Development and test of a small robotic system for in-field undisturbed soil sampling

Agricultural robot is one of the hottest topics in the field of agricultural machineries. Domestic and foreign research on robot mobile platforms for greenhouse/farmland/orchard operations（weeding，fertilization，spraying，picking，etc.）has achieved preliminary results，but mobile robotic system for soil sampling is still seldom found in literatures. Undisturbed soil sampling is an important basis for analyzing soil mechanical properties. If the original state of the soil sample cannot be guaranteed，it will be difficult to obtain accurate research results through subsequent laboratory physical and mechanical testing and analysis. To address this issue，we developed a farmland soil collection robot mobile platform with compact structure，strong pass ability，good soil extraction quality，and high soil extraction efficiency，put forward the design scheme of the mechanical system and control system and carried out preliminary field trial research. The main contents of this research are as follows：First，the design of robotic mobile platform was conducted，by determining differential steering mode，fulfilling mechanical design，selecting hardware components，and building control software framework. The wheelbase and track width of the platform were 960 mm and 600 mm，respectively. The power of the in-wheel motor was 1000 W. The movement of the platform could be controlled through both speed control knob and remote-control handle. Second，an on-board layer soil sampling equipment was developed，which worked in a hydraulic screw-in mode. The main structure parameters of the sampler were determined based on theoretical analysis，which were validated with a finite element analysis software-ANSYS. Third，field tests were also conducted to test the mobility and soil sampling performances of the robot system. The maximum obstacle crossing height and climbing slope of the robot were 80 mm and 35°，respectively. Based on the shear strength testing results of soil samples in depth 0 to 200 mm，we knew that the internal friction angle of the soil samples，which came from the proposed new system，had no significant differences compared to those coming from cutting ring sampling，with a P-value of 0.866 at the confidence level of 0.05. Similarly，for the soil samples in depth 0 to 100 mm and 100 to 200 mm，the variances of soil cohesion from our new system also had no significant differences compared to those from cutting ring sampling，with P-values of 0.145 and 0.717 at the confidence level of 0.05，respectively. The soil extraction efficiency comparison test results showed that the soil extraction device only took 3 to 5 minutes to complete one soil extraction.