Ultrasonic Doppler Vector Speed Sensor for Autonomous Tractors

本研究的目的是为自动驾驶拖拉机开发一种速度传感器。超声波或微波多普勒速度传感器用于自动驾驶系统。然而，这些传感器最初是用于拖拉机性能监测的。这些传感器的精度不足以进行位置检测。对超声多普勒速度传感器的误差因素进行了研究，研制了一种精确的速度传感器。研究结果总结如下：1。灵敏度和分辨率的提高：对于大多数传统传感器来说，很难测量非常低的速度或反向运动。利用所研制的传感器对接收信号进行倍频并与参考信号混频，解决了该问题。使用前置放大器和调谐放大器也提高了灵敏度。减少地面反射角度变化带来的误差：设计了一个偏置抛物面反射器并附加在传感器上，以保持发射和接收波的方向恒定。传感器采用频率较低的超声波发射器和接收器。提高了在光滑地面上测量的精度。对比试验：采用4m长的直线执行器构建速度传感器试验设备。通过与商用传感器的比较，证实了所研制传感器具有较高的精度。自动驾驶拖拉机的实验：利用内部传感器和GPS研制了自动驾驶拖拉机。在一个水平饲料场进行了自动驾驶实验。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.