Method and experiments of excavator bucket position and attitude measurement using BDS and IMU

High precision and intelligent degree of excavator construction can be perferred in farmland reconstruction in modern agriculture. It is a high demand to real-time acquire the bucket position and attitude for the intelligent and accurate operation of excavator. In this study, a series of approaches were proposed to measure the bucket position and attitude of excavator using BeiDou Navigation Satellite System (BDS) and Inertial Measurement Unit (IMU). A real-time solution model was established for the three-dimensional coordinates of the excavator bucket end: Firstly, the body parameters of excavator were measured to establish the body coordinate system. The IMU attitude sensors were installed at the appropriate positions of the boom, stick, and bucket of the excavator, in order to measure the attitude angle information of each actuator in the excavator. The data was finally collected to obtain the three-dimensional coordinates of the bucket end under the excavator body coordinate system; Then, the BDS dual antenna was installed on the roof to obtain the yawing angle of vehicle body and spatial position. The IMU attitude sensor was also installed on the vehicle body for the rolling angle and pitching angle of the vehicle body. Then, the Kalman filtering algorithm is used to fuse the dual antenna BDS and IMU output high-frequency and high-precision position and attitude information to construct attitude rotation matrix. Among them, the three-dimensional coordinates of the excavator bucket end under the vehicle body coordinate system were rotated to the local construction coordinate system. Static and dynamic tests were carried out to simulate the actual construction scene of the excavator. In the static test, the three-dimensional coordinates of the prism were continuously collected at the excavator bucket under each group of test actions by the total station under different heading angles and attitudes of the simulated operating excavator body and mechanical arm. The deviation was then calculated between the measured of total station and solution of bucket pose measurement. The results show that the new model performed better to accurately measure the three-dimensional coordinates at the end of the excavator bucket. The maximum absolute deviations were 17.69, 14.99, and 11.68 mm (all less than 20 mm) in the X, Y, and Z axial coordinates of bucket measuring points, respectively. The minimum deviation, maximum deviation and average deviation of the distance between the two coordinate points of the calculated and the real value (verification value) were 7.40, 20.65, and 13.57 mm, respectively. In the dynamic test, the excavator was operated in test group 1: where the body heading remained still, as each mechanism arm acted; Test group 2: the vehicle body rotated in the heading, and each mechanism arm remained still; Test group 3: The body heading and each mechanism arm acted at the same time, in order to simulate the actual construction operation scene, such as deep excavation, leveling, and slope brushing in the excavator construction. The total station was used to automatically follow the prism on the bucket. The three-dimensional coordinates of the bucket were collected in real time to verify the three-dimensional coordinate calculation of the bucket end. The results show that the average absolute deviation and root mean square deviation were less than 20 mm between the calculated values of the X, Y, Z three axial coordinates and the real value under different test actions. The proportion of the data with the absolute deviation less than 30 mm were not less than 95.35%. The calculated three-dimensional coordinates at the end of the excavator bucket were better consistent with the movement track change of the measured total station. The root mean square deviations of the distance between the two coordinate points of the calculated and the real value were 27.49, 26.30, and 23.50 mm, respectively, which were less than 30 mm. The accurate measurement for the position and posture of the excavator bucket can provide a practical basis for the intelligent guidance of the precise construction of the excavator.