Steering Analysisand Automatic Driving System Designof Pedrail Wheeled Mobile Platform

With the continuous improvement of the intelligent level of agricultural machinery and the large-scale application of satellite navigation technology,agricultural machinery with automatic driving function is more and more popular in the market.At present,the research on automatic driving of agricultural machinery mainly focuses on wheel type and crawler type,while the mobile platform with crawler wheel chassis as the structural characteristics not only has the characteristics of flexible steering of wheel type machine,but also has the characteristics of large grounding area,low grounding ratio,good adhesion performance and strong traction of crawler machine.Its function is similar to that of tractor,and can be used as the power machine of agricultural machinery,such as suspension plow,rotary tiller The fertilizing device and spraying device are used for agricultural operation.Linear driving is the main index to evaluate the automatic driving level of agricultural machinery,and the steering characteristics of machinery are the important control basis for straight line driving.Therefore,it is necessary to study the steering characteristics of automatic driving system at the same time.In this paper,the steering characteristics and autopilot design of the tracked wheeled mobile platform for paddy field operation are studied(1)Through reading the literature,we understand the research and use of tracked wheeled mobile platform at home and abroad,as well as the research status of automatic driving of agricultural machinery.(2)The steering characteristics of tracked wheeled mobile platform are analyzed,and its steering mechanism model is established and simplified;According to the relationship between piston rod displacement of steering cylinder and wheel angle,the theoretical relationship between steering wheel angle and steering radius is deduced;A wheel angle measuring device is designed to verify the theoretical relationship between the steering wheel angle and the wheel angle.It is found that the actual wheel deflection is different from the theoretical value,which indicates that the wheel deflection is affected not only by the ground conditions,but also by other factors.(3)Further analysis shows that the main influencing factors of wheel steering are ground conditions,internal friction of steering parts,mechanical transmission clearance and driving speed.Through the orthogonal test of the factors affecting the steering of the tracked wheeled mobile platform,it is found that the ground condition is the primary factor affecting the steering of the tracked wheeled mobile platform;According to this result,the horizontal tests on hard ground,soft ground and muddy ground are designed,and the correction coefficients of the theoretical relationship between steering wheel angle and steering radius under three ground conditions are 1.154,1.267 and 1.363 respectively.(4)The formation of linear deviation in the process of automatic driving of agricultural machinery is analyzed.According to the steering characteristic formula of tracked wheeled mobile platform obtained from the test,the correction method and control strategy are established;According to the composition and working process of automatic driving system of agricultural machinery,the automatic driving design,modification and installation of tracked wheeled mobile platform is carried out,enabling it to have automatic driving conditions.(5)Car Sim / Simulink co simulation platform and field test are used to simulate and verify the automatic driving of tracked wheeled mobile platform.The results show that the modified formula of steering wheel angle and steering radius can achieve better straight-line driving performance,and the deviation is less than 0.1M,which basically meets the operation requirements.