Design and experiment of a tracked weeding robot based on model predictive control

doi:10.12398/j.issn.2096-7217.2024.04.006

Abstract

Abstract:

Aiming at the problems of difficult weeding operation， low weeding efficiency and low level of intelligence in orchards in hilly and mountainous areas， a small mountain orchard weeding robot was designed. In order to improve the tracking accuracy of the tracked weeding robot's operation path， the research of tracked weeding robot's path tracking control algorithm was carried out. The ‘inverted triangle swivel structure’ was used to design an imitation floating chassis， which carried a ‘Y-type’ blade assembly for crushing and weeding and powered by an extended-range hybrid power system， and a slope steering control strategy based on model predictive control was proposed to address the problem of large slope steering slippage. The round-trip path planning method was used to plan the full coverage path of the orchard. Combined with BDS positioning and navigation technology and full coverage path planning， the crawler weeding robot was ensured to have high tracking accuracy during operation. The kinematic model of the crawler weeding robot was constructed， and the steering dynamics and control strategy of the crawler weeding robot on the slope were simulated and analyzed in MATLAB software. The simulation results show that the average error of the designed slope steering model is only 0.039 m under the condition of 15°， which demonstrates a good accuracy. Field experiments show that the MPC controller proposed in this paper can effectively improve the path tracking effect under slope steering conditions， and the average error under uphill and downhill conditions is reduced by 51.76% and 63.77%， respectively， compared with the PID controller when the slope angle is 15°. The weeding robot integrated with BeiDou navigation function has an effective weeding rate higher than 97% and can walk normally on a 25° slope. The research results provide a reference for the development of weeding robots in hilly and mountainous areas.

Key words: agricultural machinery, path planning, weeding robot, MPC, navigation

CLC Number:

ZHAO Lijun, JIA Yunfan, YIN Wenke, HUANG Hua, LI Xiang, LI Qiang. Design and experiment of a tracked weeding robot based on model predictive control[J]. Journal of Intelligent Agricultural Mechanization, 2024, 5(4): 84-94.

Figures/Tables 19

Figure 1 Overall 3D model

Table 1 Main parameters of crawler chassis

项目名称	参数
底盘重量/kg	200
底盘总体尺寸/（mm×mm×mm）	1 100×950×400
履带接地长度/mm	800
履带宽度/mm	145
轨距/mm	600
履带节距/mm	60
接地比压/kPa	8.4
最大爬坡度/（°）	30
跨沟宽度/mm	400
越障高度/mm	200

Figure 2 Composition of the weeding robot navigation system1.IMU

Figure 3 Orchard round-trip path planning diagram

Figure 4 Tracked robot model

Figure 5 Vehicle slope analysis

Figure 6 Distribution of transverse forces on the track parallel to the road surface

Figure 7 Schematic of model predictive control

Figure 8 Slope steering control strategy

Figure 9 Traction trend at different slopes （R=3 m）

Figure 10 Traction trend changes under different steering radii （a=15°）

Figure 11 Turn-by-turn driving 2D path tracking

Table 2 Positioning accuracy statistics

控制方法	最大误差/m		平均误差/m
控制方法	x方向	y方向	x方向	y方向
PID	0.231 5	0.756 3	0.063 7	0.425 8
MPC	0.192 3	0.401 5	0.014 5	0.062 6

Figure 12 Scenario for experiment

Figure 13 Uphill and downhill trajectory tracking error

Table 3 Comparison of uphill steering path tracking performance

上坡	坡度角5°		坡度角15°
上坡	最大误差/cm	平均误差/cm	最大误差/cm	平均误差/cm
PID	6.92	2.32	19.86	12.21
MPC	1.31	3.21	8.52	5.89

Table 4 Comparison of downhill steering path tracking performance

下坡	坡度角5°		坡度角15°
下坡	最大误差/cm	平均误差/cm	最大误差/cm	平均误差/cm
PID	6.73	3.45	18.21	11.73
MPC	2.31	1.15	5.72	4.25

Table 5 Measurement result of weeding rate

杂草面积/m²	漏除面积/m²			除草率/%
杂草面积/m²	区域1	区域2	合计	除草率/%
30.00	0.32	0.38	0.70	97.77
20.00	0.16	0.22	0.38	98.10
30.00	0.28	0.35	0.63	97.90

Figure 14 Effect of weeding before and after

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