茶园自走式修剪机接触式循垄导航系统设计与试验

Design and experiment of the contact-style ridge-following navigation system for a tea garden self-propelled trimming machine

针对现有自走式茶园修剪机自动化程度低、驾驶员操控难度大等问题,该研究结合茶垄轮廓边界结构化特点,提出一种接触式自动循垄导航系统及其控制算法。设计了基于激光测距传感器的接触式自动循垄检测机构,通过分析修剪机相对于茶垄的4种位姿状态,推导出修剪机的运动学导航模型,进而获取修剪机的位姿信息。基于运动学导航模型设计LQR(linear quadratic regulator,线性二次型调节器)算法控制器,以检测机构实时获取的修剪机位姿信息为输入,经导航控制器计算后输出转向信号至步进电机实现自动纠偏。茶园田间试验结果表明,修剪机以0.2、0.4与0.6 m/s速度进行自动循垄,最大绝对偏差不超过0.134 m,平均绝对偏差最大值不超过0.107 m,标准差最大值不超过0.105 m,平均绝对偏差与标准差随着行驶速度的增大而增大,但均不超过0.15 m,满足自走式修剪机在实际茶园环境下的循垄精度要求。研究结果可为茶园自走式修剪机的自动导航提供技术参考。

Currently,self-propelled trimming machines for tea gardens have problems of low automation level and poor maneuverability.In this work,a contact-style automatic ridge-following navigation system and its corresponding control algorithm for a small-scale,wheeled trimming machine in tea gardens were proposed considering the structural features of tea ridge boundaries.A contact-style automatic ridge detection mechanism based on low-cost laser ranging sensors was designed.The working principle of the detection mechanism was introduced and analyzed.The position and heading information of the trimming machine with respect to the tea ridge was derived through the opening and closing of two side baffles of the detection mechanism caused by the changing profiles of the tea ridge boundaries.The navigation system hardware included a power supply unit,remote control unit,sensing unit,steering unit,driving unit,and control unit.The sensing unit consisted of two low-cost laser ranging sensors for measuring the changing distances of the baffles of the ridge following the detection mechanism and an absolute optical encoder for determining the real-time steering angle of the steering wheel.The steering unit replaced the original manual steering mechanism of the trimming machine with a stepper motor to realize electrical control.By analyzing the four pose states of the trimming machine with respect to the tea ridge,the kinematic navigation model of the trimming machine was derived,and the lateral and heading deviations of the trimming machine with respect to the tea ridge centerline were obtained.A navigation controller was designed based on an LQR(linear quadratic regulator)algorithm derived from the kinematic model of the trimming machine.The position and heading information of the machine were taken as control inputs.After calculation by the control algorithm,proper steering signals were sent to the stepper motor for deviation correction.To validate the feasibility of the contact-style navigation system and evaluate the performance of the control algorithm,field experiments in a tea garden were conducted.The trimming machine was controlled to automatically follow a tea ridge at three different speeds,0.2,0.4,and 0.6 m/s.The experiment for each speed was repeated three times.Results showed that under three speeds,the maximum absolute deviation of the trimming machine was no larger than 0.134 m,the absolute deviation maximum was no larger than 0.107 m,and the standard deviation maximum was no larger than 0.105 m.This navigation performance was comparable to mainstream navigation systems developed based on RTK-GNSS,vision and laser sensors.The mean absolute deviation and standard deviation increased slightly as the running speed of the trimming machine increased.However,they were kept in the 0.15 m limit.This indicated that the navigation method based on the contact-style automatic ridge-following mechanism was feasible,and the LQR algorithm derived based on the kinematic model of the trimming machine could meet the accuracy requirement of tea ridge following under a practical tea garden environment.The low-cost,contact-style navigation system and its corresponding algorithm proposed in this work can provide a reference for the development of automatic navigation systems for self-propelled operation machines in tea gardens.