Development of external acceleration identification and attitude estimation system of field working vehicle
(2.College of Engineering, South China Agricultural University, Guangzhou, China 510642)
【Abstract】In the development of precision agriculture, intelligent agricultural machinery is an effective way to alleviate the current tense situation in world food security. The complex field environment and meticulous work effects require the agricultural machinery to have the ability of perceiving the attitude of the agricultural machinery accurately in real time. For example, the precision navigation control and the leveling control of agricultural machinery are all dependent on the accurate attitude measurement. What is more, the attitude of agricultural machinery is one of the key parameters of agricultural mechanics modeling and agricultural machinery safety warning learning. However, the external acceleration of the vehicle, which is commonplace under dynamic operation conditions, poses a challenge. The paper developed a minimal hardware system for external acceleration identification and attitude estimation used for field working vehicles and verified by the experiments taken place on the Innova 2100 shaker and the ZP9500 sprayer of high ground clearance in the field in order to further improve the precision operation of agricultural machinery. The modern micro-electromechanical systems (MEMS) technology provides the moderate-cost and miniaturized solutions for the development of attitude reference system. With the highly integrated inertial measurement units (IMUs) ADIS16445 provided by ADI company and micro ARM processor STM32 F446 provided by ST Company, the hardware platform was built. ADIS16445 ISensor® included tri-axial gyroscopes and tri-axial accelerometers. The raw sensors data were sampled by STM32 F446 RC processor through SPI interface. The attitude calculation was carried out based on the direction cosine matrix algorithm. Based on the gyroscope and accelerometer measurement model, a first-order external acceleration measurement model was proposed, and a Kalman filtering fusion algorithm with four state vectors was established. Since the bias of gyroscopes and accelerometers was stable after hardware pre-heating, the impact of bias of MEMS inertial sensors in the fusion algorithm was not considered. Innova 2100 shaker is standard equipment of rotary motion, and different centripetal accelerations can be achieved to verify the external acceleration identification at varying rotation speeds. Innova 2100 shaker test results show that the measurement error is less than 0.214 m/s2 under the external acceleration lower than 10 g. Field experiments were conducted on Innova 2100 shaker and the ZP9500 sprayer of high ground clearance provided by LOVOL Company with the assistance of attitude and heading reference system (AHRS) MTi300 provided by Xsens Company. The MTi300 AHRS provides high precision attitude and heading output with high stability and fast dynamic response with dynamic measurement accuracy of 0.3°, which makes it widely used in navigation implements, automobiles, agricultural machinery, and other fields. The experiment results from the sprayer of high ground clearance show that compared to the MTi300 AHRS, the average and maximum measurement errors of the roll angle are 0.069° and 0.23°, respectively. The average and maximum measurement errors of pitch angle are 0.078° and 0.39°, respectively. The test results verify that the proposed Kalman filtering algorithm is accurate and stable, which can improve the quality of agricultural machinery operations and have more applicability.
【Keywords】 agricultural machinery; sensors; attitude estimation; external acceleration; Kalman filtering; direction cosine matrix;
(Translated by ZHOU W)
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