Neural-Fuzzy-Based Adaptive Sliding Mode Automatic Steering Control of Vision-based Unmanned Electric Vehicles

This paper presents a novel neural-fuzzy-based adaptive sliding mode automatic steering control strategy to improve the driving performance of vision-based unmanned electric vehicles with time-varying and uncertain parameters.Primarily,the kinematic and dynamic models which accurately express the steering behaviors of vehicles are constructed,and in which the relationship between the look-ahead time and vehicle velocity is revealed.Then,in order to overcome the external disturbances,parametric uncertainties and time-varying features of vehicles,a neural-fuzzy-based adaptive sliding mode automatic steering controller is proposed to supervise the lateral dynamic behavior of unmanned electric vehicles,which includes an equivalent control law and an adaptive variable structure control law.In this novel automatic steering control system of vehicles,a neural network system is utilized for approximating the switching control gain of variable structure control law,and a fuzzy inference system is presented to adjust the thickness of boundary layer in real-time.The stability of closed-loop neural-fuzzy-based adaptive sliding mode automatic steering control system is proven using the Lyapunov theory.Finally,the results illustrate that the presented control scheme has the excellent properties in term of error convergence and robustness.

Development of the electric automatic steering system for agricultural vehicles

Automatic guidance of agricultural vehicles requires automatic execution of operation commands received from the navigation controller by using electronically controlled mechanisms for wheel steering,speed changing and work implementing.Automatic steering contributes as a prerequisite technique in automatic and semi-automatic agricultural navigation.This research aimed to develop an electric automatic steering system that was compact in its structure and integrated into original steering mechanism in a simply and convenient way for aftermarket modification.A brushless motor and reducer assembly was utilized to provide an adequate steering torque instead of manual maneuver.A rapid assembling approach was proposed by passing the steering shaft through the hollow output shaft.A digital proportional-integral-differential(PID)algorithm was implemented to calculate the rotation speeds and directions by comparing the desired angle and the actual angle,which was implemented in a printed circuit board with a microcontroller unit(MCU)and interface chips.An unmanned wheeled tractor was applied as test platform to integrate the newly developed electric automatic steering system.Tests were conducted to evaluate its performance in terms of stability and responsiveness.An autonomous navigation system guided the tractor along target paths in the field by sending steering commands to the electric automatic steering system.The results show that the steering angle error was less than 0.81°when desired steering angle was less than 10°.The lateral error difference was no more than 4.76 cm when repeating following the same target path,which indicated that the electric automatic steering system responded accurately and robustly to steering commands.

Proportional directional valve based automatic steering system for tractors

Most automatic steering systems for large tractors are designed with hydraulic systems that run on either constant flow or constant pressure. Such designs are limited in adaptability and applicability. Moreover, their control valves can unload in the neutral position and eventually lead to serious hydraulic leakage over long operation periods. In response to the problems noted above, a multifunctional automatic hydraulic steering circuit is presented. The system design is composed of a 5-way-3-position proportional directional valve, two pilot-controlled check valves, a pressure-compensated directional valve, a pressurecompensated flow regulator valve, a load shuttle valve, and a check valve, among other components. It is adaptable to most open-center systems with constant flow supply and closed-center systems with load feedback. The design maintains the lowest pressure under load feedback and stays at the neutral position during unloading, thus meeting the requirements for steering. The steering controller is based on proportional-integral-derivative(PID) running on a 51-microcontroller-unit master control chip. An experimental platform is developed to establish the basic characteristics of the system subject to stepwise inputs and sinusoidal tracking. Test results show that the system design demonstrates excellent control accuracy, fast response, and negligible leak during long operation periods.

Design and optimization of an automatic hydraulic steer-by-wire system for an agricultural chassis

To meet the requirements of fast steering at low vehicle speed and slow steering at high vehicle speed,the automatic steering of agricultural chassis must control both the wheel steering angle and the steering angle’s angular speed.This study applied hydraulic steer-by-wire technology to the automatic steering control of agricultural chassis.First,the transmission mechanism of the designed steering system was optimized.According to the rule of least squares,aiming at the minimum sum of squares of errors between 10 ideal outer wheel angles and real outer wheel angles,the optimal solution of hole spacing on both sides of the steering hydraulic cylinder piston rod was 925 mm.The outer wheel angle error of the optimized steering mechanism throughout the steering stroke was less than 0.15°.Additionally,a hydraulic steer-by-wire system was developed,and the parameters of its critical components were calculated.Then,the compound control strategy of the steering cylinder piston rod displacement and moving speed was formulated for this automatic steering system.The entire control system included a valve control signal calculation model,an initial velocity calculation model,a correction velocity calculation model,and an attenuation velocity calculation model,and the formulae of each model were deduced.Based on the optimized parameters and the developed control strategy,a simulation model was built in AMESim,and simulation results showed that the proposed control strategy could achieve simultaneous controls of piston rod displacement and speed at different vehicle speeds and loads.The horizontal and vertical displacements of the right wheel center were plotted for typical vehicle speeds and steering commands.The results of this study provided a new idea for the application of hydraulic steer-by-wire technology in the automatic steering of agricultural chassis.

Development and evaluation of a general-purpose electric off-road robot based on agricultural navigation

The aim of this study was to develop a general-purpose electric off-road robot vehicle by using automatic control technologies.The vehicle prototype used in this study was a commercially-purchased electricity utility vehicle that was designed originally for manual operations.A manipulating unit,an automatic steering system and a speed control system were developed and integrated into a CAN-bus network for operating on functions(forward,reverse,park or stop),realizing desired steering angles and maintaining a constant speed,respectively,in the mode of automation.An autonomous navigation system based on RTK-GPS and IMU was used to evaluate the performance of the newly developed off-road robot.Field tests showed that the maximum error in speed control was 0.29 m/s and 0.22 m/s for speed tests and autonomous runs,respectively.The lateral offset was less than 10 cm in terms of straight paths,indicating that the automatic steering control system was of good performance.