Bias estimation device, forklift, bias estimation method, and program

{
  "publication_number": "US2024044650A1",
  "country": "US",
  "kind": "A1",
  "title": "Bias estimation device, forklift, bias estimation method, and program",
  "abstract": "A bias estimation device includes a determination unit configured to determine whether a forklift is stationary based on a measurement value from a first sensor configured to detect information regarding movement of the forklift and a measurement value from a second sensor configured to detect information regarding a cargo handling device included in the forklift, an accumulation unit configured to accumulate an IMU measurement value that is a measurement value from an inertial measurement unit included in the forklift when the determination unit determines that the forklift is stationary and stop accumulation of the IMU measurement value when the determination unit determines that the forklift is not stationary, and a calculation unit configured to calculate a bias of the IMU measurement value based on the IMU measurement value accumulated in the accumulation unit.",
  "claims": [
    "1. A bias estimation device, comprising: a determination unit configured to determine whether a forklift is stationary based on a measurement value from a first sensor configured to detect information regarding movement of the forklift and a measurement value from a second sensor configured to detect information regarding a cargo handling device included in the forklift; an accumulation unit configured to accumulate an IMU measurement value that is a measurement value from an inertial measurement unit included in the forklift when the determination unit determines that the forklift is stationary and stop accumulation of the IMU measurement value when the determination unit determines that the forklift is not stationary; and a calculation unit configured to calculate a bias of the IMU measurement value based on the IMU measurement value accumulated in the accumulation unit. 2. The bias estimation device according to claim 1, wherein the determination unit determines that the forklift is stationary when a first condition that a measurement value from the first sensor does not indicate that the forklift is moving and that a measurement value from the second sensor does not indicate that the forklift is in cargo handling operation is satisfied and determines that the forklift is not stationary when the first condition is not satisfied. 3. The bias estimation device according to claim 2, wherein the determination unit acquires information on whether the inertial measurement unit is activated, determines that the forklift is stationary when the inertial measurement unit is activated and the first condition is satisfied, and determines that the forklift is not stationary otherwise. 4. The bias estimation device according to claim 1, wherein the determination unit acquires information on whether the forklift is being charged, determines that the forklift is stationary when the forklift is being charged, and determines that the forklift is not stationary when the forklift is not being charged. 5. The bias estimation device according to claim 1, further comprising a sudden change portion detection unit configured to detect a sudden change portion of the IMU measurement value accumulated in the accumulation unit, wherein the accumulation unit deletes the IMU measurement value of the sudden change portion detected by the sudden change portion detection unit, and the calculation unit calculates the bias based on the IMU measurement value remaining after deletion. 6. The bias estimation device according to claim 1, further comprising: a temperature value accumulation unit configured to accumulate time-series temperature data regarding an ambient temperature of the forklift; and a temperature change detection unit configured to detect whether the ambient temperature has changed by equal to or greater than a reference based on the time-series temperature data accumulated in the temperature value accumulation unit, wherein the accumulation unit accumulates the IMU measurement value when the temperature change detection unit determines that the ambient temperature has changed by equal to or greater than the reference and the determination unit determines that the forklift is stationary. 7. The bias estimation device according to claim 1, wherein the first sensor is a sensor that detects a rotation speed and/or a steering angle of a tire included in the forklift, and the second sensor is a sensor that detects a lifting height position of a fork included in the forklift and/or a weight of a cargo loaded on the fork. 8. A bias estimation device, comprising: a determination unit configured to acquire information on whether a forklift is being charged, determine that the forklift is stationary when the forklift is being charged, and determine that the forklift is not stationary when the forklift is not being charged; an accumulation unit configured to accumulate an IMU measurement value that is a measurement value from an inertial measurement unit included in the forklift when the determination unit determines that the forklift is stationary and stop accumulation of the IMU measurement value when the determination unit determines that the forklift is not stationary; and a calculation unit configured to calculate a bias of the IMU measurement value based on the IMU measurement value accumulated in the accumulation unit. 9. A forklift, comprising: a traveling body; a cargo handling device; the bias estimation device according to claim 1; and a positioning device configured to compensate the IMU measurement value by using the bias estimation device and determine a position of the forklift based on the IMU measurement value after compensation. 10. A bias estimation method, comprising: a step of repeatedly determining whether a forklift is stationary based on a measurement value from a first sensor configured to detect information regarding movement of the forklift and a measurement value from a second sensor configured to detect information regarding a cargo handling device included in the forklift; a step of accumulating an IMU measurement value that is a measurement value from an inertial measurement unit included in the forklift when the forklift is determined to be stationary in the step of determining; a step of stopping accumulation of the IMU measurement value when the forklift is determined to be not stationary in the step of determining; and a step of calculating a bias of the IMU measurement value based on the IMU measurement value accumulated. 11. A non-transitory computer readable storage medium storing a program that causes a computer to execute: a step of repeatedly determining whether a forklift is stationary based on a measurement value from a first sensor configured to detect information regarding movement of the forklift and a measurement value from a second sensor configured to detect information regarding a cargo handling device included in the forklift; a step of accumulating an IMU measurement value that is a measurement value from an inertial measurement unit included in the forklift when the forklift is determined to be stationary in the step of determining; a step of stopping accumulation of the IMU measurement value when the forklift is determined to be not stationary in the step of determining; and a step of calculating a bias of the IMU measurement value based on the IMU measurement value accumulated."
  ],
  "description_excerpt": "The disclosure relates to a bias estimation device, a forklift, a bias estimation method, and a program.\n\nIn position determination of a mobile body such as a forklift, measurement results of a global positioning system (GPS) and an inertial measurement unit (IMU) are used, and the position determination results are combined to achieve high position determination accuracy (for example, JP 2010-019703 A). However, since the IMU measurement value (acceleration, speed, angular velocity, and the like) includes a bias, the position determination result may become rather deteriorated unless the bias is compensated. As an example of deteriorating the position determination result, even during stopping, the measurement value of the yaw angular velocity may not become 0 due to a bias, causing the position determination result indicating that the vehicle body is rotating.\n\nIn response to this problem, WO 2021/157116 A proposes a method of using the fact that a bias element included in a measurement value can be easily separated when a mobile body is in a stationary state to estimate a bias by using a measurement value immediately after activation of the IMU in which there is a high possibility that the mobile body is stationary and a method of estimating a bias by using a measurement value of the IMU when it is determined from a camera image that the vehicle is stationary.",
  "cpc": [
    "G01C 21/183",
    "B66F 9/0755",
    "B66F 9/24",
    "G01C 21/166",
    "G01C 21/188",
    "G01C 25/005"
  ],
  "ipc": [
    "B66F 9/075",
    "B66F 9/24",
    "G01C 21/16"
  ],
  "assignees": [
    "Mitsubishi Logisnext Co Ltd"
  ],
  "inventors": [
    "Katsumasa Kitajima",
    "Yusuke Kinouchi",
    "Masahiro Yamada",
    "Takumi Fujita",
    "Takuya Akashi"
  ],
  "filing_date": "2023-04-17",
  "publication_date": "2024-02-08",
  "priority_date": "2022-08-05",
  "application_number": "US-202318135479-A",
  "family_id": "86053664",
  "cited_by_count": 0,
  "citations": [
    "US20130085646A1",
    "US20230349722A1",
    "US20240012090A1"
  ]
}