Design and experiment of four-wheel independent steering driving and control system for agricultural wheeled robot

Abstract: Aiming at the problem of agricultural wheeled robots such as single steering mode, being difficult to adapt to the complex operating environment in field, higher cost for promotion and application, this paper designed a four-wheel independent steering driving and control system for the agricultural wheeled robot. The mechanical body of agricultural wheeled robot was composed of 3 parts, which mainly included robot walking chassis, power supply system, and electrical and computer control system. The robot walking chassis adopted the structure with high ground clearance which not only ensured the farmland operation, but also optimized the function of four-wheel independent steering driving and control system. Furthermore, the agricultural wheeled robot was also equipped with a battery, BLDC (brushless direct current) driver, angle sensor and other external devices. Besides, the hardware of the control system was constructed by using the modular design method and it could be divided into 4 parts which contained central processing module, terminal actuator module, upper computer and remote controller. Among them, the central processor module was the core platform of information exchange in the whole control system. The terminal actuator module could complete the control tasks of BLDC motor and send data to the central processor module at the same time. The control system selected the PIC18F25K80 microcontroller as master chip, applied the excellent hardware circuit isolation scheme and combined with the CAN (controller area network) bus, the serial communication and the technology of sensor, which techniques assisted the control system to realize the function of data acquisition and transmission for the speed and angle for the robot wheels. In addition, by analyzing the low-speed Ackerman four-wheel steering model and the PID (proportion, integration, differentiation) control algorithm, this paper verified the effectiveness and practicability of four-wheel independent steering driving and control system for agricultural wheeled robot. The experiment results showed that: through the upper computer and the remote controller, this robot could achieve the control function of four-wheel independent steering and speed. In the process of 0-360° steering, there was strong robustness and stability for the effect of wheel control. The maximum mean absolute error of the steering control was 0.10°, and the corresponding maximum standard deviation was less than 0.03°. It meant that the result of each control was relatively stable and there were no cases with major fluctuation. The speed control process of walking motor for the left front wheel and the right front wheel was analyzed. Both of the walking motors could basically get into stable control state and reach the required speed about 0.5-1 s after accomplishing speed setting. It proved that the speed control precision of walking motor achieved the design goal and had a quick response. This paper also carried out the 30 h durability test which consisted of the rotor locking test of wheel and the over current protection test for this driving and control system. The four-wheel independent steering driving and control system with reliable and flexible function can adapt to the changes of complex environment factors, meet the actual needs of farmland operation and have better services for agricultural production.