Design of steering control system for rice transplanter equipped with steering wheel-like motor

Abstract: The steering wheel-like motor has been used as steering control mechanism for agricultural machinery navigation systems integrated in small and medium-sized dryland tractors, but it's adaptability for large-power paddy agricultural machinery or other agricultural machinery with large steering damping remains to be studied. Taking Iseki PZ-60 rice transplanter as the research objective, the steering control system based on steering wheel-like motor is designed in accordance with the steering control characteristic of the automatic navigation rice transplanter working in paddy field. The steering system is composed of steering wheel-like motor, steering controller and wheel angle sensor. The steering system model based on system in series with first-order inertia and integral system is identified in Matlab. First a step signal is applied to the front wheels while the transplanter is lift and with no-load, then the step responses of the steering angle are obtained for 28° to left and 28° right; Afterwards, the model parametersare identified by the MATLAB System Identification toolbox, which turns out that the best fit coefficient of the model (best fits) are 91.07% and 90.12%. A nested control algorithm with dead zone is designed. The inner loop of the algorithm is a PID speed control loop, and the outer loop is an incremental PID angle control loop. Given the control disturbance generated by the gap, free stroke and other nonlinearity in the steering system, the disturbance is regarded as the control dead zone, whose threshold have been tested and integrated into the control algorithm. Simulation del of the system is constructed by MATLAB/Simulink, and the simulation tests are carried out by using square wave and sine wave signals. The results show that tracking delay and adjustment time of the simulated model are about 0.1 s and 0.1 s respectively which indicates that the control system has a good steady-state performance. In other words, the feasibility of the control algorithm is verified. In order to verify the practical performance and control accuracy of the steering control system, the automatic navigation transplanter (including dual antenna differential GNSS system, the navigation controller and the steering control system mentioned above) is adopted to test in the Zengcheng Experimental Base of South China Agricultural University. Three verification tests are carried out on the developed automatic navigating transplanter. The steering signals to be performed in paddy field are sinusoid with amplitude of 10°, small-angle for testing tracking straight line and wide-angle for testing turning round. The results illustrate that the average absolute error (AAE) of sinusoidal signal tracking is 0.301 5° and average delay is 0.3 s; the AAE of straight-line tracking in paddy field conducted on flat and uneven bottom layer are 0.354° and 0.663° respectively, and maximum error of which are 1.4° and 3.6°, respectively with presence of 0.6 s delay; the delay goes up to 1.4 s when transplanter are driven into area with relatively deep mud; the settling time and steady-state error are 2.5 s and 0.6% respectively during the process of tracking a turning signal with 28° steering angle. Three experiments illustrate that the steering system developed for the rice transplanter based on the steering wheel-like motor has good dynamic response and control stability which can be applied to the automatic steering control of the rice transplanter in paddy fields and satisfies operation requirements of automatic navigation for rice transplanter.