Distributed drive adaptive skid control of facility horticulture mobile platform

Flexible operation and high handling stability are often required in the distributed electric drive mobile platform in special scenarios of facility horticulture. This study aims to design a mobile platform with distributed electric driven independently by four-wheel hub motors. An adaptive anti-slip control strategy was also proposed to improve the steering flexibility and stability. The dynamic model and Ackermann differential steering model were constructed for the distributed electric drive mobile platform. The target steering speed of each wheel was determined to combine the instantaneous center of speed and tire side deflection angle. Then, the time-varying adhesion coefficient was selected to improve the adaptability of the distributed electric drive mobile platform. A complex road identifier was designed using strong tracking adaptive untracked Kalman filter, in order to accurately estimate the road adhesion coefficient. Finally, an anti-slip controller was obtained with adaptive sliding mode. The optimal wheel slip rate was determined, according to the estimated road adhesion coefficient and control the wheel slip rate in real time, Finally, the self-adaptive anti-slip control was realized for the drive wheel of the distributed electric drive mobile platform in the facility horticulture scene. Both Carsim-MATLAB/Simulink co-simulation and vehicle tests of the distributed horticultural electric drive mobile platform were carried out to verify the effectiveness of the control strategy. The simulation results show that the estimated errors of the wheel to road adhesion coefficient were 0.009 and 0.033 on the unchanged and docked road surfaces, respectively, while 0.01 and 0.007 on the opposite road surfaces for left and right wheel, respectively; When using anti-slip control, the slip rate errors of the left wheel were 0.031, 0.015, and 0.038, respectively, and the slip rate errors of the right wheel were 0.026, 0.005, and 0.028, respectively. The test results show that the maximum slip rates of the left front, right front, left rear, and right rear wheels without anti-slip control were 0.80, 0.85, 0.90, and 0.93, respectively, indicating severe wheel slip. Under the same road conditions, there was a significant deviation in the wheel slip rate between adjacent moments, resulting in the slipping at all times unsuitable for the stable driving of the mobile platform. The adaptive anti-skid control with road recognition can be expected to accurately estimate the wheel road adhesion coefficient on complex roads, thus reducing the error of wheel slip rate. The overall estimated values were around 0.44 and 0.47 for the four-wheel road adhesion coefficient after the stable starting of the mobile platform. The maximum slip rates of the controlled wheel under two tested road conditions were approximately 0.69 and 0.68, respectively. The tire slip was greatly reduced during turning, in order to effectively improve the driving stability of the mobile platform.