Search

EP-4394539-B1 - WORK VEHICLE, CONTROL SYSTEM FOR WORK VEHICLE, AND CONTROL METHOD

EP4394539B1EP 4394539 B1EP4394539 B1EP 4394539B1EP-4394539-B1

Inventors

  • OKURA, KOHEI
  • YUASA, JUNICHI

Dates

Publication Date
20260506
Application Date
20231219

Claims (12)

  1. A control system (160) for a work vehicle (100) configured to perform auto-steer driving, the work vehicle (100) including: a positioning system (120), including a GNSS receiver (121), to output first chronological data containing positional information of the work vehicle and information indicating a reliability of positioning; and an inertial measurement system (125), including an acceleration sensor (126) and an angular velocity sensor (127), to output second chronological data based on measurement values from the acceleration sensor (126) and measurement values from the angular velocity sensor (127), the control system (160) including: a controller (180) to estimate a position and an azimuth angle of the work vehicle (100) based on the first chronological data and the second chronological data, and to perform steering control for the work vehicle based on the estimated position and azimuth angle and on a target path that is previously set, wherein the controller (180) is configured to: determine whether the GNSS receiver (121) is in a first state where no reception impediment has occurred or in a second state where a reception impediment has occurred, based on the information indicating the reliability of positioning, in the first state, consecutively estimate a first azimuth angle of the work vehicle based on the first chronological data and the second chronological data, consecutively estimate a second azimuth angle of the work vehicle based on the second chronological data, and perform steering control for the work vehicle based on the first azimuth angle, calculate a rate of change in azimuth error of the second azimuth angle based on a difference between the consecutively-estimated first azimuth angle and the consecutively-estimated second azimuth angle in the first state, and, when the first state transitions to the second state, perform steering control for the work vehicle, based on a corrected azimuth angle that is a result of causing the second azimuth angle as estimated based on the second chronological data to be corrected based on the rate of change in azimuth error, the controller being configured to perform the steering control based on the corrected azimuth angle until returning to the first state.
  2. A work vehicle (100) configured to perform auto-steer driving, comprising: the control system (160) of claim 1; the positioning system (120); and the inertial measurement system (125).
  3. The work vehicle of claim 2, wherein, in the first state, the controller (180) is configured to use a process utilizing an extended Kalman filter to estimate the position and first azimuth angle of the work vehicle (100) from the first chronological data and the second chronological data.
  4. The work vehicle of claim 2 or 3, wherein the controller (180) is configured to calculate the rate of change in azimuth error based on a rate of temporal change in difference between the first azimuth angle and the second azimuth angle in the first state.
  5. The work vehicle of claim 4, wherein the controller (180) is configured to repeatedly calculate, at a predetermined time interval, the rate of temporal change in difference between the first azimuth angle and the second azimuth angle in the first state, and to compute as the rate of change in azimuth error a statistic of rates of temporal change which have been calculated a plural number of times.
  6. The work vehicle of claim 5, wherein the predetermined time interval is not less than 1 second and not more than 20 seconds.
  7. The work vehicle of claim 5, wherein the plural number of times is not fewer than 3 times and not more than 10 times.
  8. The work vehicle of any of claims 1 to 7, wherein the controller (180) is configured to perform in the second state a correction of the second azimuth angle based on the rate of change in azimuth error only if a duration of the first state is longer than a first length of time.
  9. The work vehicle of any of claims 1 to 8, wherein the controller (180) is configured to output an alert when the first state transitions to the second state.
  10. The work vehicle of any of claims 1 to 9, wherein if the second state continues for a second length of time or longer, the controller (180) is configured to suspend automatic steering and to output an alert.
  11. The work vehicle of claim 10, wherein the second length of time is not less than 10 seconds and not more than 30 seconds.
  12. A method for controlling a work vehicle (100) configured to perform auto-steer driving, the work vehicle (100) including: a positioning system (120), including a GNSS receiver (121), to output first chronological data containing positional information of the work vehicle and information indicating a reliability of positioning; and an inertial measurement system (125), including an acceleration sensor (126) and an angular velocity sensor (127), to output second chronological data based on measurement values from the acceleration sensor (126) and measurement values from the angular velocity sensor (127), the method comprising: determining whether the GNSS receiver (121) is in a first state where no reception impediment has occurred or in a second state where a reception impediment has occurred, based on the information indicating the reliability of positioning; in the first state, consecutively estimating a first azimuth angle of the work vehicle based on the first chronological data and the second chronological data, consecutively estimating a second azimuth angle of the work vehicle based on the second chronological data, and performing steering control for the work vehicle based on the first azimuth angle; calculating a rate of change in azimuth error of the second azimuth angle based on a difference between the consecutively-estimated first azimuth angle and the consecutively-estimated second azimuth angle in the first state; and, when the first state transitions to the second state, performing steering control for the work vehicle, based on a corrected azimuth angle that is a result of causing the second azimuth angle as estimated based on the second chronological data to be corrected based on the rate of change in azimuth error, the steering control based on the corrected azimuth angle being performed until returning to the first state.

Description

CROSS-REFERENCE TO RELATED APPLICATION This application claims priority to Japanese Patent Application No. 2022-211142, which was filed on December 28, 2022. BACKGROUND OF THE INVENTION 1. Field of the Invention The present disclosure relates to work vehicles, control systems for work vehicles, and control methods. 2. Description of the Related Art Research and development has been directed to the automation of work vehicles, such as tractors, to be used in fields. For example, work vehicles have been put to practical use which travel via automatic steering by utilizing a positioning system capable of precise positioning, e.g., GNSS (Global Navigation Satellite System). Work vehicles that automatically perform speed control as well as automatic steering have also been put to practical use. The specification of U.S. Patent Application Publication No. 2018/0292212 discloses a GNSS/INS navigation system that performs positioning of a vehicle by combining a GNSS and an IMU (Inertial Measurement Unit). In situations where GNSS signals are not available, this system is able to operate in a dead reckoning mode in which positioning is performed based on signals from the IMU. The specification of U.S. Patent Application Publication No. 2018/0292212 discloses correction of drift errors in measured values of rotation around the z axis (yaw axis) of a vehicle during dead reckoning operation. In connection with a positioning system that includes a GNSS and an INS (Inertial Navigation System), the specification of U.S. Patent Application Publication No. 2021/0095965 discloses using a previously-trained neural network prediction model to predict an error in the GNSS output and to correct the INS output, in a situation where GNSS signal are not adequately available. U.S. Patent Application publication No. 2017/153649 discloses a control system for a work machine configured to perform auto-steer driving, the control system having a steering device, a posture detector configured to detect a first azimuth, a steering angle detector, an azimuth calculation unit configured to obtain a second azimuth by using the detected steering angle, and a control unit configured to control the steering device of the machine based on at least one of the first azimuth and the second azimuth; the control unit controls the steering device based on the second azimuth when the posture detector is disabled. SUMMARY OF THE INVENTION A work vehicle that travels via automatic steering performs a steering control along a target path while performing localization, i.e., estimating its own position and direction. Localization is performed based on outputs from various sensors, e.g., GNSS and IMU, for example. An environment that is traveled by a work vehicle may include obstacles which hinder reception of GNSS signals. For example, trees (e.g., shelter woods) may exist in the environment to be traveled, thus lowering the reliability of positioning based on GNSS signals. In that case, "dead reckoning" may be performed, that is, the results of positioning may be complemented by utilizing signals from an IMU. However, an azimuth angle that is estimated based on signals from an IMU may have the problem of accumulated drift errors with lapse of time. It is desired to reduce errors associated with drifts in the azimuth angle that is estimated during dead reckoning operation. Example embodiments of the present invention provide systems and methods for reducing estimation errors in an azimuth angle during dead reckoning operation. A control system for a work vehicle configured to perform auto-steer driving is defined in claim 1, and a method for controlling a work vehicle configured to perform auto-steer driving is defined in claim 12. A work vehicle according to an illustrative example embodiment of the present disclosure is capable of performing auto-steer driving. The work vehicle includes a positioning system to output first chronological data including positional information of the work vehicle, an inertial measurement system, including an acceleration sensor and an angular velocity sensor, to output second chronological data based on measurement values from the acceleration sensor and measurement values from the angular velocity sensor, and a controller configured or programmed to estimate a position and an azimuth angle of the work vehicle based on the first chronological data and the second chronological data, and to perform steering control for the work vehicle based on the estimated position and azimuth angle and on a target path that is previously set, wherein the controller is configured or programmed to, in a first state where positioning by the positioning system is possible, consecutively estimate a first azimuth angle of the work vehicle based on the first chronological data and the second chronological data, consecutively estimate a second azimuth angle of the work vehicle based on the second chronological data, and to perform steering control