Ultrasonic Doppler Speed Sensor for Agricultural Vehicles: Effects of Pitch Angle and Measurements of Velocity Vector Components

High-precision ground speed sensors could be used as a component of navigation or control systems for agricultural vehicles. This paper describes the characteristics of the speed sensor developed by the authors, focusing on the effects of pitch angle. For this purpose, experiments were carried out at various sensor depression angles. The results showed that the output was almost the same as the theoretical value for depression angles of 40 to 50 degrees, although the measurement error was relatively large in the case of artificial turf with short pile. Measurement tests at various angles between the traveling direction and the sensor direction in the horizontal plane were also carried out to determine the possibility of velocity vector measurement including sideslip. It was estimated that the measurement error would be within 3% of the absolute velocity in any direction. The results suggested that it is possible to measure the velocity vector without the effects of pitch angle by using multiple sensors facing in different directions.