided, for example, by being stored on a computer-readable non-transitory storage medium. The computer program can also be provided by downloading via a telecommunications line (for example, the Internet).

[0102] As described above, the present disclosure includes the work vehicles, control systems, and control methods described in the following items.

[0103] [Item 1] A work vehicle that performs automatic steering operation, a positioning system that outputs first time series data including position information of the work vehicle; an inertial measurement system including an acceleration sensor and an angular velocity sensor, and outputting second time series data based on measurement values ​​of the acceleration sensor and measurement values ​​of the angular velocity sensor; a control device that estimates a position and an azimuth angle of the work vehicle based on the first time-series data and the second time-series data, and performs steering control of the work vehicle based on the estimated position and azimuth angle and a predetermined target route; Equipped with The control device In a first state in which positioning by the positioning system is possible, a first azimuth angle of the work vehicle is sequentially estimated based on the first time series data and the second time series data, a second azimuth angle of the work vehicle is sequentially estimated based on the second time series data, and steering control of the work vehicle is performed based on the first azimuth angle; calculating an azimuth error change rate of the second azimuth angle based on the difference between the first azimuth angle and the second azimuth angle successively estimated in the first state; When the first state is changed to a second state in which the reliability of positioning by the positioning system is reduced, steering control of the work vehicle is performed based on the second azimuth angle estimated based on the second time-series data, corrected based on the azimuth error change rate, until the state returns to the first state. Work vehicle.

[0104] [Item 2] 2. The work vehicle described in item 1, wherein, in the first state, the control device estimates the position of the work vehicle and the first azimuth angle from the first time series data and the second time series data by processing using an extended Kalman filter.

[0105] [Item 3] 3. The work vehicle according to item 1 or 2, wherein the control device calculates the azimuth error change rate based on a time change rate of a difference between the first azimuth angle and the second azimuth angle in the first state.

[0106] [Item 4] Item 4. The work vehicle described in item 3, wherein the control device repeatedly calculates a time rate of change of the difference between the first azimuth angle and the second azimuth angle in the first state at predetermined time intervals, and calculates a statistical value of the time rate of change calculated multiple times as the azimuth error change rate.

[0107] [Item 5] 5. The work vehicle according to item 4, wherein the predetermined time interval is not less than 1 second and not more than 20 seconds.

[0108] [Item 6] 5. The work vehicle according to item 4, wherein the plurality of times is between 3 and 10 times.

[0109] [Item 7] 4. The work vehicle according to any one of items 1 to 3, wherein the control device corrects the second azimuth angle based on the azimuth error change rate in the second state only when the duration of the first state is longer than a first time.

[0110] [Item 8] 4. The work vehicle according to any one of items 1 to 3, wherein the control device outputs a warning when the first state changes to the second state.

[0111] [Item 9] 4. The work vehicle according to any one of items 1 to 3, wherein the control device stops automatic steering and outputs a warning when the second state continues for a second time period or longer.

[0112] [Item 10] Item 10. The work vehicle according to item 9, wherein the predetermined time is between 10 seconds and 30 seconds.

[0113] [Item 11] 4. A work vehicle according to any one of items 1 to 3, wherein the positioning system includes a GNSS receiver.

[0114] [Item 12] the first time-series data includes information indicating reliability of positioning; the control device determines a reliability of the first time-series data based on the information, and distinguishes between the first state and the second state based on the reliability; Item 11. A work vehicle as described in item 11.

[0115] [Item 13] A control system for a work vehicle that performs automatic steering operation, the work vehicle is equipped with a positioning system that outputs first time series data including position information of the work vehicle, and an inertial measurement system that includes an acceleration sensor and an angular velocity sensor and outputs second time series data based on measurement values ​​of the acceleration sensor and measurement values ​​of the angular velocity sensor; the control device estimates a position and an azimuth angle of the work vehicle based on the first time series data and the second time series data, and performs steering control of the work vehicle based on the estimated position and azimuth angle and a predetermined target route; The control device In a first state in which positioning by the positioning system is possible, a first azimuth angle of the work vehicle is sequentially estimated based on the first time series data and the second time series data, a second azimuth angle of the work vehicle is sequentially estimated based on the second time series data, and steering control of the work vehicle is performed based on the first azimuth angle; calculating an azimuth error change rate of the second azimuth angle based on the difference between the first azimuth angle and the second azimuth angle successively estimated in the first state; When the first state is changed to a second state in which the reliability of positioning by the positioning system is reduced, steering control of the work vehicle is performed based on the second azimuth angle estimated based on the second time-series data, corrected based on the azimuth error change rate, until the state returns to the first state. Control system.

[0116] [Item 14] A control method for a work vehicle that performs automatic steering operation, the work vehicle is equipped with a positioning system that outputs first time series data including position information of the work vehicle, and an inertial measurement system that includes an acceleration sensor and an angular velocity sensor and outputs second time series data based on measurement values ​​of the acceleration sensor and measurement values ​​of the angular velocity sensor; In a first state where positioning by the positioning system is possible, sequentially estimating a first azimuth angle of the work vehicle based on the first time series data and the second time series data, sequentially estimating a second azimuth angle of the work vehicle based on the second time series data, and performing steering control of the work vehicle based on the first azimuth angle. calculating an azimuth error change rate of the second azimuth angle based on a difference between the first azimuth angle and the second azimuth angle successively estimated in the first state; When the first state is changed to a second state in which the reliability of positioning by the positioning system is reduced, steering control of the work vehicle is performed based on an azimuth angle obtained by correcting the second azimuth angle estimated based on the second time-series data based on the azimuth error change rate until the state returns to the first state. A control method comprising: [Industrial Applicability]

[0117] The techniques of the present disclosure may be applied to work vehicles used in agricultural applications, such as tractors, transplanters, or harvesters, etc. The techniques of the present disclosure may also be applied to work vehicles used in non-agricultural applications, such as construction vehicles or snowplows. [Explanation of symbols]

[0118] 50 GNSS satellite, 60 Reference station, 70 Working area, 80 Headland, 100 Work vehicle, 101 Vehicle body, 102 Prime mover, 103 Transmission, 104 Wheels, 105 Cabin, 106 Steering gear, 107 Driver's seat, 108 Coupling, 109 Pedals, 120 Positioning system, 121 GNSS receiver, 122 RTK receiver, 123 Processor, 125 Inertial measurement system, 126 Acceleration sensor, 127 Angular rate sensor, 128 Processor, 130 obstacle sensor, 140 drive unit, 150 sensor group, 152 steering wheel sensor, 154 turning angle sensor, 156 T / M rotation sensor, 160 control system, 170 storage device, 180 control unit, 182, 183, 184, 185 ECU, 190 communication interface, 200 operation terminal, 210 operation switch group, 220 buzzer, 300 work machine, 340 drive unit, 360 control unit, 390 communication interface

Claims

1. A work vehicle that performs automatic steering operation, a positioning system that outputs first time series data including position information of the work vehicle; an inertial measurement system including an acceleration sensor and an angular velocity sensor, and outputting second time series data based on measurement values ​​of the acceleration sensor and measurement values ​​of the angular velocity sensor; a control device that estimates a position and an azimuth angle of the work vehicle based on the first time-series data and the second time-series data, and performs steering control of the work vehicle based on the estimated position and azimuth angle and a predetermined target route; Equipped with The control device In a first state in which positioning by the positioning system is possible, a first azimuth angle of the work vehicle is sequentially estimated based on the first time series data and the second time series data, a second azimuth angle of the work vehicle is sequentially estimated based on the second time series data, and steering control of the work vehicle is performed based on the first azimuth angle; calculating an azimuth error change rate of the second azimuth angle based on a difference between the first azimuth angle and the second azimuth angle successively estimated in the first state; When the first state is changed to a second state in which the reliability of positioning by the positioning system is reduced, steering control of the work vehicle is performed based on an azimuth angle obtained by correcting the second azimuth angle estimated based on the second time-series data based on the azimuth error change rate until the state returns to the first state. Work vehicle.

2. 2. The work vehicle according to claim 1, wherein, in the first state, the control device estimates the position of the work vehicle and the first azimuth angle from the first time series data and the second time series data by processing using an extended Kalman filter.

3. The work vehicle according to claim 1 or 2, wherein the control device calculates the azimuth error change rate based on a time change rate of a difference between the first azimuth angle and the second azimuth angle in the first state.

4. 4. The work vehicle according to claim 3, wherein the control device repeatedly calculates a time rate of change of the difference between the first azimuth angle and the second azimuth angle in the first state at predetermined time intervals, and calculates a statistical value of the time rate of change calculated multiple times as the azimuth error change rate.

5. The work vehicle according to claim 4 , wherein the predetermined time interval is equal to or greater than 1 second and equal to or less than 20 seconds.

6. The work vehicle according to claim 4 , wherein the plurality of times is equal to or greater than 3 times and equal to or less than 10 times.

7. 3. The work vehicle according to claim 1, wherein the control device corrects the second azimuth angle based on the azimuth error change rate in the second state only when a duration of the first state is longer than a first time.

8. The work vehicle according to claim 1 or 2, wherein the control device outputs a warning when the state changes from the first state to the second state.

9. The work vehicle according to claim 1 or 2, wherein the control device stops automatic steering and outputs a warning when the second state continues for a second time period or longer.

10. The work vehicle according to claim 9 , wherein the second time period is equal to or greater than 10 seconds and equal to or less than 30 seconds.

11. The work vehicle according to claim 1 or 2, wherein the positioning system includes a GNSS receiver.

12. the first time-series data includes information indicating reliability of positioning; the control device determines a reliability of the first time-series data based on the information, and distinguishes between the first state and the second state based on the reliability; The work vehicle according to claim 11.

13. A control system for a work vehicle that performs automatic steering operation, the work vehicle is equipped with a positioning system that outputs first time series data including position information of the work vehicle, and an inertial measurement system that includes an acceleration sensor and an angular velocity sensor and outputs second time series data based on measurement values ​​of the acceleration sensor and measurement values ​​of the angular velocity sensor; the control system includes a control device that estimates a position and an azimuth angle of the work vehicle based on the first time-series data and the second time-series data, and performs steering control of the work vehicle based on the estimated position and azimuth angle and a predetermined target route; The control device In a first state in which positioning by the positioning system is possible, a first azimuth angle of the work vehicle is sequentially estimated based on the first time series data and the second time series data, a second azimuth angle of the work vehicle is sequentially estimated based on the second time series data, and steering control of the work vehicle is performed based on the first azimuth angle; calculating an azimuth error change rate of the second azimuth angle based on a difference between the first azimuth angle and the second azimuth angle successively estimated in the first state; When the first state is changed to a second state in which the reliability of positioning by the positioning system is reduced, steering control of the work vehicle is performed based on an azimuth angle obtained by correcting the second azimuth angle estimated based on the second time-series data based on the azimuth error change rate until the state returns to the first state. Control system.

14. A control method for a work vehicle that performs automatic steering operation, The work vehicle is equipped with a positioning system that outputs first time series data including position information of the work vehicle. an inertial measurement system including an acceleration sensor and an angular velocity sensor, and outputting second time series data based on measurement values ​​of the acceleration sensor and measurement values ​​of the angular velocity sensor; In a first state in which positioning by the positioning system is possible, sequentially estimating a first azimuth angle of the work vehicle based on the first time series data and the second time series data, sequentially estimating a second azimuth angle of the work vehicle based on the second time series data, and performing steering control of the work vehicle based on the first azimuth angle. calculating an azimuth error change rate of the second azimuth angle based on a difference between the first azimuth angle and the second azimuth angle successively estimated in the first state; When the first state is changed to a second state in which the reliability of positioning by the positioning system is reduced, steering control of the work vehicle is performed based on an azimuth angle obtained by correcting the second azimuth angle estimated based on the second time-series data based on the azimuth error change rate until the state returns to the first state. A control method comprising:

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