Ultrasonic Doppler Vector Speed Sensor for Autonomous Tractors

本研究的目的是开发一种用于自动拖拉机的速度传感器。自动驾驶系统中使用超声波或微波多普勒速度传感器。然而，这些传感器最初的目的是监测拖拉机的性能。这些传感器的精度不足以进行位置检测。研究了超声多普勒测速传感器的误差因素，研制了一种高精度的测速传感器。研究结果总结如下：1.灵敏度和分辨率的提高：对于大多数常规传感器来说，很难测量极低的速度或反向运动。在研制的传感器中，通过对接收信号进行倍频并与参考信号混频，解决了这一问题。使用前置放大器和调谐放大器也提高了灵敏度。减小地面反射角变化带来的误差：设计了偏置抛物面反射器，并将其固定在传感器上，以保持发射和接收波在恒定方向上。传感器采用较低频率的超声波发射器和接收器。提高了光滑地面上的测量精度。对比试验：速度传感器的测试设备由一个4米长的线性执行器组成。通过与商用传感器的比较，验证了所研制的传感器具有较高的精度。4.自主拖拉机试验：利用内部传感器和GPS研制了一台自主拖拉机。在一个水平牧场上进行了自动驾驶试验。在以0.8m/S的速度行驶270m的情况下，距离基准线的最大位移约为0.5m。

The purpose of this study is developing a speed sensor for autonomous tractors. Ultrasonic or microwave Doppler speed sensors are used in autonomous driving systems. However, those sensors were originally intended for tractor performance monitoring. The accuracy of those sensors is not enough for position detection. The authors studied on the error factors of ultrasonic Doppler speed sensor, and developed an accurate speed sensor. Results of the study are summarized as follows,1. Improvements of sensitivity and resolution: For most conventional sensors, it was difficult to measure very low speed or reverse motion. The problem was solved by frequency multiplication of the received signal and mixing with a reference signal in the developed sensor. The sensitivity was also improved using a preamplifier and a tuned amplifier.2. Reduction of the error from the change in reflection angle on the ground: An offset parabolic reflector was designed and attached to the sensor to keep the transmission and received waves in the constant direction. An ultrasonic transmitter and a receiver of relatively low frequency were used for the sensor. Accuracy of the measurement on smooth ground surfaces was improved.3. Comparative test: Test equipment for speed sensors was constructed using a 4m long linear actuator. High accuracy of the developed sensors was confirmed by comparison with commercial sensors.4.Experiments of an autonomous tractor: An autonomous tractor was developed using internal sensors and a GPS. Experiments of autonomous driving were carried out on a horizontal forage farm. In the case of 270m driving at a speed of 0.8m/s, the maximum displacement from the reference line was about 0.5m.