Abstract
Tractors are prone to large slips when they are in field operation. The degree of slip plays a vital role in traction efficiency and fuel efficiency. This paper presents a method for measuring the slip ratio of tractors in field operation based on machine vision. The accurate measurement of slip ratio needs to obtain actual velocity and theoretical velocity separately. For obtaining the actual velocity, a monocular camera mounted on the tractor vertically faces down at the ground to collect images. Then, the feature points of inter-frame ground images are matched by the ORB (Oriented FAST and Rotated BRIEF) algorithm for calculating the translational displacement. Next, a homography matrix based on camera calibration is proposed to complete the transformation of a point from the pixel coordinate system to the world coordinate system. Aiming to acquire the theoretical velocity, a method that takes the variations in tire radius into account is proposed, and the tire radii of the driving wheels are indirectly determined by the tire inflation pressure in real-time. The proposed measurement method was verified with an experimental tractor. The results show that the mean absolute errors of the tractor driving wheels’ slip ratio measured by the machine vision method are less than 0.75%, and the maximum of the absolute errors is not more than 2.22%, which shows good performance.
Highlights
Agriculture plays a fundamental role in China’s national economy [1]
In order to meet the accurate measurement of slip ratio for tractor driving wheels, this paper presents a measuring method of the slip ratio for tractor driving wheels based on machine vision
The GPS antenna receivers, which are placed at the tractor, provide velocity measurements to validate the reliability for measuring the actual velocity Agriculture 2022, 12, x FOR PEER REbVaIEseWd on machine vision, are combined with the data obtained by the theore11tiocfa1l6 velocity acquisition system to calculate the slip ratio for tractor driving wheels
Summary
Agriculture plays a fundamental role in China’s national economy [1]. As one of the most critical types of machinery in the agricultural field, tractors have become essential for modern agriculture [2]. In [10], GPS information, inertial measurement unit (IMU), and wheel angle encoders were used to estimate the slip ratio This method requires signal fusion processing for multiple sensors. Ding et al [14] proposed and verified the slip ratio estimation methods based on visual information with high-precision analysis of the lug traces marked on the terrain. This method helps determine the slip ratio of the experimental rover in the laboratory by directly measuring the distance between the lug traces. The proposed measuring method of the slip ratio for tractor driving wheels was verified with an experimental tractor, showing good performance. This measurement technology can be used as an independent system to measure the slip ratio of tractors in field operation
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